Global Geodetic Observing System (GGOS)

1

Global Geodetic Observing System
http://www.ggos.org
Chair 2015–2017: Hansjörg Kutterer (Germany)
Chair 2017–2019: Richard Gross (USA)Vice Chair: Ruth Neilan (USA))As the observing system of the IAG, GGOS facilitates a unique and essential combination ofroles centering upon advocacy, integration, and international relations. GGOS also promotes
high‐level outcomes, such as the realization of the International Terrestrial Reference Frame
through developing and maintaining working relationships among a variety of internal andexternal groups and organizations.

GGOS Structure
The GGOS structure is illustrated in Figure 1. The decision-making entities are the Consortium,
the Coordinating Board and its Executive Committee. Permanent Standing Committees andlimited-term Working Groups are the thematic working bodies of GGOS and are distributed
over two Bureaus, the Science Panel and the Focus Areas as well as affiliated organizations. In
addition to being the Secretariat of GGOS, the Coordinating Office coordinates the activities of
GGOS including communications and outreach and is responsible for the GGOS website andmaintaining a presence on social media. The new position of Manager of External Relations
resides within the Coordinating Office.

Figure 1. Organization chart of GGOS.

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-20192

Overview
The 2015–2019 period was an active time of growth and organization within GGOS. A
summary of the new activities that began during this time period is given below. A key activity
touching on all elements of this overview was the revision and update of the GGOS Terms ofReference (ToR) in 2018 to reflect recent developments and strategic direction.
A new GGOS Focus Area on “Geodetic Space Weather Research” was established in 2017.
The main objectives of the new Focus Area are to: (1) improve positioning and navigation by
developing high-precision and high-resolution models of the electron density of the ionosphere,
and to (2) improve satellite orbit determination by developing high-precision and highresolution models of thermospheric drag.
As a mechanism to increase participation in GGOS, especially in the under-represented areasof Africa, Asia-Pacific, and South and Central America, a new component of GGOS, known as
GGOS Affiliates, has been created. A GGOS Affiliate is a national or regional organization thatcoordinates geodetic activities in that nation or region. Once established, each GGOS Affiliate
will have a representative to the GGOS Consortium and collectively they will have two
representatives to the GGOS Coordinating Board. GGOS Japan, formerly known as the GGOS
Working Group of Japan, became the first GGOS Affiliate in November 2017. GGOS Japanwas established in 2013 and its current Chair is Prof. Toshi Otsubo of Hitotsubashi University.
It provides a forum for multi-technique, space-geodetic discussions within Japan and works to
improve the quality of its space-geodetic observations. GGOS Japan also encourages thedifferent agencies in Japan that own, operate, and maintain the space-geodetic infrastructure
there to collaborate with each other.
GGOS represents the IAG within the Group on Earth Observations (GEO) where it has been
appointed to the GEO Programme Board for 2018–2020, GGOS participates in the Committee
on Earth Observation Satellites (CEOS), and GGOS has a stake in the United Nations Global
Geospatial Information Management (UN-GGIM) Subcommittee on Geodesy. Given thefundamental importance of GGOS participation in these external organizations and to better
manage GGOS’ involvement in them, the position of Manager of External Relations wascreated. Since the Manager of External Relations will coordinate GGOS engagement withexternal organizations, the position of Manager of External Relations resides within the
Coordinating Office. The Manager of External Relations is a voting member of both the GGOS
Coordinating Board and the GGOS Executive Committee. Allison Craddock became the first
Manager of External Relations in January 2018.
Essential Geodetic Variables (EGVs) are observed variables that are crucial (essential) to
characterizing the geodetic properties of the Earth and that are key to sustainable geodetic
observations. Examples of EGVs might be the positions of reference objects (ground stations,radio sources), Earth orientation parameters, ground- and space-based gravity measurements,
etc. Once a list of EGVs has been determined, requirements can be assigned to them. Examplesof requirements might be accuracy, spatial and temporal resolution, latency, etc. These
requirements on the EGVs can then be used to assign requirements to EGV-dependent products
like the terrestrial and celestial reference frames. The EGV requirements can also be used toderive requirements on the systems that are used to observe the EGVs. A Committee within the
Bureau of Products and Standards was established in order to define the list of Essential
Geodetic Variables and to assign requirements to them. The Committee consists ofrepresentatives of the IAG Services, Commissions, Inter-Commission Committees, and GGOS
Focus Areas. Richard Gross is the Chair of the Committee.

Global Geodetic Observing System (GGOS)

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Consortium
The GGOS Consortium functions as the large steering committee and collective voice of
GGOS, and is comprised of one representative from each GGOS Affiliate and up to two
representatives from each IAG Service, Commission, and Inter-Commission Committee.
According to the GGOS ToR, the Consortium membership is reviewed and refreshed every
four years, which last took place coincident to the 2015 IUGG General Assembly. The membersof the GGOS Consortium during 2015–2019 are given in Table 1.
The presiding chair of GGOS is also the chair of the GGOS Consortium. The GGOS
Consortium meets annually, which during 2015–2019 took place during GGOS Days:
1. GGOS Days 2015, Frankfurt am Main, Germany, 21–23 October 2015
2. GGOS Days 2016, Boston, Massachusetts, USA, 24–27 October 2016
3. GGOS Days 2017, Vienna, Austria, 31 October to 02 November, 2017
4. GGOS Days 2018, Tsukuba, Japan, 02–05 October 2018
Table 1. Members of the GGOS Consortium During 2015–2019
Organization
Name
Title
GGOS
Hansjörg Kutterer Chair (2015–2017)
Richard Gross
Chair (2017–2019)
GGOS Affiliate of Japan
Basara Miyahara Designated GGOS Representative
International Gravimetric Bureau
Sylvain Bonvalot Director(BGI)
International Gravimetric Bureau
Sean Bruinsma
Designated GGOS Representative(BGI)
Bureau international des poids et
Felicitas Arias
Director, BIPM Time Department
mesures, BIPM
Bureau international des poids etGérard Petit
Principal Physicist, BIPM Timemesures, BIPM
Department
International Centre for Global Earth Franz Barthelmes Director
Models (ICGEM)International DORIS Service (IDS) Laurent Soudarin Director, Central Bureau
International DORIS Service (IDS) Pascal Willis
Chair, Governing Board
International Earth Rotation andDaniela Thaller
Director, Central Bureau
Reference Systems Service (IERS)
International Geoid Service (IGeS) Mirko Reguzzoni PresidentInternational Geoid Service (IGeS) Giovanna Sona
Director
International Geoid Service (IGeS) Urs Marti
Designated GGOS Representative
International Geoid Service (IGeS) Jianliang Huang
Designated GGOS Representative
International Gravity Field Service Riccardo Barzaghi Chair(IGFS)
International Gravity Field Service Georgios Vergos Director, Central Bureau(IGFS)
International GNSS Service (IGS)
Ruth Neilan
Director, Central Bureau
International GNSS Service (IGS)
Gary Johnston
Chair, Governing Board
The International Laser Ranging
Giuseppe Bianco Chair, Governing Board
Service (ILRS)The International Laser Ranging
Erricos Pavlis
Analysis Coordinator
Service (ILRS)International VLBI Service for
Axel Nothnagel
Chair, Directing Board
Geodesy and Astrometry (IVS)Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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International VLBI Service for
Dirk Behrend
Director, Coordinating Center
Geodesy and Astrometry (IVS)
Permanent Service for Mean Sea
Lesley J. Rickards Director
Level (PSMSL)
Permanent Service for Mean Sea
Mark Tamisiea
Designated GGOS Representative
Level (PSMSL)International Geodynamics and Earth Jean-Paul Boy
Director, Central Bureau
Tides Service (IGETS)
International Geodynamics and Earth Christoph Foerste Designated GGOS Representative
Tides Service (IGETS)
International Geodynamics and Earth Alexander Kopaev Designated GGOS Representative
Tides Service (IGETS)
Commission 1: Reference Frames
Geoff Blewitt
President
Commission 1: Reference Frames
Johannes Böhm
Vice President
Commission 1: Reference Frames
Tonie van Dam
Designated GGOS Representative
Commission 2: Gravity Field
Roland Pail
President
Commission 2: Gravity Field
Shuanggen Jin
Vice President
Commission 3: Earth Rotation and Manabu Hashimoto President
Geodynamics
Commission 3: Earth Rotation and Chengli Huang
Vice President
Geodynamics
Commission 4: Positioning andMarcelo Santos
President
Applications
Commission 4: Positioning andAllison Kealy
Vice President
Applications
Inter-Commission Committee on
Pavel Novák
President
Theory (ICCT)Inter-Commission Committee on
Mattia Crespi
Vice President
Theory (ICCT)Inter-Commission Committee on
Dimitrious Tsoulis Designated GGOS Representative
Theory (ICCT)
Coordinating Board
The Coordinating Board is the decision-making body of GGOS. The members of the GGOS
Coordinating Board during 2015–2019 are given in Table 2.
The Chair of GGOS is the Chair of the Coordinating Board. The Coordinating Board meets
twice-per-year, which during 2015–2019 took place during GGOS Days and the Saturday
before EGU:
1. GGOS Days 2015; Frankfurt am Main, Germany; 21–23 October 2015
2. EGU; Vienna, Austria; 16 April 2016
3. GGOS Days 2016; Boston, Massachusetts, USA; 24–27 October 2016
4. EGU; Vienna, Austria; 22 April 2017
5. GGOS Days 2017; Vienna, Austria; 31 October to 02 November, 2017
6. EGU; Vienna, Austria; 07 April 2018
7. GGOS Days 2018; Tsukuba, Japan; 02–05 October 2018
8. EGU; Vienna, Austria; 06 April 2019

Global Geodetic Observing System (GGOS)

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Table 2. Members of the GGOS Coordinating Board During 2015–2019
Position
Voting Name
Chair
Yes
Hansjörg Kutterer (2015–2017)
Richard Gross(2017–2019)
Vice Chair
Yes
Ruth Neilan
Chair, Science Panel
Yes
Richard Gross(2015–2017)
Kosuke Heki(2017–2019)
Director, Coordinating Office
Yes
Allison Craddock (2015–2016)
Günter Stangl(2016–2017)
Matthias Madzak (2017–2018)
Helmut Titz
(2018–2019)
Manager, External Relations
Yes
Allison Craddock
Director, Bureau of Networks & Observations
Yes
Mike Pearlman
Director, Bureau of Products & Standards
Yes
Detlef Angermann
Representative, GGOS Affiliates
Yes
Toshi Otsubo
Representative, IAG President
Yes
Richard Gross(2015–2017)
Zuheir Altamimi (2017–2019)
Representative, IAG Services
Yes
Riccardo Barzaghi
Representative, IAG Services
Yes
Ruth Neilan
Representative, IAG Services
Yes
Christoph Foerste
Representative, IAG Services
Yes
Urs Marti
Representative, IAG Commissions and ICCT
Yes
Pavel Novák
Representative, IAG Commissions and ICCT
Yes
Roland Pail
Member-at-Large
Yes
Ludwig Combrinck
Member-at-Large
Yes
Luiz Paulo Fortes
Member-at-Large
YesGary Johnston
Chair, Standing Committee on Satellite andNo
Roland PailSpace Missions
Chair, Standing Committee on Data andNo
Allison Craddock (2015–2016)
Information Systems
Günter Stangl(2016–2017)
Matthias Madzak (2017–2018)
Helmut Titz
(2018–2019)
Chair, Standing Committee on Contribution to
No
Maik Thomas
Earth System Modelling
Chair, GGOS Committee/IAG WG on PLATO
No
Daniela Thaller
Chair, JWG on Establishment of the GGRF
No
Urs Marti
Chair, WG on ITRS Standards
No
Claude Boucher
Lead, Focus Area on Unified Height System
No
Laura Sanchez
Lead, Focus Area on Geohazards
NoJohn LaBrecqueLead, Focus Area on Sea Level
No
Tilo Schöne(2015–2018)
Lead, Focus Area on Geodetic Space Weather
No
Michael Schmidt
Research
Manager, GGOS Web and Social Media
No
Allison Craddock (2015–2016)
Günter Stangl(2016–2017)
Matthias Madzak (2017–2018)
Helmut Titz
(2018–2019)
Immediate Past Chair of GGOS
No
Markus Rothacher (2015–2017)
Hansjörg Kutterer (2017–2019)
Representative, GIAC/GIC*No
Per Erik Opseth (2015–2016)* Please note that GIAC was terminated at the end of 2016, so all references to GIAC or GIC
are purely for historical purposes.

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Executive Committee
The Executive Committee of the GGOS Coordinating Board serves at the direction of theCoordinating Board to accomplish the day-to-day activities of the tasks of GGOS. The members
and guest observers of the Executive Committee during 2015–2019 are given in Table 3.
The Chair of GGOS is the Chair of the Executive Committee. The Executive Committee holds
monthly conference calls and meets face-to-face during the meetings of the Coordinating Board(see above).
Table 3. Members of the GGOS Executive Committee During 2015–2019
Position
Status Name
Chair
Member Hansjörg Kutterer (2015–2017)
Richard Gross(2017–2019)
Vice Chair
Member Ruth Neilan
Director, Coordinating OfficeMember Allison Craddock (2015–2016)
Günter Stangl(2016–2017)
Matthias Madzak (2017–2018)
Helmut Titz
(2018–2019)
Manager, External Relations
Member Allison Craddock
Director, Bureau of Networks & Observations Member Mike Pearlman
Director, Bureau of Products & Standards
Member Detlef Angermann
Representative, IAG Services
Member Riccardo Barzaghi
Representative, IAG Commissions
Member Pavel Novák
Immediate Past Chair of GGOS
Guest Markus Rothacher (2015–2017)
Hansjörg Kutterer (2017–2019)
Chair, Science Panel
Guest Richard Gross(2015–2017)
Kosuke Heki(2017–2019)
Representative, IAG President
Guest Richard Gross(2015–2017)
Zuheir Altamimi (2017–2019)
Representative, GIAC/GIC*
Guest Per Erik Opseth (2015–2016)* Please note that GIAC was terminated at the end of 2016, so all references to GIAC or GIC
are purely for historical purposes.

Global Geodetic Observing System (GGOS)

7GGOS Coordinating OfficeDirector:
Manager of External Relations:

Helmut Titz (Austria)
Allison Craddock (USA)Members:

Martin Sehnal (Austria)

Purpose and Scope
The GGOS Coordinating Office (CO) serves as a centralized administrative and organisational
entity and interacts with the GGOS Bureaus and Focus Areas for organisational matters. The
CO performs the day-to-day activities and generates reports in support of the various
components of GGOS especially the GGOS Executive Committee and the GGOS Coordinating
Board. The CO ensures information flow, maintains and archives documentation and in its longterm coordination role ensures consistency and continuity in the contributions of the GGOS
components. The CO implements and operates the GGOS website and outreach.
The Manager of External Relations connects GGOS with external organisations.
The Director of the CO and the Manager of External Relations are both ex-officio members of
the GGOS Coordinating Board and GGOS Executive Committee.
History
The GGOS Coordinating Office has been transitioned twice in the period of 2015 – 2019 andthere have been 5 directors of the CO.






Until 04/2015:05/2015 – 04/2016:05/2016 – 08/2017:09/2017 – 11/2018:12/2018 onwards:

Giuseppe Bianco (ASI, Italy)
Allison Craddock (BKG, Germany)
Günter Stangl (BEV, Austria)
Matthias Madzak (BEV, Austria)
Helmut Titz (BEV, Austria)
ASI: Agenzia Spaziale Italiana
BKG: Bundesamt für Kartographie und Geodäsie
BEV: Bundesamt für Eich- und Vermessungswesen

The position of the GGOS Manager of External Relations was officially approved at the Vienna
GGOS Days in October 2017. Allison Craddock of the NASA Jet Propulsion Laboratory waselected to serve as the Manager of External Relations in January 2018.
Activities and Actions
Day-to-day activities and organisational matters






Communicate with all entities of GGOS by sending and answering on emails
Organizing GGOS Executive Committee Teleconferences
Creating posters, brochures, logos, images and templatesCollecting/Distributing reports
Meeting preparation

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GGOS website / GGOS.ORG Domain-Transfer
In September 2016 the BEV installed a server system for the implementation and operation of
the new GGOS website. In Mai 2017 the official GGOS website www.ggos.org was shiftedfrom ASI to BEV. Nevertheless it took another 2 years to finally complete the transfer of theggos.org domain successfully to the BEV in February 2019. The new GGOS website was built
from scratch while maintaining key items and historical resources. The webpages aremaintained decentral by the different GGOS components using the DJANGO content
management system. The CO is responsible for assigning usernames and access permissions
for specific pages to the responsible persons and helps to set up the webpages and subpages.
Links to the IAG Services, to metadata, datacentres and products have been established.
GGOS cloud server
An online cloud storage on the GGOS server has been installed and set operational on
September 2017 temporary using the ggosdays.com domain name, as the official ggos.org
domain was not accessible at that time. This cloud storage is based on the OwnCloud software.
It is used for external (public) file distribution as well as internal file sharing. 28 personal user
logins and 6 groups have been created and activated. Nevertheless the cloud storage has beenrarely used.
Online Meetings Calendar
A Google Calendar was created to be able to view a timeline of the major internal and external
meetings that may be interesting for GGOS. The calendar can be viewed on the GGOS website
or be imported to other applications using iCal.
GGOS social media presence via Twitter
A GGOS Twitter account named @IAG_GGOS was created to be present in the social media
and to speed up dissemination of GGOS-related information to the customers.
Online-Voting Tool
In order to use online voting possibilities more professionally, an account on
surveymonkey.com was created and several GGOS internal elections were already performed
online.
Conference attendance






European Geosciences Union (EGU) (2015, 2016, 2017, 2018, 2019)
American Geophysical Union (AGU) (2016, 2017)
GGOS Days (2016, 2017, 2018)
International Association for Geodesy (IAG/IASPEI) (2017)
Group on Earth Observations (GEO) (2016, 2017)

Global Geodetic Observing System (GGOS)

9GGOS External Relations
The position of GGOS Manager of External Relations was officially approved at the Vienna
GGOS Days in October 2017.
Group on Earth Observations (GEO)GGOS represents the IAG in the Group on Earth
Observations (GEO), contributing to the GEO
Foundational Task GEOSS In-Situ Earth Observation
Resources. This task conducted a survey of existing in-situ Earth observing systems as a firststep towards identifying gaps in the available observations. Gross participated in this survey bydescribing IAG’s geodetic observing networks. In addition, IAG/GGOS has been selected to bea member of the GEO Programme Board during 2018-2020, with Gross being the Principal
Representative and Craddock as Alternate Representative of IAG/GGOS to the Programme
Board. IAG/GGOS is now one of 32 members of the Programme Board for the next 3 years andwill have a voice in steering the activities of GEO.
Within the Programme Board, Gross has participated on behalf of IAG/GGOS in the Subgroupon Sustainable Earth Observations, which works in tandem with the GEOSS In-Situ Earth
Observation Resources foundational task to assess the current Foundational Tasks focusing on
both GEOSS Satellite and In-Situ Earth Observation Resources, and to evaluate strengths andweaknesses of observing systems for GEO’s activities over the past decade, and to clarify thechallenges in coordination of in-situ observations as well as in integrating in-situ and satellite
observations toward coordinated observation systems in the future to implement GEOSS.
Also under the auspices of the Programme Board, Craddock has participated on behalf of
IAG/GGOS in the Subgroup on the Sendai Framework. This subgroup supports GEO’s
strategic engagement priority area on the Sendai Framework for Disaster Risk Reduction, in
the realm of championing and supporting the development of policy objectives that add value,
drive efficiencies, and promote the uptake of Earth observations in alignment with Sendai andother disaster risk reduction initiatives. This is particularly relevant to supporting the GGOS
Geohazards Focus Area and its Global Navigation Satellite System to Enhance Tsunami
Early Warning Systems (GTEWS).
GGOS also participates in the GEO Communicators Network, which was established in
November 2017 as a means to connect communications professionals supporting earth
observations, open data, and other initiatives such as UN SDGs. As a collaborative function of
the Coordinating Office Director and Manager of External Relations, GGOS social media hasinteracted with GEO and other stakeholders through twitter posting, “liking” and re-posting.
Through the GEO Communicators Network, GGOS supports relevant messages on social
media with the GEO-led or supported hashtag campaigns
Participation at the Programme Board level ensures that IAG/GGOS efforts in alignment with
GEO’s global priorities (supporting the UN SDGs, Sendai Framework, as well as the Paris
Agreement on Climate Change) are well supported and complimentary to other related work –as well as preventing unnecessary redundancy of work. Geodetic observations have a clear rolein helping to reduce the risk of disasters, as well as contribute to disaster preparedness with
better mitigation and response. Earth observations also play a major role in monitoring progress
toward, and achieving, the SDGs.

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Committee on Earth Observation Satellites (CEOS)GGOS has participated in CEOS Plenaries, discussing what
GGOS might need from participation in CEOS as an
Agency/Partner Update. This is an opportunity for GGOS tospeak about its plans and strategies in relation to CEOS, as well as the benefits and expectationsof CEOS from the GGOS perspective.
GGOS has renewed its engagement with CEOS by appointing the Manager of External
Relations as the GGOS representative to their Ad Hoc Team on the Sustainable Development
Goals (AHT SDG), which highlights the potential role for Earth observations in supporting the
global indicator framework of the United Nations Sustainable Development Goals. AHT SDG
works closely with GEO (through the collaborative EO4SDG campaign) to highlight thenumerous applications of Earth observations that provide data critical to monitoring progress
toward the SDGs, and thereby further illustrate the immediate and secondary values of Earthobservation data.

UN GGIM Subcommittee on Geodesy
GGOS supports and, as needed, represents the IAG at the United Nations Committee of Experts
on Global Geospatial Information Management (UN GGIM). Harald Schuh, Mike Pearlman
represented the IAG at the most recent session of the GGIM in New York (August 2018), andthe meetings of the Sub-Committee on Geodesy (SCoG), to provide stability and long-termplanning for the GGRF. As the work of the Subcommittee transitions from ideological to
implementation-based, especially in the realm of member states making commitments forinfrastructure or other contributions, IAG/GGOS participation within both the member state
Delegations as well as IAG observers will be important to ensure best possible support of thisinitiative.
For more information, please visit the UN-GGIM website:
http://ggim.un.org/UN_GGIM_wg1.html.
Numerous GGOS Consortium members were active in the UN GGIM SCoG on behalf of the
IAG this past year: Harald Schuh, IAG; SCoG Working Group on Governance Detlef Angermann, IAG; SCoG Working Group on Policy, Standards, and Conventions
GGOS Consortium members also participate on behalf of their member state (country) and in
consultation with GGOS External Relations, including: Richard Gross, USA; SCoG Working Group on Governance Allison Craddock, USA; SCoG working Group on Communications and Outreach,
Working Group on Education, Training and Capacity Building Gary Johnston, Australia; SCoG Co-chairGlobal Geodetic Observing System (GGOS)

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Pilot External Relations Project: Connecting GGOS with the United Nations Sustainable
Development Goals and Sendai Framework for Disaster Risk Reduction
There is tremendous potential to increase the exposure andimpact of GGOS by identifying potential contributions andconnecting existing relevant work to efforts in support of both
UN SDGs and the Sendai Framework. GGOS has the potential
to facilitate linkages to agencies and other providers of geodetic
data, make existing geodetic data discoverable and easily
accessible, and to work toward standardization.
Connecting United Nations Initiatives with the GGOS Geohazards Focus Area throughthe GAR19 Report
The first External Relations Project, proposed in October 2017, sought to support the wide reachof the GATEW initiative by identifying numerous clear alignments with United Nations
Sustainable Development Goals (SDGs) and Sendai Framework for Disaster Risk Reduction.
The Manager of External Relations has worked with John LaBrecque, Lead of the Geohazards
Monitoring Focus Area, to brainstorm strategies for aligning our work in natural hazards with
the United Nations SDGs and Sendai Framework. These two prominent initiatives can clearly
benefit from the focus group's involvement, will make GGOS more visible to organizations
such as GEO, CEOS, and the UN, and could potentially lead to greater participation in
GATEW/GTEWS and other GGOS efforts.
GATEW/GTEWS successfully submitted a chapter/paper for the 2019 UN Global Assessment
Report on Disaster Risk Reduction (GAR19), which is a major UN report addressing disasterrisk reduction that contributes to regional and global platforms for disaster risk reduction, as
well as the high-level political forum on sustainable development.
The [2019] GAR will provide: a) an update on global progress made in implementing theoutcome, goal, targets and priorities of the Sendai Framework and disaster-related
Sustainable Development Goals (SDGs), b) current and future risk trends introducing
systemic risk perspectives as represented in the forthcoming Global Risk Assessment
Framework (GRAF), c) cutting edge, innovative research and practice in disaster risk
management and good practice on how to manage and reduce disaster risks, and d) an
introduction to the wider scope and systemic nature of hazards to be considered in
implementing the Sendai Framework.
Developed through an extensive set of partnerships with international organizations,
governments, businesses, academic and research institutions, the GAR is both an ongoingprocess of evidence generation and policy engagement, and a product – in the form of abiennial report published by the UNISDR. The process contributes directly to greater accessto risk information for decision-making, and identifies feasible practices that can be
employed at the local, national, regional and international levels.
The complete GAR19, published in May of 2019, is available to download here:
https://gar.unisdr.org/sites/default/files/reports/2019-05/full_gar_report.pdf
Future Connections
As GGOS connections with the SDGs and Sendai Framework mature, more opportunities tosupport these initiatives will become available. GGOS External Relations will pursue the most
relevant and impactful avenues to ensure that IAG/GGOS enables the greatest use of geodetic
data in support of these United Nations initiatives and beyond.

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GGOS Affiliate
GGOS Japan
Chair:
Secretary:

Toshimichi Otsubo (Japan)
Basara Miyahara (Japan)

Background
The GGOS Working Group of Japan was established in 2013 under IAG Subcommittee of
Science Council of Japan to strengthen the collaboration among space geodesy agencies inJapan and to get connected to international organizations. It was approved to become the first“GGOS Affiliate” in 2017 and renamed as “GGOS Japan” in 2019.
Activities 2015-2019
GGOS Japan has proposed or been involved in a number of science sessions on global geodesy
in domestic meetings (Meetings of Geodetic Society of Japan, JpGU) and international
meetings (IAG, AGU, IUGG etc). It regularly hosted its own meetings in Japan. In addition,
here is the list of what it has achieved in the 2015-2019 period.
2014-2016: GSI’s VLBI station modernization and relocation from Tsukuba to Ishioka.
May 2016: New Chair: T Otsubo (was S Matsuzaka), Secretary: B Miyahara (was T Otsubo).
August 2017: Updated the GGOS station list (7 stations of 6 institutes) of Japan whose firstversion was submitted in 2014.
October 2017: Became the first GGOS Affiliate. T Otsubo appointed as GGOS CB Member
and B Miyahara as Consortium Member.
March-April 2018: Published the GGOS special issue in Journal of the Geodetic Society ofJapan (written in Japanese); 14 papers in Issues 2 and 3, Volume 63.
May-July 2018: Issued and printed its leaflet.
June 2018: K Heki appointed as Science Panel Chair of GGOS.
October 2018: Cohosted GGOS Days 2018.
Summer-Autumn 2019 (planned): Set up its website under ggos.org.
May 2020 (planned): Propose a GGOS-related session in JpGU+AGU joint meeting.
Publications and presentations
Matsuzaka S (2015), GGOS and contributing efforts in Japan, JpGU 2015, 2015-5-28.
Pearlman MR, Schuh H, Angermann D, Noll CE (2017), The Global Geodetic Observing System (GGOS) - itsRole and its Activities, JpGU-AGU Joint Meeting 2017, 2017-5-24.
Gross RS (2017), The Contribution of Global Geodetic Observations to Understanding Dynamic Earth Processes,
JpGU-AGU Joint Meeting 2017, 2017-5-24.
Otsubo T, Yokota Y, Pearlman MR, Noll CE, Bianco G (2017), International and Japanese Activities of Satellite
Laser Ranging for Global Geodesy, JpGU-AGU Joint Meeting 2017, 2017-5-24.
Fukuda Y, Odera P (2017), GGOS and the Gravity Field Studies, JpGU-AGU Joint Meeting 2017, 2017-5-24.
Otsubo T, Miyahara B, Kawabata R, Aoyama Y, Fukuda Y, Yokota Y, Yamao H, Matsuzaka S (2017), Space
Geodetic Activities and GGOS Working Group in Japan, Joint Assembly of IAG-IASPEI 2017, 2017-8-3.
Miyahara B, Otsubo T (2018), Activities of GGOS Working Group Japan for the past five years, JpGU 2018, 20185-23.
Gross RS (2018), The Global Geodetic Observing System: Recent Activities, JpGU 2018, 2018-5-23.
Matsuzaka S (2018), Overview of GGOS and its Impact on Geodesy in Japan, J Geod Soc Japan, 63, 2, 61-64,
DOI 10.11366/sokuchi.63.61, in Japanese.

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Miyahara B (2018), Global Geodetic Reference Frame and the United Nations General Assembly Resolution, J
Geod Soc Japan, 63, 2, 65-68, DOI 10.11366/sokuchi.63.65, in Japanese.
Kawabata R (2018), Contribution of VLBI to GGOS, J Geod Soc Japan, 63, 2, 69-74, DOI 10.11366/
sokuchi.63.69, in Japanese.
Otsubo T, Yokota Y (2018), Satellite Laser Ranging as one of Global Geodetic Techniques: Current Status andFuture Prospective, J Geod Soc Japan, 63, 2, 75-79, DOI 10.11366/sokuchi.63.75, in Japanese.
Kawamoto S (2018), Contribution of GNSS to GGOS and Its Future Perspective, J Geod Soc Japan, 63, 2, 81-94,
DOI 10.11366/sokuchi.63.81, in Japanese.
Fukuda Y (2018), GGOS and the Gravity Field Studies, J Geod Soc Japan, 63, 2, 95-101, DOI 10.11366/
sokuchi.63.95, in Japanese.
Ishimoto M, Kawabata R, Miyahara B, Wakasugi T, Toyoda T, Umei M (2018), Construction of Ishioka Geodetic
Observing Station for GGOS, J Geod Soc Japan, 63, 2, 103-109, DOI 10.11366/sokuchi.63.103, in Japanese.
Yokota Y, Sato M, Fukura H, Fujita M, Sengoku A (2018), SLR Observation at the Shimosato Hydrographic
Observatory, J Geod Soc Japan, 63, 2, 111-116, DOI 10.11366/sokuchi.63.111, in Japanese.
Tamura Y, Sato T, Jike T (2018), Gravity Tide Observations at VERA Stations, J Geod Soc Japan, 63, 3, 139-156,
DOI 10.11366/sokuchi.63.139, in Japanese.
Sekido M, et al (2018), Development of Broadband VLBI System and Report of Experiments for Geodesy and
Frequency Comparison, J Geod Soc Japan, 63, 3, 157-169, DOI 10.11366/sokuchi.63.157, in Japanese.
Miyazaki T (2018), Development of Estimation method for Post Seismic Deformation Model Using Monte-Carlo
Method, J Geod Soc Japan, 63, 3, 171-185, DOI 10.11366/sokuchi.63.171, in Japanese.
Mochizuki K, Nawa K, Suzuyama T (2018), On-site Frequency Measurements of a Rubidium Oscillator for
Gravimeters, J Geod Soc Japan, 63, 3, 187-191, DOI 10.11366/sokuchi.63.187, in Japanese.
Jike T, Manabe S, Tamura Y (2018), Adoption of K-band in the VERA Internal Geodetic VLBI and its
Effectiveness, J Geod Soc Japan, 63, 3, 193-209, DOI 10.11366/sokuchi.63.193, in Japanese.
Aoyama Y, Doi K, Shibuya K (2018), Contribution of Geodetic Observations at Syowa Station, Antarctica to
GGOS, J Geod Soc Japan, 63, 3, 211-217, DOI 10.11366/sokuchi.63.211, in Japanese.
Otsubo T, Müller H, Pavlis EC, Torrence MH, Thaller D, Glotov VD, Wang X, Sośnica K, Meyer U, Wilkinson
MJ (2018), Rapid response quality control service for the laser ranging tracking network, Journal of Geodesy,
DOI 10.1007/s00190-018-1197-0.
Hattori A, Otsubo T (2019), Time-varying solar radiation pressure on Ajisai in comparison with LAGEOS
satellites, Advances in Space Research, 63, 1, 63-72, DOI 10.1016/j.asr.2018.08.010.
Otsubo T (2019), Current status and problems of geodetic observation data distribution, JpGU 2019, 2019-5-26.
Miyahara B (2019), Activities and future perspective of GGOS Working Group Japan, JpGU 2019, 2019-5-27.
Otsubo T, Miyahara B, Wakasugi T, Aoyama Y, Yokota Y, Miyazaki T, Fukuda Y (2019), Space Geodetic Activities
Organized by GGOS Working Group of Japan, IUGG 2019 Montreal, 2019-7.

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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GGOS Science Panel
Chair: Kosuke Heki (Japan)
Members: M. Rothacher (Switzerland) G. Blewitt (USA) T. Gruber (Germany) J. Chen (USA) J. Ferrandiz (Spain)
 J. Wickert (Germany) P. Wielgosz (Poland) Y. Tanaka (Japan)
 M. Crespi (Italy) B. Heck (Germany) D. Melgar (USA) D. Chambers (USA) E. Forootan (UK/Germany)

Purpose and Scope
The GGOS Science Panel is a multi-disciplinary group of experts representing the geodetic andrelevant geophysical communities that provides scientific advice to GGOS in order to help
focus and prioritize its scientific goals. The Chair of the Science Panel is a member of theCoordinating Board and a permanent guest at meetings of the Executive Committee. This closeworking relationship between the Science Panel and the governance entities of GGOS ensuresthat the scientific expertise and advice required by GGOS is readily available.
Activities and Actions
The Science Panel provides scientific support to GGOS. During the 2015-2019 quadrennium
this support included participation in Consortium, Coordinating Board, and Executive
Committee meetings and conference calls.
The Science Panel has been actively promoting the goals of GGOS by helping to organize
GGOS sessions at major scientific conferences. During the 2015-2019 quadrennium, GGOS
sessions have been organized at:
•
•
•
•
•
•
•
•
•

2015 American Geophysical Union Fall Meeting in San Francisco
2016 American Geophysical Union Fall Meeting in San Francisco
2017 American Geophysical Union Fall Meeting in New Orleans
2018 American Geophysical Union Fall Meeting in Washington DC2015 Asia Oceania Geosciences Society Annual Meeting in Singapore
2016 European Geosciences Union General Assembly in Vienna
2017 European Geosciences Union General Assembly in Vienna
2018 European Geosciences Union General Assembly in Vienna
2019 European Geosciences Union General Assembly in Vienna

Global Geodetic Observing System (GGOS)

•
•
•

15

2017 Japan Geophysical Union – American Geophysical Union Joint Meeting in Chiba,Japan2018 Japan Geoscience Union Meeting in Chiba, Japan2017 International Association of Geodesy – International Association of Seismology andPhysics of the Earth’s Interior Joint Scientific Assembly in Kobe, Japan

In addition to helping organize sessions at scientific conferences, the GGOS Science Panel alsoorganizes topical science workshops in order to foster discussion about the geodetic
observations and infrastructure required by different scientific disciplines. One such workshop
was organized during 2015-2019 as the IAU/IAG/IERS Joint Symposium on Geodesy,
Astronomy, & Geophysics in Earth Rotation held in Wuhan, China during 18-23 July 2016.:
International Symposium on Geodesy, Astronomy, and Geophysics in Earth Rotation(GAGER2016), Wuhan, China; 19-23 July 2016
The rotation of the Earth varies continuously, in both its rate of rotation and in the orientationof its axis with respect to either crust-fixed or space-fixed reference frames. Its study links
together the fields of Geodesy, Astronomy and Geophysics. In this Symposium, over 50
participants from Asia, Europe, and the Americas met in Wuhan, China to assess our current
ability to observe the Earth’s time varying rotation, to assess our current understanding of
the causes of the observed variations, to assess the consistency of Earth rotation observations
with global gravity and shape observations, to explore methods of combining Earth rotation,
gravity, and shape observations, and to identify improvements in the global geodetic
observing system needed to further our understanding of the Earth’s variable rotation. Peerreviewed proceedings of the Symposium will be published as a special issue of Geodesy andGeodynamics.
Unified Analysis Workshops are co-organized by the International Association of Geodesy’s
Global Geodetic Observing System (GGOS) and International Earth Rotation and Reference
Systems Service (IERS). The 2017 Workshop was the 5th in a series of workshops that are held
every two years for the purpose of discussing issues that are common to all the space-geodetic
measurement techniques. Attendance at the Workshops are by invitation only with each IAG
Service nominating 5-6 experts to attend and participate in the discussion.
Unified Analysis Workshop, Paris, France; 10-12 July 2017
At the 2017 Workshop the discussion focused on (1) Systematic errors and biases in GNSS
observations, (2) Systematic errors and biases in VLBI observations, (3) Systematic errors
and biases in SLR observations, (4) Systematic errors and biases in DORIS observations,(5) Site survey and co-location, (6) Reference systems and frames, (7) Conventional meanpole, (8) Standards, conventions, and formats, and (9) Interoperability of portals andmetadata.

Objectives and Planned Efforts for 2019-2023 and Beyond
During the next quadrennium the Science Panel will continue to participate in Consortium,
Coordinating Board, and Executive Committee meetings and conference calls. In addition, the
Science Panel will continue to help organize GGOS sessions at conferences and symposia
including:Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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American Geophysical Union Fall Meetings
Asia Oceania Geosciences Society Annual Meetings
European Geosciences Union General Assemblies
International Association of Geodesy General and Scientific Assemblies

A GGOS session is also planned in the 2020 JPGU-AGU joint meeting in Chiba, Japan, as we
did in 2017. The next Unified Analysis Workshop will be held in Paris, France during 02-04
October, 2019 (also planned in 2021, detail to be determined).
The Science Panel will also continue to organize topical science workshops in order todetermine the requirements that different scientific disciplines have for geodetic data andproducts.
With the GGOS Bureau of Products and Standards, the Science Panel will help conduct a Gap
Analysis to identify the gap between the data and products provided by the IAG and the needsof the user community. As part of this analysis, a list of Essential Geodetic Variables (EGVs)
will be compiled along with observational requirements on those variables. This list of EGVs
and their observational requirements can then be used to determine requirements on derived
products like the terrestrial reference frame. The Science Panel convened sessions on EGV in
the 2018 AGU Fall Meeting and the 2019 EGU General Assembly. Activities related to EGV
will continue in the newly established committee on EGV, which includes the whole Science
Panel members.

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GGOS Bureau of Networks and Observations
Prepared by Michael Pearlman, Carey Noll, Erricos C. Pavlis, Frank Lemoine, Daniela Thaller,
Guenter Stangl, Jürgen Müller, Benjamin Männel, and Sten Bergstrand
MembershipStanding Committees affiliated with this Bureau:
 GGOS Standing Committee on Satellite Missions
 GGOS Standing Committee on Data and Information Systems
 GGOS Standing Committee on Performance Simulations and Architectural Trade-Offs(PLATO) IERS Working Group on Survey and Co-location
Associated Members and Representatives:
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Director (Mike Pearlman/CfA USA)
Secretary (Carey Noll/NASA USA)
Analysis Specialist (Erricos Pavlis/UMBC USA)
IERS Representative (Sten Bergstrand/BIPM France)
Representatives from each of the member Services:o IGS (Allison Craddock/JPL USA, Gary Johnston/GA/Australia)
o ILRS (Toshi Otsubo/Hitotsubashi U. Japan, Wu Bin/SHAO China)
o IDS (Jérôme Saunier/IGN France, Pascale Ferrage/CNES France)o IVS (Hayo Hase/BKG Germany, Dirk Behrend/NASA USA)o IGFS (Riccardo Barzaghi/PM Italy, George Vergos/UT Greece)o PSMSL (Lesley Rickards/BODC UK, Tilo Schone/GFZ Germany)
Representatives from each of the member Standing Committees:o PLATO (Daniela Thaller/BKG Germany, Benjamin Maennel/GFZ Germany)o Data and Information Systems (Guenter Stangl, Matthias Madzak/BEV Austria,
Carey Noll/NASA USA)o Satellite Missions (Jürgen Müller/IfE Germany, Roland Pail/TUM Germany)o IERS Working Group on Survey Ties and Co-location (Sten Bergstrand/BIPM
France)Activities, Actions, and Publications during 2015-2019
Activities
The Bureau:•

Continued to provide a forum for the Services and Standing Committees/Working
Groups to share and discuss plans, progress, and issues, and to develop and monitor
multi-entity efforts to address GGOS requirements; meetings are held in conjunction
with AGU and EGU each year; material from the meetings are posted on the GGOS
website.

•Continued the Bureau’s “Call for Participation in the Global Geodetic Core Network:
Foundation for Monitoring the Earth System” and work with new potential groupsinterested in participating; a total of 19 submissions have been received covering 114
sites that included legacy core sites, legacy/new technology co-location sites, core andco-location sites under development, and sites offered for future participation; asummary of the CfP responses is available on the Bureau’s website. A number of othernew stations will join once they are operational.

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-201918

Several new stations have joined or are in the process of joining the network during thisperiod. Correspondence has been underway with ROSCOSMOS regarding their formal
joining in the network, but their stations have been regular participants. Certificates ofparticipation have been sent out to network sites.
•

Continued to advocate for new and increased network participation, encouraging
formation of new partnerships to develop new sites, monitored the status of the
networks; held meetings and communications with representatives from Russia, Italy,
Brazil, Japan, Spain, France, and Saudi Arabia to discuss implementation of new
stations and upgrade of legacy stations.
The BN&O has been advocating for enhanced network infrastructure for Latin America;
participated in the UNGGIM Meeting on the Americas at the UN in August 2018; plansto participate in the SIRGAS meeting in Rio de Janeiro in November.

•

Supported efforts for the integration of various ground observation networks within the
GGOS affiliated Network; continued to maintain and update the “Site Requirements for
GGOS Core Sites” document (with the IAG Services); the next major step will be toinclude the requirements for the gravity field once it is fully documented by the IGFS
and the IGRF working group; work with the IGFS in the definition of its requirements.

•

Continued to promote and advocate for GGOS and the GGOS integrated global geodetic
ground-based infrastructure through talks and posters at AGU, EGU, AOGS, APSG
(China), JpGU-AGU, IAG, etc. and meetings and special presentations at GSI (Japan),
IMPE (Brazil), IAP (Russia), etc.; supported efforts to integrate relevant parametersfrom other ground networks (gravity field, tide gauges, etc.) into the GGOS network to
support GGOS requirements.

•

Continued to maintain and update the inventory/repository of current and near-futuresatellite missions, highlighting those of most interest to GGOS; continued advocating
for new advocating new missions; wrote letters of support for the EGRASP/Eratosthenes proposals; need to stress greater cooperation between the PLATO
and Missions Standing Committees. More details are provided in the Missions Standing
Committee section below .

•Provided simulations and analyses to estimate how the data products will improve overtime as the infrastructure improves. The results from the periodic network surveys will
be used to project network data quality capability 5 and 10 years ahead. Simulations on
the e-GRASP/Eratosthenes mission and other co-location missions to strengthen thecase for support and for network planning. More detail is provided in the Standing
Committee on Performance Simulations & Architectural Trade‐Offs (PLATO) section
below.

•

Continued development and implementation of a GGOS metadata system in two stages:
a stage-one scheme (hosted by CDDIS) for GGOS and GGOS-relevant data and a longer
term, stage-two implementation, for the full GGOS requirements including site andinstrument information, based on an XML metadata scheme under development by the
Geoscience Australia, UNAVCO, and the IAG. Additional details are provided in the
Data and Information Standing Committee section below.

•

Continued working on the establishment of a common terminology for all space geodesy
techniques, a terminology which is also valid outside the space geodetic community;
the DORIS community has adapted a common terminology, and improved its surveying
procedures as well as communication of the results. The IGS terminology has done thesame, but there are differences among the techniques; continued working on outreachto increase local survey participation and standardization. More details are provided inGlobal Geodetic Observing System (GGOS)

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the IERS Working Group on Survey Ties and Co-Location (see IERS Section of theTravaux Report).
Related Bureau Documentation:
As part of the network activity, the Bureau has facilitated the creation of several key documents;
these documents will be made available on the GGOS website in the near future.
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“GGOS Site Requirements for Fundamental Stations” document.
A guidelines document for site characterization of the GGOS network sites was developed,“The Global Geodetic Core Network: Foundation for Monitoring the Earth System”.
A plan to define the process by which GGOS determines the extent of the needed
infrastructure, including the scope and specification of the network, conditioned on theexisting or plausible technology available, “GGOS Infrastructure Implementation Plan”.
A plan to assess the current and future plans for a GGOS core network, including
projections five to ten years in the future, “Space Geodesy Network Model”.
Documents developed within the context of NASA’s Space Geodesy Project, evaluating
several sites as potential core sites; these documents are available from the SGP website
at:https://space-geodesy.nasa.gov/documentation/Project_Documentation.html
A summary report issued from the TLS (Terrestrial Laser Scanner) Workshop that washeld at NASA GSFC, September 08-10, 2008.

Websites: http://www.ggos.org/en/bureaus/bno/
Publications and Presentations
M. Pearlman, C. Ma, C. Noll, E. Pavlis, H. Schuh, T. Schoene, R. Barzaghi, S. Kenyon, “The GGOS Bureau of
Networks and Observations and an Update on the Space Geodesy Networks”, Abstract EGU2015-7420,
presented at EGU 2015 General Assembly, April 13-17, 2015, Vienna, Austria, April 12-17, 2015.
M. Pearlman, E. Pavlis, C. Ma, C. Noll, D. Thaller, B. Richter, R. Gross, R. Neilan, J. Mueller, R. Barzaghi, S.
Bergstrand, J. Saunier, M. Tamisiea, “Update on the Activities of the GGOS Bureau of Networks andObservations”, Abstract No. 10095. Presented at European Geosciences Union General Assembly, April 17-22, 2016.
C. Noll, “GGOS: Global Geodetic Observing System”, presented at 2016 WDS Members’ Forum, Denver,
Colorado, September 11, 2016.
G. Stangl, C. Noll, “GGOS: The Global Geodetic Observing System” (poster), presented at 2016 WDS Members’
Forum, Denver, Colorado, September 11, 2016.
M. Pearlman, C. Noll, C. Ma, E. Pavlis, R. Neilan, J. Saunier, T. Schoene, R. Barzaghi, D. Thaller, S. Bergstrand,
J. Mueller, “The GGOS Bureau of Networks & Observations: An Update on the Space Geodesy Network &the New Implementation Plan for 2017-2018”, Abstract No. EGU2017-10698, presented at European
Geosciences Union General Assembly 2017, Vienna, Austria, April 24-28, 2017.
M. Pearlman, H. Schuh, D. Angermann, C. Noll, “The Global Geodetic Observing System (GGOS) – Its Role and
Its Activities”. JpGU-AGU Joint Meeting, Chiba, Japan, May 22-26, 2017.
M. Pearlman, C. Ma, R. Neilan, C. Noll, E. Pavlis, J. Saunier, T. Shoene, R. Barzaghi, D. Thaller, S. Bergstrand,
J. Mueller, “The GGOS Bureau of Networks and Observations: Activities and Plans”. Presented at IAGIASPEI, Kobe, Japan, July 30-August 04, 2017.
Merkowitz, S.M., Bolotin, S., Elosegui, P. et al., Modernizing and expanding the NASA Space Geodesy Network
to meet future geodetic requirements, J Geod (2018), doi: https://doi.org/10.1007/s00190-018-1204-5
M. Pearlman, J. Gipson, G. Johnston, C. Noll, E. Pavlis, J. Saunier, A. Matthews, R. Barzaghi, D. Thaller, S.
Bergstrand, J. Müller, “GGOS: Bureau of Networks and Observations”, Abstract No. EGU2018-5504,
presented at the European Geosciences Union General Assembly, Vienna, Austria, April 08-13, 2018.
M. Pearlman, D. Behrend, A. Craddock, C. Noll, E. Pavlis, J. Saunier, A. Matthews, R. Barzaghi, D. Thaller, B.
Maennel, S. Bergstrand, J. Müller, “GGOS: Current Activities and Plans of the Bureau of Networks andObservations”, Abstract No. EGU2019-6181, presented at the European Geosciences Union General
Assembly, Vienna, Austria, April 07-12, 2019.

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GGOS Standing Committee on Performance Simulations & Architectural Trade‐
Offs (PLATO)(Joint WG with IAG Commission 1)
Chair: Daniela Thaller (Germany)
Vice-Chair: Benjamin Männel (Germany)
Contributing Institutions (as of April 2019):
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R. Dach, F. Andritsch (AIUB, Switzerland)
D. Thaller, D. König (BKG, Germany)
R. Biancale (CNES/IGN, France)
M. Bloßfeld A. Kehm (DGFI-TU Munich, Germany)
M. Rothacher, I. Herrera Pinzon (ETH Zürich, Switzerland)
B. Männel, S. Glaser (GFZ/TU Berlin, Germany)J. Müller, F. Hofmann (IfE University Hannover, Germany))
D. Coulot, A. Pollet (IGN, France)
R. Gross (JPL, USA)
E.C. Pavlis (NASA GSFC/JCET, USA)
E. Mysen, G. Hjelle (NMA, Norway)
J. Böhm (TU Vienna, Austria)

Purpose and Scope

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Develop optimal methods of deploying next generation stations, and estimate thedependence of reference frame products on ground station architectures
Estimate improvement in the reference frame products as co-located and core stations
are added to the network
Estimate the dependence of the reference frame products on the quality and number ofthe site ties and the space ties
Estimate the improvement in the reference frame products as other satellites are added,
e.g., cannonball satellites, LEO, GNSS constellations
Estimate the improvement in the reference frame products as co-locations in space areadded, e.g., use co-locations on GNSS and LEO satellites, add special co-location
satellites (GRASP, E-GRASP/Eratosthenes, NanoX, etc.)

Achievements over the past four years:
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Several projects related to simulation studies became funded and even extended to asecond phase, like DIGERATI at DGFI-TUM, SORTS at TU Vienna, GGOS-SIM at
GFZ, or KoKoRef at BKG
Several geodetic software packages have been augmented by the capability to carryout realistic simulation scenarios (VieVS, DOGS, Bernese, Geodyn)
Simulations for the planned E-GRASP/Eratosthenes which was a proposal for a
dedicated co-location in space satellite mission within ESA Earth-Explorer-9 call. The
proposal was submitted by a science team led by Richard Biancale (Biancale e al.,2017).
Simulations for improved global SLR and VLBI station networks were carried out(Glaser e., 2017, Kehm et al., 2018, Anderson et al., 2018, Glaser et al. 2019).
Simulations for improved SLR tracking of GNSS satellites were performed by AIUB
(Andritsch et al., 2018).

Global Geodetic Observing System (GGOS)

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Simulations and analysis of VLBI tracking data of GNSS satellites and the Chinese
APOD cube-satellite were carried out to assess the possibilities of VLBI satellite
tracking (Hellerschmied e al., 2018).
The impact of the local ties (LT) on the reference frame products were studied
regarding different stochastic models of the LT, selection of the LT, and the impact ofsystematically wrong LT (Glaser et al., 2019).
Local baselines were analyzed to identify technique-specific systematic error sources(Herrera Pinzón and Rothacher, 2018).
The combined processing ground- and space-based GNSS observations was studied(Männel and Rothacher, 2017).
Simulation for new laser ranging on the lunar surface were carried out by IfE, Uni
Hannover (Hofmann, 2017, Hofmann et al, 2018).
A PLATO status report was published in the International Symposium on Advancing
Geodesy in a Changing World (Männel et al., 2018).
Presentations were given at IAG Assembly (July 2017), COSPAR/REFAG (July
2018), annual conferences of EGU and AGU as well as meetings of IAG Services.

Outcomes and Future Plans
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A coordinated increase of ETALON observations should be further considered at theexpense of LAGEOS observations, and specific studies based on the dedicated
ETALON tracking campaigns by the ILRS will be carried out.
In addition to building new SLR stations, existing laser telescopes should be
encouraged and supported to increase their performance, if possible, to the proposedlevel of 20%.
In terms of LLR additional stations capable to perform measurements to (new) lunar
reflectors are highly important to achieve highest accuracy.
Improved analysis methods for reference frame products will be developed with thefocus of including all existing data (especially to satellites not yet included in standard
TRF products) and all available co-locations
Simulations performed by PLATO members showed impressively the benefits of a
dedicated co-location in space satellite mission. Therefore, we recommend to strive by
all means for a satellite mission dedicated to co-location in space.
A coordinated analysis campaign with exchanged simulated observations waslaunched in 2018 and is still ongoing
Status reports will be given at IUGG General Assembly (July 2019) and IAG
Symposia (2021)
Annual meetings are foreseen in conjunction with EGU General Assembly

Publications
Anderson, J.M., Beyerle, G., Glaser, S. et al., Simulations of VLBI observations of a geodetic satellite providing
co-location in space, J Geod (2018) 92: 1023. https://doi.org/10.1007/s00190-018-1115-5
Andritsch, F., Dach R, Schildknecht T, Meyer U, Jäggi A (2018): The effect of SLR tracking scenraios to GNSS
satellites in a combined GNSS/SLR solution. Presentation given at the 21st International Workshop on Laser
Ranging, November 5, 2018. Available online athttps://cddis.nasa.gov/lw21/docs/2018/presentations/Session2_Andritsch_presentation.pdf
Biancale R, Pollet A, Coulot D, Mandea M (2017) E-GRASP/ Eratosthenes: a mission proposal for millimetric
TRF realization. In: EGU general assembly, geophysical research abstracts, vol 19. EGU2017-8752
Glaser, S., König, R., Ampatzidis, D. et al., A Global Terrestrial Reference Frame from simulated VLBI and
SLR data in view of GGOS, J Geod (2017) 91: 723. https://doi.org/10.1007/s00190-017-1021-2
Glaser, S., König, R., Neumayer, K.H. et al., On the impact of local ties on the datum realization of global
terrestrial reference frames, J Geod (2019) 93: 655. https://doi.org/10.1007/s00190-018-1189-0

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Hellerschmied, A.; McCallum, L.; McCallum, J.; Sun, J.; Böhm, J.; Cao, J. Observing APOD with the AuScope
VLBI Array. Sensors 2018, 18, 1587.
Herrera Pinzón, I. & Rothacher, M., Assessment of local GNSS baselines at co-location sites, J Geod (2018) 92:
1079. https://doi.org/10.1007/s00190-017-1108-9
Hofmann, F. (2017): Lunar Laser Ranging - verbesserte Modellierung der Monddynamik und Schätzung
relativistischer Parameter. Ph.D. thesis, Leibniz Universität Hannover. Deutsche Geodätische Kommission
bei der Bayerischen Akademie der Wissenschaften, Reihe C, Nr. 797
Hofmann, F., Biskupek, L., Müller, J. (2018): Contributions to Reference Systems from Lunar Laser Ranging
using the IfE analysis model, J Geod (2018) 92: 975. https://doi.org/10.1007/s00190-018-1109-3
Kehm, A., Bloßfeld, M., Pavlis, E.C. et al., Future global SLR network evolution and its impact on the terrestrialreference frame, J Geod (2018) 92: 625. https://doi.org/10.1007/s00190-017-1083-1
Männel, B. & Rothacher, M., Geocenter variations derived from a combined processing of LEO- and groundbased GPS observations, J Geod (2017) 91: 933. https://doi.org/10.1007/s00190-017-0997-y
Männel B. et al. (2018) Recent Activities of the GGOS Standing Committee on Performance Simulations andArchitectural Trade-Offs (PLATO). In: Freymueller J., Sánchez L. (eds) International Symposium on
Advancing Geodesy in a Changing World. International Association of Geodesy Symposia, vol 149.
Springer, Cham. https://doi.org/10.1007/1345_2018_30
Pavlis, E. C., S. M. Merkowitz, C. J. Beaudoin, M. Kuzmicz-Cieslak, D. D. Rowlands, and F. G. Lemoine(2019) GEOCON: Geodetic System Ties Using a CubeSat Constellation, EGU General Assembly 2019,
Geophysical Research Abstracts, Vol. 21, EGU2019-6158-1

Global Geodetic Observing System (GGOS)

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GGOS Standing Committee on Satellite Missions (CSM)
Chair: Jürgen Müller (Germany)
Co-Chair: Roland Pail (Germany)
Members
CSM has quite an open team of members, associate members and guests to work on the various
CSM tasks and to provide material for the website, presentation material, and otherdocumentation. CSM has about one meeting per year. The main work, however, is done via
email exchange.
Purpose and Scope
The Committee on Satellite Missions (CSM) has been set-up as an international panel ofexperts, with consultants of national and international space agencies. CSM - formerly GGOS
Satellite Mission Working Group - was established in December 2008, under the lead of C.K.
Shum. In December 2010, Isabelle Panet became Chair, in December 2013 Roland Pailfollowed. Since December 2015, Jürgen Müller is the new Chair.
The purpose and scope of CSM is the information exchange with satellite missions as part of
the GGOS space infrastructure, for a better ground-based network response to mission
requirements and space-segment adequacy for the realization of the GGOS goals. New space
missions shall be advocated and supported, if appropriate.
Satellite missions are a prerequisite for realizing a global reference for any kind of Earthobservation. They are the key for monitoring change processes in the Earth system on a global
scale with high temporal and spatial resolution. Therefore, beyond purely scientific objectives
they meet a number of societal challenges, and they are an integral part of the GGOS
infrastructure and essential to realize the GGOS goals. The role of CSM is to monitor theavailability of satellite infrastructure, to propose and to advocate new missions or mission
concepts, especially in case that a gap in the infrastructure is identified.
Activities







An inventory/repository of the GGOS satellite infrastructure has been prepared.
A list of satellite contributions to fulfill the GGOS 2020 goals has been prepared.
Both lists have been published at the CSM section of the GGOS website.
In 2018 (as in the years before), individual members of CSM have contributed to ESA’s
Earth Explorer 10 call by actively acting in the proposers’ team of the planned future
gravity satellite mission MOBILE – which finally has not been selected.
Close cooperation exists with the Bureau of Products and Standards, and the SubCommissions 2.3 and 2.6 of IAG. Additionally, there are strong interfaces to national
and international space agencies.
Exchange with PLATO has been initiated by identifying joint interests and possible
collaborations.

Objectives and Planned Efforts for 2019 and Beyond
1. The new CSM website will continuously be updated collaborating with the GGOS
Coordinating Office.
2. The inventory/repository of current and near-future satellite missions will regularly be
updated.

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3. The list of satellite contributions to the GGOS 2020 goals will regularly be updated.
4. CSM will further support advocating new satellite missions.
5. The exchange with PLATO shall be expanded, e.g., to stimulate dedicated simulations
to better understand and overcome shortcomings with respect to the GGOS 2020 goals.
6. CSM will continue to support GGOS positions in preparation to CEOS/GEO
meetings.
7. CSM will further support the Executive Committee and the GGOS Science Panel in the
GGOS Interface with space agencies.
Most of the CSM tasks are ongoing activities. These tasks require interfacing with othercomponents of GGOS, especially with the ground networks component, the simulation activity(PLATO) as well as the Bureau of Products and Standards.
Website: http://www.ggos.org/en/bureaus/bno/committee-satellite-missions/Publications and Presentations
Pail, R.; IUGG, Writing Team: Observing Mass Transport to Understand Global Change and Benefit Society:
Science and User Needs, An international multi-disciplinary initiative for IUGG; in: Pail, R. (eds.) Deutsche
Geodätische Kommission der Bayerischen Akademie der Wissenschaften, Reihe B, Vol. 2015, Heft 320,
Verlag der Bayerischen Akademie der Wissenschaften in Kommission beim Verlag C.H. Beck.

Global Geodetic Observing System (GGOS)

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GGOS Standing Committee on Data and Information Systems
Chair: Guenter Stangl/Matthias Madzak (Austria)
Co-Chair: Carey Noll (USA)Purpose and Scope
Develop a metadata strategy for all ground-based measurement techniques and data productsthat provides discoverability and interoperability, is easily transferable via web services, and isbased on internationally recognized data exchange methods; the plan is to implement a metadata
scheme in two stages: a stage-one scheme for GGOS and GGOS relevant data products and alonger term, stage-two scheme for the full GGOS requirements.
The current focus of the WG is on developing standards for metadata that can be utilized by the
space geodesy community. Metadata typically encompass critical information about themeasurements that are required to turn these measurements into usable scientific data. Metadataalso includes information that supports data management and provides a foundation for data
discovery. Data centers extract metadata from incoming data sources and also augment that
metadata with information from other sources. It is typical for data centers to store the metadata
in databases in order to manage the data in their archives and to distribute both data andmetadata to data users. Metadata can further be utilized by data discovery applications to allow
users to find datasets of interest. In order to be effective, metadata need to be simple to generate
and maintain. They must be consistent and informative for the archivist and the user.
GGOS is seeking a metadata schema that can be used by all of its elements for standardized
metadata communication, archiving, and retrieval. First applications would be automateddistribution of up-to-date stations configuration and operational information, data archives andcatalogues, and procedures and central bureau communication. Several schemas that showpromise have been under development by SOPAC (Scripps), GML (Australia/NZ), etc. The
intent is that data need be entered only from an initial source (a station, a Data Center, an
Operations Center, data products, etc.) and would then flow to and be integrated into those
metadata files where users would have access. The plan is to organize a meeting, probably inearly August at UNAVCO in Boulder, for representatives from the Services, the Data Centers,
the Science Community, etc. to give each of the schema developers an opportunity to preachhis wears and allow discussion on the pros and cons of each.
The objective is to try to come to closure on a schema that we could as a community adopt for
general implementation. Groups would not be obligated to a rapid implementation schedule,
but would commit to the agreed schema when they are ready to begin the process.
Activities and Actions






CDDIS continues to construct collection-level metadata records for implementation inNASA EOSDIS (CMR)
Concepts and plans for implementation of a GGOS metadata scheme have beenpresented at Bureau meetings; status of the activities have also been presented
IGS continues development of Site Log XML metadata (lead: UNAVCO)o Several IGS data centers and groups have worked with this schema and are
implementing/refiningo Use Cases are slowly being assembledo Software tools for text site log to XML site log conversion are being developed andwill be available to all
Geosciences Australia (GA) has released GeodesyMLReport of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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o The GeodesyML project (http://www.geodesyml.org) has been created to facilitate
the discoverability and availability of geodetic data and metadata to new (andexisting) user communities in a standardized, discoverable, and interoperable way;o Machine-to-machine communications are required to improve efficiency,
robustness, and accuracy for sharing geodetic data and their metadata.
o Implements an application schema for the Site Log XML metadata;o Nick Brown (GA) has been funded to do a scoping study that will build upon
GeodesyML, SensorML, OGC and ISO and other international standards whenpossible to enabling machine-to-machine communication. International
participation in the scoping study is invited. Results from the study are due at theend of 2019. Although the study is being carried out for GNSS, the efforts will
benefit the IGS and GGOS.
Objectives and Planned Efforts for 2019 and Beyond

Adopt and implement a metadata system to provide access to GGOS relevant data
products.
GA and groups participating in the GeodesyML activity are creating a scoping study toinvestigate and document the critical gaps in standards which restrict how to makegeodetic data, in particular precise positioning data, accessible to user communities.
Some activities to be covered by the study:o Improve and expand data standards for accessing geodetic data and enabling their
combination with other data sets;o Review and document current standards and identify critical gaps in the proposed
standards;o Review community use cases and document how they can be met by GeodesyML
and international standards.
Adopt and implement a full metadata system including site information and relevant
tools and capability (e.g., the GeodesyML scheme)o Definition of the requirements; definition of Phase 1 (March 2020)o Resolve issues and applicability of the Australian GL scheme and recommend
schema (EGU 2020)o Metadata implementation plan including definition of tasks, roles, and distributionof tasks, and plans for integration of components (June 2020)o Demonstration of Phase 1 prototype (December 2020)o Demonstration of Phase 1 first operational system (December 2021)

Global Geodetic Observing System (GGOS)

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IERS Working Group on Site Survey and Co-location
Chair: Sten Bergstrand (France)
Co-Chair: John Dawson (Australia)
Members:
https://www.iers.org/IERS/EN/Organization/WorkingGroups/SiteSurvey/sitesurvey.html
Purpose and Scope
The working group was established in 2004 as part of the IERS to homogenize local surveying
activities at different space geodetic sites. In 2014, it was agreed that the working group would
act also for GGOS under the IERS name. The overall goal is to provide a base necessary for
rigorous terrestrial reference frame realizations, and to highlight the presence of techniqueand/or site-specific biases. The main effort aspires to provide the means of an uncertainty
assessment that can be included in the next ITRF.
Activities and Actions








Recent work has first been to establish a general and common terminology to alltechniques, which is also valid outside the space geodetic community, and to fulfill the
local tie requirements set out in the GGOS book. The DORIS community has adapted
the common terminology, and improved its surveying procedure as well as
communication of results.
IGS terminology has been adapted without alterations; the concepts are there, but thetechnique specific terminologies vary. The main focus of the IGS component has beena reassessment of existing sites rather than surveying as such.
The ILRS maintains a list of current and historical sites. A combined effort from several
institutes involved a common application to the European EMPIR program. The
application fulfilled the acceptance criteria, but was not granted funding due to limited
resources.
The VLBI terminology concerning site surveys has been consolidated, and an
automated terrestrial monitoring system for telescopes called Heimdall has beendeveloped, as well as a complete model for telescope deformation.
A campaign to examine the short-term combination of VLBI, GNSS and automatedterrestrial monitoring at two baseline ends has been performed, with some processing
left to be finished.

Objectives and Planned Efforts for 2017-2019 and Beyond

Assess the ground truth uncertainty of different techniques to include in the next ITRF;
Evaluate the VLBI-GNSS-terrestrial campaign of the Onsala-Metsähovi baseline;
additionally, more sites should be surveyed. However, this is an activity that therespective station managers need to allocate funding for. The working group does nothave the means to do this, and would appreciate any help to create a pull in this direction.

Websitehttps://www.iers.org/IERS/EN/Organization/WorkingGroups/SiteSurvey/sitesurvey.html

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GGOS Bureau of Products and Standards
Director: Detlef Angermann (Germany)
Vice Director: Thomas Gruber (Germany)
Members• Michael Gerstl (Germany)• Robert Heinkelmann (Germany)• Urs Hugentobler (Germany)• Laura Sánchez (Germany)• Peter Steigenberger (Germany)
GGOS entities associated to the BPS:

Committee Contributions to Earth System Modelling, Chair: Maik Thomas (Germany)
Committee Definition of Essential Geodetic Variables, Chair: Richard Gross (USA),(Remark: This component has been newly established, the TOR are under development)
WG1 ITRS Standards for ISO TC211, Chair: C. Boucher (France)
WG2 Establishment of the Global Geodetic Reference Frame (GGRF), Chair: Urs
Marti (Switzerland)

The Bureau comprises the staff members, the chairs of the associated GGOS components aswell as representatives of the IAG Services and other entities. The present status of theassociated members as BPS representatives is summarized in Table X.1.
Tab. X.1: Representatives of IAG Services and other entities involved in standards and geodetic
products (status: May 2019)

Global Geodetic Observing System (GGOS)

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Overview
The Bureau of Products and Standards (BPS) is a key component of IAG’s Global Geodetic
Observing System (GGOS). It supports IAG in its goal to obtain consistent products describing
the geometry, rotation and gravity field of the Earth, along with its temporal variations. The
BPS is built upon existing observing and processing systems of IAG.
Mission and overall objectives of the BPS:

to serve as contact and coordinating point for the homogenization of IAG/GGOS
standards and products;



to keep track of the adopted geodetic standards and conventions across all IAG
components, and to initiate steps to close gaps and deficiencies;to focus on the integration of geometric and gravimetric parameters and to develop
new products needed for Earth sciences and society.

Fig. X.1: The integration of the “three pillars” geometry, Earth rotation and gravity fieldrequires consistent standards to obtain consistent geodetic products as the basis for Earthsystem research and for precisely quantifying global change phenomena.
As regards the development of standards, there is a link with the IERS Conventions Center, theIAU Commission A3 “Fundamental Standards”, the IAU Working Group “NumericalStandards for Fundamental Astronomy”, the Bureau International des Poids et Mesures(BIPM), the Committee on Data for Science and Technology (CODATA), and the International
Organization for Standardization (ISO) with its Technical Committee ISO/TC211.
Activities
According to its charter, the BPS has the task to keep track of adopted standards across all IAG
components and to evaluate products of IAG with respect to the adequate use of standards andconventions. Based on this general task description, a major activity of the BPS was thecompilation of an inventory regarding standards, constants, resolutions and conventions
adopted and used by IAG and its components for the generation of IAG products (seeAngermann et al., 2016 and 2018).
Summary and recommendations on numerical standards
As shown in Table X.2, different numerical standards are in use within the geodetic community.
The values of the Geodetic Reference System 1980 (GRS80) are still used as official ellipsoidparameters, although it represents the scientific status of the 1970s. In the concept of GRS80,

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-201930

the tidal systems and relativistic theories are not considered (Ihde et al., 2017). The numericalstandards of the IERS Conventions 2010 are commonly used for the processing of the geometricobservations and for the generation of IERS products. The fact that the semi-major axis between
GRS80 and IERS Conventions 2010 differs by 0.4 m is critical and has to be consideredcorrectly for users of geodetic products. Table X.2 also shows the numerical standards of the
Earth Gravitational Model 2008 (EGM2008; Pavlis et al., 2012), which are partly different fromthe numerical standards given in the IERS Conventions. In cooperation between the IERS
Conventions Center and the BPS, the conventional value W0 = 62 636 853.4 m2s-2 for thegeopotential at mean sea level issued in the IAG (2015) Resolution No. 1 (Ihde et al., 2017;
Sánchez and Sideris, 2017) has been updated in Chapter 1 of the IERS Conventions in 2017.
Thus, the former difference between the IERS Conventions 2010 value and the IAG 2015 valueof about -2.6 m2s-2 (equivalent to a level difference of about 27 cm) has been resolved.
The current situation concerning numerical standards and the different use of time and tidesystems is a potential source for inconsistencies and even errors of geodetic products. Thus, it
is essential for a correct interpretation and application of geodetic results and products that theunderlying numerical standards are clearly documented. Moreover, the combination of geodetic
results referring to different time or tide systems, transformations have to be performed to get
consistent results.
Tab. X.2: Numerical standards of conventional parameters presently in use within IAG. The
defining parameters of the GRS80 are a, GM, J2 and ω. The IAG Resolution No. 1 (2015)
recommends a conventional W0 value of 62 636 853.4m2s-2. Note the consequential decouplingof W0 and LG. This W0 value could be used as a defining parameter for a new GRS20XX, thesemi-major axis a would then become a derived quantity. The advantage of W0 is that it does
not depend on the tide system, which is not the case of the semi major axis a.

The following recommendations on numerical standards have been specified in the BPS
inventory, also endorsed as recommendations of the Unified Analysis Workshop held in Paris
2017, which was co-organized by GGOS and the IERS:

Recommendation 1: The used numerical standards including time and tide systems
must be clearly documented for all geodetic products.



Recommendation 2: The geopotential value W0 = 62 636 853.4 m2s-2 issued by the
IAG resolution No. 1 (2015) should be used as the conventional reference value forgeodetic work.



Recommendation 3: The development of a new Geodetic Reference System
GRS20XX based on best estimates of the major parameters related to a geocentric level
ellipsoid is desired.

Global Geodetic Observing System (GGOS)

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Product-based review of standards and conventions
The following major topics were addressed in the product-based evaluation of standards andconventions (see chapter 4 in the BPS inventory, Angermann et al., 2016):
Celestial reference systems and frames

Terrestrial reference systems and frames

Earth orientation parameters



GNSS satellite orbitsGravity and geoid

Height systems and their realizations

IAG products exist for the celestial and terrestrial reference frames as well as for the EOP which
are provided by the responsible Product Centers of the IERS (see www.iers.org). These products
are derived from a combination of the contributing VLBI, SLR, GNSS and DORIS data. The
IERS Conventions provide the basis for the work of the geometric IAG Services (IGS, ILRS,
IVS and IDS), as well as for the definition and realization of geodetic reference systems and forthe generation of IERS products. In addition to the IERS Conventions, several techniquespecific standards are defined for the analysis of the individual geometric observations andtechnique-specific products (e.g., GNSS satellite orbits). The BPS inventory gives an overview
about the present status concerning the IERS products, it identifies gaps and deficiencies andprovides recommendations for future improvements for each product (Angermann et al., 2016).
The work of the BPS should be considered as a supplement to the extensive activities performed
within the IAG Services and the IERS. The present issues concerning the analysis andcombination of the geometric space-techniques were discussed during the Unified Analysis
Workshop 2017, which was co-organized by GGOS and the IERS.
Some general recommendations of the BPS inventory concerning the IERS products are given
below:
At present, the celestial and the terrestrial reference frames and their integral EOP
solutions are not fully consistent with each other as they are computed independently
by separate IERS Product Centers. The Resolution No.3 (2011) of the IUGG)
recommends, that the highest consistency between the ICRF, the ITRF and the EOP as
observed and realized by IAG and its components such as the IERS should be a primary
goal in all future realizations of the ICRS.

The processing standards and models should be consistently applied by all the analysis
centers of the IAG Services providing data for the generation of the IERS products.

The station networks and the spatial distribution of high quality co-location sites shouldbe improved as a fundamental requirement to achieve the GGOS accuracy requirements
as specified in the GGOS 2020 book.

The IGFS is responsible to coordinate the gravity-related IAG Services and its overall goal isto provide gravity field related data, software and information for the scientific community. In
2016, the new IGFS Central Bureau, hosted at the Aristotle University of Thessaloniki (Greece),started its activity, providing an updated IGFS website (igfs.topo.auth.gr), including a dedicatedproduct portal for the download of data and results generated by the IGFS Services. As an
example, about 170 models of the global gravity field of the Earth are made available to the
public via the ICGEM website (icgem.gfz-potsdam.de). A recommendation is that aReport of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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conventional global gravity field model might be useful as a reference model to be used for thegeneration of official IAG products, whereas scientific users should be free to use any preferredmodel for their particular purposes. The last topic of the product-based inventory focuses onheight systems and their realizations (see Report of the GGOS Focus Area “Unified Height
System”). More detailed information on the product-based evaluation are found in the BPS
inventory (Angermann et al., 2016).
Summary of further BPS activities:

The BPS is working on the update and revision of the inventory on standards andconventions. The 2nd version of this inventory will be published online on the GGOS
website. The planned release date is June 30, 2019. The major changes are summarized
as Document Change Record. These changes include updates on the organizational
structure of GGOS and on numerical standards, as well as the replacement of theprevious realizations (i.e., ICRF2, ITRF2008, EOP 08 C04) by the latest versions
ICRF3, ITRF2014 and EOP 14 C04. Furthermore, the section on GNSS orbits, theactivities of the IGFS and the developments towards the realization of the International
Height Reference System have been updated and revised.

In the field of standards and conventions the BPS closely interacts with the IERS
Conventions Centers and IAU Commission A3 “Fundamental Standards”. A topic ofdiscussion during the GGOS Days 2018 in Tsukuba (Japan) was the interaction of the
BPS and the IERS Conventions Center regarding the re-writing/revising of the IERS
Conventions. As a result, the director of the BPS has been nominated as the Chapter
Expert for the “General Definitions and Numerical Standards”.



The BPS also supports the development of new products derived from a combination ofgeometric and gravimetric observations. Towards this aim various activities have been
initiated and dedicated GGOS entities have been established to focus on thedevelopment of integrated products, such as the Focus Area “Unified Height System”,
the Focus Area “Geodetic Space Weather Research” and the Joint IAG Working Group“Establishment of the Global Geodetic Reference Frame (GGRF)”.

The director of the BPS has been nominated by the IAG Executive Committee as the
IAG Representative to the UN Global Geospatial Information Management (UNGGIM) Subcommittee “Geodesy” (the former GGRF Working Group) for the Focus
Group “Data Sharing and Development of Geodetic Standards”. The BPS contributed
to the GGRF Roadmap Implementation Plan to the UN-GGIM Committee of Experts,
provided for the 8th session in New York (August, 2018). This Focus Group (which has
been renamed in a UN GGIM Working Group) has formulated three main
recommendations on data sharing and common standards along with a number ofactions to be accomplished in these two fields.



In 2018, the Committee on the definition of Essential Geodetic Variables (EGVs) has
been established as a new GGOS component associated to the BPS. The members of
the Committee on EGVs comprise the GGOS Science Panel, representing the IAG
Commissions, the Inter-Commission Committee on Theory, and the four GGOS Focus
Areas, as well as representatives of the IAG Services. The Committee on EGVs is
chaired by R. Gross. It consists of 34 members in total. Examples of EGVs might be theposition of reference objects (ground stations, radio sources), EOPs, ground- and spacebased gravity measurements, etc. Such EGVs could then serve as a basis for a gap
analysis to identify requirements concerning observational properties and networks,
accuracy, spatial and temporal resolution and latency.

Global Geodetic Observing System (GGOS)

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BPS board meetings during the period 2015-2019:IUGG General Assembly 2015, Prague, Czech Republic, June 27, 2015



GGOS Days 2016, Frankfurt am Main, Germany, October 22, 2015

EGU 2016, Vienna, Austria, April 19, 2016

GGOS Days 2016, Cambridge, USA, October 26, 2016

EGU 2017, Vienna, Austria, April 25, 2017

GGOS Days 2017, Vienna, Austria, November 1, 2017EGU 2018, Vienna, Austria, April 10, 2018

GGOS Days 2018, Tsukuba, Japan, October 3, 2018

Selected Publications:Angermann D., Gruber T., Gerstl M., Heinkelmann R., Hugentobler, U., Sánchez L., Steigenberger P.: GGOS
Bureau of Products and Standards: Inventory of Standards and Conventions used for the Generation of IAG
Products. The IAG Geodesist’s Handbook 2016, J Geod 90(10): 1095-1156, doi: 10.1007/s00190-016-0948-z,
2016
Angermann D., Gruber T., Gerstl M., Heinkelmann R., Hugentobler, U., Sánchez L., Steigenberger P.: GGOS
Bureau of Products and Standards: Inventory of Standards and Conventions used for the Generation of IAG
Products. In: Rizos C. Willis P. (Eds.) IAG 150 Years, IAG Symposia 143, 571-577, doi:
10.1007/1345_2015_165, 2016
Angermann D., Gruber T., Gerstl M., Heinkelmann R., Hugentobler U., Sánchez L., Steigenberger P.: GGOS
Bureau of Products and Standards: Recent Activities and Future Plans. International Association of Geodesy
Symposia, doi: 10.1007/1345_2018_28, 2018
Ihde J., Sánchez L., Barzaghi R., Drewes H., Foerste Ch., GruberT., Liebsch G., Marti U., Pail R., Sideris M.:
Definition and proposed realization of the International Height Reference System (IHRS). Surveys inGeophysics 38(3), 549-570, doi: 10.1007/s10712-017-9409-3, 2017
Sánchez L., Čunderlík R., Dayoub N., Mikula K., Minarechová Z., Šíma Z., Vatrt V., Vojtíšková M.: A
conventional value for the geoid reference potential W0. Journal of Geodesy 90(9), 815-835, doi:
10.1007/s00190-016-0913-x, 2016
Sánchez L., Sideris M. G.: Vertical datum unification for the International Height Reference System (IHRS).
Geophys J Int 209(2), 570-586, doi: 10.1093/gji/ggx025, 2017

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GGOS Committee on Earth System Modeling
Chair: Maik Thomas (Germany)
Activities
Recent activities of the committee mainly concentrated on systematic comparisons of different
stand-alone and coupled model approaches as well as on the development of model interfaces
and algorithms for data assimilation. In particular, the following progress could be achieved:

A module for a realistic representation of the elastic response of the lithosphere to shortterm variations of surface mass loading has been developed and implemented into various
model approaches. Sensitivity of results to different numerical approaches (local, regional,
global) for load-induced surface deformation as well as effects due to mantle inelasticity
have been estimated.



Several time series from system model simulations are operationally provided to thecommunity via the GGFC/IERS Combination Center, e.g., time series of site displacements
due to hydrological loading derived from model simulations applying the new loading
module or effective angular momentum functions based on atmosphere-hydrospheremodels.



Kalman-based algorithms for the assimilation of (integral) geodetic observations have been
generalized and implemented into stand-alone model components in order to improve
numerical predictions of variations of surface deformation and Earth rotation parameters.
Alternative techniques for the introduction of observational data into dynamically coupledmodels (e.g., particle filtering) have been intensively discussed; however, no generalized
approach to constrain dynamically coupled models can be provided, so far.

Feasibility studies for the provision of error estimates and uncertainties based on single- andmulti-model ensembles have been performed.

Selected Publications
Dill, R., Klemann, V., Martinec, Z., Tesauro, M.: Applying local Green's functions to study the influence of thecrustal structure on hydrological loading displacements. Journal of Geodynamics, 88, p. 14-22, 2015.
Dobslaw, H., Bergmann, I., Dill, R., Forootan, E., Klemann, V., Kusche, J., Sasgen, I.: The updated ESA Earth
System Model for future gravity mission simulation studies. Journal of Geodesy, 89, 5, p. 505-513, 2015.
Irrgang, C., Saynisch, J., Thomas, M.: Ensemble simulations of the magnetic field induced by global ocean
circulation: Estimating the uncertainty. Journal of Geophysical Research, 121, 3, p. 1866-1880, 2016.
Konrad, H., Sasgen, I., Klemann, V., Thoma, M., Grosfeld, K., Martinec, Z.: Sensitivity of Grounding-Line
Dynamics to Viscoelastic Deformation of the Solid-Earth in an Idealized Scenario. Polarforschung, 85, 2, p.
89-99, 2016.
Martinec, Z., Klemann, V., van der Wal, W., Riva, R. E. M., Spada, G., Sun, Y., Melini, D., Kachuck, S. B.,
Barletta, V., Simon, K., James, T. S., G A.: A benchmark study of numerical implementations of the sea level
equation in GIA modelling. Geophysical Journal International, 215, 1, pp. 389-414, 2018.
Saynisch, J., Bergmann, I., Thomas, M.: Assimilation of GRACE-derived oceanic mass distributions with a global
ocean circulation model. Journal of Geodesy, 89, 2, p. 121-139, 2015.
Saynisch, J., Irrgang, C., Thomas, M.: Estimating ocean tide model uncertainties for electromagnetic inversion
studies. - Annales Geophysicae, 36, pp. 1009-1014, 2018.

Global Geodetic Observing System (GGOS)

35

Fig. Y1: Concept of a modular Earth system model for geodetic applications.

Fig. Y2: Explained variance of GRACE ocean bottom pressure resulting from an
unconstrained (left) and assimilated (right) ocean model simulation (Saynisch et al., 2015;
updated).

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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BPS WG1: ITRS Standards for ISO TC 211
Chair: Claude Boucher (France)
Members








Detlef Angermann (Germany)
Sten Bergstrand (Sweden) chair IERS WG Site surveys and collocations
Claude Boucher (France) chair WG, ISO project leader
Xavier Collilieux (France) IAG SC1.2 chair
Thierry Gattacceca (France) ISO project editor
Larry Hothem (USA)Guy Woppelmann (France)

Additional contributors via ISO group:

Zuheir Altamimi (France and IAG)
Michael Craemer (Canada)

Purpose and Scope
The mission of the WG is to coordinate the IAG community in the support of the developmentof the ISO standard on ITRS.
In order to ensure this support, some specific objectives has been identified (this list may be
updated if needed):
1. To establish the list of IAG contributors to the work of the WG
2. To collect comments and proposals on any draft documents provided by the ISO
TC211/19161-1
3. To establish a glossary of geodetic terms in relation with the scope of the WG
Activity report1

IAG contributors

The present status of WG members is given at the beginning of this report. Additional
contributors were provided through ISO 19161-1.
2

ISO TC211/19161-1

This group initially worked to establish a draft standard (versions 1 to 12)
In 2018, the ISO19161-1 Project Team consolidated and expanded the Working Draft, andsuccessfully presented a Committee Draft (CD) to the TC211 on September 3. The CD was
submitted in time to have the ballot completed before the TC211 plenary in Wuhan, in
November 2018. Ballot results were: P-members in favour: 25; P-members against: 0;
Abstentions: 11
A total of 130 comments (including 106 editorial ones) were received.
The first Editing Committee Meeting took place in Wuhan, China, on November 13, 2018, with
9 experts attending. All non-trivial editorial comments were processed.

Global Geodetic Observing System (GGOS)

37

The document was then edited to take into account the remaining comments (the trivial ones,
and those less trivial or non-editorial that were discussed at the meeting and for which an answer
was agreed on), thus producing the Draft International Standard (DIS). The DIS was circulated
along with the updated table of comments to the EC members by the end of November, andsubmitted to ISO Central Secretariat in January 21, 2019.
The DIS ballot started on March 26, 2019 and will end June 18, 2019.
3

Glossary of terms

For information, here is the extract of the CD document related to the terminology part:3.1

Coordinate system

Set of mathematical rules for specifying how coordinates are to be assigned to points[SOURCE: ISO 19111:2018, 3.11]
3.2

Geocentric terrestrial reference system

GTRS
System of geocentric space-time coordinates within the framework of General Relativity, corotating with the Earth and related to the Geocentric Celestial Reference System by a spatial
rotation which takes into account the Earth's orientation parameters[SOURCE: IAG and IUGG resolutions of 1991 and 2007]
3.3

Positioning process

Computational process that determines directly from measurements the geodetic coordinates ofpoints (absolute positioning), or that derives geodetic coordinates of points from previously
determined geodetic coordinates (relative positioning)
3.4

Satellite ephemeris

Numerical representation of the trajectory of the centre of mass of an Earth orbiting artificial
satellite expressed in an Earth centred terrestrial reference frame
3.5

Terrestrial reference frame

TRF
Realization of a TRS, by specifying its origin, orientation, scale, and its time evolution[SOURCE: IERS Conventions 2010]
Note 1 to entry: The realization is achieved through a set of physical points with precisely determined coordinatesin a specific coordinate system, which may include the rate of coordinate change.
Note 2 to entry: The realization is called static when no rates of coordinate change are defined, and kinematicwhen rates of coordinate change are defined without considering the underlying forces causing the motion. The
realization may be called dynamic when these external forces are considered. “Dynamic” is also used colloquiallyto describe both the dynamic and kinematic cases without distinction.

3.6

Terrestrial reference system

TRS
Set of conventions defining the origin, scale, orientation and time evolution of a spatialreference system co-rotating with the Earth in its diurnal motion in spaceReport of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

38

Note 1 to entry: The abstract concept of a TRS is realized through a terrestrial reference frame.
Note 2 to entry: In such a system, positions of points attached to the solid surface of the Earth have coordinates
which undergo only small variations with time, due to geophysical effects (tectonic or tidal deformations). In the
Newtonian framework, the physical space is considered as a Euclidean affine space of dimension 3, with an origin,a scale and an orientation.

[SOURCE: IERS Conventions 2010]

Global Geodetic Observing System (GGOS)

39

BPS WG2: Establishment of the Global Geodetic Reference Frame (GGRF)
Chair: Urs Marti (Switzerland)Members
Jonas Ågren (Sweden, Commission 2), Detlef Angermann (Germany, GGOS BPS, IERS),
Riccardo Barzaghi (Italy, IGFS), Johannes Ihde (Germany, Working Group on Height
Systems), Hansjörg Kutterer (Germany, GGOS), Jaakko Mäkinen (Finland, Tidal Systems),
Pavel Novak (Czech Republic, ICCT), Roland Pail (Germany, Commission 2), Nikolaos Pavlis(USA, Global Gravity Field Models), Laura Sánchez (Germany, Working Group on Height
Systems), Harald Schuh (Germany, IAG), Hartmut Wziontek (Germany, Global Gravity
Reference Network)
Corresponding Members
Gary Johnston (Australia, Commission 1, UN GGIM), Johannes Böhm (Austria, Commission1), Catherine Hohenkerk and Robert Heinkelmann (Representatives of the IAU)
Activities
This WG is a joint activity of IAG Commissions 1 and 2, the ICCT, the IERS and the IGFS.
The start-up meeting of this WG took place during the EGU Assembly 2016 in Vienna. In thismeeting, the tasks of the WG were discussed and defined. A clear separation between this WG
and the UN GGIM WG on the GGRF was reached. Thus, the IAG WG concentrates on thepractical issues of the realisation of the GGRF and the setup of a consistent use of geometry
and gravity field related quantities in the global reference frames. A key role in this discussion
play the realisation of the International Height Reference System (IHRS) and the definition andrealisation of a global Absolute Gravity Reference System (see corresponding reports of these
WGs).
At the GGHS2016 conference in Thessaloniki a first official meeting of the WG was held. Someconcrete tasks were defined there, such as:










Work towards a conventional global reference gravity field model
Develop or define a global, conventional combined gravity field model and aconventional Satellite only model
Study the influence of permanent tide models on all kind of data (position, potential,
gravity, gravity anomalies, heights) and develop transformation methods
Study the redefinition of a global GRS based on actual values of W0 / GM / ω andderived quantities
Study the necessity to replace GRS80
Study relativistic effects and their influence on the GRS
Get an overview of parameters and models (e.g. tides, loading effects, atmosphere) usedin products and conventions of IAG and other communities. (see BPS Inventory,
Angermann et al., 2016)
Intensify the contacts to IAU and IERS

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

40

Main discussions were the assignment of a conventional global gravity field model, where not
all WG members agree that it is necessary. A second point of disagreement was, if it is really agood idea to replace GRS80 by a new model. A good summary of the main aspects can be foundin ‘Considerations on a Concept for future handling Geodetic Parameters/Numerical Standards
in Conventions’ by J. Ihde.
The concepts and activities of the WG were presented at the TGSMM conference in St.
Petersburg in April 2016 , the GGOS days in Cambridge in October 2016, the IAG-IASPEIScientific Assembly in Kobe (August 2017), the GGOS days in Vienna (November 2017) and
the GGHS2018 conference in Copenhagen (September 2018).
Results
An overview of the parameters and models used by various groups in- and outside of Geodesy
is available in the BPS inventory (Angermann et al. 2016 and 2018). Mäkinen presented in
Kobe (2017) a study about the calculation of the permanent tide, the transformation and use of
the various systems and their influence on the ellipsoid, the gravity potential and the physicalheights. One main recommendation was to calculate all the influences in the zero tide systemand to convert the corrections at the very end into other systems and to neglect very minor
second order terms. In Copenhagen (2018), Oshchepkov presented a set of parameters of areference system, consistent with the W0 value, adopted in 2015 for the IHRS. All calculations
are based on the zero tide system and terrestrial time (TT). As defining parameters W0, GM, J2and ω were chosen. Values for the derived parameters (such as semi-major axis a, flattening f,
normal gravity at the equator γE) were calculated as well. It was shown that a new set ofparameters for a GRS has also small, but non-negligible influences on the gravity anomalies
and normal heights. Kopeikin (et al.) published several papers on relativistic effects on a GRS,
especially the effects on the reference ellipsoid, the gravity potential and the normal gravity(see list in the references).
Until now, no agreement about the definition of a “standard” global gravity field model wasreached. There is even no agreement if such a “standard model” is needed at all. However, sucha common reference model (satellite-only and combined) would be very useful for several
purposes such as the realization of the International Height Reference System (IHRS) or forconsistent regional geoid modelling. The newly installed IAG service COST-G (International
Combination Service for Time-variable Gravity Field Solutions) of the IGFS could assist in
finding such reference models, although their main focus is on the combination of time variablegravity field models.
One main task - the preparation of an IAG or IUGG resolution for the replacement of GRS80
by a new official GRS – could not be realized yet. Though we have a proposal for a new set ofdefining parameters (e.g. by Oshchepkov, alternative solutions are still calculated by othergroups), we are not ready yet to present a broadly accepted new model. Many users do not see
the necessity to change the conventional GRS80. This needs a broader discussion not only in
IAG, but also in other related organisation such as the IAU and the IUGG. In the near future,
this could become possible in the frame of the renewal of the IERS conventions and the newly
established committee working on the definition of “Essential Geodetic Variables” (EGVs),
associated with the GGOS Bureau of Products and Standards (BPS). Even if GRS80 will not
be replaced as the conventional system, it is necessary to calculate a GRS based on today’s
knowledge and to propose a consistent set of parameters and formulas.

Global Geodetic Observing System (GGOS)

41

Presentations and Publications
Angermann D. et al (2016): Inventory of Standards and Conventions used for the Generation of IAG products.
Angermann D., Gruber T., Gerstl M., Heinkelmann R., Hugentobler U., Sánchez L., Steigenberger P.: GGOS
Bureau of Products and Standards: Recent Activities and Future Plans. International Association of Geodesy
Symposia, 10.1007/1345_2018_28, 2018
IAG Executive Committee (2016): Description of the Global Geodetic Reference Frame. Position Paper. April
2016.
Ihde J. (2016): The Role of Gravity and Height for the GGRF. Presentations at the EUREF Symposium May 2016.
San Sebastian.
Ihde J. (2016): Future handling Geodetic Parameters/Numerical Standards in Conventions. Presentation at the
GGOS Days October 2016. Cambridge.
Ihde J. (2016): Considerations on a Concept for future handling Geodetic Parameters/Numerical Standards inConventions. November 2016.
Ihde J., Sánchez L., Barzaghi R., Drewes H., Foerste Ch., GruberT., Liebsch G., Marti U., Pail R., Sideris M.:
Definition and proposed realization of the International Height Reference System (IHRS). Surveys inGeophysics, 38(3), 549-570, 10.1007/s10712-017-9409-3, 2017
Kopeikin S., E. Mazurova, A. Karpik (2015): Towards an exact relativistic theory of Earth's geoid undulation,
Physics Letters A, 379, 1555.
Kopeikin S (2016): Reference ellipsoid and geoid in chronometric geodesy. Frontiers in Astronomy and Space
Sciences, 3, 5
Kopeikin S., W.-B. Han, E. Mazurova (2016): Post-Newtonian reference-ellipsoid for relativistic geodesy,Physical Review D, 93, id. 044069
Kopeikin S. et al. (2018): Normal gravity field in relativistic geodesy. Physical Review D 97(4). DOI:
10.1103/PhysRevD.97.045020.
Mäkinen J. (2017): The permanent tide and the International Height Reference System IHRS. Presentation at the
IAG-IASPEI Scientific Assembly, Kobe (Japan).
Marti U. (2016): GGRF. Presentation at the EGU General Assembly. April 2016, Vienna.
Marti U. (2016): GGRF. Presentation at the GGHS2016 Conference. September 2016, Thessaloniki.
Marti U. (2016): Presentation at the GGOS Days October 2016. Cambridge.
Marti U., L. Vitushkin, H. Wziontek (2016): The Role of a new Global Absolute Gravity Reference System in
Relation to the GGRF. Presentation at the TGSMM Conference. April 2016. St.Petersburg.
Oshchepkov I. (2018): Geodetic reference system consistent with the IHRF W 0 value. Presentation at the
GGHS2018 Conference in Copenhagen.

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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GGOS Focus Area “Unified Height System” and JWG 0.1.2 “Strategy for
the Realization of the International Height Reference System (IHRS)”
Chair: Laura Sánchez (Germany)
Members: J. Ågren (Sweden), M. Amos (New Zealand), R. Barzaghi (Italy), S. De Freitas(Brazil), W. Featherstone (Australia), T. Gruber (Germany), J. Huang (Canada), J. Ihde
(Germany), G. Liebsch (Germany), J. Mäkinen (Finland), U. Marti (Switzerland), P. Novák(Czech Republic), M. Poutanen (Finland), D. Roman (USA), D. Smith (USA), M. Véronneau(Canada), Y. Wang (USA), M. Blossfeld (Germany), J. Böhm (Austria), X. Collilieux(France), M. Filmer (Australia), B. Heck (Germany), R. Pail (Germany), M. Sideris(Canada), G. Vergos (Greece), C. Tocho (Argentina), H. Denker (Germany), D. Avalos(Mexico), H. Wziontek (Germany), M. Varga (Croatia), I. Oshchepkov (Russia), D. Blitzkow(Brazil), A.C.O.C. Matos (Brazil), J. Bouman (Germany), H.A. Abd-Elmotaal (Egypt), K.
Matsuo (Japan), S. Claessens (Australia), R. Forsberg (Denmark), T. Jiang (China), V.N.
Grigoriadis (Greece), D.A. Natsiopoulos (Greece), Q. Liu (Germany), M. Willberg(Germany), B. Erol (Turkey), M. Serkan Isik (Turkey), S. Erol (Turkey).
Activities
The objectives and planned activities of the GGOS-FA “Unified Height System” for the 20152019 period are described in the Geodesist’s Handbook 2016 (Drewes H. et al., 2016). The
main goal at present is the implementation of the International Height Reference System (IHRS)
defined by the IAG 2015 Resolution No. 1 (ibid. page 981). The progress is summarized asfollows:•

In Dec 2015, the joint working group (JWG) Strategy for the Realization of the IHRS
was installed with the objective of developing a scheme for the realization of the IHRS;
i.e., the establishment of the International Height Reference Frame (IHRF). This JWG
is supported by the International Gravity Field Service (IGFS), the IAG Commissions
1 and 2 (Reference Frames and Gravity field), the Inter-commission Committee on
Theory (ICCT), the regional sub-commissions for reference frames and geoid
modelling, and both GGOS Bureaus (Networks and Observations and Products andStandards). In particular, there is a strong cooperation with
- IAG JWG 2.2.2: The 1 cm geoid experiment (chair: Y.M. Wang, USA)
- IAG SC 2.2: Methodology for geoid and physical height systems (chair: J. Ågren,
Sweden)- ICCT JSG 0.15: Regional geoid/quasi-geoid modelling - Theoretical framework forthe sub-centimetre accuracy (chair: J. Huang, Canada)- IAG JWG 2.1.1: Establishment of a global absolute gravity reference system (chair:
H. Wziontek, Germany)- J. Mäkinen, tide systems in the IHRS (Finnland).

•A brainstorming and definition of action items took place at a JWG meeting carried out
during the International Symposium on Gravity, Geoid and Height Systems 2016
(GGHS2016) in Thessaloniki (Greece) in Sep 2016. This JWG meeting was attended
by 70 colleagues and allowed us to identify the activities to be faced immediately(Sánchez, 2016a). A main output of this meeting are the criteria for the selection of
IHRF reference stations:- GNSS continuously operating reference stations to detect deformations of thereference frame;Global Geodetic Observing System (GGOS)-

43

Co-location with fundamental geodetic observatories to ensure a consistentconnection between geometric coordinates, potential and gravity values, andreference clocks (to support the implementation of the GGRF);
Co-location with reference stations of the International Gravity Reference Frame(IGRF): the IGRF and IHRF station selection for the co-location of this two
reference frames is a contribution of IAG JWG 2.1.1;
Preference of stations belonging to the ITRF and the regional reference frames (likeSIRGAS, EPN, APREF, etc.);
Co-location with reference tide gauges and connection to the national levelling
networks to facilitate the vertical datum unification;
Availability of terrestrial gravity data around the IHRS reference stations as main
requirement for high-resolution gravity field modelling (i.e., precise estimation ofpotential values).

•

During the GGOS Days 2016 (Boston (MA), USA, Oct 2016), a preliminary station
selection for the IHRF was performed (Sánchez, 2016b). This selection was based on a
global network with worldwide distribution, including a core network (to ensuresustainability and long-term stability of the reference frame) and regional/national
densifications (to provide local accessibility to the global frame).

•

Based on the conclusions of the meetings in Thessaloniki and Boston, regional andnational experts were asked- to evaluate whether the preliminary selected sites are suitable to be included in the
IHRF (availability of gravity data or possibilities to survey them), and- to propose additional geodetic sites to improve the density and distribution of the
IHRF stations in their regions/countries.

•

After the feedback from the regional/national experts (see Table 1), the first
approximation to the IHRF is based on about 170 reference stations. This station
selection is regularly refined in agreement with changes/updates of other geodetic
reference frames (ITRF and IGRF and their densifications). Figure 1 shows the IHRF
station distribution (as of Apr 2019) and the co-location with SLR, VLBI, DORIS,
IGRF, tide gauges and levelling networks’ stations.

•With the preliminary station selection, following efforts concentrated on thecomputation of station potential values and the assessment of their accuracy. Different
approaches were evaluated (Sánchez et al., 2017):- As national/regional experts provided the JWG with terrestrial gravity data aroundsome IHRF sites, a direct computation of potential values was performed using a
combination of terrestrial gravity data and different global gravity models (GGM)
as well as different mathematical formulations (least-squares collocation, FFT,
radial basis functions, etc.).
- Computation of potential values by national/regional experts responsible for thegeoid modelling using their own data and methodologies.
- Computation of potential values based on GGM of high-degree (like XGM2016,
EIGEN-6C, EGM2008, etc.).
- Recovering potential values from existing local (quasi-)geoid models.
- Table 2 lists the colleagues contributing to this first experiment.

•

The comparison of the results showed discrepancies up to the dm-level (Sánchez et al.,2017). The main conclusions of this experiment were:Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

-

-

44

The use of only GGMs is (at present) not suitable for the estimation of precise
potential values. GGMs may be used if there is no other way to determine potential
values.
A standard procedure for the computation of potential values may be not appropriateas- different data availability and different data quality exist around the world- regions with different characteristics require particular approaches (e.g.
modification of kernel functions, size of integration caps, geophysicalreductions like GIA, etc.)
A centralized computation (like in the ITRF) is complicated due to the restricted
accessibility to terrestrial gravity data•

To overcome these inconveniences, during the IAG-IASPEI Joint Scientific Assembly(Kobe, Japan, Aug 2017) was agreed to initiate a new experiment towards:- the computation of IHRF coordinates using exactly the same input data and the own
methodologies (software) of colleagues involved in the gravity field modelling, and- the comparison of the results, to identify a set of standards that allow to get as similarand compatible results as possible.

•

In the same IAG-IASPEI 2017 Assembly, J. Ågren (Chair of IAG SC 2.2) and J. Huang(Chair of ICCT JSG 0.15) proposed to establish an interaction with the JWG 2.2.2(chaired by Y.M. Wang). Aim of JWG 2.2.2 is the computation and comparison of geoid
undulations using the same input data and the own methodologies/software ofcolleagues involved in the geoid computation. The comparison of the results should
highlight the differences caused by disparities in the computation methodologies. In thisframe, it was decided to extend the “geoid experiment” to the computation of station
potential values as IHRS coordinates. With this proposal, the US NGS/NOAA agreed
to provide terrestrial gravity data, airborne gravity, and digital terrain model for an areaof about 500 km x 800 km in Colorado, USA (Fig. 2). With these data, different groups
working on the determination of IHRF coordinates should compute potential values forsome virtual geodetic stations located in that region. Afterwards, the results individuallyobtained should be compared with the Geoid Slope Validation Survey 2017 (GSVS17),
which will provide potential differences inferred from first order levellingmeasurements and gravity corrections along a validation line (see red line in Fig. 2).

•

The Colorado data were distributed in Feb. 2018, together with a document
summarizing a minimum set of basic requirements (standards) for the computations.
Ten different groups delivered solutions (Table 3) and the results were discussed during
the Gravity, Geoid and Height Systems (GGHS2018) Symposium (Copenhagen,Denmark, Sep 2018). Main conclusions are (Wang et al., 2018; Sánchez et al. 2018a):- Two solutions were declared as outliers. They present large discrepancies (at the 1.5
m level) in (quasi-)geoid heights as well in the potential numbers with respect to theother solutions.
- In the geoid comparison, six solutions agree within 3 cm to 10 cm in terms ofstandard deviation with respect to the mean value.
- In the quasi-geoid comparison, the same six solutions agree within 1 cm to 4 cm interms of standard deviation with respect to the mean value.
- In the comparison of the potential values, four solutions agree within 1 cm to 2 cm
in terms of standard deviation with respect to the mean value.
- The discrepancies present a high correlation with the topography.
- Possible sources of discrepancy:Global Geodetic Observing System (GGOS)-

45

Different handling of terrain corrections/reductions
Inconsistent use of the zero-degree term
Precision degradation due to the conversion of quasi-geoid heights to geoid
heights and vice versa
Uncertainties in the processing of the airborne gravity data.

•

To continue the Colorado experiment, following action items were formulated:- Participants in the experiment should provide a description with the main featuresof their computations in order to identify possible sources of discrepancies.
- Participants should follow the basic standards/specifications distributed with thedata, especially in the handling of corrections/reductions like the effect of theatmosphere, the consistent use of the zero-term, the global gravity models, etc.
- The document with the standards/specifications was modified/extended to present
more clearly some confusing issues like the handling of the zero degree term andthe conversion from quasi-geoid to geoid (Sánchez et al., 2018b).
- NGS/NOAA provided a pre-processed (cleaned) version of the GRAV-D data
(down sampling 20 Hz data, de-biased data) by the end of 2018 in order to facilitate
the use of these data in the individual solutions.

•

Based on these action items, a second computation for the Colorado experiment wascompleted in Apr 2019. In total, 14 solutions were delivered (Table 4). At present, we
are working on the comparison of geoid heights, height anomalies and potential values.
The results will be discussed in the next IUGG General Assembly (Montreal, Canada,
July 2019). It is expected to present all the results in a special issue of the Journal of
Geodesy.

Outlook
To close the term 2015-2019, an executive report will be presented to the IAG and GGOS at
the IUGG General Assembly 2019. It is expected to support this executive report with a peerreviewed paper describing the strategy for the realization of the IHRS and a first solution for
the IHRF. Aim of this first solution is to evaluate the achievable accuracy under the present
conditions (data availability, computation methods, etc.) and to identify key actions to improvethe determination of the IHRS/IHRF coordinates. These key actions should be faced in the next
2019-2023 period. For the same term, a joint working group of the GGOS FA-UHS, the IAG
Commission 2 and the IGFS should investigate the best way to establish an IHRS/IHRF element
within the IGFS to ensure the maintenance and availability of the IHRF. This implies regular
updates of the IHRFyy to take account for new stations, coordinate changes with time,
improvements in the estimation of coordinates (more observations, better standards, bettermodels, better computation algorithms, etc.), geodetic products associated to the IHRF
(description and metadata), and the organizational and operational infrastructure to ensure the
IHRF sustainability.

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-201946

Fig. 1. IHRF stations as of April 2019 and the co-location with VLBI, SLR, DORIS, absolute gravity (IGRF),
tide gauges and levelling networks’ stations.

Global Geodetic Observing System (GGOS)

47

Fig. 2. Data provided by the US NGS/NOAA for the Colorado experiment. The red line represents the validation
profile of the Geoid Slope Validation Survey 2017 (GSVS17). For validation, potential differences inferred fromfirst order levelling and gravity corrections along this line will be compared with potential differences inferredfrom the different Colorado solutions (see Tables 2 and 3).
Table 1: Colleagues contributing to the station selection for the International Height Reference Frame (see Fig. 1)-

M Véronneau, J Huang - Natural Resources Canada, Canada
I Oshchepkov - Center of Geodesy, Cartography and SDI, Russia
D Roman, K Choi, K Ahlgren - US National Geodetic Service - NOAA, USA
R Ruddick - Geoscience Australia, Australia
M Amos - Land Information New Zealand, New Zealand
SRC de Freitas - Universidade Federal do Parana, Brazil
JR Chire Chira - Instituto Geográfico Nacional, Peru
DA Piñón - Instituto Geográfico Nacional, Argentina
C Estrella - Instituto Geográfico Militar, Ecuador
A Álvarez - Instituto Geográfico Nacional, Costa Rica
A Echalar Rivera - Instituto Geografico Militar, Bolivia
D Avalos-Naranjo - Instituto Nacional de Estadística y Geografía, Mexico
S Costa, R Luz - Instituto Brasileiro de Geografia e Estatística, Brazil
D Blizkow, ACOC de Matos - Universidade de São Paulo, Brazil
N Suárez - Servicio Geográfico Militar, Uruguay
J Krynski - Institute of Geodesy and Cartography, Poland
U Marti - Federal Office of Topography, swisstopo, Switzerland
K Matsuo - Geospatial Information Authority of Japan, Japan
H Abd-Elmotaal - Minia University, Egypt
G Vergos - Aristotle University of Thessaloniki, Greece
M Poutanen - Finnish Geospatial Research Institute, FinlandReport of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019-

48

PA Vaquero Fernández - Instituto Geográfico Nacional, Spain
J Ågren - Lantmäteriet, Swedish mapping, cadastral and land registration authority,
SwedenH Wziontek - Bundesamt für Kartographie und Geodäsie, Germany
V Mackern, W Martínez - SIRGASR Forsberg - National Space Institute, Denmark
I Liepinš - Latvian Geospatial Information Agency, Latvia
T Jiang - Chinese Academy of Surveying and Mapping, China

Table 2: Colleagues contributing to the first experiment for the determination of IHRS coordinates (Sánchez et al.
2017)

-

M Véronneau, J Huang - Natural Resources Canada, Canada
G Vergos - Aristotle University of Thessaloniki, Greece
D Blizkow, ACOC de Matos - Universidade de São Paulo, Brazil
JL Carrión-Sánchez, SRC de Freitas - Universidade Federal do Parana, Brazil
H Denker - Leibniz Universität Hannover, Germany
R Pail - Technische Universität München, Germany
V Lieb - Technische Universität München, Germany
L Sánchez - Technische Universität München, Germany

Table 3: Colleagues contributing to the first computation for the Colorado experiment (Wang et al., 2018; Sánchez
et al., 2018b)-

VN Grigoriadis, GS Vergos, DA Natsiopoulos - Aristotle University of Thessaloniki,
GreeceH Abd-Elmotaal - Minia University, Egypt
B Erol, M Serkan Isik - Istanbul Teknik Üniversitesi, Turkey
YM Wang, X Li, K Ahlgren - US National Geodetic Survey - NOAA, USA
M Véronneau, J Huang - Natural Resources Canada, CanadaJ Ågren - Lantmäteriet, Swedish mapping, cadastral and land registration authority,
SwedenS Claessens, M Filmer - Curtin University, Australia
EL Nicacio, JL Carrión, SRC de Freitas, R Dalazoana, VG Ferreira, Universidade Federal
do Parana, Brazil
D Blizkow, ACOC de Matos - Universidade de São Paulo, Brazil
L Sánchez - Technische Universität München, Germany

Table 4: Colleagues contributing to the second computation for the Colorado experiment (results to be presented
at the IUGG General Assembly 2019)-

VN Grigoriadis, GS Vergos, DA Natsiopoulos - Aristotle University of Thessaloniki,
Greece and R Barzaghi, D Carrion - Politecnico de Milano, Italy
T Jiang - Chinese Academy of Surveying and Mapping, China
M Véronneau, J Huang - Natural Resources Canada, Canada
S Claessens, M Filmer - Curtin University, Australia
Q Liu, M Schmidt, L Sánchez - Technische Universität München, Germany
R Forsberg - National Space Institute, Denmark
K Matsuo - Geospatial Information Authority of Japan, Japan and R Forsberg - National
Space Institute, Denmark
M Willberg, R Pail - Technische Universität München, Germany
B Erol, M Serkan Isik, S Erol - Istanbul Teknik Üniversitesi, Turkey
J Ågren - Lantmäteriet, Swedish mapping, cadastral and land registration authority,
SwedenGlobal Geodetic Observing System (GGOS)-

49

YM Wang, X Li, K Ahlgren, US National Geodetic Survey - NOAA, USA
M Varga, T Bašic - University of Zagreb, Republic of Croatia and M Pitonák, P Novák University of West Bohemia, Czech Republic
R Barzaghi, D Carrion - Politecnico de Milano, Italy
D Blizkow, ACOC de Matos, Escola Politécnica da Universidade de São Paulo, Brazil

Acknowledgements
The activities described in this report were possible thanks to the support of many colleagues.
Their contribution is deeply acknowledged: M. Véronneau, J. Huang, Y.M. Wang, J. Ågren, Q.
Liu, M. Willberg, H. Denker, R. Pail, V. Lieb, R. Barzaghi, S. Claessens, M. Filmer, V.N.
Grigoriadis, G.S. Vergos, D.A. Natsiopoulos, B. Erol, M. Serkan Isik, S. Erol, M. Varga, T.
Bašic, M. Pitonák, P. Novák, D. Carrion, I. Oshchepkov, D. Roman, K. Choi, K. Ahlgren, R.
Ruddick, M. Amos, S.R.C. de Freitas, J.R. Chire Chira, D.A. Piñón, C. Estrella, A. Álvarez, A.
Echalar Rivera, D. Avalos-Naranjo, S. Costa, R. Luz, M. Schmidt, J. Mäkinen, D. Blizkow,
A.C.O.C. de Matos, N. Suárez, J. Krynski, U. Marti, K. Matsuo, H. Abd-Elmotaal, M.
Poutanen, P.A. Vaquero Fernández, H. Wziontek, V. Mackern, W. Martínez, R. Forsberg, I.
Liepinš, T. Jiang, J.L. Carrión-Sánchez, X. Li, E.L. Nicacio, R. Dalazoana, V.G. Ferreira...
References
Drewes H., Kuglitsch F., Ádám J., and Rózsa S.: The Geodesist's Handbook 2016, J Geod, 90(10): 981 - 982,
2016.
Sánchez L.: Working Group on the Strategy for the Realization of the International Height Reference System(IHRS): Brainstorming and definition of action items. Splinter meeting at the International Symposium on
Gravity, Geoid and Height Systems 2016 (GGHS2016), https://ihrs.dgfi.tum.de/fileadmin/JWG_2015/SP_
WG_IHRS_Realization_with_Comments_from_the_Splinter_Meeting.pdf, 2016a.
Sánchez L: International Height Reference System (IHRS): Required measurements and expected products. GGOS
Days
2016,
Cambridge
(MA),
USA,
https://ihrs.dgfi.tum.de/fileadmin/
JWG_2015/
Sanchez_IHRS_Obs_Prod_GGOS2016_2.pdf, 2016b.
Sánchez L., Denker H., Pail R., Lieb V., Huang J., Roman D., Ågren J., Amos M., Ihde J., Barzaghi R., Sideris
M., Oshchepkov I., Blitzkow D., Matos A.C.O.C., Piñon D., Avalos D., Freitas S.R.C., Luz R.: A first
approximation to the International Height Reference Frame (IHRF). Joint Scientific Assembly of theInternational Association of Geodesy and the International Association of Seismology and Physics of the
Earth’s Interior (IAG-IASPEI 2017), Kobe, Japan, https://ihrs.dgfi.tum.de/fileadmin/JWG_2015/
Sanchez_et_al_A_first_IHRF_IAG2017_v2.pdf, 2017.
Sánchez L., Ågren J., Huang J., Véronneau M., Wang Y.M., Roman D., Vergos G., Abd-Elmotaal H., Amos M.,
Barzaghi R., Blitzkow D., Matos A.C.O.C., Denker H., Filmer M., Claessens S., Oshchepkov I., Marti U.,
Matsuo K., Sideris M., Varga M., Willberg M., Pail R.: Advances in the establishment of the International
Height Reference Frame (IHRF). International Symposium on Gravity, Geoid and Height Systems 2018
(GGHS2018), Copenhagen, Denmark, 2018a.
Sánchez L., Ågren J., Huang J., Wang Y.M., Forsberg R.: Basic agreements for the computation of station potential
values as IHRS coordinates, geoid undulations and height anomalies within the Colorado 1 cm geoid
experiment,
https://ihrs.dgfi.tum.de/fileadmin/JWG_2015/Colorado_Experiment_Basic_req_V0.5_
Oct30_2018.pdf, 2018b.
Wang Y.M., Forsberg R., Sánchez L., Ågren J., Huang J.: Report on Colorado geoid comparisons. International
Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, https://ihrs.dgfi.tum.de/fileadmin/JWG_2015/Wang_report_GGHS2018ColoradoGeoidReportMod.pdf, 2018.

Further reading
Web site
A web site summarizing the main characteristics, achievements and challenges of the GGOS-FA “Unified Height
System” is available at http://ihrs.dgfi.tum.de/. This information is mirrored at http://ggos.org/en/focusareas/unified-height-system/.

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-201950

Selected publications and presentations
Altiparmaki O.N., Vergos G.S.: Potential determination at coastal stations from the synergy of SAR/SARin
altimetry and local gravity data towards the IHRS. International Symposium on Gravity, Geoid and Height
Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018.
Andritsanos V., Vergos G., Gruber Th., Fecher T.: GOCE variance and covariance contribution to height system
unification. GGHS2016: International Symposium on Gravity, Geoid and Height Systems 2016, Thessaloniki,
Greece, 2016-09-22.
Blitzkow D., de Matos A.C.O.C, de Carvalho Carneiro C., Costa S.M.C.: First efforts for the IHRF establishment
in Brazil. International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen,Denmark, 2018.
Erol B., Serkan Işık M.: Methodology Assessment of High Resolution Geoid Modeling Using The GRAV-D Data
Over Colorado. International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018),
Copenhagen, Denmark, 2018.
Gerlach C., Gruber Th., Rummel R.: Höhensysteme der nächsten Generation; in: Freeden, W.; Rummel, R. (eds.)
Handbuch der Geodäsie, Vol. 2016, Springer, ISBN (Online) 978-3-662-46900-2, DOI: 10.1007/978-3-66246900-2_7-1, 2016.
Grigoriadis V.N., Vergos G.S., Natsiopoulos D.A.: Geoid/Quasi-geoid modeling based on the remove-restore
approach with the JWG2.2.2 Colorado dataset and contributions to the IHRF. International Symposium on
Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018.
Gruber Th., Willberg M., Pfaffenzeller N.: Geodetic Space Sensors for Height System Unification and Absolute
Sea Level Determination. International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018),
Copenhagen, Denmark, 2018.
Gruber Th.: Geodetic space sensors for height system unification and absolute sea level determination. Fourth
Swarm Science Meeting & Geodetic Missions Workshop, Banff, Canada, 2017-03-22.
Gruber Th.: GOCE and Heights - How does the 3rd Coordinate benefit from it? ESA Living Planet Symposium
2016, Prag, Czech Republic, 2016-05-11.
Ihde J., Sánchez L., Barzaghi R., Drewes H., Foerste Ch., Gruber Th., Liebsch G., Marti U., Pail R., Sideris M.:
Definition and proposed realization of the International Height Reference System (IHRS). Surveys inGeophysics, 10.1007/s10712-017-9409-3, 2017.
Ihde J., Sánchez L.: Physical Height and the GGRF, Earth Gravity Field and the GGRF, GGRF an Integrated
Approach. GGOS Days 2015, Frankfurt a.M., Germany, 2015-10-22.
Mäkinen J.: The permanent tide revisited. International Symposium on Gravity, Geoid and Height Systems 2016
(GGHS2016), Thessaloniki, Greece., 2016.
Mäkinen J.: The permanent tide and the International Height Reference System IHRS. Joint Scientific Assemblyof the International Association of Geodesy and the International Association of Seismology and Physics ofthe Earth’s Interior (IAG-IASPEI 2017), Kobe, Japan, 2017.
Mäkinen J.: Treatment of the permanent tide in the Global Geodetic Observing System. EGU General Assembly
2018, Vienna, Austria. Geophysical Research Abstracts, Vol. 20, EGU2018-12672, 2018.
Mäkinen J.: The permanent tide in the International Height Reference System IHRS. International Symposium on
Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018.
Marti U., Sánchez L.: Le système de référence altimétrique global. Commission Géopositionnement, Conseil
national de l’information géographique, Paris, France, 2017-03-15.
Nicacio E.L., Carrión J.L., de Freitas S.R.C., Dalazoana R., Ferreira V.G.: Strategy for calculating local potential
values as IHRS coordinates – a case study on the Colorado empirical experiment. International Symposium on
Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018.
Oshchepkov I.: Geodetic reference system consistent with the IHRF W0 value. International Symposium on
Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018.
Sánchez L., Čunderlík R., Dayoub N., Mikula K., Minarechová Z., Šíma Z., Vatrt V., Vojtíšková M.: A
conventional value for the geoid reference potential W0. Journal of Geodesy 90(9), 815-835, 10.1007/s00190016-0913-x, 2016.
Sánchez L., de Freitas S.R.C, Martínez W., Mackern M.V., Cioce V., Pérez-Rodino R.: Advances in themodernisation of the height reference systems in Latin America and their integration to the International Height
Reference System (IHRS). International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018),
Copenhagen, Denmark, 2018.
Sánchez L., Ihde J., Pail R., Barzaghi R., Marti U., Ågren J., Sideris M., Novák P.: Strategy for the Realization of
the International Height Reference System (IHRS). GGHS2016: International Symposium on Gravity, Geoid
and Height Systems 2016, Thessaloniki, Greece, 2016-09-22.
Sánchez L., Ihde J., Pail R., Gruber Th., Barzaghi R., Marti U., Ågren J., Sideris M., Novák P.: Towards a firstrealization of the International Height Reference System (IHRS). European Geosciences Union General
Assembly 2017, Vienna, Austria, 2017-04-25.

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Sánchez L., Martí U., Ihde J.: Le chemin vers un système de référence altimétrique global et unifié. Association
Française de Topographie, Revue XYZ 150: 61-67, 2017.
Sánchez L., Sideris M.G.: Vertical datum unification for the International Height Reference System (IHRS).
Geophysical Journal International 209(2), 570-586, 10.1093/gji/ggx025, 2017.
Sánchez L., Sideris M.G.: Vertical datum unification for the International Height Reference System (IHRS).
International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark,
2018.
Sánchez L., Sideris M.G.: Vertical datum unification for the International Height Reference System (IHRS).
European Geosciences Union General Assembly 2017, Vienna, Austria, 2017-04-27.
Sánchez L.: GGOS Focus Area 1: Unified Height System: Present activities, GGOS Coordinating Board Meeting,
TU Vienna, Vienna, Austria, 2016-04-16.
Sánchez L.: Working Group on the Strategy for the Realization of the International Height Reference System(IHRS): Brainstorming and definition of action items. Splinter meeting at the International Symposium on
Gravity, Geoid and Height Systems 2016, 2016-09-21.
Sánchez, L. International Height Reference System (IHRS): Required measurements and expected products.
GGOS Days 2016, Cambridge (MA), USA, 2016-10-26.
Slobbe D.C., Klees R., Verlaan M., Zijl F., Farahani H.H.: Height system connection between island and mainlandusing a hydrodynamic model: a case study connecting the Dutch Wadden islands to the Amsterdam ordnancedatum (NAP). International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018),
Copenhagen, Denmark, 2018.
Wang Y.M., Li X., Ahlgren K.: NGS Geoid computation experiment in Colorado. International Symposium on
Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018.
Willberg M., Gruber Th., Pail R.: Geoid Requirements for Height Systems and their Unification; Fourth Swarm
Science Meeting & Geodetic Missions Workshop, Banff, Canada, 2017-03-22.
Willberg M., Gruber Th., Vergos G.: Height systems in Greece and its islands - some experimental results.
GGHS2016: International Symposium on Gravity, Geoid and Height Systems 2016, Thessaloniki, Greece,
2016-09-21.
Willberg M., Zingerle Ph., Pail R.: Least squares collocation with global model information for height systems.
International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark,2018.

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GGOS Focus Area “Geohazards”
Chair: John LaBrecque (USA)
Geohazards Focus Area Representative to GGOS Science Panel: Dr. Diego Melgar (USA)The Geohazards Monitoring Focus Area (GFA) will apply geodetic science, technology, andinfrastructure to mitigate natural hazards and improve disaster response. Following thedevastating losses of the past two decades and the apparent short comings of available early
warning systems the Geohazards Focus Area (GFA) determined that it would focus theapplication of geodetic techniques upon the improvement of tsunami warning. The publicationof significant advances in real-time technology and analysis laid a compelling case for the
implementation of this geodetic capability.
The GFA formally began its first initiative with the April 1, 2016 release of a Call for
Participation (CfP) to the GNSS Augmentation to the Tsunami Early Warning Systems(GATEW)(http://kb.igs.org/hc/en-us/articles/218259648-Call-for-Participation-GNSSAugmentation-to-the-Tsunami-Early-Warning-System). The GATEW CfP identifies theformal recommendations by the IGS, IUGG, IOC, and the APSG that support the CfP. The
GATEW initiative will advance and implement the Resolution #4 of the IUGG 2015 General
Assembly. The GATEW will build upon the benefits of the IGS Real Time Service (GPSRT)
and the Multi-GNSS Experiment (MGEX) within the context of the UN-GGIM program.

Resolution 4: Real-Time GNSS Augmentation of the Tsunami Early Warning System( http://www.iugg.org/resolutions/IUGGResolutions2015.pdf ):The International Union of Geodesy and Geophysics
Considering− That large populations may be impacted by tsunamis generated by megathrustearthquakes,− That among existing global real-time observational infrastructure, the Global
Navigation Satellite Systems (GNSS) can enhance the existing tsunami early warning
systems,
Acknowledging− The need to coordinate with the UNESCO Intergovernmental Oceanographic
Commission (IOC) and the established intergovernmental coordination framework to
define GNSS network requirements, data sharing agreements and a roadmap for thedevelopment and integration of the GNSS tsunami early warning augmentation.
Urges− Operational agencies to exploit fully the real-time GNSS capability to augment andimprove the accuracy and timeliness of their early warning systems,− That the GNSS real-time infrastructure be strengthened,− That appropriate agreements be established for the sharing of real-time GNSS data
within the tsunami early warning systems,− Continued support for analysis and production of operational warning products,

Global Geodetic Observing System (GGOS)

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Resolves− To engage with IUGG member states to promote a GNSS augmentation to the existingtsunami early warning systems.
− Initially to focus upon the Pacific region because the high frequency of tsunami events
constitutes a large risk to the region’s large populations and economies, by developing
a prototype system, together with stakeholders, including scientific, operational, andemergency responders.
The GATEW CfP was distributed to the Earth science and disaster management agencies andinstitutions of more than 16 countries. The UN-GGIM-AP Secretariat distributed the GGOSGATEW CfP to the UN-GGIM membership. The GATEW working group currently comprises
17 agencies and institutions from 11 countries. The agencies and institutions of the GATEW
working group are actively involved in the development of GNSS infrastructure, analysis, anddisaster preparedness. The GATEW working group is a catalyst and motivating force for thedefinition of requirements, identification of resources, and for the encouragement ofinternational cooperation in the establishment, advancement, and utilization of GNSS for
Tsunami Early Warning. The GATEW CfP and registration to the GATEW working groupremains open.
GATEW online library:
The GATEW maintains a library containing relevant documents, presentations, newsletters,
videos and other files of interest to the GATEW community at the following link
https://www.dropbox.com/sh/fg20mtydg136vx6/AABNr2kSnMo429nCxEHhBDfoa?dl=0 .
The GFA will shift these files to the GGOS.org website when the appropriate GGOS web pageis fully implemented.
The GFA initiated this first initiative with a program to inform influential organizations of theimportant contributions that real time GNSS analysis brings to effective and efficient tsunami
warning systems. These efforts included presentations at significant scientific andgovernmental meetings.
The GATEW CfP called upon the community of agencies and institutions to join the GATEW
working group to support and promote GNSS Augmentation to Tsunami Early Warning system
as recommended by Resolution #4 of the 2015 IUGG General Assembly.

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Global Geodetic Observing System (GGOS)

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Presentations on GATEW were made at the following meetings:
2014, June 23-27, IGS Workshop 2014 , Pasadena, CA. http://kb.igs.org/hc/en-us/articles/204125433-2014-IGS
Workshop-Summary-Recommendations
2015, June-22-July 2, IUGG-2015 Prague, Czech Republic
2015, August 10-15 , 9th ACES International Workshop, Chengdu, China
2015, August 24-28, Asia-Pacific Space Geodynamics Project-2015 Moscow, Russia,
http://agora.guru.ru/display.php?conf=apsg-2015&page=program
2015, November 1-6, International Committee on GNSS-10, Boulder, US
2015, December 1-4, Asia-Pacific Regional Space Agency Forum (APRSAF 22) Bali, Indonesia
2015, December 14-18, AGU Fall Meeting, Session#8328 Global Naviga6on Satellite System for Natural Hazard
Mitigation- Invited Talk, San Francisco, US
2016, February 8-12, International GNSS Service Workshop (IGS-2016) Sydney, NSW, Australia
http://kb.igs.org/hc/en-us/articles/205944657-2016-IGS-Workshop-Information
2016, November 6-11, International Committee on GNSS-11, Sochi, Russia
2016, April 17-22, European Geosciences Union General Assembly-2016, Vienna, Austria
2016, May 3-5, COCONet Workshop, Punta Cana, Dominican Republic
2016, September 29 – October 1, Subduction Zone Observatory Workshop, Boise, US
2016, November 14-16, 8th Multi-GNSS Asia (MGA) Conference, Manila, Phillipines
2017, April 23-28, European Geosciences Union General Assembly-2017, Vienna, Austria
2017, July 3-7, 2017 IGS workshop 2017, Paris, http://kb.igs.org/hc/en-us/articles/216574478-2017-IGSWorkshop-Information
2017, July 25-26 GTEWS 2017 Workshop, Sendai, Japan
2017, July 29-30, UNGGIM TECHNICAL SEMINAR REFERENCE FRAME IN PRACTICE, Kobe, Japan
2017, July 30-Aug 4, IAG-IASPEI General Assembly and UN-GGIM-AP meeting in Kobe, Japan.
2017, August 15-18, Asia-Pacific Space Geodynamics Project-2017, Shanghai, China
http://english.shao.cas.cn/rh/ca/201705/t20170502_176593.html
2017, December 11-15, AGU Fall Meeting, Gilbert F. White Distinguished Lecture, New Orleans, US
2018, June 18, IX Hotine-Marussi Symposium, LaBrecque J, Crespi M: GGOS Focus Area on Geohazards
Monitoring – The role of real-time GNSS data processing, Rome, Italy
2018, December 10-14, AGU Fall Meeting, Washington, DC, US
2019, April 4-11, Institute of Navigation Pacific PNT Conference, Honolulu, Hawaii, US

GTEWS 2017: the 1st Meeting of the GATEW:The GATEW Working Group held its first meeting in Sendai Japan as part of the GTEWS 2017
workshop July 25-27, 2017. The GGOS Geohazards Focus Area collaborated with NASA, theAssociation of Pacific Rim Universities (APRU) and the International Research Institute ofDisaster Science (IRIDeS) of Tohoku University in support of the GTEWS 2017 workshop.
42 Participants reviewed the status and made recommendations on the development of a GNSS
enhanced Tsunami Early Warning System as recommended by Resolution #4 of the IUGG 2015
General Assembly. Over 90% of the GATEW organizations registered for GTEWS2017 andGATEW provided a majority of the presentations.

GTEWS Publications:
The GFA assumed leadership in the assembly and publication of the findings of the GTEWS
2017. The GTEWS workshop report containing video and presentations of the proceedings andworkshop recommendations is available on the website of the APRU
(http://apru.org/resource/gnss-early-warning-report/) and within the GFA online libraryhttps://www.dropbox.com/s/zo4frdmsqis9scf/GTEWS2017.pdf?dl=0 .
The UNISDR has accepted an updated report of the GTEWS 2017 initiative for its GAR19
publication. The UN Global Assessment Report on Disaster Risk Reduction (GAR) is theReport of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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flagship report of the United Nations on worldwide efforts to reduce disaster risk. The GAR ispublished biennially by the UN Office for Disaster Risk Reduction (UNISDR), and is the
product of the contributions of nations, public and private disaster risk-related science andresearch, amongst others. GAR19 report is available at this site https://gar.unisdr.org/. A copyof the updated GTEWS report is also available at the GFA online libraryhttps://www.dropbox.com/s/15rnypek9vqacp4/Global%20Navigation%20Satellite%20System%20Enhancement%20for%20Tsunami%20Early%20Warning%20Systems.pdf?dl=0.

Recommendations of the GTEWS 2017 report
1. The GGOS/IUGG, APRU and the UN-GGIM are encouraged coordinate efforts to develop a
GNSS Shield Consortium for the Indo-Pacific.
2. The GNSS Shield Consortium should work to encourage software, data exchange, andcontinued improvement of network design and performance.
3. Strengthen broadband communication to underserved regions of the GNSS Shield.
4. Work with national organizations including those mandated for natural hazards mitigation todevelop agreements for inclusion of their GNSS receivers within the GNSS Shield.
5. Design an optimal GNSS Shield network for both crustal displacement and high-resolution TEC
monitoring.
6. Understand the operational requirements of existing tsunami warning systems and determine
the steps required to interface these tsunami warning systems.

Future Actions and Milestones:

The GFA and the GATEW working group will work to develop the recommendationsof the GTEWS 2017 workshop.
o The READI Group has submitted a proposal to fund a cloud based GTEWS
analysis system available to all national prototype GTEWS networks as
proposed. (Action on Recommendation 2)
o The GFA will undertake an effort to work with global Internet Service Providers
to increase the participation of identified real-time GNSS stations with the
GNSS Shield. (Action on Recommendation 3)
o Wuhan University is in discussions to provide real-time GNSS distribution
software to one or more of the national prototype networks to advance real-timedata sharing. (Action on Recommendation 4)



The Geohazards Focus Area recommends changing the status of GATEW to a Standing
Committee for GNSS Enhancement of Tsunami Early Warning (GATEW). We expectthat the GATEW standing committee will become increasingly important as the IndoPacific begins to integrate the several prototype GNSS early warning networks into an
Indo-Pacific real time network.



Expand the membership and influence of the GATEW standing committee.

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GGOS Focus Area “Sea-Level Change, Variability and Forecasting”
Chair:
Co-Chairs:

Tilo Schöne (Germany)
CK Shum (USA), Mark Tamisiea (UK), Phil Woodworth (UK)

Purpose and Scope
Sea level rise and its impact on human habitats and economic well being have received
considerable attention in recent years by the general public, engineers, and policy makers. A
GGOS retreat in 2010 has identified sea level change as one of the cross-disciplinary themes
for geodesy. Sea Level is also a major aspect in other observing systems, like e.g. GEO or
GCOS. The primary focus of GGOS Focus Area 3 is to demonstrate and apply geodetic
techniques, under the umbrella of GGOS, to the possible mitigation or adaption of sea level risehazards including studies of the impacts of its change over the world’s coastal and deltaic
regions and islands, and to support practical applications such as sustainability. One major topic
is the identification of gaps in geodetic observing techniques and to advocate enhancements to
the GGOS monitoring network and Services where necessary.
Activities and Actions
Focus Area 3 has identified actions to be undertaken to advance geodetic techniques andtechnologies applied to sea level research. These are Identification or (re)-definition of the requirements for a proper understanding of global andregional/local sea-level rise and its variability especially in so far as they relate to geodetic
monitoring provided by the GGOS infrastructure, and their current links to externalorganizations (e.g., GEO, CEOS, and other observing systems).
 Identification of organizations or individuals who can take forward each requirement, or act
as points of contact for each requirement, where they are primarily the responsibility ofbodies not related to GGOS.
 Identification of a preliminary set of practical or application (as opposed to scientific) pilot
projects, which will demonstrate the viability, and the importance of geodetic measurements
to mitigation of sea-level rise at a local or regional level. This identification will be followedby construction of proposals for pilot projects and their undertaking.
In the long-term, the aim is to support forecasting of global and regional sea level for the 21st
century with an expected forecast period of 20 to 30 years or longer.
An open Call for Participation was issued in 2012. Special emphasis is given to local andregional projects which are relevant to coastal communities, and which depend on the global
perspective of GGOS. Three projects have been accepted. Thus, GGOS Focus Area 3 now has
approved “Landmark” projects:
The Use of Continuous GPS and Absolute Gravimetry for Sea Level Science in the UK (NERC
British Isles continuous GNSS Facility (BIGF), University of Nottingham, UK), (NERC
National Oceanography Centre (NOC), Liverpool, UK).
Revisiting the Threat of Southeast Asian Relative Sea Level Rise by Multi-Disciplinary
Research (Delft University of Technology (DUT), Delft, Netherlands; University of Leeds,
Leeds, United Kingdom; Ecole Normale Supérieure, Paris, France; Chulalongkorn
University, Bangkok, Thailand; Royal Netherlands Meteorological Institute (KNMI), De
Bilt, Netherlands)

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Bangladesh Delta Relative Sea-Level Rise Hazard Assessment (Division of Geodetic Science,
School of Earth Sciences, The Ohio State University, Columbus, Ohio, USA; University ofBonn, Bonn, Germany; GeoForschungsZentrum Potsdam (GFZ), Germany)
and additionally
Subsidence Monitoring in Urban Areas of the Republic of Indonesia with GNSS-controlled tidegauges and supporting methods (National Geospatial Agency (BIG) of Indonesia; Helmholtz
Centre Potsdam GFZ, Germany; Institut Teknologi Bandung, Indonesia) together with the
University of Cologne working on social aspects,
which is in preparation for submission.
All projects have their major focus on the combination of sea level and geodetic monitoring in
an integrative approach. Also in the reporting period, Focus Area 3 continued communications
with organizations, dealing with other than geodetic aspects of sea level monitoring. These are,e.g., the UNESCO International Oceanographic Commission Group of Experts (UNESCO/IOC
GE) and the World Glacier Monitoring Service (WGMS). In Germany in 2016 a special
research program (SPP 1889 - Regional Sea Level Change and Society, www.spp-sealevel.de)
started and is dealing with many aspects relevant to GGOS Focus Area 3. Also cooperation
with the IGS Tide Gauge Benchmark Monitoring Working is continued. A major step for
GGOS Focus Area 3 was the alignment of its activities with the GGOS Bureau of Networks
and Observations (B&O). The improvement of the observation network for sea level research
is a major open topic. In 2015, the GLOSS Group of Experts (GLOSS-GE), the IGS TIGA-WG
and the GGOS Focus Area 3 had submitted the Report "Priorities for installation of continuous
Global Navigation Satellite System (GNSS) near to tide gauges" for consideration by GGOS.
This report is now accepted by the GGOS CB and the GGOS B&O.
The GNSS-controlled tide gauges are an important monitoring component in climate andgeodetic science. Over the years, the network of collocated stations has been growing, not atleast through the constant effort of IOC/GLOSS Group of Experts, the IGS TIGA-WG, and
GGOS. Focus Area 3 plays a significant role in improving the network coverage and theestablishment of local ties between GNSS and tide gauges.
Objectives and Planned Efforts for 2017-2019 and Beyond
 Review and Refine current and future aspects of geodetic contributions for sea level researchwith groups identified in AS-SL-01/AS-SO-02
 Work on to identify and contact emerging Focus Area 3 pilot projects
 Support Focus Area 3 projects
 Establish/improve the outreach activities with the help of the GGOS-CO Work with IGS/TIGA on results of the TIGA reprocessing Work with GGOS CB and GGOS B&O on the findings of the report "Priorities for
installation of continuous Global Navigation Satellite System (GNSS) near to tide gauges"
 Identify geodetic monitoring aspects relevant to Focus Area 3
 Maintain the GGOS web space for the Focus Area 3.
Websitehttp://www.ggos.org/en/focus-areas/sea-level-change-variability-and-forecasting/Global Geodetic Observing System (GGOS)

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Publications and Presentations
Woodworth, P., Aarup, T., Gaël, A., Donato, V., Enet, S., Edwing, R., Heitsenrether, R., Farre, R., Fierro, J.,
Gaete, J., Foden, P., Pugh, J., Perez, B., Rickards, L., Schöne, T. (Eds.)(2016):Manual on Sea-level
Measurements and Interpretation, Volume V: Radar Gauges, (IOC Manuals and Guides ; 14) (JCOMM
Technical Report ; No. 89), Paris : Intergovernmental Oceanographic Commission of UNESCO, 2016
Michael R. Pearlman, Chopo Ma, Ruth Neilan, Carey Noll, Erricos Pavlis, Jérôme Saunier, Tilo Schoene, Riccardo
Barzaghi, Daniela Thaller, Sten Bergstrand, and Juergen Mueller: The GGOS Bureau of Networks andObservations: an update on the Space Geodesy Network and the New Implementation Plan for 2017 18,Geophysical Research Abstracts, Vol. XX, General Assembly European Geosciences Union (Vienna 2017),
http://meetingorganizer.copernicus.org/EGU2017/EGU2017-10814.pdf
Schöne, T., Shum, C., Tamisiea, M., Woodworth, P. (2015): GGOS Theme 3: Understanding and Forecasting SeaLevel Rise and Variability - Scientific programme, 26th IUGG General Assembly (Prague 2015).
http://gfzpublic.gfzpotsdam.de/pubman/item/escidoc:1437893:5/component/escidoc:1437892/GGOS_Theme3
Tilo Schöne, Ck Shum, Mark Tamisiea, and Philip Woodworth: GGOS Focus Area 3: Understanding and
Forecasting Sea-Level Rise and Variability, Geophysical Research Abstracts, General Assembly European
Geosciences Union (Vienna 2017), http://meetingorganizer.copernicus.org/EGU2017/EGU2017-8814.pdf
Tilo Schöne, Ck Shum, Mark Tamisiea, and Philip Woodworth: GGOS Focus Area 3: Understanding and
Forecasting Sea-Level Rise and Variability, 10th GEO European Projects Workshop 2016, Berlin, 31.5.2.6.2016, https://ec.europa.eu/easme/en/geo-european-projects-workshop-2016

Report of the IAG Vol. 41 ─ Travaux de l’AIG 2015-2019

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GGOS Focus Area “Geodetic Space Weather Research”
Chair: Michael Schmidt (Germany)
Vice-Chair: Klaus Börger (Germany)
Members:
 Andres Calabia Aibar (Spain) Fabricio dos Santos Prol (Bazil)
 Ehsan Forootan (Iran)

Purpose and Scope
The issue “Space Weather” is an interdisciplinary field of research, where the subject geodesy
contributes essentially by its expertise on ionosphere and thermosphere. The Focus Area on“Geodetic Space Weather Research” concentrates on the upper atmosphere, i.e. thecompartments ionosphere and thermosphere, being original manifestations of space weather.
Thus, in a nutshell, the main objectives of the Focus Area are (1) the development of improved
ionosphere models and (2) the development of improved thermosphere models.
Objective (1) aims at the high-precision as well as the high-resolution (spatial and temporal)modeling of the electron density. This finally allows to compute a signal propagation delay,
which can be used for different geodetic applications, in particular for “positioning, navigationand timing (PNT)”. Moreover, it is also important for other techniques using electromagnetic
waves, such as satellite- or radio-communications. Concerning objective (2), satellite geodesy
will obviously benefit when working on “precise orbit determination (POD)”, but there arefurther technical matters like the “collision analysis” or the “re-entry calculation”, which will
become more reliable when using high quality thermosphere models.
For a “Geodetic Space Weather Research”, geodesy has to extend its traditional perspective on
thermosphere and ionosphere, i.e. geodesy has to move away from the limited concept ofregarding the atmosphere as only being a disturbing effect affecting electromagnetic waves.
“Geodetic Space Weather Research” has to take into account the complete chain of cause andeffect, which means it has to start with processes and events on the Sun. Next, it has to continue
with the effects on the geosphere and finally it has to consider the impact on (geodetic)
applications and systems. Besides this general chain of cause and effect interactions, the physics
and especially coupling processes between thermosphere and ionosphere have to be regarded.
Geodetic Space Weather Research is “fundamental research” too, particularly when intending
to detect and to survey structures of the ionosphere, e.g. bubbles, or when proving special
phenomena like electrojets. Summarized, geodetic space weather research has to be based ona) the use and combination of all space geodetic observation methods, b) the use of sun
observations, c) real-time modeling, d) the development of deterministic and stochastic forecast
approaches and e) assimilation strategies.
Finally, it should be mentioned that the work within the proposed Focus Area will be carriedout in close relation to the International Association of Geomagnetism and Aeronomy (IAGA),
since this organisation is also concerned with the understanding of properties related, e.g. to theionosphere and magnetosphere as well as the Sun and the solar wind.

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Activities during the period 2017-2019
Four new GGOS Joint Study Group (JSG) and Joint Working Groups (JWG) have to beinstalled into the IAG structure within the 4-year period 2019 to 2023. These are
JSG 1:JWG 1:JWG 2:JWG 3:

Coupling processes between thermosphere and ionosphere (implemented
within the IAG ICCT and joint with GGOS)Electron density modelling (joint with IAG Commission 4)
Improvement of thermosphere models (joint with IAG Commission 4)
Improved understanding of space weather events and their monitoring bysatellite missions (joint with IAG Commission 4).

The chair positions of JWG 2 and JWG 3 are still vacant. Appropriate candidates have been
selected and approached, but they not yet confirmed their commitment. Ehsan Forootan(Institute of Physics and Meteorology, University of Hohenheim, Stuttgart, Germany) became
member of the GGOS Science Panel.
During the last two years, the work and the activities of the Focus Area were presented at
different meetings, see section “Presentations”.
Next actions of the Focus Area are:

to find the chairs of JSG 1 and JWG 1
to find the members of the JSG/JWGs andto set up the Terms of Reference of the JSG/JWGs.

In the following IAG four-year period the Focus Area will mainly work on the following three
aspects:
 extensive simulation studies have to be performed in order to assess the impact of space
weather on technical systems and to define – as a consequence – necessary actions in caseof severe space weather events
 development of ionosphere and thermosphere models as stated above as GGOS products
for direct application
 establishment of recommendations for applications of the models, e.g. in satellite orbit
determination, collision analysis and re-entry computations.
Websitehttp://www.ggos.org/en/focus-areas/geodetic-space-weather-researchPresentations
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poster presentation at the GEO WEEK 2017 in Washington D.C., October 23 to 27, 2017
poster presentation at the EGU 2018 in Vienna, GGOS Session, April 10, 2018
poster presentation at the IX Hotine-Marussi Symposium in Rome in June 18 to 22, 2018
poster presentation at the EGU 2019 in Vienna, GGOS Session, April 9, 2019
poster presentation at the ESA Living Planet Symposium in Milan, May 13 to 17, 2019