International GNSS Service

Technical Report 2011
IGS Central Bureau
http://igs.org

Editors: M. Meindl, R. Dach, Y. Jean
Astronomical Institute, University of Bern
Published in July 2012

IGS Central Bureau
Jet Propulsion Laboratory, M/S 238–540
4800 Oak Grove Drive
Pasadena, CA 91109–8099 USA
Tel: +1 − 818 − 354 − 2077
Fax: +1 − 818 − 393 − 6686
E–mail: cb@igs.org
http://igs.org

National Aeronautics and Space Administration
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California

International GNSS Service

International Association of Geodesy
International Union of Geodesy and Geophysics

Edited by Michael Meindl, Rolf Dach, Yoomin Jean
Astronomical Institute, University of Bern, Switzerland,Compiled in June/July, 2012, extended in August, 2012.

Abstract
Applications of the Global Navigation Satellite Systems (GNSS) to Earth Sciences are
numerous. The International GNSS Service (IGS), a federation of government agencies,
universities and research institutions, plays an increasingly critical role in support of
GNSS–related research and engineering activities. This Technical Report 2011 includes
contributions from the IGS Governing Board, the Central Bureau, Analysis Centers,
Data Centers, station and network operators, and others highlighting status andimportant activities, changes and results that took place and were achieved during 2011.
This report is available online as PDF version at
ftp://igs.org/pub/resource/pubs/2011_techreport.pdf.
The IGS wants to thank all contributing institutions operating network
stations, data centers or analysis centers or supporting the IGS in any otherform. All contributions are welcome. They guarantee the success of the IGS
also in future.

Contents
I

II

Executive Reports

1

The Development of the IGS in 2011 — The Governing Board’s Perspective
U. Hugentobler

3Central Bureau
S. Fisher, R. Neilan, R. Khachikyan, G. Walia and D. Maggert

11

Analysis Centers

19

Analysis Center Coordinator

21

Center for Orbit Determination In Europe
R. Dach, S. Schaer, S. Lutz, M. Meindl, H. Bock, E. Orliac, L. Prange,
D. Thaller, L. Mervart, A. Jäggi, G. Beutler, E. Brockmann, D. Ineichen,
A. Wiget, G. Weber, H. Habrich, J. Ihde, P. Steigenberger, U. Hugentobler

29

Natural Resources Canada
B. Donahue, R. Ferland, R. Ghoddousi–Fard, F. Lahaye, Y. Mireault

41

European Space Operations Centre
T. A. Springer, W. Enderle, L. Agrotis , F. Dilssner, C. Flohrer, F. Pereira,N. Romero, R. Zandbergen

51

GeoForschungsZentrum
G. Gendt, M. Ge, T. Nischan, M. Uhlemann, G. Beeskow, A. Brandt

61

Geodetic Observatory Pecný
J. Dousa

67

Centre National d’Etudes Spatiales/Collecte Localisation Satellites
S. Loyer, F. Perosanz, H. Capdeville, M. Pau, F. Mercier, J.–C. Marty,
L. Soudarin

75v

Contents
Jet Propulsion Laboratory
S. Desai, W. Bertiger, B. Haines, D. Kuang, C. Selle, A. Sibois,
A. Sibthorpe, and J. Weiss

85

Massachusetts Institute of Technology
T. A. Herring and R. W. King91

National Geodetic Survey
No report submitted99

Scripps Institution of Oceanography
No report submitted

99

United States Naval Observatory
C. Hackman, S. Byram, V. Slabinski, and J. Tracey

99

SIRGAS
L. Sánchez

107

III Data Centers

117

Infrastructure Committee
I. Romero

119

Crustal Dynamics Data Information System
C. Noll

123

Scripps Institution of Oceanography
No report submitted

131

Institut National de l’Information Géographique et Forestière
No report submitted

131

Korean Astronomy and Space Science InstituteNo report submitted

131

IV Working Groups, Pilot Projects

vi

131

Antenna Working GroupR. Schmid

133

Bias and Calibration Working Group
S. Schaer

139

Contents
Data Center Working Group
C. Noll155

Global Navigation Satellite Systems Working GroupR. Weber

159

Ionosphere Working GroupA. Krankowski

165

Space Vehicle Orbit Dynamics Working GroupM. Ziebart

169

Reference Frame Working GroupP. Rebischung, B. Garayt, X. Collilieux, Z. Altamimi

175

Real–Time Pilot Project
M. Caissy and L. Agrotis

183

RINEX Working GroupK. MacLeod and L. Agrotis

191

Tide Gauge Benchmark Monitoring Project
T. Schöne, R. Bingley, Z. Deng, J. Griffiths, H. Habrich, M. Jia, M. King,
M. Merrifield, G. Mitchum, R. Neilan, C. Noll, L. Sánchez, N. Teferle,
D. Thaller, P. Tregoning, P. Woodworth, G. Wöppelmann

195

Troposphere Working Group
C. Hackman and S. Byram

211

Clock Products Working GroupK. Senior

219

vii

Part I

Executive Reports

1

The Development of the IGS in 2011
The Governing Board’s Perspective
U. Hugentobler
Technische Universität München
Institut für Astronomische und Physikalische Geodäsie
Arcisstr. 21; 80333 Munich; Germanye–mail: urs.hugentobler@bv.tum.de

1 Introduction
Although no technical report was published for the past few years, the IGS is continuing
its success in many areas — in no small measure due to the collaborative efforts of morethan 200 organizations and institutions worldwide. The IGS continues — inline withits mission — to serve as the premier source for high–quality GNSS data, products andservices in support of a wide area of applications that benefit society. The quality of data,
products and services are continuously improved by extending and upgrading the tracking
network, implementing improved models and analysis strategies, performing consistent
data reanalysis, increasing redundancy in the production chain, amongst other things.
The IGS is taking up the challenges of the future — it is finalizing a global real time
product, takes leadership for the maintenance and development of RINEX, and preparesfor the changing GNSS landscape characterized by new constellations and signals throughits Multi–GNSS Experiment.

2 IGS Activities reflect Strategic Goals
The work of the components of the IGS is guided by the strategic goals that are definedin the Strategic Plan 2008–2012.
Deliver world–standard quality GNSS data and products to all users globally withleading–edge expertise and resources.

3

Hugentobler: Governing Board
IGS site guidelines were revised and are under review. Site tie problems related to uncalibrated radomes are being addressed by the Infrastructure Committee with dedicatedexperiments. The quality of the IGS products is continuously increasing by implementing
the most up–to–date models and analysis strategies. For example, all IGS tracking data
were reprocessed with the latest models, and a second reprocessing campaign is in preparation. The IGS is preparing for the launch of a Real–Time Service to serve real time
applications. IGS installed a joined RTCM/RINEX Working Group and assumes leadership for maintenance and development of the RINEX format. The TIGA Pilot Projecttransitioned into a Service that is providing products on a regular basis.
Develop, integrate, and participate with new and changing GNSS systems andunderstand user needs to continuously improve IGS services and to provide value
to a broad range of users.
The IGS issued a Call for Participation for the Multi–GNSS Experiment in order toinvestigate the new tracking data types and equipment, with a view to eventually upgrade
the IGS network to a multi–GNSS network. A link with JAXA’s Multi–GNSS Monitoring
Network was established. Furthermore the IGS is involved in the International Committee
on GNSS (ICG) and contributes significantly to the Global Geodetic Observing System(GGOS).
Continuously improve the effectiveness of IGS management and governance tosupport future growth.
The IGS continues to engage with professional organizations such as, e.g., the International Federation of Surveyors (FIG), and with experts from the geosciences and physicalsciences, in particular through its Working Groups. The IGS web site is being upgraded,
and web interfaces increase efficiency in collecting and handling external input.

3 Events and Highlights in 2011
A major challenge is the transition of the IGS to a truly Multi–GNSS Service. The
GNSS landscape is rapidly changing. More and more new GNSS systems and signals are
becoming available. To consistently integrate these new systems and signals, to familiarize
with new data formats, and to develop and extend existing analysis software, a Callfor Participation for a Multi–GNSS Global Experiment (M–GEX) was issued in August
2011 (IGS Mail 6459, ftp://igs.org/pub/resource/pubs/IGS M-GEX VF.pdf), soliciting
the installation of multi–GNSS observing sites, operating data centers, and performing
experimental analysis. The experiment is linked to the JAXA CfP for hosting sites fora Multi–GNSS Monitoring Network. It is initially planned to run from February 2012
to August 2012. First results will be presented at the IGS Workshop in July 2012. The

4

3 Events and Highlights in 2011
experiment is managed by the IGS GNSS WG chaired by Robert Weber. Eventually theexperimental sites could form the core of a multi–GNSS IGS network.
Real–time GNSS has been a goal of IGS strategy for more than 10 years, in the context
of providing innovative support for scientific applications and performance monitoring of
GNSS. The IGS Real–Time Working Group was established in 2001, and in 2007 a CfP
in the IGS Real–Time Pilot Project (RT–PP) was announced. By the end of 2011, 188
stations were participating in the RT–PP. In order to develop and maintain standards
for GNSS data and develop formats for real–time GNSS, the IGS in 2008 joined the Radio Technical Commission for Maritime Services Special Committee 104 (RTCM–SC104).
At its December 2010 meeting the IGS Governing Board acknowledged the efforts of the
RT–PP participants and approved the transition of the Pilot Project into a Service. Preparations for launching the IGS Real–Time Service in 2012 commenced in 2011, with a focus
on product quality and service reliability. The rationale for an open real time service
is to support public benefit applications such as geophysical hazard detection and warning systems, conventional weather and space weather forecasting, and GNSS performancemonitoring.
In December 2011, following a decision at the April IGS Governing Board Meeting, a joint
IGS/RTCM–SC104 RINEX Working Group chaired by IGS was established in order toassume leadership in the maintenance and further development of the RINEX data format.
Main tasks of the WG chaired by Ken MacLeod are: to establish RINEX 3 as a standard
for new signals and GNSS systems, to develop and implement a transition plan to the newformat, and to encourage and support the development of open software tools for data
handling and quality control.
At the December 2010 meeting the IGS Governing Board approved the transition of the
GPS Tide Gauge Benchmark Monitoring Pilot Project (TIGA–PP) into a Working Group
computing precise geocentric station coordinates and velocities for GNSS stations at tidegauges on a regular basis. In February 2011 a CfP was issued (IGS Mail 6341, http://www.igs.org/projects/tiga/TIGA_CfP_2011.pdf). A total of eight proposals werereceived, and approved by the Governing Board following its April 2011 meeting. The
chair of the TIGA WG is Tilo Schöne.
As Troposphere WG chair, Yoaz Bar–Sever was responsible for the generation of a highquality precise point positioning (PPP) based IGS troposphere product for many years.
After extensive testing, the responsibility for the production of this product transitioned
from JPL to USNO (IGS Mail 6443) in July 2011. The new chair of the Troposphere WG
is Christine Hackman.
In July 2011 the IGS Governing Board received a proposal from U.S. National Geodetic
Survey (NGS) for a continuation of the Analysis Center Coordinator (ACC) function —one of the most important functions in the IGS — for another term. The willingnessof NGS to contribute three FTE staff for four years was greatly appreciated and the
proposal enthusiastically accepted by the GB, also acknowledging the unwavering efforts

5

Hugentobler: Governing Boardof Jim Ray and Jake Griffiths in the service of the IGS. The IGS’s gratitude for thissignificant commitment was conveyed to NGS management during a visit by Ruth Neilan,
Gerhard Beutler and Urs Hugentobler to NGS headquarters in Silver Springs, Washington
D.C., in November 2011.
The IGS is well represented on the GGOS Coordinating Board. The IGS also plays a leadership role in the International Committee on GNSS (ICG), in particular by co–chairing
Working Group D on Reference Frames, Timing and Applications and participating in theplanning for the International GNSS Monitoring and Assessment System (iGMAS). The
IGS is also well–represented in the International Earth Rotation & Reference Systems Service (IERS) and in IAG Sub–Commission 1.2 on reference frames, in the RTCM SC104,
and others. GB members made presentations at conferences such as the FIG Working
Week in Marrakech (May 2011), AfricaGEO in Capetown (May 2011), Southeast Asian
Surveyors Congress in Kuala Lumpur (June 2011), GNSS–R Workshop in Shanghai (August 2011), ICG–6 Meeting in Tokyo (September 2011) among others, highlighting themission and goals of the IGS and its range of products to a broader audience. The IGS
was also given visibility as session organizers of, or presenters in, IGS–related sessions atconferences such as those of the EGU, IUGG, AGU. Tables 1 and 2 list the important
events for 2011 and — for reference — for 2010.

4 Changes in the IGS Governing Board 2011
Significant changes took place in the Governing Board over the last year or so. After theelections at the end of 2010, Carine Bruyninx (Royal Observatory of Belgium), joined the
GB at the beginning of 2011 as Network Representative. Henno Boomkamp (chair of the
dissolved LEO WG) left the Board at the end of 2010. At the GB meeting in December
2010 als Urs Hugentobler was elected as the new Chair of the GB for the term 2011–2014.
Chuck Meertens (UNAVCO) joined the Board as an Appointed Member in February 2011.
With the transition of the generation of the IGS Troposphere product from JPL to USNO
in July 2011, Yoaz Bar–Sever left the Board after chairing the Troposphere WG since 2003,
and Christine Hackman (USNO) joined the Board as the new chair of the WG. During
the IUGG General Assembly in Melbourne, the IAG appointed Zuheir Altamimi as the
IAG Representative on the IGS GB. Geoff Blewitt, the former IAG Representative and amember of the IGS GB for a total of 14 years, left the Board while Zuheir, already a regular
guest, joined the Board as a voting member. Chris Rizos has been an Appointed Member
since 2004, however he is now a member of the GB in his capacity as IAG President. In
September 2011 Yamin Dang, from the Chinese Academy of Surveying and Mapping, wasappointed to the Governing Board.
In the GB elections at the end of 2011 — conducted by Richard Wonnacott together with
Carine Bruyninx and Carey Noll — Shailen Desai (JPL) was elected and Tim Springer(ESA/ESOC) was re–elected as Analysis Center Representatives for 2012–2015. Shailen

64 Changes in the IGS Governing Board 2011
Table 1: IGS events in 2011

February 2 TIGA Call for Participation issued
February 2 Chuck Meertens, director of the UNAVCO facility, appointed to the Governing
Board
April 3 38th GB Meeting in Vienna (EGU)
June 30 GB Business Meeting in Melbourne (IUGG)
June Transition of production of IGS Troposphere product from JPL to USNO, Christine
Hackman is new Chair of the Troposphere WG and member of the IGS GB
July 5 NGS proposal received
August 31 M–GEX Call for Participation issued
September 10 Yamin Dang, director of the Institute of Geodesy and Geodynamics at
Chinese Academy of Surveying and Mapping, appointed to the Governing Board
December 4 39th GB Meeting in San Francisco (AGU)• Election of Shailen Desai, JPL, and re–election of Tim Springer, ESA/ESOC,
as Analysis Center Representatives• Installation of the joint IGS/RTCM RINEX Working Group, chaired by Ken
MacLeod

Table 2: IGS events in 2010

June/July IGS Workshop in Newcastle 28.6.–01.7.2010
June 36th GB Meeting associated with Workshop in Newcastle• New WG on Space Vehicle Orbit Dynamics, chaired by Marek Ziebart• WG on Low Earth Orbiters dissolved
December 37th GB Meeting in San Francisco• Election of Urs Hugentobler as new Chair of the IGS GB• Election of Carine Bruyninx as IGS Network Representative
December IGS Terms of Reference revised in order to better represent the current IGS
organization and Strategic Plan. Approved at the 37 GB Meeting (http://www.
igs.org/organization/IGS_ToR_2010_final.pdf)

7

Hugentobler: Governing Board
replaces Bob King, chair of the Scientific Organizing Committee of the IGS Workshop in
Newcastle 2010, who left the Board at the end of 2011. Ken MacLeod joined the Board
as chair of the newly formed IGS RINEX WG. Jim Ray left the Board after doing an
excellent job as ACC from 2008–2011. Jim Ray was succeeded by Jake Griffiths.
John Dow stepped down as the chair of the GB (2003–2010) after serving the IGS GB
since its start on January 1, 1994. John must take the major credit for the current healthy
state of the IGS. Last but not least, Gerhard Beutler left the Board after shaping the IGS
from its very beginning. He has contributed in many ways to the success of our Service.
The IGS would not be where it is without the wisdom and insight — and the hard work
— of Gerhard over these many years.
The Governing Board welcomed its new members and thanked the departing members
for their contributions to the steering body of the IGS. The IGS is fortunate to havehighly qualified and engaged individuals who contribute to our Service. The departing GB
members were honoured at the GGOS reception after the IGS Governing Board meetingin San Francisco in December 2011.

5 Outlook
The year 2012 again promises a number of highlights. Most important is the IGS Workshop organized at the University of Warmia and Mazury in Olsztyn, Poland, from July
23–27, 2012. The Scientific Organizing Committee is chaired by Shailen Desai with support from Bob King, Matt King and Andrzej Krankowski, who is also the chair of the
Local Organizing Committee. A major focus of the Workshop is the IGS Multi–GNSS
Experiment. First results will be presented and future directions defined.
In the second half of 2012 Initial Operational Capability for the new IGS Real–Time
Service will be declared. The new open service will support applications that detect,for example, in real time, motions that are precursors to natural hazards such as landslides, volcanic activity and tsunamis. Other applications may include GNSS integrity
monitoring, weather forecasting, space weather monitoring and low Earth satellite orbit
determination. Finally, preparations for a second reanalysis campaign are underway.
Twenty years after the installation of the IGS Pilot Service on June 21, 1992, the IGS continues to be at the forefront of high precision GNSS applications in a challenging, rapidlychanging environment. This is only possible with the strong involvement of individuals,
and the commitments of many institutions and organizations worldwide. The IGS GB
wishes to thank all IGS Associates for their invaluable efforts in supporting the goals of
the IGS. Special thanks go to the numerous site operators who take care that the IGS
network — our foundation component — continues to provide the highest quality GNSS
tracking data to all users.

8

5 Outlook
Table 3: IGS Governing Board Members 2011 (∗: voting members, EC: Executive Committee)
MemberInstitution

Country

Function

Technische Universität
MünchenGermany

Board Chair, Analysis
Center Representative

Institut National del’Information Géographiqueet Forestière
Bureau International desPoids et Mesures
Jet Propulsion Laboratory

FranceIAG Representative

FranceBIPM/CCTF
Representative
Troposphere WG Chair∗ Gerhard Beutler

Astronomical Institute
University of Bern

Switzerland

Appointed by IAG
President∗ Geoff Blewitt

University of Nevada

USA

IAG Representative∗ Claude Boucher

FranceIERS Representative∗ Carine Bruyninx

since start of 2011

Institut National del’Information Géographiqueet Forestière
Royal Observatory of
Belgium

Belgium

Network Representative

Mark Caissy

Natural Resources Canada

CanadaReal-Time WG Chair∗ Yamin Dang

since Sept 2011

Chinese Academy ofSurveying and Mapping

China

Appointed

John Dow (EC)
until end of 2011

ESA/European Space
Operations Centre

Germany

Immediate Past GB Chair∗ Bruno Garayt

Institut National del’Information Géographiqueet Forestière

FranceChristine Hackman
since July 2011
∗ Gary Johnston

United States Naval
Observatory
Geoscience Australia

USA

Reference Frame
Coordinator, IGS
Representative to IAG
Sub–commission 1.2
Troposphere WG Chair

Australia

Network Representative

Massachusetts Institute ofTechnology

USA

Analysis Center
Representative

University of Warmia andMazury in Olsztyn
Natural Resources Canada

PolandIonosphere WG Chair

CanadaIGS/RTCM RINEX WG
Chair∗ Chuck Meertens

UNAVCOUSA

Appointed∗ Ruth Neilan (EC)IGS Central Bureau, Jet
Propulsion Laboratory

USA

Director of IGS Central
Bureau, Secretary

∗ Urs

(EC)

Hugentobler∗ Zuheir Altamimi
since July 2011
Felicitas Arias
Yoaz Bar–Sever
until July 2011
until July 2011
until July 2011

∗ Bob King

until end of 2011
Andrzej Krankowski
Ken MacLeod
since Dec. 2011
since Feb. 2011

USA

9

Hugentobler: Governing Board
MemberInstitution

Country

Function∗ Carey Noll

Goddard Space Flight CenterUSA∗ James Park

South Korea∗ Jim Ray

until end of 2011

Korean Astronomy andSpace Science Institute
NOAA National Geodetic
SurveyData Center Representative,
Data Center WG Chair
Appointed

USA

Analysis Center
Coordinator∗ Chris Rizos (EC)

University of New South
Wales

Australia

ESA/European Space
Operations Centre
Federal Office of Topography

Germany

Technische Universität
MünchenDeutsches
GeoForschungsZentrum
PotsdamNaval Research Laboratory

Germany

President of IAG
since July 2011
before: appointed
Infrastructure Committee
Chair
Bias and Calibration WG
Chair
Antenna WG Chair

Germany

TIGA WG Chair

USA

Clock Product Coordinator

ESA/European Space
Operations Centre

Germany

Vienna University ofTechnology
Chief Directorate: National
Geospatial Information
University College London

Austria

Analysis Center
Representative, IGS
Representative to IERS,
Chair of Associate Members
Committee
GNSS WG ChairSouth Africa

Appointed

UK

Space Vehicle Orbit
Dynamics WG Chair

Ignacio Romero
Stefan Schaer
Ralf Schmid
Tilo Schöne∗ Ken Senior∗ Tim Springer (EC)Robert Weber∗ Richard Wonnacott
Marek Ziebart

10

Switzerland

IGS Technical Report 2011
Central Bureau
S. Fisher, R. Neilan, R. Khachikyan, G. Walia and D. Maggert
IGS Central Bureau
Jet Propulsion Laboratory, M/S 238–540
4800 Oak Grove Drive; Pasadena, CA 91109–8099 USA
E–mail: cb@igs.org

1 Introduction
The Central Bureau supports IGS management proactively focusing on two principal functions:
1. executive management of the service, including international coordination and outreach, and
2. coordination of IGS infrastructure, including the IGS tracking network and related
information management systems.
The Central Bureau is hosted at the California Institute of Technology/Jet Propulsion
Laboratory and is funded by NASA.

2 Central Bureau Staff
Internal staff consists of 1.75 full time equivalent (FTE) positions, including the Director,
the Operations Manager, plus Information Technology and Administrative staff. Technicalsupport services are provided by Raytheon, Inc. and UNAVCO, Inc., which provide an
additional 1.0 FTE in aggregate. In 2011, we have realigned NASA resources at UNAVCO
to more effectively support IGS network monitoring and management. This has resulted
in a better leveraging between NASA/IGS and U.S. National Science Foundation (NSF)
activities, especially regarding backend systems for network monitoring and data/productaccess. As part of this realignment, UNAVCO has been providing significant help inmaintaining the Central Bureau Information System (CBIS) and interfacing with users,
as well as providing an independent backup outside of the CB for handling routine CBIS
operations such as keeping station logs and equipment files updated.

11

Fisher et al.: Central Bureau

3 IGS Executive Management
The Central Bureau has continued providing highly effective leadership of the IGS under
the direction of the Governing Board, maintaining IGS as the gold standard for high–precision GNSS data and information. This CB role involves administering and supporting Governing Board activities; providing business strategy and leadership to all of
the IGS components; developing strategy and formulating policy; planning and managing IGS functions such as workshops, Governing Board Meetings and outreach events incooperation with external organizations; participation on IGS Working Groups and Committees; managing relations with stakeholders at all levels, including the GB, components,
participants and users; developing IGS membership and the Governing Board; overseeing community and public relations; and handling the day–to–day operation of the IGS
involving more than 200 organizations and thousands of users.

4 International Coordination and Outreach
The CB coordinates extensively with many external organizations to promote the IGS anddevelop key partnerships with participants and users. This has continued as a hallmark
activity in 2011 that has demanded significant effort on the part of the Central Bureau,
as well as the Governing Board. Driving this is an expanding participant and user baseas the service continues to mature. 2011 is highlighted by the following coordination andoutreach activities:
International Association of Geodesy/Global Geodetic Observing System(IAG/GGOS): Central Bureau Director is a Coordinating Board Member. The
Operations Manager participates on the GGOS Bureau for Networks and Communications.
United Nations/International Committee on GNSS (ICG):
Working Group D on reference frames and timing applications is chaired by the
IGS CB Director who is also participating in planning of the International GNSS
Monitoring and Assessment System (iGMAS). The 6th ICG Meeting in Tokyo wasattended by the CB Director.
International Earth Rotation & Reference Systems Service (IERS):The Operations Manager participates on the IERS Directing Board.
Radio Technical Commission for Maritime Services, Subcommittee on Differential
GNSS (RTCM/SC104): The Operations Manager coordinates the IGS RTCM
membership and participates as a voting member. The CB Director is also a voting
member.

12

6 Network Status
International Federation of Surveyors (FIG):
The CB Director participated in FIG Working Week in Marrakech, Morocco (May2011) to reach out to this significant user community, and also potential large station
contributor.
Additionally, the AfricaGEO in Capetown, the International Council of Science/World
Data System Meeting in Paris, the European Geophysical Union Meeting in Vienna, theInternational Union of Geodesy and Geophysics Meeting in Melbourne, the Institute ofNavigation in Portland and the American Geophysical Union Meeting in San Francisco
were attended by CB staff.

5 IGS Infrastructure Management
The Central Bureau’s role in infrastructure management involves coordination of the IGS
network, management of the Central Bureau Information System (CBIS) and coordination
with other IGS infrastructure components, including the Data Centers, Analysis Centers
and all Working Groups. In 2011, CB staff members have participated in activities ofprincipal IGS committees and working Groups, including the Executive Committee, theInfrastructure Committee, the Antenna Working Group, the Reference Frame Working
Group and the Real Time Pilot Project. The CB has been responsible for providing firstlevel support to all IGS users, typically handling between 60–100 inquiries per month.
A growing aspect of the CB is the IGS Institute, which is a non–profit corporation thatprovides business infrastructure and support to the IGS. The IGS Institute has supported
the IGS website hosting and development, provided meeting conference services, provided
teleconferencing services, and has supported travel for IGS participation in key events.

6 Network Status
At the end of 2011, there were 436 GNSS tracking stations within the IGS network (Figure 1). Approximately 70% of these provide data on a weekly or more frequent basis
and are included in IGS weekly combination solution. Many IGS Network stations havemultiple capabilities to support a range of applications. 141 stations deliver GLONASS
data in addition to GPS to support the generation of the IGS GLONASS orbit product.
134 stations are co–located with external high–precision frequency standards and are usedin production of the IGS clock products. A subset of the network provides meteorological
data used in the generation of the IGS troposphere product. 188 stations provide data
in real–time to support emerging low latency applications. There are additional stations,
not considered IGS network stations, being used experimentally by IGS Clock, Real–Timeand Tide Gauge projects. In all, almost 700 stations are used by IGS Analysis Centers.

13

Fisher et al.: Central Bureau

Figure 1: IGS Global Tracking Network as of December 2011. New Stations introduced during
2011 are depicted in red.

A complete listing of IGS network stations and related information can be found online
at: http://igs.org/network/netindex.html.
A number of IGS stations are co–located with other geodetic techniques to promote combination and inter–comparisons of products and systems. The number of these has remained
unchanged since 2010; 25 stations are collocated with VLBI, 37 with SLR, and 55 withDORIS. Accuracy of the tie surveys between the different observing systems remains a limiting factor in the ITRF realization. This is being addressed within the International Association of Geodesy, Global Geodetic Observing System (IAG/GGOS) Bureau for Network
and Communications (BNC), where the Central Bureau participates, and by a number ofagencies which participate in IGS.
There are 63 stations categorized as dormant, meaning we have not received data for
60 days or more. Eighteen of these are NGA stations (9 sites × 2 receivers) and 27 arelonger–term outages that we may consider reassigning to the "former" category. Delays
in data deliveries are expected for various reasons at all of the remaining 18 sites in thiscategory.
The NGA stations were upgraded with un–calibrated ITT equipment in 2010 and havesince been offline. We have received the complete configuration history since they were
upgraded, which is currently being logged and verified. We are awaiting the final absolutecalibration of the ITT antenna by NGS, though we plan to make data available to be
used experimentally as soon as we have verified site metadata and RINEX files. Fullreinstatement of ten (9 plus one additional) stations is dependent on receiving the antenna
calibration data. Backfilling of the backlogged data will occur over a slightly longer term.
Concerns about deterioration of the IGS network have arisen because a significant numberof the 232 IGS08 stations are being excluded from the weekly ITRF solutions. This is14

8 Real–time Project
what we can explain about the exclusions in week 1637:
232 IGS08 Stations
141 Stations in weekly ITR solution
91 Exclusions:
10 Former sites (all were declared former prior to IGS08 release)
2 Replaced with nearby station (prior to IGS08 release)
9 Nearby earthquake
7 Upgraded with uncalibrated antenna/radome
16 High residual on equipment change
32 Short–term data outage (most common) or unexplained
15 Degraded fit with IGS08 for unknown reason
Stations excluded because degraded fit with IGS08 or high residual on an equipmentchange must be looked into further with help from the Analysis Centers.

7 Site Guidelines
The CB has helped the IC in revising on the IGS Site Guidelines to reflect currently recommended best practices. The new Guidelines include procedures for upgrading stationequipment, prescribing periods of operation where old and new equipment are operated
simultaneously to assure that discontinuities are properly mapped. In addition, stricter
antenna requirements have been introduced as recommended during the 2008 IGS Workshop, and guidelines for real–time stations were added. The IGS Governing Board has
provisionally accepted the new guidelines and plans to formally adopt them by mid–2012
after comments by the broad IGS community are integrated. Once completed, the new
guidelines will be posted on the IGS website.

8 Real–time Project
The CB has participated in the real–time working group, helping to coordinate some
activities, especially the participation in RTCM, where standards for data and correction
formats are being addressed to assure that the RTCM remains fully compatible withRINEX v3.01. In support if real–time efforts, an Ntrip caster has been implemented on the
CBIS — see http://igs.org:2101/home. We currently have 189 stations participatingin the Real Time Pilot Project. The strategy for developing an IGS real time product is
discussed further in the RT Working Group report below.

15

Fisher et al.: Central Bureau

9 Multi–GNSS Project (M–GEX)
A focused Multi–GNSS experiment called M–GEX is being fully supported by the CB,
including developing the project website and verifying the new site logs and data files.
A call to participate in was circulated in June by the Multi–GNSS Working Group (see
IGSMAIL #6459 and ftp://igs.org/pub/resource/pubs/IGS M-GEX VF.pdf). This wasdeveloped to establish a data set of new GNSS signals, including the Russian GLONASS,
the Japanese QZSS, European Galileo, and Chinese Compass, available for experimentation. The project is to run from February to August 2012. Participating stations are
anticipated to eventually form the core of a multi–GNSS IGS network and service. Details
relating to the M–GEX project are discussed further below and are available online at
http://igs.org/mgex/.

10 Radome Experiment
Along with the Infrastructure Committee, the CB is helping to coordinate the Radome
experiment. Radomes at twenty IGS stations that are co located at SLR or VLBI sites
have not been calibrated to IGS standards. Station operators were asked to participate inan experiment to assess the effects of these radomes by removing them for a two–month
period during 2011. Six stations have been able to respond so far, though the experimentwill continue into 2012 to allow more time for additional stations to participate.
See: https://sites.google.com/a/igs.org/igsnet/infrastructure-committee/
radome-experiment-2011.

11 Central Bureau Information System (CBIS)The Central Bureau Information System (CBIS) is the primary information portal for the
IGS. It contains information about the IGS organization, network, data and products. The
CB is charged with keeping all information up to date, including IGS membership, working
group and Governing Board Information, the IGS equipment files, process descriptions,publications, the analysis summary files and reports and station logs. To improve capture
and availability of network related information, backend systems that manage network
information and QC information are being redesigned in 2011.
All site log meta data are now imported into the Site Log Manager database, which isoperating in a test mode. Though not fully operational yet, this is already facilitating improvements in site meta data accuracy. Consistency of site metadata contained on station
logs and RINEX headers has been continuously monitored through the year. Typically,
there are just a few inconsistencies at any given time, which are normally resolved within
days.

16

Publications
A prototype IGS network interface is operating at http://network.igs.org/ which isintended to provide better access to station meta data and QC information. This effort isbeing conducted using NASA funds at UNAVCO, leveraging related activities funded by
NSF.
Network performance monitoring reports, similar to the summary reports at the EUREF
website that give an aggregate view of the network (threshold compliance, availability,etc.), are being worked on now and will soon be available on the web.
Effort to update site photos has so far resulted in 132 stations submitting new photos inthe desired format. The new photos have been posted on the site pages on igs.org.
We have received estimates from two commercial web design firms to implement the front–
end part of a new IGS website, which will require significant resources to accomplished.
Funding is being sought.
Network monitoring and other information is summarized for internal IGS use online at:https://sites.google.com/a/igs.org/igsnet/igs-net.

12 Meetings Attended
A significant number of meetings and workshops were attended by IGS participantsin 2011. A listing of these is available online at http://igs.org/events/.

Publications
2009–2011 IERS Annual Report.
In addition, many papers, articles and presentations relating to IGS were published orpresented by IGS participants in 2011. A partial listing of these is available online at
http://tinyurl.com/IGS-bibli.

17

Fisher et al.: Central Bureau

18

Part II

Analysis Centers

19

Analysis Center Coordinator

IGS–Chair:
ACC 2011:
ACC 2012:

U. Hugentobler
J. Ray and J. Griffiths
J. Griffiths and K. Choi
igs.acc@noaa.gov

1 ACC Activities
IGS products were combined 2011 without interruption. Product flow and quality were
continuously monitored and systematically validated. Contact to the Analysis Centers
was kept with intensive exchange through the IGS-ACS mail exploder and personal communications. Significant effort was spent for maintaining the ACC’s web pages and withanswering frequent questions of users. The ACC was present at scientific conferences(EGU April 2011 and AGU Dec. 2011) with presentations related to IGS products, their
quality and issues. Important issues discussed in presentations, at AC splinter meetingsand e-mail exchange were over-constrained parameters, draconitic anomalous frequencies,
tidal aliasing, handling of satellite attitude for clock parameter estimation, low number ofAnalysis Centers providing clock solutions for the IGS Ultra Rapid solution.
In 2011 the switch to the reference frame IGS08 took place after dedicated testing campaigns and with distributing associated information to the users. Two Analysis Centersstarted to generate GLONASS products while one center stopped. Contacts with the
GNSS Research Center at Wuhan University - proposing to install a new Analysis Center - were established. The results of the first reprocessing campaign were finalized andpreparations for a second reprocessing campaign were initiated.

21

Analysis Center Coordinator

2 IGS Product Quality
Table 1 gives an overview of the estimated quality of the IGS core products at the endof 2011. Consistency of IGS orbit and satellite clock corrections is illustrated in figure 1,
consistency of pole coordinates and length of day estimates in figures 2. Details can befound at the Analysis Center Coordinator’s home page http://acc.igs.org/, in IGS
Mail #6053 (http://igscb.jpl.nasa.gov/mail/igsmail/2010/msg00001.html) and invarious presentations listed below. Information about performance of station clocks canbe found in IGS Mail #6511 (http://igscb.jpl.nasa.gov/pipermail/igsmail/2011/006503.html) and references therein.

Table 1: Quality of the IGS core products at end of 2011 (see http://acc.igs.org/erp/
egu12-igu-erps.pdf)
SeriesUltra-Rapid(predicted)

Ultra-Rapid(observed)

Rapid

Final

ID
IGU

IGA

IGR

IGS

Product TypeGPS orbits
GLONASS orbits
GPS satellite
clocksEOPs
GPS orbits
GLONASS orbits
GPS satellite
clocksEOPs,
GPS orbits
GPS satellite &station clocks
EOPs
GPS orbits
GLONASS orbits
GPS satellite &station clocks
EOPs
Terrestrial frames

22

Accuracy
5 cm (1D)
10 cm (1D)
3 ns RMS,
1.5 ns Sdev
250 ţas (PM)50 ţs (dLOD)
3 cm (1D)
5 cm (1D)
150 ps RMS,
50 ps Sdev
<50 ţas (PM)10 ţs (dLOD)
2.5 cm (1D)
75 ps RMS,
25 ps Sdev
<40 ţas (PM)10 ţs (dLOD)
2.5 cm (1D)
<5 cm (1D)
75 ps RMS
20 ps Sdev
<30 ţas (PM)10 ţs (dLOD)
2 mm N&E,
5 mm U

OutputInterval
15 min15 min15 minUpdateevery 6hLatency
3-9 hevery 6h

3-9 h

daily
17 UTC

17-41hweeklyeach
Thursday11-17d6h
15 min15 min15 min6h
15 min
5 min
daily
15 min15 min30 s (SVs),
5 min (sta)dailyweekly2 IGS Product Quality

COD
EMR
ESA
GFZ
GRG
JPL
MIT
NGS
SIO
IGR

Final Orbits (AC solutions compared to IGS Final)
300(smoothed)Weighted RMS [mm]

250

200

150

100

50

0
700

800

900

1000

1100
1200
1300
Time [GPS weeks]

1400

1500

1600

NOAA NGS, 30.06.2012 19:21 (GMT)(a) Weighted RMS differences of all AC’s final orbits to the IGS final combined orbit.
COD
EMR
ESA
GFZ
GRG
JPL
MIT
NGS
SIO
IGR

Final Clocks (AC solutions compared to IGS Final)
2000(weekly means)

1800
1600

Clock Std Dev [ps]

1400
1200
1000
800
600
400
200
0
700

800

900

1000

1100

1200

1300

Time [GPS weeks]

1400

1500

1600

NOAA NGS, 30.06.2012 19:21 (GMT)(b) Standard deviation of IGS final clock solutions.

Figure 1: Comparison of the GPS satellite related IGS final products with the AC contributions.

23

Analysis Center Coordinator

X-Pole Difference [mas]AC Final X-Pole Differences with IGS Final
0

COD

-1

EMR

-2

ESA

-3

GFZ

-4

GRG

-5

JPL

-6

MIT

-7

NGS

-8

SIO

-9

IRF
IGR

-10
900

1000

1100

1200
1300
1400
Time [GPS weeks]

1500

1600
NOAA NGS, 30.06.2012 19:21 (GMT)(a) X-pole differences between IGS Analysis Centers.

Y-Pole Difference [mas]AC Final Y-Pole Differences with IGS Final
0

COD

-1

EMR

-2

ESA

-3

GFZ

-4

GRG

-5

JPL

-6

MIT

-7

NGS

-8

SIO

-9

IRF
IGR

-10
900

1000

1100

1200
1300
1400
Time [GPS weeks]

1500

1600
NOAA NGS, 30.06.2012 19:21 (GMT)(b) Y-pole differences between IGS Analysis Centers.

LOD Difference [ms/day]AC Final LOD Differences with IGS Final
0.0

COD

-0.2

EMR

-0.4

ESA

-0.6

GFZ

-0.8

GRG

-1.0

JPL

-1.2

MIT

-1.4

NGS

-1.6

SIO

-1.8

IRF
IGR

-2.0
900

1000

1100

1200
1300
1400
Time [GPS weeks]

1500

1600
NOAA NGS, 30.06.2012 19:21 (GMT)(c) Length of Day differences between IGS Analysis Centers.

Figure 2: Comparison of the IGS final products with the AC contributions for the Earth rotation
parameters.

24

4 IGS08 Reference Frame Introduced

3 Events in 2011
A number of events took place in 2011. The most important of them are listed in thetable below.
Jan. 2011 GRGS starts submitting Final GLONASS orbits
March 2011 Carlos Rodriguez (TUM) provides subroutines for albedo modelling
April 2011 IGS adopts new IGS08 reference frame & igs08.atx antenna calibrations in all
its products starting 1632/0
April 2011 AC splinter meeting held in Vienna in association with the EGU 2011 meeting
May 2011 Results from reprocessing campaign 1 finalized
May 2011 BKG stops submitting Final GLONASS orbits
July 2011 Yaw attitude subroutine provided by Jan Kouba
Sept. 2011 EMR starts submitting Final GLONASS orbits
Nov. 2011 Letter of intent from the GNSS Research Center at Wuhan University proposing to establish a new IGS Analysis Center there.
Dec. 2011 AC splinter meeting held in San Francisco in association with the Fall 2011
AGU meeting.

4 IGS08 Reference Frame Introduced
Effective April 17, 2011 the IGS adopted the new IGS08 reference frame, which is closely
related to ITRF08. The IGS08 computations were based on a selected globally distributed
subset of 232 well performing ITRF08 ground stations. Coincidentally, the IGS also
adopted a new ground antenna calibration model (IGS08.atx) based on absolute calibration of the antennas. Satellite phase center offsets were also re-estimated based on
ITRF05 to ITRF08 scale differences. Details relating to IGS08 and the IGS08.atx antenna model are contained in IGSMAIL #6354 and IGSMAIL #6355 respectively. Effects
on ground station coordinates arising from the IGS05 to IGS08 datum shift, as well as thechange over to the new antenna models are discussed in IGSMAIL #6356 and IGSMAIL#6401.

25

Analysis Center Coordinator

5 Results from First Reprocessing Campaign Finalized
Results of the first IGS reprocessing campaign (Repro1) covering the period 1994-2007
were announced in April 2010 (see IGSMAIL #6136) and the product files have been
finalized and distributed to the IGS Global data Centers for access by users in May 2011,
see IGSMAIL #6445, http://igscb.jpl.nasa.gov/pipermail/igsmail/2011/006437.
html). Related product files have now been finalized and distributed to the IGS Global
Data Centers for access by users. Details relating to the Repro1 Campaign are available
online at http://acc.igs.org/reprocess.html.

6 References
For more information please refer to the Analysis Center Coordinator’s web page http://acc.igs.org/ where a large number of references, links to journal papers and presentations related to IGS products are available. A few important references are given
here:• J. Ray and J. Griffiths (2010): Status of IGS core products (2010)
http://acc.igs.org/ACC-prods_IGS10.pdf• Griffiths et al. (2012): IGS Preparations for the Next Reprocessing and ITRF
http://acc.igs.org/repro2/egu12_ig2_preps.pdf• Ray (2011): Why does the IGS care about EOPs?
http://acc.igs.org/erp/igs-eop-requirements_NGA11.ppt• Ray and Griffiths (2012): High Accuracy Subdaily ERPs from the IGS
http://acc.igs.org/erp/egu12-igu-erps.pdf• Gendt et al. (2010): IGS reprocessing – Summary of orbit/clock combination & firstquality assessment
http://acc.igs.org/repro1/repro1_IGSW10.pdf• Ray and Griffiths (2011): Status of IGS orbit modeling & areas for improvement
http://acc.igs.org/orbits/egu11-orbits.ppt• Choi et al (2011): Evaluation of GPS orbit prediction strategies for the IGS Ultrarapid products
http://acc.igs.org/orbits/gps-predictions_agu11poster.pdf• Griffiths and Ray (2011): Subdaily alias & draconitic errors in the IGS orbits
http://acc.igs.org/orbits/igs-orbit-errs_agu-f11.ppt• Ray et al. (2011): Dependence of IGS products on the ITRF datum
http://acc.igs.org/trf/igs+itrf-datum_refag10.pdf

26

6 References• Ray et al. (2011): Consistency of crustal loading signals derived from models &GPS: Inferences for GPS positioning errors
http://acc.igs.org/trf/pos-errs_agu-f11.ppt• IGS Mail #6053: status of IGS orbit products
http://igscb.jpl.nasa.gov/mail/igsmail/2010/msg00001.html• IGS Mail #6511: Final report on IGS station clocks
http://igscb.jpl.nasa.gov/pipermail/igsmail/2011/006503.html• IGS Mail #6445: repro1 product files finalized
http://igscb.jpl.nasa.gov/pipermail/igsmail/2011/006437.html• IGS Mail #5874: Status of IGS Ultra-rapid products:
http://igscb.jpl.nasa.gov/mail/igsmail/2009/msg00000.html

27

Analysis Center Coordinator28

Center for Orbit Determination in Europe (CODE)
R. Dach1 , S. Schaer2
S. Lutz1 , M. Meindl1 , H. Bock1 , E. Orliac1 , L. Prange1 ,D. Thaller1 , L. Mervarta , A. Jäggi1 , G. Beutler1
E. Brockmann2 , D. Ineichen2 , A. Wiget2
G. Weber3 , H. Habrich3 , J. Ihde3
P. Steigenberger4 , U. Hugentobler4
12
34

Astronomical Institute, University of Bern, Bern, Switzerland
E-mail: code@aiub.unibe.ch
Federal Office of Topography swisstopo, Wabern, Switzerland
Federal Agency of Cartography and Geodesy,Frankfurt a. M., Germany
Institut für Astronomische und Physikalische Geodäsie,Technische Universität München, Munich, Germany

1 The CODE consortium
CODE, the Center for Orbit Determination in Europe, is a joint venture of the following
four institutions:• Astronomical Institute, University of Bern (AIUB), Bern, Switzerland,• Federal Office of Topography swisstopo, Wabern, Switzerland,• Federal Agency of Cartography and Geodesy (BKG), Frankfurt a. M., Germany, and• Institut für Astronomische und Physikalische Geodäsie, Technische Universität
München (IAPG, TUM), Munich, Germany.
The operational computations are performed at the AIUB whereas reprocessing activities
are usually carried out at IAPG, TUM. All solutions and products are produced with thelatest development version of the Bernese GNSS Software (Dach et al., 2007).
aInstitute of Geodesy, Czech Technical University in Prague, Czech Republic

29Dach, Schaer et al.: Center for Orbit Determination in Europe

2 CODE products available to the public
A wide variety of GNSS solutions based on a rigorous combined GPS/GLONASS dataprocessing scheme is computed at CODE. The products are made available through anonymous ftp:
ftp://ftp.unibe.ch/aiub/CODE/ or http://www.aiub.unibe.ch/download/CODE/
An overview of the files is given in Tab. 1.
Table 1: CODE products available through anonymous ftp.
CODE ultra-rapid products available at ftp://ftp.unibe.ch/aiub/CODE
COD.EPH_U
COD.ERP_U
COD.TRO_U
COD.SUM_U
COD.ION_U
COD.EPH_5D

CODE ultra-rapid orbits, updated every 6 hours
CODE ultra-rapid ERPs belonging to the ultra-rapid orbit product
CODE ultra-rapid troposphere product, SINEX format
Summary of stations used for the latest ultra-rapid orbit
Last update of CODE rapid ionosphere product (1 day)complemented with ionosphere predictions (2 days)
Last update of CODE 5-day orbit predictions, from rapid analysis, including all
active GLONASS satellites

CODE rapid products available at ftp://ftp.unibe.ch/aiub/CODE
CODwwwwd.EPH_R
CODwwwwd.EPH_P
CODwwwwd.EPH_P2
CODwwwwd.EPH_5D
CODwwwwd.ERP_R
CODwwwwd.ERP_P
CODwwwwd.ERP_P2
CODwwwwd.ERP_5D
CODwwwwd.CLK_R
CODwwwwd.TRO_R
CODwwwwd.SNX_R.Z
CORGddd0.yyI
COPGddd0.yyI
CODwwwwd.ION_R
CODwwwwd.ION_P
CODwwwwd.ION_P2
CGIMddd0.yyN_R
CGIMddd0.yyN_P
CGIMddd0.yyN_P2
P1C1.DCB
P1P2.DCB
P1P2_ALL.DCB
P1P2_GPS.DCB

30

CODE rapid orbits
CODE 24-hour orbit predictions
CODE 48-hour orbit predictions
CODE 5-day orbit predictions
CODE rapid ERPs belonging to the rapid orbits
CODE predicted ERPs belonging to the 24-hour orbit predictions
CODE predicted ERPs belonging to the 48-hour orbit predictions
CODE predicted ERPs belonging to the 5-day orbit predictions
CODE rapid clock product, clock RINEX format
CODE rapid troposphere product, SINEX format
CODE rapid solution, SINEX format
CODE rapid ionosphere product, IONEX format
CODE 1-day or 2-day ionosphere predictions, IONEX format
CODE rapid ionosphere product, Bernese format
CODE 1-day ionosphere predictions, Bernese format
CODE 2-day ionosphere predictions, Bernese format
Improved Klobuchar-style ionosphere coefficients, navigation RINEX format
1-day predictions of improved Klobuchar-style ionosphere coefficients
2-day predictions of improved Klobuchar-style ionosphere coefficients
CODE sliding 30-day P1-C1 DCB solution, Bernese format, containing only the
GPS satellites
CODE sliding 30-day P1-P2 DCB solution, Bernese format, containing all GPS
and GLONASS satellites
CODE sliding 30-day P1-P2 DCB solution, Bernese format, containing all GPS
and GLONASS satellites and all stations used
CODE sliding 30-day P1-P2 DCB solution, Bernese format, containing only the
GPS satellites

2 CODE products available to the public
Table 1: CODE products available through anonymous ftp (cont.).
CODE final products available at ftp://ftp.unibe.ch/aiub/CODE/yyyy/
CODE final GNSS orbits, our official IGS orbit product
CODE final ERPs belonging to the final orbits, values for the full week
CODE final clock product, Clock RINEX format, with a sampling of
30 sec for the satellite and the reference (station) clock and 5 min for all
remaining station clock corrections
yyyy/CODwwwwd.CLK_05S.Z CODE final clock product, Clock RINEX format, with a sampling of
5 sec for the satellite and the reference (station) clock and 5 minutes for
all remaining station clock corrections
yyyy/CODwwwwd.TRO.Z
CODE final troposphere product, SINEX format
yyyy/CODGddd0.yyI.Z
CODE final ionosphere product, IONEX format
yyyy/CODwwwwd.ION.Z
CODE final ionosphere product, Bernese format
yyyy/CODwwwwd.SNX.Z
CODE daily SINEX productyyyy/CODwwww7.SNX.Z
CODE weekly SINEX productyyyy/CODwwww7.SUM.Z
CODE weekly summary files
yyyy/COXwwwwd.EPH.Z
CODE precise GLONASS orbits (for GPS week 0990–1066)
yyyy/COXwwww7.SUM.Z
CODE weekly summary files of GLONASS analysis (dito)
yyyy/CGIMddd0.yyN.Z
Improved Klobuchar-style ionosphere coefficients, nav. RINEX format
yyyy/P1C1yymm.DCB.Z
CODE monthly P1-C1 DCB solutions, Bernese format, containing only
the GPS satellites
yyyy/P1P2yymm.DCB.Z
CODE monthly P1-P2 DCB solutions, Bernese format, containing all
GPS and GLONASS satellites
yyyy/P1P2yymm_ALL.DCB.Z CODE monthly P1-P2 DCB solutions, Bernese format, containing all
GPS and GLONASS satellites and all stations used
Note, that as soon as a final product is available the corresponding rapid, ultra–rapid, or predicted
yyyy/CODwwwwd.EPH.Z
yyyy/CODwwww7.ERP.Z
yyyy/CODwwwwd.CLK.Z

products is removed from the aftp server.

Some statistical information about typical daily solutions is given in Tab. 2 as of December
2011. The network of stations, considered by CODE for the final product generation, isshown in Fig. 1.

Table 2: Statistics on CODE daily solutions(compiled over December 2011).
Number ofstations
satellites
observations
parameters

ultra–
rapid
final
rapid
90
120
250
55 (31 GPS + 24 GLONASS)
300,000
750,000 1,500,000
4,800
11,00020,000GNSS
GPS only

Figure 1: Network used for the GNSS final
processing at CODE by the endof 2011.

31

Dach, Schaer et al.: Center for Orbit Determination in Europe

3 Changes in the daily processing for the IGS
The CODE processing scheme for daily IGS analyses is constantly subject to updates andimprovements. The last published technical report was published in 2008 (Hugentobler
et al., 2008). Since that time a lot of changes in the CODE processing scheme, the data
modelling, and analysis algorithms have taken place. Highlights from the interval between
the last report and the end of 2010 are given in Tab. 3. In Sect. 3.1 we give an overview
of important development steps in the year 2011. Two of the model improvements arefurther illustrated in Sect. 3.2.
Table 3: Selected modifications of the CODE processing between 2005 and 2010.
Date
07-May-2005
13-Nov-2005
19-Mar-2006
05-Nov-2006

DoY/Year
127/2005
317/2005
078/2006
309/2006

04-Dec-2006

338/2006

04-Nov-2007
27-Apr-2008

308/2007
118/2008

04-May-2008
29-Jun-2008
29-Jun-2008

125/2008
181/2008
181/2008

28-Sep-2008
26-Apr-2009
26-Jul-2009

272/2008
116/2009
207/2009

08-Aug-2009
04-Mar-2010

220/2009
063/2010

22-Jun-2010

173/2010

15-Sep-2010
03-Oct-2010

258/2010
276/2010

32

Description
Do not set up stochastic pulses at 12:00 for ultras up to 15 UT
Use CODE RPR model as a priori for all product lines
Ocean tide model for loading changed from GOT00.2 to FES2004
Change from relative to absolute antenna phase center modelling
Use IGS05 for geodetic datum definition
Troposphere model: GPT/GMF for vertical and TANZ for gradients
Use of updated CODE RPR a priori model for all satellites
Mean pole computed according to IERS2003 standards
Shapiro effect applied to GNSS (not only SLR)
Apply ocean tidal loading related center of mass corrections
hardisp.f is used to interpolate ocean tidal loading model constituents
Phase wind–up, polarization effect for clock estimation
Real-time data collection established using the bnc tool to complete
hourly and daily RINEX files
Use zero-model as RPR a priori for all GLONASS satellites
Inclusion of all available NGA stations in the CODE final analysis
Set up GNSS satellite antenna PCV parameters specific to eachindividual satellite (for later retrieval)Phase-consistent high-rate (5-sec) GPS satellite clock corrections
Time resolution for EOP estimation increased internally (from 2 to 1 hr)
Do not resolve ambiguities between Block IIR-M and other satellites for
LEICA and NOV receivers (L2C 0.25 cycle problem)
Numerous new GLONASS tracking stations (global coverage achieved)
New version of hardisp.f: more tidal constituents, phase bug corrected
No three day arc if the RMS of the orbit fit exceeds:
5 cm for GPS and 10 cm for GLONASS(for GLONASS no automated arc split was included so far)Handle more cases regarding the quarter-cycle problem
Higher order ionosphere (HOI: 2nd and 3rd order with IGRF v.11)
implemented; enabled in rapid procedure for test purposes
GNSS code bias retrieval from RINEX files
GPS & GLONASS P1C1 for satellites and receivers
GPS & GLONASS P2C2 for satellites and receivers
Verification of ambiguity resolution results activatedTroposphere model VMF1 for final, rapid, ultra-rapid
HOI corrections also activated for the final

3 Changes in the daily processing for the IGS

3.1 Overview of changes in the processing scheme in 2011
Table 4 gives an overview of the major changes implemented during year 2011. Details on
the analysis strategy can be found in the IGS analysis questionnaire at the IGS Central
Bureau (ftp://igscb.jpl.nasa.gov/igscb/center/analysis/code.acn).
Table 4: Selected modifications of the CODE processing, over 2011.
Date
09-Jan-2011
15-Jan-2011

DoY/Year009/2011
015/2011

Description
Orbit repeatability unit changed from cm to mm
An extra set of four parameters is set up for each GLONASS observing
station to characterize• one GLONASS-GPS receiver antenna offset vector (threecomponents) and• one GLONASS-GPS ZPD troposphere bias.

during Feb-2011
27-Feb-2011
17-Apr-2011

058/2011
107/2011

04-Jul-2011

185/2011

06-Sep-2011
27-Oct-2011

249/2011
300/2011

Extension of CODE final and rapid orbit validation (step-by-step)
New source of orbit quality measure table in the weekly CODE summary
starting with week 1625
GLONASS ambiguity resolution enabled (details below)
Use IGS08 for geodetic datum definition and receiver/satellite antennamodel (instead of IGS05)
ANTEX update from IGS08_1639 to IGS08_1643(GLONASS-K1 Z-offset value change from 0.0 to 1.75 m)
Extract a priori coordinates/velocities with 5 digits from IGS08.SNX.
Complete Ocean tidal loading table updated fromhttp://www.oso.chalmers.se/~loading/ because of detectedinconsistencies between recent and older results

Of course, several other improvements not listed in Tab. 4 were implemented. Thosemainly concern data download and management, sophistication of CODE’s analysis strategy, software changes (improvements), and many more. As these changes are virtually not
relevant for users of CODE products, they will not be detailed on any further.

3.2 Details on selected model changes
As an indicator of the influence of the model changes on the CODE orbit quality, the threeconsecutive one–day orbit solutions are fitted by one arc solving for the inital conditions,
three constant and six once–per–revolution parameters in the Sun–oriented coordinate
system at the satellite. The median from the RMS of this orbit fit from all satellites of
GPS and GLONASS is plotted for each day between October 2010 and April 2012 inFig. 2.

33

Dach, Schaer et al.: Center for Orbit Determination in Europe

F

M

A

M

J

2012

J

A

S

O

N

D

J

F

M

A

GLONASS satellites
GPS satellites
Switch to IGS08

4J

GLONASS ambiguity
resolution

Median of RMS in cm

6

2011
D

GPS−GLONASS bias added

N

Unit changed from cm to mm

2010
O
8

050

100

2

0
300

350

150

2010

200

250

300

350

2011
Day of year

050

100

2012

Figure 2: Median of the RMS from a three–day orbit fit.

GPS/GLONASS ambiguity resolution

MW/NL

L1/L2
L5/L3

The following strategies are applied depending on the lengths of the baselines:

QIF

In particular the benefit from the ambiguity resolution for the GLONASS is clearly visible
in Fig. 2. It is remarkable that this also did improve the orbits for the GPS satellites.

100 %Resolved ambiguities

L1/L2 (<20 km): Direct ambiguity reso90 %lution to the original observations using the SIGMA–strategy; for GPS
80 %and GLONASS (no restrictions re70 %garding freq.
and receiver type;
60 %GLONASS–SD bias retrieval)Baselines contain
WL/NL (<6000 km): Ambiguity resolu50 %GPS+GLONASS (65.9% resolved)
only GPS(89.1% resolved)
tion based on Melbourne–Wübbena
observations
40%
and afterwards narrow–lane linear
0
2000
4000
6000
combinations using the SIGMA–
Baseline length in km
strategy; only for GPS
L5/L3 (<200 km): Ambiguity resolution Figure 3: Ambiguity resolution with different
strategies for day 350 of year 2011.
based on wide– and narrow–lane linear combinations using the SIGMA–
strategy; for GPS and GLONASS (norestrictions regarding frequency and receiver type; GLONASS–SD bias retrieval andintroduction)
QIF (<2000 km): Unresolved ambiguities from the two steps above are resolved with the
QIF –strategy; for GPS and GLONASS (only the same frequency channels)

34

3 Changes in the daily processing for the IGS
2011

2011
D

J

F

M

A

M

J

J

A

S

O

N

D

D

J

90 %
80 %
70 %
60 %
Baselines contain
GPS+GLONASS
only GPSobservations

50 %Number of ambiguities

Resolved ambiguities

J

F

M

A

M

J

J

A

S

O

N

D

J

25000

100 %

GPS−ambiguities
are counted inthis period, only.

20000

15000
total number of ambiguities
number of resolved ambiguities

40 %
350

050

100

150

200

2011
Day of year250(a) Success rate in percent

300

350

350

050

100

150

200

250

300

350

2011
Day of year(b) Absolute success rate

Figure 4: Success rate of the ambiguity resolution in the CODE processing.

The success rate of the ambiguity resolution for the GPS observations was not reduced by
activating the resolution algorithms for GLONASS (see Fig. 4). As confirmed by Fig. 3,
the limited resolution rate for the combined GPS/GLONASS baselines with respect to
the GPS–only baselines can mainly be explained by the restrictions introduced by the
GLONASS ambiguity resolution algorithm (see above explanation). More details on themulti–GNSS ambiguity resolution at CODE are given in Schaer and Meindl (2011).

GPS/GLONASS biases in IGS05– and IGS08–frame and –antenna solutions
The network processed by the CODE analysis center in the years 2009 and 2010 has been
re–processed twice:
1. using the IGS05 antenna corrections together within the IGS05 reference frame
2. using the new IGS08 antenna corrections together within the IGS08 reference frame
In both solution series (based on IGS05 and IGS08) so called GPS/GLONASS bias parameters are included:• for the station coordinates equivalent to independent sets of weekly coordinatesfor GPS and GLONASS (applying a zero mean condition on the XYZ-components
inbetween them) and• the troposphere parameters (one constant bias for each week) to absorb a potential
mismodeling in the receiver antenna phase center variations.
When adding the GPS/GLONASS bias parameters the RMS of the post-fit residuals forthe weekly normal equation is reduced by about 1 % — this cannot only be explained by
the change of the degree of freedom (400 additional parameters with respect to 350,000
other parameters and nearly 27,000,000 observations). This improvement is achieved inboth series, based on IGS05 or IGS08 modeling standards.

35

Dach, Schaer et al.: Center for Orbit Determination in Europe
LEIAR25NONE
TPSCR.G3
NONE
TRM57971.00 NONELEIAT504GG
LEIS
TPSCR.G3
TPSH
TRM59800.00 NONELEIAT504GG
TPSCR3_GGD

NONE
CONE

LEIAX1202GG
TRM29659.00

NONE
NONE

4
2
0
−2
−4
4
2
0
−2
−4

BJCO

O
TXE
S
UFP
R
VTS
P
AZG
B

SAV

S
MNL
MNL

REC
F
REU
N
ROS
A
SALU

ETJI
GAN
P
LMM
F
ETJI
GAN
P
LMM
F

ASP
A
CNM
R
ETA
D
ETD
D

Z

ADIS
POV
E
ABM
F

WTZ

O
AZC

CON
Z
HOF
N
MCC
J
STR
2

IQAL

VALD
REY
K
ANK
R

ILHA

GLS
V
KHA
R
BAK
E
FRD
N

S
PDE
L
BAR
H
HNP
T
IDDR

NTU

LPAL
MAT
E

C

HER
T
HYD
E
JOZ2

FUN

TSE
A
BRS
T
FLRS

E

NICO
PEN
C
RCM
N

IQUI
LAM
A

M0S

DAR

W

8
6
4
2
0
−2
−4
−6
−8
YAR
3
BAK
O
CAL
L
CPX
F

Up in mm

East in mm North in mm

ASH700936D_M NONE
NOV702GG
NONE
TRM55971.00 NONE

4
2
0
−2
−4
4
2
0
−2
−4

VTS
P
AZG
B
BJCO

A

SALU
SAV
O
TXE
S
UFP
R

ROS

S
REC
F
REU
N

CNM
R
ETA
D
ETD
D

ABM
F
ASP
A

E
POV

Z
ADIS

WTZ

O
AZC

CON
Z
HOF
N
MCC
J
STR
2

IQAL

VALD
REY
K
ANK
R

ILHA

GLS
V
KHA
R
BAK
E
FRD
N

T
IDDR

HNP

H
BAR

S
PDE
L

NTU

LPAL
MAT
E

JOZ2

C
HER
T
HYD
E

FUN

TSE
A
BRS
T
FLRS

NICO
PEN
C
RCM
N

A

E

LAM

M0S

DAR

CAL
L
CPX
F
IQUI

8
6
4
2
0
−2
−4
−6
−8
W
YAR
3
BAK
O

Up in mm

East in mm North in mm(a) IGS05-based solution(b) IGS08-based solution

Figure 5: Differences in the computed weekly station coordinates between the default and thesolution with the GPS/GLONASS bias estimation.

The coordinate differences between the standard solution without GPS/GLONASS biases
and the new solution schemes with solving for one set of biases per week are plotted inFig. 5. It is noticeable that all differences in the IGS05-based solution have a positive
sign in the vertical component. This may be explained by a GLONASS-related scale
inconsistency, e.g., due to the satellite antenna offsets. In the IGS08-based solution thisfeature is not visible. Nevertheless, there are systematic effects in the vertical component
as well, e.g., most of the TRIMBLE-antennas show negative differences but in the results
for stations equipped with LEICA- or TOPCON-antennas positive signs dominate.

36

5 Reprocessing activities at CODE in 2011

4 Contribution to GLONASS satellite antenna calibration
CODE has reprocessed the GPS/GLONASS network starting from archived observation
files from June 2003 until end of Janury 2011. The IGS08.atx receiver antenna phasecenter corrections — for more than 50% of the antenna radome combinations specific
GLONASS calibration values were available — have been applied.
For all GLONASS satellites and the GPS satellite with the SVN 62 new antenna phasecenter corrections have been estimated following the strategy introduced by Dach et al.
(2011). For the GPS satellite antennas (with exception of SVN 62) the antenna phasecenter corrections according to the IGS08.atx model have been introduced to guarantee
the full consistency of the antenna phase center corrections for the additional satellites.
An alternative solution for GLONASS satellite antenna corrections have been provided by
the analysis center at ESOC. Further information on a comparison and combination canbe found in Dilssner et al. (2011). The combined antenna phase center model is a part of
the IGS08.atx .

5 Reprocessing activities at CODE in 2011
The release of the IGS08 reference frame and the corresponding antenna phase center
corrections for the receivers and satellites together with other updates in the CODE processing scheme gave the motivation for a reprocessing of the data starting in January 1996.
The processing followed the latest IERS 2010 conventions (Petit and Luzum, 2010).
The processing until May 2003 has started from RINEX. For the period until end of2008 an existing set of pre–processed GPS/GLONASS observation files from a previous
reprocessing have been reused. Starting with 2009 the screened observation files from theoperational CODE processing were taken. Note, that for the full time span starting inMay 2003 the GLONASS ambiguity resolution algorithm has been applied. A detailed
description of the used models is given in ftp://ftp.unibe.ch/aiub/REPRO_2011/CODE_REPRO_2011.ACN .
Table 5: CODE reprocessing products available through anonymous ftp.
CODE final products available at ftp://ftp.unibe.ch/aiub/REPRO_2011/CODE/yyyy/
yyyy/CODwwwwd.EPH.Z CODE final GNSS orbits, correspond to our official IGS orbit productyyyy/CODwwww7.ERP.Z CODE final ERPs belonging to the final orbits, values for the full week
yyyy/CODwwww7.SNX.Z CODE weekly SINEX product
Note that more results are available in Bernese (version 5.2) specific formats in ftp://ftp.unibe.ch/aiub/REPRO_2011/BSWUSER52/yyyy/ .

37

Dach, Schaer et al.: Center for Orbit Determination in Europe
The reprocessing did include atmospheric pressure loading (APL) deformation from Wijaya et al. (2011). It has been introduced with scaling factors for each station. The products from this reprocessing made available at ftp://ftp.unibe.ch/aiub/REPRO_2011/(see Tab. 5) are generated without correcting for the APL effect by enforcing the scaling
factor to zero.
There are plans to extend the list of products by clock corrections (starting with 2008 also
for GLONASS).

References
Dach, R., G. Beutler, H. Bock, P. Fridez, A. Gäde, U. Hugentobler, A. Jäggi, M. Meindl,
L. Mervart, L. Prange, S. Schaer, T. Springer, C. Urschl, and P. Walser. Bernese GPS
Software Version 5.0. Astronomical Institute, University of Bern, Bern, Switzerland,jan 2007. URL http://www.bernese.unibe.ch/docs/DOCU50.pdf. User manual.
Dach, R., R. Schmid, M. Schmitz, D. Thaller, S. Schaer, S. Lutz, P. Steigenberger,
G. Wübbena, and G. Beutler. Improved antenna phase center models for GLONASS.
GPS Solutions, 15(1):49–65, 2011. doi: 10.1007/s10291-010-0169-5.
Dilssner, F., R. Dach, R. Schmid, T. Springer, and R. Zandbergen. Updating the IGS
processing standard: new GLONASS satellite antenna corrections for igs08.atx. In EGU
General Assembly, Vienna, Austria, April 2011. Poster.
Hugentobler, U., M. Meindl, G. Beutler, H. Bock, R. Dach, A. Jäggi, C. Urschl, L. Mervart,
M. Rothacher, S. Schaer, E. Brockmann, D. Ineichen, A. Wiget, U. Wild, G. Weber,
H. Habrich, and C. Boucher. CODE IGS Analysis Center Technical Report 2003/2004.
In K. Gowey, R. Neilan, and A. Moore, editors, IGS 2004 Technical Reports, pages 40–
51, Jet Propulsion Laboratory, Pasadena, California, USA, 2008. IGS Central Bureau.
Petit, G. and B. Luzum (Eds). IERS Conventions (2010). IERS Technical Note 36,
Bundesamt für Kartographie und Geodäsie, Frankfurt am Main, 2010. URL http://www.iers.org/IERS/EN/Publications/TechnicalNotes/tn36.html.
Meindl, M. Combined Analysis of Observations from Different Global Navigation Satellite
Systems, volume 83 of Geodätisch-geophysikalische Arbeiten in der Schweiz. Schweizerische Geodätische Kommission, 2011. ISBN: 978-3-908440-27-7.
Schaer, S. and M. Meindl. Multi-GNSS Ambiguity Resolution Algorithms, chapter Commission 4: Positioning and Applications, pages 95–96. Swiss National Report on the
Geodetic Activities in the years 2007–2011 to the XXV General Assembly of the IUGG,
Melbourne, Australia, 28 June — 7 July 2011. Swiss Geodetic Commission, 2011.

38

References
Wijaya, D.D., J. Böhm, H. Spicakova, M. Schindelegger, M. Karbon, D. Salstein, and
H. Schuh. Determination of atmospheric pressure loading corrections based on a newconcept of reference pressure. Journal of Geodesy, 2011. to be submitted.
All publications, posters, presentations of the Satellite Geodesy research group at AIUB
are available at www.bernese.unibe.ch/publist .

39

Dach, Schaer et al.: Center for Orbit Determination in Europe

40

NRCan Analysis Center Report for 2005-2011
B. Donahue, R. Ferland, R. Ghoddousi–Fard, F. Lahaye, Y. Mireault
Natural Resources Canada, Geodetic Survey Division
615, Booth Street, Ottawa, ON, Canada K1A 0E9
Brian.Donahue@nrcan.gc.ca

1 Introduction
The NRCan (formerly EMR) Analysis Center (NRCan–AC) contribution to the International GNSS Service began in the early days of the IAG service. The day–to–day
operations of the analysis center are performed by staff in the Geodetic Survey Division(NRCan–GSD) of the Canada Center for Remote Sensing within the Natural Resources
department of the Canadian federal government. The NRCan–GSD is responsible for the
maintenance of the national horizontal, vertical and gravitational reference frames as wellas providing the means of accessing these data.
This technical report will address in a first section the major product changes and events
that occurred within the NRCan–AC since the last issue of IGS Technical Reports. A
second section will address the strategies used for the generation of the current and planned
products for submission to the IGS and the larger community.

2 2005–2011 Review
2.1 Major Products Changes
The major changes to the NRCan–AC products are listed in Table 1 in chronologicalorder. Readers are referred to the Analysis Coordinator web site (http://acc.igs.org)
for historical combination statistics of the NRCan–AC products.

41

Donahue et al.: Natural Resources Canada
Table 1: Major changes to NRCan-AC processing strategy since 2005

CalendarDate2005 may 16

GPS Wk(day)
1323 (1)

Product
Ultra-Rapid

Change description
Bernese v5.0 (from v4.2)

2006 sep 03
2006 oct 211391 (0)1397 (6)Rapid/Final
Ultra-Rapid

2006 oct 31
2006 nov 05

1399 (2)1400 (0)Ultra-Rapid
Ultra-Rapid
Rapid/Final

Satellite clocks at 30 second interval
EMU GPS clocks rough alignment to GPStime
Production of 5-minute GPS clocks
Absolute phase centers and IGS05 referenceframe2007 jan 24
2007 mar 04

1411 (3)1417 (0)Ultra-Rapid
Final2007 oct 101448 (3)Ultra-Rapid

2008 jul 28

1490 (1)Rapid/Final

Gipsy-Oasis v5.0 and GMF troposphericmapping function

2009 oct 111553 (0)Rapid/Final

2009 oct 151553 (4)

Rapid/Final

10 degrees elevation cutoff(from 15 degrees)
IERS03 sub-daily tide model( from IERS96 )2010 apr 20

1580 (2)Ultra-Rapid

CC2nonCC correctly applied

2011 apr 171632 (0)IGS08 (from IGS05)

2011 may 221637 (2)Ultra-Rapid
Rapid/Final
Rapid

2011 jul 18
2011 sep 111645 (1)1653 (0)

Rapid
Final

Hourly production of EMU
24h satellite orbital arc(from 30h = 3+24+3)
Production of 30-second GPS clocks

Bernese GPS+GLONASS solution GPS
submitted for IGR combination(IGS Mail #6410)
ERP file LOD print format correction
Bernese GPS+GLONASS solution
GLONASS submitted to IGLOS comb

2.1.1 Ultra–Rapid Orbit and Clock Products
During the 2005 to 2011 period, the NRCan–AC continued its development and its deliveryof Ultra Rapid products (EMU) to IGS and to support NRCan–GSD services such as
CSRS–PPP (NRCan online GNSS Processing Service) and HPGPS.C (NRCan real–time42

2 2005–2011 Review
wide area GPS Corrections). Several changes were implemented to our strategy as canbe seen in Table 1. The most important changes are related to the production of 30–
second clocks along with the hourly availability of EMU products with a delay of less than
90 minutes after the last observation. This allowed offering users of the CSRS–PPP service
a near real–time GPS processing capability with a maximum delay of 90 minutes.
One bug correction in our Ultra–Rapid clock production deserves further attention. Fromthe end of 2008 to the end of April 2010 and due to an unfortunate implementation
error, the program CC2nonCC (IGS Mail #2827), which ensures consistency of precise
satellite clock information with P1/P2 code measurements, was not applied to stations
that needed it. The quality of the clock products during that period was not affected, in
terms of impact on positioning. However, the comparison of EMU clocks with respect to
IGR would show a scatter of up to 0.2 ns to 0.4 ns, depending on how many such stations
were included in our processing.

2.1.2 Rapid and Final Products
As can be seen in Table 1, several modifications were also implemented to the NRCan–AC
Rapid and Final products. Besides the estimation of 30–sec satellite clocks in September
2006, the most important changes were the switch of software from Gipsy–Oasis (Webband Zumberge, 1995) to Bernese (Dach et al., 2007) for the generation of Rapid products
and the start of our contribution of Final GLONASS solutions to IGLOS. Details of the
new Rapid strategy are described in section 3.3.

2.1.3 Real–Time Products
The NRCan–GSD has been processing real–time GNSS data since 1996, when it started
processing 4 real–time Canadian stations using in–house software and systems developedin support of a pseudorange–based wide–area correction service. As data streaming stations were added over the years, the service evolved from a strictly Canadian to a North–
American coverage service. In the early 2000’s, NRCan–GSD began development of its
next generation correction service based on pseudorange and carrier–phase observations.
These prior developments put NRCan–GSD in a good position to start contributing real–time orbital and clock corrections to the IGS Real–Time Working Group for comparisonand combination. The system is currently drawing on tracking data from the Real–Time
IGS network as well as Canadian permanent real–time stations to generate global corrections based on real–valued ambiguities. The system and its future developments aredescribed in Section 3.1.

43

Donahue et al.: Natural Resources Canada

2.2 Other Major Events
During the years 2008 and 2009 the NRCan–AC took part in the reanalysis project (repro1)of historical GPS tracking data for the years 1994 to 2008, both as contributor of asolution (em1) and as the repro1 reference frame coordination and combination center. The
objective for repro1 was for all analysis centers to estimate the products in a consistentreference frame (IGS05) using an agreed–upon set of the latest models, methodologies
and conventions. The NRCan AC solutions included all core IGS products for the years
1995 to 2008. Table 2 summarizes the models used for the NRCan–AC repro1 products
generation.
This was the first such effort being conducted at NRCan–GSD and was done using JPL’s
Gipsy–Oasis II v5.0 software (Webb and Zumberge, 1995) on 2 Linux servers with 4 quadcore CPUs (32 CPUs in total). The NRCan–AC solutions included daily satellite orbits andclocks, daily earth rotation parameters, daily station clocks, and weekly station positions
as well as satellite phase center Z–offsets. Due to the time constraints for this project, one
major change was implemented relative to the normal NRCan–AC production solution.
The repro1 solutions were independent 24h daily solutions with orbits initialized fromoriginal IGS Final solutions and bulletin B ERPs. In comparison, the normal production
NRCan–AC solutions use the previous day solution to initialize the orbits and ERPs. The
complete project took 15 months for ≈5000 daily solutions including reruns.
After more than a decade, the Reference Frame coordination role was transferred in
February 2010 (wk 1566) from NRCan–GSD to the Institut géographique national (IGN),
France. In this essential IGS role, NRCan–GSD operated the weekly combination of
weekly station coordinates, daily ERPs and weekly implicit apparent geocenter position
Table 2: NRCan repro1 model summary

Parameter
Observations
Elev Cutoff
Daily Arc
Subdaily EOPs
2nd order Iono
Earth Albedo
SRP IIR/IIA
Antenna Calibrations
Tropo Mapping Function
Satellite Z-offset
Solid Earth Tide
Pole Tide
Yaw Rates

44

NRCan repro1
UD Iono-free phase and range
10 deg
24 h
IERS96
None
None
Table Interpolation/GSPM-98
igs05.atx (Offset and PCVs)
GMF
Estimated
IERS2003
IERS2003
Nominal + Estimate

2 2005–2011 Review
from some 8 to 9 analysis centers (COD, EMR, ESA, GFZ, GRG, JPL, MIT, NGS, SIO)
using 6 to 7 independent analysis software packages along with 2 Associate Analysis Centers (MIT, NCL) contributing weekly combinations of the above. The transfer to IGN
was carefully implemented overlapping one year of weekly SINEX combinations from thetwo institutions. Table 3 provides a summary of key Reference Frame Working Group
activities between 2005 and 2010.

Table 3: Key Reference Frame coordination activities for 2005-2010
2005• The effect of updating from relative to absolute antenna phase center corrections
was analyzed using AC contributions. This effect was most noticeable in the heightcomponent which for reference frame purposes links directly into the scale. It also
caused a discontinuity on all SINEX combined products. The use of relative phasecenter was causing a 3 ppb bias in IGb00 while the use of absolute antenna phasecenter reduced the bias to less than 1 ppb in IGS05.
• As the time span of the coordinates series and the number of stations did increase so
did the number of discontinuities. Equipment changes did cause most of the discontinuities. The detection of small discontinuities was also found to be subjective.

2006• Weekly station coordinates for 335 stations (for the period 1996–2005), daily ERP’s(for the period 1999–2005) and weekly apparent geocenter (for the period 1999–2005)
were contributed to IERS for the realization of ITRF2005.
• A subset (132) of the contributed stations to ITRF05 was selected to realize IGS05,
which became official at the end of 2006. At that time, the RMS between the IGS05
and the IGS combined weekly solutions was 2mm horizontally and 6mm vertically.

2007• The reprocessing of the IGS historical data (1994–2007) became necessary to provide
fully consistent IGS products. A reprocessing test campaign was organized to prepare
for this major effort. COD, EMR, GFZ, MIT, NGS and SIO did participate.

2008• The ACs (COD, EMR, ESA, GFZ, GTZ, JPL, MIT, NGS, PDR, SIO, ULR started
to provide weekly reprocessed solutions going backward in time. By the end of theyear, preliminary combined solutions were available for the period 2003–2007.

2009• By the end of the year, all ACs reprocessed solutions were completed. They were
gradually combined and updated as needed. Weekly solutions for over 900 stations
were provided by the ACs.
• A contribution of the IGS weekly official and reprocessed combinations to ITRF2008
was also provided to IERS at the beginning of 2009. This contribution was graduallyextended to finally reach the period 1997–2009.5 by August 2009. 560 stations were
provided to IERS for the ITRF08 realization. Several exchanges of technical information with IGN helped for an upcoming smooth transition of the RFWG responsibility

2010• The transfer of the responsibilities to IGN for the Reference frame working group activities was finalized by mid-January. The final submission of the combined reprocessed
solutions (1994–2007) was made to CDDIS in the spring.

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Donahue et al.: Natural Resources Canada

3 Current Status and Future Work
Statistics of the combination/comparison of the various NRCan–AC products are given in
Table 4 for years 2010 and 2011. The Ultra–Rapid products are given for the estimatedportion and a few prediction time span with respect to the IGS Rapid products in terms of
median satellite RMS. The comparison of NRCan–AC Rapid GPS, Final GPS and Final
GLONASS submissions are the median over all RMS with respect to the respective IGS
combinations, as computed in the Analysis Center Coordinator combination reports. The
reader should note the Final GLONASS were only available for the last 112 days in 2011.
Table 4: Median Orbit and Clock RMS of NRCan–AC products compared to IGS Combinations
for years 2010 and 2011

Product
EMU estimated portion (24 h) vs IGR
EMU 3 h prediction vs IGR
EMU 6 h prediction vs IGR
EMU 12 h prediction vs IGR
EMU 24 h prediction vs IGR
EMR Rapid vs IGR
EMR Final vs IGS
EMX Final vs IGLOS

Orbits (cm)
2010
2011
2
2
5
5
5
5
5
5
10
10
2.0
1.2
1.9
1.9
—
3.1

Clocks (ns)
2010
2011
0.10
0.10
0.50
0.45
0.72
0.66
1.08
1.03
2.03
1.99
0.07
0.11
0.09
0.11
—
8.45

3.1 Real–Time Products
The real–time computation infrastructure operated at NRCan–GSD consists of two geographically separated production servers in hot stand–by, one server, identical to the
production servers, at NRCan facilities for validation of pre–production–level algorithm
updates and bug corrections, and finally one server where development occurs. Data
streams from some 60 global stations part of the Real–Time IGS network, supplemented
with a few of Canadian stations, are multicast on a Wide–Area Network to which allservers listen.
The current pseudorange and carrier–phase processing algorithm acquires the GPS station data at 1 Hz, carrying cycle–slip detection at that interval. All stations and satellites
clock synchronization error (but one) are estimated at two seconds interval, along withreal–valued ambiguities and a wet tropospheric delay at each station as a process noise.
The station coordinates are fixed at their epoch IGS08 value and the satellite positions
are obtained from the NRCan–GSD Ultra–Rapid orbit predictions produced hourly (seesection 3.2). The satellite positions and clock synchronization errors are transmitted over46

3 Current Status and Future WorkInternet as differences with respect to current broadcast satellite ephemerides parameters in a modified RTCA format (NRCan, 2003), which carries corrections with a 4mm
resolution (compared to the FAA–WAAS specification of 12.5 cm). Two other correction
streams are produced in the new state–space representation message format under development at the Radio Technical Commission for Maritime Services Special Committee 104(www.rtcm.org): one where all GPS–specific messages are produced and a second stream
tailored to the IGS Real–Time pilot project requirements.
Current development work include the implementation of the Decoupled Clock Model(Collins at al., 2008) for integer ambiguity resolution and the incorporation of GLONASS
data in view of a multi–GNSS real–time correction service.

3.2 Ultra–Rapid GPS&GLONASS Products
NRCan–GSD is currently working on a strategy to produce GNSS hourly orbit products.
The method is very similar to the current implementation of our GPS only Ultra Rapid
strategy already described in Mireault et al. (2008). The processing of both GPS andGLONASS data is done the same way as in our Rapid GNSS solutions. The development
is nearly completed and parallel testing will soon begin in 2012. GNSS clock estimation
development will most likely start in the middle of 2012. Full implementation of true
Ultra Rapid GNSS orbits and clocks should be available by early 2013. One major draw
back of producing GNSS products is the increase in processing time which might prevent
us from delivering hourly products. A longer update interval and/or a longer delay may
result from the addition of the GLONASS constellation.

3.3 Rapid GPS&GLONASS Products
The new Bernese Rapid products are run daily and consist of the usual SP3 format files(orbits and clocks at 15–minute intervals), RINEX clock format files (30–second satellite
clocks) and ERP. Both GPS and GLONASS data are processed simultaneously using theBernese v5.0 software (Dach et al., 2007). Resulting products are sent to IGS and usedinternally as well. Table 5 is a summary of the strategy used for our Rapid solution.

3.4 Final GPS&GLONASS Products
In September 2011, NRCan started contributing to the Final IGLOS combination. For thetime being and until further developments are in place, a similar approach to our Rapid
GNSS product generation is used. Mainly, station coordinates are highly constrained
and not completely loose as per the Final IGS conventions. However, our strategy was
accepted by the Analysis Center Coordinator and further work will allow us to use theproper conventions. Note that our Gipsy–Oasis GPS–only solutions are still being used47

Donahue et al.: Natural Resources Canada
Table 5: Rapid GNSS solution strategy
Software
Network
Observations
A priori orbits
A priori ERP
Troposphere
Ambiguities
Orbits and ERP
OrbitsClocksUse of Bernese 5.0
Around 120 stations (3 clusters) and 60 stations (1 cluster) are used for orbit
and clock estimation respectively
GPS and GLONASS observations are always processed together:
Orbits: double-difference phase observations
Clocks: zero-difference code and phase observations
NRCan-AC Ultra Rapid (EMU), IGU/IGV or previous day predictions
NRCan-AC Ultra Rapid (EMU)
3 h zenith delays and 24 h horizontal gradients
GPS only in orbit estimation (≈80–85% resolved)
GLONASS ambiguities remain float
Produced using a sliding two 1-day Normal Equation (NEQ)
Produced first followed by a second run for the clock estimation(orbits and ERP held fixed)
Estimated at 5-minute intervals and then interpolated at 30-second intervals

for the Final GPS combinations. The new Bernese solution is strictly used for IGLOS andis called EMX. The orbits are rotated (RX, RY and RZ) to align them to our Gipsy–Oasis
Final GPS solutions
In preparation for NRCan’s contribution to the 2nd IGS reanalysis campaign, the Final
GPS product strategy will be updated in mid–2012. The major strategy change will
be to run independent 24 h daily solutions with orbits initialized from IGS rapids andBulletin A ERP. The current NRCan–AC strategy is to use the previous day Final solution
to initialize the orbits and ERP. Many other model changes will be made at this time andare summarized in Section 3.5.

3.5 Participation in the 2nd IGS Reprocessing Campaign
Beginning in mid–2012 the NRCan–AC will start re–estimating the core IGS products
for the years 1994 to 2012. This 2nd IGS reprocessing campaign will be called repro2
and the NRCan–AC products will be named em2. The plan for repro2 is for all ACs
to estimate the products in a consistent way using the latest models and methodology.
Table 6 summarizes the major changes to the NRCan–AC solution between repro1 andrepro2.
The plan for repro2 at the NRCan–AC is to begin estimating solutions in late 2012 andto process at a rate of ≈2 years/month. This will allow for the completion of the project
before the end of 2013.

48

References
Table 6: Comparison of repro1 and repro2 NRCan–AC solutions

SoftwareSatellite System
Terrestrial Ref Frame
Antenna Calibrations
SRP Model IIR/IIA
Nutation Model
Earth Albedo
Gravity Field
Solid Earth Tide
Pole Tide
Subdaily EOPs
2nd Order Iono
SINEX Solution
Satellite Clock Rate

NRCan repro1 (em1)
JPL’s GIPSY-OASIS II,V5.0
GPS Only
IGS05
Igs05.atx
Table /GSPM-98
IAU 1980
None
JGM3
IERS 2003
IERS 2003
IERS 1996
None
7d
5 minute

NRCan repro2 (em2)
JPL’s GIPSY-OASIS II, V.6.1
GPS Only
IGS08
Igs08.atx
GSPM-2010
IAU 2000A
Applied
EGM2008
IERS 2010
IERS 2010
IERS 2010
Applied1d
30 second

3.6 Ionosphere
After a long interruption, the NRCan–AC contribution to the Final IGS ionospheric vertical TEC grid product is planned. In addition to our current process generating regionalvertical TEC grid using spherical cap harmonic analysis (Ghoddousi–Fard et al., 2011)a process is undergoing to map vertical TEC using spherical harmonic expansion on a
global geomagnetic reference frame. The process can be initialized using a global gridderived from International Reference Ionosphere (IRI2007). Vertical TEC values are estimated on a single layer model from GPS inter–frequency, phase–smoothed, geometry–freepseudorange measurements corrected for satellite and receiver differential code biases.
The planned global daily TEC grid generation for contribution to the IGS products willcomplement our near–real–time global TEC grid generation currently under preliminary
test.

References
Collins, P., F. Lahaye, P. Héroux and S. Bisnath. Precise Point Positioning with Ambiguity Resolution using the Decoupled Clock Model. Proceedings of ION-GNSS-2008,
Savannah, Georgia, 16-19 September, pp.1315–1322, 2008.
Dach, R., U. Hugentobler, P. Fridez and M. Meindl. Bernese GPS Software Version 5.0.
AIUB, Astronomical Institute, University of Bern, January 2007.

49

Donahue et al.: Natural Resources Canada
Ghoddousi–Fard, R., P. Héroux, D. Danskin, and D. Boteler. Developing a GPS TEC mapping service over Canada. Space Weather, 9:S06D11, 2011. doi: 10.1029/2010SW000621.
Mireault, Y., P. Tétreault, F. Lahaye, P. Héroux and J. Kouba. Online Precise Point
Positioning. GPS World, 19(9):59–64, September 2008.
NRCan. GPS.C Interface Control Document, v. 3.7. 2003.
Webb, F. H. and J. F. Zumberge. An introduction to Gipsy–Oasis II. Jet Propulsion
Laboratory, July 17-21, 1995.

50

The ESA/ESOC IGS Analysis Centre
T. A. Springer, W. Enderle,
L. Agrotis , F. Dilssner, C. Flohrer, F. Pereira,N. Romero, R. Zandbergen
European Space Operations Centre
Darmstadt, Germany

1 Introduction
The IGS Analysis Centre of the European Space Agency (ESA) is located at the European
Space Operations Centre (ESOC) in Darmstadt, Germany. The ESOC Analysis Centre
has been involved in the IGS since its very beginning in 1992. In this report we give asummary of the IGS related activities at ESOC in the recent years, roughly since 2004.
It focuses on the major changes in the routine processing during this period of almosta decade. It also addresses some of the activities at ESOC which are not directly IGS
related but which rely heavily on the ESA IGS products. This report will demonstratethat the the ESA/ESOC Analysis Centre has been very active and very succesful in the
recent years. Besides being an IGS analysis centre we have also become an analysis centerof the IDS and ILRS services. Furthermore, besides the routine product generation for the
IDS, IGS, and ILRS we are fully ready for the Galileo system and are capble of processing
all LEO observation types. This latter is important as it enables us to do precise orbit
determination of all LEO satellites in particular the Sentinel satellites of the GMES.

2 ESA IGS Analysis
2.1 ESA Products
The ESA IGS Analysis centre contributes to all the core IGS analysis centre products,
being:• Final GNSS (GPS+GLONASS) products– Provided weekly. Normally on Friday after the end of the observation week.
– Based on 24 hour solutions using 150 stations
51

Springer et al.: European Space Operations Centre– True GNSS solutions simultaneously and fully consistently processing of GPS
and GLONASS measurements. Means a total of around 55 satellites.
– Consisting out of Orbits, Clocks, coordinates, Ionosphere, and EOPs
• Rapid GNSS (GPS+GLONASS) products– Provided daily for the previous day.
– Available within 3 hours after the end of the observation day– Based on 24 hour solutions using 110 stations– True GNSS solutions simultaneously and fully consistently processing of GPS
and GLONASS measurements. Means a total of around 55 satellites.
– Consisting out of Orbits, Clocks, coordinates, Ionosphere, and EOPs
• Ultra–Rapid GNSS (GPS+GLONASS) products– Provided 4 times per day covering 48 hour intervals until 0, 6, 12, and 18 hours
UTC.
– Available within 3 hours after the end of the observation interval– Based on 24 hours of observations using 110 stations– True GNSS solutions simultaneously and fully consistently processing of GPS
and GLONASS measurements. Means a total of around 55 satellites.
– Consisting out of Orbits, Clocks, Ionosphere, and EOPs
– Containing a 24 hour estimated interval and a 24 hour predicted interval.
Besides these core products ESA is very active in different working groups. Most notably
are our efforts in the Real–Time pilot project where besides being one of the analysis
centres we ESA is also responsible for the analysis centre coordination. However, also
our efforts in the scope off the antenna calibarations and satellite orbit modeling working
groups are not insignificant. Furthermore, we will significantly contribute to the IGS
MGEX efforts.
An up to date description of the ESA IGS Analysis strategy may be found at:
ftp://dgn6.esoc.esa.int/products/esa.acn

2.2 ESA Reprocessing
ESA has also participated in the first IGS reprocessing efforts (repro1) for the IGS contribution to the realisation of the International Terrestrial Reference Frame 2008 (ITRF08).
Thanks to efficiency and speed of the NAPEOS software (see development section) ESOC
was able to contribute to this very demanding effort despite the limited computational
power available to our group at ESOC. Thanks to the fact that NAPEOS can process
a full day of GNSS data in less the 60 minutes the reprocessing effort could be done ona relatively simple Linux–PC within a reasonable amount of time. For this reprocessing
effort ESA has processed all historic GNSS data of the IGS from 1994 to 2008 but theresults in 1994 were considered to be off to poor quality to submit.

52

2 ESA IGS Analysis
Meanwhile ESA has repeated the reprocessing using the ITRF08 station coordinates andthe corresponding IGS08 antex corrections for the receiver and transmitter antennas. In
this reprocessing the years 1995 to 2008 are done using only GPS observations, but from2009 the reprocessing does fully include the GLONASS observations and thus are true
GNSS solutions. The products from the first ESA official reprocessing efforts based on the
ITRF05 reference frame are available from the official IGS data centres. The most recent
ESA reprocessing products, currently based on the ITRF08, are available from our ftp:
ftp://dgn6.esoc.esa.int/igs/repro2
These are our preliminary products for the second IGS reprocessing effort (repro2) andthus the products are labelled "es2". The products from the first reprocessing were,consequently, labelled "es1". Currently only the orbit products are made available. Other
products are available on request. An interesting difference between our es1 and es2
reprocessing is that, as mentioned before, from 2009 our es2 products are GNSS products.
Also our es2 products do contain 30 second clock estimates. We generate these high–rateclock products because we are also very active in processing GNSS data from Low Earth
Orbiting (LEO) receivers (see later section). For LEO processing high–rate clocks are verymuch needed to get accurate orbits based when using the well–known PPP technique. At
present it is unclear whether we as ESA will make these high–rate clocks freely available.
Last but not least it is wortwhile to mention that besides participating in the IGS reprocessing efforts ESA also contributed to the reprocessing efforts of the IDS and the ILRS.
This represents a rather unique achievement in that one single software version, NAPEOS,
contributed to the ITRF solutions of three different space geodetic techniques.

2.3 ESA Product Highlights
One of the highlights of the ESA Analysis Centre products is that they are one of the bestproducts available from the individual IGS analysis centres. Secondly the ESA products
are one of the few complete GNSS products. In fact ESA was the first IGS analysis centre
to provide a consistent set of GNSS orbit and clock products. These product constituted
the very first products that could, and are, used for true GNSS precise point positioning.
The sampling rate of the final GPS+GLONASS clock product is 30 seconds.
Another special feature of the ESA products is that they are based on completely independent 24 hour solutions. Although this does not necessary lead to the best products, asin the real world the orbits and EOPs are continuous, it does provide a very interesting
set of products for scientific investigations as there is no aliasing and no smoothing.

53

Springer et al.: European Space Operations Centre

3 ESA Analysis Developments
3.1 NAPEOS Developments
The Navigation Package for Earth Orbiting Satellites, NAPEOS, Springer (2009), has beendeveloped at ESOC over the scope of many years. It started as a rewrite, from Fortran77 into Fortran 90, for the flight dynamics section of ESOC of the old Bahn program
including all the smaller support programs. After the very successful completion of thattask it was decided to add the GNSS capabilities to NAPEOS as well. Although initiallyforeseen to be finished in 2004 it effectively took until the end of 2007 before NAPEOS
was fully ready and capable to be used for the high accuracy IGS service.
In January 2008 ESOC started to use NAPEOS for its IGS activities after having tested
the software by running a small reprocessing effort covering the full year of 2007. After the
introduction of NAPEOS for the IGS routine processing the NAPEOS developments did
not stop, on the contrary the development speed actually increased. Because NAPEOS wasused more and more in the navigation support office at ESOC more and more requirements
were put on the system but also more resources for development became available. Overthe time period from 2008 to 2010 all projects within the navigation support office of
ESOC switched from the old Bahn software to the meanwhile clearly superior NAPEOS
software. Besides being more accurate, more efficient, and much faster, NAPEOS also ismuch easier to learn, configure, and operate. Over the years since 2008 the versatility as
offered by the NAPEOS software has greatly enhanced the abilities and productivity of
the navigation support office.
In 2008 the IGS activities started with NAPEOS version 3.0, whereas meanwhile (2012)
we are working on the release of NAPEOS version 3.7. Despite the very high quality of
the current NAPEOS version 3.6., the version 3.7 will bring significant improvements andenhancements. In particular the integer ambiguity resolution was significantly improved
now giving rise to almost always 98% of resolved ambiguities compared to 90% today.
Furthermore, the integer ambiguity resolution was enhanced in such a way that it can now
also include LEO GNSS receivers and fix LEO–LEO but also Station–LEO ambiguities.
And in version 3.7 the Ionosphere estimation is incorporated into the NAPEOS software.
Last but not least some significant further speed improvements were achieved. For our
IGS type of processing an improvement of about 25% was achieved whereas for our LEO
processing a speed improvement of about 50% (meaning a factor of 2 faster!) was achieved.
With these speed improvements NAPEOS is now capable of processing an IGS type ofsolution (150 stations, 55 satellites) including a LEO (e.g. JASON) in less than 2 hours
on a single core of a standard PC. An amazing achievement!
Thanks to the excellent quality of the NAPEOS software we were one of the first GNSS
centres world–wide that noticed and documented the anomaly of the SVN 49, Springer and
Dilssner (2009). Our efforts contributed significantly to the understanding of the problem

54

3 ESA Analysis Developmentswith this satellite. Unfortunately, as it turned out, the problem cannot be resolved andthe satellites has to be considered to be lost.

3.2 The GLONASS–M satellite yaw–attitude model
The proper modelling of the satellites’ yaw–attitude is a prerequisite for high–precision
Global Navigation Satellite System (GNSS) positioning and poses a particular challenge
during periods when the satellite orbital planes are partially eclipsed. Whereas a lotof effort has been put to examine the yaw–attitude control of GPS satellites that are in
eclipsing orbits, hardly anything was known about the yaw–attitude behaviour of eclipsing
GLONASS–M satellites. However, systematic variations of the carrier phase observation
residuals in the vicinity of the orbit’s noon and midnight points of up to ±27 cm indicated significant attitude–related modelling issues. In order to explore the GLONASS–M
attitude laws during eclipse seasons, we studied the evolution of the horizontal satellite
antenna offset estimates during orbit noon and orbit midnight using a technique that werefer to as “reverse kinematic precise point positioning” . In this approach, we keep all relevant global geodetic parameters fixed and estimate the satellite clock and antenna phasecentre positions epoch–by–epoch using 30–second observation and clock data from a global
multi–GNSS ground station network. The estimated horizontal antenna phase centre offsets implicitly provide the spacecraft’s yaw–attitude. The insights gained from studying
the yaw angle behaviour have led to the development of the very first yaw–attitude modelfor eclipsing GLONASS–M satellites, Dilssner (2010); Dilssner et al. (2011). The derived
yaw–attitude model proves to be much better than the nominal yaw–attitude model commonly being used by today’s GLONASS–capable GNSS software packages as it reduces
the observation residuals of eclipsing satellites down to the normal level of non–eclipsingsatellites and thereby prevents a multitude of measurements from being incorrectly identified as outliers. It facilitates continuous satellite clock estimation during eclipse andimproves in particular the results of kinematic precise point positioning of ground–based
receivers.

3.3 ESOC contributions to PCO/PCV
Driven by the comprehensive modernization of the GLONASS space segment and theincreased global availability of GLONASS–capable ground stations, Springer and Dach(2010), an updated set of satellite–specific antenna phase centre corrections for the current GLONASS–M constellation was determined by processing 84 weeks of dual–frequency
data collected between January 2008 and August 2009 by a worldwide network of 227 GPS–
only and 115 combined GPS/GLONASS tracking stations. The analysis was performed
according to a rigorous combined multi–system processing scheme providing full consistency between the GPS and the GLONASS system. The solution was aligned to a realization of the International Terrestrial Reference Frame 2005. The estimated antenna55

Springer et al.: European Space Operations Centre
parameters are compared with the model values currently used within the International
GNSS Service (IGS). It was shown that the z–offset estimates are on average 7 cm smaller
than the corresponding IGS model values and that the block–specific mean value perfectly
agrees with the nominal GLONASS–M z–offset provided by the satellite manufacturer. It
was demonstrated that the orbit quality benefits from the updated GLONASS–M antenna phase centre model and that a consistent set of satellite antenna z–offsets for GPS
and GLONASS is imperative to obtain consistent GPS– and GLONASS–derived station
heights, Dilssner et al. (2010).
Besides these, rather unique, GLONASS PCO/PCV contributions ESOC has also contributed very significantly to the GPS PCO/PCV understanding. Our unique sphericalharmonics approach has proven to be very good and our significant abilities in analysing
also GNSS LEO data has allowed us to also play a leading role, together with the Analysis
Centre CODE, in the extension of the PCV values from the 14 degrees to the 17 degrees
nadir angle range. This extension is of prime importance for accurately processing GNSSLEO data.

4 GNSS LEO Analysis
Driven by the GMES (Global Monitoring for Environment and Security) and GGOS
(Global Geodetic Observing System) initiatives the user community has a strong demandfor high–quality altimetry products. In order to derive such high–quality altimetry products, precise and homogenously processed orbits for the altimetry satellites are a necessity.
With the launch of the TOPEX/Poseidon mission in 1992 a still on–going time series ofhigh–accuracy altimetry measurements of ocean topography started, continued by the altimetry missions Jason–1 in 2001 and Jason–2/OSTM in 2008. The Navigation Support
Office at ESA/ESOC uses its NAPEOS software for the generation of precise and homogeneous orbits referring to the same reference frame for the altimetry satellites Jason–1
and Jason–2. Data of all three tracking instruments on–board the satellites (beside thealtimeter), i.e. GPS, DORIS, and SLR measurements, are used in a combined data analysis. About 7 years of Jason–1 data and more than 1 year of Jason–2 data were processed.
Our processing strategy is close to the GDR–C standards. However, we estimated slightly
different scaling factors for the solar radiation pressure model of 0.96 and 0.98 for Jason–1
and Jason–2, respectively. We used 30 second sampled GPS data and introduced 30 second
satellite clocks stemming from ESOC’s reprocessing of the combined GPS/GLONASS IGS
solution. The fully combined solution (DORIS, GNSS, and SLR) was found to give thebest orbit results. We reach a post–fit RMS of the GPS phase observation residuals of
6 mm for Jason–1 and 7 mm for Jason–2. The DORIS post–fit residuals clearly benefit
from using GPS data in addition, as the DORIS data editing improves. The DORIS observation RMS for the fully combined solution is with 3.5 mm and 3.4 mm, respectively,
0.3 mm better than for the DORIS–SLR solution. Our orbit solution agrees well with56

5 Multi–technique Analysis
external solutions from other analysis centres, as CNES, LCA, and JPL. The orbit differences between our fully combined orbits and the CNES GDR–C orbits are of about
0.8 cm for Jason–1 and at 0.9 cm for Jason–2 in the radial direction. In the cross–trackcomponent we observe a clear improvement when adding GPS data to the POD process.
The 3D–RMS of the orbit differences reveals a good orbit consistency at 2.7 cm and 2.9 cm
for Jason–1 and Jason–2, Flohrer et al. (2011) Our resulting orbit series for both Jason
satellites refer to the ITRF2005 reference frame and are provided in sp3 file format on our
ftp server.
For Jason–1 at: ftp://dgn6.esoc.esa.int/jason1
For Jason–2 at: ftp://dgn6.esoc.esa.int/jason2

5 Multi–technique Analysis
The NAPEOS multi–technique capabilities allow combining the observations from the different techniques on the observation level. One obvious major benefit of this is that it
ensures that identical models are used for all technique and thus all the data is processedhomogeneously. A second major benefit is that the combination on the observation level
offers the unique possibility to tie the techniques together not only through the terrestrial
local site ties, at collocated sites, but also through their space ties, i.e., the physicall distances of the instruments as mounted on the satellite spacecraft body. Here it is worthwhile
to point out that these space ties are not used when generating the ITRF solutions!
At ESOC we have already demonstrated that the SLR observations of the GPS andGLONASS satellites significantly strengthen the ties between those two observation techniques. Also it is well known that the SLR observations contribute significantly to
the DORIS solutions. The strongest tie between the three techniques, however, is offered by the JASON–1 and –2 satellites which provide observations from all three techniques: DORIS, GPS, and SLR. Recent enhancements and efficiency improvements of
the NAPEOS software have made it possible to include GNSS data from LEO satellites
in a full IGS final run, i.e., a GNSS solution using 150 GNSS stations and all (≈ 60)
GNSS satellites; a rather unique capability. The NAPEOS multi–technique capabilities
make it an excellent tool for Space Geodesy in general and GMES and GGOS in particular. Especially the combination of the three space geodetic techniques on the observationlevel including LEO satellites that have observations from all three techniques, like e.g.
JASON–1 and –2, does offer an enormous strengthening of the ties between the different
observation techniques. At ESOC we have only just begun to uncover this potential!
It should be mentioned that with significant NAPEOS abilities we contribute to the effortsof the IERS working group for Combination on the Observation Level (abbreviated COL,
but we prefer to abbreviate it as COOL).

57

Springer et al.: European Space Operations Centre

6 Conclusions
6.1 Summary
Over the recent years the Navigation Package for Earth Orbiting Satellites, NAPEOS,
as developed and maintained at the European Space Operations Centre (ESOC) of theEuropean Space Agency (ESA) has evolved to a great tool for satellite geodesy. NAPEOS
is capable of processing data from all GNSS systems, all DORIS, and all SLR observations.
And, NAPEOS is used for generating state of the art products for all three satellite geodesy
techniques: IDS, IGS, and ILRS. At ESOC NAPEOS is routinely used for a large numberof tasks. Most relevant is the fact that one and the same version of NAPEOS is used forgenerating the ESOC analysis centre products for the IGS, ILRS, and IDS.
Over the years since 2004 very major changes have taken place with respect to the IGS
analysis at ESOC. These changes have made our analysis centre to be one of the bestand one of the most complete within the IGS. At the same time we have also contributed
significantly to different important aspects of the GNSS technique in general and the IGS
in particular. In particular noteworthy are our efforts and achievements as mentioned
below.
• Truly combined GNSS processing including Orbits and (30s) Clocks allowing for
GNSS precise point positioning• Attitude model for the GLONASS–M satellites, in particular during the eclipse
phases• Contributions to the IGS antenna working group for the determination of the GNSS
satellite PCO and PCV values• Analysis Centre and Analysis Centre Coordination of the Real–Time Pilot Project• Efficient, fast, and accurate simultaneous processing of GNSS ground station and
LEO data• Unsurpassed capabilities for multi–technique processing: DORIS, GNSS, and SLR• Full Analysis Centre in the IDS, IGS, and ILRS

References
Springer, T. NAPEOS Mathematical Models and Algorithms. DOPS–SYS–TN–0100–
OPS–GN, Issue 1.0, Nov 2009. Available at ftp://dgn6.esoc.esa.int/napeos
Springer, T. and F. Dilssner. SVN49 and Other GPS Anomalies — Elevation–Dependent
Pseudorange Errors in Block IIRs and IIR–Ms. InsideGNSS, July/August 2009. Available at http://www.insidegnss.com/node/1574

58

References
Springer, T. and R. Dach.
Innovation: GPS, GLONASS, and More.
GPS
World, June 1, 2010. Available at http://www.gpsworld.com/gnss-system/glonass/innovation-gps-glonass-and-more-10007
Dilssner, F. GPS IIF–1 satellite antenna phase center and attitude modeling. InsideGNSS,
September 2010a. Available at http://www.insidegnss.com/auto/sep10-Dilssner.
pdf
Dilssner, F., T. Springer, C. Flohrer, and J. Dow. Estimation of phase center corrections
for GLONASS–M satellite antennas. Journal of Geodesy, 84(8):467–480, 2010b. doi:
10.1007/s00190-010-0381-7
Dilssner, F., T. Springer, G. Gienger, and J. Dow. The GLONASS–M satellite yaw–
attitude model. Adv Space Res, 47(1):160–171, 2011. doi: 10.1016/j.asr.2010.09.007
Flohrer, C., M. Otten, T. Springer, and J. Dow. Generating precise and homogeneous
orbits for Jason–1 and Jason–2. Advances in Space Research, 48(1):152–172, 2011, doi:
10.1016/j.asr.2011.02.017

59Springer et al.: European Space Operations Centre

60

GFZ Analysis Center of IGS
Annual Report for 2011
G. Gendt, M. Ge, T. Nischan,
M. Uhlemann, G. Beeskow, A. Brandt
GeoForschungsZentrum Potsdam
Department Geodesy & Remote Sensing
Telegrafenberg A 17, 14473 Potsdam, Germany;e–mail: gendt@gfz-potsdam.de

1 SummarySince the last publication of the IGS Annual Report GFZ has enhanced its GPS software toa full GNSS capable software including GLONASS and Galileo. The new version, named
EPOS–8, was used in the standard IGS processing starting July 2009.
It should also be mentioned here that during the last reprocessing campaign the IGS
network was already analysed with EPOS–8.

2 Products
The list of products provided by GFZ is summarized in Table 1. All the orbit and clock
products include estimates for GPS and GLONASS satellites. For the IGS Rapid andFinal processing lines the GLONASS data were added starting GPS week 1579 (April2010). With the start of the generation of IGS Ultra Rapids for GLONASS (GPS week
1603, September 2010) GFZ is contributing to this new IGS product.
The GFZ Final summary report includes the station–wise mean clock offsets between
GLONASS and GPS (so–called Inter–Frequency Code Biases, IFB) which are replacing
since GPS week 1637 (May 2011) the information provided until that time by BKG in the
IGS combination to align the GLONASS broadcast clocks.

61Gendt et al.: GeoForschungsZentrum
Table 1: List of products provided by GFZ AC

Final
gfzWWWD.sp3
gfzWWWD.clk
gfzWWW7.erp
gfzWWW7.snx
gfzWWW7.sum
gfzWWWD.tro

Orbits for GPS/GLONASS satellites
5–min clocks for stations and GPS/GLONASS satellites
Summary file including ISB for GLONASS
1–hour ZPD estimates

Rapid
gfzWWWD.sp3
gfzWWWD.clk
gfzWWWD.erp

Orbits for GPS/GLONASS satellites
5–min clocks for stations and GPS/GLONASS satellites

Ultra (every 3–hours; provided to IGS every 6 hours)
gfuWWWD.sp3
gfuWWWD.erp

Adjusted and predicted orbits for GPS/GLONASS satellites

3 Processing
EPOS–8 is following the IERS Conventions 2010 (Petit and Luzum, 2010).
In July 2010 the yaw attitude modelling for GLONASS was implemented according themodel provided by ESOC (Dilssner et al., 2011). For the GPS satellites our software keeps
unchanged, i.e., the maximum yaw rate is estimated on a daily basis.
The albedo model, using the software provided by (Rodriguez–Solano et al., 2012), wasimplemented in EPOS–8 with small interface adaptations.
Some details for recent changes are listed in Table 2.
The station network used in the processing is shown in Figure 1. For the IGS Final, Rapid
and Ultra Rapid about 200, 110, and 90 sites are used, respectively.

4 Current status of GLONASS Processing
The orbit and clock products are generated from a combined GPS/GLONASS estimation
on an operational basis since week 1579.
The clock corrections are consistent to pseudo range and carrier phase observations and areprovided with a sampling rate of 300 sec. The selected standard code observable types are62

4 Current status of GLONASS Processing

Table 2: Recent Processing changes

Date2010-04-11
2010-09-26
2010-07-08
2011-12-15
2011-12-15
2011-12-15

IGS
1579

IGR/IGU

1590
1665
1665
1665

1603
1592.1
1665.1
1665.1
1665.1

2012-01-09
2012-02-13

1669
1674

1670.11674.0ChangeGLONASS data processing for Final
GLONASS data processing for Ultra
Yaw modelling for GLONASS
Atmospheric Loading S1/S2
Ocean pole tide
Bug fix for negative beta angle in yaw modellingcorrected; yaw modelling for IIF added
Albedo/IR/Antenna thrust for GPS&GLONASSZPD with 30–min sampling, internally

90˚

60˚

30˚

0˚

""

−30˚

−60˚

−90˚
−180˚ −150˚ −120˚

−90˚

−60˚

−30˚

0˚

30˚

60˚

90˚

120˚

150˚

180˚

Figure 1: Used stations (GLONASS tracking sites are marked with yellow squares).

63

Gendt et al.: GeoForschungsZentrum
P1 and P2, C1 is only used if P1 is unavailable, C2 is never used. During Pre–processing
the P1C1 Differential Code Biases (DCB) provided by CODE are used within cc2noncc
tool. One Inter–Frequency Code Bias (IFB) is introduced per station, frequency channeland day with very loose constraints. For these biases we have no fixed datum definition
and the mean of all IFB per station are used as a priori value. Additionally there exists
the possibility to set the IFB at one selected station to zero.
During the whole processing chain we apply different IFB handlings: In data cleaningand orbit/clock improvement steps we use one mean IFB per station. Only in the final
iteration step we introduce one IFB per station and frequency channel. This handlingends up in a good balance between processing time and solution quality in our parameter
estimation of actually 32 GPS+24 GLONASS satellites. The number of used GLONASS
stations within our selected network and the approximately needed computation time per
day is listed in Table 3.
The orbit quality of GFZ’s GLONASS solution is nicely shown in the weekly Final IGLOS
combination (Figure 2) where a good agreement with other ACs in the level of about
2–3 cm is reached.
The experience from two years of GLONASS data processing shows that the “Mean IFB”
handling per station during data cleaning steps can cause some problems, if the receiverdependent spreading between the channels is very large. In these cases a lot of observations

Final Orbits (AC solutions compared to IGLOS Final)

Weighted RMS [cm]30(smoothed)

BKG
COD
EMX
ESX
GFZ
GRG
IAC
MCC

20

10

0
1620

1630

1640

1650
1660
Time [GPS weeks]

1670

1680

1690

NOAA NGS, 19.05.2012 23:15 (GMT)

Figure 2: Final GLONASS orbit comparisons.

644 Current status of GLONASS Processing
Table 3: Number of stations and processing time for different kind of GFZ products.

IGS Product
Ultra
Rapid
Final

# of sites
90
110
200

# of sites
incl. GLO
50
60
90

Duration [h]
≈1
≈2
≈4

are flagged as outliers during residual screening and finally all GLONASS data of thatparticular station are rejected. In Figure 3 there are given some examples of different
receiver types which are operated at IGS stations. Clearly visible is the good performanceof Javad TRE_G3TH, Trimble NETR9 and Leica GRX1200+GNSS hardware in terms of
IFB stability and linear behaviour over the channel spectrum with a range of ≈2 m, ≈3 m
and ≈7 m, respectively. The spreading at TPS NetG3 equipped stations is obviously non–linear and larger. The station Mendeleevo in Russia (MDVJ) is with up to 20 m fluctuation
very conspicuous and GLONASS data are excluded within our processing scheme. The
reason for that behaviour is still unknown, but it seems to be station related.
JAVAD TRE_G3TH DELTA

TRIMBLE NETR9IFB [m]

5

0

ABMF
AUCK
GMSD
HARB
NKLG
REUN
TLSE

10

IFB [m]

RAMO
NURK
OUS2
POTS
TASH
ULAB
ZECK

10

-5

5

0

-5
-8

-6

-4

-2
0
2
Channel

4

6

-8

-6

-4

LEICA GRX1200+GNSS

4

6

TPS NETG3
CONZ
GRAZ
LAMA
MAC1
WTZR

10

5

0

-5

BAKE
DUBO
FLIN
GOPE
MDVJ
URUM

10

IFB [m]IFB [m]-2
02Channel

5

0

-5
-8

-6

-4

-2
0
2
Channel

4

6

-8

-6

-4

-2
0
2
Channel4

6

Figure 3: Inter–Frequency Code Biases per receiver type (mean values subtracted).

65Gendt et al.: GeoForschungsZentrum

References
Petit, G. and B. Luzum (Eds). IERS Conventions (2010). IERS Technical Note No. 36,
Verlag des Bundesamtes für Kartographie und Geodäsie, Frankfurt am Main, 2010.
Rodriguez–Solano, C. J., U. Hugentobler and P. Steigenberger. Adjustable box–wing model
for solar radiation pressure impacting GPS satellites. Advances in Space Research, 49(7):1113–1128, Elsevier, ISSN 0273–1177, 2012. doi: 10.1016/j.asr.2012.01.016. (software
download from: http://www.iapg.bv.tum.de/albedo/).
Dilssner, F., T. Springer, G. Gienger and J. Dow. The GLONASS–M satellite yaw–attitude
model. Advances in Space Research, 47(1):160–171, 2011.

66

GOP IGS Analysis Centre Report 2005–2011
J. Dousa
Geodetic Observatory Pecný,Research Institute of Geodesy, Topography and Cartography,Ústecká 98, Zdiby, Czech republic, e–mail: jan.dousa@pecny.cz

1 Introduction
This report summarizes the contribution of Geodetic Observatory Pecný (GOP) of the
Research Institute of Geodesy, Topography and Cartography to the International GNSS
Service during 2005–2011. The GOP is contributing to the GNSS ultra–rapid productseries strongly motivated by its activities in (near) real–time applications. During 2005–2011 various developments were done at GOP analysis centre, which are described inreport together with developing new GLONASS contribution. Other related activities like
product performance monitoring or experience with the use of IGS combined ultra–rapid
products in end–user applications is summarized too.

2 Processing strategy in a nutshell
The GOP orbit determination procedure is based on modified Bernese GPS Software V5.0
(Dach et al., 2007) and in–house system for a flexible use, which is common to all otherservices provided by GOP. The orbit determination system has been developed as highly
efficient based on the analysis of double–differenced observations from last 6–hour data
batch, thus avoiding redundancy in observation pre–processing. The final product is generated applying the combination of 6–hour normal equations (NEQs) over last two days.
Only the GNSS navigation messages, GNSS observations and predicted Earth rotation parameters (ERPs) are necessary for the initialization. In order to provide overall robustness,the solution consists of two orbit improvements (Fig. 1, pink blocks). The GPS satellite
manoeuvres are detected (± 10 min) through the analysing navigation messages. High efficiency is reached using a network clustering for parallel runs (Fig. 1, black boxes), which
are implemented for all processing steps. The white boxes in figures finalizes individual
parallel steps and red boxes represent preliminary daily solutions for specific parameter
estimations. The initial clusters are defined for continents, but based on real data they67

Dousa: Geodetic Observatory Pecný

Figure 1: GOP processing scheme based on 6–hour data batch and long–arc combination

are flexibly reconfigured. According to the processing load in various steps, the clusters
are setup to small (5–10 sites) or medium (20–30 sites) size. All parameters, which areout of interest, are pre–eliminated or fixed from previous iterations whenever possible. All
steps of daily results are based on a combination of four 6–hour NEQs, while the final
product is combined over 2–days (eight 6–hour NEQs). More final variants can be run inparalell after the pre–processing steps (Fig. 1, blue boxes). The long–arc orbit modellingis based on the extended CODE model (Beutler et al., 1994) with periodical solar radiation parameters constrained according to Tab. 1. The stochastic parameters in radial,
along–track and out–of–plane direction are estimated (and constrained, see Tab. 1) only
for satellites in eclipse at epoch aproximately in a mid of the interval. All satellites arealways included in the processing, but in case of a modelling problem the observations
from relevant satellite are down–weighted in 6–hour solution. The official GOP official
product is filtered based on various internal information from the processing and exclusion of individual satellites or changing their accuracy code is finally performed. Various
other checking procedures are incorporated within the processing system — e.g. single
station rejection, datum definition robustness etc.

Table 1: RPR (D,Y,X) and stochastic parameter (R,A,O) constrains
Parameter
constant D/Y/X terms
periodic D/Y/X terms
stochastic parameters (radial/along/cross)68

constrains
unconstrained
1.0E–12 / 1.0E–10 / 1.0E–11
1.E–7 / 1.E–7 / 1.E–9

units
m/s2
m/s2
m/s

4 GOP GLONASS ultra–rapid product

3 Strategy improvements during 2005–2011
In first half of 2006 we completely revised our system (processing steps, modelling etc.),
but still keeping 6–hour observations processing scheme as an efficient basis. This revision provided significant improvements in GOU solution and it is clearly visible in IGS
comparison after a gap in GOP contribution (caused by the development due to a lack of
hardware). Many small changes/improvements were done later on in order to fix bugs, toenhance an efficiency and robustness of the procesing and to support easier maintenance.
The list of significant changes is summarized in Tab. 2, while many others applied during the period of 2006–2011 are not specifically mentioned. The quality overview of theoriginal (2005) and improved (2010) GOP ultra–rapid GPS product is given in Tab. 3. A
specific processing extension concerning multi–GNSS support is described in Section 4.

4 GOP GLONASS ultra–rapid productIn 2009, GLONASS consisted of 20 active satellites and stand–alone GLONASS orbit determination solution was developed (Dousa, 2012). A revision of all processing steps ofexisting GOP solution was necessary to reach a maximum robustness of a stand–alone
GLONASS solution, which finally resulted in improvements of GOP GPS official contribution to IGS. The GLONASS solution was implemented as an extention to the original
GOP processing scheme (i.e. rigorously combining all observations). Some differences inindividual steps of the processing between GLONASS and GPS exist (e.g. in ambiguity resolution for GPS only etc.), but these are handled automatically within individual
scripts. A single option for switching between GPS, GLONASS or GNSS analysis allowed
us to perform tests between these three solutions during two 60–day periods (Nov/Dec 2008
and May/Jun 2009) for the evaluation of products (Dousa, 2012). The results shown that
the GPS orbit quality didn’t decrease in combined solution, while GLONASS orbits were
improved compared to the stand–alone GLONASS solution. The latter was due to many
common parameters estimated mainly from GPS observations. The GLONASS orbits arestill of 2–3 × lower accurate than GPS in GOP solution. The main problem remains inmodelling satellite orbits during eclipsing periods, which is demonstrated in Fig. 2. The
estimated stochastic parameters are shown at the left plot (and represents eclipsing intervals), while the orbit quality is shown at the left plot. There were some changes inconstraining of the stochastic pulses within the plotted time–span. However, the performance of estimated radial and along–track stochastic parameters seems to eliminate someremaining systematic errors in current model during eclipsing periods. Since September
2010 GOP contributes to the IGS unofficial combination of four GPS+GLONASS ultra–
rapid orbit rigorous solutions.

69

Dousa: Geodetic Observatory Pecný

Table 2: Significant changes during 2006–2011 (i.e. after the system revision)
Year:DoY
2011:2212011:106
2011:092
2011:052
2011:039
2010:354
2010:338
2010:305
2010:299
2010:258
2010:128
2009:269
2009:244
2009:229
2009:2042009:141
2008:269
2008:242
2008:078
2008:022
2008:006
2007:356
2007:338
2007:305
2006:309
2006:264

processing changes
improved outliers checking and bad station handlingswitch from IGS05 to IGS08 reference frame and PCO+PCV model
fixed long–term problem with G24 and G08 due to stochastic parameters setup
close to the start of orbit integration
reset stochastic parameters not estimated from 2011:043 (by mistake)fixed the problem with concatenated navigation files at GOP data centre
switch from teqc data concatenation to Bernese internal concatenation
fixed the problem with stochastic parameters at the beginning of short orbit arc(related to the processing batch)
added tight constrained for stochastic pulses close to the end of long–arc orbits
down–weighted GLONASS satellites in eclipse
official switch from GPS–only contribution to multi–GNSS (GPS+GLONASS)
start of GPS+GLONASS solution (in parallel to official GPS one)solution corrupted due to the CDDIS data centre problem
prolonged procedure of identifying processing start to get more (delayed) stations
solution problem due to incorrect SATELLITE.I05 during decommissioned G25
and setting new G05 satellites
DATUM definition based on 3 days instead of a single day
three–day combination decreased to two days with modified arc–splitting
procedureswitch to gfortran compiler
fixed problem with ambiguity resolution when reference satellite in manoeuverdown–weighted accuracy code for satellites temporarily marked as bad
switch from LH98 to IFC7 compiler
fixed incorrectly used I0B at one pre–processing step
X–periodical RPR constrained changed from 1.0E–10 to 1.0E–11
change setting up SP3 accuracy code based on prediction comparisonsencreased number of station > 90
switch from IGB00 to IGS05 (igs05_1390.atx)
new official solution based on the system revision

Table 3: Assessment of GOP ultra–rapid product quality between 2005–2011
Solution
GOU (2005)
GOU (2011)70

orbits
[cm]
12/24
4/10

polar–motion [PM][mas]
0.3/0.5
0.1/0.3

PM rates[mas/day]
0.4/0.4
0.2/0.4

LOD[ns]
0.07/0.09
0.03/0.07

5 Products monitoring and user assessement
GLONASS orbit comparison : GOU/6h prediction w.r.t. IGU

GLONASS - stochastic orbit pulses [radial, along-track]
R01

R03

R02

R04

R03

R05

R04

R06

R05

R08
R09
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24

305
2010

335
2010

001
2011

032
2011

060
2011

091
2011

121
2011

152
2011

182
2011

213
2011

R06
R07
R08
R09
R10
R11
R12
R13
R14
R15
R16
R17

Dousa - plot_RPR.gpt [2011-08-10]

R07

stochastic pulses (satellites shifted by +1 umeter/sec]

R02

Dousa - plot_OrbEclips.gpt [2011-08-15]

1D orbit RMS [cm] (satellite shifted by +25 cm)

R01

R18
R19
R20
R21
R22
R23
R24
308
2010

328
2010

348
2010

003
2011

023
2011

043
2011

063
2011

083
2011

103
2011

123
2011

143
2011

163
2011

183
2011

203
2011

Figure 2: Quality of GLONASS orbits w.r.t. IGS finals (left) and estimated radial (grey) andalong–track (black) stochastic pulses for eclipsing GLONASS satellites (right)

5 Products monitoring and user assessement
The ultra–rapid orbits are used in (near) real–time applications and thus its prediction
part (3–9 hours) is the most important (Dousa, 2011). GOP provides on–line evaluation
system for the orbit prediction performance. Fig. 3 shows the results of time–series ofmonthly RMS orbit prediction errors for two satellites selected because of the different
Block types. The effect of a half–year periodic degradation of the orbits is related tothe satellite eclipsing periods. The bottom figures of Fig. 3 show the dependence of theaccuracy on prediction interval for eclipsing and non–eclipsing satellites. Many detailed
figures are available at http://www.pecny.cz (GNSS, orbits), which include e.g. themonitoring of real–time IGU portions in such a way that are used in end–user real–timeapplications.
GOP is active in GNSS–meteorology (Dousa, 2010), which was one of the primary application of the IGS ultra–rapid orbits since 2000. The GOP has recently developed two new
tropospheric solutions — global hourly and GPS+GLONASS products, both contributing to the EUMETNET EIG GPS Water Vapour Programme (http://egvap.dmi.dk).
Thanks to significant improvements of IGS ultra-rapid orbits since 2000 in terms of quality and robustness, a GPS near real–time troposphere estimation is an easy task today.
However, developing a global product consisting of long–baselines more sensitive to thequality of the orbits, the user solution requires a high robustness including identificationof satellite/station rejection etc. Similar experience was gained at GOP when GLONASS
stand–alone and multi–GNSS solution based on unofficial IGS GPS+GLONASS combination was implemented. As already mentioned GLONASS orbits are still about twice lower
accurate than GPS orbits. One year multi–GNSS near real–time solution at GOP alreadyproved that the IGS unofficial GPS+GLONASS ultra–rapid product can be operationallyexploited for troposphere monitoring. Finally, stand–alone GPS and GLONASS derived
ZTD comparision revealed a bias about 1–2 mm, which dissepared after switching to IGS08

71

Dousa: Geodetic Observatory Pecný
IGU x IGSIGL : orbit position differences

IGU x IGSIGL : orbit position differences

IGU x IGSIGL : orbit position differences

60

60

60

60

2011

0
2009

2012

IGU x IGSIGL : orbit prediction
24

16
14

8
6
4
2
0
0

5

10

15

20

prediction [h]RMS [cm] (over a month)

18

10

2012

14

10
8
6
4
2
0
10

15

prediction [h]20RMS [cm]

20

10

0
2009

2012

14
12
10
8
6
4
2
0
10

15

prediction [h]

20

2012

Rad
Alo
Cro
Pos

Satellite G10

20

16

5

2011

IGU x IGSIGL : orbit prediction
22

18

0

2010

24

Rad
Alo
Cro
Pos

Satellite G12

20

12

30

IGU x IGSIGL : orbit prediction
22

16

5

2011

24

18

0

2010

Dousa - plot_OrbPredTS.gpt [2012-06-19]

RMS [cm]

0
2009

Rad
Alo
Cro
Pos

Satellite G03

20

12

10

IGU x IGSIGL : orbit prediction
22

Dousa - plot_OrbPred.gpt [2012-06-19]

RMS [cm] (over a month)

20

2011

24

Rad
Alo
Cro
Pos

Satellite G02

22

2010

20

40

prediction [h]
22h
19h
16h
13h
10h
7h
4h
1h
fit

18
16
14
Dousa - plot_OrbPred.gpt [2012-06-19]

2010

10

30

Satellite G1050

RMS [cm] (over a month)

0
2009

20

40

prediction [h]
22h
19h
16h
13h
10h
7h
4h
1h
fit

Dousa - plot_OrbPred.gpt [2012-06-19]

10

30

50

RMS [cm] (over a month)

20

40

Satellite G12

Dousa - plot_OrbPredTS.gpt [2012-06-19]30

50

prediction [h]
22h
19h
16h
13h
10h
7h
4h
1h
fit

Dousa - plot_OrbPred.gpt [2012-06-19]

RMS [cm]

40

Satellite G03

RMS [cm]50

prediction [h]
22h
19h
16h
13h
10h
7h
4h
1h
fit

Dousa - plot_OrbPredTS.gpt [2012-06-19]

Satellite G02

Dousa - plot_OrbPredTS.gpt [2012-06-19]

IGU x IGSIGL : orbit position differences

12
10
8
6
4
2
0
0

5

10

15

20

prediction [h]Figure 3: Plots show time–series of GPS satellite orbit quality (top) and the prediction of radial,
along–track and cross–track monthly dependence on prediction (bottom). Two leftplots show non–eclipsing and right eclipsing satellites. G02 and G12 are Block IIR,
while G03 and G10 Block IIA satellites. Colors shows accuracy for fitted (0h) andpredicted positions (1h, 4h, 7h, 10h, 13h, 16h, 19h, 22h) The orbits are comparedo to
IGS finals

because of inconsistencies between GPS and GLONASS satellite antenna offsets.

References
Beutler, G., E. Brockmann, W. Gurtner, U. Hugentobler, L. Mervart, and M. Rothacher.
Extended orbit modeling techniques at the CODE processing center of the International GPS Service for Geodynamics (IGS): Theory and initial results. Manuscripta
Geodaetica, 19:367–386, April 1994.
Dach, R., U. Hugentobler, P. Fridez, and M. Meindl (eds). Bernese GPS Software Version
5.0. Astronomical Institute, University of Berne, Berne, Switzerland, 2007.
Dousa, J. Precise near real–time GNSS analyses at gop — precise orbit determination andwater vapour monitoring. Acta Geodedyn. Geomater., 7:1–11, 2010.
Dousa, J. The impact of errors in predicted gps orbits on zenith troposphere delay estimation. GPS Solutions, 13(3):229–239, 2011.

72

References
Dousa, J. Development of the GLONASS ultra–rapid orbit determination at Geodetic
Observatory Pecny,. In S. Kenyon, M.C. Pacino, and U. Marti, editors, (Geodesy of
Planet Earth), volume 136 of International Association of Geodesy Symposia, pages
1029–1036, 2012.

73

Dousa: Geodetic Observatory Pecný

74

The CNES–CLS IGS Analysis Center
Annual Report 2011
S. Loyer1 , F. Perosanz2 , H. Capdeville1 , M. Pau1 ,F. Mercier2 , J.–C. Marty2 , L. Soudarin1
1
2

Collecte Localisation Satellites, 31520 Ramonville Saint Agne, FranceCentre National d’Etudes Spatiales, 31400 Toulouse, France

1 Introduction
CNES (Centre National d’Etudes Spatiales) and CLS (Collecte Localisation Satellites)
joined their efforts to officially become an IGS Analysis Center (AC) the 20th of May 2010
after more than two years of an intensive evaluation phase (Cf. IGSmail #6155). As a consequence, this is our first contribution to an IGS technical report. The main motivations
to become an IGS AC were to evaluate the performance of the GINS/Dynamo software
package developed by CNES and GRGS (Groupe de Recherche de Géodésie Spatiale),
to participate in the different IGS working groups and to contribute to the discussions
on processing strategy, standards definition, etc. The CNES–CLS IGS Analysis Center
products are called GRG and are generated using an innovative strategy to fix integer
GPS phase observation ambiguities at the zero–difference level (Laurichesse and Mercier,2007). A description of how this algorithm has been implemented into GINS/Dynamo isgiven in Loyer et al. (2012). More information on our AC activity can also be found at:
www.igsac-cnes.cls.fr .

2 Routine products delivery
Today our contribution is limited to “final” GPS and GLONASS products. We computeweekly normal equations containing all the necessary parameters like station coordinatesand Earth Orientation Parameters (EOP). In practice the normal equations are computed
on a daily basis and are combined into a weekly equation that is inverted using the Dynamo
software. The complete covariance matrix and solution is delivered in SINEX format tothe IGS. The final orbit solution is obtained after a final run using 300 s sampling data andthe weekly station coordinates and EOP solution from the previous step. This ensures

75

Loyer et al.: Centre National d’Etudes Spatiales/Collecte Localisation Satellites
Table 1: List of GRG final products delivered weekly
grgwwww7.ERP
grgwwww7.SUM
grgwwww7.SNX
grgwwwwn.SP3
grgwwwwn.CLK
grgwwww7.WSB

ERP (pole, UT1–UTC) solution for 1 week in IGS IERS ERP format
Analysis summary for the week
Weekly Solutions for EOP and Stations coordinates in SINEX format withcomplete information (covariance and used constrains)
Daily GNSS ephemeris/clock at 15–min intervals(GPS + GLONASS since week 1617, GPS–only before)
Daily GPS ephemeris/clock at 30–sec intervals(5 min sampling before week 1686)
Weekly updated GPS wide–lane satellite biases(available at ftp://ftpsedr.cls.fr/pub/igsac)that the delivered solutions (orbits and station coordinates) are expressed in the samereference frame. In order to produce GPS 30 s sampling clk files, we have implemented aneffective method in which the final orbits and the other associated parameters are fixed.
Only the 30 s clock parameters are solved for, epoch by epoch, by a “densification” of theobservations. Table 1 gives the list of the GRG products delivered to the IGS.

3 Processing strategy
Software packages
GINS is a multi–satellite software in which all the modern geodetic measurements canbe processed together. Initially dedicated to gravity field computations, the GINS software has been used since the end of the 90ties to process GPS signals. The software
has been updated several times to handle the increasing size of the IGS station networkand to improve GNSS orbit and clock computation. The model parameters are processedby least squares adjustment of the linearized observation equations. The numerous clockparameters are reduced epoch by epoch (i.e. pre–eliminated from the normal equation
before inversion). If necessary, the normal equation matrix can be stored for later use.
The Dynamo software package provides all the functions to handle the individual normal
equations (summation, reduction, and linear system resolution). Since 2007 and the beginning of our participation in the IGS we made intensive efforts to process GNSS data
in an automated mode and on a weekly basis. Many other tools or software are included
today in our processing scheme.
Network
Our site selection is a compromise between processing capabilities and product quality.
Following IGS and ITRF recommendations we include as many as possible sites co–locatedwith other systems or techniques. Our current network contains around 70 GPS–only
receivers and 70 hybrid GPS–GLONASS receivers.
76

3 Processing strategy
Models and Parameters
Like any AC we have the dual and challenging goal of:• improving the accuracy and precision of the products• follow the international conventions and improve the consistency of the products
between the ACs
This needs a careful care to models updating and parameterization strategy.
The present status of our processing characteristics is detailed at: http://igscb.jpl.
nasa.gov/igscb/center/analysis/grg.acn.
Finally Loyer et al. (2011) have compared AC’s solar radiation pressure models thanks toan innovative approach based on satellite acceleration recovering from sp3 files.
Table 2: Processing strategy history
GPS
week
1478

1497
1515
1521
1555
1580
1582
1602
1617
1632
1674

Synthetic description of the main changes between the successive versions of the
GRG processing
Initial solutions:• Network of 80 stations• 15 min clocks estimates• complete B&Wings modeling• real valued ambiguities.

One stochastic pulse during eclipse periods is added for the eclipsing satellites
Beginning of production of 30 second clocks (only 5 min clocks are delivered to the
IGS)
Network extension (up to 115 stations)Integer ambiguities fixing at the zero–difference level
Adoption of the simplified dynamic B&W modeling
The SINEX solution includes now the complete constraint matrix used. This allows
the IGS Reference Frame Coordinator to combine our solution in a rigorous way.
GRG solution official contributor to GPS IGS final products (IGSMAIL#6155)
Network extension (up to 140 stations)Tropospheric mapping function GMF
GRG solution official contributor to GLONASS IGS final products(IGSMAIL#6155)
Switch to igs08.atx center of phase offsets (see IGSMAIL#6354)
Tropospheric gradients estimation
GPS satellite attitude (Kouba’s 2009 model)

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Loyer et al.: Centre National d’Etudes Spatiales/Collecte Localisation Satellites

4 Processing characteristics history
As we recently joined the ACs of the IGS, we recall in table 2 the full story of the mainchanges in our processing strategy. The corresponding impact on our products has been
evaluated and some examples are given hereafter.
Orbit solution
Figure 1 shows the WRMS residuals of all the IGS Analysis Centers (ACs) relatively
to the IGS combined orbits (http://acc.igs.org). The main changes impacting thecomparison with the IGS final orbits are the ambiguity fixing used since October 25, 2009
(GPS week 1555) and the dynamical modeling since April 18, 2010 (GPS week 1580).
Figure 2 compares the orbit overlaps computed every day between two successive GRG
solutions without and with ambiguity fixing. The tangential and cross–track RMS decrease

Figure 1: Smoothed weighted RMS of the individual IGS analysis center solutions vs. the IGS
final orbits between GPS week 1550 (September 20, 2009) and GPS week 1618 (January
9, 2011). From Ray et al., http://acc.igs.org

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4 Processing characteristics history

Figure 2: Global un–weighted mean (left) and RMS (right) overlaps between two daily realizations of our GPS orbits. Floating solution (black) compared to ambiguity fixed solution(red) from GPS week 1545 (August 16, 2009) to GPS week 1553 (October 17, 2009).

from 6 to 3 cm while the changes in the radial RMS and the mean values of the overlaps
are not significant. After changing the satellite SRP modeling using only the solar panels
in our Box and Wing representation of the satellite (instead of a more detailed descriptionof the surface we used before), we obtained better agreement with the IGS orbits.

Stations coordinates solution
The inter–comparison of the different Analysis Center solutions provides a weekly evaluation of our global frame coordinate estimates (Rebischung and Garayt, 2012). The global
RMS residuals in the up direction between our solution and the IGS one improved from
8.5 to 5.5 mm when the ambiguity fixing was used in our solution (see figure 3). The
impact on the horizontal direction is below the millimetre level. The RMS of the GRG
solution residuals agree today at a level of 3 mm in the horizontal components and 6 mm
in the vertical component. Due to different processing and modelling used by the ACs,
systematic millimetre distortions remain. Part of these differences could be explained by
the lack of tropospheric gradient estimation in our solution (see Bar–Sever et al., 1998).
A gradient mapping function like the one described in Chen and Herring (1997) has been
already implemented in the latest GINS version. Tropospheric gradient corrections as wellas the GPS satellite attitude model recommended by Kouba (2008) are being consideredin our solutions since week 1674.
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Loyer et al.: Centre National d’Etudes Spatiales/Collecte Localisation Satellites

Figure 3: Global RMS residuals (up component) between our weekly network solution and the
IGS weekly combined solution. From February 22, 2009 (GPS week 1520) to June 6,2011 (GPS week 1640).

5 WSB and integer clocks products
The zero–difference ambiguity fixing method implemented into GINS requires a specificadditional product we call WSB (“Wide–lane satellite Biases” ) and provide to the GPS
clock solutions a specific property.
WSB
In order to recover the integer nature of (un–differenced) phase ambiguities, un–calibrated
phase delays at both the satellite and receiver level must be identified. Laurichesse andMercier (2007) have demonstrated that the wide–lane combination of the satellite phasebiases could be observed from a global network of stations. The determination of these“Wide–lane satellite Biases” is now part of our AC activity. A series of daily values
covering 2000 to 2011 has been computed (figure 4). WSB seems very stable in time
especially for recent block IIR and IIR–M satellites. The main variations (jumps) coincidewith known events or on–board maintenance operations listed in GPS Notice Advisory to
Navstar Users (NANU) delivered by U.S. Naval Observatory (USNO). The SVN 24 (PRN24) satellite exhibits unusually large variations reaching few WL cycles between 2002 and2006. The operational values used for our products are updated each week and available
on our web site at: ftp://ftpsedr.cls.fr/pub/igsac/grgwwww7.wsb .
Integer phase clocks
The satellite (phase) clock products derived from the integer zero–difference processingof GPS phase observations have a unique property: two independent solutions differ byan arbitrary value common to all satellites plus an integer number of Narrow–Lane cycles. This can be checked by comparing two successive clock solutions obtained fromthe processing of our overlapping arcs (30 hour sliding window centred on each day). This
property is illustrated in figure 5 which represents the satellite clock solutions overlap (one80

5 WSB and integer clocks products

Figure 4: Observed GPS WSB between year 2000 and year 2010. One curve per Satellite Vehicle
Number (SVN) is shown.

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Loyer et al.: Centre National d’Etudes Spatiales/Collecte Localisation Satellites

Figure 5: Example of the overlap differences between satellite clock estimates of day n+1 (March
8, 2011) and day n (one curve per satellite). Before correction (top) and after corrections (bottom).

colour per satellite) before correction (top plot) and after applying a common shift plus a±1 narrow–lane cycle bias to dedicated sets (bottom plot). In other words, a continuous
satellite (phase) clock solution could be provided to the users. Possible applications are
the improvement of kinematic point positioning of single receivers (Lescarmontier, 2012)or GPS–based continuous time transfer over long time spans (Delporte et al., 2008; Petit
et al., 2011).

References
Bar–Sever, Y. E., P. M. Kroger, and J. A. Borjesson. Estimating horizontal gradients oftropospheric path delay with a single GPS receiver. J Geophys Res 103(B3):5019–5035,
1998. doi: 10.1029/97JB03534
Chen, G. and T. A. Herring. Effects of atmospheric azimuthal asymmetry on the analysisof space geodetic data. J Geophys Res, 102(B9):20489–20502, 1997. doi: 10.1029/
97JB01739.

82

References
Delporte, J., F. Mercier, D. Laurichesse and O. Galy. GPS Carrier–Phase Time Transfer
Using Single–Difference Integer Ambiguity Resolution. Int J Navig and Obs., 2008. doi:
10.1155/2008/273785.
Kouba, J. A simplified yaw–attitude model for eclipsing GPS satellites. GPS solutions,
13:1–12, 2008. doi: 10.1007/s10291-008-0092-1.
Laurichesse, D. and F. Mercier. Integer ambiguity resolution on undifferenced GPS phasemeasurements and its application to PPP. ION GNSS 2007, 20th International Technical
Meeting of the Satellite Division, 25–28 September 2007, Fort Worth, TX, pp 839–84813,
2007.
Laurichesse, D., F. Mercier, J. P. Berthias, P. Broca and L. Cerri. Integer Ambiguity
Resolution on Undifferenced GPS Phase Measurements and its Application to PPP and
Satellite Precise Orbit Determination. Navig J Inst of Navig, ISSN: 00281522, 56(2):135–149, 2009.
Lescarmontier, L., B. Legresy, R. Coleman, F. Perosanz, C. Mayet and L. Testut. Vibrations of the Mertz glacier ice tongue. J Glaciolog, in press, 2012. doi: 10.3189/
2012JoG11J089.
Loyer, S., F. Mercier, F. Perosanz and H. Capdeville. Comparison of different radiation pressure models for GNSS orbit determination. , presentation at the European
Geosciences Union General Assembly, Vienna, Austria, 2011. http://acc.igs.org/
orbits/srp-models_cnes_egu11.pdf.
Loyer, S., F. Perosanz, F. Mercier, H. Capdeville and J.–C. Marty. Zero–difference GPS
ambiguity resolution at CNES–CLS IGS Analysis Center. Journal of Geodesy, publishedon line: 03 April 2012. doi: 10.1007/s00190-012-0559-2
Marty, J. C., S. Loyer, F. Perosanz, F. Mercier, G. Bracher, B. Legresy, L. Portier,
H. Capdeville, F. Fund, J. M. Lemoine and R. Biancale. GINS: the CNES/GRGSGNSS scientific software. 3rd International Colloquium Scientific and Fundamental Aspects of the Galileo Programme, ESA Proceedings WPP326, 31 August–2 September
2011, Copenhagen, Denmark.
Petit, G., A. Harmegnies, F. Mercier, F. Perosanz and S. Loyer. The time stability of
PPP links for TAI. Proc. Joint conference FCS and EFTF 2011. doi: 0.1109/FCS.2011.
5977299
Rebischung, P. and B. Garayt Recent results from the IGS terrestrial frame combinations.
IAG Symp REFAG2010, Marne–La–Vallée, Z. Altamimi and X. Collilieux (Eds.), inpress, 2012.

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Loyer et al.: Centre National d’Etudes Spatiales/Collecte Localisation Satellites

84

JPL IGS Analysis Center Report, 2005–2012
S. Desai, W. Bertiger, B. Haines, D. Kuang,
C. Selle, A. Sibois, A. Sibthorpe, and J. Weiss
Jet Propulsion Laboratory
California Institute of Technology
4800 Oak Grove Drive, M/S 238–600
Pasadena, CA 91001, U.S.A.
e–mail: shailen.desai@jpl.nasa.gov
phone: +1 − 818 − 354 − 6102

1 Introduction
The Jet Propulsion Laboratory (JPL) continues to serve as an Analysis Center (AC) for
the International GNSS Service (IGS). We contribute orbit and clock solutions for the
GPS satellites, position, clock and troposphere solutions for the ground stations used todetermine the satellite orbit and clock states, and estimates of Earth rotation parameters(length–of–day, polar motion, and polar motion rates). This report summarizes the evolution of the JPL’s processing approach since 2005, our contributions to the IGS reprocessing
campaigns, some IGS–related activities, and plans for future work.
The JPL AC continues to utilize the GIPSY/OASIS software package to generate ourcontributions to the IGS. Table 1 summarizes our IGS Rapid and Final products. We also
contributed “Final” products to the first IGS reprocessing campaign, and will do so for
Table 1: JPL AC Contributions to IGS Rapid and Final Products.

Product
jplWWWWd.sp3
jplWWWWd.clk
jplWWWWd.tro
jplWWWWd.erp
jplWWWWd.yaw
jplWWWW7.snx
jplWWWW7.sum

Description
GPS orbits and clocks
GPS and station clocks
Tropospheric estimates
Earth rotation parameters
GPS yaw rate estimates
Weekly SINEX file
Weekly solution summary

Rapid/Final
Rapid & Final
Rapid & Final
Rapid & Final
Rapid(d=0–6), Final(d=7)
Rapid & Final
Final
Final

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Desai et al.: Jet Propulsion Laboratory
Table 2: Evolution of Processing Standards at the JPL IGS AC Since 2005.

Date
Aug. 26, 2007
Nov. 16, 2008

Jul. 18, 2011

Description
Adopt IGS05 antenna calibrations and reference frame.
Receiver elevation angle cutoff changed from 15 to 7 degrees.
Adopt GMF troposphere mapping function (Boehm et al., 2006).
Adopt GPT dry troposphere model (Boehm et al., 2007).
Adopt hardisp ocean tide loading function. (Petit and Luzum, 2010)
Adopt IGS08 antenna calibrations and reference frame.
Adopt IERS 2010 standards. (Petit and Luzum, 2010)
Adopt GSPM10 solar radiation pressure model(Sibthorpe et al., 2010).

the next reprocessing campaign. All of our contributions are based upon daily solutions
centered at noon and spanning 30–hours. Each of our daily solutions is determined independently of neighboring solutions, namely without applying any constraints between
solutions.

2 Changes to Processing Standards and Software
Since 2005 we have applied numerous changes to our processing standards, models, andsoftware. A summary of the most significant changes to our processing approach is provided in Table 2. The most relevant change was the adoption of the IGS absolute calibrations in August 2007. A complete description of our current processing approach canbe found at: http://igscb.jpl.nasa.gov/igscb/center/analysis/jpl.acn. In addition, we have modernized the data manipulation, quality control, and product generation
software surrounding GIPSY/OASIS, first in August 2007, and again in November 2008.
We continue to favor using our GPS solar radiation pressure models instead of the DYB–
based strategies that are commonly used by other IGS analysis centers. This choice isbased upon an extensive evaluation of various internal and external metrics after testing
both approaches with the GIPSY/OASIS software (Sibthorpe et al., 2011).

3 Contributions to IGS Reprocessing Campaigns
The JPL IGS AC submitted the usual suite of “Final” products, as shown in Table 1,
to the first IGS reprocessing campaign. In this reanalysis of historical data we adopted
the IGS05–based absolute antenna calibrations. The JPL orbit and clock products fromthis IGS05–based campaign were used in the IGS combination. However, due to schedule
limitations our SINEX file contributions were not used in the IGS contribution to the
ITRF08 reference frame. We will contribute a similar suite of products to the next IGS

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3 Contributions to IGS Reprocessing Campaigns
60

Orbit
Clock

Variance Reduction (%)

50
40
30
20
10
0
-10

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

-20

Year
Figure 1: Variance reduction in orbit and clock precision of JPL’s first IGS08–based reanalysis
of historical GPS data relative to our IGS05–based reanalysis. Precision is measured
through the root–mean–square (RMS) of differences between neighboring daily 30–hour
solutions during the overlapping 6–hour period. The average orbit and clock variancereduction for 1996–2011 is 25% and 12%, respectively.

reprocessing campaign, which is expected to be completed in the 2012–2013 time frame.
In addition to the suite of “Final” products listed in Table 1 we will also deliver daily
SINEX files for the entire reprocessing period, and high–rate (30–second) clock products
for 1996 onwards.
At this writing we have completed a first reanalysis of historical GPS data from 1996–
present using the operational processing standards that we adopted on July 18, 2011(see Table 2). Our tests indicate that adopting the IGS08 absolute antenna calibrations
and JPL’s GSPM10 (Sibthorpe et al., 2010) solar radiation pressure model for the GPS
constellation provided the most significant improvements to the overall accuracy from this
IGS08–based reanalysis compared to our IGS05–based reanalysis. In particular, we haveshown an average variance reduction of 25% and 12% in GPS satellite orbit and clock
precision for 1996–2011, respectively (Desai et al., 2011).
As shown in Figure 1 the variance of the orbit and clock precision from our IGS05– to
IGS08–based reanalysis improved by as much as 50% in some years. Furthermore, thenumber of GPS satellites included in these most recent solutions has increased by an average of 0.6 satellites per day, with some days including as many as 7 additional GPS
satellites. Investigations are ongoing to understand the reduction in clock precision for

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Desai et al.: Jet Propulsion Laboratory
Table 3: Terrestrial static and kinematic station repeatability using JPL’s IGS05– and IGS08–
based reprocessed orbit and clock products, including single receiver ambiguity resolved
positioning. Results are based upon 9 stations selected for global coverage and withoccupation histories of at least 12 years. Repeatability is with respect to velocity modelfor each station. Units are mm.

Product
IGS05
IGS08(Not Resolved)
IGS05(Resolved)

Static Point Position
East
North
Up
3.5
2.4
7.5
3.0
2.1
6.1
2.0
2.0
5.8

Kinematic Point Position
East
North
Up
11.0
10.0
20.8
9.5
8.8
18.9
6.3
7.2
16.9

1996 and 1997. High–rate (30–second) clock products, only in native GIPSY formats,were already generated in this first IGS08–based reanalysis. While products from thisfirst IGS08–based reanalysis have not been delivered to the IGS, they are available at
ftp://sideshow.jpl.nasa.gov/pub/jpligsac in IGS formats, and at
ftp://sideshow.jpl.nasa.gov/pub/JPL_GPS_Products/Final in native GIPSY formats.

4 Additional Developments at the JPL AC
The JPL IGS AC also started to operationally generate Ultra–Rapid orbit and clock
products for the GPS constellation in 2009 (Weiss et al., 2010). Our Ultra–Rapid products are generated with a latency of less than 2 hours and are updated hourly. The
Ultra–Rapid orbit and clock products have 3–D RMS accuracies of 5 cm, compared to 3.5
and 2.5 cm for our Rapid and Final products, respectively. The Ultra–Rapid products
are available in native GIPSY formats at ftp://sideshow.jpl.nasa.gov/pub/JPL_GPS_
Products/Ultra-Rapid.
Since 2010, all three of JPL’s GPS product lines in native GIPSY formats (Ultra–Rapid,
Rapid, and Final) include a product that easily enables single–receiver phase ambiguity
resolved positioning when used with the GIPSY/OASIS software (Bertiger et al., 2010).
This product is referred to as the “wide–lane phase bias” , or WLPB, file. The products
from our first IGS08–based reanalysis, described in the previous section, also include thisWLPB file so that single–receiver ambiguity resolved positioning is easily achieved for theentire period 1996–present. The WLPB file provides wide–lane and phase bias estimatesfor each continuous phase arc from the network solution that is used to generate the orbit
and clock states of the GPS satellites. When performing single–receiver positioning with
GIPSY/OASIS, the orbit and clock products for the GPS satellites are used as usual,
but wide–lane and phase biases for the receiver are also determined, followed by phaseambiguity resolution using double differences with the wide–lane and phase bias estimatesfrom the network solution.

88

5 Future Activities
35
IGS05 Product30

IGS08 Product (Resolved)

2

Variance (mm )IGS08 Product (Not Resolved)
25
20
15
10

TIDB

SYOG

POL2

NYAL

MAS1

KOUR

HRAO

GOLD

0

BOR1

5

StationFigure 2: Impact of JPL’s orbit and clock product improvements (IGS05– to IGS08–based products), and single receiver ambiguity resolution (using WLPB product), on east component of station repeatability for 9 globally distributed stations with occupation histories
of at least 12 years. Station repeatability is based upon daily static point positioning
and with respect to velocity model for each station.

Table 3 summarizes the improvements to be gained in static and kinematic terrestrial
positioning when transitioning from our IGS05– to IGS08–based orbit and clock products,
and the subsequent improvements to be gained from performing single receiver phaseambiguity resolution with our IGS08–based products (Desai et al., 2011). These results
are based upon 9 stations selected for global coverage and occupation histories of longer
than 12 years. We observe variance reductions of 30–70% in station repeatability fromusing our most recent orbit and clock products and the single receiver ambiguity resolution
capability.
Figure 2 illustrates, as an example, the improvements in the east component of station
repeatability for the 9 stations used to generate the metrics in Table 3. The east component typically realizes the most significant improvements from ambiguity resolved point
positioning.

5 Future Activities
We anticipate some additional changes to our processing approach before performing asecond IGS08–based reanalysis in support of the IGS reprocessing campaign. For example,
inclusion of second order ionosphere corrections, models for the S1/S2 atmospheric load
deformation effects, and improved solar radiation pressure models are currently being
tested or developed. Furthermore, work is also underway to include reprocessed products
89Desai et al.: Jet Propulsion Laboratory
for the period 1993–1995, including generation of the associated WLPB files to enable
single receiver ambiguity resolution.

6 Acknowledgments
The work described in this report was performed at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space
Administration.

References
Bertiger, W., S. Desai, B. Haines, N. Harvey, A. Moore, S. Owen, and J. Weiss Single
receiver phase ambiguity resolution with GPS data. J. Geodesy, 84(5):327–337, 2010.
doi: 10.1007/s00190-010-0371-9
Boehm, J., A. Niell, P. Tregoning, and H. Schuh. Global Mapping Function (GMF): A
new empirical mapping function based on numerical weather model data, Geophys. Res.
Lett., 33, L07304, 2006. doi: 10.1029/2005GL025546
Boehm, J., R. Heinkelmann, and H. Schuh. Short Note: A global model of pressure
and temperature for geodetic applications. J. Geodesy, 81(10):679–683, 2007. doi:
10.1007/s00190-007-0135-3
Desai, S. D., W. Bertiger, B. Haines, N. Harvey, M. Miller, C. Selle, A. Sibthorpe, andJ. P. Weiss. Long–term evaluation of precise point positioning with single receiver phaseambiguity resolution using JPL’s GPS products. EGU General Assembly, Vienna, Austria, 2011.
Pertit, G., and B. Luzum. IERS Conventions 2010. IERS Technical Note No. 36, 2010.
Sibthorpe, A., J. Weiss, N. Harvey, D. Kuang, and Y. Bar–Sever. Empirical modeling ofsolar radiation pressure forces affecting GPS satellites. AGU Fall Meeting, San Francisco,CA, 2010.
Sibthorpe, A., W. Bertiger, S. D. Desai, B. Haines, N. Harvey, and J. P. Weiss. An evaluation of solar radiation pressure strategies for the GPS constellations. J. Geodesy, 85(8):505–517, 2011. doi: doi:10.1007/s00190-011-0450-6
Weiss, J. P., W. Bertiger, S. D. Desai, B. J. Haines, and C. M. Lane. Near real time GPS
orbit determination: Strategies, performance, and applications to OSTM/Jason–2. Adv.
Astronaut. Sci., 137: 439–452, 2010.

90

MIT IGS Analysis Center Report for 2011
T. A. Herring, R. W. King
Room 54–820A, MIT
77 Massachusetts Avenue, Cambridge, MA 02139
e–mail: tah@mit.edu;
phone: +1 617 253 5941

1 Introduction
In this report we review the products generated by the MIT Analysis Center that are
submitted to the IGS and made able through the MIT ftp site. We examine some aspects of
the MIT analysis focusing on network generation, treatment of solar radiation parameters,
and the method used to generate the MIT 30–second clock products. We also show resultsfor position repeatability and satellite antenna phase center offsets and nadir dependenceof the phase pattern.

2 MIT products
MIT generates weekly submissions to the IGS final orbit and clock products. Our submissions consist of (where WWWW is GPS week and [0–6] are the values between 0 and
6): mit<WWWW>7.sum which is a summary file consisting of site statistics (phase andposition root–mean–square (RMS) scatters, RMS scatter of clock fits to linear trends ofthe reference clocks for each day of the week, RMS scatters of the orbit overlaps (3.75 hrs
on both sides of each orbit) and Earth orientation parameters (EOP) estimates in IERS
standard format.
mit<WWWW>7.erp.Z Earth rotation parameters for 9–days IERS format
mit<WWWW>[0–6].sp3.Z Daily GPS satellite orbits tabulated at 15 minute intervals
with satellite clock estimates.
mit<WWWW>[0–6].clk.Z Daily GPS satellite clocks tabulated at 30–second intervals
for the satellites and reference ground station. Other ground station clocks aretabulated at 15 minute intervals.

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Herring and King: Massachusetts Institute of Technology
mit<WWWW>7.snx.Z Weekly coordinate and EOP SINEX file with minimum constraints applied to orient the solution to the IGS08 reference frame.
We also make available through ftp://everest.mit.edu binary global files for daily andweekly solutions, radiation parameter constraints, and position time series. GAMIT/GLOBK
users can directly use these products. The global position and orbit files have estimatesof the satellite phase centers, loosely constrained, and are a resource for analyzing theestimates of the these offsets. The estimates of the phase centers should be tightly constrained if consistency with the IGS models is needed. The files containing process noise
values for solar radiation parameters can be used to apply similar orbital constraints to
those used in the MIT analysis (see discussion below).

3 Analysis methods
The MIT analysis uses a global network made up of 6 separate networks, with each constructed to form as global a network as possible. Each network is made up of 50 stations ofwhich two sites per network are common to the other 5 networks. No sites are used morethan twice in the networks. The networks are formed simultaneously, with sites being
added to each network sequentially so as to ensure that all networks have good southernhemisphere coverage. The algorithm starts with a base group of four stations in each of
the networks although there is no requirement that data be available from these stations
on a specific day. Sites are then added from the list of core sites and available stations.
The list of available stations is determined from the FTP directories of the IGS and otherarchives. Sites are added at each iteration such that the added site has the largest possible
distance from the other sites in the network. Initially, six networks of 40 unique sites areformed, and then pairs of these sites are added to the other networks to form the ties
between the networks. The core list of sites includes the ITRF2008 reference stations,hydrogen maser timing stations, and other stations of interest. This core list currently
consists of 374 stations. On any given day, many of these stations are not available and so
the networks we form use all of the available stations in the core list and stations chosenfrom the available sites. An example of the combined network generated for the last dayof 2011 is shown in Figure 1.

3.1 Solar radiation parameter estimation.
The MIT analysis initially uses the full 15 parameter Berne orbit model; 6 initial conditions, 3 solar radiation constant terms in the direct, Y–axis, and the orthogonal B axis
directions, and 3 pairs of the sine and cosine once–per–revolution (OPR) terms directedalong the same axes. The parameters are expressed as scale factors on the direct radiation
force. This model, in general, is poorly constrained with 24–hour orbit arcs and when all
6 OPR terms are estimated the center of mass location and the rates of change of the92

3 Analysis methods

60˚

2
21 AMC2
4
31 GOL2
1
6
634
55
21
345 3 416PIE1
6
2 41

30˚
23KOKB
40˚

1All Networks (6)Blue − User defined ref
Purple − Selected tie sites
Green − Selected from Core list
Red − Selected from available list
Yellow − Available Not selected
56

2
61

5 BAKE 531
31 CHUR
62
5 STJO
12ALGO
6 HLFX4 55
6
4
5 BRMU

5
6

4
2 NYAL
351

4
6 SCUB
31 CRO1
41 MANA
3
6 BOGT 1 KOUR
5

4

3
2
61

4
5
31 4

4
6 NKLG

3
2 SUTM
3

4
2 KERG

231
2

3
6 BAKO
31 XMIS
41 COCO1

2
6 CHAT−60˚

2
5 PIMO
45
6 NURK
3

41

2
6 SANT
4
3 LPGS
61 CONZ
33
6 MAG01
21 KHAJ
5361 BJFS 655
3 42
6 WUHN
2 TWTF 2
51 KUNM3

4
61

2 46
3 REUN

2 CHPI
2
5 UNSA 4

2

2

4

5

6

1

2

63
1 ONSA
25
1 1
3
3 4
65
4WSRT
32
23612BRUS
26
344
2
6
5
1
1
2
6
WAB2
1
5
IENG
6
15 1 6 543
2 MATE42
536 32 4
5 NOT12
1
6
42
5
5
64
1
35
2

51 AREQ

5
6 TAH1THTI
45 NIUM 44
5 TONG

−30˚

1
35
6

6

4
5

3

2
2
4
21
4516BREW 5
4
3

5
5
4
3 KARR
2
4
6
YAR2
4
5
3
65 HIL1
PERT21 CEDU
36
4642 AUCK
5 MOBS
3
61 HOB24
5
61
53
3
OUS2
31 MAC1

3
61 OHI22
2

180˚ 270˚

4
5 MAW1
3
2 SYOG
5 VESL 3
3

0˚

90˚

3

180˚

Figure 1: Example of the MIT global network on day 365 of 2011. The names the sites in black
are common between 2 networks and serve to tie the networks together. The numbers
shown in different colors give the network number for the station. The green and purple
stations are from our core list of sites while the red numbered stations come from theavailable lists. The yellow dots show stations that are available but are not used in our
analyses.

Earth orientation parameters (EOP) are poorly determined. In our weekly analyses, we
examine solutions with all of the OPR terms estimated, and based on the statistics ofthe estimates determine, which ones should be retained in the final analysis. We always
estimate that the B–axis OPR terms. The estimation of the direct and Y–axis terms isbased mainly on the significance of the estimates for the week. We also use an orbital
overlap criteria set such that if the RMS scatters of the orbit overlaps for specific satellites are greater than 30 cm, all of the OPR terms for those satellites are estimated. If
the orbit overlaps are greater than 10 cm (but < 30 cm), then the Y–axis OPR terms are
retained. With recent GPS data, the orbital overlap criterion is generally not used (i.e.,
orbit overlaps have < 10 cm RMS). For most weeks only 1 or 2 satellites require more thanjust the B–axis OPR terms. Once the specific representation is set, we use daily estimatesof the OPR terms to set the random walk process noise value for each of the terms. If thechi–squared per degree of freedom of the estimates over the week is less than 1 then zeroprocess noise is assigned and a constant value for the specific term is estimated for the
week. When the chi–squared per degree of freedom is greater than 1, the process noise
value is set such that a random walk would have the same standard deviation over a week
as the observed scatter. The values of the ORP process noise values are available from theeverest.mit.edu ftp site in the MIT_SRP folder. One set of parameters is used fromeach week unless there is a specific issue that needs to be manually accounted for. Manualinterventions are only needed in the 1990’s GPS data analyses.

93

Herring and King: Massachusetts Institute of Technology

3.2 Clock estimation
The MIT phase data analysis uses a double difference strategy. To generate our clock
solutions we perform a separate analysis to determine the clocks after the weekly run iscompleted. In this analysis we take advantage of the fact that if a weighted least squares(WLS) solution is repeated with some of the parameters fixed to their WLS estimatesthen the other parameter estimates will retain their values from the original solution (thestandard deviation of the estimates will be affected but in the case of clock solutions we are
not using this information). To generate the clock estimates, we run an analysis with theorbits, EOPs, and station positions tightly constrained to their estimates from the weekly
combination, and use a direct one–way clock estimates to generate the clock values. The
apriori clock model, offsets and linear trends, is based on fitting the broadcast ephemeris
clocks. The clock solution uses a smaller network than the original analysis. We choose
the sites for this 120–station network (3–networks of 40 stations) based on the qualityof the clock estimates in the original full run. The results from the three sub–networks
are aligned and averaged. The clock estimates are generated at a 30–second rate anddecimated to a 15–minute rate for all ground sites except the reference site. The referencesite and satellites are all reported at a 30–second rate. The alignment of the clocks is an
ensemble average over the sites with smallest RMS scatters about linear trends and thelowest RMS scatter site is chosen as the reference site. The RMS fit of these clocks is
usually less than 30 ps (10 mm equivalent distance).

3.3 Position estimate quality
In Table 1 we give the statistics of the position estimates from the MIT analyses. We givethe RMS scatters about the trend through the data for the periods from 2000 to 2012
and 2010 to 2012. The RMS scatters of both the weekly and daily solutions are below
2 mm for the horizontal components and 6 mm for the vertical components. Recent results
are somewhat better than the longer–term results. The effects of correlation can be seen
Table 1: Median weighted RMS (WRMS) scatter of MIT position estimates for the periods 2000–
2012 and 2010–2012. RMS scatters are computed from daily and weekly solutions. Dueto temporal correlations the weekly solution scatter is only 70% smaller than the daily
solution scatter compared to the 38% reduction expected for white noise. The final row
is the average median scatter of the daily estimates within each week reported in the
MIT summary files.
Analysis
Daily 2000–2012
Daily 2010–2012
Weekly 2000–2012
Weekly 2010–2012
Daily in Week 2010+

94

North (mm)
1.7
1.6
1.2
1.1
1.2

East (mm)
1.8
1.6
1.3
1.1
1.2

Height (mm)
5.6
5.3
4.0
3.6
3.9

# stations
814
467
812
463
259

4 Ancillary analyses
in the table because the scatter from the weekly averages is not reduced by the amount
expected for a white noise process. Also the daily values within one week have the same
RMS scatter as weekly solutions computed over longer periods. The similarity all the RMS
scatters in the east and north components indicates that ambiguity resolution on these
global networks is largely successful. Statistics on the percentage of ambiguities resolved
generally ranges between 90 to 95% for narrow lane ambiguities, and a higher percentage
for wide lanes, which are based on the Melbourne–Wubbena wide lane expression.

4 Ancillary analyses
In our routine analyses we also estimate positions of the satellite phase centers. For the
products that we submit to the IGS, including SINEX file, the phase center offsets aretightly constrained to their values given in the ANTEX file. In Table 2, we give the meanvalues of the adjustments to the XYZ positions of the satellite phase center locations since
the adoption of the IGS08 system (week 1632; 2011–04–17). Up to 55 weekly estimates
are available since this change. Analysis of the temporal behavior of the offsets show there
are systematic variations with time and in the X and Y components suggest that there
are yaw modeling errors that are being absorbed into the phase center position estimates.
We are still analyzing results. In our recent analyses, we have started to save the averagevalues of the phase residuals as a function of elevation angle at individual stations and as
a function of nadir angle for satellites. In Figure 2, we show the RMS scatter of the meanvalues, as a function of nadir angle, of these residuals for each of the satellites. PRNs 16
and 20 have the largest RMS and the values of the average residuals as a function on nadir
angle for PRN 16 are shown in figure 3. The satellites with the lowest RMS scatters show
very little systematic trend with the mean residuals lying within a mm of zero. The phasecenter variations seen at some the ground stations can be large and systematic. GPS site
FAIR has very large systematic residuals with a deviation of nearly −10 mm at the highest
elevation angle (80 deg). These large average residuals may explain the low quality of thesurvey tie at this site. The recent removal the radome at the site had only a small impact
on the average residuals.

95Herring and King: Massachusetts Institute of Technology

Table 2: Mean values of the adjustments to the IGS08 phase center locations based on analysisof data after GPS week 1632.

96

PRN

Type

01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32

IIF
IIR–B
IIA
IIA
IIR–M
IIA
IIR–M
IIA
IIA
IIA
IIR–A
IIR–M
IIR–A
IIR–A
IIR–M
IIR–A
IIR–M
IIR–A
II
IIR–A
IIR–A
IIA
IIR–B
IIR–M
IIF
IIA
IIA
IIR–A
IIR–M
IIA
IIR–M
IIA

Mean dX
(mm)
4.9
37.9
5.7
−5.4
22.7
−1.0
17.7
−13.8
−21.8
−6.7
−2.2
36.9
18.4
25.8
28.4
39.8
31.1
37.5
36.1
25.0
30.5
21.5
37.5
−10.6
−8.1
−5.8
−17.4
24.3
39.1
0.6
19.2
7.6

RMS
(mm)
22.8
35.1
21.4
20.4
29.6
19.4
10.7
13.9
6.6
18.3
20.2
20.7
18.5
21.9
20.4
24.0
31.2
32.0
32.0
33.1
33.1
29.4
20.1
31.3
10.6
10.9
8.8
23.5
33.5
16.0
10.4
19.8

Mean dY
(mm)
−16.9
−4.8
−4.1
21.8
−3.0
−5.2
2.7
50.7
1.7
17.8
−16.0
−12.7
−4.1
−2.9
−5.0
−11.8
−4.7
−7.3
−8.1
−0.9
2.8
2.2
−4.9
12.7
−29.1
27.4
32.8
3.5
−9.8
−13.7
−0.0
38.6

RMS
(mm)
19.3
8.8
25.5
11.0
11.0
14.1
8.0
30.7
12.4
13.0
12.5
8.8
10.0
6.9
9.5
9.2
9.1
8.2
10.7
9.4
9.2
11.8
8.4
23.5
16.8
11.1
13.6
8.4
10.4
17.7
7.2
20.2

Mean dZ(mm)−100.8
−32.6
39.8
−72.6
−21.9
36.0
−0.9
−30.6
−69.8
−73.0
82.7
−72.0
38.4
31.5
−47.2
38.1
−29.6
−20.9
23.9
71.3
−11.8
−26.7
23.2
122.8
−112.1
−90.2
−73.9
0.5
−41.9
27.6
−1.5
10.6

RMS
(mm)
65.5
73.9
81.0
80.0
74.7
87.2
60.1
68.8
66.9
61.4
87.1
58.1
65.3
63.1
102.9
92.0
64.2
92.9
60.2
67.8
82.8
83.7
65.8
51.8
82.1
88.9
62.2
57.1
94.5
68.7
69.6
79.8

#
44
55
55
55
55
55
55
55
55
55
55
55
55
55
55
55
55
55
55
55
55
55
55
21
55
55
55
55
55
42
55
55

4 Ancillary analyses

Site G16
10RMS G16 1.74 mm # 43174 data from 650 files
WRMSMEAN G16 0.67 mm, NRMS 20.35

Mean Phase Residual (mm)

5

0

−5

−10
0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Nadir Angle (degrees)

PCV RMS (mm)Figure 2: RMS scatter of the mean phase residuals by satellite based on the accumulation of
18 weeks of nadir averaged phase residuals.

0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

0

5

10

15
20
PRN

25

30

Figure 3: Phase residuals to PRN 16 as function of nadir angle. Each line is from one day ofdata and the color of line progresses from blues to reds as a function of time. The
green dots show the average values. The phase center location is fixed to the IGS08
value.

97

Herring and King: Massachusetts Institute of Technology

98United States Naval Observatory Analysis Center
Report 2011
C. Hackman, S. Byram, V. Slabinski, and J. Tracey
United States Naval Observatory
3450 Massachusetts Avenue Northwest
Washington DC 20392 USA
e–mail: christine.hackman@usno.navy.mil
phone: 202 762 1428

1 Introduction
The United States Naval Observatory (USNO), located in Washington, DC, USA has
served as an IGS Analysis Center (AC) since 1997, contributing to the IGS Rapid andUltra–rapid Combinations since 1997 and 2000, respectively. At present, USNO contributes a full suite of rapid products (orbit and clock estimates for the GPS satellites,
earth rotation parameters (ERPs), and receiver clock estimates) once/day to the IGS
by the 1600 UTC deadline, and contributes the full suite of ultra–rapid products (post–processed and predicted orbit/clock estimates for the GPS satellites; ERPs) four times/day
by the pertinent IGS deadline. USNO submitted 100% of its rapid products and 99% of
its ultra–rapid products to the IGS on time in 2011.
In a new role assumed in 2011, USNO now serves as the production center for IGS Final Troposphere Estimates, computing and distributing 5–min GPS–based troposphereestimates for all 300+ receivers of the IGS network. USNO also now chairs the IGS
Troposphere Working Group (IGSTWG).
The USNO AC is hosted in the GPS Analysis Division (GPSAD) of the USNO Earth Orientation Department (EOD). Dr. Christine Hackman, GPSAD chief, directs AC activities
and chairs the IGSTWG. Dr. Sharyl Byram oversees production of the IGS Final Troposphere estimates. All GPSAD members, including Dr. Victor Slabinski and Mr. Jeffrey
Tracey, participate in AC work.
USNO AC products are computed using Astronomical Institute of the University of Bern99

Hackman et al.: United States Naval Observatory
Bernese GPS Software (Dach et al., 2007).1 In 2011, rapid products were generated using
a combination of network and precise point positioning (PPP) (Zumberge et al., 1997)
methods. Ultra–rapid products were generated using network solutions.
In addition to its AC and troposphere products, GPSAD generates a UT1–UTC–like quantity, UTGPS, four times/day. UTGPS is used by the IERS Rapid Combination/Prediction
Service in predicting UT1–UTC as an extrapolator for VLBI UT1–UTC measurements.
Mr. Tracey oversees UTGPS. For more information, please contact the AC.
USNO rapid, ultra–rapid and UTGPS products can be downloaded immediately after computation from http://www.usno.navy.mil/USNO/earth-orientation/gps-products.

2 Accomplishments/Strengths 2011
As mentioned previously, the AC maintained 100% and 99% on–time submission rates
for the rapid and ultra–rapid products in 2011, making a successful transition to the new
IGS08 reference frame on 17 April 2011 with no interruption in operations. Dr. Slabinski
played a key role in on–time submissions by continually improving AC code to handle
previously unseen failure modes.
Dr. Byram, with help from Mr. Tracey, set up IGS Final Troposphere operations, with the
AC assuming full computation/distribution duties in July 2011, as promised to the IGS
Governing Board in April 2011. Dr. Byram also back–filled missing troposphere estimatesfor 17 April 2011 — July 2011, presenting all of the above work at ION GNSS 2011 (cf.
“Publications” ).
Dr. Hackman meanwhile re–organized the IGSTWG, recruiting new members (and confirming the continued interest of existing ones), re–drafting the charter, drafting initialaction plans, and planning a member survey that was ultimately distributed in 2012. Further details of IGS troposphere–related work can be found in IGS Troposphere Working
Group 2011 (this volume).
Other accomplishments: Dr. Sharyl Byram conducted an experiment in which she added
GLONASS data to USNO processing. This bore fruit in 2012: she presented said workin an oral presentation at the ION PLANS 2012 conference. In addition to chairing IGS
troposphere activities, Dr. Hackman was appointed to the IGS Associated Membership
Committee and the IGS Governing Board.
1

Prior to 2009, the rapid products were computed using Jet Propulsion Laboratory (JPL) GPS Inferred
Positioning System (GIPSY; Webb and Zumberge, 1997).

100

4 Product Performance 2011

3 2011 Publications/Presentations Pertaining to USNO IGS
Work
Byram, S., C. Hackman, and J. Tracey. Computation of a High–Precision GPS–Based
Troposphere Product by the USNO. Proc. ION GNSS 2011, 572–578, 2011.
Hackman, C. Impact of Network De–Densification on GPS–Estimated Polar Motion: aSimulation Study. Poster, European Geosciences Union General Assembly. 2011a.
Hackman, C. and D. Matsakis. Precision and Accuracy of USNO GPS Carrier Phase Time
Transfer: Further Studies. Proc. 2011 Joint Conference, IEEE International Frequency
Control Symposium (IFCS) & European Frequency and Time Forum, 1046–1051, 2011.
Hackman, C.. High–Precision Low–Latency GPS–Carrier–Phase–Based Satellite Orbits,
Clocks and Geophysical Parameters Available from the USNO. Proc. 2011 Joint Navigation Conference, 1163–1177, 2011b.

4 Product Performance 2011
Figures 1–4 show the 2011 performance of USNO rapid and ultra–rapid products, withsummary statistics given in Table 1. USNO rapid orbits had a median weighted RMS(WRMS) of 14 mm with respect to (wrt) the IGS rapid combined orbits. The USNO ultra–
rapid orbits had median WRMSs of 21 mm (24–h post–processed segment) and 50 mm (6–h
USNO ORBITS WRT IGS RAPIDS
Jan - Dec 2011
180

160

140

wrms, mm

120

100

rapid
ult, pastult, pred

80

60

40

20

0
55500

55600

55700

55800

55900

56000

MJD

Figure 1: Weighted RMS of USNO GPS orbit estimates with respect to IGS Rapid Combination,
2011. “Ult, past” refers to 24–hour post–processed section of USNO ultra–rapid orbits.
“Ult, pred” refers to first six hours of ultra–rapid orbit prediction.

101

Hackman et al.: United States Naval Observatory

RMS, USNO ULTRA-RAPID CLOCK PREDICTIONS WRT IGS RAPIDS

RMS & STDEV, USNO RAPID CLOCKS WRT IGS RAPIDS

Jan - Dec 2011

300

12000

250

10000

200

8000
rms
stdev

150

ps

ps

Jan - Dec 2011

6000

100

4000

50

2000

0
55500

55600

55700

55800

55900

0
55500

56000

55600

MJD

55700

55800

55900

56000

MJD

Figure 2: RMS/standard deviation of USNO rapid GPS clock estimates (left) and RMS of USNO
ultra–rapid GPS clock predictions (right) with respect to IGS Rapid Combination,
2011.

USNO ERPS MINUS IGS FINALS
800

600

400

micro arc sec

200
rap x

0

rap y

-200

-400

-600

-800
55500

55600

55700

55800

55900

56000

MJD

Figure 3: Difference between USNO rapid polar motion estimates and IGS Final Combination,
2011.

predict) wrt the IGS rapid combined orbits. In the future, a comparison of AC ultra–rapid
orbits to the IGS ultra–rapid combination will be considered as well.

102

4 Product Performance 2011

USNO ERPS MINUS IGS FINALSUSNO ERPS MINUS IGS FINALS

1000

600
400

ult past x

0

ult past y-200

micro arc sec

micro arc sec

500
200

ult pred x

0

ult pred y

-500
-400
-600
55500 55600 55700 55800 55900 56000-1000
55500 55600 55700 55800 55900 56000

MJD

MJD

Figure 4: Difference between USNO ultra–rapid polar motion estimates and IGS Final Combination, 2011.

USNO rapid clocks had a 57 ps standard deviation (STDEV) and 144 ps RMS wrt IGS
combined rapid clocks. USNO ultra–rapid clock predictions (first six h) had a 2449 ps
RMS wrt IGS combined rapid clocks. While the RMS of USNO rapid clocks decreased
after MJD 55800/27 Aug 2011 (Fig. 2), the STDEV became slightly larger; the RMS of
the ultra–rapid predictions increased after this date as well. The cause of this change is
unknown.
USNO rapid polar motion (PM) estimates had RMS differences wrt IGS final combined
values of (x, y) 196 and 162 micro arc sec. USNO ultra–rapid PM estimates differed from
IGS final combined values (x, y) by 158 and 164 micro arc sec for the 24–h post–processedsegment and 362 and 303 micro arc sec for the 24–h predict.
The troposphere production center is still in the process of developing quality metrics.
Table 1: RMS Performance of USNO Rapid and Ultra-rapid Products 2011 (date: 1/1/11–
12/31/11).
USNO GPS satellite orbits
Statistic: median weighted
RMS wrt IGS combined rapid
orbit estimatesunits: mm
rapid
ultra–rapid
past 24 h 6–h predict
14
21
50

USNO GPS–based polar
motion estimates
Statistic: RMS difference wrt
IGS combined final productunits: 10−6 arc sec
rapid
ultra–rapid
past 24 h 24–h predict
x:196
x:158
x:362
y:162
y:164
y:303

USNO GPS–based clock
estimates
Statistic: median RMS,
standard dev. wrt IGS
combined rapid clock productunits: ps
rapid
ultra–rapid
past 24 h
6–h predict
STDEV: 57
RMS: 2449
RMS: 144

103

Hackman et al.: United States Naval Observatory

Figure 5: Comparison of USNO test troposphere solutions to existing IGS Final Troposphereestimates, in preparation for operational transition to USNO. ZPD = total zenith
troposphere delay. Days of year 50–74 (28 Feb—14 Mar) 2011. From Byram et al.
(2011).

However, Fig. 5 shows a comparison of USNO test troposphere solutions (computed prior
to assumption of duties) and existing IGS final troposphere estimates. The USNO estimates agreed with existing IGS Final Estimates with RMSs of 2.95 mm (total vertical
zenith delay) and 0.42 mm (both north and east components). Once duties were transferred, USNO submitted more than 82,000 IGS Final Troposphere Estimate files, covering
the period 17 Apr–31 Dec 2011.

5 Areas Requiring Improvement
USNO excels in on–time product submission. Its post–processed orbits and ultra–rapid
clock products (both post–processed and predicted) contribute usefully to the IGS combinations. The assumption of IGS final troposphere estimation duties went according toplan. However, we recognize the need for improvement in several areas.

104References
First, we need to increase the number of stations processed in the network solution.
Whereas most ACs process approximately 100, we are presently limited to 34 or so. This
problem can be solved by exploiting the Bernese capability to process multiple small network solutions and combine the normal equations. We have had test versions of thisrunning since 2010 but have yet to obtain satisfactory results.
Next: USNO rapid and ultra ERPs, while unbiased, are noisy relative to other AC submissions and are thus not included in the combinations. We adjusted several processing
parameters in 2011 in an effort to address this — for example, we were not implementing the IGS reference stations optimally — and while this helped, the problem remains.
Adding more stations to the network solution would likely improve the situation, as thesimulation studies of Hackman (2011a) showed. Work continues, with a resolution goal
date of December 2012.
Finally: USNO rapid clocks have a large STDEV wrt IGS combined rapid clocks, comparedto other–AC submissions, and are thus also omitted from the combination. The matter isunder continuing investigation.

6 Future Plans
The primary work of 2012 will be to address the problems above. Additionally, the USNO
AC will be very active at the IGS 2012 Workshop, attending all governing board meetings,
chairing the troposphere plenary, poster and splinter sessions, and presenting three posters
re the AC, the troposphere production center, and USNO GLONASS processing. Lastly,
GLONASS processing will be implemented into AC submissions if ongoing tests indicate
it is so warranted.

References
Dach, R., U. Hugentobler, P. Fridez, M. Meindl (eds). Bernese GPS Software Version 5.0(user manual). Astronomical Institute of University of Bern, Bern, Switzerland, 2007.
Zumberge, J. F., M. B. Heflin, D. C. Jefferson, M. M. Watkins, and F. H. Webb. Precise
Point Positioning for the Efficient and Robust Analysis of GPS Data from Large Networks. J. Geophys. Res., 102(B3):5005–17, 1997.
Webb, F. H. and J. F. Zumberge (eds.). An Introduction to GIPSY/OASIS–II: Precision
Software for the Analysis of Data from the Global Positioning System. JPL internal
publication D–11088, Jet Propulsion Laboratory, Pasadena, California, 1997.

105

Hackman et al.: United States Naval Observatory

106

IGS Regional Network Associate Analysis Centre
for SIRGAS (IGS RNAAC SIR)
L. Sánchez
Deutsches Geodätisches Forschungsinstitut (DGFI)
Alfons–Goppel–Str. 11, D–80539 Munich, Germanye–mail: sanchez@dgfi.badw.de

1 Introduction
The IGS Regional Network Associate Analysis Centre for SIRGAS (IGS RNAAC SIR) was
installed in June 1996 under the responsibility of the Deutsches Geodätisches Forschungsinstitut (DGFI) (Seemüller and Drewes, 2008; Sánchez et al., 2010). The main objective isthe permanent analysis of the SIRGAS reference frame, which is given at present by about
250 continuously operating GNSS stations (Fig. 1). The activities of the IGS RNAAC SIR
concentrate on:
1. The computation of loosely constrained weekly solutions for further combinations of
the network (e.g. integration into the IGS polyhedron, computation of cumulative
solutions, etc.). These solutions are weekly delivered to the IGS in SINEX format to
be combined together with those generated by the other IGS Global and Regional
Analysis Centres. They are named sirwww7.snx (wwww stands for the GPS week);
2. Weekly station positions aligned to the same reference frame in which the IGS GNSS
orbits are given; i.e. the IGS reference frame. These positions are applied as reference
values for surveying applications in Latin America. Their name is siryyPwwww.crd(yy indicates the last two digits of the year).
3. Multi–year solutions providing station positions and velocities to estimate the kinematics of the reference frame and as support for applications requiring coordinate
time–dependence. They are identified by SIRyyPnn.SNX (being nn the number ofthe cumulative solutions computed in one year).
The SIRGAS reference frame was regularly computed by the IGS RNAAC SIR as only one
network until August 31, 2008 (GPS week 1495) (Seemüller et al., 2012). Afterwards, due
to the increasing number of stations, different sub–networks were defined and, at present,

107

Sanches: RNAAC SIRGAS
-120°

-90°

-30°

-60°

GOLD

SIRGAS-CON
18/03/2012

BRMU

MDO1

30°

30°

CRO1

SCUB

15°

15°

GUAT

BOGT
0°

GLPS

0°

BRFT

BRAZ

-15°

-15°

UNSA
ISPA
-30°

-30°

CONZ

LPGS

-45°
entre
nalysi
sC
AS A

PARC

SIRG

IGS08 core station
Core network
Northern network-60°
Middle network
Southern network

at DG
FI

-45°

-60°

OHI2

PALM

-120°

-90°

-60°

-30°

Figure 1: SIRGAS Reference Frame (status 2012–03–12).

the analysis strategy is based on the combination of individual solutions including (Brunini
et al., 2012):• One core network with about 120 stations distributed over the whole continent, and• different densification sub–networks distributed regionally on the northern, middle,
and southern part of the continent (Fig. 1).

108

1 Introduction
SIRGAS Working Group on Reference System
SIRGAS-C

3 SIRGAS-D(core network)(densification sub-networks)

1 Regional Data Centre

National Data Centres(DGFI)(entities in charge ofnational reference frames)

1 Analysis Centre

8 Local Processing
Centres(DGFI as IGS-RNAAC-SIR)

CEPGE, CIMA, CPAGS-LUZ, IBGE,
IGAC, IGN-Ar, INEGI, SGM-Uy

2 Combination Centres(DGFI, IBGE)

Final solutions for the
SIRGAS reference frame
Loosely constrained
weekly solutions for
IGS polyhedron andmulti-year solutions- Weekly station positionsaligned to the ITRF
- Multi-year solutions(positions + velocities)

Figure 2: Dataflow within the weekly analysis of the SIRGAS Reference Frame.

The SIRGAS core network provides a direct densification of the ITRF in Latin America and the regional sub–networks improve the geographical density of the core network.
This hierarchy guarantees the precise accessibility to the global reference frame at national and local levels. Although, core and regional sub–networks appear as two different
categories, their stations match requirements, characteristics, performance, and quality of
ITRF stations.
The different sub–networks are individually processed by the SIRGAS Analysis Centres:
the core network is computed by DGFI (Germany, Sánchez and Seitz, 2011), the othersub–networks by the SIRGAS Local Processing Centres: CEPGE (Ecuador), CIMA (Argentina), CPAGS–LUZ (Venezuela), IBGE (Brazil), IGAC (Colombia), IGN (Argentina),
INEGI (Mexico), and SGM (Uruguay). These Processing Centres deliver loosely constrained weekly solutions for the assigned SIRGAS sub–networks. In these solutions,satellite orbits, satellite clock offsets, and Earth orientation parameters are fixed to thefinal weekly IGS values, and positions for all sites are constrained to ±1 m. The individual
contributions are integrated in a unified solution by the SIRGAS Combination Centres:
DGFI (Sánchez et al., 2012a) and IBGE (Costa et al., 2012). The distribution of the
SIRGAS stations within the SIRGAS Processing Centres guarantees that each station is
included in three solutions. Fig. 2 shows the dataflow within the SIRGAS processing.
According to this, the IGS RNAAC SIR is now responsible for (Seemüller et al., 2012;
Sánchez and Seitz, 2011)109

Sanches: RNAAC SIRGAS
1. processing the SIRGAS core network;
2. combining this core network with the densification sub–networks; and3. making available the SIRGAS products, i.e.: loosely constrained weekly solutions,weekly station positions aligned to the ITRF, and multi–year solutions describing
the kinematics of the reference frame.
The analysis of the SIRGAS reference frame as a regional densification of the ITRF is basedon the IGS final products (Sánchez and Brunini, 2009). Consequently, the SIRGAS weekly
solutions are given in the same reference frame applied by the IGS for the calculation of
its products; namely, the IGS05 until week 1631 and the IGS08 since week 1632 (Sánchez
and Seitz, 2011). Here it should be mentioned that the former SIRGAS weekly solutions
from GPS week 1042 to 1399 using relative antenna phase centre corrections and referring
to different ITRF or IGS reference frames were reprocessed using the igs05.atx model andthe IGS05 frame (Seemüller et al., 2012). Reprocessed solutions are identified with thename si1wwww.snx to be distinguished from the old weekly solutions.

2 Kinematics of the SIRGAS reference frame
To estimate the kinematics of the SIRGAS reference frame, a cumulative (multi–year) solution is computed (updated) every year, providing epoch positions and constant velocities
for stations operating longer than two years. The coordinates of the multi–year solutions
refer to the latest available ITRF and to a specified epoch, e.g. the most recent SIRGAS–
CON multi–year solution SIR11P01 (Fig. 3) refers to ITRF2008, epoch 2005.0. It includes
230 stations with 269 occupations and its precision was estimated to be ±1.0 mm (horizontal) and ±2.4 mm (vertical) for the station positions, and ±0.7 mm/a (horizontal) and±1.1 mm/a (vertical) for the constant velocities (Sánchez and Seitz, 2011).
Since the switch to IGS08 reference frame causes a discontinuity of some millimetres inthe station position time series, this solution is the last one that can be computed with theavailable data. A new multi–year solution of the SIRGAS reference frame demands there–processing of all previous weekly solutions using the IGS08 frame and the phase centre
correction model igs08.atx. For that, it is necessary to wait until the IGS has generated
the corresponding IGS08–related products (e.g. satellite orbits, EOPs, terrestrial reference
station positions, etc.).

3 Impact of seismic events on the SIRGAS reference frame
The western part of the SIRGAS region, i.e. the plate boundary zone between the Pacific, Cocos, and Nazca plates in the west and the North American, Caribbean, and SouthAmerican plates in the east, is an extremely active seismic area. The frequent occurrenceof earthquakes causes episodic station movements, which have to be precisely determined110

3 Impact of seismic events on the SIRGAS reference frame

SIRGAS
Figure 3: Horizontal velocities of the multi–year solution SIR11P01.

111

Sanches: RNAAC SIRGAS

83,5

305,2

cm

cm

Figure 4: Horizontal displacements caused by the Maule earthquake on 2010–02–27.

and modelled to guarantee the appropriate transformation of station positions between
the pre–seismic and the post–seismic (deformed) reference frame (Sánchez et al., 2012b).
According to this, always when a strong earthquake shakes the SIRGAS region, the IGS
RNAAC SIR attempts to process as soon as possible the available GNSS measurements toestimate the impact on the reference frame. The usual procedure includes the computation of daily normal equations, which are separately solved with respect to IGS reference
stations located outside the SIRGAS region, i.e. in Europe, North America, and Africa.
By comparing daily station positions before and after the earthquake, it is possible todetermine displacements of the SIRGAS–CON reference stations associated to the seism.
As an example, Fig. 4 presents displacements computed by DGFI after the earthquake inChile on 2010–02–27.

4 Improvement of the IGS station coverage in Latin America
After the strong earthquake of February 2010 in the Chilean Region Maule, a huge percentage of existing IGS reference frame stations in South America suffered an irreparable
discontinuity in their time series. According to Fig. 4, this earthquake produced co–seismic displacements between 5 m at the Pacific Coast and 2 cm at the Atlantic Coast inArgentina and Uruguay. Additional movements due to the post–seismic relaxation during
the first months after the main earthquake and its aftershocks are also evident in the station position time series. Thereby, the reliability of the recently launched IGS08 reference
frame decreased considerably in South America and the affected stations are no longer

112

4 Improvement of the IGS station coverage in Latin America
-120°

-90°

GOLD

SIRGAS-CON

PIE1

18/03/2012

BRMU

CIC1

30°

-30°

-60°

MDO1

30°

HER2
MTY2
LPAZ/IPAZ

NAS0

TAMP

INEG

CAM2/ICAM

MERI
SCUB

GCGT

CRO1

15°

GUAT
SSIA
SLOR MANA

ABMF

15°

BDOS

SAMA
CART

MARA
CUCU
CANO
BOAV

QUI1

0°

KOUR

BOGT

BUEN

GALA/GLPS

SAGA

RIOP

0°
SALU

NAUS

IQUI

FORT/BRFT
IMPZ
RECF

POVE

RIOB

TOPL

SAVO/SALV

CALL

-15°

AREQ

SCRZ

URUS
IESL/ISPA

BOMJ
BRAZ

CUIB

IQQE
UNSA

SIRGAS station in IGS Repro2
IGS station
VALP
SIRGAS station
SANT
Decommissioned
CONZ

CHAC

COPO

-30°

ANTC

CEFE

PPTE

YCBA

CATA
CFAG
CORD

-15°

CHPI
STHL

NEIA
UFPR
POAL

-30°

BUE2
LPGS
LHCL
VBCA
RWSN

-45°

-45°
Centr
e at

DGFI

COYQ

lysis

FALK

AS A
na

RIOG/RIO2

SIRG

PARC

-60°

-60°
OHIG/OHI2

PALM

VESL
-120°

-90°

-60°

-30°

Figure 5: SIRGAS stations to be included in the second IGS reprocessing campaign.

usable as a basis for the GNSS data analysis or to guarantee the long–term stability of
the ITRF in this region. Keeping in mind the achievements reached within the regionalreference frame SIRGAS and the planned second reprocessing campaign of the IGS global
network, a set of continuously operating SIRGAS stations was proposed to be included inthis reprocessing with the main objective of improving the IGS station coverage in Latin
America. Initially, the IGS RNAAC SIR, with the support of the national organizations

113

Sanches: RNAAC SIRGAS
responsible for the reference frames in the Latin American countries, made a selection of
about 70 SIRGAS stations which satisfy the IGS requirements. This selection was evaluated by the IGS Reference Frame Working Group, and after some interaction with the IGS
Global Analysis Centres, it was decided to include 40 SIRGAS stations (Fig. 5) not only in
the IGS reprocessing but also in the present routine IGS processing. The IGS RNAAC SIR
provided the IGS data centres with the metadata and all existing observations (historicaldata) of the selected stations by the end of January 2012. Present measurements (since
the beginning of 2012) of the operational stations are directly provided by the responsible
Latin American agencies to the IGS. The next step is to manage, together with the IGS
Network Coordinator, the formal integration of these stations in the IGS network.

5 Outlook
In addition to the routine activities, the IGS RNAAC SIR is at present focused on:
1. To analyse and model the seasonal variations within the reference frame computation
to increase the reliability and long–term stability of regional reference frames;
2. To determine the best possible strategy for the computation of deformation models
that allow the appropriate transformation of station positions between pre–seismic
and the post–seismic (deformed) reference frames;
3. To prepare a second reprocessing campaign of all SIRGAS observations available
based on the IG2 products.

Acknowledgments
The operational infrastructure and results described in this report are possible thanks tothe active participation of many Latin American and Caribbean colleagues, who not only
make the measurements of the stations available, but also operate SIRGAS Analysis Centres processing the observational data on a routine basis. The achievements of SIRGAS
are a consequence of a successful international geodetic cooperation not only following andmeeting concrete objectives, but also becoming a permanent and self–sustaining geodetic community to guarantee quality, reliability, and long–term stability of the SIRGAS
Reference Frame. The SIRGAS activities are strongly supported by the International Association of Geodesy (IAG) and the Pan–American Institute for Geography and History(PAIGH). The IGS RNAAC SIR highly appreciates all this support. More details about
the activities and new challenges of SIRGAS, as well as institutions and colleagues working
on can be found at www.sirgas.org.

114

References

References
Brunini, C., L. Sánchez, H. Drewes, S. Costa, V. Mackern, W. Martínez, W. Seemüller,
and A. da Silva. Improved Analysis Strategy and Accessibility of the SIRGAS Reference
Frame. In: Kenyon S., M. C. Pacino, U. Marti (Eds.), Geodesy for Planet Earth, IAG
Symposia, 136: 3–10, 2012.
Costa, S. M. A., A. L. Silva, and J. A. Vaz (2012). Report on the SIRGAS–CON Combined
Solution by IBGE Analysis Center. In: Kenyon S., M. C. Pacino, U. Marti (Eds.),
Geodesy for Planet Earth, IAG Symposia, 136: 853–858, 2012.
Sánchez, L. and C. Brunini. Achievements and Challenges of SIRGAS. In: Drewes H.
(Ed.): Geodetic Reference Systems, IAG Symposia; 134: 161–166, 2009. doi: 10.1007/
978-3-642-00860-3_25.
Sánchez, L., W. Seemüller, M. Seitz, B. Forberg, F. Leismüller, and H. Arenz. SIRGAS:
das Bezugssystem für Lateinamerika und die Karibik. Zeitschrift für Vermessungswesen,
135(2), 2010.
Sánchez, L. and M. Seitz. Recent activities of the IGS Regional Network Associate Analysis
Centre for SIRGAS (IGS RNAAC SIR). DGFI Report No. 87, Munich, 2011.
Sánchez, L., W. Seemüller, and M. Seitz (2012a). Combination of the Weekly Solutions
Delivered by the SIRGAS Processing Centres for the SIRGAS–CON Reference Frame.
In: Kenyon S., M. C. Pacino, U. Marti (Eds.), Geodesy for Planet Earth, IAG Symposia,
136: 845–852, 2012.
Sánchez, L., W. Seemüller, H. Drewes, L. Mateo, G. González, A. da Silva, J. Pampillón,
W. Martínez, V. Cioce, D. Cisneros, and S. Cimbaro. Long–term stability of the SIRGAS
Reference Frame and episodic station movements caused by the seismic activity in the
SIRGAS region. Proceedings of the IAG Symposium REFAG2010, Springer (in press),
2012.
Seemüller, W. and H. Drewes. Annual Report 2003–2004 of IGS RNAAC SIR. In: IGS
2003–2004 Technical Reports, IGS Central Bureau, (eds), Pasadena, CA: Jet Propulsion
Laboratory, 2008.
Seemüller, W., M. Seitz, L. Sánchez, and H. Drewes. The new Multi–year Position and
Velocity Solution SIR09P01 of the IGS Regional Network Associate Analysis Centre(IGS RNAAC SIR). In: Kenyon S., M. C. Pacino, U. Marti (Eds.), Geodesy for Planet
Earth, IAG Symposia, 136: 877–884, 2012.

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Sanches: RNAAC SIRGAS

116

Part III

Data Centers

117

Infrastructure Committee Report 2011
I. Romero
ESA/ESOC, Darmstadt, Germany

The Infrastructure Committee is set with the task of studying and advising on infrastructure issues to the IGS Governing Board and the IGS network Coordinator. The latest
status and recent progress of the Committee is detailed below for 2011.

1 Membership
Current Members appointed 3 April, 2011 for 2 year terms:• Carine Bruyninx (OMA)• Lou Estey (UNAVCO)• Gary Johnston (GA)
• Ignacio (Nacho) Romero — Chairman — (ESA/ESOC)• Mike Schmidt (NRCan)• Georg Weber (BKG)
Ex-officio Members:• Steve Fisher — Central Bureau• Jim Ray — Analysis Coordinator• Mark Caissy — Real time Working Group Chair• Bruno Garayt — Reference Frame Coordinator• Carey Noll — Data Center Working Group Chair• Ken Senior — Clock Products Coordinator

2 Activities in 2011:• Continued refinement with the IGS CB of the updated Site Guidelines, waiting for
publication by the CB after further review and open comment period.

119Romero: Infrastructure Committee• Helped to organize and support the test campaign to assess the impact of un–calibrated Domes at co–located sites (together with CB, ACC, RFWG and AWG:
– This campaign has requested from organizations with co–located stations using
un–calibrated Domes over their GNSS antennas that they remove the Domesfor an 8–week period, and then returns the Dome to its position, so as not
to break the long–term position time series. This test campaign attempts todetermine whether the effect of the un–calibrated Dome can be properly characterized from the AC Sinex solutions by the Reference–Frame Working Group
combination and analysis method.
So far the following stations have participated with removing their uncalibrated
Domes:
RemovalRe–installation
CRO1 01–Apr–2011
24–Jun–2011
TSKB
01–Jul–2011
30–Aug–2011
TSK2
01–Jul–2011
30–Aug–2011
AREQ 19–Aug–2011
03–Feb–2012
FAIR
28–Apr–2012
On–going
YAR2 28–Apr–2012
On–going• Supported the IGS CB (Robert K., David M.) on station issues; introduction of new
stations in India (lcki, pbri) and elsewhere, decommissioning of stations (bran, etc),
handling un–calibrated Antenna+Dome pairs, etc. .
• Making some progress to recover long dormant stations: such as yibl, bhr1/2, pre1/2,
and many other NGA stations no longer submitting data due to un–calibrated antennas at previously available IGS stations (with DCWG, CB, AWG, ACC).
• Maintained the internal IC webpage with information for the IC members, GB and
NC on station data arrival statistics, station availability, Reference Frame station
usage, RINEX header / station log inconsistencies, etc. .
• Participated in the Real–Time Pilot Project telecons and discussions on the “Multi
Signal Message” definition to ensure full compatibility of the streaming standard andRinex 3.01 .
• Assisted in the RINEX “way forward” helping to establish the RINEX working groupwithin the IGS and the RTCM (with RTPP, ACC, GB).
• Made recommendations and comments on the QZSS data format as sample files havebecome available from JAXA to ensure that they follow the RINEX definition.
• Assisted in the selection of additional reference frame candidate stations from Central
and South America and from Africa (with RFWG and ACC).
• Clarified with the CB and the RFWG the location of the station logs for the IGS“proposed stations” .

120

4 Activities planned to support IGS MGEX:

3 Continued activities for 2012–2013:• Finalize the un–calibrated Dome experiment for co–located stations and promote
in–depth result analysis for IGS WS 2012 presentation.
• Promote continued progress on the streaming and RINEX data formats to accommodate the new systems (QZSS, etc) (with RTPP).
• Help the IGS in the IGS WS 2012 preparations to properly cover infrastructure
issues (with CB, Workshop organizing committee, etc).

4 Activities planned to support IGS MGEX:
Continued evaluation and assessment of capabilities by different GNSS equipment vendors
as to their compliance to the RINEX standard for GNSS data (Rinex 3), provision ofregional GNSS data (QZSS, Compass), etc.

121Romero: Infrastructure Committee

122

CDDIS Global Data Center Technical Report 2011
C. NollNASA Goddard Space Flight Center, Code 690.1
Greenbelt, MD 20771 USA
Carey.Noll@nasa.gov

1 Introduction
The CDDIS is NASA’s data archive and information service supporting the international
space geodesy community. For over 30 years, the CDDIS has provided continuous, longterm, public access to the data (mainly GNSS — Global Navigation Satellite System, SLR— Satellite Laser Ranging, VLBI — Very Long Baseline Interferometry, and DORIS —Doppler Orbitography and Radiopositioning Integrated by Satellite) and products derived
from these data required for a variety of science observations, including the determinationof a global terrestrial reference frame and geodetic studies in plate tectonics, earthquake
displacements, volcano monitoring, Earth orientation, and atmospheric angular momentum, among others. The specialized nature of the CDDIS lends itself well to enhancement
to accommodate diverse data sets and user requirements. The CDDIS is one of NASA’s
Earth Observing System Data and Information System (EOSDIS) distributed data centers; EOSDIS data centers serve a diverse user community and are tasked to provide
facilities to search and access science data and products.
The CDDIS serves as one of the primary data centers and core components for the geometric services established under the International Association of Geodesy (IAG), an organization that promotes scientific cooperation and research in geodesy on a global scale.
The system has supported the International GNSS Service (IGS) as a global data center
since 1992. The CDDIS activities within the IGS during 2011 are summarized below; thisreport also includes any recent changes or enhancements made to the CDDIS.

2 System Description
The CDDIS archive of IGS data and products are accessible worldwide through anonymous
ftp. The CDDIS is located at NASA’s Goddard Space Flight Center (GSFC) and isavailable to users 24 hours per day, seven days per week.

123Noll: Crustal Dynamics Data Information System
The CDDIS computer system consists of incoming, outgoing, and processing servers. All
ftp and web access is performed on the outgoing server, which is equipped with a hot spare.
Data centers, stations, and analysis centers push files to the CDDIS incoming server, whichis also configured with a hot spare. Processing of incoming files for the on–line archiveis performed in a separate environment that also includes a database server for managing
metadata extracted from incoming data.

3 Archive Content
As a global data center for the IGS, the CDDIS is responsible for archiving and providing
access to GNSS data from the global IGS network as well as the products derived fromthe analyses of these data in support of both operational and working group/pilot project
activities. Approximately 6 Tbytes of the CDDIS archive are devoted to GNSS data
(5.5 Tbytes), products (250 Gbytes), and ancillary information. All data and products areaccessible through subdirectories of ftp://cddis.gsfc.nasa.gov/gnss (a symbolic linkto ftp://cddis.gsfc.nasa.gov/gps).

3.1 GNSS Tracking Data
The user community has access to the on–line archive of GNSS data available through theglobal data center archives of the IGS. Over 50 operational and regional IGS data centersand station operators make data (observation, navigation, and meteorological) available
in RINEX format to the CDDIS from selected receivers on a daily, hourly, and sub–hourly
basis. The CDDIS also accesses the archives of the other three IGS global data centers,
Scripps Institution of Oceanography (SIO) in California, the Institut Géographique National (IGN) in France, and the Korea Astronomy and Space Science Institute (KASI) to
retrieve (or receive) data holdings not routinely transmitted to the CDDIS by an operational or regional data center. Tables 1 and 2 summarize the types of GNSS data archived
at the CDDIS.
Data, in RINEX V2.10 or V2.11 format, from GPS and GPS+GLONASS receivers arearchived within the GNSS directory structure /gnss/data.
The CDDIS archives four major types/formats of GNSS data, all in RINEX format, as
described in Table 1. Daily RINEX data are quality–checked, summarized, and archived to
public disk areas in subdirectories by year, day, and file type; the summary and inventory
information are also loaded into an on–line database. Nearly 150K station days from 490
distinct GNSS receivers were archived at the CDDIS during 2011; a complete list of thesesites can be found in the yearly summary reports at URL ftp://cddis.gsfc.nasa.gov/
reports/gnss/.

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3 Archive Content
Table 1: GNSS Data Type Summary.
Data Type
Daily GNSS
Hourly GNSS
High–rate GNSS
Satellite GPS

Sample Rate
30 sec.
30 sec.
1 sec.
10 sec.

Data Format
RINEX and compact RINEX
Compact RINEX
Compact RINEX
Compact RINEX

Available On–line
Since 1992
2+ years
Since May 2001
Since 2002

Table 2: GNSS Data Archive Summary for 2011.
Data Type

Avg. No.
Sites/Day
Daily GNSS
425
Hourly GNSS
260
High–rate GNSS
135
LEO GPS
1

Avg.
Vol./Day
850 Mb300 Mb1500 Mb
0.5 Mb

Total
Vol./Year285 Gb95 Gb
460 Gb200 MbDirectory Location/gnss/data/daily/gnss/data/hourly/gnss/data/highrate/gnss/data/satellite

Latency of
Majority ofData
1 hour10 minutes
10 minutes
10 daysWithin minutes of receipt, the hourly GNSS files are archived to subdirectories by year,
day, and hour. These data are retained on–line indefinitely; the daily files delivered at theend of the UTC day contain all data from these hourly files and thus can be used in lieu
of the individual hourly files.
High–rate (typically 1–second sampling) GNSS data are archived in files containing fifteen
minutes of data and in subdirectories by year, day, file type, and hour. Many of thesedata files are created from real–time streams.
The CDDIS generates a global broadcast ephemeris file on an hourly basis. This fileis derived from the site–specific ephemeris data files for each day/hour. These files areappended to a single file that contains the orbit information for all GNSS satellites forthe day up through that hour. This merged ephemeris data file is then copied to theday’s subdirectory within the hourly data file system. Within 1–2 hours after the end of
the UTC day, after sufficient station–specific navigation files have been submitted, thisconcatenation procedure is repeated to create the daily broadcast ephemeris file, using
daily site–specific navigation files as input. The daily file is copied to the corresponding
subdirectory under the daily file system. Users can thus download this single, daily (orhourly) file to obtain the unique navigation messages rather than downloading multiple
broadcast ephemeris files from the individual stations.
The CDDIS continues to archive data from space–borne GPS receiver data from selectedmissions (e.g., SAC–C). The staff hopes to add data from other satellites such as Jason,
GRACE, and ICESat.

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Noll: Crustal Dynamics Data Information System

3.2 IGS Products

The CDDIS routinely archives IGS operational products (daily, rapid, and ultra–rapid
orbits and clocks, and weekly ERP and station positions) as well as products generated by
IGS working groups and pilot projects (ionosphere, troposphere, real–time clocks). The
CDDIS currently provides on–line access through anonymous ftp or the web to all IGS
products generated since the start of the IGS Test Campaign in June 1992 in the filesystem /gnss/products; products from GPS+GLONASS products are available throughthis filesystem. Products derived from GLONASS data only continued to be archived at
the CDDIS in a directory structure within the file system /glonass/products.
The CDDIS also continued to archive combined troposphere estimates in directories by
GPS week. Global ionosphere maps of total electron content (TEC) from the IONEX
AACs were archived in subdirectories by year and day of year. New ionosphere products
include hourly and sub–hourly rapid products and predicted products. Real–time clock
comparison products have been archived at the CDDIS in support of the IGS Real–Time
Pilot Project since 2009. Table 3 summarizes the GNSS products available through the
CDDIS.
In 2011, the archive of products for the first IGS reprocessing campaign (repro1) wascompleted. GNSS data collected by the IGS network from 1994 through 2007 (GPS weeks
0730 through 1459) were re–analyzed by the IGS ACs in a consistent way using the latest
models and methodology. The reprocessed files were submitted to the data centers forarchive in a “repro1” directory structure (/gnss/products/WWWW/repro1); to maintainconsistent access, the original set of IGS products continue to be archived in the weekly
directories (/gnss/products/WWWW).
Table 3: GNSS Product Summary.
Product Type
Orbits, clocks,
ERP, positions

Number of
ACs/AACs
13+Combinations

Troposphere

Combination

Ionosphere

4+Combination

Real–time clocks

Combination

126

Volume750 Mb/week

2.5 Mb/day,
930 Mb/year
4 Mb/day,
1.5 Gb/year
5.5 Mb/week

Directory/gnss/products/WWWW(GPS, GPS+GLONASS)/glonass/products/WWWW(GLONASS only)/gnss/products/troposphere/YYYY/gnss/products/ionex/YYYY/gnss/products/rtpp/YYYY

4 System Usage

3.3 Supporting Information
Daily status files of GNSS data holdings, reflecting timeliness of the data delivered as well
as statistics on number of data points, cycle slips, and multipath, continue to be generated
by the CDDIS. By accessing these files, the user community can receive a quick look ata day’s data availability and quality by viewing a single file. The daily status files areavailable through the web at URL ftp://cddis.gsfc.nasa.gov/reports/gps/status.
The daily status files are also archived in the daily GNSS data directories. Ancillary
information to aid in the use of GNSS data and products are also accessible through the
CDDIS. Weekly and yearly summaries of IGS tracking data (daily, hourly, and high–rate)archived at the CDDIS are generated on a routine basis. These summaries are accessible
through the web at URL ftp://cddis.gsfc.nasa.gov/reports/gps. The CDDIS also
maintains an archive of and indices to IGS Mail, Report, Station, and other IGS–related
messages.

4 System Usage
Figure 1 summarizes the usage of the CDDIS for the retrieval of GNSS data and products
in 2011. This figure illustrates the number and volume of GNSS files retrieved by the user
community during 2011, categorized by type (daily, hourly, high–rate, products). Over500 million files (40 Tbytes) were transferred in 2011, with an average of over 40 million
files per month. Figure 2 illustrates the profile of users accessing the CDDIS IGS archive
during 2011. The majority of CDDIS users are from hosts in North America and Europe.

350,000,000	
  25,000	  Oceania	
  1%	
  South	
  America	
   Africa	
  
0%	
  
0%	
  

300,000,000	
  20,000	
  

Asia	
  
20%	
  

15,000	
  200,000,000	
  150,000,000	
  10,000	
  Volume	  (GBytes)	
  Number	  of	
  Files	  250,000,000	
  North	
  America	
  
52%	
  

100,000,000	
  5,000	
  50,000,000	
  

0	
  

Europe	
  
27%	
  

0	
  
Daily	
  Hourly	  High-­‐Rate	  Products	
  File	
  Type	  Files	
  Gbytes	  Figure 1: Number and volume of GNSS files
transferred from the CDDIS in
2011.

Figure 2: Geographic distribution of IGS
users of the CDDIS in 2011.

127

Noll: Crustal Dynamics Data Information System

5 Recent Developments
The CDDIS is cooperating in the development of Geodetic Seamless Archive Centers(GSAC) with colleagues at UNAVCO and SIO. The activity will provide web services tofacilitate data discovery within and across participating archives. A prototype implementation of these GSAC web services at the CDDIS is under development and should be
operational in mid–2012. In addition, the CDDIS is currently implementing modifications
to the metadata extracted from incoming data and product files pushed to its archive.
These enhancements will facilitate cross discipline data discovery by providing information about CDDIS archive holdings to other data portals such as Earth Observing System(EOS) Clearinghouse (ECHO) and integration into the Global Geodetic Observing System(GGOS) portal.

6 Publications
The CDDIS staff attended several conferences during 2011 and presented papers on or
conducted demos of their activities within the IGS, including:Noll, C., N. Pollack, P. Michael. Improvements in Space Geodesy Data Discovery
at the CDDIS. Abstract IN41B–1410 presented at 2011 Fall Meeting, AGU, San
Francisco, CA, 05–09 Dec., 2011
Electronic versions of this poster and other publications can be accessed through the
CDDIS on–line documentation page on the web at URL http://cddis.gsfc.nasa.gov/
reports.html.

7 Future Plans
In 2011, the CDDIS staff procured new server hardware to further enhance the capabilitiesof the system and ensure a robust archive environment. The new system will be fully
redundant with the primary and secondary/failover system located in different buildingson the GSFC campus. Each system will utilize a distributed functionality (incoming,
outgoing, processing servers) and will be configured with a local backup system as well asa full backup system located in a third building at GSFC. The archive is equipped witha 32 Tbyte RAID storage system and is scaled to accommodate future growth. The newserver environment will become operational in early 2012.
The CDDIS successfully submitted a proposal to the IGS Multi–GNSS Experiment (M–GEX) call for proposals for archive and distribution of data and products. During 2012
the CDDIS will expand its data archive and distribution service to include data fromparticipating multi–GNSS receivers, products derived from the analysis of these data, and128

References
any required metadata for the experiment. The data will include newly available signals(e.g., Galileo, QZSS, and Compass). The CDDIS data ingest procedures will be modified
to accommodate these new data sets, the majority of which will be archived in RINEX
V3. This data format will require development of new software to extract metadata fromincoming data files; the software package currently used for summarization and metadata
extraction on RINEX V2 data, teqc, will not process data in RINEX V3 format.
The CDDIS is supporting the IGS Real–Time Pilot Project as a data center. During
2012, the CDDIS will implement an NTRIP Castor to transmit real–time data streams
from stations to users. CDDIS will set up a dedicated server for this task. Possible future
activities include capturing the streams for generation of 15–minute high–rate files forarchive at the CDDIS.

8 Contact Information
To obtain more information about the CDDIS IGS archive of data and products, contact:
Ms. Carey E. Noll
Manager, CDDIS
Code 690.1
NASA GSFC
Greenbelt, MD 20771

Phone:
Fax:
E–mail:WWW:(301) 614–6542(301) 614–6015
Carey.Noll@nasa.gov
http://cddis.gsfc.nasa.gov
http://cddis.nasa.gov

9 Acknowledgments
The author would once again like to thank the CDDIS contractor staff, Maurice Dube andNathan Pollack (Science Systems and Applications, Inc./SSAI), Patrick Michael (Catholic
University of America), and Lori Tyahla and Lisa Lee (Stinger Ghaffarian Technologies/SGT). The recognition and success of the CDDIS in many international programs
can be directly attributed to the continued dedicated, consistent, professional, and timely
support of its staff.

References
Noll, C. The Crustal Dynamics Data Information System: A resource to support scientificanalysis using space geodesy. Advances in Space Research, 45(12):1421–1440, ISSN
0273–1177, 2010. doi: 10.1016/j.asr.2010.01.018.

129

Noll: Crustal Dynamics Data Information System
Noll, C., Y. Bock, H. Habrich and A. Moore. Development of data infrastructure to
support scientific analysis for the International GNSS Service. Journal of Geodesy, 83(3–4):309–325, 2009 doi: 10.1007/s00190-008-0245-6.

130

Part IV

Working Groups, Pilot Projects

131

IGS Antenna Working GroupR. Schmid
Institut für Astronomische und Physikalische Geodäsie,Technische Universität München, Germany

1 Generation of the absolute phase center model igs08.atx
On 17 April 2011 (GPS week 1632), the IGS adopted an IGS–specific realization of the
ITRF2008, called IGS08, together with an updated antenna phase center model called
igs08.atx. Details can be found in the IGSMAILs 6355 and 6374.
Main reasons for the update:• scale difference of −0.94 ppb between ITRF2008 and ITRF2005 corresponding to achange of about +12.2 cm in the satellite antenna z–offsets• lack of satellite–specific z–offset estimates for all satellites launched since the releaseof igs05.atx (affected about one quarter of the GPS constellation and more or lessthe complete GLONASS constellation)• receiver antenna calibrations had not been updated since the release of igs05.atx
Main contributors:• Martin Schmitz (Geo++ GmbH): preparation of type mean robot calibrations including GLONASS–specific correction values• Paul Rebischung (IGN): investigation of the impact of receiver antenna calibration
updates on station coordinates; compilation of IGS08• Xavier Collilieux (IGN): compilation of GPS z–offset time series derived from reprocessed AC SINEX files• Rolf Dach (CODE) and Florian Dilssner (ESOC): estimation of GLONASS satellite
antenna corrections from combined GPS/GLONASS long–term solutions• Ralf Schmid (TUM): coordination, estimation of mean GPS z–offsets from IGN timeseries, compilation of final model
Major changes of igs08.atx with respect to igs05.atx:• satellite antenna z–offsets from igs08.atx are consistent with IGS08, whereas thosefrom igs05.atx were approximately consistent with IGS05

133

Schmid: Antenna Working Group• improved redundancy of satellite antenna z–offsets: GPS values contained in igs08.atx
are based on results of 5 ACs (igs05.atx: 2), GLONASS values on those of 2
(igs05.atx: 1)• preliminary block–specific z–offsets for satellites launched since the release of igs05.atx
replaced by satellite–specific estimates• z–offsets no longer trend–corrected due to improved quality of the ITRF verticalrates (ITRF2008 compared to ITRF2000)• increased maximum nadir angle for GLONASS satellite antenna phase center variations (PCVs; 15◦ instead of 14◦ )• availability of information on historical (GPS Block I and GLONASS) satellites• availability of GLONASS–specific receiver antenna corrections from robot calibrations• additional and updated robot calibrations• conversion of relative receiver antenna corrections with updated AOAD/M_T values

2 Updates and content of the antenna phase center model
In case the satellite constellation changes or new receiver antenna calibrations become
available, the absolute antenna phase center model of the IGS has to be updated. The
GPS week of the release date is coded in the model name (igs08_wwww.atx). Table 1 lists
14 updates in 2011. Further details can be found in the corresponding IGSMAILs whose
numbers are also given. Until GPS week 1631, igs05.atx was in use, on 17 April 2011, the
IGS switched to igs08.atx.
Table 2 gives an overview of the data sets contained in the IGS phase center model.
The numbers refer to igs08_1685.atx that was released in April 2012. For GPS andGLONASS, there are 68 and 81 file entries, respectively. These numbers are bigger than
the number of actual satellites, as certain satellites were assigned with different PRN codes
or almanac slots, respectively.
For Galileo, Compass and QZSS, the IGS model does not provide any information sofar. On the one hand, the system providers didn’t make official phase center offset values
available and on the other hand, there is not enough observation data to get reliable
satellite antenna offset estimates from terrestrial data. During the IGS Workshop in
Olsztyn the adoption of conventional IGS offset values will be discussed.
Apart from the satellite antennas, the IGS model also contains phase center calibration
values for 231 receiver antennas. 151 of them are certain combinations of an antenna
and a radome, whereas the remaining 80 antenna types are not covered by a radome. As
Tab. 2 shows, igs08_1685.atx contains, among others, 96 absolute robot calibrations and
90 converted field calibrations.

134

2 Updates and content of the antenna phase center model

Table 1: Updates of the phase center models igs05.atx and igs08.atx in 2011.
week

date

IGSMAILchangeigs05.atx

1617

04-JAN-11

6324

1627

15-MAR-11

6365

Added R714 (R17), R722 (R14), R727 (R03)
Decommission date: R715 (R14), R718 (R17),
R722 (R03), R727 (R04)
Corrected date: G010
Added R715 (R03)
Decommission date: R727 (R03)
igs08.atx

1629

29-MAR-11

6374

1633

28-APR-11

6396

1636

19-MAY-11—

1639

06-JUN-11

6409

1643

30-JUN-11

6418

1644

14-JUL-11

6428

1645
1648

18-JUL-11
11-AUG-11

6433
6450

1657

13-OCT-11

6474

1664

01-DEC-11

6496

1666

14-DEC-11

6506

1667

20-DEC-11

6507

first release of igs08.atx(used as of week 1632; see Sect. 1)
Added R801 (R04)
Added JAVRINGANT_DM JVDM
NAX3G+CNONE
STXS9SA7224V3.0 NONE
Added APSAPS-3
NONE
LEIGG02PLUS
NONE
LEIGS08NONE
LEIGS12NONE
TPSPG_A1+GP
NONE
Added G035 (G01)
Decommission date: G049
z-offset updated: R801
Added TRM59900.00
NONE
TRM59900.00
SCIS
Decommission date: G035 (G01)
Added ASH701946.2
SNOW
Added G063
Added G035 (G30)
Decommission date: G030
Added R715 (R14), R742 (R04), R801 (R03)
Decommission date: R715 (R03), R722 (R14),
R801 (R04)
Added R744
Decommission date: R801 (R03)
Added SEPCHOKE_MCNONE
SEPCHOKE_MC
SPKE
Added R745
Decommission date: R712
Added R746
Decommission date: R714 (R17)135Schmid: Antenna Working Group
Table 2: Number of data sets in igs08_ 1685.atx (released in April 2012).
satellite antennas
GPS
GLONASS
Galileo
Compass
QZSS
receiver antennas
ROBOT
FIELD
COPIEDCONVERTED

number68
81
0
00
number96
90
31
14

As the IGS Site Guidelines ask for elevation– and azimuth–dependent calibration values
down to 0◦ elevation, 130 different antenna types (96 ROBOT + 31 COPIED + 3 CONVERTED) are currently approved for the installation at new or upgraded IGS stations.
The remaining 101 types are no longer allowed, but their calibration values are still necessary for existing installations (see Sect. 3) as well as for reprocessing purposes.

3 Calibration status of the IGS network
Table 3 shows the percentage of IGS tracking stations with respect to certain calibration
types. For this analysis, 441 IGS stations as contained in the file logsum.txt (available
at ftp://igs.org/igscb/station/general/) on 30 May 2012 were considered. At thattime, 99 different antenna/radome combinations were in use within the IGS network. The
calibration status of these antenna types was assessed with respect to the phase centermodel igs08_1685.atx that was released in April 2012.
For three quarters of the IGS stations absolute robot calibration results are available
comprising elevation– and azimuth–dependent PCVs down to the horizon. 8% of thestations are equipped with antenna types for which purely elevation–dependent PCVs
derived from relative field calibrations have to be applied. The latter is not ideal, but also
not a dramatic problem.
Really problematic are the remaining 17% of the stations. Their antennas are either
covered by uncalibrated radomes, or there are subtypes of the antenna that are notproperly modeled so far. The latter problem is currently known for two Javad antennas (JPSREGANT_DD_E, JPSREGANT_SD_E) and could be corrected soon. Deficiencies in
the phase center modeling are especially disadvantageous at co–location sites where theabsolute antenna position is important for comparisons with local tie measurements.

136

3 Calibration status of the IGS network
Table 3: Calibration status of 441 stations in the IGS network (logsum.txt of 30 May 2012,
igs08_1685.atx).
absolute calibration(azimuthal corrections
down to 0◦ elevation)

converted field calibration(purely elevation–dependent
PCVs above 10◦ elevation)

uncalibrated radome(or unmodeled
antenna subtype)

74.6%

8.2%

17.2%

In December 2009, the percentages for the three categories shown in Tab. 3 were 62%,18% and 20%, respectively. The improvement after 2.5 years could mainly be achieved by
the switch from igs05.atx to igs08.atx (see Sect. 1). However, part of the improvement isalso due to the fact that old installations were upgraded or even decommissioned.

137

Schmid: Antenna Working Group138

Activities of the IGS Bias and Calibration
Working Group
S. Schaer
Swiss Federal Office of Topography swisstopo
Seftigenstrasse 264, CH–3084 Wabern, Switzerland
stefan.schaer@aiub.unibe.ch / stefan.schaer@swisstopo.ch

1 Introduction
The IGS Bias and Calibration Working Group (BCWG) coordinates research in the fieldof GNSS bias retrieval and monitoring. It defines rules for appropriate, consistent handling of biases which are crucial for a “model–mixed” GNSS receiver network and satellite
constellation, respectively. At present, we consider: P1−C1, P2−C2, and P1−P2 differential code biases (DCB). Potential quarter–cycle biases between different phase observables(specifically L2P and L2C) are another issue to be dealt with. In the face of GPS andGLONASS modernization programs and upcoming GNSS, like the European Galileo and
the Chinese Compass, an increasing number of types of biases is expected.
The IGS BCWG was established in 2008. More helpful information and related internet links may be found at http://igs.org/projects/bcwg/. The initial IGS BCWG
membership is given in Tab. 1.

2 Relevant Bias and Calibration Products
2.1 P1−C1 differential code biases for the GPS constellation
This is still one of our primary bias products. Corresponding P1−C1 bias values (as shownin Fig. 1) are determined as part of CODE’s IGS clock analysis. The so–called indirect
P1−C1 DCB estimation method was introduced by Schaer (2000). The initiation of a
dedicated CODE DCB data archive could be announced at the beginning of 2001 (Schaer,2001).

139

Schaer: Bias and Calibration Working Group

Table 1: IGS BCWG membership 2008.
Stefan Schaer (swisstopo/CODE, Switzerland), Chair
Mahdi Alizadeh (TU Vienna, Austria)
Shailen Desai (JPL, USA)
Brian Donahue (EMR/NRCan, Canada)Peng Fang (SIO, USA)
Yang Gao (U of Calgary, Canada)
Gerd Gendt (GFZ, Germany)
Christine Hackman (USNO, USA)
Thomas A. Herring (MIT, USA)
Robert Khachikyan (IGSCB, USA)
Kristine M. Larson (U of Colorado, USA)
Rodrigo Leandro (Trimble, Germany)
Gerard Petit (BIPM, France)
Jim Ray (NGS, USA)
Nacho Romero (ESA/ESOC, Germany)Peter Steigenberger (TU Munich/PDR, Germany)
Sonya Todorova (TU Vienna, Austria)
Ex officio:
Chair of the Clock Products WG
Chair of the Ionosphere WG
Chair of the Reprocessing WG
Chair of the GNSS WG
IGS Analysis Coordinator
IGS Network Coordinator
Representative of the BIPM

5BLOCK IIABLOCK IIR−M

BLOCK IIF

BLOCK IIR−ABLOCK IIR−B

3
2
1
0
−1
−2

G31

G29

G17

G15

G12

G07

G05

G23

G22

G19

G02

G28

G21

G20

G18

G16

G14

G13

G11

G25

G01

G32

G30

G27

G26

G10

G09

G08

G06

−4

G04

−3
G03

DCB(p1c1) in ns

4−5

Satellites
Figure 1: Monthly set of P1−C1 differential code biases for the GPS constellation, for December
2011, computed at CODE.

140

2 Relevant Bias and Calibration Products
2.1.1 CC2NONCC RINEX converter utility
The CC2NONCC RINEX converter utility was developed by Ray (2000, 2001) in order toconvert cross–correlation (CC) (or C1/P2) pseudorange data to data being consistent toP1/P2 (non–CC) data. Officially starting with data collected on 18 March 2001 (start of
GPS week 1106), the CODE P1−C1 bias values were recommended for use by all IGS ACs
and users of IGS clock products (Ray, 2001). We appreciate it very much that further
developed and regularly updated versions of the CC2NONCC RINEX converter utility
were made available by Romero (2008, 2011) from ESA/ESOC.
2.1.2 Verification of receiver tracking class
The knowledge of — to which receiver tracking class a particular receiver model may be
attributed to — is of fundamental importance for consistent P1−C1 DCB correction. A
reliable method to verify the receiver tracking class on the basis of RINEX data samples
was developed and widely tested by Schaer (2002). At present, we use to distinguishbetween three classes (for GPS): C1/X2, P1/P2, C1/P2. Receiver tables, such as that
one used for the analyses at CODE and that one dedicated to CC2NONCC, are updatedwith new receiver types (as they appear in the IGS, EUREF, and other prominent receiver
networks).

2.2 P1−P2 differential code biases for GPS and GLONASSP1−P2 DCB information, a conventional by–product of the IGS ionosphere analysis (andtherefore included in IONEX results), is compared and combined as part of routine IGS
20

BLOCK IIABLOCK IIR−M

BLOCK IIFGLONASS−M

BLOCK IIR−ABLOCK IIR−B

10
5
0
−5
−10
−15

G03
G04
G06
G08
G09
G10
G26
G27
G30
G32
G01
G25
G11
G13
G14
G16
G18
G20
G21
G28
G02
G19
G22
G23
G05
G07
G12
G15
G17
G29
G31
R01
R02
R03
R04
R05
R06
R07
R08
R09
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24

DCB(p1p2) in ns

15

−20

Satellites
Figure 2: Monthly set of P1−P2 differential code biases for the GPS and GLONASS constellation, for December 2011, computed at CODE.

141

Schaer: Bias and Calibration Working Group

DCB(p1p2) in ns

60

AOA BENCHMARK ACT
ASHTECH Z−XII3
JAVAD TRE_G3TH DELTA
JPS LEGACYNOV OEM4−G2
SEPT POLARX3ETRTPS GB−1000
TPS ODYSSEY_E
TRIMBLE 5700

AOA SNR−12 ACT
ASHTECH Z−XII3TJPS EGGDTLEICA GRX1200+GNSSNOV OEMV3TPS EGGDTTPS LEGACYTRIMBLE 4000SSE
TRIMBLE NETR5AOA SNR−8000 ACT
ASHTECH Z18
JPS EUROCARD
LEICA GRX1200GGPROROGUE SNR−8000
TPS EUROCARDTPS NET−G3A
TRIMBLE 4000SSITRIMBLE NETR8ASHTECH UZ−12
JAVAD TRE_G3T DELTA
JPS E_GGD
LEICA GRX1200PROSEPT POLARX2TPS E_GGD
TPS NETG3
TRIMBLE 4700
TRIMBLE NETR9

40
20
0
−20
−40
−60

Stations

DCB(p1p2) in ns

60

AOA BENCHMARK ACT
ASHTECH Z−XII3
JAVAD TRE_G3TH DELTA
JPS LEGACYNOV OEM4−G2
SEPT POLARX3ETRTPS GB−1000
TPS ODYSSEY_E
TRIMBLE 5700

AOA SNR−12 ACT
ASHTECH Z−XII3TJPS EGGDTLEICA GRX1200+GNSSNOV OEMV3TPS EGGDTTPS LEGACYTRIMBLE 4000SSE
TRIMBLE NETR5AOA SNR−8000 ACT
ASHTECH Z18
JPS EUROCARD
LEICA GRX1200GGPROROGUE SNR−8000
TPS EUROCARDTPS NET−G3A
TRIMBLE 4000SSITRIMBLE NETR8ASHTECH UZ−12
JAVAD TRE_G3T DELTA
JPS E_GGD
LEICA GRX1200PROSEPT POLARX2TPS E_GGD
TPS NETG3
TRIMBLE 4700
TRIMBLE NETR9

40
20
0
−20
−40
−60

Stations
Figure 3: Monthly set of P1−P2 differential code biases for the GPS (top) and GLONASS (bottom) receiver components, for December 2011, computed at CODE.

ionosphere WG activities. P1−P2 DCB results as produced by the CODE AC with respect
to GLONASS still seem to be unique within the IGS analysis community. Corresponding(ionosphere–dependent) GNSS DCB results are shown in Fig. 2 and Fig. 3.

142

2 Relevant Bias and Calibration Products

2.3 P1−C1 and P2−C2 differential code biases for GPS and GLONASS
A new tool was developed for direct GNSS DCB estimation for P1−C1 and P2−C2 values
based on RINEX data (Schaer and Dach, 2010). The main features of this tool are:• P1−C1 and P2−C2 observation differences are analyzed file by file (typically station
by station for a particular day) and stored for subsequent least–squares combination, which can be recalled for: selected receiver types, selected receiver groups, orultimately for all considered receivers/stations (overall combination).
• Sophisticated outlier detection scheme using quantities responding to the interquartile range (IQR = Q0.75 − Q0.25 ) is applied. Consequently, just one scalar quantity
has to be selected to cope with observation data with most various noise levels andcharacteristics, respectively• Least–squares combination is performed with an outlier detection scheme concerning
station–specific, or file–specific DCB determinations.
This tool has been considerably further developed to be able to cope with all possible
RINEX data scenarios, specifically with historical data, where we got confronted withnumerous problems and anomalies.
A complete GPS/GLONASS DCB reprocessing was carried out at CODE on the basisof 1990–2011 RINEX data. The outcome of this P1−C1 and P2−C2 DCB reprocessing
effort is: daily sets, a multitude of daily subsets, and in addition monthly sets. Analysis
and combination of these remarkably long time series must be seen as a medium–term(or long–term) goal. Examples for P1−C1 and P2−C2 monthly results (as computed for
December 2011) are shown in Figures 4, 5, 6. Fig. 7 includes four subfigures showing thetime evolution of the contributing number of GNSS satellites and corresponding receivercomponents for the 1990–2011 DCB reprocessing.

2.4 GLONASS ambiguity resolution and associated SD biases relevant for
GLONASS ambiguity initialization
As documented in the CODE analysis summary of GPS week 1625 (Schaer et al., 2011a),
ambiguity resolution was extended to GLONASS for three resolution strategies. CODE’s
extended GNSS ambiguity resolution scheme as performed in an operational mode may
be summarized as follows:• Up to 6000 km (3000 km in a first POD step): Melbourne–Wübbena widelane andsubsequent narrowlane ambiguity resolution (AR) are restricted to GPS only.
• Up to 2000 km: Quasi–Ionosphere–Free (QIF) L1/L2 AR for GPS and in addition
for GLONASS DD ambiguities with the same frequency channel numbers.

143

Schaer: Bias and Calibration Working Group5

BLOCK IIABLOCK IIR−M

BLOCK IIFGLONASS−M

BLOCK IIR−ABLOCK IIR−B

3
2
1
0
−1
−2
−3
−4

G03
G04
G06
G08
G09
G10
G26
G27
G30
G32
G01
G25
G11
G13
G14
G16
G18
G20
G21
G28
G02
G19
G22
G23
G05
G07
G12
G15
G17
G29
G31
R01
R02
R03
R04
R05
R06
R07
R08
R09
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24

DCB(p1c1) in ns

4−5

Satellites
BLOCK IIR−M

GLONASS−M

5

0

−5

G01
G25
G05
G07
G12
G15
G17
G29
G31
R01
R02
R03
R04
R05
R06
R07
R08
R09
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24

DCB(p2c2) in ns

BLOCK IIF

Satellites
Figure 4: Monthly set of P1−C1 (top) and P2−C2 (bottom) differential code biases for the GPS
and GLONASS constellation, for December 2011, computed at CODE.

144

2 Relevant Bias and Calibration Products

DCB(p1c1) in ns????????????????????
ASHTECH UZ−12
JAVAD TRE_G3T DELTA
JPS E_GGD
TPS EGGDTTPS LEGACYTRIMBLE NETR5

AOA BENCHMARK ACT
ASHTECH Z−XII3
JAVAD TRE_G3TH DELTA
JPS LEGACYTPS EUROCARDTPS NET−G3A
TRIMBLE NETR8AOA SNR−12 ACT
ASHTECH Z−XII3TJPS EGGDTSEPT POLARX2TPS E_GGD
TPS NETG3
TRIMBLE NETR9AOA SNR−8000 ACT
BLACKJACKJPS EUROCARDSEPT POLARX3ETRTPS GB−1000
TPS ODYSSEY_E

5
4
3
2
1
0
−1
−2
−3
−4
−5
−6
−7
−8
−9
−10

Stations

DCB(p1c1) in ns????????????????????
ASHTECH UZ−12
JAVAD TRE_G3T DELTA
JPS E_GGD
TPS EGGDTTPS LEGACYTRIMBLE NETR5

AOA BENCHMARK ACT
ASHTECH Z−XII3
JAVAD TRE_G3TH DELTA
JPS LEGACYTPS EUROCARDTPS NET−G3A
TRIMBLE NETR8AOA SNR−12 ACT
ASHTECH Z−XII3TJPS EGGDTSEPT POLARX2TPS E_GGD
TPS NETG3
TRIMBLE NETR9AOA SNR−8000 ACT
BLACKJACKJPS EUROCARDSEPT POLARX3ETRTPS GB−1000
TPS ODYSSEY_E

5
4
3
2
1
0
−1
−2
−3
−4
−5
−6
−7
−8
−9
−10

Stations
Figure 5: Monthly set of P1−C1 differential code biases for the GPS (top) and GLONASS (bottom) receiver components, for December 2011, computed at CODE.

145

Schaer: Bias and Calibration Working GroupJAVAD TRE_G3TH DELTA
TPS NETG3
TRIMBLE NETRSLEICA GRX1200+GNSS
TRIMBLE NETR5

SEPT POLARX3ETRTRIMBLE NETR8TPS NET−G3A
TRIMBLE NETR9

3

1
0
−1
−2
−3
−4
−5
−6

WTZZ
CONZ
LAMA
TORI
VALA
WTZR
HERS
CHUR
IQAL
SCH2
WHIT
BAKE
DUBO
FLIN
FRDN
GOPE
UNBT
VALD
AZGB
ETAD
ETDD
ROSA
UNB3
ZIM2
GANP
MORP
GMSD
PGC5
UCLU

DCB(p2c2) in ns

2−7

Stations
JAVAD TRE_G3TH DELTA
TPS NETG3
TRIMBLE NETRSLEICA GRX1200+GNSS
TRIMBLE NETR5

SEPT POLARX3ETRTRIMBLE NETR8TPS NET−G3A
TRIMBLE NETR9

3

1
0
−1
−2
−3
−4
GMSD

UNB3

GOPE
UNBT

SCH2
WHIT

−6

HERS

−5
WTZZ

DCB(p2c2) in ns

2−7

Stations
Figure 6: Monthly set of P2−C2 differential code biases for the GPS (top) and GLONASS (bottom) receiver components, for December 2011, computed at CODE.

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2 Relevant Bias and Calibration Products
GNSS P2−C2 DCB
Number of GNSS satellites

Number of GNSS satellites

GNSS P1−C1 DCB
35GPS
GLONASS

30
25
20
15
10
5
0
1990

1995

2000

2005

2010

2015

300
GPS
GLONASS

250
200
150
100
50
0
1990

1995

2000

2005

Time (years)

20

GPS
GLONASS

15
10
5
0
1990

1995

2000

2005

2010

2015

2010

2015

Time (years)
GNSS P2−C2 DCB
Number of GNSS stations

Number of GNSS stations

Time (years)
GNSS P1−C1 DCB

25

2010

2015

40
GPS
GLONASS
30

20

10

0
1990

1995

2000

2005

Time (years)

Figure 7: Time evolution of contributing number of GPS and GLONASS satellites (top) andcorresponding receiver components (bottom), for P1−C1 (left) and P2−C2 (right)
GNSS DCB reprocessing, carried out at CODE on the basis of 1990–2011 RINEX
data.

• Up to 200 km: Phase–based widelane AR for GPS and GLONASS, including retrieval of GLONASS SD ambiguity initialization biases; narrowlane AR for GPS
and GLONASS, considering the previously retrieved SD bias values.
• Up to 20 km: Direct L1/L2 AR for GPS and GLONASS, including retrieval of
GLONASS SD ambiguity initialization biases. Optionally, the widelane–based SD
bias retrievals could be considered as a priori bias information.
We consider the following rules essential for successful GLONASS ambiguity fixing:• GNSS ambiguity parameters are generally treated at SD level.
• GNSS ambiguities are resolved at DD level (differences of SD ambiguities).
• The SD ambiguity parameters directly respond to (always) existing SD (ambiguity
initialization) biases. Implicitly, they act as SD bias calibration parameters and thus
may absorb present SD biases in the LS parameter adjustment.
• The initial singularity concerning all involved SD ambiguity parameters has to beeliminated by imposing loose constraints on these parameters. After fixing a first
GLONASS DD ambiguity for a pair with unequal frequency channel numbers, SD
ambiguity parameters become determinable.
• There are absolutely no extra bias parameters at DD level, apart from (unresolved)
intersystem ambiguity parameters (see next item).
• GPS–GLONASS intersystem ambiguities are generally treated unresolved.
• A self–calibrating AR procedure (as used at CODE) is definitively indispensable.
• Our AR principles are also applicable to rapid static positioning using LAMBDA
methods generalized for multi–GNSS (Schaer et al., 2009).

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Schaer: Bias and Calibration Working Group
Table 2: Compilation of a long–term averaged set of GPS code biases (conforming to receiverclock synchronization) playing a decisive role for GLONASS ambiguity initialization at
SD level.
Receiver type
ASHTECH Z18
JAVAD TRE_G3TH DELTA
JPS EGGDTJPS E_GGD
JPS LEGACYLEICA GRX1200+GNSS
LEICA GRX1200GGPRONOV OEMV3SEPT POLARX3ETRTPS EGGDTTPS EUROCARDTPS E_GGD
TPS LEGACYTPS NETG3TPS ODYSSEY_E
TRIMBLE NETR5
TRIMBLE NETR8

SD bias+22.120+218.901+58.271+128.505+111.921−269.900−242.546−247.286−501.984+70.275+155.776+121.529+92.682+52.682+57.586+96.551+74.919

RMS error (ns)
2.268
0.675
0.606
0.565
0.609
0.753
0.484
0.516
0.533
0.726
0.652
0.868
0.517
0.507
0.611
0.515
0.908

Last but not least, an additionally implemented BPE processing step dedicated to (baseline–wise) verification of all fixed GNSS ambiguities for the ionosphere–free LC (and otherLCs, if indicated) turned out to be utmost valuable for detection of any anomalies, suchas unexpectedly occurring GPS quarter–cycle biases (see also Section 2.9).
Tab. 2 contains a compilation of a long–term averaged set of GPS code biases relevant
for GLONASS ambiguity initialization at SD level, namely for IGS–representative GNSS
receiver types. It should be emphasized that the determined SD biases are interpreted as
differential code biases, DCB. They are finally applied (as differential phase biases, DPB)
to SD phase measurements. That implies that this type of bias must be addressed as
differential code–phase bias (DCPB). For interpretation (and eventually the use) of thebias values given in Tab. 2, it is important to add that GPS code data is used for GNSS
receiver clock synchronization.

2.5 GLONASS−GPS station–specific intersystem translation parameters as
introduced at CODE
Since GPS week 1619, an extra set of (3+1) parameters is set up for each GLONASS
observing station to characterize• a GLONASS−GPS receiver antenna offset vector and• a GLONASS−GPS ZPD troposphere bias.
148

2 Relevant Bias and Calibration Products
Starting with GPS week 1625, these GLONASS−GPS bias parameters (4 for each GNSS
station) are determined on a weekly basis and subsequently used for generation of our daily
IGS analysis results (Schaer et al., 2011a). The most decisive analysis characteristics interms of these new extra bias parameters are:
• The datum definition used for the GLONASS−GPS receiver antenna offset vectors issimilar to that used for station coordinates: no–net translation and no–net rotation
conditions with respect to all GLONASS observing stations are imposed.
• GLONASS−GPS ZPD troposphere biases are generally treated unconstrained.
• Our weekly SINEX contribution implicitly includes these GLONASS−GPS bias parameters (4 for each GNSS station).
Fig. 8 shows the time evolution of the mean GLONASS−GPS troposphere ZPD bias as
extracted for CODE IGS weekly results (for GPS weeks 1619–1635). The so far very significant mean GLONASS−GPS troposphere bias did vanish completely in coincidence with
the IGS ANTEX model switch from IGS05 to IGS08 (stipulated to be adopted startingwith GPS week 1633). The primary reason for the clearly visible model improvement may
most likely be attributed to the update concerning antenna phase center Z–offsets for the
GLONASS constellation.
The ultimate consequences of the newly accomplished, rather trendsetting developments
on GNSS–based ITRF and thus on SINEX (potentially in addition on ANTEX) are notyet clear to us. We believe that consideration of station–specific intersystem translation
parameters for each additionally observed GNSS is a logical step and will become standard for highest–precision, “as–consistent–as–possible” multi–GNSS analysis (in particular
for consistency monitoring purposes, as demonstrated in Fig. 8). For more details, theinterested reader is referred to (Schaer and Meindl, 2011).

Figure 8: Time evolution of mean GLONASS−GPS troposphere ZPD bias as extracted for
CODE IGS weekly results, for GPS weeks 1619–1635.

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Schaer: Bias and Calibration Working Group100

ISB in ns

0

ASHTECH Z18
JPS EUROCARD
LEICA GRX1200GGPROTPS E_GGD
TPS NETG3
TRIMBLE NETR9JAVAD TRE_G3T DELTA
JPS E_GGDNOV OEMV3TPS GB−1000
TPS ODYSSEY_E

JAVAD TRE_G3TH DELTA
JPS LEGACYSEPT POLARX3ETRTPS LEGACYTRIMBLE NETR5JPS EGGDTLEICA GRX1200+GNSSTPS EGGDTTPS NET−G3A
TRIMBLE NETR8

−100
−200
−300
−400
−500

Stations
Figure 9: GLONASS−GPS intersystem clock/time biases/differences as computed for a set of
IGS stations, for 12 January 2012.

2.6 GPS−GLONASS intersystem time differences
Fig. 9 shows corresponding intersystem time/clock differences/biases as computed for aset of IGS stations. The computation was done using GPS and GLONASS broadcast
clock information. From Fig. 9, it is obvious that the size of the computed differences/biases does depend on the receiver type and, in some cases, even on the receiver firmware.
Moreover, the spread of the intersystem time differences clearly indicates that absolutedetermination of the GPS−GLONASS system time difference is impossible. Absolute
receiver calibrations would be actually desirable for this purpose.

2.7 GLONASS interfrequency code biases
For computation of precise GLONASS clock offsets, it is common to set up differential code
bias (DCB) parameters for each GLONASS satellite (or alternatively for each frequency
channel number) and for each involved GLONASS tracking station (Dach et al., 2010).
The same is by the way also valid for GLONASS–based PPP (at least when relying on
GLONASS code data). It is intended to make detailed comparisons of AC–specific sets of
GLONASS interfrequency code biases for the first time for the planned IGS Workshop on
GNSS Biases 2012 (see Section 4).

2.8 GLONASS−GPS intersystem phase bias variability
The stability of phase biases among all considered GNSS at a level of the phase measurement noise would be a basic requirement for our multi–GNSS analysis. However,150

3 Redesign of GNSS DCB combination/estimation processing environment at CODE
we could show that the GLONASS−GPS intersystem phase bias variability may reach,in extreme cases, a level which should no longer remain neglected (Schaer et al., 2007).
Further investigations are needed in this area in order to exploit the full potential of“as–consistent–as–possible” multi–GNSS analysis.

2.9 GPS quarter–cycle phase bias issue
L2(C) phases (for GPS Block IIR–M/IIF satellites) may reveal quarter–cycle biases withrespect to L2(P) (for previous, “non–C2” GPS generations), particularly in case of: Javad,
Leica, NovAtel. GPS quarter–cycle phase biases are a serious issue, even when analyzing
latest IGS data samples (Schaer and Meindl, 2012). It is quite evident that the listof potentially affected receivers has to be completed. A consequence of this (in fact
RINEX2–inflicted) bias issue is that ambiguity resolution may suffer considerably as soon
as a receiver type belonging to the affected receiver group becomes involved. To be more
specific, ambiguity differences between modernized GPS satellites (Block IIR–M and IIF)
and older generations may be fixed occasionally to constants biased by ±0.25 cycle. It
should be mentioned that the CODE AC is in a good position for detection of any kind of
potential GNSS phase biases due to the (intended) circumstance that a significant numberof shortest (≤ 20 km) baselines is considered for direct ambiguity resolution of the original
GPS/GLONASS L1/L2 phase integers (see also Section 2.4).

3 Redesign of GNSS DCB combination/estimation
processing environment at CODE
The outdated (reliably working) processing environment used at CODE for• regular GNSS DCB combination,• ionosphere prediction and monitoring,• generation of Klobuchar–style ionosphere coefficients (on the basis of various CODEIONEX products),• associated visualization, web update, and many other DCB/ionosphere related tasks
has been completely revised and fully redesigned in 2011 (and 2012). A coordinatedeffort was made in 2011 to upgrade all involved extra Bernese GNSS Software modules
from development version 4.3 to 5.1. Whenever possible, the upgraded modules were
further generalized (also in terms of multi–GNSS). A dedicated BPE (Bernese Processing
Engine) procedure was developed, also including the recently developed direct GNSS DCB
estimation capabilities as introduced in Section 2.3. Completion of this redesign work may
be expected in 2012.

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Schaer: Bias and Calibration Working Group

4 IGS Workshop on GNSS Biases 2012
A Workshop on GNSS Biases will be organized by the Astronomical Institute of the University of Bern (AIUB) on behalf of the IGS Bias and Calibration WG:
Date: 18–19 January 2012
Place: University of Bern, Hochschulstrasse 4, CH–3012 Bern
This workshop is foreseen as a roundtable conference with a limited number of participants(max. 35). We will consider this mostly an invitation–only meeting. Current issues (concerning GPS and GLONASS) as well as issues related to new signals and further GNSS
shall be discussed. This shall become a forum for the IGS ACs/BCWG and representatives
from relevant GNSS receiver manufacturers and RTCM/RINEX side.
Detailed information is available at: http://www.biasws2012.unibe.ch
Note that an RTCM SC–104 Meeting is scheduled for 16–17 January 2012 at the same
location.

5 IGS–BCWG Mailing List
The IGS–BCWG (Bias and Calibration Working Group) mailing list has been created in2011 (see http://igscb.jpl.nasa.gov/mailman/listinfo).
It is our intention to open the newly created IGS–BCWG discussion forum to a broader focused group of experts with experience and strong interests (including the RTCM/RINEX
community and key experts from GNSS receiver manufacturers). Therefore, we proposethat all interested persons (interested in the planned bias workshop 2012, or just interested
in tracking the discussions) shall register to:
http://igscb.jpl.nasa.gov/mailman/listinfo/igs-bcwg
Additional notes:• BCWG members were subscribed automatically. The initial group member list did
include 29 addresses.
• Membership requires approval from the moderator.
• Archiving is enabled. Only list members may view the archive.
• The e–mail address to the group is: igs-bcwg@igscb.jpl.nasa.gov

References
Dach, R., S. Schaer, M. Meindl, S. Lutz, E. Orliac, and H. Bock (2010). Biases in GNSS
Data Processing. AGU Fall Meeting, San Francisco, USA, December 13–17, 2010.

152

References
Dach, R., M. Meindl, S. Schaer, S. Lutz, R. Schmid, and G. Beutler (2011). Systemdependence of GNSS receiver antenna calibrations. EGU General Assembly, Vienna,
Austria, April 3-8, 2011.
Ray, J. (2000). IGS MAIL #2744: New pseudorange bias convention. http://igscb.jpl.
nasa.gov/pipermail/igsmail/2000/002818.html.
Ray, J. (2001). IGSMAIL #3220: Updated <P1-C1> biases and cc2noncc. http://igscb.
jpl.nasa.gov/pipermail/igsmail/2001/003294.html.
Romero, I. (2008). IGSMAIL #5778: A new CC2NONCC. http://igscb.jpl.nasa.
gov/pipermail/igsmail/2008/005849.html.
Romero, I. (2011). IGSMAIL #6398: CC2NONCC important software update. http://igscb.jpl.nasa.gov/pipermail/igsmail/2011/006390.html.
Schaer, S. (2000). IGSMAIL #2827: Monitoring (P1-C1) code biases. http://igscb.
jpl.nasa.gov/pipermail/igsmail/2000/002901.html.
Schaer, S. (2001). IGSMAIL #3212: CODE DCB data archive initiated. http://igscb.
jpl.nasa.gov/pipermail/igsmail/2001/003286.html.
Schaer, S. (2002). IGSMAIL #3887: TRIMBLE 4700. http://igscb.jpl.nasa.gov/
pipermail/igsmail/2002/003961.html.
Schaer, S and M. Meindl. (2012) IGSMAIL #6583: GPS quarter-cycle biases. http://igscb.jpl.nasa.gov/pipermail/igsmail/2012/006575.html.
Schaer, S., E. Brockmann, and D. Ineichen (2007). Inclusion of GLONASS for EPN
Analysis at CODE/swisstopo. In: Torres, J.A. and H. Hornik (Eds): Subcommission
for the European Reference Frame (EUREF), London, 2007. EUREF Publication No. 17,
pp. 86–94.
Schaer, S. (2008). Differential code biases (DCB) in GNSS analysis. IGS Workshop, Miami
Beach, FL, USA, June 2–6, 2008.
Schaer, S, E. Brockmann, M. Meindl, and G. Beutler (2009). Rapid Static Positioning
Using GPS and GLONASS. In: Ihde, J. and H. Hornik (Eds): Subcommission for theEuropean Reference Frame (EUREF), Firenze, 2009.
Schaer, S. and R. Dach (2010). Biases in GNSS Analysis. IGS Workshop, Newcastle upon
Tyne, England, 28 June – 2 July, 2010.
Schaer, S. et al. (2011a). IGSREPORT #19560: Wk 1625 COD Analysis Report. http://igscb.jpl.nasa.gov/pipermail/igsreport/2011-March/019573.html.
Schaer, S. and M. Meindl (2011). Consideration of Station-Specific Intersystem Translation
Parameters at CODE. EUREF Symposium, Chisinau, May 25–28, 2011.

153

Schaer: Bias and Calibration Working GroupSchaer, S., H. Bock, R. Dach, S. Lutz, M. Meindl, E. Orliac, D. Thaller (2011b). Contributions to the IGS, chapter Commission 1:Reference Frames, pages 1–2. Swiss National
Report on the Geodetic Activities in the years 2007–2011 to the XXV General Assembly of the IUGG, Melbourne, Australia, 28 June — 7 July 2011. Swiss Geodetic
Commission, 2011.
Schaer, S. and R. Dach (2011). GNSS Data Calibration Parameters, chapter Commission
1:Reference Frames, pages 7–9. Swiss National Report on the Geodetic Activities in theyears 2007–2011 to the XXV General Assembly of the IUGG, Melbourne, Australia, 28
June — 7 July 2011. Swiss Geodetic Commission, 2011.
Schaer, S. and M. Meindl (2011). Multi-GNSS Ambiguity Resolution Algorithms, chapter
Commission 4: Positioning and Applications, pages 95–96. Swiss National Report on the
Geodetic Activities in the years 2007–2011 to the XXV General Assembly of the IUGG,
Melbourne, Australia, 28 June — 7 July 2011. Swiss Geodetic Commission, 2011.

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IGS Data Center Working Group 2011
C. NollNASA Goddard Space Flight Center, Code 690.1
Greenbelt, MD 20771 USA
Carey.Noll@nasa.gov

1 Introduction
The IGS Data Center Working Group (DCWG) was established in 2002. The DCWG
tackles many of the problems facing the IGS data centers as well as develops new ideas
to aid users both internal and external to the IGS. The direction of the IGS has changed
since its start in 1992 and many new working groups, projects, data sets, and products
have been created and incorporated into the service since that time. The DCWG wasformed to revisit the requirements of data centers within the IGS and to address issues
relevant to effective operation of all IGS data centers, operational, regional, and global.

2 Recent Activities
A Data Center Working Group meeting was held during IGS 2010 Workshop. The viabilityof the group was confirmed. Recommendations where made resulting from presentations
during workshop and meeting discussion (see Future Planning below). The WG supported
the IGS Infrastructure Committee and began implementation of daily data status summary files at all GDCs. The file summarizes the daily data holdings and extracts key
metadata and data quality information from all files. Further discussions have been madeto improve and generalize software. The WG also coordinated product archival with otherdata centers, including working with the IGS ACC in the final archiving of IGS repro1
products with the IGS Global Data Centers. The WG began coordination on data center
infrastructure support for upcoming IGS M–GEX activity.

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Noll: Data Center Working Group

3 Future Plans
In 2012–2013, the DCWG will continue to work on addressing recommendations from the
IGS 2008 and 2010 Workshops. Topics the WG hopes to address follow.
Support of the IGS Infrastructure Committee: A major focus of the DCWG for the next
two years will be to support the IC in its various activities to coordinate the resolution of issues related to the IGS components. These activities will address recommendations from recent IGS Workshops including assessment and monitoring ofstation performance and data quality, generating metrics on these data.
Data center harmonization: The working group will consider methodologies for ensuring
key data sets are available at all GDCs. Following recommendations from the IGS
2010 Workshop, the WG will coordinate with GDCs to ensure all GDCs archive datafrom all IGS stations as identified on the IGS network website; ODCs push data, andany subsequent resubmissions, from their stations to ALL GDCs and ODCs issues
advisory for ALL resubmissions.
Compression: As per a recommendation from the IGS 2010 Workshop, the DCWG willdevelop a plan for the introduction of a new compression scheme into the IGS infrastructure by evaluating tests of available tools, surveying the IGS infrastructure,making a recommendation on a new IGS compression scheme, and coordinating
recommendations with the IC to develop implementation schedule.
Real–time data streams/high–rate GNSS data handling: Another recommendation fromthe 2008 IGS Workshop concerned transfer of high–rate data to data centers via traditional file transfer or through accumulation of real–time data streams. IGS data
centers must ensure that files generated from these streams are sufficiently reliable.
The DCs must also coordinate to ensure consistent copies of high–rate files arearchived. This recommendation was updated in the 2010 IGS Workshop to include
definition and development of
1. tool for comparison of RINEX files from various construction approaches,
2. minimum requirements for acceptance of an accumulated data stream of observations as a RINEX file in IGS data archives,
3. mandatory/optional observation types to be included,
4. procedures to fill the gaps in the case data streams have been interrupted.
This activity should be coordinated with the RTPP, ACs, DCs, and IC.
M–GEX: As the IGS Multi–GNSS Experiment begins, the DCWG will advise and coordinate archival of the experiment’s data from other GNSS and products derived fromthese data sets.
The DCWG will meet during the 2012 IGS Workshop in Olsztyn, Poland.

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5 Membership

4 Publications
The DCWG gave several presentations in the last two years, including:• Noll, C., M. Schmidt, H. Habrich, and B. Garayt. The Evolution of the IGS Flowof Data (and Products and Information) and Steps Ahead. IGS Analysis Workshop,
Newcastle, UK, June 2010.
• Noll, C., M. Schmidt, B. Michael, Y. Lu. Updates to the IGS Data Center Infrastructure. Abstract G11B–0642 presented at 2010 Fall Meeting, AGU, San Francisco,Calif., 13–17 Dec., 2010.
Electronic versions of this poster and other publications can be accessed through the
CDDIS on–line documentation page on the web at URL http://cddis.gsfc.nasa.gov/
reports.html.

5 Membership• Carey Noll (NASA GSFC/USA), Chair• Yehuda Bock (SIO/USA)• Ludwig Combrinck (HRAO/South Africa)• Bruno Garayt (IGN/France)• Paul Jamason (SIO/USA)• Heinz Habrich (BKG/Germany)• Michael Moore (GA/Australia) (tbc)• Ruth Neilan (JPL/USA), ex–officio• Markus Ramatschi (GFZ/Germany)• Jim Ray (NOAA/USA), ex–officio• Nacho Romero (ESA/Germany)• Mike Schmidt (NRCan/Canada)• Giovanni Sella (NOAA/USA)• Grigory Steblov (RDAAC/Russia)• Dave Stowers (JPL/USA)

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Noll: Data Center Working Group

158

IGS GNSS Working GroupR. WeberInstitute of Geodesy and Geophysics,
University of Technology Vienna, Austria
Gusshaussstrasse 27–29, A–1040 Vienna;
E–mail: robert.weber@tuwien.ac.at

According to the recommendations decided at the IGS Workshop 2010 in Newcastle the
IGS GNSS Working Group (WG) was refocused in 2011. The WG shall concentrate on
recent developments of GPS, GLONASS, Galileo, Compass/Beidou, QZSS (and to theextent necessary also overlay systems) and establish on the one hand suitable interfaces
to organizations operating GNSS–systems or multi–GNSS networks and to receiver manufacturers on the other. In this context the WG shall set up and conduct a multi–GNSS
tracking experiment (MGEX) based on GNSS receivers capable of tracking most of the
new signals and systems.
The new directions are reflected by the WG–Charter adopted recently by the IGS Governing Board. Below an excerpt of this document is provided:
With the imminent introduction of new civilian signals in GPS, the modernization of
GLONASS as well as the development of other Global Navigation Satellite Systems like
Galileo and Compass, and further regional overlay systems the IGS is facing a changing
landscape. It is essential that the implications for the service are fully analysed and that the
new factors affecting its operations are duly taken into account in IGS strategic planning.
Even all currently active constellations comprise a gradually changing mix of satellites
transmitting the standard and the new signals. New receiver types will have to be introduced
into the network and there will be new requirements on software for handling the data in
the Analysis Centres. The long lasting IGS experience of introducing GLONASS in all
chains of observation, data transfer and analysis will assist in minimizing the impact ofthese further changes on the service operations and in integrating the new features into the
IGS infrastructure to the advantage of users of the IGS products.
Thus, in order to prepare for upcoming new signals and systems it is essential that IGS
gathers experience with tracking the new signals and systems, new receiver and antenna
types, inter system biases, and analysis of the new signals. To facilitate these studies the
WG sets up and conducts a multi–GNSS tracking experiment (MGEX) based on GNSS

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Weber: GNSS Working Group
receivers capable of tracking most of the new signals and systems, including experimental
satellites. In addition suitable interfaces to organizations already operating or planning tosetup multi–GNSS tracking networks have to be established to ensure data availability to
IGS components.

Activities in 2011
In 2011 the membership of GNSS–WG has changed to a certain extent. As of end 2011
the Working Group consisted of 15 scientists well known in the GNSS community. For a
more detailed information see http://www.igs.org/projects/gnss/index.html.
The major activity was the preparation of the Call for Participation of the IGS demonstration campaign MGEX focusing on tracking new signals and constellations by deployedmulti GNSS receivers (hard– and software receivers). The IGS MGEX is coordinated by
an Experiment Organizing Committee. This Committee is appointed by the IGS GB for
the duration of the experiment and will then be dissolved. Further activities are coordinated by the IGS GNSS Working Group. Further support is sought after from the IGS
Working Groups which are deeply involved in the exploration and use of the new signals,
e.g. the Antenna WG, the Bias and Calibration WG and the RINEX WG. Furthermore
MGEX will be supported by the IGS Infrastructure Committee.
The main purpose of IGS MGEX campaign is to conduct a global multi–GNSS signals
tracking experiment in parallel to the regular IGS operations, to focus on tracking the
newly available GNSS signals. This includes all signals from the modernized satellitesof the GPS and GLONASS systems, as well as for the first time in IGS operations, allavailable or applicable signals of the Compass/BeiDou, Galileo and QZSS systems andany space–based augmentation system (SBAS) of interest. In first instance the experiment is focused on collecting and making publicly available observation data suitable forpost–processing and engineering analysis. However, Real–Time (RT) data flow from participating individual sites or organizations contributing via tracking data exchange withthis experiment is also very welcome, and will be coordinated by the IGS RT Working
Group http://www.rtigs.net/.
The IGS M–GEX Call for Participation(CfP) has been issued end of August 2011 via
IGSMail (Hugentobler and Neilan, 2011). The campaign was also announced during the
3rd Int. Colloquium on Galileo Science Aspects in Copenhagen (Weber et al., 2011).
The CfP was seeking participation through the following components:• Multi–GNSS Observing sites• Multi–GNSS Data Centers• Multi–GNSS Experiment Analysis Centers and/or Engineering Analysis Centers• Multi–GNSS Collaborating Organisations and Networks
160

Concerning receivers only geodetic–type receivers (capable of collecting pseudorange andcarrier phase observations) should be used. Receivers should be able to track GPS
or GPS+GLONASS signals and in parallel signals of further systems such as Galileo(GIOVE/IOV), Compass/BeiDou and, if possible QZSS, on at least two frequencies. The
goal is to track as many signals as possible with a clear focus on GNSS but tracking data
can include also SBAS signals. It is essential to note that the IGS MGEX experiment isin conjunction with ongoing IGS operations and shall not disturb stable IGS stations nor
compromise any further IGS routine delivery of data and products.
Data Center support was requested from organizations with the capability to expand
their archives to include data and products from participants in this tracking campaign.
Data centers interested in handling IGS MGEX data and products were asked to operateaccording to agreed upon IGS data format standards and follow accepted file and directorynaming conventions, etc. as outlined on the IGS website. The data centers were asked toensure that the data and products related to the experiment are archived separately fromthe IGS operational data set and do not affect routine operations. The data should beavailable online within hours after reception from the observing organizations and for atleast 3 months after the experiment. Offline availability upon request should be maintained
for at least 2 years.
Concerning collaborating Organizations and Networks the IGS is interested in fostering
cooperation with international organizations that already operate, or are planning to operate multi–GNSS tracking networks in the near future. In this context, IGS MGEX isinterested in data exchange to fill gaps in site distribution and signal coverage and torealize synergies between organizations in the exploitation of the new GNSS signals andsystems.
Analysis Centers are encouraged, on a best effort basis, to use the IGS MGEX data to
determine inter–system calibration biases, to compare equipment performance and to test
and further develop processing software capable of handling multiple GNSS observation
data. Finally, the development of multi–GNSS IGS products shall be stimulated, eventually leading to a Multi–GNSS Pilot Project.
Finally this CfP will be followed (most probably in autumn 2012) by a more definitiveplan focusing on the analysis of the unique set of observations collected in the course ofthis call.
The due date of the proposals was October 30th, 2011 but accompanied with the clear
statement that institutions may propose and join at any time. Afterwards the proposals
were evaluated by the Organizing Committee until end of December. All but one proposals were accepted and the proposing organisations received individual letters covering
administrative details, e.g., about the proposed data flow but also stating remaining issuesof the individual proposal. As of Jan 2012 MGEX received proposals for• 3 RINEX Data Centers (CDDIS, IGN, BKG)
• 1 Real Time Data Center (BKG)
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Weber: GNSS Working Group• 7 Analyses Proposals (4 proposals from existing IGS AC +3 other institutions)• about 25 individual sites• 3 collaborating networks identifying altogether another 15 sites
A good mix of the most recent receiver types including also software receivers was offered.
The site distribution on the other hand was not optimal with a clustering in Europe andAsia.
The official begin of MGEX was February 1st, 2012 but only a few stations started providing data exactly that date. Most of the sites started data transmission in March andApril 2012. Further proposals also enhanced the global distribution of the sites. All active
systems including Galileo–IOV, Compass/Beidou and QZSS as well as various SBAS satellites can be tracked. Even during the first weeks of MGEX a number of issues concerning
RINEX and real–time data formats capable of handling multi–GNSS observation data
came up. First details about the Analysis of the MGEX data will be presented during theupcoming IGS Workshop in Olsztyn, Poland (July 23rd–27th ,2012). The experiment isscheduled to formally end on August 31st , 2012 but there are several plans and proposals
to continue MGEX operations after that date. Eventually the experiment will form a core
for a Multi–GNSS IGS network providing data to generate Multi–GNSS products.
In the framework of the MGEX experiment the WG plans to involve in future also receiver
manufacturers to set up a test bed for various receiver and antenna types as a prototype
receiver validation facility (see also Weber, 2012).
In 2012 the IGS GNSS WG plans to prepare a white paper on the strategy for IGS
participation in the mid– and longer term exploitation of the next generation of GNSS

Figure 1: MGEX campaign — map of proposed sites as of March 2012162

References(facilitate transition of MGEX–network to regular IGS network).
Aside of MGEX, the members of the WG have contributed in 2011 to the preparation ofa document listing the required satellite pre–launch calibration information relevant for
IGS data processing.

References
Hugentobler, U. and R. Neilan. IGS Multi–GNSS Global Experiment, Call for Participation. [IGSMAIL #6459], 2011.
Hugentobler, U. New Satellite Systems and New Signals. Presentation at GNSS–R Workshop, Shanghai Astronomical Observatory, August 2011.
Weber, R., U. Hugentobler, and R. Neilan. IGS MGEX — The IGS Multi–GNSS Global
Experiment. Proceedings of the 3rd International Colloquium, Scientific and Fundamental Aspects of the Galileo Program, 30.8.–2.9.2011, Copenhagen, 2011.
Weber, R. IGS MGEX — The IGS Multi–GNSS Global Experiment Proceedings ofthe Workshop on GNSS Biases 19.01.2012 , Bern, Switzerland, 2012. http://www.
biasws2012.unibe.ch/ .

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Weber: GNSS Working Group

164

IGS Ionosphere Working Group
Technical Report 2011
A. Krankowski
University of Warmia and Mazury in Olsztyn, Poland

1 General goals

The Ionosphere Working group started the routine generation of the combine Ionosphere
Vertical Total Electron Content (TEC) maps in June 1998. This has been the main activity
so far performed by the four IGS Ionosphere Associate Analysis Centers (IAACs):• CODE: Center for Orbit Determination in Europe, Astronomical Institute, University of Bern, Switzerland,• ESOC: European Space Operations Center of ESA, Darmstadt, Germany,• JPL: Jet Propulsion Laboratory, Pasadena, California, U.S.A., and• UPC: Technical University of Catalonia, Barcelona, Spain.
Independent computation of rapid and final VTEC maps is used by the each analysis
centers: Each IAACs compute the rapid and final TEC maps independently and withdifferent approaches including the additional usage of GLONASS data in the case of
CODE.

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Krankowski: Ionosphere Working Group

2 Membership
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.

Dieter Bilitza
Ljiljana R. Cander
M. Codrescu
Anthea Coster
Patricia H. Doherty
John Dow
Joachim Feltens
Mariusz Figurski
Alberto Garcia–Rigo
Manuel Hernandez–Pajares
Pierre Heroux
Norbert Jakowski
Attila Komjathy
Andrzej Krankowski
Richard B. Langley
Reinhard Leitinger
Maria Lorenzo
A. Moore
Raul Orus
Michiel Otten
Ola Ovstedal
Ignacio Romero
Jaime Fernandez Sanchez
Schaer Stefan
Javier Tegedor
Rene Warnant
Robert Weber
Pawel Wielgosz
Brian Wilson
Michael Schmidt
Mahdiă Alizadeh

GSFC/NASA
RAL
SEC
MIT
BC
ESA/ESOC
ESA/ESOC
MUT
UPC
UPC
NRCAN
DLR
JPL
UWM
UNB
TU Graz
ESA/ESOCJPL
UPC
ESA/ESOC
UMB
ESA/ESOC
ESA/ESOC
CODE
ESA/ESOCROB
TU Wien
UWM
JPL
DGFI
TU Vienna

3 Products
1. final GIM(please note that GIMs also include GPS and GLONASS stations’ and satellites’
DCBs)• combination of CODE, ESA, JPL and UPC iono products conducted by UWM• temporal and spatial resolution — at 2 hours × 5◦ × 2.5◦ (UTxLon.xLat.),• availability with a latency of 11 days
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5 Key challenges
2. rapid GIM• combination of CODE, ESA, JPL and UPC iono products conducted by UWM• temporal and spatial resolution — at 2 hours × 5◦ × 2.5◦ (UTxLon.xLat.),• availability with a latency of less than 24 hours
3. predicted GIM for 1 and 2 days ahead (pilot product)• combination of ESA and UPC iono products conducted by ESA• temporal and spatial resolution — at 2 hours × 5◦ × 2.5◦ (UTxLon.xLat.),

4 Key accomplishments• IGS Global ionosphere predicted products for 1 and 2 days ahead (pilot product).
This new IGS products are currently based on predicted ionosphere maps preparedby UPC and ESA.
• IGS Global ionosphere maps with 1 hour and 15 min. time resolution (pilot products). This new IGS products are currently based on ionosphere maps prepared by
UPC and ESA.
• IGS Global Ionosphere Maps (GIMs) now include differential code biases (DCBs)
for GLONASS satellites.

5 Key challenges
The following goals should be achieved in the time period beginning 2011 to end 2012:• Increase of IGS GIMs temporal resolution from current 2 hours to 1 hour. UPC and
ESA conduct test on 15–minute maps, which have been tested successfully in termsof accuracy and reliability.
• Enhance time resolution of predicted GIMs from 2 hours to 1 hour or less.
• Investigate methodology required for near–real–time and real–time TEC maps.
• Investigate TEC fluctuation using ROTI.
• Further development of 3D ionosphere modeling.
• Potential use of improved of electron density retrieval techniques from GNSS LEO
data (F3/COSMIC) to be used in future new IGS ionospheric products.

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Krankowski: Ionosphere Working Group• Development, in cooperation with different involved colleagues of IGS, of a simple open source subroutine to correct higher order ionospheric correction (potential
companion of new section of IERS recommendations on higher order ionosphericterms).

References
Hernandez–Pajares M., J. M. Juan, J. Sanz, R. Orus, A. Garcia–Rigo, J. Feltens, A. Komjathy, S. C. Schaer, A. Krankowski. The IGS VTEC maps: A reliable source of ionospheric information since 1998. Journal of Geodesy, 83(3–4): 263–275, 2009. doi:
10.1007/s00190-008-0266-1.

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IGS Space Vehicle Orbit Dynamics Working Group
Report 2011
M. Ziebart
University College London

1 Introduction
The primary aim in initiating the working group was to stimulate and coordinate research
activity into orbit determination and orbit prediction of GNSS spacecraft within the IGS.
The level of research activity in the area has increased considerably as a direct result of
the formation of the group, although coordination between the different activities was not
yet fully developed. In this report several areas of activity are described and reported,
including:• The work of several key individuals• The acquisition of funding to support research• The convening of conference and workshop sessions on orbit dynamics• The development and testing of new software routines and models• Key meetings and visits to institutions• Publications• Plans for the review, consolidation and extension of the group’s work
All of the topics reported have been stimulated and/or supported (either directly or indirectly) by the working group.

2 People
Mari Seppannen, Tampere University of Technology, Finland.
Mari is working on her doctorate, and has spent a number of months at UCL working
with Ziebart’s group. She has carried out an extensive study of laser ranging validationof IGS GLONASS orbit products (publication in progress), and will carry on working on
GLONASS orbit determination and orbit prediction problems for the next two years, with

169

Ziebart: Space Vehicle Orbit Dynamics Working Groupa strong focus on surface force modelling. She will spend further term working at andwith the UCL group in the next two years.
Carlos Rodriguez–Solano, Technical University of Munich, Germany.
Carlos is working towards his PhD under the supervision of Urs Hugentobler. He hasdeveloped several approaches to modelling earth radiation pressure effects on GPS satellites (Rodriguez–Solano et al., 2012a,b,c) and has made available Fortran code to assist
groups in implementation. More recently he has developed a new model for the solar
radiation impacting GPS satellites, called adjustable box–wing model (Rodriguez–Solano
et al., 2012b). The model is based on the determination of novel empirical parameters,
like the optical properties of the satellites surfaces and the rotation lag angle of the solar
panels around their rotation axis.
Ant Sibthorpe, NASA Jet Propulsion Laboratory, Pasadena, USA.
Ant is working currently on the next generation orbit determination for the GPS operational control segment, and has published on the subject of orbit determination strategies
for the IGS orbit products.
Liz Petrie, University of Newcastle–upon–Tyne, UK.
Liz is working as a post–doctoral research associate under the direction of Matt King at
Newcastle. She has spent time at MIT and UCL working on updating GAMIT to trial
various aspects of non–conservative force modelling developed at UCL. These models havebeen implemented and tested within GAMIT and Liz has spoken at international meetings
on the initiative.
Stuart Grey, University College London, UK.
Stuart is one of two post–doctoral research associates at UCL working on space vehicle
force modelling. Stuart’s background is in aeronautical engineering, with a PhD in astrodynamics. He is working on a three year research grant (commenced October 2011) at UCL
concentrating on next generation approaches to earth radiation pressure modelling. He
has developed a number of routines to compute solar pressure/thermal re–radiation forceson GNSS–type spacecraft utilising high power computational resources (UCL CONDOR
cluster and Amazon virtual machine resources).
Shawn Allgeier, University College London, UK.
Shawn is the second of the UCL PDRAs and has just joined UCL after completing PhD
and Masters studies in astrodynamics and physics in the USA. He has spent some timeworking at the US Air Force Research Laboratory.
Florian Dilssner, European Space Operations Centre, Darmstadt, Germany.
Florian (working alongside Tim Springer) has made significant progress in studying theattitude behaviours of GPS and GLONASS satellites close to, and within, eclipse periods
using a reverse PPP technique that he has pioneered. He is the most recent addition to
the working group.

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5 Modelling and software developments

3 Funding and effort
UCL has won a substantive grant (≈£ 700 k) to work on LEO and MEO space vehicle orbit dynamics over three years employing two post–doctoral research fellows. That project
started in October 2011. University of Berne, through Rolf Dach, will start a PhD projectthat can contribute to the effort starting in late 2012. Tampere University of Technology, Finland has kindly allowed a fully funded PhD student to work on GLONASS orbit
prediction in collaboration with UCL. University of Newcastle–upon–Tyne has allocatedsome of Liz Petrie’s PDRA effort to orbit determination work with MIT in collaboration
with UCL. Finally TUM has Carlos Rodriguez–Solano’s PhD dedicated to several POD
force modelling topics, the PhD position is funded through the DFG Project “LEO orbit
modelling improvement and application for GNSS and DORIS LEO satellites” . Other
groups have contributed through existing operational personnel.

4 Conference and Workshop Sessions
Ziebart (with the assistance of Urs Hugentobler and Pascal Willis, respectively) proposedand coordinated conference sessions on space vehicle orbit dynamics at the 2011 EGU andthe 2011 AGU, as well as at the IGS workshop in Newcastle in 2010. These sessions were
all over–subscribed for oral presentations, and brought together both a stimulating set ofpresentations and a good audience at each event. This was particularly successful at theFall AGU meeting where the orbit dynamics session was given the graveyard (final) slotof the conference but still attracted a good turn out.

5 Modelling and software developments
Carlos Rodriguez–Solano has been very active, making a strong contribution. He developed, tested and distributed some routines to model earth radiation pressure forces using
a strategy that enables ease of implementation and speed of computation. The routines
are available at: http://www.iapg.bv.tum.de/albedo/.
Liz Petrie has implemented a sub–set of the UCL space vehicle force modelling routines
into GAMIT, and has carried out initial tests.
Stuart Grey has created and tested an updated version of the UCL SRP/TRR modellingcode to run on massively parallelised UCL resources and has also trialled it on Amazon virtual machine services. A programme of modelling runs is scheduled for the next
few months developing state of the art models for several GPS, GLONASS and DORIS
satellites (including Cryosat, Jason–2, SPOT–4 and SPOT–5)

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Ziebart: Space Vehicle Orbit Dynamics Working Group
Florian Dilssner has produced several excellent contributions in the understanding andmodelling of yaw behaviour of several satellite blocks (Dilssner et al., 2011).

6 Key meetings and visits to other institutions• Petrie: Research visits to UCL and MIT• European Geosciences Union conference (2011) session on orbit dynamics• American Geophysical Union conference (2011) session on orbit dynamics• Ziebart: US Air Force Space Command, Colorado Springs, USA; US Air Force Research Laboratory, Albuquerque, USA; International DORIS Service meeting, Paris,
2011

7 Future Plans
There will be a plenary session, as well as a splinter group meeting at the IGS workshop
in Poland in 2012, where the next steps can be discussed. A review will be held there
to assess whether or not the group needs more direction and structure to its activities.
Several initiatives (highlighted in this report) are underway, and they need to roll out
and be extended as necessary. Several new researchers are involved in the group with
substantive funding — it is anticipated that the number of tests, models, publications andgeneral developments in insight, expertise and scientific contribution is set to grow overthe next year substantially.

8 Acronyms and Abbreviations
PDRA
SRP
TRR
UCL

Post–Doctoral Research Associate
Solar Radiation Pressure
Thermal Re–radiation
University College London

Publications and References
Dilssner, F., T. Springer, G. Gienger, and J. Dow. The GLONASS–M satellite yaw–
attitude model. Advances in Space Research, 47(1): 160–171, 2011. doi: 10.1016/j.bbr.
2011.03.031.

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Publications and References
Rodriguez–Solano, C. J., U. Hugentobler, P. Steigenberger, and S. Lutz. Impact of Earthradiation pressure on GPS position estimates. Journal of Geodesy, 86(5): 309–317,
2012a. doi: 10.1007/s00190-011-0517-4.
Rodriguez–Solano, C. J., U. Hugentobler, and P. Steigenberger. Adjustable box–wingmodel for solar radiation pressure impacting GPS satellites. Advances in Space Research,
49(7): 1113–1128, 2012b. doi: 10.1016/j.bbr.2011.03.031.
Rodriguez–Solano, C. J., U. Hugentobler, and P. Steigenberger. Impact of Albedo Radiation on GPS Satellites. Geodesy for Planet Earth, S. Kenyon, M. C. Pacino and U. Marti(Eds.), Springer Berlin Heidelberg. 136: 113–119, 2012c.

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Ziebart: Space Vehicle Orbit Dynamics Working Group174

IGS Reference Frame Working Group Coordinator
Report 2011
P. Rebischung1 , B. Garayt2 , X. Collilieux1 , Z. Altamimi1
1

2

IGN, Institut National de l’Information Géographique etForestière, LAREG and GRGS
6–8 avenue Blaise Pascal, 77455 Marne–la–Vallée Cedex 2, France
E–mail: paul.rebischung@ign.fr
IGN, Institut National de l’Information Géographique etForestière, SGN and GRGS

1 Introduction
Since February 2010, the Institut Géographique National (IGN) has replaced Natural Resources Canada (NRCan) as coordinator of the IGS Reference Frame Working Group. On
the operational side, this coordination consists in combining the weekly SINEX solutions
provided by the IGS final Analysis Centers (ACs) and updating a long–term cumulative
solution each week (Kouba et al., 1998; Ferland and Piraszewski, 2009). The switch from
NRCan to IGN was the opportunity to bring some changes to the SINEX combination
strategy (Rebischung and Garayt, 2012). But the formats and contents of all products
were kept unchanged so as to ensure a smooth transition.
Besides a continuous monitoring of the SINEX combination results, the main achievementof the Reference Frame Working Group in 2011 was the publication of IGS08 (Rebischunget al., 2011), a new IGS reference frame based on ITRF2008 (Altamimi et al., 2011).
Another specific effort was made to obtain a homogeneous set of weekly solutions based on
the IGN combination strategy back to 1994 and to form a new, modernized IGS cumulative
solution. Finally, a website that promotes the SINEX combination products has started
to be developed and should be made publicly available in 2012.

2 Recent SINEX combination results
Since 2000, the IGS Reference Frame Working Group Coordinator combines the weekly
SINEX solutions provided by the IGS final ACs, which include station positions and Earth175

Rebischung et al.: Reference Frame Working Group
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were low–pass filtered with a 5 cpy cut–off frequency.)

orientation parameters (EOPs). The combination residuals reflect the level of agreementof AC solutions with each other and are thus traditionally used as precision indicators forthe combined products.
Figure 1 shows the RMS of the station position residuals of each AC from January 2010 toMarch 2012. While ACs which dominate the SINEX combinations (MIT and GFZ) haverather constant RMS over that period, significant progress can be seen for other ACs,
mainly:• for ESA and GRG, in the North component, thanks to the introduction of horizontal
tropospheric gradients on GPS weeks 1637 and 1659, respectively,• for JPL, in the East component, thanks to the fix of a bug related to ground antennaphase center corrections on GPS week 1674.
AC contributions to the SINEX combination have thus recently become more homogeneous, with RMS of station position residuals now below 2 mm in North, East and 5 mm
in Up for all ACs.
Figures 2 and 3 show the AC EOP residuals from January 2010 to March 2012. Over
this period, the internal consistency of the AC pole coordinates, pole rates and LODs
have been at the 20 − 50 µas, 100 − 200 µas/day and 10 − 15 µs RMS levels respectively.
These consistency levels are in fact stable since 2008 (Ferland and Piraszewski, 2009),
confirming that IGS final EOP errors seem to have reached an asymptotic limit probably
due to limitations in orbit modeling and subdaily EOP models (Ray and Ferland, 2009).

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2 Recent SINEX combination results

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Figure 2: AC pole coordinate residuals from January 2010 to March 2012177

Rebischung et al.: Reference Frame Working Groupxp rate residuals (mas/d)

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4 The “igb” re–combination and the new IGS cumulative solution

3 IGS08 and IGb08
On April 17, 2011, a new reference frame called IGS08 (Rebischung et al., 2011) was
adopted by the IGS and replaced IGS05 (IGS Mail #5447). IGS08 is based on an extraction of 232 stable GNSS stations from ITRF2008 (Altamimi et al., 2011). But in order tomake IGS08 consistent with the new set of antenna calibrations simultaneously adopted by
the IGS (igs08.atx, IGS Mail #6354), corrections were applied to the ITRF2008 positionsof 65 IGS08 stations. A smaller well–distributed network of 91 stations was additionallydesigned and called IGS08 core network. It is intended to reduce the “network effect” that
occurs when aligning quasi–instantaneous frames to a secular reference frame. The IGS08
core network is in particular used to align the IGS weekly combined solutions to IGS08
since its adoption.
However, many IGS08 stations have already been affected by position discontinuities thathave made them unusable as reference stations, and the geometry of the IGS08 core
network has thus seriously degraded. That is why a first update of IGS08, called IGb08, hasbeen proposed. IGb08 includes new sets of coordinates for 28 IGS08 stations having been
affected by position discontinuities and 3 new stations co–located with decommissioned
IGS08 stations (Figure 4). The adoption of IGb08, planned before the end of 2012, would
increase the number of usable core stations by a dozen (Figure 5).
In parallel to the maintenance of IGS08 and in preparation of the second IGS reprocessing
campaign, actions were taken in view of strengthening the IGS network and reference framein South America, Africa, Asia and Pacific. Concerning South America, discussions with
Laura Sanchez (DGFI/SIRGAS) and station operators led to a selection of 38 potential
IGS stations whose data have been made available to IGS ACs. ACs were encouraged toprocess these new stations, especially in the second reprocessing campaign, so that they
could become part of the next IGS reference frame.
The African Geodetic Reference Frame (AFREF) and Asia–Pacific Reference Frame (APREF)
sub–commissions have similarly been asked to propose candidate stations.

4 The “igb” re–combination and the new IGS cumulative
solution
In early 2011, new combinations of AC reprocessed SINEX solutions for weeks 0730–
1459 and of AC operational solutions for weeks 1460–1631 were performed at IGN. The
main goal of this effort was to obtain a homogeneous set of weekly combined solutions,based on the latest IGN combination strategy and covering the whole IGS time period.
The igb weekly combined solutions, available in the repro1 directories of the IGS global
data centers, show little differences with the official ig1/igs solutions, except that they
include all stations processed by the ACs (more than 900 in total). A special set of179

Rebischung et al.: Reference Frame Working Group

tixi
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Figure 4: State map of the IGS08 network on GPS week 1674. Green dots are usable IGS08
stations. Orange dots are the 31 IGS08 stations which would be recovered with the
adoption of IGb08. Black dots are unrecoverable IGS08 stations.

tixi

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Figure 5: State map of the IGS08 core network on GPS week 1674. Green dots are usable IGS08
core stations. Orange dots are those which would be recovered with the adoption ofIGb08. Black dots are unrecoverable IGS08 core stations.

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5 The SINEX combination website
weekly combined solutions aligned in orientation only to ITRF2008 was also derived andis available on request. The absence of network effect due to alignment in origin andscale makes those latter solutions more suited for studying station displacements and forresearch purposes.
The igb re–combination was also an opportunity to modernize the IGS cumulative solution. Until week 1631, the IGS cumulative solution was indeed obtained by stacking theoperational weekly combined solutions. It is now based on the longer, homogeneous igb
dataset and on the operational weekly solutions since week 1632. The new IGS cumulative
solution also benefits from a revised list of position and velocity discontinuities and fromthe addition of constraints that impose station velocities to be equal before and after aposition–only discontinuity.

5 The SINEX combination website
In order to promote the use of the IGS SINEX combination products and improve theiraccessibility, the project of developing a “showcase website” was initiated in 2011. Its mainfeatures are:• a map interface providing access to all stations processed by the IGS ACs (Figure 6),• time series visualization and manipulation tools (Figure 6),• web services that will provide access to all products of the SINEX combinations.

Figure 6: Map interface and time series visualization interface of the SINEX combination website

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Rebischung et al.: Reference Frame Working GroupThe website should be made publicly available in 2012 at: http://webigs.ign.fr.

References
Altamimi, Z., X. Collilieux and L. Métivier. ITRF2008: an improved solution of theInternational Terrestrial Reference Frame. Journal of Geodesy, 85(8):457–473, 2011.
Ferland, R. and M. Piraszewski. The IGS–combined station coordinates, earth rotation
parameters and apparent geocenter. Journal of Geodesy, 83(3–4):385–392, 2009.
Kouba, J., J. Ray, and M. M. Watkins. IGS Reference Frame Realization. IGS Analysis
Center Workshop Proceedings, Darmstadt, Germany, 139–172, 1998.
Ray, J. and R. Ferland. Status and prospects for IGS polar motion measurements. IERS
Workshop on EOP combination and prediction, Warsaw, Poland, 2009.
Rebischung, P., J. Griffiths, J. Ray, R. Schmid, X. Collilieux, and B. Garayt. IGS08: the
IGS realization of ITRF2008. GPS Solutions, published online, 2011. doi: 10.1007/
s10291-011-0248-2
Rebischung, P. and B. Garayt. Recent results from the IGS terrestrial frame combinations.
IAG Symp. 138, Springer, in press, 2012.

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Real–Time Working Group and Real–Time Pilot
Project
M. Caissy1 and L. Agrotis2
12Natural Resources Canada, Geodetic Survey Division
615 Booth Street, Ottawa, Canada K1A 0E9
Mark.Caissy@nrcan.gc.ca
European Space Operations Centre

1 Introduction
The IGS Real-Time Working Group (RTWG) was established in 2001 with the goal todesign and implement real-time infrastructure and processes for the delivery of real-timedata to analysis centres, and the dissemination of real-time products to users. In June
2007, the IGS announced the Call for Participation in the IGS Real-Time Pilot Project(RTPP) with a three-year target to accomplish its goals. In December 2010 a new consolidated charter was adopted for both the RTWG and RTPP with new goals for the period
2011-2012. These goals would demonstrate the IGS’s ability to offer real-time GNSS data
and real-time GPS orbits and clocks as part of a new IGS Real-Time Service (RTS).
Under this joint framework, the pilot project has been demonstrating existing real-time
capabilities while the working group has been focused on enhancing and extending thesecapabilities through the implementation of the recommendations from both the Miami(2008) and Newcastle (2010) workshops. A complete list of these recommendations canbe found at: http://igscb.jpl.nasa.gov/overview/pubs.html. This Technical Reportcovers the period beginning the 3rd quarter of 2010 and ending December 31st, 2011.
During this period, the RTWG and pilot project participants began to implement several
key recommendations which came out of discussions at the workshops. These included:• The decision for the IGS to join the Radio Technical Commission for Maritime
Services Special Committee 104 (RTCM-SC104).
• The need to implement a robust data distribution model to real-time analysis centres.
• The need to implement a robust real-time clock combination product.
• The need to provide quality assurance of real-time orbit and clock corrections.

183

Caissy and Agrotis: Real–Time Pilot Project2 The IGS Real-Time Network

The real-time network is fundamentally the source of the real-time GNSS data which
is needed to generate real-time GNSS products. Figure 1 illustrates the distribution ofreal-time tracking stations as of October 2011. This network contains approximately 130
globally-distributed stations maintained by a wide variety of local and regional operators.
These stations deliver one-hertz data to the real-time data centres with typical latenciesof 3 seconds or less. Global coverage is essential and the presence of redundant stations in
geographical regions enhances the reliability of data available from these regions. Station
operators are required to adhere to a minimum set of standards and are also encouraged
to adopt a number of best practices including:• Real-time data should be transmitted to a minimum of two separate real-time data
centres.
• Stations that contribute to the realisation of the IGS reference frame should be
operated in real-time in order to guarantee a reliable alignment of the real-time
products to a stable reference frame.

LYR1
HOFN NYA2 KIRU
OSL1 SPT0
REYK
SCH2
ONSA
WSRT
AV26
FFMJ ZWE2
PRDS
DR2O
DLFT
STJO
AV24
POTS
NRC1
BRUS
ALBH
WTZJ
ALGO
IENG
OBE3
HLFX
EPRT BARH
FLRS
P140
ISTA
HNPT
CEBR VILL
P015
P059
USNO NRL1
FUNC
NICO
PDEL
P066
MSSC BRMU
LPAL
MAS1
EUR2

WHIT

KOKB
MAHO

YELL

CHUR

VIKH
P780
PRMI
ISCO

IQAL

BIS2
TASH

ULAB
URUM

SUWN
LHAZ

ADH1

RECT
NKLG

SALU
CEEU
BRFT
RECF

GUUG

ADIS
NTUS

RCMN

NURK

SATO

MAL2

JOGJ
XMIS

SAVO

UFPR

ONRJ

WIND
SBOK

UCOR

MFKG

TDOU

YAR2
NNOR

ALIC

CEDU
PERT

STR1

KOUC
NRMD

AUCK

MOBS
WGTN
DUND CHTI
OUS2

RIO2
SMR5

TOW2

KARR

ULDI

SUTM SUTT
HNUS CTWN

LPGS

DARW

COCO

BRAZ
UNSA

OHI3
MAW1

DAV1

CAS1

2011 Oct 14 17:42:15

Figure 1: The IGS Real-Time Network.

184

TACC
CNMR

POVE

CONZ

WUH2

BDOS
KOUR

ISPA

TOKY

VITH

MARA

THTI
FAA1

MIZU

KIT3

4 Robust Data Distribution to Real-Time Analysis Centres

3 Radio Technical Commission for Maritime Services Special
Committee 104
Following a decision made at the Miami workshop, the IGS became a member of the Radio Technical Commission for Maritime Services Special Committee 104 (RTCM-SC104)
in 2009. In 2010 and 2011 members of the RTWG represented the IGS at six RTCM
meetings. RTWG members have been able to influence RTCM decisions pertaining to
the development and adoption of formats for real-time GNSS observation data, and orbit
and clock correction information. The working group and pilot project have adopted the
RTCM-3 format for GPS and GLONASS observation streams and the RTCM-State Space
Representation (RTCM-SSR) format for orbit and clock correction message streams. The
working group continues to influence the development of RTCM Multiple Signal Messages(MSM) modelled on the RINEX 3 data format, another Miami recommendation. The new
MSM format is expected to become an RTCM standard in 2012.
The RTWG has adopted the Network Transport of RTCM by Internet Protocol (NTRIP)
for internal operations and for the delivery of real-time products to users. The adoption of
NTRIP supports the Newcastle recommendation to promote the development and use of
freely available positioning software and standards. Real-time users can gain access to RTS
products through the use of open source software that uses RTCM standards (RTCM-3,
SSR, MSM, and NTRIP). Two examples of software that is currently available include
BKG’s NTRIP Client (BNC) and RTKLIB software, developed by T. Takasu. Both software products support a variety of GNSS positioning applications. It is predicted that in
the future GNSS receiver manufacturers will perform real-time precise point positioning(RTPPP) directly in their receivers using an NTRIP client front end and embedded algorithms that use SSR correction information to compute sub-decimetre accurate positions
in real time.

4 Robust Data Distribution to Real-Time Analysis Centres
The Newcastle workshop identified a weakness in the manner in which data was being
delivered to RTACs. In an effort to address this weakness a network topology has been
implemented by several agencies. Figure 2 illustrates the single tracking station andregional network architecture. This arrangement specifies that data streams from thetracking stations should be sent to two separate real-time data centres where they become
available to RTACs. In this architecture, analysis centres can source reference station
data from more than one data centre. This design reduces the likelihood of single pointsof failure, making the data network and delivery to RTACs more robust.

185

Caissy and Agrotis: Real–Time Pilot Project
TRACKING STATIONSREGIONAL TRACKING STATIONSREGIONAL
DATA CENTREREGIONAL
DATA CENTRE

DATA
CENTREDATA
CENTRE

USERS

AC

AC

ANALYSIS CENTRESAC CLOCK AND ORBITPRODUCTS

Figure 2: GNSS station to data centre architecture.

5 Robust Real-Time Clock Combination Product
The Newcastle workshop also identified a weakness due to a lack of redundancy in the
combination process. To address this weakness, a second combination server was installedat an independent location. Figure 3 illustrates the analysis-centre to combination-centre
to user-network architecture. As with the classical orbit and clock products, the reliabilityof real-time products is assured through the creation of a combined product that is basedon submissions from a minimum of three real-time analysis centres. Analysis centres
are encouraged to adopt the best practice of sending generated product streams to thetwo independent combination centres. To ensure the availability of products, users haveredundant data centres from which to choose real-time products.

AC

AC

AC

AC
ANALYSIS CENTRESAC CLOCK AND ORBITPRODUCTS

COMB1

COMB2

COMBINATIONCENTRESDATACENTRE-2

DATA
CENTRE-1

USERS

Figure 3: RTS GNSS product distribution architecture.

186

6 Quality Assurance of Real-Time Orbit and Clock Corrections

6 Quality Assurance of Real-Time Orbit and Clock
Corrections
Quality assurance of real-time clocks and orbits was identified at the Newcastle workshop
to be an area needing improvement. Since 2009 the quality of the individual RTAC clock
solutions has been derived using comparisons with IGS rapid clock products. Table 1 shows
snapshots of the performance of RTAC and combined products in the RTPP since 2009.
The quality of the individual RTACs and the combined products is assessed through theroot-mean-square (RMS) and standard deviation (sigma) of the difference between theindividual products and the IGS rapid clock product. The target for the pilot project was
to produce a combined clock product accurate to within 0.3 nanoseconds when comparedto IGS rapid products. This was achieved early on in the project.
The real-time analysis centre coordinator (RTACC) combination method detects and removes outliers that may be present in individual solutions. The combination is generated
by first aligning all the solutions to a reference solution by removing a common solutionspecific offset from all the satellite clocks. After alignment, clock differences between pairsof solutions are processed for outlier detection and for generation of a combination product. Satellite orbits are combined using solution averages after outlier detection. Figure 4
shows the history of the clock RMS performance of the single-epoch combination solution against the IGS “rapids” . This was the first combination product generated by the
RTPP. It started as a batch combination from daily orbit and clock file submissions by the
RTACs. Early in 2010, ESOC started providing the first real-time combination product,
generated directly by processing the real-time correction streams. The batch combination
is in blue, while the real-time combination, starting in 2010, is in red. After an initial
improvement phase, the results are stable except for occasional outliers. The outliers are
Table 1: Real-time pilot project clock product comparisons.
Analysis Centre
Comb
RTComb
BKG / CTU
CNES
DLR
ESOC
GFZ
NRC
GMV
TUW
WUH

Feb 6 2009
Clock
Clock
RMS
Sigma
(ns)
(ns)
0.22
0.22
—
—
6.72
2.97
—
—
0.38
0.10
0.42
0.38
—
—
0.67
0.62
1.67
1.66
—
—
—
—

June 8 2010
Clock
Clock
RMS
Sigma
(ns)
(ns)
0.16
0.10
0.15
0.11
0.20
0.12
—
—
0.20
0.12
0.21
0.12
—
—
0.24
0.10
0.28
0.14
0.70
0.53
—
—

June 15 2011
Clock
Clock
RMS
Sigma
(ns)
(ns)
0.14
0.07
0.18
0.08
0.30
0.07
0.30
0.03
0.25
0.12
0.17
0.12
0.33
0.06
0.23
0.07
0.34
0.10
0.73
0.53
0.57
0.07

187

Caissy and Agrotis: Real–Time Pilot Project

Clock	  CombinaAon	
  RMS	  Comparison	
  Against	
  IGS	
  Rapids	
  
1	
  
0.9	
  

Comb	
  
RTComb	
  RMS	
  Clock	
  Diﬀerence	
  (ns)	
  

0.8	
  
0.7	
  
0.6	
  
0.5	
  
0.4	
  
0.3	
  
0.2	
  
0.1	
  
0	
  
2008.0	
  2008.5	  2009.0	
  2009.5	  2010.0	
  2010.5	  2011.0	
  2011.5	  2012.0	
  2012.5	  Figure 4: Combination solution clock performance.

1	
  Daily	  RT	  Combina7on	
  Clock	
  Diﬀerences	
  from	  IGS	
  Rapids	
  (New	
  Outlier	
  Detec7on)	
  

0.9	
  

RMS	
  

0.8	
  

Sigma	
  

0.7	
  

0.6	
  

0.5	
  

0.4	
  

0.3	
  

0.2	
  

0.1	
  

0	
  
-­‐65	   -­‐60	
   -­‐55	
   -­‐50	
   -­‐45	
   -­‐40	
   -­‐35	
   -­‐30	
   -­‐25	
   -­‐20	
   -­‐15	
   -­‐10	
  

-­‐5	
  

0	
  

5	
  

10	
  

15	
  

20	
  

25	
  

30	
  

35	
  

40	
  

45	
  

50	
  

55	
  

60	
  

65	
  

70	
  

75	
  

80	
  

85	
  

Days	
  Since	
  31	
  December	
  2010	  Figure 5: RT Combination solution performance with improved outlier detection.

188

References

G25 ”event’Unhealthy sv
introduction
Outlier
Detection
AC
Problem

Figure 6: Combination solution orbit performance.

due to problems in the individual solutions, and these should be removed by a properly
executed combination methodology. Outliers in the combination towards the end of 2010
and beginning of 2011 were caused by RTCM encoding errors in some RTAC streams.
Improvements to the outlier detection algorithm were introduced in early 2011 and it
can be seen that the incidence of results with high RMS have been drastically reduced.
Most outliers are now caused by poor orbit results after satellite manoeuvres. Figure 5
illustrates the effectiveness of the outlier-detection algorithm.

7 Further Reading• http://www.rtigs.net/docs/IGS-Report-2010-RTWG-RTPP.pdf• http://www.rtigs.net/docs/IGS-Report-2011-RTWG-RTPP.pdf

References
Agrotis, L., P. Alfaro Sanz, J. Dow, R. Zandbergen, D. Svehla, and A. Ballereau. ESOC’s
RETINA System and the Generation of the IGS RT Combination. IGS Workshop,
Newcastle, June 2010.

189

Caissy and Agrotis: Real–Time Pilot Project
Caissy, M., L. Agrotis, G. Weber, M. Hernandez–Pajares, and U. Hugentobler. The International GNSS Real–Time Service. GPS World Innovation, 1June 2012.
http://www.gpsworld.com/gnss-system/augmentation-assistance/
innovation-coming-soon-13044
Caissy, M., G. Weber, L. Agrotis, G. Wübbena, and M. Hernandez–Pajares. The IGS
Real-time Pilot Project — The Development of Real–time IGS Correction Products for
Precise Point Positioning. Presented at EGU, Vienna, April 2011.
Weber, G., L. Mervart, L. Agrotis, and A. Stürze. Real–time Combination of GNSS Orbit
and Clock Correctors for Precise Point Positioning. presented at IUGG/IAG General
Assembly, Melbourne, July 2011.
Weber, G. and L. Mervart. Real–time Combination of GNSS Orbit and Clock Correction
Streams Using a Kalman Filter Approach. ION GNSS, 2010.
Weber, G., D. Dettmering, H. Gebhard, and R. Kalafus. Networked Transport of RTCM
via Internet Protocol (Ntrip), IP-Streaming for Real–Time GNSS Applications. ION
GNSS, 2005.

190

IGS RINEX Working Group Report 2011
K. MacLeod1 and L. Agrotis2
12Natural Resources Canada
E–mail: ken.macleod@nrcan.gc.ca
European Space Agency
E–mail: loukis.agrotis@esa.int

Membership:Name
A. Boriskin
A. Hauschild
A. Zinoviev
B. Lemoine
D. Stoecker
D. Kolosov
D. Kozlov
F. PacheF. Takac
G. Lu
G. WeberG. Wübbena
G. Roesler
H. J. Euler
Y. Hatanaka
H. Habrich
J. M. SleewaegenJ. Sass
K. Kaori
K. Ferguson
L. Estey
M. Schmitz
M. Kirchner
M. Miyoshi
M. Schmidt

Institution
AshtechDLR
TopconHemisphere
Alberding University
TopconAshtechLeica Geo.
Leica Geo.
TrimbleBKG
Geo++
NovatelInposition
GSI
BKG
Septentrio
Ashtech
JAXA
TrimbleUNAVCO
Geo++
Astrium
JAXA
NRCan

Country
RussiaGermany
RussiaCanadaGermany

E–mailaboriskin@ashtech.com
andre.hauschild@dlr.deazinoviev@topcon.com
blemoine@hemispheregps.com
dirk.stoecker@alberding.eu

RussiaRussiaSwitzerland
Switzerland
USA
Germany
Germany
CanadaSwitzerland
Japan
Germany
Belgium
USA
Japan
USA
USA
Germany
GermanyJapan
Canadadkolosov@topcon.com
dkozlov@ashtech.com
franck.pache@leica-geosystems.com
frank.takac@leica-geosystems.com
gang_lu@trimble.com
georg.weber@bkg.bund.degerhard.wuebbena@geopp.degreg.roesler@novatel.com
h-j.euler@inposition.ch
hata@gsi.go.jp
heinz.habrich@bkg.bund.dejm.sleewaegen@septentrio.com
jsass@ashtech.com
kawate.kaori@jaxa.com
kendall_ferguson@trimble.com
lou@unavco.org
martin.schmitz@geopp.demichael.kirchner@astrium.eads.net
miyoshi.motoyuki@jaxa.jp
mschmidt@nrcan.gc.ca

191

MacLeod and Agrotis: RINEX Working GroupName
I. Romero
O. Colombo
P. Alves
P. Kopcha
B. Renfro
R. DachS. Hilla
T. Stansell
U. Rossbach
T. Willems
T. Noack
T. Springer
T. Petersen
L. Agrotis
K. MacLeod

Institution
ESA
NASA
NovatelNGA
U of Texas
U of BernNGSStansell C
IFEN
Septentrio
DLR
ESA
TrimbleESA
NRCanCountry
EU
USA
CanadaUSA
ESA
Switzerland
USA
USA
Germany
Belgium
Germany
Germany
USA
GB
CanadaE–mailnacho@canaryadvancedsolutions.com
oscar.l.colombo@NASA.GOV
paul.alves@novatel.com
peter.d.kopcha@nga.mil
renfrob@arlut.utexas.edu
rolf.dach@aiub.unibe.chsteve.hilla@noaa.gov
tom@stansell.com
u.rossbach@ifen.com
t.willems@septentrio.com
thoralf.noack@dlr.detim.springer@esa.int
tim_petersen@trimble.com
loukis.agrotis@esa.int
ken.macleod@nrcan.gc.ca

Charterlast updated: 2011

1 Overview:
RINEX 2.1X is currently the primary archival format used within the IGS and the GNSS
industry. However, since RINEX 2.1X was designed in the mid 1990s, primarily to support
GPS, it has proved difficult to extend RINEX 2.1X to support new GNSS constellations
and signals. As a result of the shortcomings of RINEX 2.1X, RINEX 3.0X was designed toprovide generic and systematic support for: GNSS constellations, signals and observations.
Given the needs of the IGS community and the strengths of RINEX 3.0X, the IGS plans
to support RINEX 3.0X.
It is understood by the IGS that the transition from RINEX 2.1X to 3.0x, has to be done inpartnership with the GNSS community. One of the first steps in this transition occurred in2009 when the IGS joined the Radio Technical Commission for Maritime services–Special
Committee 104 (RTCM–SC104). The primary objective of joining RTCM–SC104 was tomore effectively communicate the needs of the IGS community to the GNSS industry andreceiver manufacturers in particular. Since joining RTCM–SC104 the IGS has contributed
to the development of an open, generic, high precision and multi–GNSS binary observation
format called RTCM–Multiple Signal Messages (RTCM–MSM). The RTCM–MSM format
supports the creation of fully defined, phase aligned RINEX 3.0x observations files. In
2011 the IGS and RTCM–SC104 further agreed to jointly manage development and documentation of the RINEX 3.0X format. It is believed that the synergy derived by having
RINEX within the RTCM–SC104 will help both the IGS and the GNSS industry achieve192

5 Publications/Presentations:an orderly and efficient transition to RINEX 3.0X. Furthermore, to facilitate the transition to RINEX 3.0X the IGS/RTCM–SC104 RINEX Working Group is encouraging andsupporting the development of several open source software tools that will both convert
RTCM to RINEX 2.1X and 3.0X formats and provide data quality control measures.

2 Activities in 2011:• Loukis Agrotis attended January RTCM meeting in Germany.
• Ken MacLeod attended RTCM meetings in May (St. Pete’s Beach, Florida) and
September(Portland, Oregon). RTCM–SSR message format approved.
• Contributed to the RTCM–Multiple Signal Message definition.
• Proposed additional RTCM messages to support the creation of a RINEX file froma binary station stream. Also included a change control parameter to enable/disable
real–time stream processing and trigger the automatic updating of IGS station logs.
• RINEX Working Group established. Consists of both IGS and RTCM–SC104 participants.
• Updated RINEX 3.0X to version 3.02 and added support for the QZSS Constellation• Distributed draft RINEX 3.02 document to Working Group

3 Key challenges:• Communicating the need to transition from RINEX 2.1X to 3.02
• Getting support from IGS members• Getting software developers to support RINEX 3.02
• Implementing the transition plan from RINEX 2.1x to 3.0X

4 Products:• RINEX 3.02 Documentation• Contributed to the definition of high precision RTCM–SC104: Multiple Signal Messages

5 Publications/Presentations:• Prepared RINEX 3.02 Draft• Prepared RTCM presentation, concerning proposed new messages for: station, receiver, antenna, met. sensor and met data.
• IGS Governing Board presentation (December 2011)193

MacLeod and Agrotis: RINEX Working Group6 2012–2013 Activities:• Continue to update RINEX 3.02 to meet the needs of both industry and the IGS.
• Develop a RINEX version to support experimental (QZSS: SAIF, LEX) and poorly
documented constellations and signals (Compass).
• Develop and recommend an IGS transition plan from RINEX 2.1X to 3.0X to IGS
GB.
• Develop and communicate a RINEX 3.02 implementation plan to IGS and industry
partners at the 2012 Workshop.
• Work with IGS and industry partners to encourage RINEX 3.02 support• Attend RTCM–SC104 and IGS meetings• Contribute to the definition the RTCM–Multiple Signal Message Format and other
RTCM messages that meet the needs of the IGS• Encourage the development of Open Source software that supports the RINEX 3.0X
format

7 IGS Multi–GNSS Experiment Support:• The RINEX 3.02 draft supports all the current GNSS constellations and signals thatare available to be tracked by the IGS Multi–GNSS Experiment.

8 IGS Strategic Plan Support:• The IGS/RTCM RINEX Working Group develops GNSS observation formats to
support all GNSS constellations and signals.

9 References/Links
1. RTCM–Multiple Signal Message Document: 034-2012-SC104-693.doc
2. GPS Interface Control Documents: http://www.gps.gov/technical/icwg/
3. GLONASS Interface Control Documents:
http://www.spacecorp.ru/en/directions/glonass/control_document/
4. Galileo ICD: http://ec.europa.eu/enterprise/policies/satnav/galileo/
open-service/index_en.htm
5. QZSS ICD: http://qz-vision.jaxa.jp/USE/is-qzss/index_e.html
6. Compass ICD: http://www.beidou.gov.cn/attach/2011/12/27/
201112273f3be6124f7d4c7bac428a36cc1d1363.pdf

194The Tide Gauge Benchmark Monitoring Project
T. Schöne, R. Bingley, Z. Deng, J. Griffiths, H. Habrich, M. Jia,
M. King, M. Merrifield, G. Mitchum, R. Neilan, C. Noll,
L. Sánchez, N. Teferle, D. Thaller, P. Tregoning,
P. Woodworth, G. Wöppelmann

1 Introduction
Present–day sea level rise with its potential impact on people living close to the oceans is
an important societal issue. For decades to centuries the sea level with its tides has beenmeasured using coastal tide gauges. However, these measurements only constitute a local
datum, affected not only by climate related changes but also by local land changes. Many
studies have estimated global sea level rise using selected sets of tide gauge records (mostprominent, Douglas, 1991). Throughout time the geodetic fixing of the tide gauge zerohas been improved allowing to relate the readings from different occupations to a common
local datum. However, even with a large number of well–established benchmarks the tidal
readings and derived sea level quantities remain in a local reference frame. Thus, today’s
challenges are still the establishment of a height reference for tide gauges connected to a
global long–term stable reference system (e.g., Carter et al., 1989; Carter, 1994; Blewitt etal., 2010), establishing a global vertical height datum (e.g., Ihde et al., 2007; Sánchez andBosch, 2009) and to provide correction to facilitate the distinction between the relativeand geocentric sea level changes by accounting for the vertical uplift of the station (e.g.,
Wöppelmann et al., 2007).
Space geodetic techniques are the most viable technique to establish this necessary reference for large numbers of globally distributed sites. With the advent of GPS in the late1980s the establishment of an easily to access and global stable reference system became
feasible. In 1994 the first continuous GPS stations started operation near tide gauges.
Over the years the number of co–located GPS/tide gauge has increased constantly andstudies demonstrated the potential for tide gauge fixing. A workshop held in Pasadena
in 1997 (Neilan et al., 1997) brought together the oceanographic and geodetic communityand started with the implementation of a long–term plan for the establishment of a global

195

Schöne et al.: Tide Gauge Benchmark Monitoring Project
network of GPS–equipped tide gauges. A technical committee jointly setup by the International GNSS Service (IGS, formerly International GPS Service), the Permanent Service
for Mean Sea Level (PSMSL) and GLOSS defined the technical standards for stations(Bevis et al., 2002). A GLOSS workshop (Group of Experts Meeting) in Hawaii (IOC2001) concluded the findings, and a Charter and Terms of References for a dedicated IGS
Pilot Project were drafted. The IGS formally established the Tide Gauge Benchmark
Monitoring Pilot Project (TIGA) in 2001 (adsc.gfz-potsdam.de/tiga, Schöne et al.,2009). The aim of the service was to derive geocentric coordinates and time series ofvertical motion for a large set of globally distributed tide gauges co–located with GNSS
stations in support of scientific studies.
This pilot project was successfully operated for more than nine years. Over this period
many achievements have been made; single products are now widely used in many different applications. To reflect the successful initial period, at its 37th meeting the IGS
Governing Board accepted the proposal for a transition of the TIGA Pilot Project to an
IGS Working Group. The generation of the primary product — geocentric coordinates,
velocities and time series of coordinates of the TIGA network — will become more regular. In addition, the TIGA Working Group will analyze the results of TIGA to identify
station discontinuities and to further improve the way the height component is modeled
and computed in GNSS processing.
The IGS has the experience, the infrastructure as well as a stated interest to perform amonitoring of tide gauge benchmarks with GNSS. With its global distribution, the IGS
network of stations provides a work framework for the TIGA activities. For the specificgoals of TIGA this network is further densified by inclusion of non–IGS stations collocatedwith tide gauges, which, except for the latency criteria, follow the IGS station guidelines.
The oversight of the coverage and utility to sea level studies of the network of GNSS
stations at tide gauges is provided by the GLOSS Group of Experts.
The aims of the TIGA Working Group are:
1. Compute precise station coordinates and velocities for the GNSS TG stations on aregular, but not necessarily continuous, basis. Newly available stations or publishedstation data of already existing stations will be included into the repeated reprocessing in order to process the largest possible number of stations. The combined
solution will have a maximum latency of one year after the reprocessing.
2. Global network of GNSS stations at tide gauges (Fig. 1)• Maintain and expand the global GNSS TG network• Accept varying latency in GNSS data delivery• Promote the establishment of more continuously operating GNSS stations inparticular in the southern hemisphere• Promote the establishment of links to other sites which may contribute to vertical motion determination, e.g., DORIS, SLR, VLBI, and/or absolute gravity
stations.

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Figure 1: Current TIGA Network. Only stations are accepted as TIGA where, tide gauge, GNSS
and leveling data is made public. (green triangles: TIGA Observing Stations, red stars:
pending station approval)

3. Contribute to the procedures in which IGS realizes a global reference frame in orderto improve its utility for global vertical geodesy. This may involve reprocessing asignificant subset of the (past and present) IGS global tracking data set.
GNSS and the other space geodetic techniques are only one tool for the determinationof vertical rates. Establishing ties to absolute gravity sites near tide gauges is strongly
promoted and results will be evaluated as part of the Working Group activities.

2 TIGA Data Centers
Since 2001 SONEL (www.sonel.org) acts as the primary TIGA data center (TDC); the
CDDIS acting as secondary or back–up. SONEL assembles archives and distributes GNSS
observations and metadata that can be accessed through the web–based facility, as wellas anonymous FTP server. It focuses on GNSS observations from stations at or near tidegauges, but also from the IGS core stations to support each TIGA Analysis Center (TAC)
in its processing and reference frame alignment. Nearly 700 station records, representing
about 2,100,000 daily RINEX files, are currently archived, out of which 503 station records
are (or were, if decommissioned) located at or near a tide gauge. Indeed, only 112 out of

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the above 503 stations are formally committed to TIGA. The SONEL database is being
expanded and automatic procedures are developed based on mapping and web–based tools
to fulfill the above needs. Some of these tools still necessitate refinement or tuning, forinstance to cope with the providers specific data latency in order to set accurate alerts.
Last but not least, it is worth noting the formal acknowledgement of SONEL as the GLOSS
data assembly center for GNSS stations at or near tide gauges, focusing on GLOSS needs
in addition to TIGA requirements. SONEL is encouraged to develop user–friendly web–based tools to support newcomers who are not familiar with the IGS or GNSS practices
in order to enable them to commit to TIGA more easily (e.g., DOMES numbers request,
submission of a compliant station site–log). Technical support in RINEX conversion andquality control is also important for sea level agencies that are not processing GNSS data
for their own purposes and thus may not notice when their observation files are corrupted.
In this latter respect collaboration has been established between the GNSS research groupat the Royal Observatory of Belgium and the University of La Rochelle.
The role of TIGA network coordinator (TNC) was missing during the TIGA pilot projectera (2001–2010) and only filled in 2011. It is related to the TDC activities and has been
provided by the same institution running the SONEL data center at the University of La
Rochelle. It requires monitoring and reporting on the status of the observation actually
made available in the form of daily RINEX files. The role also requires checking theavailability and consistency of the associated metadata, which are mostly condensed in
the station site–logs.

3 TIGA Analysis Groups
TIGA Analysis Center at the IAG Reference Frame Sub–Commission for
Europe (EUREF)
The EUREF solution for TIGA is a combination of up to 18 so–called Local Analysis
Center (LAC) contributions. In the first re–processing of the EUREF Permanent Network(EPN) archived observations for the period from GPS week 834 to 1408 have been analyzed. The computation of weekly station coordinate solutions was completed in 2011 andnow also the cumulative solution is finalized and is considered a regional densification of
ITRF in Europe.
The second EUREF re–processing for TIGA is in the preparation phase. According to
the specifications for TIGA Analysis Centers EUREF will apply the IGS–Repro2 analysis
options. An important difference to the first EPN re–processing is given by the extensionof the analysis of tracking stations from European to global stations. There is no intention
by EUREF to calculate satellite orbits, clocks and EOPs. It has been agreed to accept thenewest CODE orbits/clocks due to the lack of IGS products of the IGS–Repro2 solution.

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3 TIGA Analysis Groups
The majority of EUREF LACs use the Bernese GNSS Software for data analysis and for the
next TIGA re–processing campaign a new version in needed to fulfill the requirements for
TIGA analysis centers. This new version has not yet been released and also the mentioned
re–processed CODE orbits and clocks that shall be used for the re–processing are not yet
available. To date seven LACs confirmed their willingness to participate in the next TIGA
re–processing. Some of them will add global tracking stations, where others will re–process
a European network only. A preliminary solution of EPN and global stations has been
calculated by one LAC and will be presented at the IGS 2012 workshop.

TIGA Analysis Center ULR Consortium (ULR)

The ULR Consortium (ULR) is composed by the University of La Rochelle, and the national mapping agencies of Spain and France. The ULR has carried out several GPS datareanalysis campaigns with an increasing tracking network, an improving processing strategy and the best available models (Wöppelmann et al., 2007, 2009; Santamaría–Gómez
et al., 2012). The software used for the GPS data processing is the GAMIT/GLOBK
package. Currently, the ULR is processing a global network of 446 stations from which
300 are co–located with a tide gauge (see black dots in Fig. 2). The data included in the
reprocessing has been extended from the beginning of precise orbits (1994) to present.
To cope with the increased available data, the ULR computing facilities have also been
upgraded into a cluster composed by 512 processors and 1.2 TB of memory. ULR is also
involved with the reprocessing campaigns of the IGS.

Figure 2: Global GNSS network processed by ULR as a TIGA Analysis Centre

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TIGA Analysis Centre at the Deutsches Geodätisches Forschungsinstitut(DGFI)DGFI participated in the IGS TIGA Pilot Project (2001–2010) by (i) operating continuously observing GPS stations at six tide gauges, and (ii) processing a network of about
sixty GNSS sites as a TIGA Analysis Centre (Fig. 3). The processing strategy was basedon the double difference approach and included the main standards outlined by the IERS
and the IGS. The computed daily free normal equations were combined to get a loosely
constrained weekly solution for station positions, in which satellite orbits, satellite clockoffsets, and EOPs were fixed to the final weekly IGS products, while a priori positions
for all sites were constrained with ±1 m. These solutions were provided in SINEX format to the TIGA Associated Analysis Centres and to other users through the web site
adsc.gfz-potsdam.de/tiga. To guarantee homogeneously computed weekly solutions forthe generation of time series of station positions, weekly solutions from January 2000 (GPSweek 1043) to October 2006 (GPS week 1399) formerly computed with relative antennaphase centre corrections for the GPS antennae and referring to previous ITRF solutions
were reprocessed including absolute phase centre corrections and the IGS05 as reference
frame.
The loosely constrained weekly solutions generated by DGFI were further combined in
multi–year solutions including those stations operating more than two years. The latest
solution of this type (DGF09P01–TIGA) refers to the IGS05, epoch 2000.0 and provides
station positions and linear velocities for 57 GNSS sites (Fig. 3). Determination, combination, and solution of the normal equations were carried out with the Bernese GPS
Software, V. 5.0 (Dach et al., 2007). Results obtained by DGFI in the frame of TIGA processing are used to determine tide gauge motions with respect to the geocentric reference
frame (ITRS/ITRF). These motions are reduced from the tide gauge registrations and theresults are compared with the time series derived from satellite altimetry analysis. This
procedure is fundamental for the development of further studies related to the vertical
datum standardisation at regional and global levels.
Considering the new role of TIGA as an IGS Working Group and with the objective tosupport the determination of a global vertical reference frame, DGFI decided to extend
its computations to a global network including:• GNSS stations (close or) at tide gauges used for vertical datum definition;• GNSS stations on insular areas;• GNSS stations (close or) at those tide gauges with long–time registrations available
at the PSMSL (Permanent Service for Mean Sea level) or GLOSS (Global Sea Level
Observing System);• Additional GNSS stations (close or) at tide gauges to make the geographical distribution as homogeneous as possible;• IGS reference stations for datum definition purposes. In this case, the so–called
IGS08 core stations were included.

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Figure 3: Vertical velocities of the GPS network processed at DGFI within the IGS TIGA Pilot
Project between 2000 and 2010.

The processing strategy of this global network is further based on the double difference
approach using the Bernese Software V. 5.0 (Dach et al., 2007) and follows the IGS conventions and standards. The main difference with respect to the previously delivered
solutions is that daily and weekly SINEX files will include estimates for satellite orbits.
The present activities are concentrated on aligning the processing strategy to the agreements outlined during the TIGA Working Group Meeting held at GLOSS GE XII, on
November 11, 2011, in Paris, France. The reprocessing of the proposed global network
for the period covered between the GPS weeks 886 (January 1997) and 1668 (December2011) shall be ready by the end 2012.

4 TIGA Combination
TIGA Combination by Astronomical Institute of the University of Bern
(AIUB)The AIUB is one of the two TIGA Combination Centers. The Bernese GPS Software (Dachet al., 2007) in an extended version is used for the import of the SINEX files generated by

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Figure 4: Flowchart of the TIGA combination implemented at AIUB.

Figure 5: Weighted RMS of weekly station heights after removing the vertical trend. The stations are sorted according to the length of their time series (left side: 11 years; rightside: 4.5 years).

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4 TIGA Combination
the individual TIGA Analysis Centers, as well as for the combination on normal equationlevel. The flowchart of the TIGA combination is already set up and is shown in Fig. 4.
The SINEX files available from the TIGA Pilot Project have been analyzed so far. Combined weekly solutions have been generated for the time span 1998.0 – 2009.0, i.e., altogether eleven years or 574 weeks. The most important result from the TIGA analysis isthe vertical trend of each station. As a quality measure of the vertical trends we computed
the weighted RMS of the weekly time series of station heights after removing the trend
computed from an 11–year solution. The weighted RMS of the de–trended station heighttime series is shown in Fig. 5. Only those stations with a time series longer than 4.5 years
are considered as the estimation of a reliable trend is not possible with shorter time series.
We see that most of the stations are better than a few millimeters only.

TIGA Combination Center University of Luxembourg (UOL)
During 2011 the Geophysics Laboratory of the University of Luxembourg (UOL), was established as one of two IGS TIGA Combination Centers (TCC) within the TIGA Working
Group. In its proposal the UOL TCC proposed to use the Tanya combination softwaredeveloped and used by the IGS GNAAC at Newcastle University (NCL) since the late
1990s (e.g., Davies, 1997; Davies and Blewitt, 2000; Lavallée and Blewitt, 2002; Nurutdinov et al., 2004). The NCL GNAAC produces their weekly combination from the
IGS global AC contributions using a free–network approach with outlier detection and an
evolving variance co–variance component procedure (Nurutdinov, 2008). Although Tanya
serves mainly as the production software at the NCL GNAAC, it has also enabled a number of fundamental science results (e.g., Lavallée and Blewitt, 2002; Blewitt and Clarke,
2003; Lavallée et al., 2010). The latter is of particular relevance for the development andimprovement of global geophysical models required in high–precision GNSS processing.
The stochastic properties of coordinate time series have been shown to affect the uncertainties associated with the estimated parameters, most importantly the velocity estimate.
The standard method for this is based on maximum likelihood estimation (MLE), and the
CATS software (Williams, 2008) is widely used for this purpose within the IGS community.
An alternative method can be based on the use of Monte Carlo Markov Chains (MCMC),
which also simultaneously provides an uncertainty for the estimated spectral index andthe correlations between the parameters. Using MLE, these can only be obtained after
the MLE found a solution and the likelihood function was obtained. A comparison of
the results from CATS and the MCMC method will be presented at the IGS Workshop
2012.

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5 Scientific applications
The GLOSS Implementation Plan (Update 2012) gives a comprehensive overview about
the application of TIGA products, primarily estimates of vertical velocities, for different
applications. Most prominent are climate applications. To name a few, TIGA provides
important input for global sea level rise estimates (Santamaría–Gómez et al., 2012) orradar altimetry calibration (Mitchum et al., 2010). In addition, the TIGA products areworth for the establishment or maintenance of local height or depth datums (Ihde et al.,2007; Sánchez and Bosch, 2009; Wöppelmann et al., 2007), but also e.g., in the estimationof trough flow at straits or in the study of geophysical processes such as the Glacial Isostatic
Adjustment (Bouin and Wöppelmann, 2010).
Sea level is estimated to have risen globally at a rate of around 1.7 mm/year over the past
century (see Meyssignac and Cazenave, 2012, for an update). To be useful for long–term
sea level trend studies, vertical land movements should be estimated with standard errorsof one order of magnitude less. In this context, the quality of the estimated vertical GPS
velocities at tide gauges has been given considerable attention within the TIGA analysis
groups. This quality has clearly increased by applying the latest state–of–the–art models
and corrections all over the entire observation span, henceforth supporting the TIGA
rationale of regular reanalysis campaigns. For instance, Santamaría–Gómez et al. (2011)
show a significant reduced noise content in the GPS position time series compared to theprevious solution obtained by Wöppelmann et al. (2009). The nature of the noise remains,
however, mostly dominated by a flicker noise–like process. Its source appears elusive andrequires further investigation.
Despite the remarkable advances made recently in the reanalysis of GPS data, we areaiming at a level of performance where serious consideration of the terrestrial reference
frame and its long–term stability need to be addressed. The stability of the origin andscale of the frame has repeatedly been spotted as one of the main factors limiting thedetermination of accurate vertical velocities today (Blewitt et al., 2010). A terrestrialreference frame accurate and stable at the sub–millimeter per year level is required. In thisrespect, Legrand et al. (2010) have underscored the importance of global versus regional
GPS data processing. Differences up to 3 mm/year in the vertical velocities were foundthat strongly affect the geophysical inferences. In addition, Collilieux and Wöppelmann(2011) have investigated how the errors in the rates of the reference frame scale and origin
propagate into the sea level change estimates. They conclude with an uncertainty of
0.7 mm/year in the estimates of global sea level change using tide gauges and GPS datain the ITRF2005, likely reduced to 0.5 mm/year with the ITRF2008 (updated study).

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5 Scientific applications

Contribution of the BLT AC
F. N. Teferle1 , R. M. Bingley2 , A. Sowter3 , D. Hansen2 , L. Adamska3 , S. D. P. Williams412
3
4Geophysics Laboratory, University of Luxembourg,
British Isles continuous GNSS Facility (BIGF), University of Nottingham,
Nottingham Geospatial Institute (formerly Institute of Engineering
Surveying and Space Geodesy), University of Nottingham,
National Oceanography Centre, Liverpool

During 2011 the consortium consisting of the NERC British Isles continuous GNSS Facility (BIGF), hosted by the Nottingham Geospatial Institute (NGI) (formerly Institute ofEngineering Surveying and Space Geodesy), University of Nottingham and the Geophysics
Laboratory (GL), University of Luxembourg, proposed to become the BIGF–Universityof Luxembourg TIGA (BLT) Analysis Center. Together both institutions have a history of working in the field of monitoring vertical land motions at tide gauge sites in the
United Kingdom using a combination of GPS, absolute gravity and persistent scatterer
interferometry.
Persistent scatterer interferometry @ TG in the United Kingdom As part of a Natural
Environment Research Council SOFI funded project the use of Persistent Scatterer Interferometry (PSI) using ERS1/2 and ENVISAT data was investigated at four TG sites(North Shields, Liverpool, Sheerness and Newlyn) in the United Kingdom. PSI is a powerful technique for measurement and monitoring of vertical land movements (VLM) by
the analysis of the time series of especially selected pixels in satellite imaging radar data.
Contrary to other geodetic techniques, such as precise leveling and/or continuous GPS,
which are used at tide gauge (TG) sites to monitor their stability, PSI is capable of providing estimates over a wide spatial extent. Over the past years, PSI has been successfully
applied to the monitoring of urban and rural areas, as well as volcanoes and land slides,
providing millimeter–level accuracy.
The application of PSI to coastal areas and to monitoring TG sites has not been wellinvestigated. Furthermore, this application seems not as straightforward as it maybe issuggested from the technique’s other successes. For example, the levels of urbanization
and/or vegetation at TG sites, affects the ability of different algorithms to identify thescatterers from the stack of radar images. Ocean tide loading (OTL), a fairly well–known
process and modeled effect in GPS analyses, has so far largely been ignored in PSI, but
has been reported to introduce significant displacement gradients of more than 3 cm per
100 km. Fig. 6 and Fig. 7 show the regional and local results for North Shields using
ENVISAT ASAR data over the period from 2003 to 2008.
We conclude that PSI for sea level studies has two main applications: regional and local.
For regional applications, PSI can provide maps of relative changes in land level over alarge coastal area. This application is clearly achievable using past satellite missions (ERS205

Schöne et al.: Tide Gauge Benchmark Monitoring Project

Figure 6: ENVISAT ASAR result for North Shields (2003–2008). TG site with GPS station are
depicted as pink dot. Clearly visible are the various areas of relative land uplift andsubsidence with respect to the reference scatterer (not shown). The VLM in the region
around the TG are shown to be consistently between −2 and +2 mm/year (yellow toturquoise).

Figure 7: Persistent scatterer points in the areas around the TG (left) and the nearby Lighthouse(right) where the TG benchmarks are located. The PS points indicate that both areas
are stable with respect to each other.

206

Referencesand ENVISAT) and future satellite missions (Sentinel–1), but is reliant on having archived
and new data available for a particular site. For local applications, PSI can complement
the leveling of benchmark networks. This application is more difficult when using pastsatellite missions (e.g., ERS and ENVISAT) and future satellite missions (e.g., Sentinel–1), as it is both reliant on having archived and new data available for a particular site
but also reliant on obtaining PS points on the structure that supports the tide gauge, e.g.
we have had success at the ‘quays’ in Liverpool and North Shields but not on the ‘pier’at Newlyn or the ‘jetty’ at Sheerness. This application should be more achievable withhigh–resolution SAR satellites, but this raises the question of data availability for such
scientific applications.

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TIGA Working Group Members• Tilo Schöne (Deutsches GeoForschungsZentrum (GFZ), Germany) (Chair of TIGA–
PP)• Ruth Neilan, IGS Central Bureau, Director (ex officio)• Philip Woodworth (PSMSL, UK)• Gary Mitchum (University of South Florida, USA)
• Mark Merrifield (UHSLC, GLOSS, USA)
• Paul Tregoning (Australian National University, Australia)• Heinz Habrich (Bundesamt für Kartographie und Geodäsie, Germany (Analysis Coordinator of EUREF Permanent Network)), [TAC]209

Schöne et al.: Tide Gauge Benchmark Monitoring Project• Laura Sánchez (Deutsches Geodätisches Forschungsinstitut, Germany) [TAC]• Guy Wöppelmann (University La Rochelle, France) [TAC, TNC, TDC]
• Zhiguo Deng (Deutsches GeoForschungsZentrum (GFZ), Germany) [TAC]• Minghai Jia (GEOSCIENCE Australia, Australia)• Matt King (University of Newcastle, UK)• Daniela Thaller (University of Bern, Switzerland), [TCC]• F. Norman Teferle (Geophysics Laboratory, University of Luxembourg) [TCC, TAC]
• Richard M. Bingley (British Isles continuous GNSS Facility (BIGF), University of
Nottingham) [TAC]• Carey Noll (CDDIS, Goddard Space Flight Center, NASA) [TDC]• Jake Griffiths, IGS Analysis Center Coordinator (ex officio)

Former members (till end of 2011):• Sergei Rudenko (Deutsches GeoForschungsZentrum (GFZ), Germany)• Jim Ray, past IGS Analysis Center Coordinator

The TIGA Technical Report was compiled by the TIGA Working Group members. Specificindividual contributions are marked.

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IGS Troposphere Working Group 2011
C. Hackman and S. Byram
United States Naval Observatory
3450 Massachusetts Avenue Northwest
Washington DC 20392 USA
e–mail: christine.hackman@usno.navy.mil
phone: 202 762 1428

1 Introduction
The IGS Troposphere Working Group (IGSTWG) was founded in 1998. In 2011, chairmanship of the WG as well as responsibility for producing IGS Final Troposphere Estimates(IGSFTE) was transferred from the Jet Propulsion Laboratory (JPL, where Dr. Yoaz
Bar–Sever had chaired the IGSTWG) to the United States Naval Observatory (USNO).
Dr. Christine Hackman now chairs the IGSTWG. Dr. Sharyl Byram oversees productionof the IGSFTEs. Both are part of the GPS Analysis Division (GPSAD) in the Earth
Orientation Department at USNO. GPSAD also hosts the USNO IGS Analysis Center.
The IGSTWG comprises approximately 40 actively–confirmed members (cf. Appendix A).
A revised charter approved by the IGS Governing Board (GB) at the close of 2011 is shownin Appendix B.
Products : At present, the IGS (via USNO) produces final troposphere estimates only,
consisting of total zenith delay (ZPD), N gradient and E gradient spaced at five minuteintervals. These are generated for the 300+ stations of the IGS network with three
weeks latency and can be downloaded from ftp://cddis.gsfc.nasa.gov/gps/products/
troposphere/zpd.

2 Activities/Milestones 2011
The first major 2011 task was to transfer generation of IGSFTEs from JPL to USNO.
USNO did not have confirmation from IGS that it would be assuming its IGS troposphereroles until early Spring 2011; however, USNO promised the IGS Governing Board at the211

Hackman and Byram: Troposphere working group

Figure 1: Comparison of USNO test troposphere solutions to existing IGS Final Troposphereestimates, in preparation for operational transition to USNO. ZPD = total zenith
troposphere delay. Days of year 50–74 (28 Feb—14 Mar) 2011. From Byram at al.
(2011).

Spring 2011 Meeting that it could assume computation duties in July 2011. This, in fact,
came to pass, due primarily to the efforts of Dr. Byram (with IT assistance from USNO
GPSAD UTGPS manager Mr. Jeffrey Tracey).
Having set up the troposphere estimation routines but prior to the JPL–USNO transfer,
Dr. Byram compared several weeks of USNO troposphere estimates for 18 IGS stations
to IGSFTEs computed by then–chair JPL. The USNO estimates agreed with existing
IGSFTEs with RMSs of 2.95 mm (total vertical zenith delay) and 0.42 mm (both northand east components). Drs. Yoaz Bar–Sever and Urs Hugentobler (IGS GB chair) reviewed
the results and agreed that the processing transfer could go forward.
Dr. Byram presented details of her comparison at the ION GNSS 2011 meeting (Section 3/Fig. 1).
The second major 2011 task, performed by Dr. Hackman, was to re–organize the IGSTWG.
Dr. Hackman confirmed the continued interest of existing members and recruited new ones,2125 Plans for 2012
re–drafted the charter and created initial action plans. She presented progress reports to
the IGS GB at the Spring and Fall 2011 meetings. Mr. Robert Kachikyan, JPL, assisted
by setting up an email server for the group.

3 Publications
Byram, S., C. Hackman, and J. Tracey. Computation of a High–Precision GPS–Based
Troposphere Product by the USNO. Proc. ION GNSS 2011, 572–578, 2011.

4 Products, 2011
USNO uses Bernese GPS Software (Dach et al., 2007) for producing troposphere estimates
whereas the previous producers, JPL, used GPS Inferred Positioning System (GIPSY;
Webb and Zumberge, 1997). USNO’s first priority in assuming troposphere–production
duties was to reproduce existing estimates created by JPL, optimizing continuity in the
troposphere–delay series over time. As mentioned previously and shown in Fig. 1, thiswas achieved at millimeter level.
In 2011, JPL produced the IGSFTEs for dates 1 Jan–16 Apr. USNO produced estimatesfrom 17 Apr–31 Dec, contributing 82,000+ 24 h files to the IGS.

5 Plans for 2012
Working group: Dr. Hackman circulated a survey to IGSTWG members in Jan 2012
designed to ascertain what direction they thought the IGSTWG ought to take in terms ofresearch, product quality and new products. The results of this will be discussed and anaction plan drafted at the IGSTWG splinter meeting at the IGS 2012 Workshop (Olszytn,
Poland).
The IGSTWG will be quite active at the IGS 2012 Workshop, hosting an oral plenary
troposphere session, a troposphere poster session, an IGSTWG splinter meeting, and with
Dr. Byram presenting a poster on IGSFTE generation. A splinter meeting is planned forthe 2012 Fall AGU meeting as well.
Dr. Byram and the IGSTWG plan to participate in IGS Reprocessing Campaign 2 (“Repro 2” ). The a priori vision is to produce Repro 2 troposphere estimates with a PPP(Zumberge et al., 1997) technique, as is done now, using Repro 2 orbits, clocks and earth–rotation–parameter estimates.

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Hackman and Byram: Troposphere working group
An on–going comparison between IGSFTEs and troposphere estimates produced by (a)other IGS ACs or (b) other techniques might provide useful information. However, USNO
may not have resources to support this, and it is only worth doing if someone is committed
to reviewing comparison data. This matter will remain under consideration pending input
from interested parties.
Finally: the IGSTWG wishes to update its portions of the IGS website (http://www.igs.
org), and will cooperate with the website owners as needed to accomplish this.

References
Dach, R., U. Hugentobler, P. Fridez, M. Meindl (eds). Bernese GPS Software Version 5.0(user manual). Astronomical Institute of University of Bern, Bern, Switzerland, 2007.
Zumberge, J. F., M. B. Heflin, D. C. Jefferson, M. M. Watkins, and F. H. Webb. Precise
Point Positioning for the Efficient and Robust Analysis of GPS Data from Large Networks. J. Geophys. Res., 102(B3):5005–17, 1997.
Webb, F. H. and J. F. Zumberge (eds.). An Introduction to GIPSY/OASIS–II: Precision
Software for the Analysis of Data from the Global Positioning System. JPL internal
publication D–11088, Jet Propulsion Laboratory, Pasadena, California, 1997.

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A IGS Troposphere Working Group Members

A IGS Troposphere Working Group Members
NameAmirkhani, Mohammad
Bar–Sever, Yoaz
Bevis, Mike
Bosser, Pierre
Braun, John
Byram, Sharyl
Byun, Sung
Calori, Andrea
Chen, Junping
Colosimo, Gabriele
Crespi, Mattia
Dick, Galina
Dousa, Jan
Drummond, Paul
Ghoddousi–Fard, Reza
Guerova, Guergana
Gutman, Seth
Hackman, Christine
Heinkelmann, Robert
Herring, Tom
Hilla, Steve
Langley, Richard
Leighton, Jon
Moeller, Gregor
Moore, Angelyn
Negusini, Monia
Nordman, Maaria
Pacione, Rosa
Penna, Nigel
Perosanz, Felix
Pottiaux, Eric
Prikryl, Paul
Rocken, Chris
Santos, Marcelo
Schaer, Stefan
Schön, Steffen
Sguerso, Domenico
Tracey, Jeffrey
van der Marel, Hans
Wang, Junhong
XuZong–qiu, Liaoning
Zhang, Shoujian

Institution
Islamic Azad Univ. Tehran
JPL
OSU
ENSG/DPTS
UCAR
USNO
JPL
Univ. Roma “La Sapienza”
Shanghai Astronomical
Observatory
Univ. Roma “La Sapienza”
Univ. Roma “La Sapienza”
GFZ
GOP
TrimbleNatural Resources Canada
Univ. Sofia
NOAA
USNO
Deutsches Geodätisches
ForschungsinstitutMIT
NGS/NOAA
Univ. New Brunswick
3vGeomatics
TU Wien
JPL
Inst. Radioastronomy (IRA);
National Inst. Astrophysics(INAF)
Finnish Geodetic Inst.
ASI/CGS
Univ. Newcastle
CNES
Royal Obs Belgium
Communications ResearchCentre, Canada
GPS Solutions
Univ. New Brunswick
swisstopo
Inst. Erdmessung, Leibniz Uni
HannoverLab. Geodesy, Geomatics, GIS;
Univ. Genoa
USNO
TU Delft
UCAR/NCAR
TU
Wuhan Univ.

Country
Iran
USA
USA
FranceUSA
USA
USA
ItalyaChina

email
m.amirkhani2008@gmail.com
yoaz.bar-sever@jpl.nasa.gov
mbevis@osu.edu
pierre.bosser@ensg.eu
braunj@ucar.edu
sharyl.byram@usno.navy.mil
sung.h.byun@jpl.nasa.gov
calori@mendoza-conicet.gob.arjunping.chen@shao.ac.cn

Italy
Italy
GermanyCzech
New Zealand
CanadaBulgaria
USA
USA
Germanygabriele.colosimo@uniroma1.it
mattia.crespi@uniroma1.it
dick@gfz-potsdam.dejan.dousa@pecny.cz
paul_drummond@trimble.com
rghoddou@nrcan.gc.ca
guerova@phys.uni-sofia.bg
seth.i.gutman@noaa.gov
christine.hackman@usno.navy.mil
heinkelmann@dgfi.badw.de

USAUSA
CanadaCanada/UK
AustriaUSA
Italy

tah@mit.edu
steve.hilla@noaa.gov
lang@unb.ca
jonny2vests@gmail.com
gregor.moeller@tuwien.ac.atangelyn.w.moore@jpl.nasa.gov
negusini@ira.inaf.it

Finland
Italy
UK
FranceBelgium
Canadamaaria.nordman@fgi.fi
rosa.pacione@e-geos.it
nigel.penna@newcastle.ac.uk
felix.perosanz@cnes.fr
eric.pottiaux@observatoire.bepaul.prikryl@crc.gc.ca

USA
CanadaSwitzerland
Germany

rocken@gps-solutions.com
msantos@unb.ca
stefan.schaer@aiub.unibe.chschoen@mbox.ife.uni-hannover.deItaly

domenico.sguerso@unige.it

USA
Netherlands
USA
China
China

jeffrey.tracey@usno.navy.mil
H.vanderMarel@tudelft.nl
junhong@ucar.edu
zongqiuxu@gmail.com
shjzhangwhu@gmail.com

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Hackman and Byram: Troposphere working group

B IGS Troposphere Working Group Charter
IGS TROPOSPHERE WORKING GROUP CHARTERGNSS can make important contributions to meteorology, climatology and other environmental disciplines through its ability to estimate troposphere parameters. Along withthe continued contributions made by the collection and analysis of ground–based receivermeasurements, the past decade has also seen new contributions made by space–based
GNSS receivers, e.g., those on the COSMIC/FORMOSAT mission [1]. The IGS therefore
continues to sanction the existence of a Troposphere Working Group (TWG).
The primary goals of the IGS TWG are to:• Assess/improve the accuracy/precision of IGS GNSS–based troposphere estimates.
• Improve the usability of IGS troposphere estimates.
– Confer with outside agencies interested in the use of IGS products.
– Assess which new estimates should be added as "official" IGS products, andwhich, if any, official troposphere product sets should be discontinued.
• Provide and maintain expertise in troposphere–estimate techniques, issues and applications.

Science background
The primary troposphere products generated from ground–based GNSS data are estimatesof total zenith path delay and north/east troposphere gradient. Ancillary measurementsof surface pressure and temperature allow the extraction of precipitable water vapor fromthe total zenith path delay.
Water vapor, a key element in the hydrological cycle, is an important atmosphere greenhouse gas. Monitoring long–term changes in its content and distribution is essential forstudying climate change. The inhomogeneous and highly variable distribution of the atmospheric water vapor also makes it a key input to weather forecasting.
Water vapor distribution is incompletely observed by conventional systems such as radiosondes and remote sensing. However, ground– and space–based GNSS techniques provide complementary coverage of this quantity. Ground–based GNSS observations produce
continuous estimates of vertically integrated water vapor content with high temporal resolution over a global distribution of land–based locations; coverage is limited over theoceans (where there is no land). Conversely, water vapor can be estimated from space–borne GNSS receivers using ray tracing techniques, in which case solutions with high vertical resolution (laterally integrated over few hundred kilometers) and good oceanic/landcoverage are obtained; these solutions however are discontinuous in geographic locationand time.

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B IGS Troposphere Working Group Charter

Be it resolved that the IGS troposphere WG will:• Support those IGS analysis centers providing official IGS troposphere products.

• Increase awareness/usage of IGS troposphere products by members of the atmospheric, meteorology and climate–change communities. Solicit the input and involvement of such agencies.
• Create new IGS troposphere products as needed (as determined by consultation withthe potential user community).
• Determine the uncertainty of IGS troposphere estimates through comparison of solutions with those obtained from independent techniques, or through other means
as appropriate.
• Promote synergy between space–based and ground–based GNSS techniques throughinteraction with researchers in both fields.

References:[1] Schreiner, W., C. Rocken, S. Sokolovskiy, S. Syndergaard and D. Hunt, Estimates ofthe precision of GPS radio occultations from the COSMIC/FORMOSAT–3 mission,
GRL, 34, L04808, doi:10.1029/2006GL027557, 2007.
[2] Teke, K., J. Böhm, T. Nilsson, H. Schuh, P. Steigenberger, R. Dach, R. Heinkelmann,
P. Willis, R. Haas, S. García–Espada, T. Hobiger, R. Ichikawa and S. Shimizu, Multi–
technique comparison of troposphere zenith delays and gradients during CONT08,
J Geod, 85:395–413, doi: 10.1007/s00190–010–0434–y, 2011.

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Hackman and Byram: Troposphere working group218

Clock Products Working GroupK. Senior
U.S. Naval Research Laboratory
4555 Overlook Ave SW; Washington DC 20375
ken.senior@nrl.navy.mil; Phone: +1 202 767 2043

In 2011 the IGS Clock Products Working Group (CPWG) migrated the IGS Rapid andFinal clock products to new reference timescales based on a new version 2.0 algorithm
developed at the U.S. Naval Research Lab (NRL). The new algorithm was implemented
primarily to improve upon the longer term stability of the legacy v1.0 timescale. The
improvements include changes to clock modeling, the UTC alignment (steering), as wellas to changes to the clock weighting approach used. Additional states were also added to
the Kalman filter to model up to two fixed period harmonics in order to better compensate
contributions from the GPS satellite clocks. The algorithm is fully automated requiring
no regular user intervention. A brief description of the algorithm improvements is given
below along with its current performance status.

1 Basic Model for all Clocks
The basic clock model used for each clock in the new version 2.0 IGS timescale (bothground and GPS satellite clocks) includes the clock‘s time (or phase), its first derivative

Figure 1: The basic clock model used in the IGS v2.0 timescale includes the clock‘s phase x,
frequency y, and drift w, each driven by integrated white noises (random walks) as
well as an additional phase state x̃, necessary to model also a pure white phase noise.
Up to two pure harmonics may also be included. Each of the phase, frequency, anddrift states are modelled stochastically by an independent random walk, random walkphase (RWPH), random walk frequency (RWFR), and random walk drift (RWDR).

219

Senior: Clock Products Working Group(frequency), and its second derivative (drift), each modeled stochastically with an independent random walk as shown in Figure 1. An additional phase state x̃ is included tomodel a pure white phase noise and to couple to optionally specified pure fixed period
harmonics as described below.
The perfect integrator model of Figure 1 (or subcomponents of it) has been used to model
well the behavior of most clocks dating back to the 80 s (Jones and Tryon, 1983). Although
the legacy version of the IGS timescale employed only a two state model of a clock‘s
behavior the new version has employed the new full version.

2 Additional Pure Harmonic States
It has been well investigated that significant harmonics are present throughout the GPS
constellation clocks nominally at periods of 12–h, 6–h, 4–h and 3–h with amplitudes up to
2 ns (c.f., Senior et al., 2008; Montenbruck et al., 2011). Figure 2 shows the amplitude
spectra of the GPS constellation clocks where all spectra were calculated individuallyfor each clock and then averaged over the constellation in the Fourier domain. As thefigure shows the pervasiveness and prominence of particularly the 12–h and 6–h harmonics
in most GPS satellite clocks dictates the need to compensate or model these variations
explicitly in the timescale filter. For this reason four additional states have been includedin the v2.0 IGS timescale filter to compensate up to two fixed period harmonics which canbe specified per clock. Two states are required for each harmonic, one in–phase and one
quadrature, and are coupled only to a single phase state as shown in Figure 1 above.

Figure 2: Amplitude spectrum for the GPS constellation clocks. Spectra were calculated individually for each satellite and averaged over the entire constellation of clocks.

220

3 Timescale Constraints

3 Timescale Constraints
The geodetic estimation technique necessarily produces phase offset observations of eachclock that are rank deficient in the sense that each clock‘s phase must be estimated withrespect to the phase of some other reference clock, or timescale. The goal of a timescalealgorithm is to generate a reference (paper) clock that is both stable but also independentof any single clock, or equivalently to produce better estimates of each individual clock‘s
behavior; these are equivalent since for example estimating perfectly an individual clock isequivalent to generating a perfect reference. The rank deficiency of the phase observations
represents an observability problem in estimating the individual clocks and is typicallyaddressed by introducing additional constraints into the estimation process, typically an
additional assumption(s) about how the ensemble behaves on average.
Since each type of random input–random walk phase (RWPH), random walk frequency(RWFR), and random walk drift (RWDR)–represents from an ensemble of clocks a separate
ensemble of noises, three separate recursive weighted conditions are imposed to constrain
the ensemble timescale solution (Stein, 1993):
NX

ai (t) · (xi (t) − xi (t|t − δ)) = 0

i=1
N
X
i=1

N
X
i=1

bi (t) · (yi (t) − yi (t|t − δ)) = 0(1)ci (t) · (wi (t) − wi (t|t − δ)) = 0

where the notation, (t|t + δ), denotes a prediction of the given quantity to epoch t fromsome previous epoch t + δ. These constraints impose that the weighted sum of the differences between the clock‘s true states and their predictions be zero on weighted (ensemble)
average. Provided the correctness of the model each clock‘s state differs from its prediction
exactly by its random noise inputs. Thus, the optimal weights ai , bi , and ci are chosen
inversely to the variances of the noises contributing to each state, that is, inversely to thelevel of each random walk noise input. This selection of weighting has the effect of normalizing each clock‘s contribution to the noise of the ensemble and will typically result ina reference ensemble timescale more stable than its constituents. The additional weights
also have the benefit of effectively optimizing separately the different random walk typenoise contributions–RWPH, RWFR, and RWDR–perturbing each of the states x, y, andw, respectively.
An example showing the benefits of multiple clock weighting is depicted in a simulation
example below (Figure 3). In the example twelve clocks were simulated from three classesof clocks, each class differentiated by differing levels of RWPH and RWFR noise. The relative levels of each simulated clock‘s noise are represented in the figure using the Hadamard

221

Senior: Clock Products Working Group1ENSEMBLE 1 2
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Hadamard Deviation

9
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Averaging Interval

Figure 3: Timescale frequency stability results as measured by the Hadamard deviation statistic
for a twelve clock simulation example based on three classes of clocks, where each classis differentiated by a relative different level of RWPH and RWFR noise.

deviation statistic where the simulated true values (blue) are plotted on a log–log scale
plot of the Hadamard deviation versus averaging interval; a smaller deviation indicateslower noise at that averaging interval and the slope indicates the type of noise. Notethat a slope of −1/2 in the plot is consistent with RWPH noise whereas a slope of +1/2
is consistent with RWFR. The simulated measurements were then processed in the v2.0
timescale filter with per clock weights specified inversely according to their levels of noise
type. The plot also shows (green) the resulting noise of the filtered timescale. As thefigure shows the ensemble timescale is more stable than any of the constituent clocks andoptimally utilizes each class accordingly.

4 UTC (steering) Alignment
The steering control approach used in v2.0 to align the timescale to UTC is based on a
Linear Quadratic Gaussian (LQG) drift steering control in which the amount of steering
is determined via a weighted quadratic cost functional that relatively penalizes deviationsof the timescale from UTC versus the relative amount of control effort (drift steering)
applied. This approach is the same as that used in the legacy timescale. However, whileboth the legacy and v2.0 use an LQG steering control approach the UTC datum is handled222

5 Timescale Outputs
differently in the new version. In the legacy version the timescale was steered to GPS Time.
The new version utilizes a weighted average of calibrated UTC(k) realizations as well as
GPS Time, where the weighting is determined relative to the noise characteristics of each
input, similar to the timescale clock weighting.
A method for the determination of IGS station calibration biases was determined by(Senior et al., 2004). Using information from the BIPM Circular T publication the method
allows for a determination of the station clock bias offset of an IGS station clock from acollocated UTC(k) at the 1 ns level provided that the clock driving the IGS station is stable
by a fixed offset relative to UTC(k) at that level. As of 2009 when the CPWG last reported
on the status of the collocated stations there was sufficient timing laboratory participationin the IGS to include between five and ten IGS UTC(k) stations of sufficient quality.
However, the calibration algorithm has not yet been implemented operationally in v2.0.
Currently, only USN3, AMC2, and GPS Time are included as UTC steering references.
These stations were included because their pseudorange data and therefore their geodetic
estimates are already adjusted to compensate their UTC calibration offsets.
It is a pending CPWG item to include additional UTC(k) references.

5 Timescale Outputs
The timescale filter output includes states (from four to eight in number) and covariancesfor each clock relative to the ensemble timescale as well as numerous debugging andclock status information outputs. The IGS product files are re–aligned to the resulting
timescale using the phase estimates from the filter in the following way. In order to avoid
impacting the raw clock–clock information represented in the ACC combination clocks, the
IGS clock products are not replaced directly with the phase estimates from the timescalefilter. Instead, the clock measurements zir (tk ) that are output from the ACC combinationand that are subsequently input to the timescale filter are re–aligned to a new set ofmeasurements zie (tk ) relative to the ensemble timescale according to the calculation,zie (tk ) , zir (tk ) + mediani {zir (tk ) − x̂ei (tk )}(2)

where x̂ei (tk ) are the phase estimates of each clock relative to the ensemble as determinedin the timescale filter. While this retains additional measurement noise in the re–aligned
products as compared to the phase estimates themselves it has the added benefit of remaining unchanged any relative clock–clock differences in the re–alignment, i.e.,zie (tk ) − zje (tk ) = zir (tk ) − zjr (tk )(3)for any two clocks i and j. Thus, the timescale re–alignment does not impact the use of
the newly align clocks in any navigation solution that uses the products.

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Senior: Clock Products Working Group
Clock products of both the IGS Final and Rapid lines have been re–aligned to the IGS v2.0
timescales as described above, available as before in both SP3 and Clock RINEX formats.
Additional timescale re–alignment information is also provided in the clock summary files
as before with only one new modification that individual clock weighting now reflects
multiple weights per clock. A sample of the addition made to each clock summary files by
the timescale re–alignment is shown below in the Appendix A.
New timescale combination plots have also been developed to accompany the usual timescale
processing outputs and may be found at https://goby.nrl.navy.mil/IGStime/igrt.
php and https://goby.nrl.navy.mil/IGStime/igrt.php under the “plots_monthly” subdirectory; note that only monthly plots are currently available. Appendix B contains
several samples of various plots now included.
Figure 9 shows a sample filter state/sigma output for the IGS BRUX station clock over themonth of May 2012. In the plot the clock’s phase estimates including harmonics (black),phase without harmonics (gray) state, frequency state (red), and drift state (blue) areplotted on separate scales along with accompanying sigmas (middle panel) and respective
weights (bottom panel), all referenced to the new timescale. The legend of each plot shows
any polynomials removed from the respective series for plotting as well as any phase or
frequency breaks detected by the filter; for example, a frequency break was clearly detected(with lag) on 11 May in the plot shown
Figure 10 shows a sample frequency stability plot in which the Hadamard deviations of
the highest weighted clocks are shown. Since each clock now has four weights in the combination all four weights are now shown in the legend. Changes to the clock combination
summary files also now include the multiple weights per clock.
Figure 11 shows an example (AMC2) of another new plot recently added late in 2011at ACC request showing the phase measurements of each clock relative to the timescale
as gleaned from the measurement re–alignment described above in Equation 2. These“data vs timescale” phase–only plots more accurately reflect the timescale re–alignment
actually made in the IGS product files for the reasons described above. Also, in the eventthat a clock has recently been added or reset within the filter its estimates may not have
yet reached steady–state. Although the filter sigmas will indicate this condition these
additional plots have been added for observing or monitoring clock behavior during suchstates.

6 Additional Features
The implementation of the v2.0 algorithm is a U–D Kalman filter that is fully automated,
requiring no additional user input once the filter has been started. A new feature of the v2.0
algorithm is its ability to adaptively update the clock noise parameters corresponding to
the random walks. Whenever a clock is first introduced into the timescale it‘s entered with224

7 Current Status of IGS Time Scales
zero weights and its state and covariance are initialized using a quadratic fit procedure that
reduces the otherwise large initial uncertainties of its covariance. Values for its clock model
noise parameters are also initially determined automatically according to the following.
The clock‘s RWPH level is determined relative to another stable clock using 1 day ofdata and using the Hadamard deviation statistic (Hutsell, 1995). Its RWFR and RWDR
levels are initially set high and depend on the RWPH level determined. The adaptive
filter mechanism subsequently adjusts the noise parameters adaptively utilizing the filter‘sinnovation sequence (pre–fit residuals).
Other necessary practical features of a fully automated timescale include the ability to introduce new clocks into the timescale filter (or remove older ones) without unduly affecting
the performance of the timescale. Also, the ability to respond to bad data or to a discretechange in the states of a clock as might for example occur during a station equipmentchange or upgrade is also necessary. These additional features have been implemented in
the new v2.0 timescale.

7 Current Status of IGS Time Scales
Figure 4 summarizes the current overall phase offset status of the IGS Rapid (IGRT) and
Final (IGST) timescales as compared against GPS Time and UTC from late 2010 throughJuly 2012, utilizing information from the BIPM Circular T publication. The plot clearlyshows an overall UTC alignment improvement as of the transition to version 2.0 thoughsome remaining instabilities in the Rapid timescale are occasionally present. Although the
IGS products did not transition until Spring 2011 the plot shows v2.0 data beginning at
Jan 1, 2010 where the new timescale was run for this longer period before the transition.
Table 1 below shows the overall comparison of the tie to UTC before and after the transition to v2.0. The Final products now show a very tight relationship to UTC better than
3 ns over the period.

Table 1: Mean and Standard Deviation of the Rapid (IGRT) and Final(IGST) IGS timescales relative to UTC before and after thetransition to v2.0.

IGST − UTC
IGRT − UTC

LegacyMean ± STD−6.9 ± 13.1
−6.3 ± 13.7

v2.0
Mean ± STD−2.2 ± 2.7−4.5 ± 7.9

225

Senior: Clock Products Working Group

50

0

−50

50

0

−50

50

0

−50

2000

2001

2002

52500

52500

53000

53000

53000

2004

IGST−GPST

2003

UTC−IGRT

52500

UTC−GPST (Circular T)

52000

UTC−IGST

52000

52000

2005

2006

54000

54000
MJD

IGRT − IGST

54000

UTC−IGS(R)T*

IGRT−GPST

53500

53500

53500

2007

56000

2012

55500

56000

2011

55000

55500

56000

2010

54500

55000

55500

2009

54500

55000

2008

54500

Figure 4: IGS Timescales measured against GPS Time and UTC. Note that data on this plot from the new v2.0 timescale begins
Jan 1, 2010 though the products were not transitioned until Spring 2011.

226

Nanoseconds
Nanoseconds
Nanoseconds

7 Current Status of IGS Time Scales
Estimated clocks using Legacy
Estimated clocks using new v2.0
v2.0 Timescale (estimated lower bound)−13

Hadamard Deviation, Hσy(τ)

10

−14

10

−15

10

3

10

4

10
τ (seconds)

5

10

6

10

Figure 5: Instabilities (Hadamard deviation) of the most stable IGS clocks relative to the legacy(black) and new v2.0 (red) IGS timescales calculated over the first three months of
2011. Also shown is a lower–bound estimate of the resulting timescale assuming thevalidity of the phase estimates and the weights used during the period shown. This isa lower bound estimate of the timescale not an estimate of the timescale realized.

Figure 5 shows the frequency stability performance plot of the new v2.0 timescale comparedwith the legacy version as measured by the Hadamard deviation statistic. The statistics
shown were calculated using IGS Final data over the first three months of 2011 and only
the most stable clocks over the period are plotted. As may be gleaned by the banding of
the clock estimates from each the old (black) and the new (red) versions the new version
2.0 algorithm shows improved stability over the longer term averaging intervals as desired.
It‘s also clear that for shorter averaging intervals there‘s essentially no difference between
the old and new versions consistent with the effectively equivalent short–term weighting
constraints in both versions (inverse of RWPH levels).
As a measure of the performance consistency over time of the v2.0 timescales a histogramof the number of clocks having frequency stability as measured by the Hadamard deviationof the (internal) phase estimates better than 3 · 10−15 at an averaging interval of 21,600 s
plotted daily since 2011 is shown in Figure 6 below. As the figure shows there is generally
uniform consistency over time of the performance of the products with average numbersof clocks have such stability being 16.6 ± 3 and 12.9 ± 3 for IGST and IGRT, respectively.
However there are sporadic days over this period in which the number of such stabilities
drops below five clocks. Because these “internal” measures of stability depend on the227Senior: Clock Products Working Group

30

2010
N
D

J

F

M

A

M

J

2011
J

A

S

O

N

D

J

F

M

2012
M

A

J

J

A

S

Final
Rapid
25

20

15

10

5

0
55500

55600

55700

55800 55900 56000
Modified Julian Date

56100

56200

Figure 6: Histogram of the daily number of clocks in the IGS Final and Rapid timescale filters
having phase estimate stabilities better than 3 · 10−15 at τ = 21, 600 s as measured by
the Hadamard deviation statistic.
12

2010
N
D

J

F

M

A

M

J

2011
J

A

S

O

N

D

J

F

M

A

2012
M

J

J

A

S

Rapid
Final

Maximum Clock Weight

10

8

6

4

2

0
55500

55600

55700

55800 55900 56000
Modified Julian Date

56100

56200

Figure 7: Maximum daily a weight (in %) per clock for the v2.0 IGS Final and Rapid timescales
since 2011.

228

7 Current Status of IGS Time Scales
relative clock weights assigned to each clock the maximum a weight (see Equation 1) for
each clock is also plotted over the same period in Figure 7.

As detailed above the addition of new fixed period harmonic states to the timescale filter
was made in order better compensate the GPS constellation clock errors. Harmonics at
frequencies of 2.003 and 4.006 cycles/day are estimated for each of the GPS constellation
clocks in both the Rapid and Final timescales. Figure 8 below shows each of the twophase state estimates for PRN 25 versus IGST over a one week period in May 2012. The
black series shows the phase state that includes the influence of the harmonics while thegray series shows the other phase state that is estimated without their influence. The
magnitude of the difference between the black and gray series demonstrates both the needfor estimating these harmonics as well as the effectiveness of the filter in isolating them.

2012
MAY

0.8

23

0.6

24

25

26

27

JUN

28

29

30

31

1

phase with harmonics
phase without harmonics

Nanoseconds

0.4
0.2
0
−0.2
−0.4
−0.6
−0.8
56072

56074
56076
Modified Julian Date

56078

Figure 8: Timescale filter phase estimates of PRN 25 versus the IGS Final timescale IGST over
the one week period 25 May through 31 May 2012. The black series shows the timescale
phase state with harmonics while the gray series shows the phase minus the harmonics.
An overall quadratic was removed from both series for plotting.

229

Senior: Clock Products Working Group

References
Hutsell, S. T.; 1995. Relating the hadamard variance to MCS Kalman filter clock estimation. Proc. of the 27th Annual Precise Time and Time Interval (PTTI) Applications
and Planning Meeting, p. 293, San Diego, Calif, USA, December 1995.
Kouba J. and T. Springer; 2001. New IGS station and satellite clock combination. GPS
Solutions, 4(4):31–36. doi: 10.1007/PL00012863.
Jones J and P. V. Tryon; 1983. Estimating time from atomic clocks. Journal of Researchof the National Bureau of Standards, 88(1):17–24.
Montenbruck O., U. Hugentobler, R. Dach, P. Steigenberger, and A. Hauschild; 2011.
Apparent clock variations of the Block IIF–1 (SVN62) GPS satellite. GPS Solutions,16(3):303–313. doi: 10.1007/s10291-011-0232-x.
Senior K., P. Koppang, and J. Ray; 2003. Developing an IGS time scale. IEEE TransUltrason Ferroelectr Freq Control, 50:585–593.
Senior K., G. Petit, and J. Ray; 2004. Comparison of instrumental and empirical station
timing biases for a set of Ashtech Z12T GPS receivers. Proc. 18th European Frequency
and Time Forum EFTF 2004, Guildford, UK, 4–7, April, 2004.
Senior K., J. Ray, and R. Beard; 2008. Characterization of periodic variations in the GPS
satellite clocks. GPS Solutions, 12(3):211–225. doi: 10.1007/s10291-008-0089-9.
Stein, S. R.; 1993. Advances in time–scale algorithms. Proc. of the 24th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting, pp. 289–303,
Greenbelt, Maryland, USA, December 1993.

230

A Sample of New Combinationa Clock Summary

A Sample of New Combinationa Clock Summary
Sample of New v2.0 IGS Timescale Filter Additions to the Combination Clock Summary
Files:RESULTS OF TIME SCALE COMBINATION:| STABILITY RESULTS FROM IGS CLOCK ENSEMBLE|NFRQ NEPO
MEAN
MEAN
MEAN
MEAN
| HADAMARD DEVIATION AT TAU = || NREPO NBEPO BRKS USEDWGT1(%) WGT2(%) WGT3(%) WGT4(%) |
300s
3600s
21600s |------+---------------------------------------------------------------+------------------------------+
NISU |
288
288
0
288
6.63
9.95
0.51
0.51
| 8.94e-15 4.08e-15 2.62e-15 |BRUS |
288
288
0
288
4.55
7.13
8.70
8.70
| 9.78e-15 7.07e-15 2.13e-15 |BREW |
288
288
0
288
4.54
7.10
0.67
0.67
| 1.04e-14 4.44e-15 1.63e-15 |AMC2 |
288
288
0
288
3.73
4.77
5.16
5.16
| 1.15e-14 5.53e-15 9.16e-16 |DRAO |
288
287
1
288
3.73
4.77
9.97
9.97
| 1.13e-14 5.13e-15 4.72e-15 |NLIB |
288
288
0
288
3.72
4.76
7.97
7.97
| 1.07e-14 7.40e-15 3.61e-15 |NPLD |
287
286
1
287
3.71
4.73
1.24
1.24
|
- |
USNO |
288
288
0
288
3.62
4.49
0.86
0.86
| 1.01e-14 5.12e-15 1.87e-15 |YELL |
288
287
1
288
3.56
4.36
9.31
9.31
| 7.83e-15 4.95e-15 2.08e-15 |WSRT |
288
288
0
288
3.53
4.27
9.97
9.97
| 6.14e-15 5.73e-15 2.58e-15 |STJO |
288
288
0
288
3.49
4.19
5.57
5.57
| 7.52e-15 5.86e-15 2.55e-15 |SPT0 |
288
288
1
288
3.24
3.59
3.97
3.97
| 8.20e-15 4.52e-15 2.65e-15 |WES2 |
288
288
0
288
3.11
3.32
0.65
0.65
| 7.18e-15 5.83e-15 1.43e-14 |NRC1 |
288
288
0
288
3.00
3.09
1.14
1.14
| 8.10e-15 8.88e-15 1.90e-15 |USN3 |
288
288
0
288
2.95
2.97
1.53
1.53
| 1.71e-14 6.35e-15 1.31e-15 |GPST |
288
287
1
288
2.90
2.89
0.17
0.17
| 7.68e-15 4.47e-15 9.57e-16 |CHUR |
288
288
1
288
2.67
2.45
2.44
2.44
| 1.06e-14 7.81e-15 5.05e-15 |HOB2 |
288
287
1
288
2.61
2.32
0.11
0.11
| 3.94e-14 1.70e-14 3.30e-15 |KOKB |
288
288
0
288
2.57
2.27
3.31
3.31
| 1.35e-14 1.24e-14 5.00e-15 |TWTF |
288
288
0
288
2.41
1.98
2.10
2.10
| 1.16e-14 1.39e-14 3.17e-15 |NYAL |
288
288
0
288
2.22
1.69
0.19
0.19
| 1.23e-14 2.36e-14 3.26e-14 |NYA1 |
288
288
0
288
2.03
1.41
0.17
0.17
| 1.20e-14 2.33e-14 3.21e-14 |BRFT |
288
288
0
288
1.90
1.24
0.56
0.56
| 1.74e-14 1.95e-14 8.67e-15 |KHAJ |
288
288
0
288
1.88
1.21
0.56
0.56
| 1.74e-14 2.17e-14 1.74e-14 |GODE |
288
284
2
288
1.73
1.02
0.11
0.11
| 1.52e-13 4.70e-14 4.09e-14 |NOT1 |
288
288
0
288
1.66
0.94
0.37
0.37
| 1.44e-14 1.35e-14 5.84e-15 |USUD |
288
288
0
288
1.50
0.77
0.05
0.05
| 8.28e-14 2.30e-14 3.75e-15 |MDVJ |
288
287
1
288
1.47
0.74
1.21
1.21
| 2.50e-14 5.82e-15 6.25e-15 |MATE |
288
288
1
288
1.35
0.62
1.05
1.05
| 1.65e-14 1.21e-14 2.59e-14 |PIE1 |
288
287
1
288
1.33
0.60
1.92
1.92
| 2.97e-14 1.34e-14 3.98e-15 |ALGO |
288
288
1
288
1.01
0.35
0.01
0.01
| 2.29e-14 9.17e-15 2.80e-15 |
G14 |
288
288
0
288
0.45
0.34
0.10
0.10
| 4.65e-13 5.63e-14 2.34e-14 |CRO1 |
285
285
0
285
0.91
0.28
1.50
1.50
|
- |
G23 |
288
288
0
288
0.51
0.27
2.50
2.50
| 4.38e-13 5.35e-14 9.98e-15 |
G02 |
288
288
0
288
0.51
0.26
0.46
0.46
| 4.60e-13 4.27e-14 1.55e-14 |
G11 |
288
288
0
288
0.40
0.25
0.02
0.02
| 5.95e-13 5.81e-14 4.78e-14 |IRKJ |
283
280
1
283
0.81
0.23
3.43
3.43
|
- |
G13 |
288
288
0
288
0.47
0.23
0.26
0.26
| 4.57e-13 6.08e-14 4.02e-14 |
G17 |
287
287
0
287
0.43
0.20
0.01
0.01
|
- |
G16 |
288
287
0
288
0.48
0.18
2.85
2.85
| 5.67e-13 7.15e-14 2.90e-14 |
G20 |
288
288
0
288
0.38
0.18
4.17
4.17
| 5.77e-13 6.13e-14 1.57e-14 |
G19 |
288
287
0
288
0.47
0.18
0.82
0.82
| 5.32e-13 6.49e-14 4.43e-14 |
G18 |
288
288
0
288
0.30
0.17
0.54
0.54
| 7.92e-13 8.85e-14 2.52e-14 |HRAO |
288
288
0
288
0.67
0.15
0.10
0.10
| 7.60e-14 2.93e-14 4.63e-14 |PTBB |
288
288
0
288
0.67
0.15
0.56
0.56
| 1.58e-13 6.46e-14 2.60e-14 |MAR6 |
288
288
0
288
0.62
0.13
0.00
0.00
| 1.59e-13 6.57e-14 3.05e-14 |
G07 |
275
275
0
275
0.42
0.13
0.00
0.00
|
- |
G22 |
288
288
0
288
0.37
0.12
0.00
0.00
| 4.80e-13 5.51e-14 1.22e-14 |231

Senior: Clock Products Working Group
G26 |
288
288
0
288
0.42
0.11
0.31
0.31
| 2.93e-13 1.30e-13 6.36e-14 |
G29 |
288
288
0
288
0.40
0.10
0.31
0.31
| 3.18e-13 1.17e-13 6.19e-14 |PRDS |
288
288
0
288
0.51
0.09
0.09
0.09
| 2.00e-13 7.15e-14 2.46e-14 |
G04 |
288
288
0
288
0.35
0.09
0.19
0.19
| 3.29e-13 1.15e-13 5.94e-14 |
G05 |
288
288
0
288
0.33
0.08
0.01
0.01
| 1.69e-13 5.49e-14 1.19e-13 |TLSE |
288
288
0
288
0.42
0.06
0.19
0.19
| 2.88e-13 1.12e-13 2.02e-14 |BOR1 |
287
287
0
287
0.35
0.04
0.04
0.04
|
- |
PIE1 |
288
287
1
288
1.33
0.60
1.92
1.92
| 2.97e-14 1.34e-14 3.98e-15 |PRDS |
288
288
0
288
0.51
0.09
0.09
0.09
| 2.00e-13 7.15e-14 2.46e-14 |SPT0 |
288
288
1
288
3.24
3.59
3.97
3.97
| 8.20e-15 4.52e-15 2.65e-15 |STJO |
288
288
0
288
3.49
4.19
5.57
5.57
| 7.52e-15 5.86e-15 2.55e-15 |SYOG |
288
288
0
0
0.00
0.00
0.00
0.00
| 6.88e-13 2.13e-13 1.71e-13 |THTI |
216
161
29
0
0.00
0.00
0.00
0.00
|
- |
TIDB |
288
287
1
0
0.00
0.00
0.00
0.00
| 7.39e-14 2.39e-14 8.39e-15 |TLSE |
288
288
0
288
0.42
0.06
0.19
0.19
| 2.88e-13 1.12e-13 2.02e-14 |TWTF |
288
288
0
288
2.41
1.98
2.10
2.10
| 1.16e-14 1.39e-14 3.17e-15 |USNO |
288
288
0
288
3.62
4.49
0.86
0.86
| 1.01e-14 5.12e-15 1.87e-15 |WAB2 |
0
0
0
0
0.00
0.00
0.00
0.00
|
- |
WES2 |
288
288
0
288
3.11
3.32
0.65
0.65
| 7.18e-15 5.83e-15 1.43e-14 |WSRT |
288
288
0
288
3.53
4.27
9.97
9.97
| 6.14e-15 5.73e-15 2.58e-15 |YELL |
288
287
1
288
3.56
4.36
9.31
9.31
| 7.83e-15 4.95e-15 2.08e-15 |GPST |
288
287
1
288
2.90
2.89
0.17
0.17
| 7.68e-15 4.47e-15 9.57e-16 |WROC |
288
243
19
0
0.00
0.00
0.00
0.00
| 3.35e-12 1.15e-12 1.13e-12 |PTBB |
288
288
0
288
0.67
0.15
0.56
0.56
| 1.58e-13 6.46e-14 2.60e-14 |SFER |
0
0
0
0
0.00
0.00
0.00
0.00
|
- |
STR1 |
288
288
0
0
0.00
0.00
0.00
0.00
| 6.05e-13 2.16e-13 3.86e-14 |SYDN |
0
0
0
0
0.00
0.00
0.00
0.00
|
- |
USN3 |
288
288
0
288
2.95
2.97
1.53
1.53
| 1.71e-14 6.35e-15 1.31e-15 |USUD |
288
288
0
288
1.50
0.77
0.05
0.05
| 8.28e-14 2.30e-14 3.75e-15 |ZIMM |
287
68
146
0
0.00
0.00
0.00
0.00
|
- |
YEBE |
0
0
0
0
0.00
0.00
0.00
0.00
|
- |
WHIT |
288
288
2
0
0.00
0.00
0.00
0.00
| 5.07e-13 5.38e-13 3.64e-13 |ALBH |
287
48
167
0
0.00
0.00
0.00
0.00
|
- |
BREW |
288
288
0
288
4.54
7.10
0.67
0.67
| 1.04e-14 4.44e-15 1.63e-15 |HOB2 |
288
287
1
288
2.61
2.32
0.11
0.11
| 3.94e-14 1.70e-14 3.30e-15 |MEDI |
287
285
1
0
0.00
0.00
0.00
0.00
|
- |
NISU |
288
288
0
288
6.63
9.95
0.51
0.51
| 8.94e-15 4.08e-15 2.62e-15 |NPLD |
287
286
1
287
3.71
4.73
1.24
1.24
|
- |
TNML |
288
280
5
0
0.00
0.00
0.00
0.00
| 3.26e-13 1.28e-13 1.19e-13 |TSKB |
288
288
0
0
0.00
0.00
0.00
0.00
| 8.94e-13 2.22e-13 1.05e-13 |CEDU |
287
46
168
0
0.00
0.00
0.00
0.00
|
- |
GMAS |
288
275
8
0
0.00
0.00
0.00
0.00
| 1.00e-12 3.29e-13 1.14e-13 |OUS2 |
287
48
170
0
0.00
0.00
0.00
0.00
|
- |
MAD2 |
0
0
0
0
0.00
0.00
0.00
0.00
|
- |
IENG |
0
0
0
0
0.00
0.00
0.00
0.00
|
- |
IRKT |
0
0
0
0
0.00
0.00
0.00
0.00
|
- |
DAEJ |
287
204
48
0
0.00
0.00
0.00
0.00
|
- |
TOW2 |
288
288
0
0
0.00
0.00
0.00
0.00
| 4.10e-13 1.16e-13 1.53e-13 |------+---------------------------------------------------------------+------------------------------+STEERS APPLIED TO TIME SCALE:| 9.23e-23 9.47e-23 3.04e-22 |----------------------------------------------------------------------+------------------------------+MOST STABLE CLOCKS:
|
WSRT
NISU
NISU |----------------------------------------------------------------------+------------------------------+

232

B Sample of Plots

B Sample of Plots
Figure 9, page 234
Sample plotting output of the v2.0 timescale filter states/sigmas for the IGS site
BRUX. The plot shows the four base states, sigmas, and weights for the clock overa one month period.
Figure 10, page 234
Sample combination stability plot showing the frequency stability of the highest
weighted clocks in the IGS timescale for the period 1 May to 31 May, 2012.
Figure 11, page 234
Sample “data vs timescale” plot showing the timescale input phase data for the clock
at AMC2 referenced to the timescale IGST for May 2012. These phase “data” plots
differ from the phase estimates as they include measurement noise but also since aclock may not be in steady–state within the filter because the clock is new or has
undergone a reset.

233

Senior: Clock Products Working Group

0.1

0.05

0

−0.05

−0.1

−0.15
0.2
0.15
0.1
0.05
0
10
5
0

1

2

3

4

5
2

6

7

8

9

phase + WHPH + periodic( 0.0039t − 0.09t+ 1.5e+02)

2

1.5

1

0.5

0

−0.5

−1

−1.5

−2
1

0.5

10

12

Filter States & Sigmas

2

13

14

15

2012
MAY

16

17

19

20

1

21

22

frequency ( 0.0039t − 0.26)

18

BRUX
01−May−2012 through 31−May−201211phase ( 0.0039t − 0.09t+ 1.5e+02)

23

25
drift ( 0.09)

24

A clock‘s phase (gray and black)frequency (red) and drift (blue)
states are all shown.
Sigmas

25

26

27

28

29

30

14 phase reset(s)

30

31

1.5

1 freq reset(s)

1

0.5

0

−0.5

−1

−1.5

1.5

1

0.5

0

0

0

U.S. Naval Research Laboratory, 14−Jun−2012 12:02:42

10

20

0

15

MJD − 56048

10

10

5

5

5

0

Figure 9: Sample plotting output of the v2.0 timescale filter states/sigmas for the IGS site BRUX. The plot shows the four basestates, sigmas, and weights for the clock over a one month period. The black series correspond to the phase (including
harmonics), the gray the phase without harmonics, the red series correspond to frequency and blue to drift. The legend
also indicates any polynomials removed for plotting and/or phase or frequency breaks detected.

234

frequency (ns/day)

fr. sigma (ns/day)wf (%)

phase (ns)ph. sigma (ns)wφ (%)

drift (ns/day2)
dr. sigma (ns/day2)
wd (%)

−13

10

2

10

−15

−14

10

10

3

10

4

10
Averaging Interval (τ seconds)

01−May−2012 through 31−May−2012

5

10

6

10

WAB2: 4% / 5% / 5% / 5%
YELL: 4% / 5% / 5% / 5%
WSRT: 4% / 5% / 5% / 5%
ONSA: 4% / 5% / 5% / 5%
AMC2: 4% / 5% / 5% / 5%
OPMT: 4% / 4% / 5% / 5%
BRUX: 4% / 4% / 4% / 4%
PTBB: 4% / 4% / 4% / 4%
TWTF: 3% / 4% / 5% / 5%
PIE1: 3% / 4% / 5% / 5%
USN3: 3% / 4% / 4% / 4%
BJNM: 3% / 4% / 4% / 4%
USNO: 3% / 3% / 4% / 4%
NRC1: 3% / 4% / 3% / 3%
G25: 4% / 0% / 5% / 5%

U.S. Naval Research Laboratory (NRL), 14−Jun−2012, 12:01

Figure 10: Sample combination stability plot showing the frequency stability of the highest weighted clocks in the IGS timescale forthe period 1 May to 31 May, 2012. The a, b, c, and d weights for each clock are shown in the legend.

Overlapped Hadamard Deviation σH(τ)

Stability of Highest Weighted Clocks (phase breaks removed)

B Sample of Plots235

Senior: Clock Products Working Group

1.5

1

0.5

0

−0.5

−1

−1.5

−2

−2.5

1

2

3

4

5

6

7

8

9

10

12

Clock Data vs Timescale

13

14

2012
MAY

16

17
2

18

19

phase ( 0.026t + 0.17t− 3.4)

15

20

21

AMC2
01−May−2012 through 31−May−2012
11

22

23

24

25

26

27

28

56075

29

30

U.S. Naval Research Laboratory, 14−Jun−2012 12:03:32

56070

31

0

10

0

56065

MJD − 0

10

56060

5

56055

5

56050

wf (%)10
50wφ (%)

Figure 11: Sample “data vs timescale” plot showing the timescale input phase data for the clock at AMC2 referenced to the timescale
IGST for May 2012. These phase “data” plots differ from the phase estimates as they include measurement noise but also
since a clock may not be in steady–state within the filter because the clock is new or has undergone a reset.

236

wd (%)