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2000
TECHNICALREPORTSIGS Central Bureau
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California U.S.A.
http://igscb.jpl.nasa.gov/

JPL Publication TBD

CEThis publication was prepared by the Jet Propulsion Laboratory, California
Institute of Technology, under a contract with the National Aeronautics and Space
Administration.
Reference herein to any specific commercial product, process, or service by tradename, trademark, manufacturer, or otherwise, does not constitute or imply its
endorsement by the United States Government, the National Aeronautics and Space
Administration, or the Jet Propulsion Laboratory, California Institute of Technology.
Edited by Ken Gowey, Ruth Neilan, Angelyn Moore, JPL/IGS Central Bureau,
11/2001.

ii

Abstract
Applications of the Global Positioning System (GPS) to Earth Science are numerous. The
International GPS Service (IGS), a federation of government agencies and universities, plays
an increasingly critical role in support of GPS-related research and engineering activities.
Contributions from the IGS Governing Board and Central Bureau, analysis and data centers,
station operators, and others constitute the 2000 Technical Reports. This report has acompanion publication, the 2000 Annual Report. Hard copies of each volume can beobtained by contacting the IGS Central Bureau at the Jet Propulsion Laboratory. Electronic
versions can be viewed at http://igscb.jpl.nasa.gov/overview/pubs.html.

iii

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Preface
This volume documents the technical progress of the International GPS Service in theyear 2000. While the detail in this report is generally compiled for the benefit and interestof the internal IGS participants, more often recently, universities, libraries and otherorganizations request copies of the documentation for reference purposes. Attempts are
made by the editors to obtain submissions from the many contributors to the IGS –Analysis Centers, Data Centers, IGS Coordinators (for Analysis, Network and Reference
Frame), Network Operators, Projects, Working Groups, and status reports from theGoverning Board and the Central Bureau. A companion volume is the 2000 Annual
Report which serves as the executive summary of key annual activities for this uniqueorganization.
The year 2000 saw many new technical developments in the IGS, notably theestablishment of two new projects, the Low Earth Orbiter Pilot Project and theInternational GLONASS Pilot Project. During the latter half of the year, the IGS
Governing Board was engaged in a strategic planning effort resulting in a renewed mission
statement and identified goals and objectives for the period 2002-2007. The final plan
document will be available by early 2002.
The Analysis Center Coordinator, Tim Springer at the University of Bern in Switzerland,
departed for a new position with very fond farewells from long-time IGS colleagues, The
University of Bern succeeded in seamlessly reassigning responsibility for this vital role,and continues to produce the combined IGS products, orbits, clocks, station position andvelocities under the leadership of Robert Weber. The IGS through its Analysis Centerscollectively produces the most precise GPS orbit products available anywhere. The IGS
Network continued to grow, not just in number of stations and affiliated regional arrays,
but in functionality as stations become identified as meeting requirements necessary for
one or more of the IGS projects. Data Centers are a critical link in the smooth processingof the IGS, and find themselves responding to an increasing user base with decreasing
latencies as many groups and applications push towards real-time availability of data andproducts. The IGS as an organization continues to leverage the resources of over 200
contributing organizations and fosters the evolution of many GPS applications throughprojects and working groups.

vvi

Table of Contents

Contents
1

Executive Reports
IGS Governing Board in 2000 ...................................................................................3
Ch. Reigber
Central Bureau Annual Report 2000 ........................................................................9R. Neilan

2

Analysis Center Reports
2000 Analysis Coordinator Report..........................................................................15
R. Weber, T. Springer
Current State of IGS Analysis: Quality Assessment ..............................................51
T Herring, T. Springer
Reference Frame Working Group Technical Report...............................................61
R. Ferland

Analysis Centers
CODE IGS Analysis Center Technical Report 2000 ...............................................73
U. Hugentobler, et al.
The ESA/ESOC IGS Analysis Center Annual Report 2000 .....................................83
J. M. Dow, et al.
GFZ Analysis Center of IGS - Annual Report for 2000............................................95
G. Gendt
JPL IGS Analysis Center Report, 2000...................................................................99
D. Jefferson, et al
GPS Orbit and Earth Orientation Parameter
Production at NOAA for the International GPS Service for 2000 .........................107
W. Kass, et al
NRCan IGS Analysis Centre Report for 2000........................................................111
P. Tétreault, et al
Scripps Orbit and Permanent Array Center 2000
Global Analysis Center Report(Refer to Section 3, Global Data Centers)

Associate Analysis Centers
GNAACsThe Newcastle GNAAC Annual Report for 2000 ...................................................121
K. Nurutdinov, et alvii

Table of Contents

RNAACsThe EUREF Permanent Network Report .................................................................131
M. Becker, C. Bruyninx, D. Ineichen
AUSLIG RNAAC – 2000 Annual Report .................................................................137
G. Luton
GSI RNAAC Technical Report 2000 ......................................................................139
A. Yamagiwa, et al
Annual Report 2000 of RNAAC SIR .......................................................................141
W. Seemueller, H. Drewes

IERS Contributions
The IERS International Terrestrial Reference Frame ...........................................147
Z. Altamimi

3

Data Center Reports
Global Centers
CDDIS 2000 Global Data Center Report ................................................................153
C. Noll
Scripps Orbit and Permanent Array Center 2000 SOPAC Report ........................165
Y. Bock, B. Gilmore, et al
Regional/Operations Centers
BKG Regional IGS Data Center Report 2000 ........................................................183
H. Habric, K. Herzberger
Hartebeesthoek Radio Astronomy Observatory (HartRAO)..................................187
L. Combrinck

4

Network and Station Reports
Global, Regional, and Local Networks
Growth of the IGS Station Network in 2000 ..........................................................197
A. Moore
Australian Regional GPS Network - Report for 2000 ...........................................201
R. Twilley, P. Digney
New Zealand Continuous GPS Network................................................................205
J. Beavan
The GPS Receiver Network of ESOC....................................................................209
C. Garcia, et al
Status Report of IGS Stations Monitored by GFZ..................................................213
M. Ramatschi, et al.

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Table of Contents

NASA-Sponsored Global GPS Network Activites .................................................215
D. Stowers, et al
NRCan - GSC Western Canada Deformatiom Array GPS
Network 2000 Report.............................................................................................219
M. Schmidt, H. Dragert, et al
Permanent GPS Tracking Station UPAD...............................................................223
A. Caporali
Technical Report on LAMA IGS Station for Year 2000 .........................................225
P. Wielgosz et al.

5Working Groups/Pilot Projects/Committees
IGS/BIPM Time Transfer Pilot Project...................................................................229
J. RayDensification of ITRF (see IGS Reference Frame Coordinator Report(Refer to Section 2, Analysis Center Reports)
Report of the Tropospheric Working Group ..........................................................231
G. Gendt
2000 IGS Activities in the Area of the Ionosphere ...............................................235
J. Feltens
IGS LEO Pilot Project............................................................................................241
M. Watkins
International GLONASS Service Pilot Project ......................................................243
J. Slater

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IGS

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R E P O R T S

IGS Governing Board in 2000

IGS Governing Board in 2000
Christoph Reigber
GeoForschungsZentrum Potsdam,
Germany
Introduction
Over the past year, the IGS again experienced great success in many areas. The IGS
continues to thrive as new applications emerge and fundamental IGS systems andprocesses continually improve. This vitality is due to the concerted effort of each of ourcontributing organizations and individuals. On behalf of the Governing Board, I would
like to sincerely thank each contributor.
The year 2000 was also a new experience for the Board, beginning with importantchanges in membership. December 1999 saw the departure of Ivan Mueller, Bill
Melbourne, Jan Kouba, and Yehuda Bock. Each of these individuals had been membersof the Board since the inception of the IGS and their collective talents greatly helped toshape the organization.
The main activities this past year addressed by the Governing Board include thedevelopment of a strategic plan for the IGS for the coming years and a focus on IGS
working group activities.
IGS Strategic Planning Summary
With the tremendous growth of IGS and an increase in demanding applications, theBoard appointed a planning committee in June to coordinate a strategic planning process
for the IGS. The IGS is mature and diverse enough to warrant a close look at theorganization’s focus over the next five years, how to achieve the key goals and objectives
that are identified, and how best to continue the success and benefits accomplished todate. The Governing Board is committed to completing the IGS strategic plan in 2001.
The planning group approved by the Board includes:•

Norman Beck, Natural Resources Canada•

Gerhard Beutler, University of Bern, Switzerland•

John Manning, Australian Survey and Land Information Group•

Bill Melbourne, Jet Propulsion Laboratory, California Institute of Technology•

Angelyn Moore, IGS Central Bureau, Jet
Propulsion Laboratory, California Institute of Technology•

Ivan Mueller, Professor Emeritus, Ohio State University

3

IGS 2000 Technical Reports•

Ruth Neilan, IGS Central Bureau, Jet Propulsion Laboratory, California
Institute of Technology•

Jim Ray, United States Naval Observatory•

Christoph Reigber, GeoForschungsZentrum Potsdam•

Robert Serafin, National Center for Atmospheric Research

The Central Bureau retained an excellent planning consultant, Haig Bazoian, to facilitate
the strategic planning process.
The planning committee was involved in preparation of materials with Bazoian
throughout the summer of 2000, and met as a smaller group at Bundesamt für
Kartographie und Geodäsie (BKG) in Frankfurt during early September. This initial
meeting was a two-day session aimed at preparing material for a retreat with the entire
Governing Board in December. The main points discussed were the strengths andchallenges of the IGS, the three most important strategies that should be adopted, the IGS
mission, and long-term objectives. This preliminary material was distributed to theGoverning Board in October. Additional input was solicited from each Board member
and we met as a large group in Napa Valley, California, on 12–13 December, just prior to
the AGU. Additional invitees to this meeting were Werner Gurtner (AstronomicalInstitute, University of Bern/AIUB), Gordon Johnston (RACAL), David Simpson(Incorporated Research Institutions for Seismology/IRIS), and Pascal Willis (Institut
Géographique National/IGN).
This was a very good meeting with refinement of the strategies and identification ofactions that need to be taken over the next few years. The next steps are to complete themeeting summary and develop the draft document of the strategic plan by March. The
Governing Board plans its next meeting in conjunction with the European GeophysicalSociety (EGS) in Nice, France, on 25 March 2001. The document will be reviewed andthe IGS hopes to make a future presentation to the International Association of Geodesy(IAG) Executive Committee and gain approval of the plan.
The strategic plan discussions resulted in a broadening of the stated missions of the IGS
specifying our “long-term commitment to provide the highest quality global navigation
satellite systems data and products,” reflecting IGS inclusion of GLONASS and future
global navigation satellite systems (GNSS) such as Galileo into the IGS GPS
infrastructures.
Much discussion centered on consideration of the establishment of the IGS as an“official” or legal international entity, the benefits of such action, and how this could
improve the ability of the IGS to conduct its tasks. Recommitment to IGS participation isenvisioned and strategies for stabilizing and acquiring agency sponsorships will be
explored.
Two key strategies identified by the Board include that the IGS affirms to continuously
provide users with the highest quality, reliable data and products in a readily accessible

4

IGS Governing Board in 2000

manner and to achieve worldwide acceptance of IGS products as the “world standard” fordata and products — the provider of choice.
These two strategies address the vital interest in keeping the IGS on the leading edge ofthis technology and encouraging broader recognition and use of IGS data products. Thisis especially important with regards to the global reference systems and the utility of GPS
and GLONASS to provide access to the international terrestrial reference frame. Of
course, many other issues and considerations were addressed in addition to these topics.
The detailed plan will be will be made available in the next few months.
IGS Governing Board Business Meeting Summary
On 14 December, following the two days of strategy meetings, the Governing Board met
for its 15th official meeting. The agenda began with a wrap-up of the two-day strategy
session, defining the schedule for completing the documents as described above.
A pivotal event this past year was the decision by Tim Springer to resign his position as
Analysis Center Coordinator. Tim was able to attend the Governing Board meeting andprovided an excellent report on the state of IGS products. He was presented with the IGS
certificate of appreciation, noting his long involvement and commitment to the IGS sincepre-IGS days. The IGS is most fortunate that Prof. Beutler and his staff at the Universityof Bern were able to provide an excellent candidate as Tim’s replacement, Prof. RobertWeber. The Analysis Center representatives and the Governing Board unanimously
accepted Robert. This demonstrates Bern’s remarkable commitment to complete the next
two years of the Analysis Center Coordinator term. Many thanks again to AIUB for thisperfect solution. Robert, in his new position, was also welcomed to the Governing Board
and will represent the IGS on analysis issues. Tim was congratulated on his new position
with wishes for success being expressed by the Board.
The issue concerning data centers for the IGS was also discussed at length, while noting
the increased pressure on the data flow and access as a result of IGS sub-daily “ultra”
products and moving closer to real-time processes. It was agreed that a solution must be
found to ensure redundant capabilities and provide more efficient and timely access by
the Analysis Centers to network data. Carey Noll agreed to work with the Analysis
Center Coordinator and the Central Bureau to redefine data center requirements andprocesses. The IGS components and the Governing Board will review this in 2001 in
anticipation of acquiring additional data centers and realizing enhancements at ourexisting data centers.
The remainder of the time was devoted to the IGS working groups and pilot projects. The
current projects of the IGS are:•

IGS/BIPM Precise Time and Frequency Project — Jim Ray, U.S. Naval
Observatory and Felicitas Arias, Bureau International des Poids et Mesures,
Co-Chairs•

LEO Pilot Project — Mike Watkins, Jet Propulsion Laboratory, Chair

5

IGS 2000 Technical Reports•

Ionosphere Working Group — Joachim Feltens, European Space Operations
Center, Chair•

Atmospheric Working Group — Gerd Gendt, GeoForschungsZentrum, Chair•

Reference Frame Working Group — Remi Ferland, Natural Resources
Canada, Chair•

International GLONASS Service Pilot Project (IGLOS PP) — Jim Slater,
National Imagery and Mapping Agency, Chair

According to IGS policy, each working group must be reviewed every two years todetermine its status and continuance or dissolution of the activity. The IGS/BIPM timing
project had been extended through 2001 previously, and the IGLOS-PP was approved at
the June meeting of the Governing Board. All groups provided an update and it was
decided to continue the working groups, with additional technical and organizational
details to be considered at the next Board meetings. Reports on the progress of thesegroups are contained in the IGS Annual Report and in the Technical Reports. Progress is
described generally in the IGS Report series or details may be obtained via the IGS
website (http://igscb.jpl.nasa.gov). The organizational meeting of the IGS LEO Projectwill take place on 6–8 February at GFZ Potsdam; for more information, visit
http://op.gfz-potsdam.de/D1/LEOW/LEOW_index.html.
The Central Bureau noted that, due to budgetary challenges, the finalization of the 1999
report series had been delayed since midsummer, but should be completed very soon,with electronic versions becoming available first.
Mike Bevis and I discussed the formalization of a working group on sea-level monitoringwith continuous GPS measurements at tide gauges and tide gauge benchmarks. This has
been a “seed” initiative of the IGS since the joint Permanent Service for Mean Sea Level(PSMSL)/IGS “Workshop on Methods for Monitoring Sea Level” in 1997 (see theproceedings, subtitled GPS and Tide Gauge Benchmark Monitoring and GPS Altimeter
Calibration, in the “Publications” section at the IGS website). A proposal will be
prepared for the next meeting of the IGS Governing Board. Mike is the responsible chairfor the International Association for the Physical Sciences of the Ocean (IAPSO)
Commission on Mean Sea Level and Tides and has established a website to further
discussion of this activity at http://www.soest.hawaii.edu/cgps_tg. The Sea Level Change
Project (SEAL), carried out by a number of German research institutions —GeoForshungsZentrum Potsdam (GFZ), GKSS Research Center Geesthacht (GKSS), andAlfred Wegener Institute for Polar and Marine Research (AWI). The project will put aconcerted effort into GPS monitoring of global tide gauges. An introduction to thecomplete program can be found at http://op.gfz-potsdam.de/seal/. Additional
recommendations at the meeting were to form two additional committees, reinstate theInfrastructure Committee, and create a new IGS Real Time Working Group.
The next meeting of the Governing Board is scheduled for 25 March 2001 in Nice,
France, during the 26th General Assembly of the EGS.

6IGS Governing Board in 2000

One further note — it was decided to plan the next IGS workshop based on a theme as
opposed to having separate analysis and network workshops. This is tentatively plannedfor early in 2002. Proceedings from the Network workshop in Oslo in July 2000 and theAnalysis Center workshop at U.S. Naval Observatory in September will be published andavailable in spring 2001. The Network Workshop proceedings will be published by
Elsevier in the peer-reviewed journal publication Physics and Chemistry of the Earth; theAnalysis Center workshop proceedings will be published by the GPS Solutions journal.
Important IGS-related events and influences in 1999 and 2000
1999
9–11 March

Low-Earth Orbiter Workshop, Potsdam, Germany

8–10 June

Analysis Center Workshop, La Jolla, California

July

International Union of Geodesy and Geophysics General
Assembly, Birmingham, UK

27 July

12th IGS Governing Board Meeting, Birmingham, UK

AugustIGS Adopts ITRF97

15 August

GPS Week Roll-over

13 December

13th IGS Governing Board Meeting

2000
January

Call for Participation in IGS Low-Earth Orbiter Project announced

2 May

Selective Availability – removed!

March

IGS Tutorials in Capetown and Hartebeesthoek, South Africa

27 April

AFREF Planning Meeting, Nice, France

June

14th Governing Board Meeting, USNO, Washington, DC

12–14 JulyIGS Network Workshop, joint with COST 716: “Towards
Operational Meteorology,” Oslo, Norway

15 July

Successful CHAMP launch

13–14 September

IGS Strategic Planning Committee meets in Frankfurt, Germany

19–22 September

Institute of Navigation GPS2000 Annual Meeting, Salt Lake City,
Utah; IGS User Forum conducted

25–29 September

IGS Analysis Center Workshop, USNO; two days devoted to the
IGS-BIPM Precise Time Transfer Project7

IGS 2000 Technical Reports

8

IGS Central Bureau - Status in 2000

IGS Central Bureau - Status in 2000
Ruth Neilan
Jet Propulsion Laboratory,
Pasadena, California

Introduction
After the quiet and uneventful passage of “Y2K,” the year 2000 for the Central Bureau
was marked by significant outreach for the IGS organization, as described below. The
IGS exhibit display and materials were completely redesigned to reflect the continuous
IGS technical advancements and growth of projects. The exhibit is easily transportableand quite cost effective. The IGS tutorial, first developed in 1999 for the International
Symposium on GPS (GPS99 Tsukuba) was revised, updated, and integrated into a single
document available both as hardcopy and via the IGS website. The tutorial is an
important tool for promoting the straightforward use of IGS data and products andoutlines the IGS conventions as the accepted international standard.
A key task of the Central Bureau was the support for the organization of the IGS strategicplanning committee, as addressed by Christoph Reigber in this Annual Report. The
Central Bureau worked to prepare materials with the very experienced facilitator, Haig
Bazoian, to organize interim documents, as well as managing the logistics for the various
meetings of the planning groups and the Governing Board throughout the year. One of
the factors resulting from the planning process is a critical consideration of theorganization, staffing, and resources of the Central Bureau, and how this should be
structured to properly support the IGS in the future. Resource issues of the Central
Bureau delayed the publications of the 1999 and 2000 report series; however, the issues
have largely been resolved at present and these important annual records should resume
normal preparation and publication schedules.
The Central Bureau was very much involved in the preparation of the Call for
Participation in the Low-Earth Orbiter (LEO) Pilot Project, as described in the reports by
Christoph Reigber and Mike Watkins (this Annual Report). This is an IGS project withappropriate structure involving every component of the IGS (station, data centers,
analysis centers, etc.). This activity is expected to have a significant effect on the IGS andto bring substantial enhancements technically and in terms of broadening partnerships.
IGS Outreach and Tutorial
The new IGS booth was first displayed in March 2000 at Capetown, South Africa, at the28th International Symposium on Remote Sensing of the Environment entitled“Information for Sustainable Development.” The IGS sponsored a tutorial during thevenue of this symposium hosted by Richard Wonnacott, Director of Survey Services,9

IGS 2000 Technical Reports

Chief Directorate of Surveys and Mapping, and Prof. Charles Merry, University ofCapetown. The following week, the tutorial was again offered outside of Johannesburg at
the Hartebeesthoek Radio Astronomy Observatory (HARTRAO) hosted by Ludwig
Combrinck. HARTRAO is recognized as a fundamental station for geodetic positioning,where a number of techniques are collocated: very long baseline interferometry (VLBI),
Global Positioning System (GPS), satellite laser ranging (SLR), and precise range andrange-rate experiment (PRARE). The tutorial was well received in both locations andthere was valuable feedback from attendees for making the IGS products more accessible
to the user community. The IGS tutorial and product details were updated after theremoval of selective availability on 2 May .
Expanding Partnership of IGS
The Chinese Seismological Bureau (CSB) is the designated project head for the Crustal
Motion Observation Network of China (CMONOC), a newly implemented state-of-theart national GPS network collocated with their existing seismic network. The CMONOC
sent a letter to the Governing Board outlining their intention to participate in the IGS. The
Governing Board responded very favorably to this with hopes to develop significant
collaboration with CMONOC and its contributing organizations, while pursuing an open
data policy as advocated by IGS values. Discussions with the CSB took place in China
during January, where the U.S. National Science Foundation coordinators delegation
negotiated the renewal of the 20-year U.S.–China protocol agreement on earthquake
science research.
AFREF
A meeting on developing and implementing an African Reference System (AFREF), washeld in Nice, France, organized by Claude Boucher as head of the International
Association of Geodesy (IAG) Commission X devoted to Global and Regional Geodetic
Networks. About 13 people attended, including representatives from and United Nations
Food and Agricultural Organization (UN–FAO), the IGS Central Bureau, the Norwegian
Mapping Authority, the European Reference Frame (EUREF), Sistema de Referencia
Geocéntrico para América del Sur (SIRGAS), and the U.S. National Imagery and
Mapping Agency. Lamentably, none present were African due to the ad hoc nature of themeeting. A meeting is expected to occur in Africa to encourage broad-based African
participation in generating a project plan and structure. An e-mail list service wassubsequently established by the Central Bureau to facilitate contacts between IAG, IGS,
Africans, and people from the global community interested in such an activity. The IGS
and International Earth Rotation Service (IERS), as IAG services and with IAG
endorsement, have pledged strong support. It was noted that GPS is a truly viable andsustainable technology that can be adopted by the African organizations and maintainedin the future for continental and national infrastructures. The Central Bureau has been
invited to the Congress on South African Surveyors Meeting (CONSAS) to be held inMarch 2001 in Capetown where an AFREF planning meeting will be conducted. A
regional realization based on IGS conventions may be the more practical approach given
the numerous nations within Africa and the extensive infrastructure of the IGS. A

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IGS Central Bureau - Status in 2000

previous activity known as ADOS (African Doppler Survey) was initiated in 1981 andbased on the TRANSIT satellite system. This was organized within the IAG International
Coordination of Space Techniques of Geodesy and Geodynamics (CSTG), in cooperation
with the IAG Commission for Geodesy in Africa.
International Geodynamics Research Center in Kyrgyz Republic
In June 2000, a dedication of the International Research Center–Geodynamic Proving
Ground (IRC-GPG), took place in Bishkek, Kyrgyz Republic, followed by a four-day
workshop on the geodynamics of the Tien Shan. This occasion was to dedicate newfacilities collocated with the scientific station research facility of the Institute of High
Temperatures, Russian Academy of Sciences (IVTAN). It was well attended by theinternational science community. The purpose of the new center is to facilitate not only
regional but international collaborative research in geodynamics. Since 1992, a GPS
network has been established through collaborations with Indiana University and
Massachusetts Institute of Technology, consisting of more than 300 stations in the region
and an impressive nine-station permanent GPS network. Two of these stations arerecognized as global stations of the IGS and therefore of great importance for analysis
and global network stability. One of these is located at IRC-GPG and known as the
Poligan GPS station, and one is at Selezaschita, Almaty, Kazakhstan. A subsequentgeological field trip included exploring various locations, some measured by GPS,revealing the intriguing geology and spectacular beauty of the Tien Shan region. The
facility was the vision of Yuri Trapeznikov, former director of the IVTAN scientificstation. The IRC-GPG was presented an IGS certificate of appreciation for outstanding
contributions. For more information on this center and its activities see
http://tiger.gdirc.ru/irc/ or http://helios.gdirc.ru/.
Workshops
Network Workshop
The second major IGS Network Workshop was hosted by the Norwegian Mapping
Authority, 10–14 July 2000 in Oslo, Norway. The purpose of this workshop was to focus
on aspects of the network targeted at improving the infrastructure and network operations
in support of the quality and timeliness of IGS products. Angelyn Moore, IGS Network
Coordinator and Deputy Director of the IGS Central Bureau at the Jet Propulsion
Laboratory in Pasadena, California, convened this workshop, which was considered agreat success by all who attended. The local organization and logistics were excellently
managed by the Norwegian Mapping Authority’s Hans-Peter Plag, within the Geodesy
Division under the direction of Bjorn Engen, a member of the IGS Governing Board. The
workshop was held at the beautiful Soria Moria Hotel on a hill overlooking Oslo andprovided a unique atmosphere enjoyed by all, which will be long remembered.
This was the first occasion that the IGS Network Workshop was convened as amultidisciplinary meeting. It was co-organized with “COST Action 716”– “European
Cooperation in the Field of Scientific and Technical Research.” Action 716 is

11

IGS 2000 Technical Reports“Exploitation of Ground-Based GPS For Climate and Numerical Weather Prediction
Applications.” COST is a framework for scientific and technical cooperation, allowing
the coordination of national research on a European level. The main objective of COST
716 is assessment on an international scale of the operational potential for exploiting
ground-based GPS networks to provide near real-time observations for numerical weather
prediction and climate applications. In parallel, the IGS has a dedicated Tropospheric
Working Group estimating total zenith path delays (ZPD) and precipitable water vapor(PWV) at a number of the IGS stations (see Gerd Gendt’s report in this Annual Report).
Also, a number of the IGS agencies and their networks have either implemented or are
moving towards real-time processing activities, many pursuing similar applications interms of ground-based meteorology.
The Network workshop proceedings were published in the peer reviewed journal
publication Physics and Chemistry of the Earth by Elsevier.
Analysis Center Workshop and IGS/BIPM Precise Time and Frequency Project
The IGS Analysis Center Workshop 2000 was held in September at the U.S. Naval
Observatory, where Jim Ray and his USNO Earth Orientation Department colleagues did
an outstanding job in organizing and hosting this superb workshop. This was a very goodoccasion for many interesting presentations and fruitful discussions. The first two days
were devoted to the IGS/BIPM Timing Project (see Jim Ray’s account in this Annual
Report). The remaining days focused on IGS near-real-time products and theirapplications, and the potential interactions between the IGS and various Global
Navigation Satellite Systems (GNSS, e.g., GPS, Galileo, GLONASS). A subset of thepresented papers has been published as a special issue of the journal GPS Solutions.
The next IGS workshop will be based on the theme “Towards Real-Time” and will behosted by the Natural Resources Canada Geodetic Division. This will be acomprehensive IGS workshop addressing all components, projects, and working groups.
It is planned for early 2002.

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IGS

A N A L Y S I S

C E N T E R

R E P O R T S

2000 Analysis Coordinator Report

2000 Analysis Coordinator Report
R. Weber, T.A. Springer
Astronomical Institute, University of Berne, Switzerland
Institute of Geodesy and Geophysics, Austria

Introduction
Similar to the year before this report complements the Analysis Activities Report given in
the IGS Annual Report 2000 (Weber, Springer, 2001). A summary of the most importantchanges and topics of the IGS Analysis Activities in 2000 will be presented,
complemented by a huge number of figures focusing on the combination statistics oforbits, clocks and ERPs. Most of this figures are freely accessible and can be retrieved
from the IGS ACC web-page at http://www.aiub.unibe.ch/acc.html.
Current IGS and AC product quality
The primary objective of the IGS is to provide a Reference System for a wide variety of
GPS applications. To fulfil this role the IGS produces a large number of different
combined products which constitute the practical realization of the IGS Reference
System. Table 1 gives a brief overview of the estimated quality of these different IGS
Reference Frame products at the beginning of the year 2001.
Table 1: Quality of the IGS Reference Frame products as of March 2001 (for details see
http://igscb.jpl.nasa.gov/components/prods.html)
Products
Delay

Orbit
Clock
Polar Motion
LOD
Stations h/v
Troposphere

Predicted
Real Time

50.0
150.0
(note: deliveryof IGP–products
terminated in
March 2001)

UltraRapid
Real
Time
25.0
5.0

Rapid
17 hours

Final
13 days

Units

5.0
0.2
0.2
30.0

< 5.0
0.1
0.1
20.0
3.0/6.0
4.0

cm
ns
mas
µ s/d
mm
mm ZPD

The quality improvement of the IGS products since 1994 has been demonstrated in the
IGS Annual Report 2000. Figure 1 shows the weighted orbit RMS (WRMS) of the Final
Analysis Centre solutions with respect to the combined IGS final orbit products in 2000.
Most Analysis Centres and also the IGS rapid orbit products have reached the 3-6
centimeter orbit precision level (Table 2). Similar levels of accuracy are indicated by the
IGS 7-day arc orbit analysis and by comparisons with satellite laser ranging observationsof the GPS satellites PRN 5 and 6. Figure 3 is related to the IGS rapid orbit combination.
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IGS 2000 Technical Reports

The orbit consistency is about 5-8 cm, which is a quite small number having in mind thelatency of only 17 hours and subsequently the lower amount of available tracking data.
The yearly averages of weighted orbit RMS values of the Rapid Analysis Centre
submissions with respect to the IGS Rapid combination (IGR) are also shown in Table 2.
Table 2: Yearly average weighted orbit RMS (cm) of the Final Analysis Center orbit
submissions and the IGS Rapid (IGR) orbit solution with respect to the IGS final orbits +Yearly average weighted orbit RMS (cm) of the Rapid Analysis Center submissions withrespect to the IGS Rapid orbit combination.
Year
COD
Fin 2000
3
Rap2000
5

EMR
7
14

ESA
6
9

GFZ
3
6

JPL
3
9

NGS
9
12

SIO
5
7

IGR
3
--

Figures 6-20 illustrate the time series of Helmert Transformation Parameters between theindividual center submissions and the combined orbits, both for the Final and the Rapid
IGS orbit.
Reference Frame
The most striking change in the implementation of the reference frame was the alignmentof the IGS final orbit products to the IGS reference frame realization (based on a set ofabout 50 stations), starting with GPS week 1051. IGS reference frame products areavailable in SINEX format and issued by the IGS Reference Frame Coordinator on a
weekly basis. The alignment ensures product consistency but delays the calculation anddistribution of the combined orbits for an additional day (13 days after end of GPSweek). Detailed information may be inferred from (Kouba, Ray and Watkins, 1998),(Ferland, 2001) or from the weekly IGS Sinex Combination Reports (e.g. Ferland,
Hutchison, 2001). The IGS realization of the ITRF97 has been labelled IGS97. An updateof the ITRF (ITRF2000) and subsequently for the accompanying IGS realization (IGS00)
is planned for end of December 2001.
Ultra Rapid Products
In September 2000 the IGS Analysis Center workshop was held at the U.S. Naval
Observatory in Washington D.C. Current progress in carrier phase time transfer and therealization of an internal IGS time scale had been identified as major goals in thismeeting. Furthermore, as proposed in a position paper by G.Gendt et al. the year before,
IGS products have to move towards real-time availability. Thus this workshop discussed
the quality of the recently implemented Ultra-Rapid products as well as theirapplications, e.g. for the derivation of ground-based GPS meteorological parameters usedin numerical weather prediction.
In October 1999 the first Analysis Centre (GFZ) provided the new ultra rapid products.
These products, delivered every 12 hours (two times per day), will contain a 48 hour orbit
arc from which 24 hours are real orbit estimates and 24 hours are orbit predictions. The

16

2000 Analysis Coordinator Reportlatency of this product is 3 hours. The generation of a combined ‘ultra-rapid’ product(IGU) has started in March 2000 based on contributions from up-to five different
Analysis Centres. This product has been made available for real-time usage, like the IGS
predicted orbits (IGP), but the quality is significantly better because the average age ofthe predictions was reduced from 36 to 9 hours. The next months the quality and thereliability of the IGS Ultra rapid (IGU) orbits were assessed against the IGS Predicted(IGP) and the IGS Rapid (IGR) products. Figure 5 shows a consistency of the individual
orbit submissions at the 25 cm level during the year 2000 and figures 21-27 deliver the
related series of Helmert Transformation Parameters with respect to the IGS Rapid orbits.
Currently seven different Analysis Centres deliver contributions to the ultra-rapid
products.
In November 2000 the IGU products became an official IGS product and subsequently
the submission of predicted orbits (IGP) could be terminated in March 2001 (Wk 1105).
Figures 28a,b show the year-2000 time series of Helmert Transformation Parameters of
the IGS Predicted Orbits with respect to the IGS Rapid orbits.
Clock Combination
A new station and satellite clock combination, which is based on the RINEX clock
format, has been implemented in November 2000 (about Wk 1088). This combination
provides the regularly combined satellite clocks in the orbit (SP3) format and it also
provides both satellite and station clocks in the RINEX clock format. These clock
products have a sampling rate of 5 minutes, compared to the 15 minutes in SP3. Some
Analysis Centres even provide higher sampled clock products, e.g., JPL provides clocks
with a sampling rate of 30 sec. The new clock combination is distinguished by the highquality of the provided clocks and it has improved the robustness of the combination
process tremendously by handling clock jumps. Figures 2 (IGS final) and 4 (IGS Rapid)
illustrate impressively the considerable improved consistency of the submitted AC clock
solutions at the 0.1 nsec level after implementation of the new clock combination in week
1088.
Summary and Outlook
Contrary to widely expressed concerns, the increasing ionospheric activity did not reallyharm IGS operations in 2000. Nevertheless, the policy of phasing out an old generation of
GPS-receivers at the IGS sites and their replacement by updated technology has to be
pursued continuously.
Logically the goal of IGS analysis groups is to further improve accuracy and consistencyof IGS products. Besides these ongoing efforts there are a few special challenges like theclarification of remaining radial orbital biases with respect to orbit determination of GPS
satellites based on SLR tracking data. Another challenge is of course the complete
integration of GLONASS tracking data into IGS operations and analysis.

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IGS 2000 Technical Reports

On July 15, 2000 the ‘Challenging Minisatellite Payload for Geophysical Research andApplication (CHAMP)’ has been launched. CHAMP and the number of upcoming LEO
missions have the potential to fundamentally increase the demands on IGS-products as
we know it today. In this context the generation of more frequent IGS products for nearreal-time use is an urgent need. Near real time products as well as orbit predictions arealso a topic in view of the increasing number of RT surveying applications. Therefore thenext IGS Analysis workshop in Ottawa is dedicated to real-time requirements and IGS
real-time products.
Last but not least its my pleasure to acknowledge my predecessor Tim A.Springer, wholeft the position of an IGS AC Coordinator in December 2000 for his efforts and his
continuous support. He was heavily involved in most of the activities described above,
especially in establishing the new clock combination and in launching smoothly the Ultra
Rapid Products.

References
Ferland, R. (2001). IGS Reference Frame Coordination and Working Group Activities, in
IGS Annual Report 2000,pp. 24-27.
Ferland, R., D. Hutchison (2001).
IGSREPORT-8898, Wk 1144 IGS SINEX Combination.
Kouba, J., J.R. Ray and M. Watkins (1998). IGS Reference Frame Realisation, inProceedings of the 1998 IGS Analysis Center workshop, pp. 139-172.
Springer, T.A., J.F. Zumberge, J. Kouba (1998). The IGS Analysis Products and theConsistency of the Combined Solutions, in Proceedings of the 1998 IGS Analysis
Center workshop, pp. 37-54.
Weber, R., T.A. Springer (2001). Analysis Activities, in IGS Annual Report 2000,
pp. 14-17.

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2000 Analysis Coordinator Report

Figure 1: Weighted orbit RMS(mm) of the Final AC submission w.r.t the IGS Final combination.

Figure 2: Weighted clock RMS(ns) of the Final AC submission w.r.t the IGS Final combination.

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IGS 2000 Technical Reports

Figure 3: Weighted orbit RMS(mm) of the Rapid AC submission w.r.t the IGS Rapid
combination The daily RMS values of the combination summaries were smoothed forplotting purposes, using a sliding 7 day window.

Figure 4: Weighted clock RMS(ns) of the Rapid AC submission w.r.t the IGS Rapid combination.
The daily RMS values of the combination summaries were smoothed for plotting
purposes, using a sliding 7 day window.

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2000 Analysis Coordinator Report

Figure 5: Weighted orbit RMS(mm) of the Ultra Rapid AC submission w.r.t the IGS Ultra-Rapid
combination The RMS values of the combination summaries (twice per day) weresmoothed for plotting purposes, using a sliding 7 day window.

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IGS 2000 Technical Reports

Figures 6a,b: Daily Transformation parameters of the COD Final orbits w.r.t. the IGS
Final orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

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2000 Analysis Coordinator Report

Figures 7a,b: Daily Transformation parameters of the EMR Final orbits w.r.t. the IGS
Final orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

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IGS 2000 Technical Reports

Figures 8a,b: Daily Transformation parameters of the ESA Final orbits w.r.t. the IGS
Final orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

24

2000 Analysis Coordinator Report

Figures 9a,b: Daily Transformation parameters of the GFZ Final orbits w.r.t. the IGS
Final orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

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IGS 2000 Technical Reports

Figures 10a,b: Daily Transformation parameters of the JPL Final orbits w.r.t. the IGS
Final orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

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2000 Analysis Coordinator Report

Figures 11a,b: Daily Transformation parameters of the NGS Final orbits w.r.t. the IGS
Final orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

27

IGS 2000 Technical Reports

Figures 12a,b: Daily Transformation parameters of the SIO Final orbits w.r.t. the IGS
Final orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

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2000 Analysis Coordinator Report

Figures 13a,b: Daily Transformation parameters of the IGS Rapid orbits w.r.t. the IGS
Final orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

29

IGS 2000 Technical Reports

Figures 14a,b: Daily Transformation parameters of the COD Rapid orbits w.r.t. the IGS
Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

30

2000 Analysis Coordinator Report

Figures 15a,b: Daily Transformation parameters of the ESA Rapid orbits w.r.t. the IGS
Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

31

IGS 2000 Technical Reports

Figures 16a,b: Daily Transformation parameters of the GFZ Rapid orbits w.r.t. the IGS
Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

32

2000 Analysis Coordinator Report

Figures 17a,b: Daily Transformation parameters of the JPL Rapid orbits w.r.t. the IGS
Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

33

IGS 2000 Technical Reports

Figures 18a,b: Daily Transformation parameters of the NGS Rapid orbits w.r.t. the IGS
Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

34

2000 Analysis Coordinator Report

Figures 19a,b: Daily Transformation parameters of the SIO Rapid orbits w.r.t. the IGS
Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

35

IGS 2000 Technical Reports

Figures 20a,b: Daily Transformation parameters of the USN Rapid orbits w.r.t. the IGS
Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 1 mas.

36

2000 Analysis Coordinator Report

Figures 21a,b: Daily Transformation parameters of the COD Ultra Rapid orbits w.r.t. the
IGS Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 2
mas.

37

IGS 2000 Technical Reports

Figures 22a,b: Daily Transformation parameters of the EMR Ultra Rapid orbits w.r.t. the
IGS Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 2
mas.

38

2000 Analysis Coordinator Report

Figures 23a,b: Daily Transformation parameters of the ESA Ultra Rapid orbits w.r.t. the
IGS Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 2
mas.

39

IGS 2000 Technical Reports

Figures 24a,b: Daily Transformation parameters of the GFZ Ultra Rapid orbits w.r.t. the
IGS Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 2
mas.

40

2000 Analysis Coordinator Report

Figures 25a,b: Daily Transformation parameters of the JPL Ultra Rapid orbits w.r.t. the
IGS Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 2
mas.

41

IGS 2000 Technical Reports

Figures 26a,b: Daily Transformation parameters of the SIO Ultra Rapid orbits w.r.t. the
IGS Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 2
mas.

42

2000 Analysis Coordinator Report

Figures 27a,b: Daily Transformation parameters of the USN Ultra Rapid orbits w.r.t. the
IGS Rapid orbits. Translations are shifted by 50 mm, Rotations are shifted by 2
mas.

43

IGS 2000 Technical Reports

Figures 28a,b: Daily Transformation parameters of the IGS Predicted orbits w.r.t. the IGS
Rapid orbits. Translations are shifted by 100 mm, Rotations are shifted by 10
mas.

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2000 Analysis Coordinator Report

Figure 29: Daily AC Final x-Pole Differences w.r.t. the IGS Final x-Pole.
ACs are shifted by 1 mas.

Figure 30: Daily AC Final y-Pole Differences w.r.t. the IGS Final y-Pole.
ACs are shifted by 1 mas.

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IGS 2000 Technical Reports

Figure 31: Daily AC Final x-Pole-rate Differences w.r.t. the IGS Final x-Pole-rates.
ACs are shifted by 3 mas/day.

Figure 32: Daily AC Final y-Pole-rate Differences w.r.t. the IGS Final y-Pole-rates.
ACs are shifted by 3 mas/day.

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2000 Analysis Coordinator Report

Figure 33: Daily AC Final LOD Differences w.r.t. the IGS Final Pole.
ACs are shifted by 0.2 ms/day.

Figure 34: Daily AC Rapid x-Pole Differences w.r.t. the IGS Final x-Pole.
ACs are shifted by 1 mas.

47

IGS 2000 Technical Reports

Figure 35: Daily AC Rapid y-Pole Differences w.r.t. the IGS Final y-Pole.
ACs are shifted by 1 mas.

Figure 36: Daily AC Rapid x-Pole-rate Differences w.r.t. the IGS Final x-Pole-rates.
ACs are shifted by 3 mas/day.

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2000 Analysis Coordinator Report

Figure 37: Daily AC Rapid y-Pole-rate Differences w.r.t. the IGS Final y-Pole-rates.
ACs are shifted by 3 mas/day.

Figure 38: Daily AC Rapid LOD Differences w.r.t. the IGS Final Pole.
ACs are shifted by 0.2 ms/day.

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50Current State of IGS Analysis: Quality Assessment

Current State of IGS Analysis: Quality Assessment
Thomas Herring 1) and Tim Springer2)
1) Massachusetts Institute of Technology,
77 Massachusetts Avenue,
Cambridge, MA 02139 USA
e-mail: tah@mit.edu
2) Astronomical Institute
University of Bern,
Sidlerstrasse 5
CH-3012 Bern / Switzerlande-mail: tim.springer@aiub.unibe.ch
Abstract
In this paper we examine the current state of the IGS analysis of GPS data and the needsof users. Since the initial sessions of the meeting examine near real-time analysis issues,
we will examine the conventional IGS products. We will examine the needs of users forknowing the quality of both IGS products, and more fundamentally the quality of
individual satellites and stations in the IGS network. There already exists a number ofmethods that can be used to assess IGS quality and we will review the contents of these
existing mail, ftp, and web sites. We will consider how best to report marginal satellites
and sites to users particularly in the form of interactive web based tools that could be
developed, and how to integrate the existing information into a coherent assessment toolfor users.
Introduction
The International GPS Service generates products from the analysis of GPS data that are
made available through international data centers. The primary IGS data center is locatedat the Goddard Space Flight Center in Greenbelt, Maryland (cddisa.gsfc.nasa.gov). The
products are stored in directories, accessible with anonymous ftp, with names of the form
gps/products/[WWWW] where [WWWW] is the GPS week number. The current IGS
products are (a) orbits for the GPS satellites that are available in three forms: final orbits;
rapid orbits; and predicted orbits, (b) Earth orientation parameters, (c) tropospheric delay
estimates, and (d) combined terrestrial reference frame SINEX files, one for the week andthe other an accumulation to the week. In addition to the products themselves there aremany summary and log files that contain a wealth of information about the products if thecorrect files are examined. In addition to these official products, there are other products
in development that are available but are not deposited in the standard IGS product areas.
These include satellite and ground receiver clock estimates, ionospheric delay maps, andcombined GPS/GLONASS analyses. In this paper, we will discuss mainly the quality ofthe official products.

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IGS 2000 Technical Reports

Within the area of quality we will consider timeliness and accuracy. For accuracy, weneed to consider not only the accuracy of the products but also the quality of the data
input to the analyses. In the latter area, we consider not only the GPS stations andreceivers but also the satellites. In addressing these issues we also consider the needs ofthe users. We start the discussion, with user needs and then consider timeliness andaccuracy.
User Needs
There has not been a recent widespread survey of the users of the IGS products but based
the activities of the research community the main uses of the IGS products are reasonably
clear. Probably the most used IGS products are the orbit files, although for volume ofdata transferred, the RINEX files from the IGS stations are the largest. The Earthorientation parameter (EOP) files are also widely used by the International Earth Rotation
Service (IERS) but because the IGS orbits are distributed in an Earth fixed frame, theEOP parameters are not necessarily needed for processing GPS data. As users become
more aware of the availability of the new IGS combined SINEX files, their use should
increase for tectonic studies. The ways the tropospheric delay files are used is not clear
at the moment although most likely these are used to evaluate the utility of these types ofdata in meteorological forecasts. Since these files are currently only available about 4weeks behind real-time, their latency is too large to be of use in forecasting. The clock
estimates are being studied by the international timing community as a means oftransferring time globally with sub-nanosecond accuracy. We will concentrate here on
the needs of users for precise positioning using IGS products and data. We will alsoemphasize that the IGS supports the research community and because all of the major
GPS analysis programs are used by the IGS analysis centers, the IGS provides a natural
framework for making significant improvements to accuracy of GPS results. Such
improvements are very evident when the evolution of quality of GPS results is examinedover the last decade.
Timeliness
For many users, the timeliness of products is important. For groups working near realtime this is particular important. But also many geophysical researchers who operatecontinuous GPS networks want results to be available at known times so that they can be
sure that their processing can be done in autonomous fashion. To evaluate the timelinessof the IGS orbit products we examined the difference between the product date and thetime-stamp on the file at the cddisa.gsfc.nasa.gov data center. We did this for files fromlate 1998 to the current date. (We can’t use this technique to go back too far in time
because the file time stamps may have been reset when files are moved between storage
areas). The results are shown in Figure 1 for the IGS final, rapid and predicted orbits.
The two large excursions in the results starting in late July 1999 and the beginning of2000 corresponds to a large disk failure and a particularly difficult Y2K transition,
respectively. Excluding these intervals, the delivery of the IGS final orbit has been very
reliable and generally within 3-weeks of real-time. The rapid and predicted results are
more erratic and some of the excursions here may be due to re-posting of results rather

52Current State of IGS Analysis: Quality Assessment

than date of original transmission. However, if results are re-posted then users working
with these products, in near real-time, would not have the best product at the time.
Probably the most worrisome feature of Figure 1, is the “single-point” failure mode of theresults. The loss of the cddisa data center caused large delays until the use of alternative
data centers was implemented by the IGS analysis center. The IGS should develop moreformal contingency plans for the loss of a data center, and encourage the organizations
that fund the data centers to allocate greater resources to ensure redundancy within thedata centers themselves.

Figure 1: Difference between product date and file stamp for the interval between Oct
18, 1998 and July 2, 2000 shown as a function of GPS week number. The IGS final orbit(black line) is posted once per week, which explains the saw-toothed structure of theresults. The rapid (red curve) and predicted (green curve) are posted daily. For results
prior to Week 1042, the time difference has 1-day resolution of due to the nature of thetime stamps.
Product Quality
There are a number of methods available for assessing the quality of the IGS products
and the contributions of the individual analysis centers. The longest running product of
the IGS is the final orbit of each satellite given in the SP3 format and these files have53

IGS 2000 Technical Reports

accuracy assessments each satellite. In addition, there are summary files that report thequality of each analysis center. Users can assess the accuracy of the products, if theyknow to look in the correct places in the files. However, what is not clear from thesesummaries is why a particular satellite is bad on a given day, and which parts of the orbits
may be good to use for satellites that have thruster firings during the day. It is also not
clear from these summaries, how individual analysis centers can improve their results forpoorly behaved satellites. In particular, there are a group of satellites whose momentum
wheels have either partially or fully failed, and while the list of these satellites is given insome IGS reports, conveniently finding this information is not easy. Efforts to improve
the overall quality of the IGS analysis centers should concentrate on sharing this type of
information and making available likely causes of problems rather than simply reporting(through RMS scatters of results) that a problem exists. These types of studies are carriedout and disseminated in IGS reports by individual centers but what seems to be needed in
more directed access to these results.
The other major effect on the quality of the IGS products is the operation of the GPS
receivers in the network. Problems with receivers and/or the configuration of the stations
are probably one of the greatest issues facing the IGS. In this category there are many
facets that effect both the IGS analysis centers and the users of IGS data. The overall
quality of the IGS data set and position results is impressive. Shown in Figure 2 are
histograms of the RMS scatters of the position estimates from the 67 weeks of the
combined IGS SINEX files after linear trends are removed from the results. The medianRMS scatter for the horizontal components is about 2 mm and for the vertical 6 mm.
The average statistics of the IGS position determinations does not reveal the important
fact that there are failures of some stations that can dramatically effect users if they areusing these stations as the primary link to the IGS reference frame. Also not revealed in
the statistics are the temporal and spatial correlations with the results. Within the IGS
community there are some well-known receiver failures such as the MADR/MAD2
where for almost 3-years the station returned data regularly but the position estimates
showed multi-centimeter scatters. Similarly, near the end of 1996 the WETT site started
to show anomalous position estimates although the RINEX data from the site was not
obviously corrupt. As far as we know, the data from these sites can still be obtained
during these intervals by anyone doing “historical data” processing, nor do the IGS log
files make any mention of the problems with these data during these times.
There are web sites that can be accessed to see the time series either from the IGS
analyses or individual analysis centers. The Jet Propulsion Laboratory site
http://sideshow.jpl.nasa.gov/mbh/series.html shows results from the JPL analysis. The
Scripps Institution of Oceanography (SIO) site http://lox.ucsd.edu shows results from the
SIO analysis. Both of these analyses show daily position estimates. MIT maintains a site
http://www-gpsg.mit.edu/~fresh/MIT_IGS_AAC.html that shows results from different
IGS analysis centers and recently from the IGS combined SINEX file. The IGS
combined results are now updated weekly. This latter site allows results from the
combination and from thee different analysis centers to be overlaid pair-wise. In all thesesites, a possible problem with assessing the quality of data from site is that times when54Current State of IGS Analysis: Quality Assessment

results from are poor, the data is likely not be included in the time series plots. This isparticularly the case when sites are trying to present geophysical results (such as velocity
fields) in addition to the time series. For a user of IGS data, the problem arises that it is
not always clear when results from a site are missing whether this is due to poor quality
data or if, due to communication problems, the data were simply not available in a
sufficiently timely fashion to be included in the IGS analyses. Currently, there is no easy
way for a user to access this information.

Figure 2. Histograms of the RMS scatter of the site position estimates (about a linear
regression) from the weekly IGS combined SINEX files. In North, East and Up the
median RMS scatters are 1.8, 2.0, and 6.2 mm, respectively.
In Figure 3, we show a recent example of the subtle failure of an IGS station and the waythat this can effect IGS analysis (these results can be viewed and obtained from the MIT
IGS web site). (On both the JPL and SIO web sites, the time series end near the55

IGS 2000 Technical Reports

beginning of 2000 although SIO continues to include the site their IGS submissions.)
What has precisely happened at this site is not clear although all three components of thesite position are affected. It is also that the data from the site is not obviously corrupt
especially in early 2000 with the first northward motion where the error bars do notappreciably change size. (The most recent results have larger error bars suggesting thatlarge portions of the data from the site are either not in the RINEX files or are being
deleted during data analysis.) It is also clear that the COD analysis center stopped
processing data from this site although the reason is not clear. Currently there is noformal forum for analysis centers to exchange information about the problematic sites. A
user of data from this site would also find it difficult to know that data from this site wasproblematic.

Figure 3: Recent time series for the North component of the IGS site ZWEN. There
clearly is some failure of the site although it continues to generate results that are
sufficiently high quality to be included in some IGS analysis center submissions.
Examination of all the results from the IGS analyses and other regional analyses such as
the SCIGN array in California show a variety of failure modes of GPS receivers whose
precise origins are rarely clear. In some cases, the reason is known. A specific case is
the IGS SELE in Central Asia. In early 1999, the horizontal coordinates of the site show
erratic daily deviations with amplitudes of 10-20 mm although the quality of the phasedata seemed largely unaffected. The reason for the problem was traced to a loose antenna56Current State of IGS Analysis: Quality Assessment

mounting (the antenna was literally being blown around by the wind). Although many
IGS analysis centers include this station, there was never any report to the station
operator that there was a problem. For many IGS stations, it is not clear that theoperators of the stations process their own data because one of the advantages of being an
IGS station is that your data is processed by the IGS. Currently, there is no formal
feedback mechanism to station operators from the IGS analysis centers. Various sites in
the Southern California Integrated Geodetic Network (SCIGN) have shown failure modes
which appear to be related to water entering antennas and cables. Again, these failuremodes do not necessarily produce obviously corrupt phase data; just the position
estimates can be erratic.
One other class of failure mode is weather related. A number of IGS stations are locatedin regions where snow can accumulate during the winter. Depending in the raydome
configuration, the present of snow near, in and on the antenna can have a dramatic effecton the position estimates. One of the extreme cases in the Antarctic site CAS1 where theheight changed nearly 100 mm over a six-month interval. A visit to the site showed thatthe raydome on the antenna had been damaged and it was replaced. However, careful
examination of date the raydome was replaced shows that the height of the site had
returned to its nominal value about 1-month before the replacement. The implication isthat the anomalous height changes were not due to damage to the raydome but rather due
to snow entering the area through the hole in the raydome. This is a very remote site andso there were no direct observations of the sites at the time the height was anomalous.
The effects of the presence of snow and other corrupting signals can be quantified using
the signal-to-noise ratio (SNR) from the GPS receivers. Standalone software is available(http://www-gpsg.mit.edu/~tah/snrprog) that will read RINEX files with SNR included(e.g., by using the S1 and S2 observable types in the teqc program) and generates
estimates of phase residuals to be expected from interfering signals. This analysis
technique has been very successful at detecting the corrupting effects of the presence ofsnow. It can also show whether an anomalous change in station position is due to thereceiver or to motion of the monument.
Some IGS sites show non-secular position variations whose origin is not clear. One veryclear example is the permafrost site at Yakutsk. This site shows annual deviations in it
north position with peak-to-peak variations of nearly 20 mm. The height shows evenlarger variations. Local measurements to a nearby site on a building have shown thatthese motions are due to the movement (most likely tilting) of the monument in thepermafrost. Again, there is no easy way for a general user of IGS data to know that thissite is problematic. Nearly all IGS sites show annual height variations whose cause is notdirectly known. In some cases, a portion of the movement could be due to atmosphericpressure loading and in other cases they could be due to ground water effects, either
through loading and/or soil expansion and contraction. In many of the IGS log files, theprecise configuration of geologic setting of a site is not given (in other cases, thedescriptions can be quite expansive). As interest in interpreting non-secular motions ofsites increases, there will need to be greater emphasis placed on the configurations ofstations.

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Enhancement of IGS Quality
Fundamentally, the quality of IGS products is controlled by the quality of station andsatellite data used in the analyses. Currently a number of IGS stations yield problematic
data and the characteristics of a number of satellites is less than desirable. Correction ofthese problems or increased dissemination of information about the causes of problems
would increase the quality if IGS analysis and aid users of both the products and data.
A subtler problem is the overall accuracy of the GPS results being currently obtained.
This is a more difficult problem because of the uniqueness of GPS in its temporal
resolution and the overall number of stations. The IGS is at the forefront of developing
standards that allow combination of initially results from different IGS analysis centers
but now also includes results from different techniques. These rigorous combination
procedures are now being investigated by the IERS and possibly in the future the IERS
will the lead operational entity that makes the combinations. Such studies are now intheir infancy but in long run will hopefully provide improvements to all techniques in thesame way that IGS analysis centers have all improved over the last few years. Some
recent combination results of merging VLBI and GPS with internally consistent earthorientation parameters have suggested that the VLBI results may be degraded by the
combination. In examining time series from both systems the indication is that some partof the annual signals seen in GPS results may be artifacts (possibly induced by orbit
modeling errors that have an annual modulation due to the orbital period of the GPS
satellites). However, the assessment is difficult due to the sparse temporal and spatial
coverage of VLBI measurements. Satellite Laser Ranging (SLR) results are starting tobecome available and these data may help clarify the situation.
Conclusions and Recommendations
While the overall quality and timeliness of IGS products is very high, we have somerecommendations that should enhance these characteristics even more.
Timeliness
The IGS is very dependent on its data centers and we recommend that••Formal contingency plans be developed and tested that allow transition between data
centers in the event of a failure of one the centers; andThe funding agencies for the data centers be made aware of their importance and be
encouraged to provide sufficient funds to make the data centers more robust.

58

Current State of IGS Analysis: Quality Assessment

Quality
Since the IGS depends so much on the quality of the data from the IGS stations and theusers of the products depend on these same data, we recommend that
•

•
•
•

The IGS develop plans to have a more positive feedback between the site operators,
the IGS analysis centers, and the IGS product and data users. Such plans, we imagine
would include autonomous system to monitor station quality through both phase andposition quality. When a station appears to be failing the IGS should be proactive incontacting the site operator to ascertain the problem and in informing users of the
problems. A web site, maintained by the central bureau, could have a ranked list ofsites that would be updated at frequent intervals. A historical ranked list should also
be maintained for users that are processing older data.
The IGS data centers should be encouraged to move data files for stations that were
known to be corrupt from the main data areas to other areas where users will be awarethat they use the data at their own risk.
Station operators should be encouraged to make measurements to local reference sites
at sites that are suspected of being unstable and that these local data be madeavailable to the IGS data centers for anyone to process.
The IGS encourage regional data centers to include the SNR in RINEX files. The
impact on the size of the files is about a 10% increase in compressed files. TheseRINEX files can then be used as part of the monitoring system and provide a meansof assessing quickly whether the degradation of site positions is receiver ormonument related.

59

IGS 2000 Technical Reports60

Reference Frame Working Group Technical Report

Reference Frame Working Group Technical Report
R. Ferland
Natural Resources Canada, Geodetic Survey Division456-615 Booth Street, Ottawa, Ontario, Canada.
Tel: 1-613-995-4002; Fax: 1-613-995-3215.
e-mail: ferland@geod.nrcan.gc.ca;
Abstract
Natural Resources Canada’s (NRCan) Geodetic Survey Division (GSD), on behalf of theInternational GPS Service (IGS) and its Reference Frame Working Group, combines aconsistent set of station coordinates, velocities, Earth Rotation Parameters (ERP) andapparent geocenter to produce the IGS official station position/ERP solutions in the
Software Independent Exchange (SINEX) format. The weekly combination includes
solutions from the Analysis Centers (AC), while the Global Networks Associates
Analysis Centers (GNAAC) provides quality control.
The weekly AC solutions include estimates of weekly station coordinates, apparent
geocenter positions and daily ERPs. The ACs also provide separately, satellite orbit andclock estimates as part of their daily products, which are independently but consistently
combined by the IGS AC Coordinator to produce the IGS orbit/clock products. All the
AC products are required to be in a consistent reference frame. The combination of
station coordinates originating from different ACs involves removing all available
constraints and re-scaling the covariance information. The weekly combined station
coordinates are accumulated in a cumulative solution containing estimated station
coordinates and velocities at a reference epoch.
The weekly combination generally
includes estimates of coordinates for
120 to 140 globally distributed
stations. While the cumulative
solution currently includes
approximately 250 stations, about 180(Figure 1) of them have complete
information and reliable velocity
estimates. The IGS combined
products are required to be consistent
Figure 1. Stations in the Cumulative Solution
with the most recent realization of
ITRF (currently ITRF97 (Boucher etal., 1997)). This is done bytransforming the weekly and cumulative solutions, respectively using 7 and 14 Helmert
transformation parameters (3 translations, 3 rotations, 1 scale and their respective rates).
The transformation parameters are determined from a subset of 51 high quality, globally
distributed and collocated (with other space techniques) stations, also known as
Reference Frame (RF) stations.

61

IGS 2000 Technical Reports

Since the beginning of 1996, weekly comparisons with ITRF97 show an accuracy of 3-4
mm horizontally and 10-12 mm vertically. Gradual improvements are apparent. Various
non-random effects are present in the station coordinates time series residuals, such as
periodicities and discontinuities. Equipment, local environment and processing changes
are the causes for a number of discontinuities.
Introduction
The IGS contribution to ITRF can be
subdivided into two main initiatives.
First, the participation of ACs and IGS
in the ITRF solutions and second, therealization and dissemination of ITRF.
The IGS contribution to ITRF2000
consisted essentially in a cumulative
solution that included data between
GPS weeks 0837 and 1088 (96/01/21 –00/11/18). The solution involved 167
Figure 2. IGS stations used to realize
stations distributed as shown above in
ITRF97
Figure 1. The ITRF realization isaccomplished with a station subset of
the IGS network. For the realization of ITRF97, 51 high quality stations were selected(Figure 2) (Kouba et al., 1998). The accessibility to the reference frame is facilitatedthrough the combined “IGS core products” of station coordinates, the Earth Rotation
Parameters and/or the precise orbits, and the satellites/stations clock solutions. The IGS
Reference frame realization of ITRF can be accessed, by GPS users, with the precise
code and phase observations. The IGS participation (IGS stations) and the IGS realization
aspects are very closely related. Data used to realize an IGS ITRF will also be
subsequently contributed to the IERS combination process to generate ITRF at future
epochs.
IGS Participation to ITRF2000
The ITRF2000 combines solutions from a number of space techniques including VeryLong Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Doppler
Orbitography by Radio-positioning Integrated on Satellite (DORIS) and GPS. The IGS
solution was part of a group of about 20 global solutions used for the realization of
ITRF2000. Five other GPS (AC) global solutions were also submitted as well as six
densification solutions.
Between GPS weeks 0837 (96/01/21) and 0977 (98/10/03), the weekly combined
solutions from JPL, MIT and NCL Global Associates Analysis Centers (GNAAC) wereused in the cumulative solution. Since GPS week 0978 (98/10/04), the seven Analysis
Centers (AC) (CODE, ESA, GFZ, JPL, NGS NRCan and SIO) are used in the
combination, while the GNAAC are used to quality control the weekly combination(Table 1).
62Reference Frame Working Group Technical Report

The AC solutions are combined using the least-squares technique. All the available
covariance information between the station coordinates within each AC solution is used.
Since GPS week 1013 (99/06/06) the weekly combination also includes daily ERP (poleposition and rate, calibrated length of day (Mireault et al. 1999)) and since GPS week
0978 (98/10/04) weekly apparent geocenter estimates. The cumulative combination is
updated every week with the latest weekly combination. This cumulative solution
includes station coordinates and velocities for about 250 sites. Of those, about 180 havereliable velocity estimate. The cumulative solution is currently aligned to ITRF97 by
applying a 14-parameter transformation estimated using the set of 51 RF stations. Inner
constraints in origin, orientation and scale (and their rates) are applied to the solution.
Due to the large number of input solutions used and the variety of sources, there are someconcerns for potential numerical instabilities; but, at this time, they appear to be that
under control.
Table 1IGS Analysis Centers (AC)CODE
Center for Orbit Determination in Europe, AIUB, Switzerland
ESOC
European Space Operations Center, ESA, Germany
GFZ
GeoForschungsZentrum, Germany
JPL
Jet Propulsion Laboratory, USA
NOAANational Oceanic and Atmospheric Administration / NGS, USA
NRCanNatural Resources Canada, Canada
SIO
Scripps Institution of Oceanography, USA
IGS Global Network Associate Analysis Centers (GNAAC)
NCL
University of Newcastle-upon-Tyne
MIT
Massachusetts Institute of Technology
JPL
FLINN Analysis Center Jet Propulsion Laboratory
IGS Analysis and Associate Analysis Centers
160

140

Number of Stations

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Figure 3. Number of AC/GNAAC/IGS
stations in the weekly solutions

63

The number of stations contributing toweekly SINEX solutions has increased
steadily since the beginning of IGS. The
number of stations has gone from 25 to 60
stations in 1996 to between 40 and 130
stations currently (Figure 3). There is asignificant overlap between the stations
used by each AC. Out of the 130 stations
actively used in the IGS network, about
95 are used weekly by 3 or more ACs.
Human and computer resource limitations
are the main factors constraining thenumber of stations used by each AC. The
ACs have continuously upgraded theirsoftware and approaches, which has

IGS 2000 Technical Reports

resulted in gradual improvements of their solution results. Ideally, all the processed data
should be done in a consistent manner. But, due to the large quantity of data andprocessing load involved, none of the ACs has yet to complete the reprocessing. On the
hardware side, receiver/antenna, communication and computer technologies have also
progressed, resulting in higher quality data, faster access and processing.

Table 2.
Position
Velocity(mm)(mm/y)
Latitude
1.1
1.8
Longitude
0.9
2.3
Height3.1
5.1
IGS standard deviations (STD) with respect
to ITRF2000

25

Standard Deviation (mm)

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25

20Standard Deviation (mm)The standard deviations of residuals between
the ITRF2000 and the IGS solution aresummarized in Table 2. They show ahorizontal position precision approaching the
1mm level and the vertical component
approaching 3mm. The velocity precision isapproaching 2mm/y horizontal while thevertical component is about 5mm/y. Theseare probably somewhat optimistic, since theGPS solutions in the ITRF2000 combination
used, to a large extent a common set of IGS
stations. As mentioned above, the common
station coordinates are to a large extent
derived from a common set of code andphase measurements.

cod
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Standard Deviation (mm)2014Standard Deviation (mm)

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Figure 4 a-b-c
Latitude, Longitude and Height weekly STD
with respect to Cumulative Combinationncl

Figure 5. AC/GNAAC Station
Coordinates Residuals STD withrespect to the Cumulative Solution64

Reference Frame Working Group Technical Report

The standard deviations of the residuals between the weekly and the cumulative solutions
for all stations have been estimated for each center (AC/GNAAC/IGS). Figure 4 a-b-c
shows the time series of the standard deviations for the latitude, longitude and heightcomponents. The IGS and GNAAC standard deviations are 3-4mm horizontal and 710mm vertical (Figure 5). The ACs are also generally close to that level. Also noticeable
is the gradual improvement of the statistics, especially in the height component (Figure4c). The bandwidth of the standard deviations is also decreasing, indicating a better levelof agreement between the various solutions. Similar improvements have been reported
for the precise orbit/clock combinations also done weekly by the IGS AC Coordinator(http://www.aiub.unibe.ch.acc.html).

6530

Residuals (mm)

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Residuals (mm)At the station level, a detailed look at theresidual position time series shows thelonger-term systematic effects present atsome stations. For example, Figure 6 a-b-c
shows residuals of the weekly
AC/GNAAC/IGS solutions with respect tothe cumulative solution for the latitude,
longitude and height components at station
Penticton (DRAO). An annual period withamplitude of about 7mm is noticeable in
the height component. Some periodic
effects can also be seen in the longituderesiduals. The level of agreement among
the AC’s also improves with time. The
RMS of the residuals for the
AC/GNAAC/IGS are respectively(Lat:5.4/2.4/2.4, Lon: 5.3/2.7/2.7, Hgt:
8.2/5.7/5.4). This station shows a rather
large periodic signal (although not thelargest). Most stations have little or no
significant periodic signal. This periodic
effect is possibly caused by variations inseasonal atmospheric pressure loading,which are not currently modeled in AC
solutions. A detailed analysis of theperiodic effects will be possible once thereprocessing is completed. Occasionally,
biases do exist between the solutions,
usually in the height component. Those
biases are sometimes caused by incorrectantenna height used in the processing. The
redundant time series are very useful toseparate isolated outliers from ongoingbiases. As part of the reprocessing of the
AC solutions, a number of stations

emr
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Figures 6 a-b-c. Latitude, Longitude andHeight residuals between the weekly andcumulative solutions at station Penticton(DRAO)

IGS 2000 Technical Reports

coordinate residuals time series discontinuities problems have been explained andcorrected. Comparisons done in the past between the weekly and the cumulative solutions
statistics have indicated that 60-70% of the noise is caused by short-term effects, while
the rest has a longer-term signature. Those long-term signatures often take the form of
discontinuities, which tend to affect mainly the height. They are generally caused byeither blunders, equipment or processing changes.
Figure 7 shows height differences
between the IGS and the GNAAC
solutions at station Penticton. The
standard deviation is 3 mm over a
period of about 5 years. Differencesof this magnitude are expected, due
to differences in the processing
strategies of the GNAACs. A small
bias is apparent in the early weeks,a more refined analysis is expected
to explain and potentially correct
this artifact.
The reprocessing of the AC SINEX
Penticton (DRAO) Height differences
solutions between GPS weeks 0837
(IGS-GNAAC)(96/01/21) and 0977 (98/10/03) isFigure 7
currently underway. Two iterations
have at this time been completed. During the first iteration, the most obvious
inconsistencies were removed. Nearly 9000 outliers were flagged. Explanations for manyoutliers could be found, thus allowing for corrective measures to be applied. A second
iteration was run. This allowed to test the validity of the corrective measures applied to anumber of weekly solutions, and to uncover new outliers. The exact number of iterations
required is yet unknown. Once complete, the reprocessing will improve the quality of theweekly and cumulative solutions as well as its consistency and traceability by using aconsistent strategy (Ferland et al. 2000). This reprocessing is using all the available
information provided by the ACs and GNAACs. Each solution (AC/GNAAC) is
unconstrained, its covariance information is rescaled with an estimated variance factor(chi squared per degree of freedom). AC/GNAAC station coordinates estimates arecompared and rejected if they exceed the thresholds of 5 sigmas or 50mm (8 sigmas and
80mm for the first iteration). The residuals in the in the variance factor estimation aredetermined by taking the difference between each AC and the cumulative solution. The
AC and GNAAC solutions are considered independent during the processing. In reality
there is a significant level of correlation between the AC solutions mainly because they
use the same code and phase observations for all the common stations. The differences
between the AC solutions are mainly caused by variations in the processing strategies andthe network distribution. A variance factor is also estimated and applied to the weekly
IGS combination, again by using the cumulative solution as a reference. This should
partially compensate for the neglected correlation between the AC solutions during theweekly solution combination. Similar correlations also exist between the IGS and the
GNAAC weekly solutions. This is somewhat less of a concern, because the GNAAC are
15

Differences (mm)

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66

Reference Frame Working Group Technical Reportused mainly for quality control. The cumulative solution also needs to be rescaled,because the parameters covariance information gradually becomes unrealistically small
as weekly solutions are added. More investigation is required to properly rescale thecumulative solution.
IGS Realization and Dissemination Of ITRF2000
The current IGS realization of ITRF97
has been shown in Figure 2. It includes
51 globally distributed RF stations.
The proposed set of stations to realize
the ITRF2000 is shown in Figure 8. It
currently includes 55 stations. All the
proposed additions/changes are in theSouthern Hemisphere with theobjective to improve the station
distribution. Two new stations areproposed in South America while one
would be removed. Three otherstations are proposed, one on
Ascension Island in the Atlantic Ocean
and one on Diego Garcia Island in the
Indian Ocean as well as one in Australia.

Proposed IGS Stations for the Realizationof ITRF2000
Figure 8

Figure 9, shows the quality of the fit
between the successive IGS/ITRF
realizations and the weekly updated
cumulative solutions in ITRF96,
ITRF97
IGS97
ITRF96
starting with GPS week 0999
(99/02/28). There were already some
improvements between therealization of ITRF96 and theoriginal realization of ITRF97, andfurther improvements were madewith the implementation of the
IGS97. For ITRF96, ITRF97 andWeekly Reference Frame Station Coordinates
IGS97, the horizontal standard
Residuals STD between each Reference Frame
deviations went down from 5-8mm,
Realization and the IGS Cumulative solutions
to 3-4mm and to 1-2mm. In the
Figure 9vertical component they decreased
from 13-14mm, to 10-12mm and to 2-6mm, respectively. The gradual degradation iscaused mainly by propagated errors in the station coordinates and velocity of thereference frame realizations, as the extrapolation time increases. Preliminary tests donewith the proposed IGS realization of ITRF2000 would result in sub-mm standard
deviations for GPS week 1110-1114 (May 2001). The use of ITRF2000 directly would
14

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67

IGS 2000 Technical Reports

results in standard deviationsof about 3mm horizontallyand 6mm vertically for thesame epoch.

30

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The weekly estimated IGS
geocenter is also affected by
the proposed realization.
Figure 10 a-b-c shows the X,
Y and Z estimated geocenterwith respect to the realizationof ITRF97. The estimatedweekly geocenter positions
currently rely on COD, ESA
and JPL SINEX solutions.
The Figure 10 a-b-c also
shows the position of theorigin of the proposed IGS
realization of ITRF2000 withrespect to ITRF97. The timeseries show an average offset
1.6mm, 4.0mm and –17.4mm
for the X, Y, and Z
components in ITRF97.

Apparent Z Geocenter (mm)The average offsets of the
ITRF2000 geocenter for thesame period are 5.5mm,
4.0mm and –22.7mm. This
leaves a difference of 3.9mm,
0.0mm and 5.3mm for eachcomponent. This shows an
improvement for each axis,
specially the Z component.
The ERPs are combined in
Figure 10 a-b-c . Apparent Geocenter Weekly
the weekly SINEX solution
estimates and formal sigmas as well as proposed IGS
along with the station
realization of ITRF2000 origin with respect to current coordinates by making use of
IGS realization of ITRF97.
all covariance information.
The best AC pole (and rates)
are consistent at the 0.050.10mas (0.10–0.20mas/d), while the calibrated LOD are consistent at 20-30us. Figure 11
show the daily time series residuals for the X and Y pole (Top) and their rates (Middle)
between the combined solution “igs00p02” and the AC/GNAAC. The bottom portion
shows the daily difference between the combined solution and Bulletin A. The IGS
combined solution and the Bulletin A are not independent, since the AC solutions
0

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X Pole Residuals (0.01mas)

Reference Frame Working Group Technical Report

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Figure 11 a-b (top) c-d (middle) e-f (bottom).
Daily X Pole, Y Pole, (top) X Pole Rate, Y Pole Rate (middle) differences between the
combined solution “igs00P02” and the AC/GNAAC estimates.
Daily X Pole, Y Pole, (bottom) differences between the combined solution “igs00P02” andthe Bulletin A.

contribute significantly to Bulletin A. The Bulletin A daily estimates were linearlyinterpolated to match the IGS combined values epochs. Small differences between the
AC combined pole and pole rates are due to differences in processing strategy (e.g.:different weighting and rejection criterion). Similar daily ERPs are also estimated as partof the final GPS orbit combination process “igs95p02”. Comparison between theigs00p02 and igs95p02 show no significant average difference between them, and a noiselevel of about 0.07mas which is similar to the differences with respect to Bulletin A (bias
removed). The combined ERPs are consistent with those combinations at about 0.05mas(0.10-0.20mas/d).

69

IGS 2000 Technical Reports

Summary
The IGS cumulative solution now contains about 270 stations among which 167 were
submitted to ITRF for inclusion in ITRF2000. Analysis of the residuals of the ITRF2000
combination show horizontal/vertical position RMS of about 1mm / 3mm andhorizontal/vertical velocity RMS of 2mm/y / 5mm/y. The IGS realizations of ITRF uses a
subset of the IGS cumulative solution. This improves the internal stability andconsistency of the weekly product alignment. The use of the 7 ACs and the 3 GNAACs
provide significant redundancy and robustness to the analysis. The analysis has also
shown that station statistics have a gradually improved over the years. The weekly
apparent geocenter estimates show improved agreement with the proposed IGS
realization of ITRF2000 origin compared to the IGS realization of ITRF97.
Acknowledgements
A large number of agencies contribute to IGS. Among them are the agencies responsible
for the installation and maintenance of the tracking stations, the regional and global data
centers in addition to the ACs and GNAACs already mentioned. A complete list ofcontributors can be found at the IGS web site (http://igscb.jpl.nasa.gov/ ).
References
Boucher, C., Z. Altamimi, P. Sillard (eds.), The 1997 International Terrestrial Reference
Frame (ITRF97). IERS Technical Note 27, Observatoire de Paris, Paris.
Ferland, R., J. Kouba and D. Hutchison, (2000) Analysis Methodology and Recent
Results of the IGS Network Combination, Earth, Planets and Space, 52, 953-957.
Kouba, J., J. Ray and MM. Watkins, (1998) IGS Reference Frame Realization, 1998 IGS
Analysis Center Workshop Proceedings (ed. J. M. Dow at al.), European Space
Operations Center, Darmstadt, Germany, pp. 139-172.
Mireault, Y., J. Kouba and J. Ray, (1999). IGS Earth Rotation Parameters, GPS
Solutions, Vol. 3, No. 1 pp 50-72.

70

IGS

A N A L Y S I S

C E N T E R S

CODE IGS Analysis Center Technical Report 2000

CODE IGS Analysis Center Technical Report 2000
U. Hugentobler, S. Schaer, T. Springer, G. Beutler, H. Bock,
R. Dach, D. Ineichen, L. Mervart1, M. Rothacher2
Astronomical Institute, University of Bern
U.Wild, A. Wiget, E. Brockmann
Federal Office of Topography, Wabern
G. Weber, H. Habrich
Bundesamt für Kartographie und Geodäsie, Frankfurt
C. Boucher
Institut Géographique National, Paris
Introduction
CODE, the Center for Orbit Determination in Europe, is a joint venture of the following
four institutions:• the Federal Office of Topography (L+T), Wabern, Switzerland,• the Federal Agency of Cartography and Geodesy (BKG), Frankfurt, Germany,• the Institut Géographique National (IGN), Paris, France, and• the Astronomical Institute of the University of Berne (AIUB), Berne, Switzerland.
CODE is located at the AIUB. All solutions and results are produced with the latest
version of the Bernese GPS Software [Beutler et al., 2001].
This report covers the time period from January through December 2000. It focuses on
major changes taken place in the routine processing during this period and shows new
developments and products generated at CODE. The processing strategies used until
December 1999 are described in the CODE annual reports of previous years [Rothacher
et al., 1995, 1996, 1997, 1998, 1999, Hugentobler et al., 2000].
CODE did commit to take over the responsibility for the IGS ACC activities from 1999
through 2002 and Dr. Tim Springer was assigned to manage this task. His unexpectedannouncement to leave our institute by the end of 2000 for a job in telecommunicationindustry was a real surprise for us and raised a number of vital questions. We had toaccept his decision and the fact to loose a supporting member of AIUB’s GPS researchgroup. We were encountered with the problem to find a valuable successor and were gladthat Dr. Robert Weber from the Technical University of Vienna, Austria, accepted to takeover Tim Springer’s position as IGS ACC.
An essential, but rather time-consuming step in 2000 was the transfer of our routine
processing from a VAX/VMS cluster to a Sun E6500 server. While the IGS combination
procedures were already running on the Sun system since beginning of 1999, the CODE
products could be generated on the new platform starting with June 4, 2000. The related
12Technical University of Prague, Czech RepublicTechnical University of Munich, Germany

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IGS 2000 Technical Reports

conversion was taken as an opportunity to review and partly restructure processing
sequences. The change-over was performed without noteworthy problems in terms of
product quality and availability.
A severe crash of the Unix server on January 29, 2000, caused a temporary interruptionof the IGS rapid combination for two days. An unrelated malfunction of the VMS system
during the same weekend did prevent the use of that system as a backup system. For thesame reason, we were not able to generate the CODE rapid products for the mentioned
two days.
A wide variety of GPS solutions are computed at CODE. Tables 1 and 2 give an
overview of the products which are made available through anonymous ftp. In addition, a
regional analysis considering about 40 stations of a sub-network of a European
permanent network are processed on a daily basis. The main product of this analysis,
weekly coordinate solutions in SINEX format, are regularly delivered to EUREF(European Reference Frame, Subcommission of IAG Commission X). Details concerning
the delivered solution as well as a description of the different test solutions may be foundin [Hugentobler et al., 2000].
Table 1: CODE products made available through anonymous ftp.
CODE rapid and predicted products available at ftp://ftp.unibe.ch/aiub/CODE
CODwwwwd.EPH_R
Rapid orbits
CODwwwwd.EPH_P
24-hour orbit predictions
CODwwwwd.EPH_P2
48-hour orbit predictions
CODwwwwd.EPH_5D
5-day orbit predictions
CODwwwwd.ERP_R
Rapid ERPs belonging to the rapid orbits
CODwwwwd.ERP_P
Predicted ERPs belonging to the predicted orbits
CODwwwwd.ERP_P2
Predicted ERPs belonging to the 2-day predicted orbits
CODwwwwd.ERP_5D
Predicted ERPs belonging to the 5-day predicted orbits
CODwwwwd.CLK_R
Rapid clock product, 5-minute values, clock-RINEX format
CODwwwwd.TRO_R
Rapid troposphere product, SINEX format
CODGddd0.yyI
Rapid ionosphere product, IONEX format
COPGddd0.yyI
1-day or 2-day ionosphere predictions, IONEX format
CODwwwwd.ION_R
Rapid ionosphere product, Bernese format
CODwwwwd.ION_P
1-day ionosphere predictions, Bernese format
CODwwwwd.ION_P2
2-day ionosphere predictions, Bernese format
GLOwwwwd.EPH_5D
5-day GLONASS orbit predictions (based on broadcast)
CGIMddd0.yyN_R
Improved Klobuchar-style coefficients, RINEX format
CGIMddd0.yyN_P
1-day predictions of improved Klobuchar-style coefficients
CGIMddd0.yyN_P2
2-day predictions of improved Klobuchar-style coefficients
P1C1.DCB
Moving 30-day P1-C1 DCB solution, Bernese format
P1P2.DCB
Moving 30-day P1-P2 DCB solution, Bernese format

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CODE IGS Analysis Center Technical Report 2000

Table 2: CODE products made available through anonymous ftp.
CODE final products available at ftp://ftp.unibe.ch/aiub/CODE/yyyy
CODwwwwd.EPH.Z
Final orbits, our official IGS product
CODwwww7.ERP.Z
Final ERPs belonging to the final orbits, values for full week
CODwwwwd.TRO.Z
Final troposphere product, SINEX format
CODGddd0.ION.Z
Final ionosphere product, Bernese format
CGIMddd0.yyN.Z
Navigation messages containing improved Klobuchar-styleionosphere coefficients
CODwwww7.SNX.Z
Weekly SINEX product
CODwwww7.SUM.Z
Weekly summary files
COXwwwwd.EPH.Y
Precise GLONASS orbits (for GPS weeks 0990-1066)
COXwwww7.SUM.Z
Weekly summary files of GLONASS analysis
P1C1yymm.DCB.Z
Monthly P1-C1 DCB solutions, Bernese format
P1P2yymm.DCB.Z
Monthly P1-P2 DCB solutions, Bernese format
Currently, no real ultra rapid orbits are computed at CODE. The solution delivered to the
IGS since March 2000 for comparison purposes is actually a pure prediction on the basisof our daily rapid orbit solutions. It is excluded from the IGS ultra rapid orbit
combination, but might be considered as an adequate backup solution. The comparatively
good quality of this solution, at least for the satellites not experiencing modelingproblems, is due to the fact that the orbit extrapolation relies on long-arc data, specificallyon 3-day arcs. Tests towards a true ultra rapid solution are foreseen for 2001.
The computation of precise GLONASS orbits in the framework of IGEX was stopped onJune 18, 2000. CODE proposed a full participation for the IGLOS Pilot Project as soon as
new GLONASS satellites are launched to provide a reasonable constellation. The
combined computation of GPS and GLONASS orbits has not been started until the end of
2000. The reasons for the reserved engagement are the termination of the possibility for acontinuation ‘as is’ (associated with the shut-down of the VMS cluster), the manpower
effort considered substantial for the complete implementation of a routinely combined
processing, and the steadily declining GLONASS satellite.
Changes in the Routine Processing
The major changes implemented in the CODE routine analysis for the year 2000 are
listed in Table 3. During the time period covered by this report, the used models
remained essentially unchanged. For details we refer to the analysis questionnaire of
CODE available at the IGS CB.
Several changes are related to the modeling of the tropospheric delay. Until the end of
August 2000, the total tropospheric zenith path delay was mapped with the dry-Niell
mapping function. Afterwards an a priori dry delay based on the Saastamoinen model isintroduced and mapped with the dry-Niell mapping function. The wet-Niell mapping
function is used to map the corrections due to the wet component. Starting in October
2000, the minimum elevation angle in the rapid analysis was lowered from 10 to 5
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IGS 2000 Technical Reports

degrees, and the estimation of troposphere gradient parameters (two per station and day)was enabled. The number of troposphere zenith parameters was increased from 4 to 6 per
station-day.
Table 3: Modifications to the CODE processing strategy accomplished between January
2000 to December 2000.
Date
Doy/Year Description of Change and Impact
30-Dec-99 364/99
Download additional station data for the GIM generation.
27-Feb-00
058/00Create, distribute, and archive satellite and station clock files
in RINEX clock format.
09-Apr-00
100/00Differential (P1-C1) code bias values are determined as partof the global clock solution. An improvement of the clock
estimates is clearly detectable.
16-Apr-00
107/00Switch to another routine to create weekly IGS ERP file asfrom GPS week 1058 (solving a problem with the delivered
LOD values).
06-May-00 127/00
Use of P1-C1 DCB values based on a moving 30-day
combination (instead of JPL values) as a priori information.
04-Jun-00
156/00
Official CODE products are generated on the new platform.
04-Jun-00
156/00
Rapid and final clock solution based on code and phase(instead of smoothed code).
27-Aug-00 240/00
Instead of mapping the total tropospheric delay with the dryNiell mapping function, an a priori, Saastamoinen-based dry
delay is mapped with the dry-Niell mapping function, now
solving for the wet component mapped with the wet-Niell
mapping function.
24-Sep-00
268/00
Minimal elevation decreased from 10 to 5 degrees for the
rapid solution. Solving for L1-L2 satellite antenna offset
parameters as part of the ionospheric solution. Two sets ofsuch parameters (w.r.t. Block-II/IIA and Block-IIR) are set up
and heavily constrained.
03-Oct-00
277/00
Solve for troposphere gradient parameters. Number of
troposphere zenith parameters increased from 4 to 6 per
station and day for the rapid analysis.
29-Oct-00
303/00
Clock estimation in rapid analysis using global clusters
combined via satellite clocks (instead of regional station
clusters).

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CODE IGS Analysis Center Technical Report 2000

Contribution to ITRF2000
In March 2000, CODE submitted its contribution to the ITRF2000 reference frame
realization. The solution was produced using GPS observations spanning a time intervalfrom GPS week 0782 (Jan. 1, 1995) to GPS week 1050 (Feb. 26, 2000) and includes
coordinates and velocities for 164 stations. The coordinates of all stations are constrained
to the reference frame ITRF97 using a minimum constraint condition (three rotations) at
the reference epoch (April 1, 1993). Figure 1 shows a comparison of the estimatedvelocity vectors (arrows) with the ITRF97-derived vectors (lines) for a solution which isconstrained to the ITRF97 reference frame.

Figure 1: Velocity vectors estimates from a constrained solution (arrows) and fromITRF97 (lines).
Estimation of Satellite and Receiver Clock Parameters
A main effort in 2000 was put into the improvement of our station and receiver clock
products. Relevant changes were activated in the course of the switch of the routine
computations from the VMS cluster to the Unix Sun/Solaris server on June 4 (doy156/2000). Prior to this date, the clocks delivered with the final solution were based onsmoothed code, and the rapid solution did contain broadcast clock information. With theswitch to the new platform, CODE started to deliver clocks based on code and phaseobservations in both the final and the rapid solution taking advantage of the experience
gained in a transatlantic time transfer campaign using GPS carrier phase data [Dach et al.,1999]. The final clock solution is based on about 100 stations while the rapid solution
contains typically 80 stations. Starting on February 27 (doy 058/2000), satellite and77

IGS 2000 Technical Reports

station clock results are archived and distributed with a sampling rate of five minutes
following the RINEX clock format.
The clock zero-difference processing is based on the results from the double-difference
processing. The satellite orbits as well as the station coordinates and troposphereparameters are introduced as fixed into the clock solution. The coordinates andtroposphere zenith delay parameters are estimated for additional stations. Three solutions
with about 33 stations each are computed independently and combined in a final step.
The computing time of a complete solution is of the order of three hours. A significant
fraction is due to the data cleaning procedures.
The stations are selected according to the quality of their delivered observations. The
three clusters are constructed such that an optimum geometry results for each of them. Asa matter of fact stations need not necessarily appear in one cluster only. Modifications in
the data cleaning procedures and in particular the use of global instead of regional
clusters resulted in a further improvement of the clock results as of October 29 (doy303/2000).
Determination of Differential Code Bias Values
As part of the process of the estimation of ionosphere parameters, P1-P2 DCB values are
determined for all active GPS satellites and for about 160 IGS/EUREF stations. The daily
repeatability of these parameters is of the order of 0.1 ns. Combined values are computed
taking into account the last 30 daily sets of values. Monthly P1-P2 DCB solutions areavailable as of October 1997.
Starting with GPS week 1056, the IGS analysis centers have to take P1-C1 code biases
into account in order to ensure that their precise clock information is fully consistent toP1/P2 code measurements. CODE is accounting for this type of code bias as of GPS
week 1057 (April 9, 2000) by solving for satellite-specific code bias parameters as part ofthe clock estimation procedure. The bias values are estimated directly from the data sets
for which they will be applied. No use is made of C1 code measurements from non-crosscorrelation style receivers (providing C1/P1/P2). Instead of these measurements, C1/P2'
code measurements from cross-correlation receivers are considered. In other words, ourP1-C1 DCB estimates directly reflect the code bias differences between non-CC and CC
receivers as seen by an analysis center in its clock estimation procedure. Our approachworks as long as a mixture of data from CC receivers and modern receivers is processed.
At present, about 30-40 of about 80 stations used for the clock estimation may be related
to a CC style receiver providing C1 and P2' code measurements. Our analysis includes alarge number of receivers, usually a superset of those used by other analysis centers anddoes not explicitly rely on any particular receiver models.
The daily repeatability of the (satellite-specific) P1-C1 values is of the order of 0.1 ns
rms. The improvement of our clock estimates due to the consideration of the P1-C1 DCB
parameters is clearly detectable. Since doy 127/2000, P1-C1 DCB a priori information istaken from a 4-week combination, available as of May 2000.

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CODE IGS Analysis Center Technical Report 2000

We continue in monitoring P1-C1 and P1-P2 differential code biases since they are not as
constant as one might like. Another motivation to continue with this service is thecircumstance that CODE P1-C1 bias values are recommended to be adopted for use with
the IGS official products from GPS week 1097 onwards (see IGS Mail 3160).
More details on CODE’s DCBs and ionosphere products may be found on ourionosphere-dedicated web site http://www.aiub.unibe.ch/ionosphere.html.
Klobuchar-Style Ionosphere Parameters
Since mid of July 2000, Klobuchar-style ionospheric coefficients (alphas and betas) best
fitting CODE IONEX global ionosphere maps are computed on a regular basis. A
validation study based on two months of data confirmed that our predicted coefficients
perform significantly better than the coefficients broadcast by the GPS system for the
single-frequency user. Coefficients derived from CODE final and rapid IONEX data (fordays where the final product is not yet available), as well as coefficients based on 1-day
and 2-day IONEX predictions are generated. They are made available via anonymous ftp
in form of content-reduced RINEX navigation data files (see Tables 1 and 2). Moreover,
the CODE analysis center is able to supply post-processing users of the GPS broadcast
ionosphere model with a unique, continuous time series of RINEX files containing
improved Klobuchar-style ionospheric coefficients starting with January 1, 1995 [Schaer,2001].
60
GPS-GIM
CODE-GIM
CODE-INX

50

Mean TEC (TECU)

40

30

20

10

0
1995

Figure 2:

1995.5

1996

1996.5

1997

1997.5
1998
Time (years)

1998.5

1999

1999.5

2000

2000.5

Mean TEC of the ionosphere derived from GPS broadcast model
coefficients, CODE generated model coefficients, and CODE IONEX
reference, compared from 1995.0 to 2000.5, gathered from [Schaer,2001].

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Sensitivity of GPS and GLONASS Orbits to Geopotential Resonance Terms
Studies are carried out to evaluate the sensitivity of GPS and GLONASS orbits on
resonant geopotential terms. The most important terms for satellites near the 2:1commensurability with the Earth’s rotation are the C32 and S32 terms in the harmonic
expansion of the geopotential, followed by the terms C44, S44 and C22, S22 [Hugentobler,
1998]. The GPS satellites are in exact resonance (revolution period of half a sidereal day)and are, thus, significantly affected by the resonance terms. As a consequence, quite
frequent along-track orbital manœuvers are necessary to keep the satellites at theirrequested position. GLONASS satellites, on the other hand, perform 21/8 revolutions
within one sidereal day and are, therefore, not in deep resonance with the Earth’s gravity
field. Infrequent orbital manœuvers are a positive aspect of this configuration.
Our studies indicate, however, that the GLONASS satellites show a higher sensitivity to
the resonant geopotential terms than the GPS satellites. The reason is a strong coupling of
the resonance terms with the radiation pressure coefficients, in particular the y-bias: Thevery similar signal of some of the radiation pressure parameters and the resonantgeopotential terms along the satellite’s orbit impedes the decoupling of the effects for
GPS satellites due to their equal periods. For GLONASS satellites the periods of theeffects are non-commensurable which makes a decoupling possible. GLONASS satellites
may, therefore, be more adequate to extract the gravity signal caused by the resonant
terms.
Kinematic and Dynamic Orbit Determination for Low Earth Satellites
The AIUB is participating in the IGS LEO Pilot Project. In this context a new program(SORBDT) for orbit integration was developed as well as techniques for generating highrate GPS clock corrections and kinematic LEO orbits based on code and phasedifferences from one epoch to the next [Bock et al., 2000].
Program SORBDT allows a highly flexible selection of the physical model in terms of
the force field and of the parameters to be set up. It includes new capabilities necessary
for LEOs such as air drag modeling. The setting up of an arbitrary number of stochastic
parameters is possible. Furthermore, the program allows to introduce accelerometermeasurements to remove the effect of the non-conservative forces. Input to the program
are cartesian satellite positions, i.e., a kinematic orbit, as pseudo-observations.
The current approach to generate kinematic orbits for LEOs is based on a precise point
positioning generating positions from code observations as well as position differencesfrom phase differences from one epoch to the next. Positions and position differences are
combined to high precision positions in a second step. GPS orbits are introduced as fixed
while high rate clocks are generated by combining clock corrections derived from codewith clock correction differences from one epoch to the next derived from phase, both
based on observations of the IGS tracking network.
The procedure for generating kinematic orbits is very efficient, but depends heavily on
the quality of the code observations as well as on the number of receiver resets.

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CODE IGS Analysis Center Technical Report 2000

Significant effort has to be put into the development of sophisticated data cleaningalgorithms. First tests of the procedures were performed using data fromTOPEX/POSEIDON as well as from the released day 220/2000 of CHAMP data.
Summary and Outlook
The year 2000 has seen a number of changes at CODE, the most important being theleave of Tim Springer at the end of the year, which was a significant loss for CODE andour institute. With Robert Weber, a well-established scientist and ‘veteran’ of the AIUB
could be won to continue the tasks of the IGS ACC as of January 2001.
With the release of a new version of our software, the Bernese GPS Software Version
4.2, and a number of improvements in routines and procedures, the high standard of our
products delivered to the IGS could be assured and increased. The transfer of thecomplete routine processing to the new platform was certainly a milestone and a chance
to review our processing strategies – although it was a harsh task.
In the near future, developments are foreseen in different fields and the existing
involvement will be extended by new challenges. The modeling of atmospheric delays
will be reviewed and the estimation of troposphere gradient parameters will be activatedfor the final analysis. Significant effort will be put into the zero-difference processing andthe clock correction generation. In this context it is worth mentioning that theimplementation of clock extrapolation and of high-rate clock generation are planned.
Studies into the direction of an ultra-rapid orbit product are in preparation. They shallindicate the procedure to make optimum use of the rapid orbit information forstrengthening the ultra-rapid solution. Studies of GLONASS orbits are underway as well,and, provided that the satellite constellation remains stable enough, an engagement in the
IGLOS Pilot Project may be envisaged. Finally, the development and adaptation ofalgorithms and procedures for the computation of kinematic and dynamic LEO orbits inthe framework of the IGS LEO Pilot Project will continue and increase.
References
Bock, H., U. Hugentobler, T. A. Springer, G. Beutler (2000), Efficient Precise Orbit
Determination of LEO Satellites using GPS, to appear in Adv. Space Res., 33rd
COSPAR Scientific Assembly, Warschaw, Poland, July 17-21, 2000.
Dach, R., T. Schildknecht, T. Springer, G. Dudle, L. Prost (1999), Recent Results withTransatlantic GeTT Campaign, in Proceedings of the 31th Annual Precise Timeand Time Interval (PTTI) Systems and Applications Meeting, Dana Point,
California, December 7-9, 1999.
Hugentobler, U (1998), Astrometry and Satellite Orbits: Theoretical Considerations andTypical Applications, Geodätisch-geophysikalische Arbeiten in der Schweiz,
Schweizerische Geodätische Kommission, Vol. 57, Institut für Geodäsie und
Photogrammetrie, Eidg. Technische Hochschule Zürich, Zürich.

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Hugentobler, U., T. Springer, S. Schaer, G. Beutler, H. Bock, R. Dach, D. Ineichen,
L. Mervart, M. Rothacher, U. Wild, A. Wiget, E. Brockmann, G. Weber,
H. Habrich, C. Boucher (2000), CODE IGS Analysis Center Technical Report
1999, in IGS 1999 Technical Reports, edited by K. Gowey et al., IGS Central
Bureau, JPL, Pasadena.
Hugentobler, U., S. Schaer, P. Fridez (Eds.), Bernese GPS Software, Version 4.2,
Astronomical Institute, University of Berne.
Ineichen, D., T. Springer, G. Beutler (2000), Combined Processing of the IGS- and the
IGEX-Network, accepted for publication in Journal of Geodesy.
Rothacher, M., G. Beutler, E. Brockmann, L. Mervart, R. Weber, U. Wild, A. Wiget,
H. Seeger, S. Botton, C. Boucher (1995), Annual Report 1994 of the CODE
Processing Center of the IGS, in IGS 1994 Annual Report, edited by
J. F. Zumberge et al., pp. 139-162, IGS Central Bureau, JPL, Pasadena, CA.
Rothacher, M., G. Beutler, E. Brockmann, L. Mervart, S. Schaer, T. A. Springer,
U. Wild, A. Wiget, H. Seeger, C. Boucher (1996), Annual Report 1995 of the
CODE Processing Center of the IGS, in IGS 1995 Annual Report, edited by
J. F. Zumberge et al., pp. 151-174, IGS Central Bureau, JPL, Pasadena, CA.
Rothacher, M., T. A. Springer, S. Schaer, G. Beutler, E. Brockmann, U. Wild, A. Wiget,
C. Boucher, S. Botton, H. Seeger, (1997), Annual Report 1996 of the CODE
Processing Center of the IGS, in IGS 1996 Annual Report, edited by
J. F. Zumberge et al., pp. 201-219, IGS Central Bureau, JPL, Pasadena, CA.
Rothacher, M., T. A. Springer, S. Schaer, G. Beutler, D. Ineichen, U. Wild, A. Wiget,
C. Boucher, S. Botton, H. Seeger, (1998), Annual Report 1997 of the CODE
Processing Center of the IGS, in IGS 1997 Technical Reports, edited by
I. Mueller et al., pp. 73-87, IGS Central Bureau, JPL, Pasadena, CA.
Rothacher, M., T. A. Springer, G. Beutler, R. Dach, U. Hugentobler, D. Ineichen,
S. Schaer, U. Wild, A. Wiget, E. Brockmann, C. Boucher, E. Reinhart, H. Habrich(1999), Annual Report 1998 of the CODE Processing Center of the IGS, in IGS
1998 Technical Reports, edited by K. Gowey et al., pp. 61-73, IGS Central
Bureau, JPL.
Schaer, S. (2001), Generating Klobuchar-Style Ionospheric Coefficients for SingleFrequency Real-Time and Post-Processing Users, Astronomical Institute,
University of Berne.
Springer, T. A. (2000), Modeling and Validating Orbits and Clocks Using the Global
Positioning System, Geodätisch-geophysikalische Arbeiten in der Schweiz,
Schweizerische Geodätische Kommission, Vol. 60, Institut für Geodäsie und
Photogrammetrie, Eidg. Technische Hochschule Zürich, Zürich

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The ESA/ESOC IGS Analysis Centre Annual Report 2000

The ESA/ESOC IGS Analysis Centre
Annual Report 2000
J.M. Dow, R. Zandbergen, J. Feltens†, C. Garcia‡, I. Romero‡, H. Boomkamp‡
ESA/European Space Operations Centre,
Robert-Bosch-Str. 5, D-64293 Darmstadt, Germany†
EDS at ESA/ESOC‡
GMV at ESA/ESOC
Introduction
This Report gives an overview of the ESOC Analysis Centre activities and a presentationof the activities during the year 2000, plus the direction for the future.
During this year the main development has been the launch of the ESOC Ultra-Rapid
submission to the IGS, as part of the routine GPS data processing for POD. All the otherroutine activities, including GLONASS data processing, have continued and some minor
internal modifications have been introduced to further automate the processing.
Currently ESOC’s GPS-TDAF (Tracking and data Analysis Facility) handles
automatically the ESA ground receiver network, the IGS network data retrieval andstorage and all of the routine daily and weekly data processing of the different IGS
products. The system is capable of performing autonomous operations for up to about
five days.
Changes and activities in 2000
These have been the changes and activities that ESOC has been involved in from January
to December, 2000:
Jan 2000Feb 2000

Mar 2000
Apr 2000

Jun 2000
Sep 2000

Tested Niell mapping function for the dry and wet tropospheric component,
to substitute the inverse cosine mapping function currently used. Results
encouraging but not implemented into IGS processing yet.
Switched the GLONASS POD to a 5 day processing arc, also eliminated all
combined receivers which do not track both constellations in dual frequency
mode.
Started twice-daily GPS POD Ultra-Rapid submissions to the AC
Coordinator for combination and comparisons to other AC results.
Ceased making any changes to pseudorange data from modern receivers andbegan modifying data from cross-correlation style receivers, as explained in
IGS mail #2744.
Switched from ITRF97 to IGS 97, the IGS realisation of the reference frame.
Introduced undifferenced data processing for LEO on-board GPS receivers,
tested with Topex data. As preparation for the analysis of CHAMP data.

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IGS 2000 Technical Reports

Routine Activities
ESOC participates in the IGS as an Analysis Centre providing the following routine
products either to the Analysis Centre coordinator or to the IGS Global Data Centre
CDDIS:
•
•
•
•
•
•
•
•
•
•
•
•

Final GPS Orbits plus clocks
Final GLONASS Orbits plus clocks
Rapid GPS Orbits plus clocks
Twice Daily Ultra-Rapid GPS Orbits plus clocks
Daily Rapid EOP file
Daily Ultra-Rapid EOP file
Weekly final EOP file
Weekly final processing summaries
Weekly free network solution in SINEX format
Daily final tropospheric files
Daily rapid RINEX clock files with 5 minutes sampling
Daily final RINEX clock files with 5 minutes sampling

Processing Method
The ESOC GNSS precise orbit determination processes for all the cases are based on abatch least squares estimation solution of RINEX IGS station data using various numbers
and distributions of stations based on availability, past performance and processing time
available. The average numbers of stations used for each of the processes at ESOC are as
follows:••••

Final GPS POD:
Final GLONASS POD:
Rapid GPS POD:
Ultra-Rapid GPS POD:

52 stations
27 to 30 stations
40 to 45 stations
25 to 30 stations

The distribution of the stations selected for GPS POD processing aims at providing
worldwide coverage with stations of the latest ITRF whenever possible. Figure 1 shows
the station distribution for a typical GPS Final processing day. The stations selected for
the Rapid and the Ultra-Rapid processes are subsets of this group, selection being madeon data availability and processing time before submission.

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The ESA/ESOC IGS Analysis Centre Annual Report 2000

Figure 1: GPS stations typically selected for Final processing.
On the other hand the IGEX station network is still of limited number and distribution.
The stations selected for a typical GLONASS processing day are shown in Figure 2.
These can be seen to be poorly distributed around the globe, with a heavy concentrationof stations in Europe (only dual-frequency data for both GNSS systems are processed at
ESOC, so they are the only ones shown). The stations in capital letters are ITRF corestations, which are very highly constrained in the processing to fix the solution to thelatest ITRF.

Figure 2: GPS/GLONASS stations typically selected for IGEX processing.

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IGS 2000 Technical Reports

The estimation method for all the POD activities uses an in-house estimation program,
BAHN, currently in version 7 and which can handle most types of data for satellite POD
activities (ranges, range rates, SLR, Doris, Prare, altimetry, GNSS observables in un-,single- and double- differenced modes). The quantities estimated by the program arevariable depending on the focus of the run. For the IGS submissions the quantities
estimated are:
•
•
•
•
•
•
•
•
•

The station coordinates
The satellite state vectors
The solar radiation pressure extended force model parameters
Cycle-per-revolution empirical accelerations
The undifferenced carrier phase ambiguities for the ionospheric linear combination
The GPS-GLONASS receiver biases (for the GLONASS processing only)
The Earth rotation parameters: x and y pole position and rates and Length of Day,
The tropospheric zenith delay for every station every 2 hours
Station and satellite clock biases, estimated as time-dependent parameters (one value
for every observation epoch).

More information on our routine GPS and GLONASS processing, processing description,model usage, result plots, etc can be found at:
http://nng.esoc.esa.de/
http://igscb.jpl.nasa.gov/igscb/center/analysis/esa.acn

Ultra-Rapid implementation
As proposed in the 1999 IGS Workshop in La Jolla, CA, a new IGS product should be
produced by the Analysis Centres (ACs) called the Ultra Rapid orbits (Gendt, et al.
1999). As their name indicate these are GPS satellite orbits produced very soon after thedata gathering has occurred, and they cover an existing gap in the IGS products between
the official rapid and predicted orbits. Initially, the product was to contain only orbit
information, no clock bias estimations, but now that SA has been turned off it has beenfeasible to develop the satellite clock predictions and include clocks for the entire UltraRapid period. This is currently done by up to 4 IGS Analysis Centres. The orbit files arein the standard sp3 format but contain 48 hours of orbit positions and clock biases insteadof the usual 24 hours as for the other IGS products. The first 24 hours are from fitting thedata available over the period and the last 24 hours from predicting the solution into thenext day.
The implementation of the new product at ESOC borrows heavily from both the Rapidand the Predicted processing strategies. The Ultra-Rapid processing steps can besummarised as follows:
1. RINEX data is downloaded and checked for a period covering the 24 hour arc of theorbit to be determined, plus the previous 24 hours (Figure 3). This 48 hour arc of
RINEX data is normally used. Data from up to 30 stations are used, depending ondata availability from the IGS receiver network.

86The ESA/ESOC IGS Analysis Centre Annual Report 2000

2. A number of days of Earth fixed positions are also used as observations either fromthe IGS rapid orbits or from the ESOC rapid orbits for the 3 or 4 days before the
RINEX data start. These Earth fixed positions of the GPS constellation are used as
observations together with the RINEX observations (Figure 1, where the arrow
indicates the start time of processing).
Data processing arc Step 1

Day 215

Day 216

Day 217

IGS Earth Fixed Pos.

Day 218

Day 219

Day 220

Day 221

RINEX Receiver obs.
Ultra rapid 03:00 contents

Figure 3. ESA Ultra rapid solution first step, data types and processing arc.
3. The two frequency RINEX data is combined in a zero difference ionospheric-freecombination and antenna phase corrections are applied. The pseudo-range and carrier
phase observations are written to an observation file together with the satellite Earthfixed positions, from the previous 3 days as described above.
4. ESOC’s least squares dynamic parameter estimation program, BAHN, is run and thesatellite orbits, satellite dynamic models, station positions, satellite and station clock
biases and Earth Rotation Parameters (ERP) are estimated.

5. The satellite orbit results from the estimation are formatted into satellite Earth fixed
positions and used in a second estimation step which fits all of the Earth fixed
positions (Figure 4). This second step tends to produce higher quality orbit
predictions for the Ultra rapid submission.
Data processing arc Step 2

Day 215

Day 216

Day 217

IGS Earth Fixed Pos.

Day 218

Day 219

Day 220

Day 221

Earth Fixed Pos.
Ultra rapid 03:00 contents

Figure 4: ESA Ultra rapid solution second step, data types and processing arc.

This strategy is still being refined in-house as more experience and more results
accumulate. Tests have been run without the use of the Step 2 with good results, aslong as enough station data exists, therefore the processing strategy will continue to
evolve.

87

IGS 2000 Technical Reports

6. Currently the clocks are predicted at ESOC by post processing the results of the leastsquares estimator and fitting a simple curve for each of the satellites:clki (t ) = Bi + Dit + Ei sin (Fit + Gi )where i is the PRN number of each satellite, and Bi, Di, Ei , Fi , and G i are theestimated coefficients. If the curve fitting satisfies a convergence criterion of 10
nanoseconds over the 48 hours of fitted data, in a least squares sense, then the clock
for the entire 48 hour arc is sent out. If for some reason the function is not fitted
correctly then no clock is provided for the satellite.
7. Finally the results are formatted into the appropriate sp3 orbit files, and ERP filespanning the necessary periods, and the satellite exponential correction values areapplied, based on the overlap comparisons to the previous day solution.
ESOC’s Ultra-Rapid orbit-only submissions began on March 3rd, 2000. Whereas orbits +clocks started being submitted by ESOC on March 9th, 2001.
In week 1052 the first combination and comparison results started to appear which
combined each centre’s solution into an IGS Ultra-Rapid product and then comparedeach centre’s solution to the combination. Excluding short periods of problems with theprocessing, or with specific satellites, the ESOC overall rms value for the Ultra-Rapid
orbits in the combinations has stabilised at a 15 to 25 cm level for each of the two daily
submissions. A real-time plot of the comparison results for all the AC’s submissions canbe seen at: http://nng.esoc.esa.de/gps/igs_ana.html for both ultra-rapid
submissions.
It is nonetheless unsatisfactory most of the time to analyse the performance of the UltraRapid submission based on one RMS error value for the entire 48 hour file, considering
the mixed character of the product (fit + prediction). Therefore at ESOC we also
produce, for quality analysis, epoch-by-epoch comparison plots versus the combined
product (igu). The plots are made in order to detect the character of the agreement or
disagreement of our submission with the other ACs and with the combined solution.
Two examples of these plots are shown in Figure 5.

88

The ESA/ESOC IGS Analysis Centre Annual Report 2000

Data Fit

Data Fit

Prediction

Prediction

JPL
SIO

RMS Error (m)RMS Error (m)

GFZ
ESOC
USNO
EMR

ESOC

USNO

EMR
GFZ
00

48

00

48

hours

hours

Figure 5: Epoch by epoch unweighted RMS error versus IGU for October
26th,2000 (00300) on the left and May 19th, 2001 (01139) on the right.
The weighted RMS values for these two days are as shown in Table 1. Analysing theseplots together with the values in Table 1 clearly show that the majority of the error in the
combination of the AC submissions occurs for the predicted part of the Ultra-Rapid orbit.
Table 1: Weighted RMS values for Ultra-Rapid Orbits
for two specific days (ACC summaries).
AC
EMR
ESA
GFZ
JPL
SIO
USNO

00300
22 cm
14 cm
16 cm
-52 cm
26 cm

01139
12 cm
14 cm
11 cm
27 cm
15 cm
24 cm

The plots in Figure 6 also show the well-known effect of linear prediction degradation(Fang, et al., 2001), and support the call to eventually increase the frequency of the UltraRapid product, so that the prediction available to users is always less than 6 hours old.
At the same time, whenever possible, a different series of plots comparing the predicted
part of the Ultra-Rapid with the IGS Rapid, once it is available, are produced to monitor
the degradation over time of the orbit predictions. The plots in Figure 6 show these
epoch-by-epoch comparisons89

IGS 2000 Technical Reports

JPL
GFZ

ESOC
USNO

RMS Error (m)RMS Error (m)

EMR

SIO
USNO

ESOC

IGS
Ultra-Rapid
(IGU)

00

EMR

GFZ
IGU

00

24

24

hours

hours

Figure 6: Epoch by epoch unweighted RMS error of predicted part of Ultra-Rapid
AC submissions and the IGU versus the IGR for October 26th,2000(00300) on the left and May 19th, 2001 (01139) on the right.
The four plots presented above are sample plots for specific days. They are not intended
to be representative of the state of the Ultra-Rapid, since day to day variations in thesatellite constellation as well as in the timely availability of station data can affect theresults greatly.
Clock predictions show agreement to the observed values down to the 3 to 5 nanoseconds
level over the entire GPS constellation. Figure 7 shows the satellite clock bias epoch-byepoch for GPS satellite PRN05 (sv-35, Cesium internal clock), and for GPS satellite
PRN07 (sv-37, Rubidium internal clock) for the entire 48 hour period. Currently at ESOCthe clock predictions are based on fitting with a function the 5 minute clock values,
solved for in the least squares process, after the relativistic effect of non-zero orbital
eccentricity is corrected, and applying a continuity condition at the switch over.
(seconds)

Estimation

Estimation

Prediction

Prediction(seconds)
100 ns

500 nsFigure 7: PRN 05 (left) and PRN07 (right) Satellite clock bias estimated andpredicted for May 19th,2001 (01139).
It can be seen from Figure 7 that Cesium clocks have worse short term stability, whereas
Rubidum clocks have better stability but much larger drifts. Examples of two other90The ESA/ESOC IGS Analysis Centre Annual Report 2000

Cesium clocks, are given in Figure 8. The satellites shown in both Figures highlight thedifficulties of improving the clock bias predictions beyond the current level (3 to 5
nanoseconds) across the entire GPS constellation.
(seconds)

Estimation

Estimation

Prediction

Prediction

10 ns(seconds)

20 ns

Figure 8: PRN 25 (left) and PRN06 (right) Satellite clock bias estimated andpredicted for May 19th,2001 (01139).
Even accounting for the difficulty of modelling the satellite on-board clock behaviour themost important thing to produce good clock predictions is to select a known stablereference station for the clock bias estimations. At ESOC the IGS station Algonquin isused if it is available for all of the processing epochs, otherwise another one of the IGS
stations with an H-maser is selected. This ensures good orbit stability and smooth clock
bias calculations and predictions.

GLONASS Processing
GLONASS processing at ESOC has continued following the activities of the processing
campaign IGEX-98 (Willis et al., 1999). Since most of the IGEX stations have continued
to gather and transfer their GPS + GLONASS data to the IGEX Data Centres at ESOC it
was deemed appropriate to continue calculating GLONASS precise ephemerides.
The GLONASS constellation of satellites has continued to decrease in numbers. Even
with the launch of three new satellites in November 2000 (which were introduced into
active service after some delay), the number of satellites being decommisioned meantthat the total number of active dual-frequency satellites by the time of this writing was
only eight. At the same time the IGEX station network has continued to increase, which
has made for more stable day to day solutions for each of the remaining satellites, as
more data is available.
Figure 9 shows the orbit comparisons between the solutions from CODE, BKG, MCC(Moscow Control Centre) and ESOC versus the GLONASS combination up to the timeof writing. CODE orbit contributions ceased during 2000, and the ESOC comparison to
the combination stabilised at an error level of around 20 cm. The degradation observedin the plot for the beginning of 2001 could be due to the new satellites introduced, new91

IGS 2000 Technical Reports

stations, or a difference in the combination processing (in particular with respect to thetreatment of the MCC orbits).

Year 2000

Figure 9: IGLOS/IGEX AC orbit comparisons versus the combination.
In anticipation of the IGLOS Pilot Project kick off ESOC has also purchased andinstalled a Topcon (formerly Javad) GPS+GLONASS receiver at our permanent stationin Kourou (French Guyana), which will start supplying dual system data during 2001,
both for IGS and IGLOS activities.
Ionosphere Processing
Routine processing of ionospheric Total Electron Content (TEC) maps andsatellite/receiver differential code biases (DCBs) continued during 2000.
The processing in final mode continued with the rapid orbits. The number of groundstations used could be increased to about 150. The 24 hours time resolution with which
the TEC maps are produced, could not be increased yet. The daily routine ionosphereprocessing is now as follows:
1) A nighttime TEC data fit is made to obtain a set of reference DCB values for that day.
The nighttime TEC itself is absorbed in this fit with a low degree and order sphericalharmonic. In the other fits 2) - 4) these DCBs are then introduced as constraints.
2) A Chapman profile model is fitted to the TEC data of that day, where the layer ofmaximum electron density N0 and its height h0 are estimated as surface functions ofgeomagnetic latitude and local time. h0 is restricted to have values within a92

The ESA/ESOC IGS Analysis Centre Annual Report 2000

predefined range only, currently 350 km =< h0 =< 450 km or 400 km =< h0 =< 450km.
3) A Chapman profile model is fitted to the TEC data, where h0 is estimated as a global
constant.
4) A Chapman profile model is fitted to the TEC data, where h0 is kept fixed as global
constant at a height of 450 km, and the influence of the solar zenith angle is notaccounted for. This run is made for test reasons and theoretical studies.

Figure 10: Global TEC map obtained from a fit of type 2) for 28 March 2000, a
day during a period in the current solar maximum, when the TEC level
was very high.
Beyond the routine processing of our own TEC maps, ESOC is also chairing the IGS
Ionosphere Working Group (Iono_WG) and is thus responsible for the weekly
comparisons of Iono_WG products and for the coordination of the activities of thisworking group.
Future Activities
ESOC Analysis Centre will remain active during the next year, continue the regularcontributions to the IGS orbit and clock products, troposphere, ionosphere and station
network solutions. The Ultra-Rapid processing development at ESOC will continue as
more experience is accumulated over time, including improvements to the clock
prediction.

93

IGS 2000 Technical Reports

A new activity will also start during 2001 as the IGS LEO Pilot Project gets underwaywith the release of Champ on-board GPS data. The ESOC Analysis Centre will act as
Associate Analysis Centre for the Pilot Project, and also as AAC Coordinator for thefurther Centres. The initial task as AAC will be to move towards routine LEO dataprocessing, leading to stable data products that include at least precise CHAMP orbit andclock solutions but perhaps also some associated products (e.g. improved gravity fieldmodels). Once that a nominal set-up has been reached, applications of LEO data for
improving other IGS products will be considered. The responsibilities as AAC
Coordinator will initially be aimed at exchange of information between the various
AACs, and at quality monitoring of independent solutions. In the longer term the LEO
output should include an IGS combination solution for the CHAMP orbit and clock,similar to what is presently done for GPS. The moment at which routine combination
solutions can become available depends of course on the availability of routine output
from all IGS LEO AACs.
References
Gendt, G., Fang, P., Zumberge, J., Moving IGS products towards real-time, IGS Analysis
Centre Workshop Proceedings, La Jolla, 1999.
Fang, P., Gendt, G., Springer, T., Mannucci, T., IGS Near Real-Time Products and Their
Applications, 2000 IGS Analysis Centre Workshop Proceedings, Washington DC,
GPS Solutions, Vol. 4, Num. 4, Spring 2001.
Dow, J.M., Feltens, J., Garcia, C., Romero, I. Kahle R., The ESOC IGS Analysis Centre,
1999 IGS Technical Report, IGS Central Bureau eds., Pasadena CA, Jet
Propulsion Laboratory, 2000.
Dow, J.M., Feltens, J., Garcia, C., Romero, I., The ESOC IGS Analysis Centre, 1998 IGS
Technical Report, R. Neilan, A. Moore, K. Gowey, eds., Pasadena CA, Jet
Propulsion Laboratory, 1999.
Martin-Mur T., Dow, J.M., Feltens, J., Garcia, Bernedo P., The ESOC IGS Analysis
Centre, 1997 IGS Technical Report, I. Mueller, R. Neilan, K. Gowey, eds.,
Pasadena CA, Jet Propulsion Laboratory, 1998.
Willis P., Slater J., Gurtner J., Noll C., Beutler G., Weber R., Neilan R., Hein G., The
GLONASS IGEX-98 Campaign: From its genesis to its realisation, IGEX-98
Workshop Proceedings, IGS Central Bureau, Jet Propulsion Laboratory, 1999.
Romero, I., Garcia, C., Kahle, R., Dow, J., Martin-Mur, T., Precise Orbits Determinationof GLONASS Satellites at the European Space Agency, COSPAR 2000
Proceedings, Warsaw, Poland, July 2000.

94

GFZ Analysis Center of IGS - Annual Report for 2000

GFZ Analysis Center of IGS - Annual Report for 2000
Gerd Gendt, Galina Dick, Wolfgang Söhne
GeoForschungsZentrum Potsdam (GFZ)
Telegrafenberg, 14473 Potsdam
Division Kinematics & Dynamics of the Earth
Summary
In 2000 no significant changes for the classical IGS/IGR products were introduced.
Improvements were performed for the Ultra-Rapid analysis especially for the clock
predictions.
Classical IGS/IGR products
During 2000 the P1-C1 corrections on the RINEX files were introduced. While GFZ not
followed the older unification of RINEX files on this topic, where the new non-crosscorrelation (non-cc) observation were transformed to be compatible to the observations
from the older cross-correlation (cc) receivers , the new standard correction from cctype to non-cc-type was followed accordingly. This way the ongoing replacements of theolder receivers will have no significant influence on the consistency of the clock products
anymore.
Ongoing effort was concentrated improving the robustness of the GFZ software toguaranty the high quality of the results also under the increasing burden which raised
from additional projects.
Table 1. Changes in the analysis strategy
Week
Date
1063 2000-05-21
1065 2000-06-04
1097 2001-01-14

Description
Generation of station clock solutions for the Rapid product
P1-C1 bias corrections from cc to non-cc receivers
Generation of clock predictions with the Ultra-Rapid Product

The quality of the main IGS Final/Rapid products are summarized in the Figures 1 and 2.
The Final satellite orbits have reached an accuracy of 2-3 cm and the satellite clocks areapproaching the 0.05 ns level. The Rapid products, available each day at 9:00 UTC for
the day before, have with 4-6 cm (median) for the satellite orbits and 0.08-0.12 ns for theclocks already a high level which is sufficient for many applications.
The weekly computed SINEX files contain solutions for the station coordinates andEarth rotation parameters (ERP) and enter into the official IGS combination. The qualityof the GFZ station coordinates can be extracted from the corresponding combination
reports (Fig. 2). Compared to the weekly combined solution the quality of the horizontal
and vertical components is about 1.5 to 2.5 mm and 5 to 8 mm, respectively. The
corresponding values from the comparisons to the cumulative solution show slightly

95

IGS 2000 Technical Reports

higher values (~ 30 %) which indicate that small periodic fluctuations in the station
positions exists which are similarly in all weekly analysis center submissions.
Ultra-Rapid Products
As already reported last year (Gendt et al. 2000) GFZ had started the generation of UltraRapid products in October 1999. In 2000 other Analysis Centers had joined this activity
so that a combined product was feasible. At the beginning of 2001 daily reports are
generated by the AC coordinator which compare the individual AC predictions (first 12
hours of the prediction only) with the latest Rapid product. The quality of the GFZ UltraRapid products retrieved from these reports are shown in Figure 1. The daily median forthe orbits is about 10 to 15 cm. This accuracy is sufficient for near real-time estimationsof tropospheric water vapor for numerical weather prediction, which is the most striving
applications for this product within IGS.
The GFZ technique for generation of Ultra-Rapid products can be described in thefollowing way:a. The hourly RINEX data are continuously retrieved using ftp and accumulated
into daily RINEX files. The P1-C1-biases is corrected for during this process.
b. In the general case, data are extracted for the analysis the from two daily RINEX
files using a sliding window of 24 hours. In the preprocessing step only the dataof the last hour (with a small overlap) are cleaned in a two step procedure:• Larger cycle slips are identified by using wide-lane and geometry-free linear
combination on a site-by-site basis.
• Double-difference cleaning procedure in a network follows to identify further
zero-difference cycle slips.
c. Based on the pre-cleaned data the orbit analysis is performed in the usual way the
rapid products are generated, i.e. iterative orbit improvement and post-fit residual
editing. In the final iteration stochastic impulses are introduced for all satellites in
the middle of the arc.
The procedure is organized in such a way that our Ultra-Rapid product would be identicalwith the Rapid one, if the same number of stations could be used. That means, if the
global hourly network would improve in such a way that its site distribution is identicalwith the daily sites used in the Rapid analysis, the orbits would have an accuracy quite
below the 10 cm level (see Zumberge, Gendt 2000; Fang, Gendt, et al., 2001).
Results from this step are the fitted SP3 orbits for the 24-hour data part and the ERPs, aswell as the clock solutions for the satellites and stations (frequently updated stations
clocks are not provided yet, but are available if there is interest in).
d. In the final step the predictions are performed on the basis of the above SP3
product and the Rapid SP3 orbit from the day before (either IGR or GFZ). A long96

GFZ Analysis Center of IGS - Annual Report for 2000

orbital arc is fitted through all SP3 positions using the Bernese 9-parameterradiation model (Beutler, et al. 1994). This model is applied instead of theimpulses because its sinusoidal terms are better suited for prediction purposes.
The GFU product (48-hour SP3) is generated from the long arc solution.
The described technique yields a continuous orbit, and it should be noticed that it is not
the best one for the part covered with data. However, tests showed that the differences tothe orbits derived in step (c.) are in the range of 2-5 cm, which is not relevant for the nearreal-time applications.
The whole Ultra-Rapid analysis takes about 25 minutes (10 minutes for preparation partand 15 minutes for the analysis).
Clock predictions. The high quality Ultra-Rapid clocks can be used to compute clock
predictions. Based on the experiences at USNO we used the most recent two days to fit alinear trend plus sinusoidal terms to the clock values, for the rubidium clocks even aquadratic term is added. The adjusted functions used for the computation of the clocks forthe predicted part in the SP3 product. The fit for the clocks is usually of the level of 1-3
ns. If the fit is worse than 5 ns no prediction is generated, presently this happens rather
often for satellites PRN 17, 19, 21, 23.
The quality of the predicted clocks for the 12-hour prediction interval are already at thelevel of the broadcast clocks (5-7 ns, see Fig. 1) and can easily be improved at least by afactor of two if the Ultra-Rapid products will be updated more frequently.
References
Beutler, G., E. Brockmann, W. Gurtner, U. Hugentobler, L. Mervart, M. Rothacher, A.
Verdun (1994):Extended orbit modeling techniques at the CODE processing centerof the international GPS service for geodynamics (IGS): Theory and initial results,
Manuscripta Geodetica (1994)19, pp. 367-386
Gendt, G., G. Dick, W. Söhne (2000): GFZ Analysis Center of IGS - Annual Report for
2000, in "IGS 1999 Technical Reports," Eds. K. Gowey, R. Neilan, A. Moore,
JPL/IGS Central Bureau, Pasadena, CA, November 2000, pp. 77-84
Gendt, G., P. Fang, J. F. Zumberge (1999): Moving IGS towards real-time. Proceedings
IGS Analysis Center Workshop, 8-10 June 1999, La Jolla, CA, USA, in "IGS 1999
Technical Reports", Eds. K Gowey, R Neilan, A Moore, JPL/IGS Central Bureau,
Pasadena, CA, November 2000, pp. 375-384
Fang, P., G. Gendt, T. Springer, T. Manucci (2001): IGS Near Real-time Products and their
Applications IGS Analysis Center Workshop, 25-29 Sept 2000, Washington, GPS
Solutions, Vol.4, No.4, 2001, p. 2-8
Zumberge J., G. Gendt (2000): The demise of the selective availability and implications
for the International GPS Service, IGS Network Workshop, Oslo, 12-14 July 2000,
submitted to "Physics and Chemistry of the Earth" (Nov. 2000)

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IGS 2000 Technical Reports

25.

Median [cm]

20.
15.

Orbit quality for
Final
Rapid
Ultra-Rapid-Predictions

10.
5.
0.
1010.

1020.

1030.

1040.

1050.

1060.

1070.

1080.

1090.

1100.

1110.

1120.

1040. 1050. 1060. 1070. 1080. 1090.
GPS week (1043 is 2000.0, 1095 is 2001.0)

1100.

1110.

1120.

0.8

RMS [Nanoseconds]

0.7
0.6
0.5

Clock quality for
Final
Rapid
Ultra-Rapid-Predictions(divided by 10)

0.4
0.3
0.2
0.1
0.0
1010.

1020.

1030.

Figure 1. Quality of the various GFZ satellite orbit and clock products taken from theofficial combinations reports (Rem.: Clock resolution until GPS week 1085 was only
0.1 ns)RMS [mm]15.

Difference to cumulative solution

East

Up

5.
0.
1010.

1020.

1030.

15.
RMS [mm]

North

10.

1040.

1050.

1060.

1070.

1080.

Difference to weekly solution

1090.

North

1100.

East

1110.

Up

10.
5.
0.
1010.

1020.

1030.

1040.
1050.
1060.
1070.
1080.
GPS week (1043 is 2000.0, 1095 is 2001.0)

1090.

1100.

1110.

Figure 2. Quality of GFZ station coordinate solutions extracted from the IGS SINEX
combination reports

98

JPL IGS Analysis Center Report, 2000

JPL IGS Analysis Center Report, 2000
D. C. Jefferson, Y. E. Bar-Sever, M. B. Heflin, R. J. Muellerschoen,
Y. Vigue-Rodi, F. H. Webb, and J. F. Zumberge
Jet Propulsion Laboratory/California Institute of Technology
Pasadena, California 91109 USA
J.C. Ceva, T. J. Martín-Mur, and R. F. Meyer
Raytheon
Pasadena, California 91101 USA

Summary
JPL activities as an IGS Analysis Center continued throughout 2000 with regulardeliveries of rapid, precise, and high-rate GPS orbits and clocks, Earth orientation
parameters, and free-network ground station coordinates. Submissions of ultra-rapid
products were began in February, and 15-minute solutions based on real-time 1-second
data began in November. Our rapid products realized an improvement in latency due tomore efficient allocation of system resources, as well as in improvement of productquality due to the use of more global stations and higher-quality reference clock sites.
Multi-platform versions of our analysis software have allowed us to expand our
processing capability, leading to lower latency for our final precise solutions. Rapid
clock products in RINEX clock format are now being produced. New strategies include
accounting for pseudorange biases between the P1 and C1 data types and the use of
nominal core station coordinates in the IGS97 terrestrial reference frame. Overall
performance continued to improve; the accuracy of our final orbit product is at the 3-cm
level compared with the IGS Final orbit solution.
Evolution in 2000
Material relating to JPL participation as an IGS analysis center, beginning in 1992, can befound in [1] and references therein. Table 1 indicates the evolution of our activities
during 2000.

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IGS 2000 Technical Reports

Table 1: 2000 Analysis Evolution____________________________________________________________________________
ActionDate
Begin production of ultra-rapid products
Feb 20
Apply P1-C1 pseudorange bias corrections in cross-correlating receivers
Apr 2
Begin submission of rapid clock solutions in RINEX clock format
May 28Adopt IGS97 coordinates and velocities for 20+ subset of 51 IGS core sites
Jun 4
Apply recomputed Benchmark-based P1-C1 bias corrections
Oct 15Adopt R. Ray sub-daily extended Earth orientation model (IERS, 1996)
Nov 12Begin 15-minute deliveries of orbits and clock products from 1-sec data
Nov 29____________________________________________________________________________
Product Summary
Tables 2 and 3 summarize the regular products that result from JPL IGS AC activities.
Newly added products are the ultra-rapid (twice daily) and real-time (15-minute) GPS
satellite orbit and clock products. Table 4 contains addresses of World Wide Web pages
with related information.
Table 2: Regular products from the JPL IGS Analysis Center, at
ftp://sideshow.jpl.nasa.gov/pub/jpligsac___________________________________________________________________________
Example File
Contents
1095/jpl1050.sum.Z

narrative summary for GPS week 1050

1050/jpl1050[0-6].sp3.Z

free-network precise orbits for days 0-6 (Sun throughSat) of GPS week 1050

1050/jpl1050[0-6].yaw.Z

free-network yaw-rate data for eclipsing satellites,days 0-6, GPS week 1050

1050/jpl10507.erp.Z

free-network Earth orientation parameters for GPS
week 1050 (fixed-network prior to week 0947)

1050/jpl10507.snx.Z

free-network station coordinates for GPS week 1050
(7-parameter transformation to ITRF beginning wk0947) (3-parameter rotation to ITRF beginning wk
0964)

1050/jpl1050[0-6].tro.Z

free-network troposphere solutions, days 0-6, GPS
week 1050 (fixed-network prior to week 0949)

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JPL IGS Analysis Center Report, 2000

Table 2: Regular products from the JPL IGS Analysis Center, at
ftp://sideshow.jpl.nasa.gov/pub/jpligsac (cont'd)___________________________________________________________________________
Example File
Contents
1050/jpl1050[0-6].clk.Z

free-network 30-sec GPS and 5-min station clocks,
days 0-6, GPS week 1050, in RINEX clock format

hirate/JPL1050[0-6].sp3.Z

fixed-network 30-s GPS orbits and clocks, days 0-6,
GPS week 1050

2000.eng.Z

engineering data for 2000, sites in global solution

2000_p.eng.Z

engineering data for 2000, point-positioned sites

ytd.eng

year-to-date engineering data, sites in global solution

ytd_p.eng

year-to-date engineering data, point-positioned sites___________________________________________________________________________

Table 3: Other products at ftp://sideshow.jpl.nasa.gov/pub/gipsy_products;(†15-minute products are in ftp://sideshow.jpl.nasa.gov/pub)___________________________________________________________________________
Contents
Example File
RapidService/orbits/jpl1050[0-6].sp3.Z
quick-look fixed-network precise
orbits for days 0-6 (Sun through Sat),GPS week 1050
RapidService/orbits/jpl1050[0-6]_pred.sp3.Z

quick-look fixed-network 3-day
predicted orbits for days 0-6,
GPS week 1050

RapidService/orbits/jpl1050[0-6].clk.Z

quick-look fixed-network 5-minclocks, days 0-6, GPS week 1050, in
RINEX clock format

RapidService/orbits/2000-01-01.*

daily quick-look and predicted fixednetwork files for use in GIPSY

UltraRapid/00h/jpu1050[0-6].sp3.Z.../jpu1050[0-6].erp.../jpu1050[0-6].sum

ultra-rapid fixed-network precise
orbits, earth orientation, and text
summary for days 0-6, GPS week
1050, 1st delivery

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IGS 2000 Technical Reports

Table 3: Other products at ftp://sideshow.jpl.nasa.gov/pub/gipsy_products;(†15-minute products are in ftp://sideshow.jpl.nasa.gov/pub) (cont'd)___________________________________________________________________________
Contents
Example File
UltraRapid/12h/jpu1050[0-6].sp3.Z
ultra-rapid fixed-network precise.../jpu1050[0-6].erp
orbits, earth orientation, and text.../jpu1050[0-6].sum
summary for days 0-6, GPS week
1050, 2nd delivery
2000/clocks/2000-01-01.*

precise daily free- and fixed-network
clocks and yaw-rates for use in
GIPSY

2000/orbits/2000-01-01.*

precise daily free- and fixed-network
precise orbits, polar motion,
shadow-events data for use in
GIPSY

hrclocks/2000-01-01.*high-rate free- and fixed-network
clocks (in TDP format) for use in
GIPSY

15min/2000-12-01*

15-minute† orbits (eci and sp3
format), clocks, earth orientation,
yaw rates, and tropospheres for use
in GIPSYIERSB/*

IERS Bulletin-B information___________________________________________________________________________

Table 4: Addresses of Relevant Web Pages___________________________________________________________________________
Contents
Address
http://sideshow.jpl.nasa.gov/mbh/series.html
graphical time-series of site coordinates
http://sideshow.jpl.nasa.gov/mbh/all/table.txt
table of site coordinates and velocities
http://milhouse.jpl.nasa.gov/eng/jpl_hp2.html
summaries and plots of station and satellite
performance___________________________________________________________________________

102

JPL IGS Analysis Center Report, 2000

Strategy Update: P1-C1 Bias Corrections
As described in IGS Mail Message Nos. 2320, processing data from a network of mixed
receiver types reveals a bias in pseudorange observables between different receivers.
Cross-correlating receivers (typically TurboRogues and Trimbles) report C/A (C1) codethat is unexpectedly offset from the P1 code of non-cross correlating receivers (typicallyAshtechs, Benchmarks, and ACT upgraded TurboRogues). Beginning with GPS week
1056 (April 2, 2000), we account for these biases, which are satellite-dependent, byapplying long-term estimated bias values (http://gipsy.jpl.nasa.gov/igdg/demo/camp) to
the C1 code of any cross-correlating receivers in our chosen daily station network.
When these biases are applied, they have a direct effect on the ability to resolve carrierphase ambiguities and estimated clock solutions. In testing, we observed an averageincrease of about 16% more phase biases being fixed, a 0.07-0.067 ns RMS change inGPS clocks, and an improvement of 1-2 cm in daily GPS orbit repeatability. These
results and a further description of the P1-C1 bias estimation methodology can be foundin [2].
Strategy Update: Use Of IGS97
At the outset of the year, station coordinates and GPS orbits were aligned with ITRF97.
Beginning with GPS week 1065 (June 4, 2000), monument coordinates and velocities aretaken from ftp://igscb.jpl.nasa.gov/igscb/station/coord/IGS00P04_RS51.SNX, andantenna heights from ftp://igscb/igscb/station/general/igs.snx. (Antenna reference points
to L1 and L2 phase centers are from ftp://igscb/igscb/station/general/igs_01.pcv.) Pleasesee IGS Mail Message Nos. 2899 and 2904 for ITRF97/IGS97 comparisons and further
details.
Clock Solution Update
Beginning with GPS week 1064 (May 28, 2000), JPL began to submit a contribution to
the IGS rapid combined clock product. These files contain our daily quick-look estimatesof the GPS and ground station at 5-min intervals for each satellite and station used in our
rapid solution; station position estimates are also included in the file headers. The fileformat is the RINEX clock format as described at http://maia.usno.navy.mil/gpst/clockformat.
New Products
Ultra-Rapid:
Delivery of ultra-rapid products to the IGS AC began on GPS week 1050 (February 20,
2000). Both orbits and clocks are provided. The solutions for year 2000 are based onprocessing 20 ground stations, acquiring hourly data and then processing batches of 3hour arcs. At 3-hour intervals, a 3-hour arc is processed and then at every 12 hours, 8batches are smoothed for a product using 24 hours of data. The challenge is to produce

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IGS 2000 Technical Reports

orbits not later than two and one-half hours after the last data taken. GPS NANU
messages are automatically processed to exclude data from maneuvering or unhealthysatellites. End products are delivered to the IGS in the NGS SP3 orbit file format twice
daily. At each 12-hour interval the orbits cover 48 hours with 24 hours fitted and 24
hours predicted.
Ultra-rapid products were delivered from GPS week 1050 through week 1081 for theyear 2000. Accuracies of the products are 8-25 cm for the fitted orbit and 25-110 cm forthe prediction, measured as a WRMS with respect to the IGS rapid orbits (IGR).
Real-Time 15-minute
JPL has established a global network of roughly 20 real-time sites that send data every
second via Internet for estimation of GPS orbits and clocks. The GPS clock estimates are
updated every second while the GPS orbits are updated every minute. The real-time
products are converted to standard GIPSY format every 15 minutes and made public via
Internet at ftp://sideshow.jpl.nasa.gov/pub/15min.
The new 15-minute products include orbits, clocks, tropospheric delay estimates for the
tracking sites, yaw rates, and earth orientation parameters. Availability was announced to
the IGS on November 21, 2000 in IGS Mail Message No. 3108. Typical quality for the
15-minute orbits is 30-40 cm.
Results And Performance
Table 5 below displays the relative delivery schedule and accuracy of solutions producedby the JPL IGS analysis center:
Table 5: Latency and Accuracy of JPL IGS AC Products
15-minute and Ultra-Rapid, and Rapid product accuracies are mean RMS relative to the
IGS combined rapid orbit solution. The Final products are relative the IGS combined
final orbit.
________________________________________________________________________
Latency
Accuracy (cm)Orbit Product15-Minute
Every 15 minutes
35
Ultra-Rapid
Twice per day
20
Rapid
Once per day
12
Final/FLINN
Once per week3________________________________________________________________________

Figure 1 chronicles the progression of the final orbit solution quality since 1995. As in
the past, our metric for orbit quality is the day-to-day consistency of the solutions, i.e. thedegree to which estimates from adjacent days agree near the midnight boundaries.
Contributing factors to improvement are the continuing expansion of the global network

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JPL IGS Analysis Center Report, 2000

median weekly orbit repeatability (cm)and quality of receivers used, the use of global phase ambiguity resolution (implemented
in April 1996), the estimation of tropospheric gradients (implemented in August 1997,
and the application of P1-C1 bias corrections (implemented in April 2000).
30

30

25

25

20

20

15

15

10

10

5

5

0
1995

0

1996

1997

1998

1999

2000

2001

year

Figure 1: JPL orbit repeatability (3drms) since 1995. Each data point represents themedian over all satellites and days for a particular GPS week. (The daily number for agiven satellite indicates the degree to which the precise orbit agrees with those ofadjacent days near the midnight boundary.) Weeks during which AS was off are indicatedwith an ‘X’.
Another measure of performance is how well the JPL GPS solutions for station
coordinates and velocities compare with those from other geodetic techniques. The firsttwo columns in Table 6 below show the level of agreement between JPL derived station
velocities and those independently realized from Very Long Baseline Interferometry(VLBI) and Satellite Laser Ranging (SLR). The last column shows dependent agreementwith ITRF. Coordinates and velocities for this table are now in ITRF2000 and can beobtained from http://sideshow.jpl.nasa.gov/mbh/all/table.txt.

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IGS 2000 Technical Reports

Table 6: Geodetic Velocity Comparisons________________________________________________________________________JPLGPS-VLBI
JPLGPS-SLR
JPLGPS-ITRF00
N (mm/yr)

0.8

1.6

0.8

E (mm/yr)

0.8

1.7

0.7

V (mm/yr)

2.0

3.2

1.5

No. common sites

34

18

123

_________________________________________________________________________

Acknowledgment
This work was performed at the Jet Propulsion Laboratory, California Institute ofTechnology, under contract with the National Aeronautics and Space Administration, andat Raytheon.
References[1] J. F. Zumberge, M. B. Heflin, D. C. Jefferson, M. M. Watkins, and F. H. Webb, Jet
Propulsion Laboratory IGS Analysis Center 1994 Annual Report, in IGS 1994
Annual Report, edited by J. Zumberge, R. Liu and R. E. Neilan, IGS Central
Bureau, Jet Propulsion Laboratory, Pasadena CA, 1995, JPL Publication 95-18[2] D. C. Jefferson, M. B. Heflin, R. J. Muellerschoen, “Examining the C1-P1
Pseudorange Bias, GPS Solutions, Volume 4, Number 4 (IGS Special Issue), J.
Wiley & Sons, Inc., Spring 2001.

106

GPS Orbit and Earth Orientation Parameter Production at NOAAFor the International GPS Service for 2000

GPS Orbit and Earth Orientation Parameter Production at NOAA for
the International GPS Service for 2000
National Geodetic Survey
National Ocean Service
National Oceanic and Atmospheric Administration
Silver Spring, MD USA
Spatial References System Division
William G. Kass, Robert L. Dulaney III, Robert B. Leonard Jr.
Geosciences Research Division
Gerald L. Mader, Mark S. Schenewerk, William H. Dillinger

Introduction
The GPS orbit and Earth Orientation Parameter ( EOP) solutions submitted to the IGS by
the National Geodetic Survey (NGS) are a joint effort between the Spacial Reference
System Division (SRSD) and the Geosciences Research Division (GRD). The GRD is
responsible for the development of the processing software and techniques while the
SRSD is responsible for the operational production. SRSD and GRD are both activities
within NGS which is part of the National Ocean Service (NOS) of NOAA (National
Oceanic and Atmospheric Administration). A detailed description of the techniques andmodels can be found in the Analysis Strategy Summary located at
http://www.ngs.noaa.gov/GPS/noaa_acn.html .
Station Network
Figure 1 shows a typical set of baselines used for forming double differences and forconnecting the stations in the tracking network. NGS used an average of 65-70 tracking
stations which are submitted to the IGS for the GPS orbit and EOP production. This list is
not static but changes occasionally to include new stations that offer a more favorable
geometry or new geographical coverage. If new stations are added in a region where thetracking network density is greater or redundant, other stations are dropped thereby
keeping the total number at less than or equal to 70. This number appears adequate toprovide overall tracking network stability that is relatively insensitive to daily tracking
site drop outs within the global network. Included tracking sites are listed in the weekly
summary available at the Crustal Dynamics Data Information System (CDDIS) at
ftp://cddisa.gsfc.nasa.gov .
Software Changes
No major software enhancements were made during 2000. PAGES/GPSCOM, bothdeveloped at NGS, remain the software tools used for orbit production. Since thebeginning of 2000, NGS has modelled deformations driven by ocean tidal loading using
the Schwiderski model (Schwiderski 1983).

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IGS 2000 Technical Reports

Figure 1.
On June 4, 2000 NGS, along with the other Analysis Centers, switched from the ITRF97
reference frame to the IGS realization of the ITRF97 referenceframe (IGS97).

Product Evaluation
Figure 2 shows the daily RMS differences between the NGS and IGS final ephemerides
for the year 2000 after a "best fit" seven parameter transformation has been applied to the
NGS ephemerides. It also shows the values of the associated seven parametertransformations. The subplots are: (left column, top to bottom) RMS of fit in meters, X
translation in meters, Y translation in meters, Z translation in meters; (right column, top
to bottom) scale in parts per billion, X rotation in milliarcseconds, Y rotation in
milliarcseconds, and Z rotation in milliarcseconds. All available GPS satellites were
included and universally the outlying points seen in the RMS subplot are caused by asingle poorly estimated satellite within a day. On average over all 2000, NGS EOP
match the National Earth Orientation Service Bulletin A values at: X pole -0.119 +/0.332 milliarcseconds and Y pole 0.164 +/- 0.253 milliarcseconds. The NGS software
only uses double difference carrier phase as an observable and does not attempt torecover a UT1 time series.

108

GPS Orbit and Earth Orientation Parameter Production at NOAAFor the International GPS Service for 2000

Figure 2

Orbit Products
I.

Constrained Precise GPS Orbit: Up to 51 constrained IGS fiducial tracking sites
in the IGS97, epoch 1997.0 reference frame available - 3 to 6 days from date ofobservation contact - http://www.navcen.uscg.mil/gps/precise/default.htm
accuracy - approximately 5-10 centimeters

II.

Minimally Constrained Precise GPS Orbit: A consistent minimally constrained
weekly solution in the IGS97, epoch 1997.0 reference frame available - 4 to 10

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IGS 2000 Technical Reports

days from date of observation contact ftp://gracie.grdl.noaa.gov/dist/cignet/Ngsorbits accuracy - approximately 5-10
centimeters
III.

Rapid GPS Orbit: Up to 50 constrained IGS fiducial tracking sites in the IGS97,
epoch 1997.0 reference frame available - 16 hours from last observation contact ftp://www.ngs.noaa.gov/cors/orbits/rapid accuracy - approximately 8-12
centimeters

IV.

Ultra-Rapid GPS Orbit: A constrained estimated/predicted solution in the IGS97,
epoch 1997.0 reference frame will be available - within 2 to 3 hours from last
observation contact - under development accuracy - approximately 20-60
centimeters

V.

Earth Rotational Parameters: Rapid and precise polar motion values available 16 hours from date of last observation recipient - Bureau International de L'Heure(BIH) United States Naval Observatory( USNO) International GPS Service (IGS)
accuracy - approximately 0.25 milli-arcseconds

VI.

Troposheric estimates for the zenith path delay available - 4 to 10 days from dateof observation recipient - GeoForschungsZentrum, Potsdam, Germany
International GPS Service (IGS)

References
Schwiderski, E., 1983, "Atlas of Ocean Tidal Charts and Maps, Part I: The Semidiurnal
Principal Lunar Tide M2", Marine Geodesy, 6, 219-256.

110

NRCan IGS Analysis Center Report for 2000

NRCan IGS Analysis Center Report for 2000
P. Tétreault, Y. Mireault, B. Donahue, P. Héroux and C. Huot
Geodetic Survey Division
Natural Resources Canada
Ottawa, Canada

In addition to contributing to the classical IGS products, the Geodetic Survey Division(GSD) of Natural Resources Canada (NRCan) also initiated in 2000 contribution to the
IGS Ultra Rapid Product. Unfortunately NRCan contribution to the IGS Rapid products
had to be interrupted for most of 2000 until problems with NRCan estimation of Earth
Orientation Parameters could be resolved. The following report documents the activitiesof the NRCan IGS Analysis Center during 2000.
The Classical IGS Products
In 2000, NRCan continued contributing to IGS all the classical products with the
exception of the rapid products, which were interrupted between GPS Weeks 1054 to
1094. The NRCan estimation strategies and contributed products are described in
ftp://igscb.jpl.nasa.gov/igscb/center/analysis/emr.acn. All NRCan products with the
exception of the ionospheric grid and the recent Ultra Rapid, described further, arecomputed using the Jet Propulsion Laboratory (JPL) GIPSY-OASIS software. The
NRCan ionospheric grid is computed using an in-house software suite. Its estimation
strategy remained unchanged in 2000.
Besides implementing the IGS recommendations for the computation of Rapid and Final
products, see Table 1, efforts were also devoted to the optimization of the NRCan
estimation strategy using GIPSY Version 2.5 which had been implemented in late 1999
in preparation for the infamous Y2K expected problems. Improved apriori validation of
the GPS RINEX observations files was also implemented. Single station procedures toautomatically reject bad or weak data were implemented using a point positioning
approach. Table 2 lists the modifications that affected the GPS satellite constellation in
2000.
Table 1. Final/Rapid Processing Strategies Modifications and Improvements
GPS Week
1056
1065

1066

Modification_________________________________________________
Adoption of IGS convention to transform cross-correlated pseudo-range
observations into synthesized non cross-correlated
Adoption of IGS realization of ITRF97 (IGS97) station coordinatesand velocities
Adoption of new set of bias values to transform cross-correlated
pseudo-range observations into synthesized non cross-correlated

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IGS 2000 Technical Reports

Table 1. Final/Rapid Processing Strategies Modifications and Improvements (cont'd)
GPS Week
1070
1070

Modification_________________________________________________
Implementation of a station selection algorithm based on network
geometry and station spacing
Implementation of validation of data files based on precise point
positioning using IGS rapid orbits and clocks products

Table 2. GPS Constellation Changes in 2000
Date
April 14
May 11
June 28
July 21
July 27
November 28

PRN
14
20
18
28
16
14

Changeremovedadded
removedadded
removedadded

EMR Regional Processing
Since the beginning of 2000, NRCan has been computing a regional GPS solution for
Canada. This initiative is in support of the Canadian Spatial Reference System (CSRS)
realization and positioning activities and for a future contribution to the International
GPS Service (IGS) ITRF densification. Starting at the beginning of 2001, these solutions
will be submitted to the North American Reference Frame (NAREF) Technical Working
Group of the International Association of Geodesy (IAG) Commission X(http://www.naref.org) to be included in a North American solution. The regional
solution is estimated using JPL’s GIPSY/OASIS II software. The strategy follows theguidelines proposed by the IGS and those adopted by the NAREF Technical Working
Group. The current strategy used for producing weekly coordinate solutions is to fix the
IGS final orbits, IGS final weekly Earth Rotation Parameters (ERP), and one reference
station clock, and to estimate station coordinates, station and satellite clocks, and station
tropospheric delays. Daily SINEX coordinate files are combined into a weekly SINEX
combination for distribution to NAREF.
We estimate 29 stations including all stations of the Canadian Active Control system(CACS) as well as 6 IGS stations located close to Canada. All stations have 100m apriori
station coordinate weight except algo, drao, nlib, wes2, yell, and thu1 which are tightly
constrained to their estimated IGS00P04_RS51.SNX coordinates and standard deviations.
These six stations are the so-called anchor stations used to tie the local network to theglobal IGS network. The constraints placed on the anchor stations are removed using
SINEX software during the computation of the weekly combination. Figure 1 depicts thestations currently included in the NRCan regional solution.

112

NRCan IGS Analysis Center Report for 2000

Figure 1. Stations included in NRCan Regional Processing
NRCan Ultra Rapid Products
The development of a strategy to compute Ultra Rapid orbits was initiated towards theend of 1999 and early 2000. It uses the Bernese v4.2 software (Hugentobler et al.) alongwith numerous in-house scripts. NRCan officially started submitting its Ultra Rapid
products (emu) to the IGS Analysis Centre Coordinator (ACC) on March 20, 2000 (GPS
Week 1054/ Day 1). User intervention is minimized and only required in "difficult
times" such as several hours without enough IGS hourly station data files from the IGS
Data Centres.
Processing Strategy
The processing strategy was adapted to our limited CPU capabilities at the time ofdevelopment. In order to meet the IGS AC submission deadlines of 2h45m and 14h45m
UT (i.e. 2h45m after the last observation), it was decided to process 3-hour batches,
forming Normal Equations (NEQ) and stacking them to generate our Ultra Rapid
products. The time required to process a 3-hr session, including the stacking of NEQ and
the production of our Ultra Rapid orbit was about 1h20 min for a 35-station network.
This strategy has some disadvantages like the shortage of timely hourly RINEX files andftp connection problems to name a few. The main advantage however is that NRCan has
a new Ultra Rapid solution every 3 hours reducing the average time of latency from 9hours (IGU) to about 4.5 hours. Also, if the IGS decided to increase the number of IGU
submissions per day from 2 to 4 (and possibly 8!), NRCan would not have to change its
strategy!
About 60 IGS hourly stations are downloaded via ftp regularly and up to 45 stations canbe used in our processing. The main ftp download is done from the Crustal Dynamics
Data Information System (CDDIS) site every 15 minutes. Only missing stations from a
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IGS 2000 Technical Reports

pre-determined station list are downloaded. Frequent downloads are required to minimize
ftp related problems and to obtain timely hourly data for our 3-hr session processing. We
also retrieve data from a secondary ftp site located at the Federal Agency for Cartography
and Geodesy in Germany (IFAG) to complement the ftp downloads from CDDIS indifficult times. To maximize the number of hourly stations used, the processing isdelayed by at least 1h after the last observation but never more than 2h45m. NRCan
relies heavily on the fact that hourly data files must be sent and be available at CDDIS assoon as possible at all times and not only prior to the two IGS Ultra Rapid combinations.
This is very critical for us since we do not process a complete day (24 hours) of GPS data
every time we generate our Ultra Rapid products, nor do we reprocess older 3-hr
sessions.
A number of different sources of apriori orbits can be used ranging from our own Ultra
Rapid products to the less precise Broadcast ephemeris. As far as the apriori Earth
Rotation Parameters (ERP) are concerned, we use the IERS Bulletin A at all times. IERS
Bulletin A has been very reliable and is one of the most precise ERP series available forreal time applications.
Products Generated and Results
NRCan Ultra Rapid products consist of a 48-hr orbit file (24h estimated and 24h
predicted) along with a 2-day ERP file (the first day is estimated and the second day is
predicted). Although NRCan produces such product every 3 hours, only the sessions
ending at 0h0m UT and 12h0m UT are sent to the ACC for the IGS Ultra Rapid
combination (IGU). At this time, NRCan does not provide any satellite clocks in its Ultra
Rapid.
Since we started the production in March 2000 and until the middle of December 2000,
our Ultra Rapid orbit was strictly based on stacking at most sixteen 3-hr NEQ files
corresponding to (at most) 48h worth of Ultra Rapid GPS processing (Strategy A).
Starting in the middle of December 2000, we implemented an extra step (Strategy B),
which consisted in fitting IGS Rapid and/or Ultra Rapid orbits (already available) alongwith our own Ultra Rapid orbit coming from Strategy A. Altogether, a minimum of twodays and a maximum of three days worth of Rapid/Ultra Rapid orbit fitting are performed
on a regular basis. As mentioned in Fang et al, 2001, the poor network geometry andlack of global GPS hourly data can harm the Ultra Rapid orbit precision quite heavily
when compared to the IGS Rapid products and network coverage. The fitting process
somewhat compensates for the poor coverage resulting in an overall better orbit
prediction for real time applications.
Strategy B proved to be very beneficial for the NRCan Ultra Rapid orbit precision.
Depicted in Figure 2 is the NRCan daily Ultra Rapid orbit Median RMS (with respect toIGR) for both strategies A and B and for 3 different time intervals. Interval 9-12 hours of
the estimated portion is shown on Figure 2a while intervals 3-6 and 9-12 of the predicted
portion are shown on Figures 2b and 2c respectively. The plots cover the end of 2000
starting from December 14 at which time we implemented Strategy B. The mean and114

NRCan IGS Analysis Center Report for 2000

standard deviation of each series are also printed on top of each graphic. There is no
doubt that Strategy B has a definite advantage over Strategy A!
NRCan Ultra Rapid Orbit Median RMS (wrt IGR)
Estimated Portion: Interval 9-12 hrs
1.0

A: 0.22±0.04m
0.9

B: 0.14±0.03m

Median RMS (m)

0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
348

350

352

354

356

358

360

362

364

366

Day of Year 2000
Strategy A

Strategy B(a)
NRCan Ultra Rapid Orbit Median RMS (wrt IGR)
Predicted Portion: Interval 3-6 hrs
1.0

A: 0.44±0.09m
0.9

B: 0.32±0.08m

Median RMS (m)

0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
348

350

352

354

356

358

360

362

364

366

Day of Year 2000
Strategy A

Strategy B(b)
NRCan Ultra Rapid Orbit Median RMS (wrt IGR)
Predicted Portion: Interval 9-12 hrs
1.0
0.9

A: 0.56±0.12m
B: 0.38±0.1m

Median RMS (m)

0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
348

350

352

354

356

358

360

362

364

366

Day of Year 2000
Strategy A

Strategy B(c)Figure 2:

NRCan Ultra Rapid Orbit Median RMS (wrt IGR) for Strategies A and B
during December 14-31, 2000.
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IGS 2000 Technical Reports

Finally, for completeness we show in Figure 3 the NRCan daily Ultra Rapid orbit median
RMS (with respect to IGR) for the whole NRCan Ultra Rapid orbit, i.e. 48 hours, divided
into 3-hour intervals for the same period as Figure 2. Strategy A and B are both included
on the same graphic. The comparison is quite interesting and reveals again a clear
improvement for Strategy B.
NRCan Orbit Median RMS (wrt IGR)
(Dec. 14-31, 2000)
Strategy A

Strategy B

80

Estimated Portion
0-24 hrs

Median RMS (cm)70

Predicted Portion
24-48 hrs

60
50
40
30
20

21-24

18-21

15-18

12-15

09-12

06-09

03-06

00-03

21-24

18-21

15-18

12-15

09-12

06-09

03-06

0

00-03

10

Time Interval (hours)

Figure 3:

NRCan Ultra Rapid Orbit Median RMS (wrt IGR) for all 3-hour Intervals ofStrategies A and B. Period covered: December 14-31, 2000.

Future WorkIn the near future, we will investigate the quality of our Ultra Rapid Tropospheric Zenith
Delays (TZD). We would also like to improve our Ultra Rapid orbit along with theassociated ERP. Looking at the longer term, the broadcast satellite clocks or perhaps
estimated satellite clocks could be added to our Ultra Rapid products. The latter will bedifficult to implement due to (again) CPU limitations. New computers may facilitate andspeed up the implementation.
Acknowledgment
NRCan IGS activities are performed in support of the Geodetic Survey Division's
Canadian Active Control System. We thank all of our colleagues of the Active Control
System Operations team. We also thank Dr. Jan Kouba for is invaluable support andadvice.
References
Hugentobler U., S. Shaer and P. Fridez (2001). Bernese GPS Software Version 4.2,
Astronomical Institute University of Berne, Switzerland.
Fang P, G. Gendt, T. Springer and T. Mannucci (2001). IGS Near Real-Time Products
and their Applications, GPS Solutions, Vol. 4, No. 4, John Wiley & Sons, Inc.,
pp. 2-8.

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IGS

A S S O C I A T E

A N A L Y S I S
C E N T E R S

IGSG L O B A L

N E T W O R K

A S S O C I A T E

A N A L Y S I S

C E N T E R S

The Newcastle GNAAC Annual Report for 2000

The Newcastle GNAAC Annual Report for 2000
Konstantin Nurutdinov, David Lavallee, Peter Clarke and Geoffrey Blewitt*
Department of Geomatics
University of Newcastle upon Tyne, NE1 7RU, UK*

Also at Nevada Bureau of Mines, University of Nevada at Reno, USA

The GNAAC at University of Newcastle continued activities with submissions of aweekly G-network and P-network SINEX files. The analysis procedure outlined
previously (P. Davis, G. Blewitt, 2000; Nurutdinov et al., 2000) remained unchanged
throughout the year 2000. Starting with GPS week 1021 the ITRF-97 (51 stations) has
been used instead of ITRF-96 (47 stations) to constrain the solution. Starting with GPS
week 1065 the ITRF-97 from IERS has been replaced with IGS-97 realization of
ITRF-97.
G-network Results
A-network SINEX data from all seven global analysis centres (COD, EMR, ESA, GFZ,
JPL, NGS, SIO) were processed in the year 2000, the appearance of a station in aminimum of 3 solutions defining a global station and inclusion in the combined NCL
G-network (Figure 1). Any remaining stations and RNAAC (AUS, EUR, GSI, SIR)
stations (Figure 2) are defined as regional stations and are included in P-network alongwith global stations. During 2000 an average of 100 global and 60 regional stations
appeared in weekly P-network, this contrasts with 90 and 54 during 1999.
The loose G-network solution (GNET) is estimated from block of normal equations
composed of each deconstrained A-network. The corresponding covariance matrix is
augmented to remove Helmert rotation parameter constraints. This solution is constrainedlater to the CORE 51 stations of ITRF-97 for the year 2000 producing constrained
G-network.
Figure 3 shows the weighted RMS of residuals for each weekly A-network solution afterHelmert transformation to the weekly loose G-network solution for all weeks of the year.
RMS values for weighted RMS are in the region 0.6-2.0 mm describing repeatability of
the G-network estimates.
Figures 4 through 7 show the translation (for X, Y, Z coordinates) parameters for
7-parameter Helmert transformation from deconstrained AC and GNET solutions to
ITRF-97. Mean values for scale parameter are in the range (1 + (1.48 ÷ 2.74) *10-9) with
RMS values (2.73 ÷ 8.46) *10-10.

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110

100

90

80

70

60

Number of global stations

COD
EMR
ESA
GFZ
JPL
NCL
NGS
SIO

50

40

30
1040

1050

1060

1070

1080

1090

1100

GPS week

Figure 1. Number of global stations in AC data
110
100
90
80
70
60

AUS_glob
AUS_reg
EUR_glob
EUR_reg
GSI_glob
GSI_reg
SIR_glob
SIR_reg
NCL_glob
NCL_reg

50
40

Number of stations

30
20
10
0
1030

1040

1050

1060

1070

1080

1090

1100

GPS week

Figure 2. Number of global and regional stations in RNAAC and P-network solutions

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13
COD
EMR
ESA
GFZ
JPL
NGS
NGS
SIO

12
11
10
9
8
7
6
5

Weighted RMS, mm

4
3
2
1
0
1040

1050

1060

1070

1080

1090

GPS week

Figure 3. Weighted RMS of residuals for AC networktransformation to loose NCL G-network
COD
EMR
ESA
GFZ
JPL
NGS
SIO

0.06

0.04

0.02

x

, mT

0.00

-0.02

-0.04

1040

1050

1060

1070

1080

1090

1100

GPS week

Figure 4. Time series of Tx transformation parameter for the ACs to ITRF

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COD
EMR
ESA
GFZ
JPL
NGS
SIO

0.06

0.04

0.02

y

, mT

0.00

-0.02

-0.04

1040

1050

1060

1070

1080

1090

1100

GPS week

Figure 5. Time series of Ty transformation parameter for the ACs to ITRF
0.15

COD
EMR
ESA
GFZ
JPL
NGS
SIO

0.10

0.05

z

, mT

0.00

-0.05

-0.10
1040

1050

1060

1070

1080

1090

1100

GPS week

Figure 6. Time series of Tz transformation parameter for the ACs to ITRF

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0.02

0.01

0.00

z

y

, m, T , TT

-0.01

x

-0.02

-0.03
Tx_GNET
Ty_GNET
Tz_GNET
-0.04
1040

1050

1060

1070

1080

1090

1100

GPS week

Figure 7. Time series of Tx , Ty , T z transformation parameters for the NCL GNET to ITRF

16
AUS
EUR
SIR
GSI

14

12

10

8

RMS, mm

6

4

2

0
1030

1040

1050

1060

1070

1080

1090

1100

GPS week

Figure 8. RMS of residuals for RNAAC R-network transformation to loose NCL G-network

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P-network Results
Creation of P-network is based on G-network and the weekly input R-SINEXes from the
RNAACs. A minimum of 3 global and 1 regional stations is required for inclusion ofsolution in the P-network. However this was not the case sometimes. More often, latesubmission (later than three weeks after the G-network process) of SINEX files by some
RNAACs was the main reason of why their solutions have not been included in
P-network.
From the RNAACs the solutions from AUS, EUR, SIR, GSI were included 51, 53, 45
and 3 times respectively during 2000, contrasting with 11, 52, 31 and 0 times during
1999.
In the used “attachment” method of network combination the G-network is not allowed tobe perturbed by the R-networks. Figure 8 shows time series of the RMS residuals of
station coordinates after 7-parameter Helmert transformation of deconstrained R-network
to GNET.
Other activity
The NCL GNAAC’s solution (NCL) 00 P 01 has been used by IERS to produce
ITRF-2000 reference frame. The solution is a kinematic combination of weekly P-sinex
solutions from the Newcastle GNAAC. The data span is four years (Aug 95 - Aug 99)
and the minimum observation period for individual sites is 2 years.
The transformation parameters between (NCL) 00 P 01 and ITRF-2000 can be found on
the web-page http://lareg.ensg.ign.fr/ITRF/ITRF2000-PA/gcomb/stat.dat.
NCL GNAAC P-sinex solutions on five years interval have been used to detect seasonalvariations of station coordinates and geocenter position (G. Blewitt et al, 2000; G. Blewitt
et al, 2001).
Summary and Outlook
The GNAAC at University of Newcastle continued successfully to submit weekly
G-network and P-network SINEX files to IGS. The most problems encountered were
because of inversion problems with covariance matrix and late submission of solutions
from ACs and RNAACs,
In 2001, the Newcastle GNAAC will continue to submit combined solution to IGS.
TANYA software will be updated to combine Earth rotation parameters. TANYA will be
the base for a new software to be developed within GPSVEL project (G. Blewitt et al.
2000).

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References
P. Davis, G. Blewitt, Methodology for global geodetic time series estimation: A new toolfor geodynamics, Journ. Geophys. Res., Vol. 105, No. B5, pp. 11,083-11,100,
2000.
K. Nurutdinov, D. Lavallee, P. Clarke, G. Blewitt. The Newcastle GNAAC Annual
Report for 1998-1999. International GPS Service for Geodynamics (IGS) 1999
Technical Reports, 125-130, 2000.
G. Blewitt, P.J. Clarke and D. Lavallee. Spatially coherent oscillations in longitude andlatitude linked to seasonal variation in Earth's shape. EOS Trans. AGU, 81(48),
Fall Meeting supplement, F332, 2000.
G. Blewitt, P.J. Clarke, D. Lavallee and K. Nurutdinov. Degree one harmonic
deformations weigh interhemispheric mass transport; a new method for
determining geocenter variations. EOS Trans. AGU, 82(20), Spring Meeting
supplement, S19, 2001.
G. Blewitt, D. Lavallee, P.J. Clarke, K. Nurutdinov, W.E. Holt, C. Kreemer, C.M.
Meertens, W.S. Shiver and S. Stein. GPSVEL project: towards a dense global
GPS velocity field. In 10th General Assembly of the WEGENER Project,extended abstracts book, Bulletin RAO 3/2000.

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R E G I O N A L

N E T W O R K

A S S O C I A T E

A N A L Y S I S

C E N T E R S

The EUREF Permanent Network Report 2000

The EUREF Permanent Network Report 2000
Carine Bruyninx, Fabian Roosbeek
Royal Observatory of Belgium, B-1180 Brussels, Belgium
Heinz Habrich, Georg Weber
Federal Agency of Cartography and Geodesy, D-60598 Frankfurt am Main, Germany
Ambrus Kenyeres
FOMI Satellite Geodetic Observatory, H-1373 Budapest, Hungary
Gunter Stangl
Institute of Space Research, A-8042 Graz, Austria
Introduction
Within the IAG Commission X, EUREF is the sub-commission, which is responsible forthe maintenance of the European Reference System ETRS89. Members of the group aremainly federal survey authorities, universities and research institutes interested in therealization of a unified horizontal and vertical reference frame. Since 1995, the epochwise EUREF GPS campaigns were replaced to a great extent by the installation of theEPN, the EUREF Permanent GPS Network (EPN). This was done in close collaboration
with the IGS seeking for regional densifications. In 1996 the EPN was accepted as aregional Network Associate Analysis Center (RNAAC) of the IGS for Europe.
EPN Management and new Structure
Since its start in 1995, the activities within the EPN are coordinated and guided by the
EUREF Technical Working Group (EUREF TWG). A dedicated network coordinator
took care of the day-to-day management of the permanent network. With the growth of
the network and the tasks involved, EUREF started a re-organization at its 10th yearly
Symposium in Tromsø, Norway, June 22nd-24th, 2000. Three units will, from now on,
be involved in the management and development the EPN. These are the EPN
Coordination Group (CG), the EPN Central Bureau (CB) and the EPN Special Projects(SP).
The EPN CG coordinates all activities related to the EPN. Members are the network
coordinator, the data flow coordinator, the analysis coordinator, a representative of the
TWG and the special projects liaison persons. The special projects are intended to study
newly developing demands and activities based on EPN data and their potential use.
Presently two special projects are ongoing, the "Generation of an EUREF-troposphere
product" and "Monitoring of the EPN to produce coordinate time series suitable for
geokinematics". Special projects, if successful, may, turn to EPN products after a 4-year
project term.
Extensions of the EPN Tracking Network
Figure 1 shows the status of the EUREF permanent tracking network as in June 2001.
The number of stations is 118. From these, 47 % of them belong also to the IGS network.

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To encourage the installation of EPN stations in less dense regions, the EUREF TWG has
adopted (November 24, 2000) a new guideline concerning the station location: a minimal
distance of 300 km to already existing EPN stations is required, accepting the interest ofeach nation to have at least one EPN station. Exceptions to this rule are possible forstations submitting hourly data or contributing to EPN Special Projects. Thanks to thisnew guideline 45% of the EPN stations are now submitting hourly data.
30˚

0˚

VARS
TRO1
KIRU SODA
KIR0
REYK
HOFN
VIL0

60˚

TRDS

60˚

JOEN

VAAS

SVTL
MAR6

METS

OSLS
STAS
ONSA

45˚

ACOR
PDEL
GAIA

CASC

VALE
ALAC
SFER

RIGA

MDVO
ZWEN

LAMA
HELG
BORK
HOBU
TERS
BOGO
WSRT
POTS BOR1
DELF KOSG
JOZE
GLSV
NPLD
PTBB
DRES
DENT
WROC
WARE EIJS
HERSBRUS EUSK KLOP
GOPE
DOUR
UZHL
BRST
KARL WTZR
MLVL
MOPI
MANS
OBER
PENC
SBGZ
PFAN
HFLK
GRAZ
CHIZ
ZIMM
BZRG GSR1
SJDV
OSJE
BUCU
UPAD VENE
TORI
GENO
CANT
SRJV
MEDI
TLSE
GRAS UNPG CAME
SOFI
MARS
ESCO LLIV
DUBR
ISTA TUBI
CREU
AJAC
BELL
ORID
VILL YEBE
EBRE
MATE

LAGO

30˚

VIS0

45˚
ZECK

NSSP
TRAB

ANKR

MALL
CAGL
NICO

ALME

30˚

NOT1
LAMP

RABT

DRAG
RAMO

30˚
0˚

Figure 1 – EPN tracking network, as of June 2001
EPN Data Flow
During the year 2000, the data flow within the EPN was considerably increasing since
several EPN stations started transmitting hourly data together with daily data. Up to now,the delivery of daily transfers is still advisable for approximately 10% of the stations:they are still not delivering routinely the full 24 files/day.
The quality of the daily data flow has improved: at the EUREF Data Centre (BKG), theproportion of bad files (unreadable or wrong contents) fell from 1% to 0.05%. A part ofthis improvement was achieved by introduction of checking routines at the EPN Data
Centers (DC). Unfortunately the checking procedures are not yet consistent at all DCs.

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Recommended checks are:
• The unix/Hatanaka compression/decompression test
• Teqc, to get a basic overview of the data quality• A test for the correspondence between file name and contents (e.g. wrong day).
If an error was found during transfer the file should be rejected.
The Regional Data Centre at BKG is the only EPN data center holding the majority of the
EPN data. This single-center-dependency puts the EPN is a vulnerable position. A
preparation for a mirror DC is under way. In case of outages users will have thepossibility to switch from the Regional DC to the mirror, and this for both data input asdata retrieving. This procedure is already working for the Local DCs.
Data Analysis
The observations of the EPN are currently analyzed by 13 Local Analysis Centers(LACs): ASI (Nuova Telespazio S.p.A., Space Geodesy Centre, Italy), BEK(International Commission for Global Geodesy of the Bavarian Academy of Sciences,
Germany), BKG (Bundesamt für Kartographie und Geodäsie, Germany), COE (European
solution created at CODE (Centre for Orbit Determination in Europe), DEO (Delft
Institute for Earth-Orientated Space Research, Delft University of Technology,
Netherlands), GOP (Geodetic Observatory Pecny, Czech Republic), IGN (Institut
Géographique National, France), LPT (Bundesamt für Landestopographie (L+T),
Switzerland), NKG (Nordic Geodetic Commission), OLG (Observatory Lustbühel Graz,
Austria), ROB (Royal Observatory of Belgium), UPA (Universita di Padova, Italy) andWUT (Warsaw University of Technology, Poland).
The LACs submit weekly solutions of their subnet in the SINEX format (SINEX, 1996)
to the EUREF Data Center at BKG .
The EPN Network Coordinator selects the subset of stations of each LAC in order toguarantee that each station is processed by at least 3 LACs. This resulting redundancy isused for quality control and outlier detection ; the individual LAC solutions are
successively compared to the combined solution. Stations or even complete LAC
solutions which show such a difference to the combined quantity that exceeds apredefined range (5 mm for the position or 10 mm for the height) are excluded in the
final combined solution. Graphical visualization tools, e.g., the plot of correlation
coefficients of the coordinates, are used for quality control.
Combination Scheme
The ADDNEQ program of the Bernese Software (Beutler et al., 1996) is used to combine
the weekly SINEX files. At that time the a priori constraints of the station coordinates are
removed. The normal equations are first combined into a free network solution, where 13
stations are selected to define the "minimum constrained conditions" in the ADDNEQ
program. This solution is used for outlier detection.

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After the exclusion of all outliers the official EUREF solution is generated where thecoordinates of 13 stations are fixed to the ITRF-97.
In order to check the coordinate time series, a free network combination of the last seven
EUREF combined solutions is routinely computed. This may lead to the exclusion of
more stations and may require an additional iteration of all combination steps.
Introduction of a new Local Analysis Center
A new LAC located at the Delft University of Earth-Orientated Space Research,
Netherlands (DEO) submitted its first solution on GPS week 1095. It is the first LAC
within the EPN using GIPSY software (Web and Zumberge, 1995). The original solution
from DEO could not be combined, as is, with the other 12 contributions, using theADDNEQ program. However, using a different scheme, the combination could be
performed. This different scheme was based on the estimation of a seven-parameter
Helmert transformation between the station coordinates of the individual solutions and a"reference solution". In a second step those transformed coordinates were combined.
Some investigations explained that the original combination could not be performed
because of the very small (0 to 0.1) correlation coefficients between the station
coordinates in the DEO SINEX solution. After some small changes in the processing
scheme of DEO, significant correlations of 0.5 to 1.0 between the station coordinates
showed up in the DEO SINEX files. As a result, since the beginning of GPS week 1100,
the ADDNEQ program has successfully been used to add the DEO solution to the
EUREF combined solution.
Weighting of Solutions
The various analysis softwares used by the LACs requires a scaling of the co-variances ofeach solution before the combination, and this in order to remove the software specificdifferences. For the LACs working with the Bernese Software, the SINEX files include
the RMS of unit weight (d), which is used as the weighting factor : all elements of thecovariance matrix are multiplied with the factor 1/d2 when the SINEX files are converted
to normal equations. However, the RMS of unit weight is not available from the GIPSY
and Microcosm solutions, which are the two other GPS data analysis packages
contributing to the EPN. In addition to the weighting with 1/d2, an external weight file isintroduced to scale each normal equation file in the combination. The factors given in thisweight file are currently empirically determined to result in an equal contribution of all
LAC solutions to the combined solution. It is clear that the weighting scheme is currently
still one of the topics of investigation.
Time Series Special Project
The EPN may be considered as a kinematic network, where the stations have an
increasing role in geokinematic interpretation as well. The quality of the EPN kinematic
products (coordinate time series, velocities) is highly dependent on the station

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monumentation/data quality and the combination scheme used. In 2000, an EPN SP has
been established in order to improve the EPN performance with a careful analysis andoverview of each station encompassing the coordinate time series, the stability of themonumentation and the environmental effects. The SP is a joint effort of 6 different
groups, where each group is responsible for a specific sub-region of the whole EPN. The
groups are also encouraged to involve additional, non-official EPN sites into the analysis
in order to derive a more detailed kinematic pattern of Europe.
To help the assessment of station quality and kinematic relevance, the SP contributed
significantly to the preparation of the new IGS GNSS log format.
In the 1st work phase, the coordinates jumps and outliers are determined and collected
into a uniform station problem file. This work is in progress, a retrospective analysis will
be completed by the end of 2001. In the following work phases the spectral properties(periodical effects, noise spectra) of the time series will be analyzed.
Using all collected information an improved multi-year combination solution and timeseries are computed and also updated regularly. The improved time series including atable with station problems are displayed on the EPN CB Web pages(www.epncb.oma.be/series_sp.html). These pages also summarize all activities related to
the SP.
Troposphere Special ProjectWithin the routine analysis of a network of ground-based GPS receivers, troposphericparameters are part of the estimation. Longer series of the zenith path delays, forexample, support climate research. Therefore EUREF decided to create a Special Project"Troposphere Parameter Estimation".
Similar to combining weekly SINEX files for the derivation of a combined coordinate
product, BKG is going to produce a combined troposphere solution with input from theindividual troposphere solutions of all ACs, which contribute to the coordinate solution.
Their analysis is carried out in post processing mode on the basis of precise orbits.
Initially supported by GFZ, the combination will be done following today’s IGS
standards (Gendt, 1997): epoch-wise combination of the single solutions as weighted
mean with rigorous outlier detection in consecutive steps; biases between the individual
solutions have to be taken into account. As a result two weekly files will be produced. (1)A summary file with some statistics about e.g. the frequencies of the analyzed sites andabout the accuracies of a single AC solution. This file provides feedback to thecontributing ACs. (2) An output file (EURwwwwd.TRO) with the combined troposphereestimates from which the estimates for a single site can easily be extracted. The
coordinates, as a necessary part of this file, will be taken from EUREF’s official
combined SINEX file.
Beginning with GPS week 1108 the first ACs delivered their daily troposphere solution
files to BKG. Thus, the testing of the combination software could be started. A common

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tropospheric sampling rate of 1 hour is desirable while at the beginning most of thesolutions have a two-hour sampling rate.
Outlook
The analysis guidelines, adopted in April 1997 by the EUREF AC's to guarantee thehomogeneity of the EUREF solution have aged. New analysis guidelines have beendeveloped at the EUREF Analysis Centers Workshop held in Warsaw, Poland in May
2001. The EPN AC’s have agreed to switch to the new analysis guidelines on GPS week
1130 (September 2, 2001). More details about the new guidelines will be available innext year’s annual report.
References
SINEX (1996): "Solution Independent Exchange Format Version 1.0", Proceedings of the
IGS Analysis Workshop, JPL Pasadena, California, USA, March 19 – 21, 1996
Beutler G., Brockmann E., Fankhauser S., Gurtner W., Johnson J., Mervart L., Rothacher
M.,Schaer S., Springer T., Weber R. (1996): "Bernese GPS Software Version
4.0 Documentation", Astronomical Institute University of Bern
Gendt, G.: IGS Combination of Tropospheric Estimates (Status Report). Proceedings IGS
Analysis Center Workshop, 1997, Pasadena.
Web F.H. and Zumberge J.F. (1995), "An Introduction to GIPSY/OASISII", JPL
Acknowledgements
Without the labor and the commitment of the responsible agencies, their representatives
at the observation sites, the data centers and the analysis centers, the EUREF network
would not be the success that is it today. The authors would like to acknowledge
especially the responsibles of the EUREF analysis centers.

136

AUSLIG RNAAC - 2000 Annual Report

AUSLIG RNAAC – 2000 Annual Report
Geoff Luton
Australian Surveying and Land Information Group (AUSLIG)
Canberra, Australia
Introduction
AUSLIG continued processing all stations in the Australian Regional GPS Network(ARGN) during 2000. The weekly combined SINEX result files were submitted to the
Crustal Dynamics Data Information System (CDDIS) as AUSLIG’s role as an IGS type 2
Associate Analysis Centre.
Station Network
The station network processed by the AUSLIG RNAAC is shown in Figure 1. Thirteen of
the seventeen stations in this network are operated by AUSLIG. DST1, PERT, TID2 andYAR1 are owned and operated by non-Australian agencies.
Data Analysis and Results
The Bernese GPS Software version 4.0 (Rothacher and Mervart 1996) is used for the
GPS data processing. Daily solutions are computed using the following strategy:•

L3 double differenced phase observable.

•

No resolution of integer ambiguities.

•

Elevation cut-off angle of 20°.

•

Estimation of tropospheric zenith delay parameters at 2 hourly intervals.

•

IGS antenna phase centre variation model applied.

•

IGS final orbits and EOPs held fixed.

•

Station coordinates for a single station constrained (either TID2 or YAR1).

Seven daily solutions are combined at the normal equation level to obtain the weekly
solution output in SINEX format submitted to the CDDIS. These solutions up to andincluding GPS week 1064 were tightly constrained to the ITRF97 coordinates at thefollowing IGS reference stations; CAS1, DAV1, HOB2, MAC1, PERT, TID2 and YAR1.
From GPS week 1065 onwards the IGS97 realisation of ITRF97 was used for coordinate
constraint at these seven stations.
The AUSLIG RNAAC weekly SINEX solution files were included in the Type 2
GNAAC combination generated by the Massachusetts Institute of Technology (MIT) andthe University of Newcastle upon Tyne GNAAC Polyhedron solutions.

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Figure 1. AUSLIG RNAAC station network as of 31 December 2000

Future Plans
AUSLIG plans to participate as an IGS Associate Analysis Centre (AAC) in support ofLow Earth Orbiter (LEO) Missions.
References
Rothacher, M. and L. Mervart (eds.), Bernese GPS Software Version 4.0, AstronomicalInstitute, University of Berne, 1996.

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GSI RNAAC Technical Report 2000

GSI RNAAC Technical Report 2000
A. Yamagiwa
Geodetic Observation Center
Geographical Survey Institute, Japan
Introduction and Overview
Since 1996, Geographical Survey Institute (GSI) has been contributing as a Regional
Network Associate Analysis Center (RNAAC).
In 1999, our fiducial IGS site TSKB (located in Tsukuba, Japan) had suffered from GPS
End of Week Rollover Problem and we had had to re-convert navigation files for
RNAAC processing. This problem was fortunately solved in March 2000 andcomplemental analysis was finished in March 2001.
Outline of Processing
7 domestic GPS sites, as well as 10 IGS global sites, are selected for this regional
analysis (Figure 1a, 1b). Daily coordinate solutions are generated using GAMIT version
9.95 and they are combined with GLOBK version 5.04 to generate weekly constraint
solutions.
Characterizing features of the performed solutions are as follows;• Finale IGS orbits and Earth orientation parameters are applied.
• Measurement elevation angle cut off 20 degrees, sampling interval 60 secs for
single-day adjustments.
• Tropospheric zenith delays are estimated every 3 hours.
• Station coordinates estimated in the International Terrestrial Reference Frame(ITRF), applying a priori sigma of ~10m.
Estimated parameters are obtained as Software/Solutions Independent Exchangeable(SINEX) format and submitted to Crustal Dynamics Data Information System (CDDIS).
Current State
The standard deviation of GSI RNAAC analysis 2000, which represent the reliability
about this analysis, is shown in Figure 2.

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Figure 1. GPS observation sites for GSI RNAAC analysis(a) IGS global sites (b) domestic sites

Figure 2. Standard Deviation of GSI RNAAC weekly solution

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Annual Report 2000 of IGS RNAAC SIR

Annual Report 2000 of IGS RNAAC SIR
Wolfgang Seemüller and Hermann Drewes
Deutsches Geodätisches Forschungsinstitut
München, Germany
Introduction
Since July 1996, the Deutsches Geodätisches Forschungsinstitut (DGFI), Munich, acts as
the IGS Regional Network Associate Analysis Center for the South American geocentricreference system SIRGAS, RNAAC SIR (Seemüller and Drewes, 1998, 1999, 2000). Allavailable data in this region are routinely processed with the automated version of theBernese software (Rothacher et al., 1996) on a weekly basis and submitted as SINEX
files to the IGS Data Centers. The RNAAC SIR solutions are then included in the global
combined polyhedron solutions of the IGS GNAACs.
Station Network
The RNAAC SIR strives permanently for densifying its regional network. This year, four
new global GPS stations were added to the network. These stations are Guatemala(GUAT), San Lorenzo (SLOR), and San Salvador (SSIA) in Central America, and Puerto
Rico (PUR3) in the Caribbean Sea. The network consists at present of 47 stations, 31
stations are global and 16 are regional (Figure 1).
Solutions
Since GPS week 1053 the processing strategy was slightly modified. The sampling rate
was changed from 2 min. to 30 sec., and the troposphere is estimated once per two hours
instead of four hours. These changes produce better results of the solutions.
In the last Annual Report (Seemüller and Drewes, 2000) we presented the first IGS
RNAAC SIR solution for coordinates and velocities (DGFI00P01) generated by acomplete reprocessing based on the latest realization of the IERS Terrestrial Reference
Frame (ITRF1997). At the end of year 2000 a new solution was computed including all
weekly RNAAC SIR solutions from 1996 to 2000. It provides position and linear velocity
estimates of sites being in operation since at least one year. IGS combined orbits andEarth orientation parameters were held fixed. The datum was constrained with respect tothe ITRF97 coordinates and velocities of stations CRO1, FORT, SANT, AREQ, BRAZ,
LPGS, and OHIG. The reference epoch is 2000:000 (see figure 1).
The observations of the IGS RNAAC SIR stations were also included in the SIRGAS
2000 campaign. By this means the RNAAC stations contribute to this latest realization of
the American Reference System (Figure 2) where emphasis is given to the establishmentof a unified continental vertical reference system by including all the tide gauges thatdefine the classical national height systems.

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260º

280º

320º

300º

340º

0º

BRMU

RCM6

INEG

20º

20º

PUR3
JAMA

GUAT
TEGU
SSIA
SLOR
MANA ESTI
MOIN

CRO1
BARB

CART

MARA

BOGA BOGT

KOUR

0º

0º
GALA

RIOP

FORT

MANU
IMPZ

BOMJ

CUIB

UNSA

PARA

EISL

POAL

CORD
IGM0

-40º

-20º

VICO
(RIOD)

UEPP

SANT

SALV

BRAZ

AREQ

-20º

ASC1

RECF

LPGS

VBCA

-40º

GOUG

RWSN

RIOG

-60º

-60º
PALM

OHIG

2 cm/a NNR NUVEL-1A
2 cm/a ITRF97
2 cm/a DGFI00P02

260º

280º

VESL

300º

320º

340º

0º

Figure 1: Horizontal velocities of IGS RNAAC SIR stations
Conclusion
Figure 1 shows the velocities of the new solution DGFI00P02 compared with thevelocities of ITRF97 and the geophysical model NNR NUVEL-1A. The comparison with
the ITRF97 yields a good agreement for most of the stations. Discrepancies exist withrespect to the NUVEL-1A model in stations close to plate boundaries (e.g. AREQ and
SANT). This is because NNR NUVEL-1A does not model deformations in plateboundary zones. Obvious are the discrepancies between both solutions in stations withshort time series. The velocities tend much more to the east, like in the stations RWSN,VBCA, POAL, SALV, and RECF. The reason for these deviating velocities is still
unknown, and has to be investigated. The same is valid for station INEG, where thevelocities have opposite azimuths.

142Annual Report 2000 of IGS RNAAC SIR

220º

240º

260º

280º

300º

320º

YELL

TSEA

WHIT

60º

60º
CHUR
SCH2

FLIN
WILL

CALG

HOLB
NEAH
PABH

DUBO

DRAO
ALBH
KELS
REDM

STJO
ALGO

EPRT
BARH
WES2
NPRI

YBHB
TMGO
AMC2

40º
CNDR

SIO3

USNA
USNO

ASHV
COLA
CHA1

MEXI
HER2

LPAZ

CHI3
CULI

COL2

BRMU

GAL1
AOML

MTY2
TAMP

INEG
20º

40º

GODE
SOL1
VIMS

MERI
CAM2
VIL2 CHET
ELEN
BATL
AURO
TEGU
NPAC
ESTI
MANA

OAXA

BALT
GALA

0º

20º

PUR3

TOLU

JAMA

CRO1

AMUA
GUAI CARU F118
CA00
MARA JUNQ USB1
CANO
SANA
GEOB
ELEV
AGUA
TTWR
KOUR
BOGA
KAMA
BTUR
INIR
PAST
IPIA
TULC
PSAN
LATA
RIOP
LIBE
IQUI
MANU
FOR1
TALA
LETI
ZAMO
IMPZ
PIUR
CART

MAIC

0º
FORT
CRAT

PUCA
LIMA
ERP1

RECF
RIBE
MALD
RIAB
IXIA

LAPU
AREQ
MATA
ARIC
IQQE
UAPF
ANTO
ANTF

SALV

BOMJ

CUIB
BRAZ
CLAR
CHIQ
CORU
PICA
CAMI
VICO
OLLAENRI
UEPP
MCAE
CAC1
CHAJ
RIOD
PA-1
UNSA
CANA
IGUA PARA
TUCU
CHAM
COPO
IMBI
RBLS
GALP POAL
CFAG
BELL
CORD
CPIE
SANT
RINC
VIGI
VALP CRIC MORR IGM0SHEE
LPGS MONT PEST
CASU
LHCL
MRD1
ANTC LOTE
TAND
VBCA
PUER
MAI1

-20º

EISL

-40º

HUIC

-20º

-40º

RWSN
COYQ
BLMC

PARC
PTAS

LO10

IBAN
RIOG
AUTF

-60º

-60º

SIRGAS 95
New SIRGAS
Tide Gauge

220º

OHIG

DGFI
240º

260º

280º

Figure 2: Network of the SIRGAS 2000 campaign

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References
ROTHACHER, M. and L. MERVART (eds): Bernese GPS software version 4.0.
Astronomical Institute, University of Berne, 1996.
SEEMÜLLER, W. and H. DREWES : Annual Report 1997 of the RNAAC SIRGAS 1997
Technical Reports, I. MUELLER , R. NEILAN, K. GO W E Y, eds. Pasadena, CA: Jet
Propulsion Laboratory, 1998.
SEEMÜLLER, W. and H. DREWES : Annual Report 1998 of RNAAC SIRGAS,1998
Technical Reports, R. NEILAN, A. MOORE , K. GOWEY, eds. Pasadena, CA: Jet
Propulsion Laboratory, 1999.
SEEMÜLLER, W. and H. DREWES: Annual Report 1999 of RNAAC SIRGAS, 1999
Technical Reports, IGS Central Bureau, eds., Pasadena, CA: Jet Propulsion
Laboratory, 2000.

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I E R SC O N T R I B U T I O N S

The IERS International Terrestrial Reference Frame

International Earth Rotation Service (IERS) /International Terrestrial Reference System (ITRS) Contributions
Zuheir Altamimi
Institut Géographique National,
FranceIntroduction
Following its terms of reference, IGS works in close cooperation with the International
Earth Rotation Service (IERS). The Product Center of the International Terrestrial
Reference System (ITRS) of the IERS, hosted by the Institut Géographique National,
cooperates very closely with the different IGS components (Central Bureau, Analysis
Centers, and tracking stations) for ITRF station coordinates and analysis of solutions
provided by IGS analysis centers as well as site information and local ties of thecollocation sites. For more information, see http://lareg.ensg.ign.fr/ITRF.
ITRF and IGS Relationship
Since the beginning of the IGS preliminary test activities in 1992, the IGS Analysis
Centers have used ITRF coordinates for some subset of stations in their orbit
computations. Moreover, the combined IGS ephemerides are expressed in ITRS because
the coordinates used by the IGS are based on ITRF91 from the beginning until the end of
1993; ITRF92 during 1994; ITRF93 during 1995 until mid-1996; ITRF94 since mid-1996
until the end of April 1998; ITRF96 starting on March 1, 1998; ITRF97 starting on 1
August 1999, and ITRF2000 in late 2001.
IGS supports the continuous improvement of the ITRF by contributing to the extension of
the ITRF network, providing new collocations or by improving position accuracy. The
IGS Analysis Centers contribute greatly to ITRF by providing IGS/GPS solutions, which
are included in the ITRF combinations.
IGS provides also a very efficient method to densify the ITRF network: one can now
obtain millimetric positions directly expressed in ITRS by processing suitable GPS data
together with IGS products.
ITRF2000
The ITRF2000 solution is the most dense and accurate frame ever developed, containing
about 800 stations located at about 500 sites. It has been achieved by simultaneous
combination of positions and velocities using full variance/covariance matrices of theindividual solutions provided by the IERS analysis centers. It includes primary corestations observed by very long baseline interferometry (VLBI), lunar laser ranging(LLR), satellite laser ranging (SLR), GPS, and DORIS (usually used in previous ITRF

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versions), as well as regional GPS networks for its densification (Alaska, Antarctica,
Asia, Europe, North and South Americas, and Pacific). Figure 1 shows the distribution of
the primary sites of ITRF2000, highlighting the collocated techniques.

any single technique (GPS, VLBI, SLR, DORIS)
70 collocations (any two of the techniques at one location)

25 collocations (any three)
6 collocations (all four)

Figure 1. The ITRF2000 primary network. Symbols indicate collocations of space
geodetic techniques (GPS, VLBI, SLR, DORIS).
The ITRF2000 is intended to have an accurate datum definition, achieved as follows:• The origin and its rate by a weighted average of most consistent SLR solutions.
• The scale and its rate by a weighted average of VLBI and most consistent SLR
solutions. Unlike the ITRF97 scale expressed in the Geocentric Coordinate Time
Frame, that of the ITRF2000 is expressed in Terrestrial Time Frame.
• The orientation is aligned to that of ITRF97 at 1997.0 epoch and its rate to be suchthat there is no-net-rotation rate with respect to NNR-NUVEL-1A. Note that theorientation as well as its rate are defined upon a selection of ITRF sites with highgeodetic quality.
The ITRF2000 long-term stability, evaluated over 10 years, is estimated to be better than
4 millimeters in origin and better than 0.5 parts per billion in scale, equivalent to a shift instation heights of approximately 3 millimeters over the Earth’s surface.
All the ITRF2000 related files are available at: http://lareg.ensg.ign.fr/ITRF/ITRF2000.

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D A T AC E N T E R

R E P O R T S

IGSG L O B A L

C E N T E R S

CDDIS 2000 Global Data Center Report

CDDIS 2000 Global Data Center Report
Carey E. Noll
Terrestrial Information Systems BranchNASA Goddard Space Flight Center, Code 922
Greenbelt, MD 20771

Introduction
The Crustal Dynamics Data Information System (CDDIS) has supported theInternational GPS Service (IGS) as a global data center since 1992. The CDDIS activities
within the IGS during 2000 are summarized below; this report also includes any changes
or enhancements made to the CDDIS during the past year. General CDDIS backgroundand system information can be found in the CDDIS data center summary included in the
IGS 1994 Annual Report (Noll, 1995) as well as the subsequent updates (Noll, 1996,
Noll, 1997, Noll, 1998, Noll, 1999, and Noll, 2001).
System Description
The CDDIS archive of IGS data and products are accessible worldwide throughanonymous ftp. The CDDIS is located at NASA’s Goddard Space Flight Center (GSFC)
and is accessible to users 24 hours per day, seven days per week.
Computer Architecture
The CDDIS is operational on a dedicated Compaq AlphaServer 4000 running the UNIX
operating system. All GPS data and product files are archived in a single filesystem,
accessible through anonymous ftp, and are stored in UNIX compressed format. At
present, nearly 100 Gbytes of on-line magnetic disk space is devoted to the storage ofdaily GPS tracking data and products.
The CDDIS staff continues to archive older GPS data, not currently on-line, to CD-ROM
for eventual access through a 600-platter CD-ROM jukebox. Thus far, GPS data from1992 through 1999 have been archived to CD, at least one week per CD. These data are
migrated from magneto-optical disks (in VAX/VMS format) to the UNIX system where a
CD-ROM image is created. After mounting the resulting CDs in the jukebox, users canaccess the data contained on these CDs in a transparent fashion, i.e., the jukebox software
creates a filesystem similar to on-line magnetic disk filesystems.
Archive Content
As a global data center for the IGS, the CDDIS is responsible for archiving and providing
access to both GPS data from the global IGS network as well as the products derived
from the analyses of these data.
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GPS Tracking Data
The GPS user community has access to the on-line and near-line archive of GPS data
available through the global archives of the IGS. Operational and regional data centersprovide the interface to the network of GPS receivers for the IGS global data centers. The
following operational or regional data centers make data available to the CDDIS fromselected receivers on a daily (and sometimes hourly) basis:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

Australian Survey and Land Information Group (AUSLIG) in Belconnen,
Australia
Alfred Wegener Institute (AWI) for Polar and Marine Research in Bremerhaven,
Germany
Bundesamt für Kartographie und Geodäsie (BKG) in Frankfurt, Germany
Chinese Academy of Surveying and Mapping (CASM) in Beijing, China
Centre National d'Etudes Spatiales (CNES), France
Deutsches Geodätisches ForschungsInstitut (DGFI) in Munich, Germany
European Space Operations Centre (ESOC) in Darmstadt, Germany
GeoforschungsZentrum (GFZ) in Potsdam, Germany
Geographical Survey Institute (GSI) in Tsukuba, Japan
Jet Propulsion Laboratory (JPL) in Pasadena, California
Korean Astronomy Observatory (KAO) in Taejeon, Korea
National Geography Institute (NGI) in Suwon-shi, Korea
National Imagery and Mapping Agency (NIMA) in St. Louis, Missouri
NOAA’s Geosciences Laboratory (NOAA/GL) Operational Data Center(GODC) in Rockville, Maryland
Natural Resources of Canada (NRCan) in Ottawa, Canada
Pacific Geoscience Centre (PGC), NRCan in Sidney, Canada
Regional GPS Data Acquisition and Analysis Center on Northern Eurasia(RDAAC) in Moscow, Russia
University NAVSTAR Consortium (UNAVCO) in Boulder, Colorado
United States Geological Survey (USGS) in Reston, Virginia

In addition, the CDDIS accesses the other two IGS global data centers, Scripps
Institution of Oceanography (SIO) in La Jolla California and the Institut Géographique
National (IGN) in Paris France, to retrieve (or receive) data holdings not routinely
transmitted to the CDDIS by an operational or regional data center. Table 1 lists the data
sources and their respective sites that were transferred daily to the CDDIS in 2000. Over
62K station days from 199 distinct GPS receivers were archived at the CDDIS during thepast year; a complete list of these sites can be found at URL
ftp://cddisa.gsfc.nasa.gov/pub/reports/gpsdata/cddis_summary.2000.

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Daily GPS Data Files
Once the daily RINEX data files arrive at the CDDIS, these data are quality-checked,
summarized, and archived to public disk areas in daily subdirectories; the summary andinventory information are also loaded into an on-line data base.
The CDDIS daily GPS tracking archive consists of observation, navigation, andmeteorological data, all in compressed (UNIX compression) RINEX format.
Furthermore, summaries of the observation files are generated by the UNAVCO qualitychecking program TEQC (Estey 1999) and are used for data inventory and quality
reporting purposes. During 2000, the CDDIS archived data on a daily basis from anaverage of 170 stations. Each site produces approximately 0.8 Mbytes of data per day(compressed RINEX, compressed compact RINEX, navigation, meteorological, andsummary); thus, one day’s worth of GPS tracking data totals nearly 130 Mbytes.
Although the “compact RINEX” data format is the operational format for exchange ofGPS data between the IGS and analysis centers, the CDDIS continues to archive andmake data available in the compressed RINEX format for use by the general user
community. In 2000, the CDDIS GPS data archive totaled over 50 Gbytes in volume;
this figure represents data from nearly 62K observation days. Of the 170 or more sites
archived each day at the CDDIS, not all are of “global” interest; some, such as those inSouthern California, are regionally oriented. The CDDIS receives data from these sites aspart of its NASA archiving responsibilities.
The ephemeris data files for a given day are decompressed and then merged into a single
file that contains the orbit information for all GPS satellites for the day. This daily
ephemeris data file, named brdcddd0.yyn.Z (where ddd is the day of year and yy is theyear), is then copied to the ephemeris subdirectory as well as a general directory of all
merged ephemeris files (/gps/gpsdata/brdc). Users can thus download this single daily fileinstead of all broadcast ephemeris files from the individual stations.
At this time, the CDDIS on-line archive of daily GPS data contains data from January
1998 through the present. Prior to early 2001, these data are available in compact RINEX
only; later data are archived in both compact RINEX and uncompacted RINEX formats.
As the disks supporting this archive fill up, older uncompact RINEX observation data aredeleted. The CD-ROM jukebox contains GPS data from 1992 through 1997; it is hoped
the software interface to this device will be operational in mid-2001.
The majority of the data delivered to and archived in the CDDIS during 2000 wasavailable to the user community within six hours after the observation day. As shown in
Figure 1, nearly fifty percent of the data from the global sites delivered to the CDDIS
were available within three hours of the end of the observation day; over twenty percent
were available within one hour. These statistics were derived from the results of the dailyarchive report utilities developed by the IGS Central Bureau and executed several times
each day on the CDDIS.

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Hourly GPS Data Files
By the end of 2000, seven operational/regional data centers (BKG, ESOC, JPL, NOAA,GFZ, PGC, and NRCan) were transmitting hourly data files to the global data centers.
Each file of observation (in compact RINEX format only), navigation, and meteorological
data contains a single hour’s worth of thirty-second data. These individual hourly files
are labeled by incrementing the sequence number digit in the RINEX file naming
convention; e.g., the file mmmmddda.yyo.Z contains the observation data for the first hourof day ddd (or the first file transmitted for day ddd) in year yy for site mmmm. Withinminutes of receipt, the files are archived to separate subdirectories (/gps/nrtdata) by day
and hour on the CDDIS. These data are retained on-line for three days. After that time,
the hourly data files are deleted; the daily file, transmitted through normal channels with atypical delay of one to two hours, will have been received and archived already and thus
the hourly data are of little use. Furthermore, to ensure the most rapid delivery of thesedata to the user community, no validation or checks on data quality are performed. As
shown in Figure 2, in 2000, fifty percent of these hourly data files were available to theuser community within 15 minutes of the end of the hour; nearly eight-five percent wereavailable within thirty minutes. GPS sites supplying hourly data to the CDDIS in 2000
are denoted by an * in Table 1; over seventy sites transmitted hourly data files to theglobal data centers in 2000.
Meteorological Data
The CDDIS currently receives meteorological data from over thirty sites, as noted inTable 1. The meteorological data provided are dry temperature, relative humidity, andbarometric pressure at thirty minute sampling intervals. These data are stored on CDDIS
with the daily GPS observation and navigation data files in parallel subdirectories.
IGS Products
The seven IGS data analysis centers (ACs) retrieve the GPS tracking data on a daily basis
from the global data centers to produce daily orbit and clock products as well as weekly
Earth rotation parameters (ERPs) and station position solutions; the seven IGS associate
analysis centers (AACs) also retrieve IGS data and products to produce station position
solutions. The CDDIS archives the products generated by both types of IGS analysis
centers. These files are delivered to the CDDIS by the IGS analysis centers to individualuser accounts, copied to the central disk archive, and made available in compressed format
on the CDDIS by automated routines that execute several times per day. The IGS
Analysis Coordinator then accesses the CDDIS (or one of the other global analysis
centers) on a regular basis to retrieve these products and derive the combined IGS orbits,
clock corrections, and Earth rotation parameters as well as to generate reports on data
quality and statistics on product comparisons. Users interested in obtaining precision
orbits for use in general surveys and regional experiments can also download the IGS
products. 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.

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Regional Network Associate Analysis Centers (RNAACs) routinely generate station
position solutions for regional networks in Software INdependent EXchange (SINEX)
format. The three Global Network AACs (GNAACs) perform a comparison of thesefiles and submit the resulting SINEX files to the CDDIS. The GNAACs also access the
SINEX files from the IGS ACs and RNAACs and produced comparison and combined,
polyhedron station position solutions. The CDDIS provides “short-SINEX” files,
designated with an .ssc extension, for all AC and AAC SINEX files. These files containthe site information from the SINEX file but no matrices. All RNAAC solution files arealso stored in the weekly IGS product subdirectories. The official IGS combined weekly
SINEX solutions and cumulative combined SINEX solutions generated by the IGS
Reference Frame Coordinator are also available in the weekly IGS product subdirectories.
Both the rapid (designated IGR) and the predicted orbit, clock and ERP (designated IGP)
combined products generated by the IGS Analysis Coordinator continued to be available
through 2000. Furthermore, a new product, the IGS ultra-rapid combination (designated
IGU) were made available twice daily (at 03:00 and 15:00 UTC) starting in September
2000 (GPS week 1080). The IGS global data centers, including the CDDIS, download therapid, predicted, and ultra-rapid products from the Analysis Coordinator and made themavailable in a timely fashion to ensure their usefulness to the user community.
Since January 1997, the IGS has conducted a pilot experiment on the combination of
troposphere estimates. Using a sampling rate of two hours, the zenith path delay (ZPD)
estimates generated by the IGS analysis centers were combined by GFZ to form weekly
ZPD files for approximately 150 global GPS sites. As of early 1998, these troposphere
products are available through the IGS global data centers; at the CDDIS the files are in a
subdirectory of the weekly GPS products directories (i.e., /gps/products/wwww/trop,
where wwww is the GPS week number).
As of June 1, 1998, several IGS Analysis Centers began supplying daily, global
ionosphere maps of total electron content (TEC) in the form of IONEX (an official
format for the exchange of ionosphere maps) files. These products are also available fromthe IGS global data centers. At the CDDIS, the IONEX files are located in daily
subdirectories of the main product area (e.g., /gps/products/ionex/yyyy where yyyy is thefour-digit year), rather than under the weekly subdirectory structure, since the files areproduced daily.
Supporting Information
Daily status files of GPS 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 at a
day’s data availability and quality by viewing a single file. The daily status files areavailable through the web at URL ftp://cddisa.gsfc.nasa.gov/pub/reports/gpsstatus/. The
daily status files are also archived in the daily GPS data directories.

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Ancillary information to aid in the use of GPS data and products are also accessible
through the CDDIS. Weekly and yearly summaries of IGS tracking data archived at the
CDDIS are generated on a routine basis and distributed to the IGS user community
through IGS Report mailings. These summaries are accessible through the web at URL
ftp://cddisa.gsfc.nasa.gov/pub/reports/gpsdata. The CDDIS also maintains an archive ofand indices to IGS Mail, Report, and Network messages.
GLONASS Data and Products
In early 2000, the IGS Governing Board approved the International GLONASS Pilot
Project (IGLOS-PP) as a formal working group within the service. The CDDIS proposed
to continue its role as a global data center for GLONASS data and products to the
IGLOS-PP Call for Participation issued in 2000. The CDDIS archived GLONASS datafrom over forty sites totaling nearly 10K station days of data; the data centers and sites
active during 2000 are shown in Table 2. GLONASS products from four analysis centers(BKG, CODE, ESA, and MCC) as well as the Analysis Coordinator (at the Technical
University of Vienna) were also made available to the public. GLONASS data andproducts are accessible via anonymous ftp to host cddisa.gsfc.nasa.gov, in the filesystem/igex. At present, the CDDIS continues to archive both GLONASS data and products ina filesystem separate from IGS data and products.
System Usage
Figures 3 through 5 summarize the monthly usage of the CDDIS for the retrieval of GPS
and GLONASS data and products for February through December 2000. Figure 3
illustrates the amount of GPS data retrieved by the user community during 2000. Over
fourteen million files were transferred in 2000, with an average of 1.3 million files permonth. The chart in Figure 4 shows the number of product files retrieved from the
CDDIS in 2000; these files are categorized by type, the orbit, clock, ERP, and SINEX
product files, ionosphere product files, and troposphere product files. Figure 5 shows
the amount of GLONASS data and products retrieved from the CDDIS in 2000. Figures
6 and 7 illustrate the profile of users accessing the CDDIS IGS archive during 2000.
Most accesses were through network gateways, which did not yield sufficient
information about the user. Both education and government users constituted the next
largest user category of CDDIS users of GPS data and products. Figure 7 displays theusage information by geographic region; the majority of CDDIS users are from hosts inNorth America.
The figures referenced above present statistics for routine access of the on-line CDDIS
GPS data archives. The CDDIS staff continues to satisfy special requests from the user
community for data from the off-line archive as well as field routine questions about thesystem and the IGS in general. Table 3 summarizes the type and amount of special
requests directed to the CDDIS staff during 2000. To satisfy requests for off-line data,
the CDDIS staff must copy data from the optical disk archive to an on-line magnetic disk
area. As CD-ROMs of older data become available through the on-line jukebox thisprocess will become easier for both the user and the CDDIS staff.

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Other Activities
The CDDIS staff assisted in the preparation and editing of the proceedings from the 1999
IGEX Workshop.
Publications
The CDDIS staff attended several conferences during 2000 and presented papers on or
conducted demos of their activities within the IGS, including:
•
•
•
•
•

“1999 IGS Data Center Reports” (Carey Noll) for 1999 IGS Annual Report(submitted in 2000, to be published in 2001)“CDDIS 1999 Global Data Center Report” (Carey Noll) for 1999 IGS Technical
Report (submitted in 2000, to be published in 2001)“Current Status of and Backup Plans for Flow of IGS Data and Products” (Carey
Noll) was presented at the IGS Network Workshop in July 2000
“The IGS Global Data Center at the CDDIS – An Update” (Carey Noll and
Maurice Dube) was presented at the IGS Network Workshop in July 2000
“IGS Data Centers” (Carey Noll) was presented as part of the IGS Forum during
the ION GPS 2000 Meeting in September 2000

Electronic versions of these and other publications can be accessed through the CDDIS
on-line documentation page on the web at URL http://cddisa.gsfc.nasa.gov/reports.html.
Future Plans
Computer System Enhancements
The AlphaServer 4000 computer supporting the CDDIS has been operational for overthree years. Additional RAID disk space will be procured in 2001, as well as a dedicatedtape backup system.
Changes in the Data Archive
In early 2000, the IGS Governing Board approved the International GLONASS Pilot
Project (IGLOS-PP) as a formal working group within the service. The IGLOS-PP
committee issued a Call for Participation in early 2000. Later that year, the steeringcommittee, in conjunction with representatives of various IGS components, developed
recommendations for incorporating the flow of GLONASS data and the generation of
official products into the existing IGS infrastructure. Plans are to complete this transitionin mid-2001.
In 2000, the CDDIS proposed to serve as a data center supporting the IGS Pilot Projectfor Low Earth Orbiting (LEO) Missions. The GPS products required by these missions
require one second GPS data on an hourly basis. The CDDIS will begin the archive anddistribution of one-second data, stored in files containing fifteen minutes of data, from a

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network of thirty to forty sites during the mid-2001 timeframe. The CDDIS will also
become involved in the archive of space-borne GPS receiver data. A pilot program for theuse of this flight data will begin operation in 2001.
Contact Information
To obtain more information about the CDDIS IGS archive of data and products, contact:
Ms. Carey E. Noll
Manager, CDDIS
Code 920.1
NASA GSFC

Phone: (301) 614-6542
Fax:(301) 614-5970
E-mail: noll@cddis.gsfc.nasa.gov
WWW:
http://cddisa.gsfc.nasa.gov/cddis_welcome.html

Greenbelt, MD 20771
Acknowledgments
The author would once again like to thank members of the CDDIS staff, Dr. Maurice
Dube, Ms. Ruth Kennard, and Ms. Laurie Batchelor (from Raytheon Information
Technology and Scientific Services, RITSS). Their continued professional and timely
support of the CDDIS have made this system a success in the eyes of the internationaluser community.
References
Estey, L. “TEQC Summary” in IGS Network Systems Workshop Proceedings. March
1999.
Noll, C. E. “CDDIS Global Data Center Report” in IGS 1994 Annual Report. September
1995.
Noll, C. E. “CDDIS Global Data Center Report” in IGS 1995 Annual Report. September
1996.
Noll, C. E. “CDDIS Global Data Center Report” in IGS 1996 Annual Report. November
1997.
Noll, C. E. “CDDIS Global Data Center Report” in IGS 1997 Technical Report. October
1998.
Noll, C. E. “CDDIS Global Data Center Report” in IGS 1998 Technical Report. November
1999.
Noll, C. E. “CDDIS Global Data Center Report” in IGS 1999 Technical Report. 2001.

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CDDIS 2000 Global Data Center Report

Table 1: Sources of GPS data transferred to the CDDIS in 2000
SourceAUSLIG
AWI
BKG
CASM
CNES
DGFI
ESA
GFZ
GSI
IGN

JPL

KAO
NGI
NIMA
NOAA/GL

NRCan

PGC
RDAAC
SIO
UNAVCO
USGS
Totals:
Notes:

ALIC
KARR
GOUG
EBRE
BJFSm
GRAS
BRAZ
KIRU*
KIT3m
ZWEN*mSYOG
ANKR
HERS*m(KSTU)NOUM(THTI)
AOA1*
CRO1*
GUAM*
KWJ1*
PIE1*
SUTH*
DAEJ
SUWN
BAHRm
AMC2
GUAT*
TEGU*
(ALBHm)(NANO)(WILL)
ALBH*m
WHIT*
ARTU
YSSK
AMMN
RAMO
CHUM
RIOP
AMUN

CAS1
MAC1
VESL
HOFN*

CEDU
MAW1

Sites
COCO
DARW
STR1
TID1

NVSK

ORID

TUBI

HARB

KERG

NKLG

THTI

KOUR*
KSTU

MALI
LPGS

MAS1*
OBER*

PERT*
POTS*m

UNSA*

URUMm

TSKB
BOR1*
(HOFN*)
LHASm
NTUS
TRO1
AREQ*
DGAR
HARV*
MAD2*
PIMO*
THU1

BRUS*m (EBRE)GLSV(GRAS)
GRAZm
IRKT
JOZE
(KERG)(KIRU)(KIT3)(LPGS)(MAS1) MATE*m MDVO
METSm
NYA1
NYAL
OHIG
ONSA*
(POTS)TROMWSRT
WTZR*mZECKZIMM*mASC1
AUCK*mCASA
CHAT m
CIC1*
m
EISL*
FAIR*
GALA*
GODE*
GOL2*
HRAO*
IISC
JPLM* KOKB*mKRAK
MADR* MCM4* MDO1*m MKEA*
NLIB*
QUIN*
RBAY*
(RIOP)
SANT*
SEY1
TID2*
TIDB*
USUD*
YAR1

(HARK/B)
KOSG
NICO
REYK*m(ZWENm)CORD*
GOLD*(KUNM)
NSSP*
SHAO

DAV1
TOW2

HOB2
YAR2

JAB1

UZHL

WTZT

YEBE*

VILL*
RIOG*

No.
Sites
15
2
8
1
5
1
6
9
2
27
(40)

44
(45)

1
1
1
21

AOMLm
HNPT
USNA
ALGO*m
NRC1*m(WSLR)
CHWK
WILL
BILI

BARB
JAMA
USNOm
CHUR*mNRC2*
YELL*mDRAO*m
WSLR
MAG0

BARH*
KELY
WES2m
(CHWK)
PRDS*m

BRMU
MANA*
WUHN
(DRAO*)
SCH2*m

EPRT*
SLOR

ESTI*
SOL1m

FORT
SSIA*

(DUBO)STJO*m(FLIN)(UCLU)(HOLB)(WHIT)

8
(19)

DUBO

FLIN

HOLB

NANO

UCLU

11

NRIL

PETPm

TIXI

YAKA

YAKZ

9

BAKO
SIO3m
KAYT
SELE
PALM

DRAG
VNDPm
KAZA
SHAS

INEGm

KODK

MONP

PIN1

PVEP/3

11

KUMT
SUMK

KUNM
TALA

NSSP
TVST

PODG

POL2

14

2
199 sites from 21 data centers during 2000

Sites in () indicate backup delivery route
Sites in italics indicate sites new to the CDDIS in 2000
* Indicates site also providing hourly data to the CDDIS in 2000m
Indicates site providing meteorological data to the CDDIS in 2000

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IGS 2000 Technical Reports

Table 2: Sources of GLONASS data transferred to the CDDIS in 2000
SourceAUSLIG
BKG

CSIR
DLR
DNR
ENRI
GSFC
GSI
D. Hogarth
IGN
IMVP
NPL
UFl
USGS
USNO
Totals:
Notes:

DARR
BORG
LHAZ
VS0G
CSIR
NTZ1
SUNM
MTKA
GODZ
TSKA
DWH1 mBIPD
IRKZ
NPLC/E
GATR
CRAR
USNX

DAVR
BRUG
METZ
VSLD

GRAC
KHAB

LINR
DLFT
MR6G
WROC

Sites
STR2
YARR
GJOV
GOPE
MTBG
OS0G
WTZZ
ZIMJ

GRAB
REYZ
ZIMZ

HERP
THU2

KR0G
TIGZ

1
1
1
1
1
1
1
3
2
1
1
1
1
43 sites from 15 data centers during 2000

REUN

Sites in italics indicate sites new to the CDDIS in 2000m
Indicates site providing meteorological data to the CDDIS in 2000

Table 3: Summary of special requests for GPS data and information in 2000
Type of Request
General IGS/CDDIS information
Off-line GPS data
Amount of off-line data requested
Volume of off-line data requested
Notes:

No.
Sites
5
22

Totals~160 requests (phone, fax, e-mail)~25 requests (phone, fax, e-mail)~10,000 station days†~7.5 Gbytes† In this context, a station day is defined as one day’s worth of GPS

data (observation and navigation file in RINEX format)

162

CDDIS 2000 Global Data Center Report

5 minute delay
11%

45 minutes or more
13%

1 hour delay
21%
9 or more hour
delay
33%

40 minute delay3%

10 minute delay
22%
30 minute delay
15%

2 hour delay
22%

8 hour delay
2%
6 hour delay
7%
4 hour delay
5%

20 minute delay
18%

3 hour delay
10%

Figure 1: Average delay in delivery of GPS daily data
files to the CDDIS in 2000

1,800,000

15 minute delay
18%

Figure 2: Average delay in delivery of GPS hourly data
files to the CDDIS in 2000

80,000
Misc. Files

1,600,000

Troposphere Files
IONEX Files

70,000Hourly 30-Second Files
Daily 30-Second Files

Orbit, SINEX, Clock, ERP Files

1,400,000

60,0001,200,000
50,0001,000,000
40,000800,000
30,000600,000
20,000400,000

10,000200,000
00
Feb MarApr May

Jun

Jul

Aug

Sep

Oct Nov

Dec

Month

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month

Figure 3: Number of GPS data files transferred fromthe CDDIS in 2000

163

Figure 4: Number of GPS product files transferredfrom the CDDIS in 2000

IGS 2000 Technical Reports

90,00080,000GLONASS Product Files
GLONASS Data Files

70,00060,00050,00040,00030,00020,00010,000
0
Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Month

Figure 5: Number of GLONASS data and product files transferred from the CDDIS in 2000

Non-Profit
0%Commercial
13%

Pacific
2%

Africa0%

S. America
0%
Asia
3%

Europe29%

Network
38%

Education
27%

N. America
66%

Government
22%

Figure 6: Distribution of IGS users of the CDDIS in
2000

164

Figure 7: Geographic distribution of IGS users of the
CDDIS in 2000

Scripps Orbit and Permanent Array Center (SOPAC) 2000 Report

Scripps Orbit and Permanent Array Center (SOPAC)
2000 Report
Cecil H. and Ida M.
Green Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, CA 92037 USA
http://sopac.ucsd.edu; ftp://lox.ucsd.edu
Prepared by
Yehuda Bock, Director
Peng Fang, Rosanne Nikolaidis, Matthijs van Domselaar, Karen Watson (Analysis)
Brent Gilmore, Michael Scharber, Paul Jamason, David Malveaux (Archive)

Summary
The Scripps Institution of Oceanography's Orbit and Permanent Array Center (SOPAC)
at the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics (IGPP)
has served as a Global Data Center and Global Analysis Center since the inception of the
IGS in 1994. SOPAC is responsible for the collection, archiving, processing andpublication of high-precision continuous GPS data to support the global GPS community.
SOPAC's archive and analysis functions for the IGS overlap and complement otherarchiving and development activities at SIO for the Southern California Integrated GPS
Network (SCIGN), NOAA/NOS' National Geodetic Survey, the California Spatial
Reference Center (http://csrc.ucsd.edu), NOAA's Forecast Systems Laboratory (FSL),
and UNAVCO, Inc.
Highlights of SOPAC activities through the end of 2001 of interest to the IGS, include:
•
•
•
•
•
•
•
•

Complete redesign of the SOPAC Web Pages (http://sopac.ucsd.edu).
Increase in the number of continuous GPS sites archived to just over 900.
Maintenance of all historical (since 1990) and current data on-line, aided byconverting from RINEX storage of UNIX-compressed files to Hatanaka
compressed files.
Complete redesign of the Site Information Manager (SIM).
Increase in the number, scope, and utility of interactive user applications.
Archive of one-hour global data files.
Archive of all IGS orbital products including ultra-rapid orbits posted every 12hours.
Computation of real-time orbits based on hourly solutions of sliding 24-hour data
window.

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IGS 2000 Technical Reports••

Production of daily ITRF coordinates and SINEX solution files produced for over
600 sites, including all continuous GPS sites in Western North America (the "PBO"
region).
Production of decade-long consistent ITRF position time series, orbits, zenith
delays, and EOP based on re-analysis of a large subset of global and regional data on
SOPAC archive, starting in January, 1991.
Development of GPS Seamless Archive (GSAC) for UNAVCO, Inc.

••
Data Archive

The SOPAC GPS archive currently has about 2.8 TB of on-line storage and includes
current and historical data and data products since 1990. All operations are controlled byan Oracle 8.1 RDBMS (see Figure 1), supported by an equipment base significantly
upgraded in 2000-2001 (Figure 2). See Appendix A for a complete list and locations ofdata and data products in the SIO archive. SOPAC continuously probes and collects
RINEX data from more than 30 different global, regional and sub-regional GPS archives
around the world. The automated processes which collect this data are continuously being
upgraded and modified. The collection process compares the database description of the
SIO archive to the remote archives, ftp's any needed files, quality checks the data, andmakes them immediately available for on-line access. In addition, site log files are also
compared and archived to provide current and historical listings of site equipment.

GPS Data
Retrieval

GPS Data

External
GPS Data
Centers
Retrieve data
for about
600 GPS sites
from 30 data
centers

SOPAC
GPS Data
CenterServices

SOPAC Operations
DLT Library
Off-line 2TB
Capacity

1 TB

FTP Data

GPS Data Mgt
Servers
Data Download
and Drop Off
Quality Check &Capture Metadata

MO Jukebox
600 GB

1.2TB

Data Archive
2.8 TB On-Line
Capacity

RINEX
Site Logs

FTP Products
SINEX
OrbitsFTP Server

Database Server
Oracle RDBMSMetadata

Web Apps
Web Server

Download PCs

40 SCIGN Sites

ModemsAnalysis PC s

Qty: 4SIM
SCOUT
Mapserver
Data Browsers
Timeseries
Velocity Maps

Qty: 20

Figure 1. Schematic of SOPAC archive. See Figure 2 for a detailed hardware description.

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Scripps Orbit and Permanent Array Center (SOPAC) 2000 Report

SOPAC's publicly available data archive is accessible via anonymous ftp at the following
URL: ftp://lox.ucsd.edu.
SOPAC makes every attempt to provide data that it collects or produces in a timely
manner. All data on SOPAC's public archive may be obtained without restriction. An
open data policy is intended to provide public users with the easiest means of collecting
data from SOPAC on both a regular and irregular basis. Although private commercial use
of such data is permitted, additional services and/or requests by private entities are given
lowest priority. These policies are encouraged by SIO for other data centers wherever
possible.
In addition to the regular nature of data collection and publication at SOPAC, older data
and/or products are also added to the public archive, typically on an irregular basis.
Various data formats are available from the SOPAC archive, such as ASCII and UNIXcompressed. In addition, formal requests for off-line data are handled by SOPAC anddealt with in a timely and appropriate manner.
In 2000 SOPAC saw its total archive size (first-copy data, excluding backups) actually
decrease by nearly 400 hundred gigabytes thanks to the reclamation of over 500 gigabytes
of space by the conversion of every RINEX file on SOPAC's archive from standard
UNIX-compressed format to Hatanaka UNIX-compressed format. In addition to the
obvious space savings are significantly reduced network usage and RINEX ftp transfer
times for SOPAC's users. Accordingly, SOPAC's total archive usage decreased fromaround 1.4 terabytes in 1999 to roughly 1.0 terabyte by the end of 2000.
The steady increase in the number of permanent GPS sites archived at SOPAC since 1996
is shown in Figure 3, and by GPS network affiliation in Figure 4. By the end of 2000,
SOPAC was collecting data from about 830 sites, by the end of 2001 that number had
exceeded 900 sites.
The year 2000 was also a year where SOPAC saw continual growth in the number of filetransfers by both public and private users, locally and from around the world (Figure 5).
Nearing 5 million transfers for the year 2000 SOPAC continues to provide GPS data toan ever-growing constituency of GPS users the world over. By the end of 2001, thenumber of file transfers was almost 7 million. The most frequently downloaded GPS data
at SOPAC were those affiliated with the IGS (Figure 6). By the end of 2001, we could
identify more than 8000 unique ftp clients (Figure 7). The number of unique clients
domains (e.g., ".gov", ".edu", ".com") leveled off in 2000-2001 to over 70 (Figure 8).
SCIGN, the Southern California Integrated GPS Network (http://www.scign.org), also
grew substantially in 2000. SOPAC is the primary data archive for the SCIGN network.
By the end of 2000 the SOPAC had at least one day of data from 229 different SCIGN
sites. That number has climbed to over 250 by the end of year 2001 making SCIGN thelargest RINEX data constituent at SOPAC, in terms of the number of total sites archived(Figure 4). Among file transfers from SOPAC, the SCIGN network was the second mostpopular network downloaded (Figure 6).

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IGS 2000 Technical Reports

Figure 2. Schematic of SOPAC/CSRC hardware components.

168

Scripps Orbit and Permanent Array Center (SOPAC) 2000 Report

Figure 3. Number of continuous GPS sites archived at SOPAC between 1996-2001.

Figure 4. Number of continuous GPS sites archived at SOPAC between 19962001 by GPS array for 14 different arrays. "IGS-C" include core sites (that define
the global reference frame) and "IGS" contain other IGS sites.

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IGS 2000 Technical Reports

Figure 5. Number of files transferred from SOPAC via ftp://lox.ucsd.edu between
1996-2001.

Figure 6. Number of files transferred from SOPAC via ftp://lox.ucsd.edu between
1996-2001 for 14 different GPS arrays.

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Scripps Orbit and Permanent Array Center (SOPAC) 2000 Report

Figure 7. Number of unique ftp clients transferring data from SOPAC in theyears 1996-2001. An ftp client is counted as a unique address for a user of the
SOPAC archive. We have made an effort to ensure that ftp users provide a
legitimate username.

Figure 8. Number of unique ftp client domains (e.g., ".gov", ".edu", ".com")obtaining data from SOPAC in the years 1996-2001.

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IGS 2000 Technical Reports

From the standpoint of a user constituency SOPAC, U.S. educational institutions
accounting for the largest use of the archive with nearly 2 million file transfers alone. U.S.
government and German domains were the second and third largest user groups of
SOPAC's archive in 2000.
RINEX observation format GPS data files continue to be far and above the mostfrequently accessed data at SOPAC, accounting for over 90% of the total file transfers in
2000. As such, there is a high correlation between the number of permanent GPS sites
archived on a daily basis at SOPAC and both the total size of the SOPAC archive and thenumber of file transfers from SOPAC. We expect this trend to continue to rise in the
future and are taking appropriate steps to ensure SOPAC can maintain its high level ofservice to the global GPS community.
Information Management
SOPAC is dedicated to providing the GPS community with useful and timely information
describing GPS data. In this effort SOPAC utilizes a relational database to track
information about data, creates web-based software to assist with user entry and retrievalof site information (e.g., Figure 9), and maintains ftp statistics about the data's access by
the GPS community.
Over the past few years, SOPAC has integrated an Oracle Relational Database
Management System into its archiving operations. This has enabled us to increase theefficiency of both local and remote GPS data downloading, and improve the accuracy of
GPS site metadata stored at SIO.
Front- and back-end database applications continue to be a top priority for SOPAC's
archive management team each year. The "archive browsers" on SOPAC's web page feed
directly off of our relational database server, providing a centralized and integral
information source for numerous web-related utilities and services.
The SIO database catalogs and organizes SIO data holdings, and the tools used to obtainthese data. Revised remote collection software then utilizes this information to determine
which remote archive files are needed.
SOPAC continues to improve its management of GPS site-related information. The Site
Information Manager (SIM) is a web-based application that allows users access to site
information
contained
in
the
SOPAC
database(http://sopac.ucsd.edu/scripts/SIMpl_launch.cgi). It provides secured users with a single
mechanism of updating site information, which is then propagated to several applications.
Alternatively, users may manually generate products such as site logs from the SIM. The
SIM has relevant help sections with URL links to helpful resources, and limits equipment
types to those recognized by the IGS.

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Scripps Orbit and Permanent Array Center (SOPAC) 2000 Report

Several of SOPAC's automated database applications make direct use of site information
managed via the SIM. These include:
•
•
•
•
•

Submission of SCIGN site logs to the IGS Central Bureau.
GPS site log parsing into the database.
SCIGN site log creation and updating.
SCIGN mail generation.
Updating of site equipment local download software to allow correct equipment
types to be entered into RINEX headers.
• Automated station.info (GAMIT configuration file) creation.
• Automated SINEX creation.
FTP access statistics for the SIO archive are updated semi-hourly in the database. The
number of transfers from the archive may be queried based on GPS site name, array,several temporal parameters, and by remote host types. This allows for a timely, detailed
description of the data archive's usage, and creates a usage profile which enables SIO tobetter deliver its products to the GPS community (see http://sopac.ucsd.edu/cgibin/dbFtpStats.cgi).

Figure 9. An example of a SOPAC user application. This application allows the user tobrowse the data archive for RINEX data availability. All interactive tools are interfaced to
SOPAC's Oracle 8.1 RDBMS.
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IGS 2000 Technical Reports

Analysis
In 2000-2001 SOPAC initiated computation of real-time orbits based on hourly solutionsof a sliding 24-hour data window, primarily to support short-term weather forecastingfor NOAA. Production of daily ITRF coordinates and SINEX solution files exceeded
600 sites, including all continuous GPS sites in Western North America (the "PBO"
region). SOPAC completed production of an 11-year consistent ITRF position timeseries, orbits, zenith delays, and EOP based on re-analysis of a large subset of global andregional data on SOPAC archive, starting in January, 1991 (e.g., Figure 10). See
Appendices A and B for a summary of analysis products and their locations in the
SOPAC archive.

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Scripps Orbit and Permanent Array Center (SOPAC) 2000 Report

Figure 10. Typical coordinate time series of analyzed by SOPAC. The time series shows
the north position component of the SCIGN site at Pinemeadows (ROCH). The timeseries is modeled by a linear trend, three coseismic offsets (Joshua Tree, Landers, Hector
Mine), two postseismic decay (Landers and Hector Mine), an annual term, and one
equipment-change offset (early 1997). The weighted rms is only 1.3 mm but exhibits
some non-linear behavior.

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IGS 2000 Technical Reports

Appendix A. Directory structure and directory information for SOPAC archive(ftp://lox.ucsd.edu)------------------------------------------------------------------------------DIRECTORY STRUCTURE------------------------------------------------------------------------------Directory
Filenames
Description------------------------------------------------------------------------------rinex/YYYY/DDD

ssssDDD0.YYd.Z

Hatanaka compressed RINEX obs
files for stations 'ssss',day 'DDD', year 'YY'

ssssDDD0.YYo.Z

UNIX-compressed RINEX obs(last 60 days only)

autoDDD0.YYn.Z

RINEX navigation files
concatenated from all stations
day 'DDD', year 'YY'

ssssDDD0.YYn.Z

RINEX nav files
for stations 'ssss',day 'DDD', year 'YY'

autoDDD0.YYn.Z

RINEX navigation files
concatenated from all stations,day 'DDD', year 'YY'

met/YYYY/DDD

ssssDDD0.YYm.Z

RINEX met files
for station 'ssss',day 'DDD', year 'YY'

raw/YYYY/DDD

ssssDDDS.YYr.Z

ROGUE raw obs files
for station 'ssss',day 'DDD', year 'YY', sess 'S'

ssssDDDY.rSS

Trimble raw obs filefor station 'ssss',day 'DDD', year 'Y', sess 'SS'

rssssSYY.DDD

Ashtech raw obs files
for station 'ssss',day 'DDD', year 'YY', sess 'S'

igsWWWWD.sp3.Z

IGS Final Orbits
for GPS week 'WWWW' andday 'D' in SP3 format,
D=0,..,6

igrWWWWD.sp3.Z

IGS Rapid Orbits
for GPS week 'WWWW' andday 'D' in SP3 format,
D=0,..,6

iguWWWWD_HH.sp3.Z

IGS Ultra-Rapid Orbits
for GPS week 'WWWW'
day 'D' hour 'HH' in SP3 format,(H=00 or H=12)

iguWWWW7_HH.erp.Z

IGS Ultra-Rapid Earth Rotation
Parameter filefor GPS week 'WWWW', hour 'HH'
(H=00 or H=12)

nav/YYYY/DDD

products/WWWW

176

Scripps Orbit and Permanent Array Center (SOPAC) 2000 Report

iguWWWW7_HH.sum.Z

IGS Ultra rapid summary fileproduced by center 'ccc'
for GPS week 'WWWW', hour 'HH'
(H=00 or H=12)

cccWWWWD.sp3.Z

Orbits produced by center 'ccc'
for GPS week 'WWWW' andday 'D' in SP3 format,
D=0,..,6

cccWWWW7.erp.Z

Earth Rotation Parameter fileproduced by center 'ccc'
for GPS week 'WWWW'

cccWWWW7.sum.Z

Data Analysis Summary fileproduced by center 'ccc'
for GPS week 'WWWW'

cccWWWW7.clk.Z

Combined Clock Estimates filefor satellite and station clocks
produced by center 'ccc'
for GPS week 'WWWW'

cccWWWW7.cls.Z

Summary of Clock Combination fileproduced by center 'ccc'
for GPS week 'WWWW'

jplWWWWD.yaw.Z

JPL Satellite Yaw Filefor GPS week 'WWWW', day 'D'
D=0,..,6

sirWWWWD.sp3.Z

SIO (SOPAC) Rapid Orbits
for GPS week 'WWWW' andday 'D' in SP3 format,
D=0,..,6

siuWWWWD_HH.sp3.Z

SIO (SOPAC) Ultra-Rapid Orbits
for GPS week 'WWWW' andday 'D' in SP3 format,
D=0,..,6
Updated every 12 hrs(24 hours actual+ 24 hour predicted)

sihWWWWD.sp3.Z

SIO (SOPAC) Hourly Orbits
for GPS week 'WWWW' andday 'D' in SP3 format,
D=0,..,6
Updated hourly(24 hours actual+ 12 hour predicted)

sioigsWWWW7.snx.Z

Station Solution SINEX filefor global sites
produced by SIO
for GPS week 'WWWW'

siopboWWWW7.snx.Z

Station Solution SINEX files
for "PBO" sites in Western NA
produced by SIO
for GPS week 'WWWW'
PBO: Plate Boundary Observatory

177

IGS 2000 Technical Reports

gpggaY.DDD.Z

Satellite initial conditions
file (GAMIT/GLOBK users)
generated from final analysis
year 'Y', day 'DDD'

gpggaY.DDD.rap.Z

Satellite initial conditions
file (GAMIT/GLOBK users)
generated from rapid analysis
year 'Y', day 'DDD'

gpggaY.last.Z

Most recent satellite initialconditions file
(GAMIT/GLOBK users)
Generated from SIO hourly
solutions ('sih')year 'Y'
Updated hourly------------------------------------------------------------------------------MISCELLANEOUS DIRECTORY INFORMATION------------------------------------------------------------------------------Directory
Description------------------------------------------------------------------------------GSAC

SOPAC GPS Seamless Archive (UNAVCO GSAC) holdings

docs

GPS sitelogs and SOPAC data reports (SCIGN, all sites)

misc

Miscellaneous data and products

nrtdataHourly GPS RINEX data files

softwarePublicly-available software

troposphere

IGS combinations of tropospheric estimates

For GAMIT/GLOBK users:
processing

GAMIT/GLOBK related tables

globalGAMIT solution files for daily SOPAC global analyses

regional

GAMIT solution files for daily SOPAC regional analyses

hfilesGlobal and regional GAMIT/GLOBK h-file solutions

combinations

SOPAC's weekly GLOBK solutions

gfilesOrbits in the GAMIT g-file format-------------------------------------------------------------------------------

178

Scripps Orbit and Permanent Array Center (SOPAC) 2000 Report

Appendix B. SIO orbital products----------------------------------------------------------------------------Software Used

| GAMIT v. 10.05, GLOBK v. 5.05,

developed at MIT/SIO----------------------------------------------------------------------------Final Products| siowwwwn.sp3

GPS ephemeris files in 7 daily

generated for|files at 15 min intervals in SP3 format,

GPS week 'wwww'|

including accuracy codes computed fromday of week 'n'|overlapping analysis wrt previous day.

(n=0,1,...,6)| siowwww7.erp

ERP (pole, UT1-UTC) weekly solution| siowwww7.sum

Summary of weekly solution combining both|

IGS global and regional solutions.

| siowwww7.snx

Weekly coordinates in SINEX format| siowwwwn.tro

Daily files of 1-h troposphere delay|

estimates in SINEX format (based|on 1-day solutions).

| sirwwwwn.sp3

Daily orbits for current-1 day. ~8 hour|

delay.

| sirwwwwn.erp

Daily EOP for current-1 day. ~8 hour|

delay.

Ultra Rapid| siuwwwwn.sp3

Daily orbits for 24h(post)+24h(predicted).

Products|

3 hour delay (twice daily).

| siuwwwwn.erp

Daily EOP for 4day(post)+3day(predicted).

|

3 hour delay. (twice daily)

Hourly| sihwwwwn.sp3

Hourly orbits for 24h(post)+12h(predicted).

Products|

1 hour delay (24 times daily).

Rapid Products

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R E G I O N A L / O P E R A T I O N A L

C E N T E R S

BKG Regional IGS Data Center Report 2000

BKG Regional IGS Data Center Report 2000
Heinz Habrich, Kurt Herzberger

Federal Agency for Cartography and Geodesy
D-60598 Frankfurt at Main, Germany

Introduction
The Federal Agency for Cartography and Geodesy (BKG) operates the Regional IGS
Data Center for Europe since the beginning of the IGS Test Campaign in June 21, 1992.
GPS tracking data from permanent GPS sites in Europe are obtained from Operational
Data Centers (ODC’s), Local Data Centers (LDC’s), or directly from the stations. Also
tracking data from stations outside of Europe are transferred to BKG, if these stations areoperated by an European institution. The received data are uploaded to the Global Data
Center (GDC) at the Institut Géographique National (IGN) in Paris, and are also madeavailable to other users. The IGS products as computed by the IGS Analysis Centers aredownloaded from the GDC’s to BKG in order to provide these information to European
users.
GPS observation data from the permanent GPS network of the European Reference
Frame (EUREF) and mixed GPS/GLONASS observation files from the International
GLONASS Experiment 1998 (IGEX) are also available. The continuation of the IGEX
campaign is now proposed to become an IGS pilot service for a period of four years(2000-2003) named International GLONASS Service – pilot project (IGLOS-PP). A
subset of the IGS , EUREF, and IGEX stations deliver hourly observation files to BKG
additionally to the daily files.
Computer Architecture
The data center runs on an HP-workstation under HP-UX. This workstation is connectedto the Internet with a maximum transfer rate of 2 MB/s and a disk capacity of about 100
GB. The directory structure (see Figure 1) shows three project related directories (IGS,
EUREF, and IGEX). The various projects show analogous directory structures. The data
are accessible through both, ftp and http. The RINEX observation files of the stations are
now online available for 3 years. During 2000 a new http-server (http://igs.ifag.de) had
been installed, and the html pages had been newly created. They correspond now very
well to the disk structure, to make the use of ftp and http as similarly as possible.
Hourly Observation FilesThe hourly RINEX observation files may be used for near real time applications andcould replace the daily files if all hourly files of one day are concatenated to one filesuccessively. As soon as the daily observation files are available at the data center thehourly observation files are no longer of interest. Therefore, the hourly files are deleted
after 7 days in the “nrt” subdirectory. For test purposes, BKG compares the183

IGS 2000 Technical Reports

http://igs.ifag.de
ftp://igs.ifag.de

IGS

EUREF

IGEX

Miscellaneous

igsin

eurefinigexin

ITRF<year>

obs

obs

obs

WVR

nrt

nrt

nrt

SoftwarePublications

nrtin

nrtin

nrtin
Data Holdings<Day>/<Hour><Day>/<Hour><Day>/<Hour>

products

products

products

stationstationstationigsmail

eurefmailigexmailreports

reports

reports

Figure 1: Access and Structure of the BKG Data Centerconcatenated hourly files with the daily observation files, which are submitted by eachstation at the end of a day, using the program RNXDIF (Habrich H., 2001). Detecteddifferences are saved into summary files for each station and publicly available. This longterm study may be contribute to decide, that the daily observation files should no longer
be submitted additionally.
Figure 2 shows the latency of hourly RINEX observation files for GPS week 1115.
About 40 % of the hourly IGS observation files had been available at BKG at 8 minutes
after the full hour, and only 1 % show a latency of more than 30 minutes. The files of the
EUREF and IGEX projects show a latency of 8, i.e., 10 minutes for the majority of thesites.

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Figure 2: Latency of Hourly RINEX Files for GPS Week 1115

User Activity And Future Plans
The total number of stations (i.e. of receivers) of BKG’s data center has increased to 160.
Approximately 100 distinct users contact the data center and perform some 10,000 filetransfers every day. In order the make the success to the data center more comfortable, itis planed to extend the html pages with dynamic links and the possibility of user queries.

References
Habrich H. (2001): Concatenation of Hourly RINEX Files, Physics and Chemistry of the
Earth, Vol. 26, No. 6-8,pp, 561-567, 2001, Elsevier Science Limited, Oxford,
England.

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186

Hartebeesthoek Radio Astronomy Observatory (HartRAO)

Hartebeesthoek Radio Astronomy Observatory (HartRAO)
Ludwig Combrinck
Abstract
This report gives an overview of our IGS activities during the year 2000. A brief
description of our involvement with other space geodesy techniques is given.
Geodesy at HartRAO
HartRAO is located north of Johannesburg, South Africa, in a valley of the foothills of
the Wit-waters mountain range (see Table 1). HartRAO uses a 26 metre equatoriallymounted Cassegrain radio telescope built by Blaw Knox in 1961 (Figure 1). The telescope
was part of the NASA deep space tracking network until 1975 when the facility wasconverted to an astronomical observatory. The radio telescope is collocated with an IGS
GPS station HRAO and an SLR station MOBLAS6. HartRAO is the IGS regional data
centre for Africa.

Figure 1. The 26 metre radio telescope. Solid panels have been fitted on the outer ring aspart of a surface upgrade. All panels will eventually be replaced with non-perforated,higher tolerance panels. Typical rms accuracy of these panels is 170 microns.
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IGS Activities
HartRAO supported an IGS tutorial presented by Ruth Neilan (IGSCB), Angelyn Moore(IGSCB) and Jan Kouba (NRC) on the 3rd of April 2000. The tutorial was well attended
by delegates from local universities, the Weather Bureau, local surveying companies andthe Council for Geosciences. After the necessary equipment procurement, HartRAO will
be able to operate as a mirror site for the IGSCB, which will facilitate the use of all its
products by local users. The IGS tutorial was greatly appreciated and we wish to thankthe IGSCB for visiting South Africa.
The author attended the Second Network workshop of the IGS in Oslo, Norway, during
July 2000. A position paper was presented at the conference (Combrinck & Chin 2001).
The author acted as one of the guest editors for the conference proceedings. The kindnessof Hans-Peter Plag, Oddgeir Kristiansen and Gunnar Elgered led to very interesting andworthwhile visits to Statens kartverk (Norwegian Mapping Authority) and the OnsalaSpace Observatory. A special effort by Jan Johansson and his wife must be mentioned as
this led to a day of sailing.
Regional Data Centre
Rinex data for 16 IGS stations and one regional station (NAMI, see Figure 2) werearchived. The IGS station SUTH (Figure 3), located at Sutherland suffered data outage
due to a nonfunctional receiver at the end of December 2000, but was restored to working
order soon afterwards. An additional 20 GB hard disk was procured for GEOID, the data
centre server, to cope with the increasing amount of data. Due to the exposure the IGS
achieved during the year 2000, rinex data and IGS product retrievals have increased withregular access by local users and neighbouring countries.

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Hartebeesthoek Radio Astronomy Observatory (HartRAO)

Figure 2. The NAMI GPS antenna monumentation located in Windhoek, Namibia. The
antenna needed to be elevated to alleviate the possible adverse effect of multi-pathingfrom a nearby corrugated iron roof. The pole is thick-walled and stayed for rigidity.
NAMI is a regional station at the moment, but it is hoped that an equipment upgrade canbring it to IGS status. (Donors?)

Figure 3. The SUTH IGS GPS antenna monumentation. The antenna is situated on a hill
overlooking the barren semi-desert of the Karoo.

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IGS 2000 Technical Reports

Current Activities
We are continuing our footprint survey, which has as its main purpose the determinationof eccentricities between the GPS, VLBI and SLR reference points as well as themaintenance of a control network to enable stability monitoring of the site on a local scale.
The current eccentricities between VLBI and SLR (Table 2) were determined using GPS(Combrinck & Merry 1997) and the SLR to GPS eccentricities values are from 1998
footprint results. We are processing HRAO ina17 station regional (IGS) network andenvisage processing the SLR (MOBLAS 6) data for eccentricity determinations. This will
strengthen collocation and with accurate eccentricities should tie the independent ITRF
coordinates to a high degree of accuracy.
Table 2. Table of eccentricities, VLBI telescope to SLR and GPS (HRAO) reference
points.

Future Plans
In order to bring geodesy closer to home and the African continent, the Geodesy
Programme is in the process of establishing a Geodetic Institute for Africa. The purposeof this Institute at HartRAO will be to establish strategic alliances and collaborative
projects with other African countries. These projects will be tied in a unifying structure
which will advance and support Africa's role in geodesy. It will support and promote theactivities of the IVS, ISLRS and IGS. It will also support the objectives of the African
Reference Frame (AFREF).
With the addition of the MOBLAS-6 SLR unit, several new staff members were recruited
as part of the SLR project. Plans are in progress to expand GPS activities and to develop
an active research component as an IGS Associate Analysis Centre. We are in the process
to equip Zambia, Malawi, Mocambique, Madagascar, Botswana, Namibia and Zimbabwewith IGS stations. Members of the IGS who upgrade stations and have redundantequipment available should please contact the author.

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Hartebeesthoek Radio Astronomy Observatory (HartRAO)

References[1] Combrinck W.L. and Merry, C.L. Very long baseline interferometry antenna axis
offset and intersection determination using GPS. JGR, Vol.102, NO.B11, pp
24,741-24,743, 1997.
[2] Combrinck W.L and Chin, M. IGS Stations: Station and Regional Issues. Phys. Chem.
Earth (A), Vol. 26, N0.6-8, pp. 539-544, 2001.

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N E T W O R K

A N D

S T A T I O N
R E P O R T S

IGSG L O B A L ,R E G I O N A L ,L O C A L

A N D

N E T W O R K S

Growth of the IGS Station Network in 2000

Growth of the IGS Station Network in 2000
Angelyn Moore
IGS Central Bureau
NASA Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California
Introduction
The IGS network of permanent dual-frequency GPS tracking stations formed by thecooperative efforts of the IGS site-operating agencies welcomed the addition of 25 sites
in 2000:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

AMMN Amman, Jordan
DRAG Metzogi Dragot, Israel
DUBR Dubrovnik, Croatia
DYR2 Diyarbakir, Turkey
ESTI Esteli, Nicaragua
GUAT Guatemala City, Guatemala
HARB Pretoria, South Africa(Replacing HARK)KODK Kodiak, Alaska, USA
MANA Managua, Nicaragua
NKLG Libreville, Gabon
NOT1 Noto, Italy(Replacing NOTO)
NRIL Norilsk, Krasnoyarsk Region, Russian Federation
NVSK Novosibirsk, Russia
ORID Ohrid, Macedonia
OSJE Osijek, Croatia
RABT Rabat, Morocco(Replacing IAVH)
RBAY Richardsbay, South Africa
SFDM Piru, California, USA
SLOR San Lorenzo, Honduras
SPT0 Boras, Sweden
SSIA San Salvador, El Salvador
TEGU Tegucigalpa, Honduras
UNSA Salta, Argentina
YAR2 Dongara, Western Australia, Australia
YEBE Yebes, Spain

This set includes sites which improve coverage in important areas such as Central
America, Africa, northern Asia, and the Middle East, as well as desirable colocations
with other geodetic techniques.
Figure 1 depicts stations added in 2000 emphasized by large circles, along with thecomplete network distribution at the end of 2000, which totalled 248 stations. Of these,
92 (shown in Figure 2) earned the "Global" classification for being regularly analyzed by

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IGS 2000 Technical Reports

Figure 1. IGS Stations Added in 2000

at least three analysis centers (one on a continent other than that of the station). The Data
Centers report in this volume notes that the number of sites participating in the hourly
data subnetwork grew to more than 70.

198

Figure 2. IGS Stations Earning Global Classification

Growth of the IGS Station Network in 2000

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IGS 2000 Technical Reports

2000 Oslo Network Workshop and Proceedings
The workshop and its expert local organizers from the Norwegian Mapping Authority
have already been lauded in the Central Bureau article in this Annual Report. Anotherhighlight was the selection for "On Hourly Orbit Determination" by Jan Dousa and Leos
Mervart of the Research Institute of Geodesy, Topography, and Cartography in the
Czech Republic for the best poster of the joint meeting. A committee comprising
representatives of the IGS and COST Action 716 considered all the posters and waspleased to see Dousa, as first author, presented with two Locus GPS receivers generously
donated by Ashtech as a prize. The productivity of the entire event is apparent in theProceedings, available as a special issue of Physics and Chemistry of the Earth, Part A,
vol. 26, published by Elsevier Science. Coordinating editor Hans-Peter Plag, fellow IGS
guest editors Mark Caissy and Ludwig Combrinck, the COST Action 716 team, and eachauthor made the production of this document a pleasure and an education. This peerreviewed, indexed journal probably represents the deepest penetration of a collection of
IGS network articles into the world's libraries to date.
Network Coordination
As was suggested in the Network section of the 1999 Annual Report, the well-publicizedY2K rollover was readily handled by the IGS. Indeed, the new Central Bureau server
installed to handle the rollover enabled enrichments such as self-service subscription
management for the IGS email lists. Many users welcomed a noticeable improvement inresponse time.
Following the near-eradication of station metadata errors in calendar 1999, automatic
quality audits of site logs and RINEX observation data file headers were increased totwice weekly. In this maintenance mode, station operators are notified by targeted email
should a metadata error be inadvertently introduced by equipment or software changes.
This system continues to maintain near-zero metadata error rates with minimal humaneffort and has enabled the long-envisioned SINEX combination and consistency of all
products in the IGS realization of ITRF.
Looking Ahead
The expanding usage of the IGS network into new applications brings requirements forthe collection and dissemination of such metadata. In late 2000, a revised site log
template supporting GNSS equipment other than GPS was drafted, in anticipation ofincorporating GLONASS stations into the IGS network. This provided an opportunity toalso improve the collection of site eccentricity information, describing the spatial relation
between a geodetic marker and a GPS antenna, and other geophysical information
regarding each site. When reviewed and adopted, the new log format will allow theCentral Bureau to provide increased and standardized station information to the user
community.

200

The Australian Regional GPS Network - Report for 2000

The Australian Regional GPS Network - Report for 2000
Bob Twilley, Paul Digney
AUSLIG

Introduction
The Australian Regional GPS Network (ARGN) continued a period of consolidation
during 2000, following the Y2K and GPS week rollover concerns of the previous year.
All 15 sites across Australia, Antarctica, Macquarie Island in the Southern Ocean andCocos Island in the Indian Ocean maintained a high level of output. All information isavailable at www.auslig.gov.au/geodesy/argn/argn.htm.
Performance
Figure 1 shows the quantity of data acquired on each day of the year, at each of the
ARGN stations. The vertical bar in these diagrams indicates the relative size of the Rinex
data file available and the line of joined dots shows the percentage of valid observations
with respect to the total theoretically possible.
A number of significant events are apparent in Figure 1. The receivers at both Yarragadee& Tidbinbilla were relocated early in the year to maximize resources for the rollout of
upgraded receivers at more remote sites, but JPL receivers continued to operate at thesesites during this time. Improvement in performance is evident at sites where receivers
were upgraded, as shown in Table 1. As expected, extreme weather conditions affected
some sites, with lightning strikes taking Jabiru out of action for almost two months andcausing communication problems at Darwin later in the year. A cyclone also caused
severe disruptions at Karratha in early March and cyclone induced flooding in lateNovember caused a loss of communications. Data loss at Davis late in the year was
eventually traced to a faulty in-line amplifier, while also late in the year, decreased
performance at Yarragadee was caused by problems with the external clock.
Improvements
In 1999 ARGN GPS receivers were upgraded at critical sites to cope with the GPS week
rollover, the Y2K and increasing ionospheric disturbance. However, the remoteness of
the Antarctic sites meant that some receivers were not upgraded until 2000. Some
Australian mid-Latitude sites were also upgraded during the year as a lower priority. The
effect of these receiver upgrades is apparent in Figure 1.

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Table 1: GPS receiver upgrades during 2000
Site
Alice Springs
Casey
Davis
MawsonYarragadee
Tidbinbilla
CedunaKarratha

Date Upgraded
14 January 2000
24 January 2000
6 February 2000
8 February 2000
3 March 2000
8 March 2000
30 March 2000
11 May 2000
13 June 2000

Old Receiver
AOA ICS-4000ZAOA SNR-12 ACTAOA ICS-4000ZAOA ICS-4000ZAOA ICS-4000ZAOA SNR-12 RM
AOA SNR-12 RM
AOA ICS-4000Z
ASHTECH Z-II3

New receiverAOA SNR-12 ACTAOA ICS-4000Z ACTAOA ICS-4000Z ACTASHTECH Z-XII3
AOA ICS-4000Z ACTAOA ICS-4000Z ACTAOA ICS-4000Z ACTAOA ICS-4000Z ACTAOA ICS-4000Z ACT

A number of software amendments were made during 2000. These developments
included refinement of receiver download programs and upgrading of data conversion
and archiving processes. These changes were made to minimize data loss and increase theefficiency of the data transfer & conversion system
Local Monitoring Surveys
Although all ARGN sites were carefully selected for geological stability, they all include
three stable reference marks, usually within about twenty metres of the main monument.
Repeated accurate local surveys of these marks and the GPS monument allows any
possible local movement to be detected. During 2000, local surveys were carried out at
Ceduna and Mawson using a Leica TC2003 Total Station and Topcon DL-101C digitallevel to give sub-millimetre results. No significant local movement was found.

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The Australian Regional GPS Network - Report for 2000

ALICE SPRINGSCASEYCEDUNACOCOSDARWINDAVISJABIRU

Figure 1 – Data availability at ARGN sites for 2000

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IGS 2000 Technical Reports
HOBART

KARRATHA

MACQUARIE

MAWSONSTROMLOTIDBINBILLATOWNSVILLEYARRAGADEE

Figure 1 (cont.) – Data availability at ARGN sites for 2000
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New Zealand Continuous GPS Network

New Zealand Continuous GPS Network
John Beavan
Institute of Geological and Nuclear Sciences
P O Box 30-368, Lower Hutt, New Zealandj.beavan@gns.cri.nz
Introduction
It is timely to review the status of New Zealand’s continuous GPS (CGPS) stations,because a major upgrade of CGPS monitoring is beginning in 2001/2002 and there will
be a substantial increase in the data we will be providing to the IGS.
The CGPS array at December 2000 is shown in Figure 1, and the following paragraphs
provide some notes on the stations.

Year of
Installation
1995
1996
1997

AUCK
QUAR

1998

CNCL

1999

KARA

2000

NETT
MTJO

HOKI
PAEK

LYTT

CHAT

MQZG

5034
WGTT

OUSD

WGTN

DUNT

Figure 1. CGPS Array - December 2000
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IGS 2000 Technical Reports

AUCK and CHATAUCK and CHAT are the original New Zealand IGS stations, installed in 1995 in
partnership between the Institute of Geological and Nuclear Sciences (GNS), Land
Information New Zealand (LINZ), JPL, and UNAVCO. These are the only New Zealandstations whose data are presently submitted to the IGS. Both stations have been
operating with Turborogue SNR-8000 receivers since their inception, but we plan to
upgrade both to Ashtech Z-12 CGRS receivers in 2001.
Sea Level Network
Since late 1999/early 2000, GNS and Otago University have operated CGPS receivers at
three of New Zealand’s longest-running tide gauges. These are stations DUNT, LYTT,
and WGTT, and a fourth station will be established at the Auckland tide gauge in 2001.
Funding for this network is from the New Zealand Foundation for Research, Science andTechnology (FRST).
Southern Alps Network
The Southern Alps network (QUAR, KARA, CNCL, NETT, and MTJO) is primarily
aimed at measuring the distribution of vertical motion across the Southern Alps in order
to better understand processes of continental collision. The experiment started in
February 2000 and will run at least 5 years. It is a joint project between MIT, theUniversity of Colorado, Otago University, GNS, and UNAVCO. The primary funding is
an NSF grant to Peter Molnar (with U.S. co-investigators Brad Hager and Tom Herring),with the New Zealand institutions funded by FRST and an Otago University Research
Grant. As well as the continuous stations, a number of “semi-continuous” stations areoperated for several months per year, mainly during the summer.
GNS Network
Five stations (WGTN, HOKI, 5034, MQZG, and PAEK) have been installed by GNS,
sometimes in partnership with other institutions. HOKI was established in cooperation
with Lamont-Doherty Earth Observatory of Columbia University, while PAEK wasestablished in cooperation with the Geographical Survey Institute, Tsukuba, Japan. LINZ
has contributed to the installation of several of the stations.
Otago University Station
OUSD is the longest-running CGPS station in New Zealand, dating from January 1995
some 8 months before AUCK and CHAT were established.

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New Zealand Continuous GPS Network

Near Real Time Precipitable Water
Most of the stations described above are downloaded hourly, and are processed todetermine precipitable water with a delay of about 2 hours. These results may be foundat www.gns.cri.nz/earthact/crustal/precip/gpspw.html.

References
Graeme Blick, Land Information New Zealand, Wellington, New Zealand.
gblick@linz.govt.nz
Paul Denys, Otago University, Dunedin, New Zealand.
pdenys@stonebow.otago.ac.nz
Mark Falvey, Victoria University of Wellington, Wellington, New Zealand.

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208

The GPS Receiver Network of ESOC:
Maspalomas, Kourou, Kiruna, Perth, Villafranca and Malindi

The GPS Receiver Network of ESOC:
Maspalomas, Kourou, Kiruna, Perth, Villafranca and Malindi
C. Garcia, J.M. Dow, R. Zandbergen, J. Feltens, I. Romero
ESA/European Space Operations Centre
Darmstadt, Germany

Overall Hardware Configuration
PublicPublicTelephone
Network

ASHTECH
Z-12III

Telephone
Network

KourouESOC
dedicated
lines

cesiumAOA SNR-8100
ACT

LOCAL MODEMSInternet(futureinstallation)

Internet

PublicKirunaESOC
dedicated
lines

Telephone
NetworkcesiumInternet
PublicTelephone
Network

PublicTelephone
Network

ASHTECH
Z-12IIIInternet

Villafranca
cesiumESOC
dedicated
lines

TOPCON
LegacyInternet

ESOC
dedicated
lines

ESOC
dedicated
lines

cesiumKourou (KOU1)
GPS + GLONASS

Number cruncher
PublicASHTECH
Z-12III

Telephone
Network

ESOC, Darmstadt

Internet

PublicASHTECH
Z-12III

Telephone
Network

LOCAL MODEMSASHTECH
Z-12III

Publiccesium

Maspalomas

Telephone
Network

Internet

Internet(ISP)

Malindiquartz

ESOC
dedicated
lines

Perth

cesiumFigure 1 shows the configuration of the ESA stations by the end of 2000.
Receiver Performance
As it was reported in the IGS Network Systems Workshop, held in Annapolis 2-5
November 1998, the TurboRogues located at equatorial stations show many limitations in
the cross correlation mode tracking during the solar maximum. The only solution is a
replacement by new receivers.
Over the year 2000 ESOC has continued the plans to upgrade its network with receivers
capable of tracking techniques with higher SNR than the cross correlation. ACT (AOA)
and Z-tracking (Ashtech) receivers have been deployed to the tracking stations. It was abusy year with the following upgrades:

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In Kiruna (KIRU) the receiver was upgraded to an AOA SNR-8100 ACT in September
2000.
In Kourou (KOUR) the TurboRogue was replaced by an ASHTECH Z-XII3 in March
2000.
In Malindi (MALI) the upgrade was delayed till April 2001 due to several problems withshipments arriving in bad condition to the African station.
Maspalomas (MAS1) was the first ACT upgrade in August 1999, but the upgradedreceiver failed some months later and had to be replaced by an ASHTECH Z-XII3 in
December 2000.
In Perth (PERT), due to the geographical location, the cross correlation receiver had an
acceptable performance and the receiver was only replaced in 2001 after failure of theTurboRogue.
Villafranca (VILL) was upgraded to an AOA ACT receiver in July 2000. A similar
situation to Maspalomas with a failure of the upgraded receiver some months later madenecessary the replacement by an ASHTECH Z-XII3 by the beginning of 2001.
A Topcon Legacy combined GPS+GLONASS receiver was installed at Kourou (KOU1).
A technical problem with the cable attenuation delayed the data distribution which is
expected to start in 2001 to support IGS and IGLOS activities.
Communications
The communication from the ESA stations to the Control Centre at ESOC has been
implemented based on the ESA permanent leased lines for those locations where they areavailable (Kiruna, Kourou, Perth and Villafranca) and based on dial-up modems where
they are not. These lines are shared by other operational ESA projects and have a
bandwidth limitation of 2400 baud. This rate is approximately twice the needed for 1 Hz
receiver tracking and can be enough for data streaming but it is very tight if the data arepacked in 15 minutes or 1 hour files.
To offer a better connectivity an effort has been undertaken to upgrade the stations with
TCP/IP communications based on the Internet connectivity of the stations. The lines are
not as reliable as the operational links, but accept higher throughput.
The new remote computers that support the receivers are Windows NT PCs with remotecontrol for computer and receiver housekeeping. The operation is automatic andautonomous.

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The GPS Receiver Network of ESOC:
Maspalomas, Kourou, Kiruna, Perth, Villafranca and Malindi

High Rate Data Capability
Thanks to the new Ashtech receivers and the new TCP/IP communications the ESA
stations are able to produce 1 Hz data in subdaily downloads. It has been demonstrated invarious high rate data collection campaigns like the HIRAC/Solarmax in April 2001.
The new Ashtech Z-XII receivers can internally store an download 1 HZ data. The
AShtech receivers also do not present any problems in the second frequency tracking at
equatorial stations caused by high ionospheric activity. The old TurboRogues where only
capable of 0.33 Hz sampling by using the internal memory and CPU resources.
The Internet lines, developed for the bandwidth requirements of the web browsers, candownload the 1 Hz data collected during one hour in a few minutes.
One-Hour Downloads
One-hour data of Kiruna, Kourou, Perth and Villafranca are available since September
1998. These stations have permanent leased data links to ESOC. The data flow has been
continuos with only one hour latency during 1999 and 2000.
Maspalomas joined the hourly group in December 2000, at the beginning by using
connectivity from a local Internet Service Provider and finally by using a 2 Mbits line of
the station.
Malindi started the hourly downloads in 2001 using the Internet connection provided by
the University of Rome at the San Marco station.
The hourly data are currently used for the computation of the ESA Rapid and Ultra Rapid
products.
References
GPS-TDAF Stations Configuration Manual. Version 1.4, October 1999.
The GPS receiver Network of ESOC: Maspalomas, Kourou, Kiruna, Perth, Villafrancaand Malindi. C. Garcia-Martinez, J.M. Dow, T. Martin-Mur, J. Feltens, P.
Bernedo. 1998 Technical Reports. IGS Central Bureau.
ESA/ESOC IGS Analysis Centre Poster Summary. C. Garcia-Martinez, J.M. Dow, T.
Martin-Mur, J. Feltens, P. Bernedo. 1998 IGS Network Systems Workshop.

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212

Status Report of IGS Stations Monitored by GFZStatus Report of IGS Stations Monitored by GFZM. Ramatschi, J. Neumeyer, Th. Nischan
Geoforschungszentrum Potsdam (GFZ), Telegrafenberg, 14473 Potsdam, Germany
Division 1
Kinematics and Dynamics of the EarthIntroduction
The improving of the data availability is in fact the most important and a permanent task
in monitoring the IGS GPS-sites. Some IGS sites operated by GFZ were extended tomeet the requirements of the GFZ Champ mission, showing the possibilities andlimitations of the current concept. Effort was taken to add new sites to the IGS net.
Data Transfer
The software for transferring the data via FTP was improved. Regarding the Windows
based GPS sites new software was developed to increase the transfer reliability andspeed. The station KIT3 shows still poor data availability due to the remote location. We
are now working on an internet solution at this site.
Champ Support
Some GPS sites, e. g. LPGS, were extended to work at higher sample rates. Higher
sample rates with increased file sizes could result in increased latencies depending on thestrength of the data transfer routes. Compromises had to be taken to meet both
requirements, low latency and high sample rates.
New Station
The station ULBA located at the Ulaanbaatar Astronomical Observatory in the Mongolia
is about to obtain the IGS status. This station is equipped with an radio modem link type
WIMAN /1/, connecting the GPS site over a distance of about 10 km to the internet.
Efforts were taken to find new partners for building up new GPS sites in Africa and firstcontacts are very promising.
References
Neumeyer J., Nischan Th., Ramatschi M., Status Report of IGS Stations Monitored by
GFZ, http://igscb.jpl.nasa.gov/overview/99_tech_reports.html

213

IGS 2000 Technical Reports

Table 1: Status of IGS stations operated by GFZ (07/2001)
File
Size

Data
link

Latency

Meteo
StationTcomp +
ZIP

HourlyInternet<15 min

Yes

LINUX

Tcomp +ZIP

Daily

Internet(offline)

~ 10
days

Yes

Turbo
BinaryLINUX

Tcomp +
ZIP

HourlyInternet<15 minNo

TrMonitor

Turbo
Binary

LINUX

Tcomp

HourlyInternet<15 minYes

AOA SNR
8000 ACT

TrMonitor

Turbo
Binary

LINUX

Tcomp

HourlyInternet<15 min

Yes

ULBA(Mongolia)

AOA SNR
8000 ACT

TrMonitor

Turbo
BinaryLINUX

Tcomp +
ZIP

Hourly<15 min

No

UNSA(Argentina)

AOA SNR
8000 ACT

TrMonitor

Turbo
BinaryLINUX

Tcomp +
ZIP

HourlyRadiolink +
Internet
Internet<15 min

No

URUM(China)AOA SNR
8000 ACT

TrMonitor

Conan
Binary

LINUX

ZIP

Daily

<2 h

No

RIOG
(Argentina)

AshtechZ 12

GBSS

BinaryWin / NT4

ZIP

HourlyModem+
Internet(offline)
Internet<15 min

No

ZWEN(Russia)AOA SNR
8000 ACT

TrMonitor

Turbo
BinaryLINUX

Tcomp +
ZIP

HourlyInternet<15 minNo

StationOperating
SystemReceiver

Download
Software

Receiver
FormatKSTU(Russia)AOA SNR
8000 ACT

TrMonitor

Turbo
Binary

LINUX

KIT3

AOA SNR
8000 ACT

TrMonitor(Uzbekistan)

Turbo
BinaryLPGS(Argentina)

AOA SNR
8000 ACT

TrMonitor

OBER(Germany)

AOA SNR
8000 ACT

POTS(Germany)214

Compression

NASA Sponsored GPS Global Network Activities

NASA-Sponsored GPS Global Network Activities
D. Stowers
Jet Propulsion Laboratory, Pasadena, CA, USA
M. Jackson, O. Ruud
University NAVstar Consortium, Boulder, CO, USA
R. Khachikyan
Raytheon Systems Company, Pasadena, CA, USA
Activities in 2000
NASA supported IGS sites established in 2000/2001, and partner agencies:
NRIL Norilsk, Russia - RDAAC/IRISMOBN Moscaw/Obninsk, Russia - RDAAC
CHPI Cachioera Paulista, Brazil - INPE
MBAR Mbarara, Uganda - IRIS/Geological Survey and Mines Dept. of Uganda
MSKU Franceville, Gabon - IRIS/Universite des Sciences et Techniques de Masuku
DYR2 Diyarbakir, Turkey - MIT/ERLYAKT Yakutsk, Russia - RDAAC/IRIS
RBAY Richards Bay, South Africa - Hartebeesthoek Radio Astronomy Observatory
RABT Rabat, Morroco - MIT/ERL
CHUM Chumysh, Kazakhstan - IVTANNASA supported IGS sites upgraded with modern receivers:
AREQ, CRO1, IISC, GALA, GOLD, GUAM, HRAO, MADR, SANT, TIDB, USUD

High-rate data available with global distribution:
Partnered ground support commitment for the CHAMP LEO mission, the IGS call for
support for LEO missions in general, and real-time GPS data applications provided theimpetus to expand the high-rate subnetwork to 25 (and growing) sites. In most cases,
these sites provide both 1s data and what are now typical hourly and daily 30s RINEX
file products.
Formats of data publicly available from ftp://bodhi.jpl.nasa.gov/pub/
Daily 30s-samplerate RINEX
Hourly 30s-samplerate RINEX
15m 1s-samplerate compressed TurboBinary (GFZ tcomp utility);
CHAMP LEO support
15m
1s-samplerate CompactRINEX (Hatanaka/unix compressed);
IGS LEO Pilot Project format

215

IGS 2000 Technical Reports

Continued L2 troubles:
TurboRogues continue to have problems w/L2 tracking during solar maximum. A
firmware fix did not materialize. An external fix running the TurboRogue receiver at 1s
provides some improvement, but is not feasible at many locations. Receiver replacement
has provided the best solution.
Y2K and other issues:
Other than some minor date formatting issues that were resolved almost immediately, andbit of a flurry to continue to provide continuous IGS support with a reduced number of
Global Data Centers and an unusual number of key facility electrical power outages(unrelated to Y2K issues), this particular date rollover was largely uneventful.

80

60

40

20

0

-20

-40

-60

NASA supported IGS sites
Hourly sites
High-Rate sites

-80
-250

-200

-150

-100

* 1s data available + hourly 30s data available

216

-50

0

50

NASA Sponsored GPS Global Network Activities

NASA Supported IGS Sites
AOA1 ROGUE SNR-8000+AREQ AOA SNR-8000 ACTARTU ASHTECH Z-XII3
ASC1 AOA SNR-8000 ACT+AUCK ROGUE SNR-8000
BILI ASHTECH Z-XII3
BOGT non-operational
CASA ROGUE SNR-8000
CHAT ROGUE SNR-8000
CHPI ROGUE SNR-8000
CHUM ROGUE SNR-8000+CIC1 ROGUE SNR-8000*+CORD ROGUE SNR-8000*+CRO1 ASHTECH Z-XII3
DGAR AOA SNR-8000 ACT
DYR2 ROGUE SNR-8000+EISL ROGUE SNR-8000*+FAIR AOA SNR-8100 ACT*+GALA ASHTECH Z-XII3*+GODE AOA SNR-12 ACT+GOL2 ROGUE SNR-12 RM*+GOLD ASHTECH Z-XII3*+GUAM ASHTECH Z-XII3
HARV AOA SNR-8000 ACT*+HRAO ASHTECH Z-XII3
IAVH (replaced by RABT)*+IISC ASHTECH Z-XII3+JPLM ROGUE SNR-8000*+KOKB AOA SNR-8100 ACT
KUNM ROGUE SNR-8000+KWJ1 AOA SNR-8100 ACT+MAD2 ROGUE SNR-12 RM*+MADR ASHTECH Z-XII3
MAGO ASHTECH Z-XII3*+MBAR ASHTECH Z-XII3

MCM4 ROGUE SNR-8000+MDO1 ROGUE SNR-8000*+MKEA ASHTECH Z-XII3*MOBN ASHTECH Z-XII3
MOIN non-operational*+MSKU ASHTECH Z-XII3+NLIB ROGUE SNR-8000*+NRIL ASHTECH Z-XII3
NSSP ROGUE SNR-8000
PETP ASHTECH Z-XII3+PIE1 ROGUE SNR-8000*+PIMO ROGUE SNR-8000
POL2 ROGUE SNR-8000+QUIN ROGUE SNR-8000
RABT ROGUE SNR-8000+RBAY ROGUE SNR-8000
RIOP ROGUE SNR-8000*+SANT ASHTECH Z-XII3
SELE ROGUE SNR-8000
SEY1 ROGUE SNR-8000
SHAO ROGUE SNR-8100+SUTH ROGUE SNR-8100
THU1 ROGUE SNR-12 RM+TID2 ROGUE SNR-12 RM*+TIDB ASHTECH Z-XII3
TIXI ASHTECH Z-XII3*+USUD ASHTECH Z-XII3
XIAN ROGUE SNR-8100*YAKT ASHTECH Z-XII3
YAR1 ROGUE SNR-8100
YKRO ROGUE SNR-8000
YSSK ASHTECH Z-XII3*Auxiliary Z-12 receiver (GODF) providing 1s data from GODE antenna/monument.
*Auxiliary Z-12 receiver (MCMZ) providing 1s data from MCM4 antenna/monument.
*Auxiliary Z-12 receiver (JPLT) providing 1s data from JPL Frequency Standard Test
Lab
*Auxiliary Z-12 receiver (OKC2) providing 1s data from ARM Facility in Oklahoma

217

IGS 2000 Technical Reports

218

NRCan - GSC Western Canada Deformation Array GPS Network - 2000 Report

NRCan – GSC
Western Canada Deformation Array GPS Network
2000 ReportMichael Schmidt, Herb Dragert
Geological Survey of Canada, Natural Resources Canada
Introduction
The Western Canada Deformation Array (WCDA) is a regional network of continuous
GPS stations operated by the Geological Survey (GSC) of Canada primarily for the studyof crustal deformation in the Cascadia Subduction Zone. In addition two sites, DUBO
and FLIN, (supported under a joint GSC – NASA/JPL research agreement), are operated
as part of a continental postglacial rebound study involving the analysis of GPS data fromvarious agencies. Absolute gravity measurements are carried out at a subset of eight ofthese sites. In 2000, the operation of station WHIT was transferred to the Geodetic
Survey Division (GSD) of NRCan. The WCDA network grew by a number of new
stations bringing the total number of sites up to 14. Of these, 10 are posted to the IGS.
Data from all sites are available from the WCDA ftp server.

Figure 1: WCDA GPS Network
Data Retrieval, Validation and Distribution
No significant changes were made to the GPS data retrieval, validation and distribution
systems in 2000. Data are retrieved on an ongoing automated basis. Data from the two
IGS global sites, ALBH and DRAO are forwarded hourly to CDDIS. The remaining
sites’ data are distributed to the IGS in 24-hour files. All file distribution and posting on
the WCDA server is in the compressed Hatanaka RINEX format. Data validation processcontinues to use three separate programs: GIMP, GPSPACE (both GSD/NRCan) and
TEQC (UNAVCO).

219

IGS 2000 Technical Reports

GIMP provides arc-by-arc statistics including number of observations, data gaps, cycle
slips, ionospheric and multipath parameters. GPSPACE uses either broadcast orbits or‘SP3’ format orbits to calculate single point position, clock offset and clock drift. TEQC,
in addition to providing data quality control, is also used to RINEX all WCDA data.
Summary statistics from all three validation programs are tabulated in summary files used
for evaluating site performance, generating plots, etc..
Metadata contained in the RINEX observation file headers are generated at the time of
RINEX conversion based on time-stamped entries in station log files. UNIX-Hatanaka
compressed RINEX files are posted on the WCDA FTP server and forwarded to CDDIS
immediately after automated data retrieval and validation is complete. Data files and IGS
site logs are available via the web (http://www.pgc.nrcan.gc.ca/geodyn ) or via
anonymous FTP from WCDA server: ftp://sikanni.pgc.nrcan.gc.ca
WCDA Site Upgrades:
The summary of site upgrades includes receiver, receiver firmware, antenna and domechanges carried out in 2000 and in effect as of Dec 31, 2000. Changes made subsequent
to Dec 31. 2000 are not reflected in these tables.
Receiver Upgrades 2000
Three stations were upgraded to the AOA BenchMark ACT technology.
Site
ALBH
WHIT*
WSLR

Date Installed
15-MAR-2000
11-JUL-2000
AOA SNR-8000 ACT

Firmware Version
3.3.32.2N
3.3.32.4
3.3.32.3

Table 1: AOA BENCHMARK ACT GPS receiver installation
as of Dec. 31, 2000
* WHIT: operation transferred to GSD, NRCan Oct. 4, 2000

Firmware Upgrades 2000
Table 2 lists the receiver type and firmware changes carried out prior to December 31,
2000.
Site

Receiver Type

Date Installed

Firmware Version

ALBH
DRAO
WHIT*
WSLR

AOA BENCHMARK ACTAOA BENCHMARK ACTAOA SNR-8000 ACTAOA SNR-8000 ACT

15-MAR-2000 18:18 UT
06-DEC-2000 22:36 UT
04-OCT-2000 00:00 UT
29-MAR-2000 21:53 UT

3.3.32.2N
3.3.32.4
3.3.32.2N
3.3.32.3

Table 2: Receiver Firmware: Date of Upgrade and Version Number
as of December 31, 2000
* WHIT: operation transferred to GSD, NRCan Oct. 4, 2000

220

NRCan - GSC Western Canada Deformation Array GPS Network - 2000 Report

Antenna / Dome Upgrades 2000
All WCDA sites are equipped with AOAD/M_T antennas. Several models of this antenna
are used. Table 3 summarizes antenna changes and Table 4 dome changes made at
WCDA sites.

Site
UCLU
WSLR

AntennaType
AOAD/M_T
AOAD/M_T

Antenna Part
Number7490582-B
7490582-2

Change Effective
01-JUN-2000 23:00 UT
29-MAR-2000 21:53 UT

Table 3: Antenna and Changes, 2000
as of December 31, 2000

Site
UCLU
WSLR

Dome Type + RF screen
SCIS + RF screen
SCIS

Change Effective
SCIS Dome installed 01-JUN-2000 23:00 UTSCIS Dome installed 29-MAR-2000 21:53 UT

Table 4: Antenna Dome changes, 2000
as of December 31, 2000

External Frequency (Clock) Changes 2000

Site
ALBH
NANO
WSLR

Clock Change
Rubidium to Hydrogen Maser
Rubidium to Clock Steering
Rubidium to Clock Steering

Change Effective
06-OCT-2000 19:45 UT
07-NOV-2000 17:08 UT
31-MAR-2000 17:20 UTTable 5: External Frequency (clock) changes, 2000
as of December 31, 2000

221

IGS 2000 Technical Reports

WCDA IGS Global Sites
The following tables summarize the data collection status of WCDA IGS Global sites(ALBH, DRAO) as indicated by the total number of daily observations. The clock
performance as derived from GPSPACE with IGS Rapid orbits is also indicated.

ALBH- upgrade to AOA BenchMark
ACT D075 (8 ch to 12 ch)- difference(s) in daily No. ofdata points due to changes inconstellation;.

ALBH- Rubidium clock used until
Oct. 6 (D280);- Hydrogen Maser installed
D280;> Output from GPSPACE
with Rapid Orbits;

DRAO- difference(s) in daily No. ofdata points due to changes inconstellation;

DRAO- large number of apparent
clock resets due to problem
with receiver offloads causing
receiver resets;- problem resolved byfirmware upgrade D341
> Output from GPSPACE with
Rapid Orbits;

Complete site information is available at: http://www.pgc.nrcan.gc.ca/geodyn
222

NRCan - GSC Western Canada Deformation Array GPS Network - 2000 Report

Permanent GPS Tracking Station UPAD
A. Caporali
University of Padova, Italy(alessandro.caporali@unipd.it)
Presentation
The GPS station UPAD of the University of Padova operates since 1994 as a permanent
installation in support of the International GPS Service for Geodynamics (IGS), of
EUREF (European Reference Frame) and the project CERGOP of the Central Europe
Inititative. In 1997 our University joined the University Navstar Consortium UNAVCO.
The UPAD station serves the scientific and tutorial needs of the Department of Geology,
Paleontology and Geophysics, as to the application of GPS data to Earth Sciences, and of
the Interdipartimental Center for Space Activities (CISAS), as to the application of GPS
techniques to Space Engineering, Space Communication and Navigation. The station is
located downtown Padova, on the roof of the University Main Building, near a Geodetic
Dome formerly used for astrolabe observations.
Instrumentation
In 1997 the station operated with the TRIMBLE 4000SSE receiver and geodetic antenna
with ground plane. In September 1997 new equipment included a TRIMBLE 4000 Ssi,
choke ring antenna and the control software URS, under OS2. The local PC is configured
as a FTP and WEB server. Since September 1999 the URS operates under the Operating
system Windows NT4.
Data
Data production consists of :• Real time differential corrections RTCM/RTK obtainable at free of charge at
the phone number 049 8273442 (modem)• Hourly files in compressed RINEX format. Compression is according to IGS
standards (Unix+Hatanaka). Observation and Navigation files are available.
Sampling time is 5 seconds.
• Hourly files in compressed RINEX format. Compression is according to IGS
standards (Unix+Hatanaka). Observation and Navigation files are available.
Sampling time is 30 seconds.
• Daily files in compressed RINEX format. Compression is according to IGS
standards (Unix+Hatanaka). Observation and Navigation files are available.
Sampling time is 30 seconds.
The FTP target hosts are, at this time:
1.
2.
3.
4.
5.

University of Padova
Observatory Graz Lustbuehl, Austria
BKG, Frankfurt, Germany
GFZ, Potsdam, Germany
Italian Space Agency, Matera Space Geodesy Center, Italy

223

IGS 2000 Technical Reports

224

Technical Report on LAMA IGS Station for Year 2000

Technical Report on LAMA IGS Station for Year 2000
L.W. Baran, J. Kapcia, P. Wielgosz

The IGS permanent station LAMA is located in Poland, 25 kilometres northwards from
Olsztyn and 200 kilometres northwards from Warsaw, the capital city of Poland. It is
maintained by the Institute of Geodesy of the University of Warmia and Mazury in
Olsztyn. The station has carried out GPS observation within IGS since 1994 and also
within EPN (EUREF Permanent Network). It is equipped (nowadays) with ASHTECH ZXII-3 receiver, ASH700936F_C antenna, rubidium frequency standard and LAB EL
meteo station.
In year 2000 the station experienced problem with its GPS antenna AOAD/M_T. The
problem started about April 9, 2000. We got known about this situation when our station
was excluded from EUREF weekly solutions due to large residuals on May 16, 2000. We
were informed about the problem with over one month of delay, because of theavailability of the EUREF combined solution. We did not get any information about low
quality of LAMA observations from IGS. We know also that EPN management works to
improve this situation in order to nearly real-time data quality checking (Takacs andBruyninx, 2001). Anyway, we checked this problem and found out, that our antenna wastracking very few satellites (2-4 satellites less than nearby IGS/EPN stations). So we sent
our AOAD/M_T antenna to repair and replaced it by ASH700936F_C antenna (withAshtech radome) on October 6, 2000. Since then the station has operated without major
problems. It is a pity we could not use the new antenna until October 2000. The changeof the antenna caused a few millimetres shift in station coordinates.
On the basis of GPS observations collected at LAMA and other IGS/EPN stations we
conduct studies, primarily on ionospheric TEC behaviour during geomagnetic storms andalso on monitoring vectors connecting LAMA with several EPN stations forgeodynamics purposes (Baran et al., 2000; Chenyakov et al., 1999).

225

IGS 2000 Technical Reports

Fig.1 Changes in coordinate time series of LAMA station caused by malfunction
and next replacement of GPS antenna (bywww.epncb.oma.be/series/lama.html, C. Bruyninx).

References
Baran L.W, Krankowski A., Wielgosz P. (2000) The Use of GPS Permanent
Observations for Regional Deformation Monitoring, The 9th International
Symposium on Recent Crustal Movements (CRCM ’98), Cairo – EGYPT,
November 14-19, 1998, Proceedings, Vol. II, SESSION E, pp. 441-447, January
2000
Chenyakov I.I., Shagimuratov I.I, Baran L.W. (1999) High Latitude Measurements of
Ionospheric TEC from GPS Signals, Physics of Auroral Phenomena, Proceedingsof the 22nd Annual Seminar, 23-26 March 1999, Russian Academy of Sciences,
Kola Science Center, Polar Geophysics Institute, Apatity, pp. 14-17
Takacs B., Bruyninx C.: Quality Checking the Raw Data of the EUREF Permanent
Network, Presented at the EUREF Symposium, May 16, 2001, Dubrovnik,
Croatia226

IGS

W O R K I N G
P I L O T

G R O U P S /P R O J E C T S / C O M M I T T E E SIGS/BIPM Time Transfer Pilot Project

IGS / BIPM Time Transfer Pilot Project
Jim R. Ray
United States Naval Observatory, USA
Introduction
The IGS/BIPM Pilot Project to Study Accurate Time and Frequency Comparisons using
GPS Phase and Code Measurements is sponsored jointly with the Bureau Internationaldes Poids et Mesures (BIPM). The project has been underway since early 1998, with themain goal being to investigate and develop operational strategies to exploit geodetic GPS
methods for improved global availability of accurate time and frequency comparisons.
The respective roles of the IGS and BIPM are complementary and mutually beneficial.
The IGS brings a global GPS tracking network, standards for continuously operating
geodetic, dual-frequency receivers, an efficient data delivery system, and state-of-the-art
data analysis groups, methods, and products. The BIPM and the timing laboratories
contribute expertise in high-accuracy metrological standards and measurements, timing
calibration methods, algorithms for maintaining stable time scales, and formation anddissemination of UTC.
Recent activities generally fall into the following areas:•

Workshop — Two days during the “IGS 2000 Analysis Center Workshop,” held
25–26 September 2000 at the U.S. Naval Observatory, were devoted to the pilot
project.

•

Deployment of GPS receivers — The IGS network currently consists of about 250
permanent, continuously operating stations globally distributed. Of these, externalfrequency standards are used at ~38 with H-masers, ~23 with cesium clocks, and ~17with rubidium clocks; the remainder use internal crystal oscillators. Table 1 lists the
IGS stations currently located at timing laboratories. The former timing lab at theTechnical University of Graz, TUG (GRAZ receiver) ended operations in 2000, while
the NPLD and SPT0 stations are new. Figure 1 shows the locations of the stations.

•

GPS data analysis — A new method to combine satellite and receiver clock estimates,
both sampled at 5-minute intervals, was implemented officially by the IGS on 5
November 2000.

•

Instrumental delays — The BIPM has demonstrated techniques to calibrate theinstrumental biases of the Ashtech Z-XII3T receiver. Efforts are underway to measure
the biases of similar receivers deployed at timing laboratories.

•

Comparison experiments — Studies are underway comparing geodetic timing resultswith simultaneous, independent measurements using the common-view and two-way
satellite techniques.

For further information, please refer to http://maia.usno.navy.mil/gpst.html.

229

IGS 2000 Technical Reports

Table 1. IGS Stations Located at BIPM Timing Laboratories (in 2000)
AMC2

AMC*

AOA SNR-12 ACT

H-maser

Colorado Springs, Colorado, USA

BOR1

AOS

AOA TurboRogue

CesiumBorowiec, Poland

BRUS

ORB

Ashtech Z-XII3T

H-maser

Brussels, Belgium

MDVO

IMVP

Trimble 4000SSE

H-maser

Mendeleevo, Russia

NPLD

NPL*

Ashtech Z-XII3T

H-maser

Teddington, UK

NRC1

NRC*

AOA SNR-12 ACT

H-maserOttawa, Canada

NRC2

NRC*

AOA SNR-8100 ACT

H-maserOttawa, Canada

OBER

DLR

AOA SNR-8000 ACT

RubidiumOberpfaffenhofen, Germany

PENC

SGO

Trimble 4000SSE

RubidiumPenc, Hungary

SFER

ROA

Trimble 4000SSI

CesiumSan Fernando, Spain

SPT0

SP

JPS Legacy

CesiumBoras, Sweden

TLSE

CNES

AOA TurboRogue

CesiumToulouse, France

USNO

USNO*

AOA SNR-12 ACT

H-maser

Washington, DC, USA

WTZR

IFAG

AOA SNR-8000 ACT

H-maser

Wettzell, Germany

Figure 1. Locations of IGS stations at BIPM timing laboratories

230

Report of the Tropospheric Working Group

Report of the Tropospheric Working Group
Gerd Gendt
GeoForschungsZentrum Potsdam, Division 1, Telegrafenberg A17,
D-14473 Potsdam, Germany; e-mail: gendt@gfz-potsdam.de
Product Generation
Since 1997 the IGS regularly generates a combined tropospheric product. It is based on
the submission of the individual IGS Analysis Centers (AC), which compute theirtropospheric estimates during or after the generation of the IGS final products. Since SIO
has joined these activities in February 1998 all IGS ACs contribute to the combination.
The product is the weighted mean of the total zenith path delay (ZPD) of the neutral
atmosphere (Gendt, 1996). The individual AC biases are calibrated on a weekly basis.
The product delay is 2 to 4 weeks. The standards for the analysis are converging, so six
ACs have implemented the Niell mapping function, and elevation cut-off angles of 10, 15
and 20 degrees are used by 2 , 4 and 1 centers, respectively.
For more than 210 sites the product is available now (Fig. 1). Nearly 150 sites are usedby three or more ACs, which allows to derive reasonable quality measures. The number
and quality of the meteorological sensors is slowly improving (Figs. 2, 3). Up to now
only 30 sites have reported meteorological data, typically about 25. Information on thequality of all sites to support the selection for new installations were compiled. Presently
there are tendencies by some meteorological institutions to assimilate the ZPD directly
into the numerical weather prediction (NWP) models. If this proves to be the final
strategy then it will have an impact on the installation of meteorological sensors for theregional applications devoted to NWP. However, for sites used in climate studies, whichis the case for the global IGS network, meteorological sensors are important, and theusual daily RINEX-met files are sufficient. Therefore IGS should strive to complete theinstallation of sensors in its global network.

.

217 total
150 used by > 2 AC
22 used by 2 AC
45 used by 1 AC

Figure 1. IGS Stations with Tropospheric Estimates231

Number

IGS 2000 Technical Reports

40.
30.

20.

10.
0.
890.

910.

930.

Figure 2.

950.

970.

990.
1010.
GPS-Week

1030.

1050.

1070.

1090.

Number of sites with meteorological sensors

Product Quality and Validation
The quality of the product (internal consistency between ACs) is at the level of 3 to 5 mmin the ZPD, which corresponds to ≤ 1 mm in the water vapor (Fig. 4). The biases are evensmaller. However, changes in the analysis parameters of the ACs can be seen in mostcases in the series.
The histograms in Figure 5 reveal that for most sites the standard deviation is below the
4 mm level. Especially, CODE and SIO have pronounced peaks at 2 – 3 mm, caused by
the fact that both centers use many sites in the denser parts of the network where thequality is significantly better than for the sparser parts (Fig. 3). Systematic effects in thebiases can clearly be seen for CODE and SIO. The primary reason may be the different
cutoff angles applied by both centers (10o), where the weighted 10 o degrees of CODE
seems to correspond to an effective angle of about 20 o.
Regular comparisons with co-located techniques were performed for Potsdam only. Here,a water vapor radiometer (WVR) operated by the German Weather Service is available.
All AC GPS solutions monitor the fluctuations in the water vapor with high accuracy.
The scattering is of the level of ±1 mm, the best agreement is for the combined series. All
ACs have a negative bias of about –1 mm. The fluctuations in the biases are rather large
over a longer time interval (~1 mm). The biases may have various reasons, e.g. the WVR
itself (calibration) or GPS modeling deficiencies (antenna phase center patterns, mapping
functions, satellite antenna offsets). Efforts to make an extensive comparison with
globally distributed VLBI sites failed up to now, because older VLBI results had only
archived the wet delay without the corresponding pressure values. Such validations
should be done in future in a close cooperation with the IVS.
ResumeAll IGS components contributing to the combined tropospheric IGS product are
performing well. The product has reached a high quality and further investigations on a
post-processed tropospheric product in a global scale are not planned. Therefore theactivities of working group on this topic will be finished. The established procedures forthe regular product generation will be continued, and GFZ agrees to perform the
combination (see http://op.gfz-potsdam.de/S11/index_GPSS.html).

232Report of the Tropospheric Working Group

Presently near real-time (NRT) monitoring of water vapor is supported by IGS byproviding global data, NRT orbits and its Ultra-rapid predictions (Fang et al., 2001).
Although NRT activities are more suited to individual countries or regionalorganizations, where sufficient dense networks are operated, IGS plans to study thefeasibility for an Ultra-rapid or even NRT global tropospheric product. Such a product,
provided for a relative sparse network only, can be used for NRT quality control inregional network applications.
Up to now only a few users retrieve the IGS tropospheric products (looking into servers
at CDDIS, IGN and GFZ). Hopefully, the interest of meteorological community in the
product will grow in parallel with the acceptance of GPS products for NWP models. The
IGS contribution should also be seen in the context of other activities like theestablishment of a similar database (TROP-SINEX format) for Asia and Western Pacificby the Earthquake Research Institute, Tokyo, and the plan to generate a combined
tropospheric product within EUREF.
References
Fang, P, G Gendt, T Springer, T Manucci (2001): IGS Near Real-Time Products andTheir Applications IGS Analysis Center Workshop, 25-29 Sept 2000, Washington,
GPS Solutions, Vol.4, No.4, 2001, p.2-8
Gendt, G (1996): Comparison of IGS tropospheric estimates. Proceedings IGS Analysis
Center Workshop, 19-21 March 1996 Silver Sprig, Maryland USA, Eds. R E Neilan,
P A Van Scoy, J F Zumberge, pp. 151-164

ZND StdDev [mm]10.

Met Sensor

8.
6.
4.
2.
0.
-90.

-60.

-30.

0.
Latitude

30.

60.

90.

Figure 3.
Mean standard deviation for IGS sites used by three or more
Analysis Centers, sorted by latitude (mean over GPS weeks 1000 to 1087). Sites
equipped with met sensors are marked.

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12.

Stddev

ZPD[mm]

10.
8.
6.
4.
2.

COD

0.
940.

950.

EMR

ESA

GFZ

JPL

NGS

SIO

960.

970.

980.

990.

1000. 1010. 1020. 1030. 1040. 1050. 1060. 1070. 1080. 1090.

960.

970.

980.

990.

1000. 1010. 1020. 1030. 1040. 1050. 1060. 1070. 1080. 1090.

6.

ZPD[mm]

4.

Bias

2.
0.
-2.
-4.
-6.
940.

950.

No. StaFigure 4. Difference in the zenith neutral delay between the individual GPS
estimates and the IGS Combined Product. Mean values (over all sites) per week
and per Analysis Center.

500.
400.
300.

COD
EMR
ESA
GFZ
JPL
NGS
SIO

Stddev

200.
100.
0.

No. Sta

1.

300.
250.
200.
150.
100.
50.
0.
-12.

2.

3.

4.

5.

6.

7.

8.

9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

Bias

-10.

-8.

-6.

-4.

-2.

0.
2.
ZPD [mm]

4.

6.

COD
EMR
ESA
GFZ
JPL
NGS
SIO

10 deg.
15 deg.
20 deg.
15 deg.
15 deg.
15 deg.
10 deg.

8.

10.

12.

Figure 5.
Differences in the zenith path delay between the individual GPS
estimates and the IGS Combined Product. Histograms of standard deviation andbias for the GPS weeks 1080 to 1087.

234

2000 IGS Activities in the Area of the Ionosphere2000 IGS Activities in the Area of the Ionosphere
J. Feltens
EDS Informationstechnologie & Service GmbH,
based at Navigation Research Office, ESA/European Space Operations Centre,
Robert-Bosch-Strafle 5, D-64293 Darmstadt, Germany
e-mail: Joachim.Feltens@esa.int
Introduction
The IGS Ionosphere Working Group (Iono_WG) is active since June 1998. The working
group's most important short-term goal is the routine provision of global ionosphere TEC
maps plus GPS spacecraft differential code biases (DCBs) with a delay of some days.
The routine delivery of stations DCBs is in preparation and will be included soon. In themedium- and long-term, the development of more sophisticated ionosphere models andthe establishment of a near-real-time service are the major tasks. The final target is theestablishment of an independent IGS ionosphere model.
Five Ionosphere Associate Analysis Centers (IAACs) contribute with their products to
the Iono_WG activities:
1. CODE, Center for Orbit Determination in Europe, Astronomical Institute, Universityof Berne, Switzerland.
2. ESOC, European Space Operations Centre of ESA, Darmstadt, Germany.
3. JPL, Jet Propulsion Laboratory, Pasadena, California, U.S.A.
4. NRCan, National Resources Canada, Ottawa, Ontario, Canada.
5. UPC, Polytechnical University of Catalonia, Barcelona, Spain.
It is the intent of this Technical Report to give an overview over the Iono_WG activities
in 2000.
Routine Activities
Daily Ionospheric Total Electron Content (TEC) Information
Each IAAC delivers per 24 hours an IONEX file (Schaer et al., 1997) with 12 TEC maps
containing global TEC information with a 2-hours time resolution and a daily set of GPS
satellite DCBs in its header. The inclusion of ground station receivers DCBs is inpreparation.
Weekly Comparisons
On Tuesday of each week the TEC maps from the different IAACs are compared for alldays of the week before. These comparisons are done at ESA/ESOC. A weekly
comparison summary is e-mailed to the "Iono_WG members" via IONO-WG mail.

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Furthermore, the daily summaries, the daily IONEX files with the "mean" TEC maps &GPS satellite DCBs and daily TEC & DCB difference files with respect to the "mean" foreach IAAC, and also plots of these maps, are made available to the "Iono_WG members"
on ESOC's FTP account. The algorithm used in the comparison program is described in(Feltens, 1999 - Appendix A). This algorithm is currently being upgraded with a newweighting scheme, for more details (see next chapter "Improvement of the Comparison
Scheme/Validations").

Figure 1: The IGS "weighted mean" TEC maps of 28 March 2000 in [TECU](1st row: 1h, 3h, 5 h, 7 h ; 2nd row: 9 h, 11 h, 13 h, 15 h ; 3rd row: 17 h, 19 h, 21 h, 23 h).
On the northern hemisphere the deviations of the different IAAC TEC maps from the IGS"mean" are under normal conditions 5 TECU or less. At the equator and on the southernhemisphere the situation is more problematic, because of gaps in the station coverage atthese latitudes. However, the deployment of new IGS stations in these areas has reduced
these gaps since 1999. Figure 1 above shows the sequence of IGS "weighted mean" TEC
maps of 28 March 2000, a day during a period in the current solar maximum, when the
TEC level was very high.
The day-by-day variations of the different IAAC DCB sets are normally less than 0.3
nanoseconds, sometimes 0.5 nanoseconds. IAAC DCB sets showing deviations of one 1
nanosecond and more with respect to the IGS "mean" are excluded from the comparison.
According to a presentation of S. Schaer at the IGS Workshop, 27 - 29 September 2000,
Washington, mean IAAC satellite DCB series show an agreement of about 0.1
nanoseconds. For his analysis Schaer took three months (GPS weeks 1065 - 1077) of
daily satellite DCB sets from the IAACs IONEX files and computed from these daily
values IAAC-specific mean DCB sets. The five mean DCB sets thus obtained were thencompared with respect to each other and also with respect to an overall mean set (All).
Table 1 below is an extract of Schaer's presentation and shows the obtained rms errors (in2362000 IGS Activities in the Area of the Ionospherenanoseconds). When interpreting these numbers one has to keep in mind that some
IAACs estimate their DCB sets together with their TEC maps, while others makeseparate program runs for this. Some IAACs introduce constraints in their DCBs
estimation, while others do not.
Table 1: Agreement of the distinct IAACs satellite DCB sets in[nanoseconds] (according to S. Schaer).

CODE
NRCan
ESOC
JPL
UPC

NRCan
0.122

ESOC
0.106
0.109

JPL
0.110
0.144
0.118

UPC
0.370
0.371
0.373
0.393

All
0.094
0.104
0.095
0.117
0.296

Improvement of the Comparison Scheme / Validations
The current comparison/combination algorithm is based on a pure statistical approach
using weighted means. On the other hand, the methods used by the IAACs to model theionosphere are very different. In order to achieve an objective weighting for a
combination scheme the existing comparison/combination is currently upgraded: Basedon two self-consistency methods proposed by NRCan and UPC, in which directly from
GPS-observables derived TEC values are compared with corresponding TEC values
interpolated from the IAACs TEC maps, new geographic-dependent weights will becomputed and thus replace the old kind of weighting in the comparison/combination
algorithm. A detailed description on how these two methods work can be found in(Feltens, 2000a; Feltens, 2000c; Hernandez-Pajares, 2000; Heroux, 1999).
Figure 2 below shows in form of histograms the results of an analysis made at UPC with
TOPEX data for each of the five IAACs for the year 2000; the Number of TOPEX
observations are shown on the ordinate and the differences {TEC(TOPEX) - TEC(GPS)}in [TECU] are shown on the abscissa. When interpreting these histograms it should betaken into account that, in these plots, a negative bias means that the estimated TEC withGPS (h < 20200 km) is greater than the TOPEX TEC (h < 1300 km). Then a positive bias
means directly a mean underestimation of the TEC with GPS at least equal to the bias
(the TOPEX accuracy seems to be 2 TECU).

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Figure 2: TOPEX- vs GPS-TEC for the year 2000 (figure made at UPC).
Special Activities
During events which are of special interest for the ionosphere community and forionospheric research, the Iono_WG organizes special high-rate tracking campaigns withthe global IGS ground stations network. After the Solar Eclipse Campaign on 11 August
1999, the preparations for a new high-rate campaign with the name "HIRAC/SolarMax"
were started with an initiative of J. Feltens and N. Jakowski through IGSmail #3091(Feltens, 2000b): the objective was to collect in April or May 2001 one week of global
high-rate GPS/GLONASS data as a basis for analyses of ionospheric behavior under thecurrent solar maximum conditions. Further details about the HIRAC/SolarMax campaign
will then be a topic for the IGS 2001 Technical Report.
Future Tasks
As soon as the new weighting scheme is implemented into the comparison/combination
program, it is intended to start with the routine delivery of a combined IGS ionosphere
product.
Preparations are made to attach to the weekly comparison program runs validations bycomparing IAACs model vertical TEC values with vertical TEC values derived fromTOPEX (and Envisat, once launched) altimeter data. Another important aspect will be
the reduction of the time deadline for ionosphere products delivery. The ionosphere is a238

2000 IGS Activities in the Area of the Ionospherevery rapidly changing medium, and it must be the working group's intention to provide
actual ionosphere models in short time frames - especially with regard to the current solar
maximum.
References
Feltens, J. (1999): 'IGS Products for the Ionosphere - One Year of Iono_WG Activities',
Proceedings of the 1999 IGS Analysis Centers Workshop, SIO, La Jolla, CA,
U.S.A., June 8-10, 1999, in preparation.
Feltens, J. (2000a): 'Die Ionosphären-Arbeitsgruppe des Internationalen GPS Service(IGS)', Proceedings Nationaler Workshop zum Weltraumwetter, Neustrelitz,
26./27. Oktober 2000, pp. 161-169.
Feltens, J. (2000b): 'High-rate GPS-campaign', IGSmail #3091 of 8 November 2000.
Feltens, J. (2000c): 'Proposal of a new weighting scheme for weekly
comparison/combination', IONO-WG mail of 15 November 2000.
Hernandez-Pajares, M. (2000): `Self-Consistency of the IONEX TEC Maps', IONO-WG
mails of 24 May 2000 and of 31 May 2000.
Heroux, P. (1999): 'NRCan Global Ionospheric Grid', Proceedings of the 1999 IGS
Analysis Centers Workshop, SIO, La Jolla, CA, U.S.A., June 8-10, 1999, in
preparation.
Schaer, S., W. Gurtner, and J. Feltens (1997): 'IONEX: The IONosphere Map EXchange
Format Version 1', February 25, 1998, Proceedings of the 1998 IGS Analysis
Centers Workshop, ESA/European Space Operations Centre, Darmstadt,
Germany, February 9-11, 1998, pp 233-247.

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240

IGS LEO Pilot Project

IGS LEO Pilot Project
Michael Watkins
Jet Propulsion Laboratory,
California Institute of Technology, USA

The Call for Participation in the IGS Low-Earth Orbiter (LEO) Pilot Project wasannounced in January 2000. It elicited a very strong response evident by the 26 proposals
submitted to the Central Bureau. All components were represented (stations, data centers,
Associate Analysis Centers, etc.), and the Governing Board accepted all the proposals at
the June meeting at the U.S. Naval Observatory. The constitutional meeting to organize
the project was planned for January 2001 at GeoForschungsZentrum (GFZ) in Potsdam,
Germany. The CHAMP satellite launched successfully on 15 July. In November, after an
initial commissioning phase of the satellite, members of the IGS LEO Pilot Project were
provided with one day of CHAMP GPS, gravity, and magnetic field sensor data, as wellas accelerometer and attitude data plus reference frame and data format descriptions.
Data from the U.S.–Argentina mission SAC-C, which successfully launched on 21
November, are also available to the project. The benefits of a common ground-based
infrastructure to serve upcoming multimissions cannot be overlooked.
The definition and operation of a robust, high-sampling-rate, low-latency subset of the
global tracking network is progressing rapidly, and issues such as data formats, access,products, etc., will be discussed in more detail in 2001 when the project members have
had opportunity to examine the space and ground data and produce preliminary results.
One of the key questions is the structure of the project, and in particular, identifying the
Associate Analysis Coordinator for the project. Various groups will evaluate theinclusion of LEO data as a core element of the IGS. An assessment of the effects on the
traditional IGS analysis products will be performed (GPS ephemerides, clocks, Earthorientation, and troposphere), as well as an assessment of the additional computationaland data center burdens. There are clear potential benefits, but these are balanced byadditional complexity. In the spirit of the IGS, the pilot project looks to provide acollaborative approach. The data from the satellites are generated by spaceborne,
geodetic-quality GPS receivers designed by JPL. In addition to CHAMP and SAC-C,
these flight receivers will be flown on board a number of upcoming missions — Jason-1,
Gravity Recovery and Climate Experiment (GRACE), and ICESat.
It is clear that the next few years will provide interesting opportunities to explore theenhancement of the IGS through many applications projects. The LEO Pilot Projectpromises fertile cooperation, noting that by 2003 nearly a half dozen missions will be onorbit and available to the pilot project.

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International GLONASS Service Pilot ProjectInternational GLONASS Service Pilot ProjectJames A. Slater
National Imagery and Mapping Agency
Bethesda, MD 20816, U.S.A.
Introduction
Russia launched the first GLONASS satellites in late 1982. However, until theInternational GLONASS Experiment (IGEX-98) was conducted in 1998-1999, nocoordinated international effort had been organized to collect and process GLONASS
data. IGEX-98 created a global tracking network of stations with geodetic receivers,
obtained increased laser tracking support from the satellite laser ranging community,
generated a continuous archive of satellite observations, and produced post-processed
precise orbits. As a result of continued interest in GLONASS, the IGS initiated a pilot
project, the International GLONASS Service Pilot Project (IGLOS-PP), to exploit the
GLONASS system as long as it remained viable.
A Call for Participation was issued in May 2000 with the following goals and objectives:
1. Establish and maintain a global GLONASS tracking network
2 . Produce precise (10-cm level) orbits, satellite clock estimates, and station
coordinates
3. Monitor and assess GLONASS system performance
4. Investigate the use of GLONASS to improve Earth orientation parameters
5. Improve atmospheric products of the IGS
6. Fully integrate GLONASS into IGS products, operations and programs.
A pilot project committee was formed consisting of Vladimir Glotov (Russian Space
Agency), Ramesh Govind (Australian Survey and Land Information Group), Werner
Gurtner (University of Berne, International Laser Ranging Service liaison), Arne
Jungstand ( EC Joint Research Centre and DLR), Angelyn Moore (IGS Central Bureau),
Carey Noll (NASA Goddard Space Flight Center, Data Center Coordinator), James Slater(National Imagery and Mapping Agency, Chair), Robert Weber (University ofTechnology, Vienna, IGLOS Analysis Center Coordinator), and Pascal Willis (Institut
Geographique National). In addition, the IGS Central Bureau initiated a new mailservice, IGLOSMAIL, on May 25, 2000 for participants in the project.
The pilot service is based on the infrastructure already in place in the IGS for GPS.
Tracking stations forward their data to regional and global data centers where the data are
retrieved by Analysis Centers that compute precise orbits and other products. These
products are then archived at global data centers for access by the user community.

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Tracking Network
As of December 2000, there were 32 operational, dual-frequency tracking stations and 13
proposed stations in the IGLOS pilot project global tracking network. Most of theoperational receivers are Ashtech Z-18 or JPS Legacy models. The remainder are 3S
Navigation receivers. In conjunction with this, the International Laser Ranging Service
has been coordinating laser tracking of three GLONASS satellites (in slot numbers 1, 15,
and 24) as part of its routine schedule. The laser tracking takes advantage of laser
retroreflectors that are on every GLONASS satellite.
Analysis Centers and Global Data Center
Two Analysis Centers, BKG and ESA/ESOC, have been computing precise orbits on a
weekly basis using the receiver data from the tracking network. The Mission Control
Center of the Russian Space Agency and the NERC Space Geodesy Facility in the United
Kingdom have been computing orbits from the laser tracking data on an intermittent
basis. After the BKG and ESA/ESOC orbits are produced, the IGLOS Analysis
Coordinator computes a combined orbit at the University of Technology in Vienna.
Data and precise orbits are stored in the CDDIS global data center at NASA’s Goddard
Space Flight Center. Between August and November 2000, 28 organizations primarily
from Austria, Germany, Russia and the U.S. retrieved IGLOS data from the global data
center.
Precise GLONASS Orbits
Precise GLONASS orbits have been computed continuously by BKG and ESA for each
day in 2000 for all the operational satellites. BKG uses the Bernese software, while ESA
uses its GPSOBS/BAHN software. Orbit repeatability is generally in the 10-20 cm range(rms). The Analysis Centers also compute the time offset between GPS and GLONASS
times, and estimate datum transformations between the GLONASS PZ-90 reference
frame and the International Terrestrial Reference Frame using the GLONASS broadcast
message. After the individual center orbits are released, a weighted combination of thetwo orbits is generated and made available through the CDDIS.
NERC has computed GLONASS orbits using SLR data alone and compared it withmicrowave receiver-based orbits. It has also compared laser ranges directly with ranges
derived from the microwave receiver-based orbits. RMS differences between the laser
and microwave orbits are approximately 10 cm radially and 50 cm in the along-track andcross-track directions.
Plans
Efforts during 2001 will be focussed on integrating the GLONASS receiver sites with the
GPS sites in the IGS. Site log forms, data archives and analysis center software will berevised where possible to process combined GPS and GLONASS data. Stations will all

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have to meet IGS standards. Improved timeliness of orbit products will also be a goal.
There is still some uncertainty regarding the GLONASS constellation and its long term
reliability and maintenance. Nine satellites were operational in December, but without a
new launch in 2001, this number will probably go down.

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246