Global Geodetic Observing System (GGOS)

Global Geodetic Observing System
https://www.ggos.org
President: Basara Miyahara (Japan)
Vice President: Laura Sánchez (Germany)
As the observing system of the IAG, the Global Geodetic Observing System (GGOS) facilitatesa unique and essential combination of roles focused on advocacy, integration, and external
relations with affine Earth science disciplines and general stakeholders. The IAG charged
GGOS to provide the observations needed to monitor, map, and understand changes in the
Earth’s shape, rotation, and mass distribution, to provide the global geodetic frame of reference
for the measurement and consistent interpretation of key global change processes and for manyother scientific and societal applications, and to benefit science and society by providing thefoundation upon which advances in Earth and planetary system science and applications arebuilt. To accomplish its mission, GGOS develops and maintains working relationships with theother IAG components and a variety of external groups and organizations.

GGOS Structure
The structure of GGOS is shown in Figure 1. The decision-making bodies are the Consortiumand the Coordinating Board. The GGOS Executive Committee is responsible for the day-today activities necessary to carry out the mandate given by the decision-making bodies.
Permanent Standing Committees and limited-term Working Groups are the thematic working
bodies of GGOS and are distributed over two Bureaus, the Science Panel, and the Focus Areas.
The GGOS Coordinating Office serves as the Secretariat of GGOS and carries out theadministrative work as directed by the decision-making bodies and the Executive Committee.
The work of the Coordinating Office includes communications, outreach, external relations andthe maintenance and enhancement of the GGOS website and social media presence.

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Report of the IAG Vol. 43 ─ Travaux de l’AIG 2019-2023

Figure 1. Organization chart of GGOS.

Overview
GGOS renewed its structure in 2019 including the election of new President and Vice President
and the restructuring of the GGOS Consortium and GGOS Coordinating Board. A Working
Group on "DOIs for Geodetic Data Sets" was established within the GGOS Coordinating
Office. The Working Group on "ITRS Standards for ISO TC 211" completed its work and was
dissolved with successful contribution to ISO 19161-1. The Working Group on "Establishmentof the Global Geodetic Reference Frame (GGRF)" was renewed and renamed to Working
Group on "Towards a consistent set of parameters for the definition of a new GRS" andcontinues to work on the challenge to define a new Geodetic Reference System (GRS). The
GGOS Focus Area "Sea Level Change" was terminated in 2019.
The GGOS Bureau of Products and Standards (BPS) published a 2nd updated version of the
BPS inventory in the Geodesist's Handbook 2020 to compile and refine a registry of standards
and conventions used for the generation of IAG products.
The GGOS Focus Area “Unified Height System” defined a strategy for the implementation of
the International Height Reference Frame (IHRF) and is currently working in the firstcomputation of the IHRF. The IHRF operational coordination center will be launched in the
coming year under the responsibility of the International Gravity Field Service (IGFS) and this
Focus Area will be terminated at the IUGG2023 General Assembly. The Focus Area
“Geohazards” played a central role in the development of the initiative “GNSS enhancement totsunami early warning systems (GTEWS)” and presently is supporting the creation of the
GTEWS Consortium within the Community Activity “Geodesy for the Sendai Framework” of
the Group on Earth Observations (GEO). This Focus Area has started to work in Oceania andestablished GTEWS Oceania as practical implementation of the system in the region. The Focus
Area “Geodetic Space Weather Research” identified four central challenges and establishedfour dedicated working groups. In addition to these three Focus Areas, a new Focus Area
“Artificial Intelligence (AI) for Geodesy” has been established in May 2023 and will mainly
work on three study areas: GNSS remote sensing, gravity field and mass changes, and Earthorientation parameter prediction.
As a mechanism to increase participation in GGOS, the second of two GGOS Affiliates wasestablished in 2021. GGOS D-A-CH is a regional affiliate group of the German-speaking
countries: D (Germany), A (Austria) and CH (Switzerland). GGOS D-A-CH is the result of astrong cooperation between the national geodetic commissions of these countries and wasdeveloped on the basis of the strategic white paper “Geodesy 2030” (Müller, Pail et al., 2019,https://doi.org/10.12902/zfv-0243-2018). Its founding chair is Hansjörg Kutterer of the
Karlsruhe Institute of Technology, a former GGOS President. GGOS D-A-CH has formulated
its Terms of Reference with a clear focus on strategic topics in GGOS-related science. A next
GGOS Affiliate is planned to be established by Spanish and Portuguese colleagues: GGOS
Iberoatlantic. It aims to enhance participation in GGOS from counties around the Atlantic,
including African and South American countries. GGOS Iberoatlantic has been officiallyadopted by the Spanish Geodetic Commission and is currently under discussion by Portuguese
colleagues.
Web and Social Media PresenceGlobal Geodetic Observing System (GGOS)

One of the main focus of GGOS during the period 2019-2023 was devoted to outreach andcommunication. GGOS completely renewed its website (https://www.ggos.org). The new
website highlights the dual roles of GGOS: one as an organization to foster collaboration within
the IAG and among stakeholders, and the other as the IAG’s geodetic observing system,
supporting science and society as a fundamental infrastructure for monitoring the Earth. In the
new website, the IAG Services are brought to the forefront to make them more visible and toprovide easier access to their Internet portals. The new GGOS site also provides detailed
descriptions and data registries of geodetic observations and products. These web components
present the role and importance of geodesy, its observing techniques and products to nongeodesists with plain text and brief explanations, as well as eye-catching visual aids. This
information is complemented by links to background articles on geodesy that can help nongeodesists to understand what geodesy is and why geodesy it is important to science and society.
Another new fundamental tool is the repository of key documents in the GGOS Cloud(https://cloud.ggos.org), which enables us to share the GGOS related materials such as Termsof Reference, reports, papers and presentations and ensures their long-term availability.
Recently, GGOS has started to develop the GGOS-Portal. The GGOS-Portal aims to serve as acomprehensive search and access point for geodetic data and products (one-stop shop) by
combining easy-to-understand descriptions of products and observation techniques withcomplete source descriptions and detailed metadata. To this end, GGOS conducted a survey thegeodetic and affine communities from March to April 2023 to gauge the opinions of geodetic
data users on data availability and visibility and to identify requirements for a comprehensive
and user-friendly GGOS Portal. The results are being analyzed and will be utilized for thedesign of the Portal.

External relations and Digital Object Identifiers
GGOS also continued to strengthen and expand its external relations and stakeholder
engagement. Continued participation in GEO included the establishment of a Geodesy
Advocacy Community Activity within GEO entitled “Geodesy for the Sendai Framework”, aswell as continued and diverse participation in the GEO Programme Board. GGOS also
continues to strongly support the actions and initiatives of the UN GGIM Subcommittee on
Geodesy, and has extended this support to the UN Global Geodetic Centre of Excellence newly
established on March 29, 2023 in the UN Campus in Bonn, Germany.
In addition to external advocacy, GGOS routinely looks inward to identify the best ways to cite
and track the impact of the geodetic data, products, and other resources provided by the IAG
and its Services. At the 2019 Unified Analysis Workshop, Digital Object Identifiers (DOIs)
were discussed as a unique and unambiguous identifier for data as well as publications. DOIs
are already widely used by publishers, and their implementation for data sets is expected to bebeneficial for both users and data providers. The Working Group on DOIs is chaired by Kirsten
Elger of GFZ Potsdam and is composed of more than 20 colleagues, mainly from IAG Services.
The WG analyzed use cases and best practices in geodesy and other scientific fields, and has
been compiling recommendations directed to establish parameters and procedures for properly
assigning DOIs to GNSS data, as the first example. Once the best procedure is identified, it will
be extended to the other geodetic data sets.
Towards a new GGOS Strategic Plan
The current GGOS Strategic Plan was released in 2014. Given the advances in Geodesy andReport of the IAG Vol. 43 ─ Travaux de l’AIG 2019-2023

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recent developments within the IAG, it became necessary to revise and update the GGOS
Strategic Plan to meet new demands from the global geodetic community. With this purpose,
GGOS conducted a Strategy Plan Survey between July 11 and Sep 30, 2022. This survey
consisted of six closed questions (multiple choice of pre-given answers) and seven SWOT
(Strengths, Weaknesses, Opportunities, Threats) questions. Seventy colleagues from 32
countries answered the GGOS survey. 71% of them are involved in IAG and 34% involved in
the UN-GGIM’s Subcommittee of Geodesy (SCoG). The outcomes of the survey werediscussed at the GGOS Strategic Plan Workshop held in Munich, Germany in November 2022.
From these discussions, four strategic goals and 16 objectives were identified as the coreelements of the new GGOS Strategic Plan. This plan will be released after the IUGG2023
General Assembly after approval and endorsement by the GGOS Coordinating Board andconsultation with the IAG Executive Committee, respectively.
Another key recommendation arising from the Strategic Plan survey is to merge the GGOS
Consortium (steering and electoral committee) and the GGOS Coordinating Board (decisionmaking body) into one body as:1) The functions of both bodies can be performed by only one body,2) The involvement of all IAG components in the GGOS activities should be more visible, and
3) Having only one governing body would make decision-making within GGOS more efficient.

Accordingly, the GGOS Coordinating Board members were asked to vote for, against or abstain
on the proposal to merge the current GGOS Coordinating Board and the GGOS Consortium
into a single managing body called “GGOS Governing Board”. This proposal was approved by
89% of the members. As following step, the proposal was presented to the IAG Executive
Committee, whose members endorsed the decision of the GGOS Coordinating Board.
Currently, the GGOS Executive Committee is aligning the GGOS Terms of Reference with the
new Strategic Plan and governing body. Once the GGOS Coordinating Board and the IAG
Executive Committee have approved the new GGOS Terms of Reference, both the newStrategic Plan and the new structure will come into effect.

Consortium
The GGOS Consortium acts as the large steering committee and collective voice of GGOS andis 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 Terms of Reference, the Consortium membership is revised and renewed if necessary
every four years, coinciding with the IUGG General Assemblies. The members of the GGOS
Consortium for the term 2019–2023 are listed in Table 1.
The President of GGOS is the chair of the GGOS Consortium. The GGOS Consortium meetsannually. The meetings corresponding to the 2019–2023 term were held as follows:
1.
2.
3.
4.

GGOS Days 2019, Rio de Janeiro, Brazil, 12-14 November 2019
GGOS Days 2020, held virtually via Video Conference, 5-7 October 2020
GGOS Days 2021, held virtually via Video Conference, 11-13 October 2021
GGOS Days 2022, Munich, Germany, 14-15 November 2022

Global Geodetic Observing System (GGOS)

Table 1. Members of the GGOS Consortium (term 2019–2023)
Organization
Name
Title
GGOS
Basara Miyahara Chair
GGOS Affiliate: GGOS Japan
Yusuke Yokota
Designated GGOS Representative
GGOS Affiliate: GGOS D-A-CH
Markus Rothacher Designated GGOS Representative(2021-2023)
IAG Service Representatives
International Gravimetric Bureau
Sylvain Bonvalot Director(BGI)
Sean Bruinsma
Designated GGOS Representative
International Centre for Global Earth E. Sinem Ince
Designated GGOS Representative
Models (ICGEM)International DORIS Service (IDS) Laurent Soudarin Director, Central BureauFrank Lemoine
Chair, Governing Board
International Earth Rotation andDaniela Thaller
Director, Central Bureau
Reference Systems Service (IERS) Robert
Analysis Coordinator
Heinkelmann
International Service for Geoid (ISG) Urs Marti
Designated GGOS Representative
Jianliang Huang
Designated GGOS Representative
International Gravity Field Service Riccardo Barzaghi Chair(IGFS)
Georgios Vergos Director, Central Bureau
International GNSS Service (IGS)
Nicholas Brown
Designated GGOS Representative
Arturo Villiger
Designated GGOS Representative
The International Laser Ranging
Toshimichi Otsubo Chair, Governing Board
Service (ILRS)
Erricos Pavlis
Chair, Analysis Working GroupInternational VLBI Service for
Axel Nothnagel
Chair, Directing Board
Geodesy and Astrometry (IVS)
Dirk Behrend
Director, Coordinating Center
Permanent Service for Mean Seal
Elizabeth Bradshaw Director
Level (PSMSL)
Andy Matthews
Designated GGOS Representative
International Geodynamics and Earth Christoph Foerste Designated GGOS Representative
Tides Service (IGETS)
Hartmut Wziontek Designated GGOS Representative
International Digital Elevation Model Kevin M. Kelly
Director
Service (IDEMS)
Christian Hirt
Designated GGOS Representative
IAG Commissions Representatives
Commission 1: Reference Frames
Christopher
President
KotsakisTonie van Dam
Designated GGOS Representative
Commission 2: Gravity Field
Adrian Jäggi
President
Mirko Reguzzoni Vice President
Commission 3: Earth Rotation and Janusz Bogusz
President
Geodynamics
Chengli Huang
Vice President
Commission 4: Positioning andPaweł Wielgosz
President
Applications
Michael Schmidt Vice President
IAG Inter Commission Committee (ICC) Representatives
ICC on Theory (ICCT)Pavel Novák
President
Dimitrious Tsoulis Designated GGOS Representative
ICC on Climate Research (ICCC)
Anette Eicker
President
Carmen Boening Vice President
ICC on Marine Research (ICCM)
Yuanxi YANG
President
Heidrun Kopp
Designated GGOS RepresentativeReport of the IAG Vol. 43 ─ Travaux de l’AIG 2019-2023

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Coordinating Board
The Coordinating Board is the decision-making body of GGOS. The members of the GGOS
Coordinating Board in the term 2019–2023 are listed in Table 2.
The President of GGOS chairs the Coordinating Board. The Coordinating Board meets twiceper-year, usually during the GGOS Days and around the EGU. In the 2019-2023 term,
following meetings were held:
1.
2.
3.
4.
5.
6.
7.
8.

GGOS Days 2019, Rio de Janeiro, Brazil, 12-14 November 2019
GGOS CB Meeting, held virtually via Video Conference, 8 May 2020
GGOS Days 2020, held virtually via Video Conference, 5-7 October 2020
GGOS CB Meeting, held virtually via Video Conference, 7 May 2021
GGOS Days 2021, held virtually via Video Conference, 11-13 October 2021
GGOS CB Meeting, held virtually via Video Conference, 16 May 2022
GGOS Days 2022, Munich, Germany, 14-15 November 2022
GGOS CB Meeting, Vienna, Austria, 22 April 2023

Table 2. Members of the GGOS Coordinating Board (term 2019–2023)
Position
Voting Name
Chair
Yes
Basara Miyahara
Vice Chair
Yes
Laura Sánchez
Chair, Science Panel
Yes
Kosuke Heki
Director, Coordinating Office
Yes
Martin Sehnal
Manager, External Relations
Yes
Allison Craddock
Director, Bureau of Networks &Yes
Mike Pearlman
Observations
Director, Bureau of Products & Standards
Yes
Detlef Angermann
Representative, GGOS Affiliates
Yes
Toshimichi Otsubo
Yes
Hansjörg Kutterer (2021-2023)
Representative, IAG President
Yes
Zuheir Altamimi
Representative, IAG Services
Yes
Riccardo Barzaghi
Yes
Daniela Thaller
Yes
Sean Bruinsma
Yes
Robert Heinkelmann
Representative, IAG Commissions and ICC
YesTonie Van Dam
Yes
Adrian Jäggi
Member-at-Large
YesMaria Cristina Pacino (2019-2021)
Claudia Tocho (2021-2023)
Yes
Nicholas Brown
Yes
Ludwig Combrinck
GGOS Focus Area (FA) Leads
FA Unified Height System
No
Laura Sánchez
FA Geohazards
NoJohn LaBrecque
FA Geodetic Space Weather Research
No
Michael Schmidt
FA Artificial Intelligence for Geodesy
No
Benedikt Soja (May-July 2023)
GGOS Committee Chairs
Committee on Satellite and Space Missions
No
Roland Pail

Global Geodetic Observing System (GGOS)

Committee on Data and Information
No
Martin Sehnal (2019)
Systems
Nicholas Brown (2020-2023)
Committee on Contribution to Earth System
No
Maik Thomas
Modelling
Committee on PLATO (IAG WG)
No
Daniela Thaller
Committee on Essential Geodetic Variables
No
Richard Gross
GGOS Working Group Chairs
JWG: Ground Survey and Co-Location
No
Ryan Hippenstiel
JWG: Definition of a new GRS
No
Urs Marti
WG: DOIs for Geodetic Data Sets
No
Kirsten Elger
OthersManager, GGOS Web and Social MediaNo
Martin Sehnal
Immediate Past Chair of GGOS
No
Richard Gross
Executive Committee
The GGOS Executive Committee serves under the direction of the Coordinating Board toaccomplish the day-to-day business of GGOS. The members and guest observers of the
Executive Committee during 2019–2023 are listed in Table 3. The President of GGOS is the
Chair of the Executive Committee. The Executive Committee holds monthly conference calls
and meets face-to-face or virtual during the meetings of the Coordinating Board (see above).
Table 3. Members of the GGOS Executive Committee (term 2019–2023)
Position
Status Name
Chair
Member Basara Miyahara
Vice Chair
Member Laura Sánchez
Director, Coordinating OfficeMember Martin Sehnal
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 Adrian Jäggi
Immediate Past Chair of GGOS
Guest Richard Gross
Chair, Science Panel
Guest Kosuke Heki
Representative, IAG President
Guest Zuheir Altamimi

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GGOS Coordinating OfficeDirector:
Manager of External Relations:
Chair of WG on DOIs:

Martin Sehnal (Austria)
Allison Craddock (USA)Kirsten Elger (Germany)

Working Group (WG) affiliated with GGOS Coordinating Office:•

GGOS Working Group on “DOIs for Geodetic Data Sets”

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 the GGOS Executive Committee.
Activities and Actions
New Director of GGOS Coordinating Office
The director of the GGOS Coordinating Office changed in September 2019. Helmut Titz (BEV,
Austria) stepped down due to health issues and Martin Sehnal (BEV, Austria) followed himinterimistically and was finally approved by the BEV (Federal Office of Metrology and
Surveying, Austria) as the new director of GGOS CO in July 2020.
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

New GGOS website – https://ggos.org
One major goal of GGOS is to communicate and advocate the benefits of Geodesy to scientists,
user communities, policy makers, funding organizations and society. To reach this goal, it isessential to establish a strong online presence. The GGOS website serves as a source of
information about GGOS, geodetic data, products, and services, as well as other non-technicalresources for the IAG community.
After the transition of the GGOS CO from ASI (Agenzia Spaziale Italiana, Italy) to BKG(Bundesamt für Kartographie und Geodäsie, Germany) in 2015, it was transitioned again to
BEV (Federal Office of Metrology and Surveying, Austria) in 2016. BEV installed a completely

Global Geodetic Observing System (GGOS)

new server system and launched a new designed GGOS website in 2017. In 2019 the GGOS
Executive Committee decided to refresh and further develop it again to optimize the usability.

The new GGOS website (see image), which was published in December 2020, now emphasizes
more on the “Observing System” than on the “GGOS organization” itself. Therefore, thewebsite was enhanced to provide an extensive information platform to bring the IAG
observations, products and services in the focus and to attract users from other disciplines.
Visually attractive graphics navigate users to easy understandable introductions about geodetic
products or observation techniques. Observation and product descriptions are complemented
with a huge selection of web links containing scientific descriptions and data repositories
provided by the IAG Services and additional data sources.
From 2019 to 2021, the GGOS Coordinating Office worked intensively together with all GGOS
components and other important persons of the geodetic scientific community, to establish andlaunch this new information platform. Furthermore, the contributions of the IAG Services andother providers of geodetic products are gratefully acknowledged. The new GGOS website
contributes to make geodesy more visible and to promote IAG and GGOS at global andmultidisciplinary levels.
New GGOS Cloud – https://cloud.ggos.org
A first version of the GGOS Cloud service was installed in September 2017 and was based on
the OwnCloud software. But due to several organizational and technical issues it was switched
off. Together with the new GGOS Website, the GGOS Cloud was new developed and was
published again in 2020. It is now based on the worldwide often used, regularly updated andfree software Nextcloud. GGOS Cloud is fully integrated in the GGOS Website and is used as492

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a file hosting platform for public files. Additionally, it is used to share files within the GGOS
community.
GGOS Blog & GGOS Newsletter – https://blog.ggos.org
A blog was set up on the GGOS website, where users can find latest news and events of GGOS
as well as short introductions into Geodesy and GGOS. Interested persons can subscribe to the
GGOS mailing list to receive this news via the GGOS Newsletter https://ggos.org/newsletter/.
GGOS Videos
In 2021 the idea was born to produce a short film about GGOS and Geodesy in General. It was
produced within the GGOS Coordinating Office by the BEV (Federal Office of Metrology and
Surveing of Austria) to explain the applications and importance of Geodesy to non-geodesists.
The English version was published together with the Spanish, German and Japanese versions
in February 2022. Now there are 12 language versions, created with the great help of volunteer
geodesists who translated the text into their native language and made the sound recordings.
This “Discover GGOS and Geodesy” film is available on YouTube:
https://youtu.be/Jwqz097N2IY.

Due to the great success of the GGOS film by more than 11.000 views, the GGOS Coordinating
will produce more short videos about geodetic observation techniques and products. All videos
are available at the GGOS YouTube Channel www.youtube.com/@iag-ggos.
GGOS social media presence (Twitter, LinkedIn, YouTube, Facebook)
Nowadays it is very important for an organization to be active at Social Media to reach out tomore people. The GGOS CO started with GGOS first Social Media presence in 2016 by setting
up a Twitter account to be present in the social media and to speed up dissemination of GGOSrelated information to the customers. In order to extend the audience, the GGOS CO set up
further Social Media channels of GGOS at LinkedIn, YouTube and Facebook in 2021 (seetable).
Platform

Set UpFollower

Link

Global Geodetic Observing System (GGOS)

Twitter
LinkedInYouTubeFacebook

2016
May 2021
June 2021
Dec. 2021(May 2023)
1133
782
410
38

twitter.com/IAG_GGOS
linkedin.com/company/iag-ggos
youtube.com/@iag-ggos
facebook.com/iagGGOS

GGOS Portal – A unique access point for geodetic data
The services of the International Association of Geodesy (IAG) provide very important andvaluable geodetic data, information, and data products that are increasingly relevant for Earthsystem research, including monitoring of global change phenomena and a wide range of diverse
applications such as satellite navigation, surveying, mapping, engineering, geospatial
information systems, and so on.
Currently, it is difficult for many people to obtain an overview of all available geodetic products
and data. The GGOS CO aims to fill this gap by developing the GGOS-Portal (ggos.org/portal),
which will serve as a unique search and access point (one-stop shop) for geodetic data andproducts. Data and products will be described by rich metadata and remain physically locatedat their originating data centers of each contributing IAG service and other data providers. With
this future platform, GGOS will contribute to increase the visibility of geodetic data forscientific research and to make other disciplines and the society aware of geodesy and its
beneficial products.
To get an overview of the current availability of data products and their metadata, GGOS
conducted a survey within the geodetic and geoscience community. This survey also inquired
the opinions of geodetic data users on data availability and visibility, as well as desired
requirements for a comprehensive and user-friendly GGOS-Portal.

Organized Conferences & Meetings
•
•
•
•
•

Unified Analysis Workshop (UAW) – together with IERSo 2019 in Paris, Franceo 2022 in Thessaloniki, Greece
GGOS Coordinating Board (CB) meetings (virtual: 2020, 2021, 2022, hybrid: 2023)
GGOS Days 2019, Rio de Janeiro, Brasilia
GGOS Days 2020 & 2021, virtual conference
GGOS Days 2022, Munich, Germany

Conference attendance••••European Geosciences Union (EGU) (2020, 2021, 2022, 2023)
American Geophysical Union (AGU) (2019, 2020, 2021, 2022)
IAG Scientific Assembly 2021, virtualIUGG General Assembly 2023, Berlin, Germany

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GGOS External Relations
To ensure geodesy is a visible, valued, and sustainable worldwide asset, GGOS external
relations efforts within the GGOS Coordinating Office work toward proactive engagementwith the broader Earth observations community. This is done by advocating for interoperable,
discoverable, and openly available geospatial data, promoting infrastructure development,
identifying tangible geodetic contributions to UN SDG and Sendai Framework targets andindicators, as well as working with external partners in capacity building and development
initiatives.

Advocacy• GGOS participation in diverse
stakeholder organizations works
to identify synergies, making
connections acrossorganizations in the name ofgeodesy and mutual benefit.

Visibility• GGOS participation andleadership – often on behalfof the IAG -- reminds Earthobservation organizations
that geodetic
infrastructure isimportant for things likeclimate change and disasterrisk reduction.

Collaboration• GGOS participation indiverse capacity
development efforts serves
as the “human reference
frame” to link between
organizations for otherwise
overlooked opportunities.

Group on Earth Observations (GEO)GGOS represents the IAG in the Group on Earth
Observations (GEO), where it has represented theinterests of the geodetic community by promoting visibility of geodesy within the broader
Earth Observations community. IAG(GGOS) was first nominated as a member organizationof the GEO Programme Board during 2018-2020. This representation on the GEO Programme
Board was renewed for the 2020-2024 period, IAG(GGOS) continues to have a voice insteering the activities of GEO. In addition to participating on the Programme Board,
IAG(GGOS) is also one of three participating organizations to serve on the GEO Executive
Committee (2021-present). Richard Gross and Allison Craddock have served as the GGOSappointed IAG representatives to the GEO Work Programme since 2018.
In the last four years, GGOS has ensured representation of the IAG and geodesy in thefollowing GEO efforts:• Subgroup on Sustainable Earth Observations, which works in tandem with the GEOSSIn-Situ Earth Observation Resources foundational task to assess the current

Global Geodetic Observing System (GGOS)

•

•

•

•

•

Foundational Tasks focusing on both GEOSS Satellite and In-Situ Earth Observation
Resources, and to evaluate strengths and weaknesses of observing systems for GEO’s
activities over the past decade, and to clarify the challenges 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.
Subgroup on the Sendai Framework, later re-convened as the Working Group on
Disaster Risk Reduction. This group supports GEO’s strategic engagement priority
area on the Sendai Framework for Disaster Risk Reduction, in the realm ofchampioning and supporting the development of policy objectives that add value,
drive efficiencies, and promote the uptake of Earth observations in alignment with
Sendai and other disaster risk reduction initiatives. This is particularly relevant tosupporting the GGOS Geohazards Focus Area and its Global Navigation Satellite
System to Enhance Tsunami Early Warning Systems (GTEWS).
Capacity Development Working Group. IAG(GGOS) served as one of three co-chairsof the GEO Capacity Development Working Group, whose tasks included organizing
virtual capacity development seminars, developing the GEO Statement on Open
Knowledge. IAG also served in drafting and administering capacity development
components of the over-arching “Mapping the Engagement of the 2020-2022 GEO
Work Programme in Climate Action, Disaster Risk Reduction, and Capacity
Development.”
Climate Change Working Group. IAG(GGOS) is a member of GEO’s Climate Change
Working Group that was established to develop and implement a strategy to advancethe use of Earth observations for climate change adaptation and mitigation. The role of
IAG(GGOS) in the Working Group is to ensure that geodetic observations areappropriately included in the strategy.
Subgroup on Equality, Diversity, and Inclusion. IAG(GGOS) was a co-author of the
GEO Statement on Equality, Diversity, and Inclusion (EDI).The GEO five-pillar EDI
framework outlines a vision that equality, diversity, and inclusion are considered inevery aspect of GEO, answering the mandate of the GEO mission to “unlock thepower of Earth observations by facilitating their accessibility and application to
global decision making within and across many different domains.”
Review Team for Digital Earth Africa proposal. IAG(GGOS) chaired the review teamfor the Digital Earth Africa proposal, reporting the process, criteria for a GEO
Initiative, and the review team’s assessment of the implementation plan against said
criteria. This review ultimately led to Digital Earth Africa’s accession as a GEO
Initiative.

Participation at the Programme Board level ensures that IAG and GGOS efforts in alignment
with GEO’s global priorities (supporting the UN SDGs, Sendai Framework, as well as theParis Agreement on Climate Change) are well supported and complimentary to other related
work – as well as preventing unnecessary redundancy of work. Geodetic observations have aclear role in 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 inmonitoring progress toward, and achieving, the SDGs.

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GGOS also plays a leadership role in a GEO Pilot Initiative within the GEO Work
Programme, which is described below.

Group on Earth Observations: Geodesy for the
Sendai Framework Pilot Initiative

GGOS has led the establishment and administration of the first geodesy-centric component of
the GEO Work Programme, initially as a Community Activity in the 2020-2022 GEO Work
Programme, and extended as a Pilot Initiative in the 2022-204 GEO Work Programme. The
overall objective of this group is to promote visibility for Geodetic observations and their rolein helping to reduce the risk of disasters, as well as contribute to disaster preparedness with
better mitigation and response.
Key goals of the Geodesy for the Sendai Framework Pilot Initiative include:• Ministerial-level political support and funding for GNSS-enhanced tsunami early
warning systems in the Circum-Pacific Belt (Pacific Ring of Fire) and Caribbean
basin.
• Ministerial-level political support and funding for geodetic capacity building fordisaster risk reduction and resilience.
Work led by GGOS on behalf of this group included:• GGOS-Geohazards Working Group contributed content for the 2019 UN Global
Assessment Report on Disaster Risk Reduction (GAR19)• GGOS-IGS joint contribution to the 2022 UN Global Assessment Report on Disaster
Risk Reduction (GAR22)• Supporting geodetic development and capacity building for disaster risk reduction andresilience; identifying existing resources and stakeholder communities, and making
connections• Identifying geodetic elements of targets and indicators of the Sendai Framework for
Disaster Risk Reduction• Facilitating opportunity for other GEO efforts to interact with the international
geodesy community• Promoting integration of gedesy-enabled applications with UN Sustainable
Development Goals and UN-GGIM World Bank Integrated Geospatial Information
Framework
Joint collaborations with ITU, WMO, and UNEP
supporting Artificial Intelligence for Geodetic
Enhancements to Tsunami Monitoring and
Detection.

GGOS also worked to identify and support innovations through participation in the Group on
Earth Observations as well as joint initiative of the International Telecommunications Union(ITU), World Meteorological Organization (WMO), and UN Environment Programme(UNEP). The GEO Geodesy for the Sendai Framework Community Activity (later Pilot
Initiative), represented by GEO participating organizations IAG and IUGG, led a new tsunami
early warning collaboration with the recently established ITU Focus Group, organized jointlyGlobal Geodetic Observing System (GGOS)

with WMO and UNEP to enhance the management of natural disasters, such as tsunami, bydemonstrating the value of Earth Observations, namely GNSS data and infrastructure, inapplications utilizing artificial intelligence (AI) and machine learning (ML).
The Topic Group "AI for Geodetic Enhancements to Tsunami Monitoring and Detection" hasbeen set up this year under ITU Focus Group on Artificial Intelligence for Natural Disaster
Management (FG-AI4NDM). The topic group has worked on several deliverables, such astechnical use-case reports with the relevant best practices in two uses of GNSS data:
seismic/displacement observations, as well as ionospheric observations. Use cases will
include descriptions of existing cutting-edge systems, such as: 1) Japanese real-time tsunami
inundation forecast service that provides warning/forecast and estimated damage report to thePrime Minister's Office, and 2) NASA Jet Propulsion Laboratory’s GNSS-based Upper
Atmospheric Real-time Disaster Information and Alert Network (GUARDIAN system). The
group will also contribute to a future ITU Recommendation on the topic of AI for disastermanagement.
This new cooperation among the multiple international organizations aims to help lay thegroundwork for the development and implementation of AI and ML applications expanding
the use of geodetic Earth observations in places such as Small Island Developing States,
which suffer from increasing tsunami threats in addition to other climate change impacts suchas sea level rise.

Committee on Earth Observation Satellites (CEOS)GGOS is an Associate Member of CEOS and regularly
participates in its Plenary meetings, giving presentations and discussing the fundamental
importance of the global geodetic reference frame to Earth observations. 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 to speak about its plans
and strategies in relation to CEOS, as well as the benefits and expectations of CEOS from the
GGOS perspective.
GGOS also participates in the CEOS Working Group on Disasters, which supports the effortsof Disaster Risk Management authorities in protecting lives and safeguarding property bymeans of satellite-based Earth observations and science-based analyses. GGOS participationin this working group supports geodetic contributions to the group’s objective to foster
increased use of Earth observations in support of Disaster Risk Management and raise theawareness of politicians, decision-makers, and major stakeholders of the benefits of using
geodetic Earth observations in all phases of Disaster Risk Management.

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GGOS also participated in the initial establishment of the CEOS-led “EOTEC DevNet,” a
network of networks created to improve coordination and enhancement of Earth Observation
asset and training providers in support of key global sustainable development outcomes. Thisis currently a deliverable in the CEOS 2021-2023 Work Plan. The goals of this effort include:• Improving coordination and cooperation among capacity building providers andusers in order to meet existing needs and fill gaps
• Fostering information sharing and exchange on capacity building resources• Promoting effective assessment of capacity development needs at regional andnational levels
GGOS also participated in the (now disbanded) CEOS Ad Hoc Team on the Sustainable
Development Goals (AHT SDG), which worked toward highlighting the potential role for
Earth observations in supporting the global indicator framework of the United Nations
Sustainable Development Goals.

UN GGIM Subcommittee on Geodesy

GGOS supports and, as needed, represents the IAG at theUnited Nations Committee of Experts on Global Geospatial
Information Management (UN GGIM), as well as the meetings of the Sub-Committee on
Geodesy (SCoG), to provide stability and long-term planning for the Global Geodetic
Reference Frame (GGRF). GGOS supports IAG participation in major SCoG activities,
including the following efforts to:• provide an intergovernmental forum, with equitable international representation, forcommunication and cooperation on issues relating to the maintenance andenhancement of a Global Geodetic Reference Frame (GGRF);• develop a roadmap for a collaborative global geodetic observation network and theassociated infrastructure, with sustainable funding and investment, as well as
strategic partnerships between mapping, space and other interested agencies;• encourage open sharing of geodetic data and information that contribute to regionaland global reference frames;• advocate for guidelines and standards to advance the interchangeability andinteroperability of geodetic systems and data; and• address various technical, institutional and policy issues related to theimplementation of a GGRF.
Numerous GGOS Consortium members were active in the UN GGIM SCoG on behalf of the
IAG in the last four years, including Harald Schuh, Mike Pearlman, Detlef Angermann,
Zuheir Altamimi, Laura Sanchez, and Martin Sehnal in key support and participation roles.
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, and Allison Craddock (USA), SCoG Working Group on
Communications and Outreach, Working Group on Education, Training and Capacity
Building
GGOS has also served as a strong supporter of the recently-established United Nations Global
Geodetic Centre of Excellence (UN-GGCE) with its goal to assist Member States andgeodetic organizations to coordinate and collaborate to sustain, enhance, access and utilize an

Global Geodetic Observing System (GGOS)

accurate, accessible and sustainable GGRF to support science, society and global
development.
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 GGOS support of IAG enables the greatest use
of geodetic data in support of these United Nations initiatives and beyond.

GGOS Working Group Digital Object Identifiers (DOIs) for Geodetic Data Sets
WG Kickoff: December 2019
Members
Chair: Kirsten Elger (GFZ, Germany), Detlef Angermann (TU Munich, Germany), Yehuda
Bock (UCDC, US), Sylvain Bonvalot (GET, France), Markus Bradke (GFZ, Germany),
Elisabeth Bradshaw (NOC, UK), Carine Bruyninx (ROB, Belgium), Daniela Carrion(Politecnico Milan, Italy), Glenda Coetzer (SARAO, South Africa), Pierre Fridez (CODE/
AIUB, Switzerland), Elmas Sinem Ince (GFZ, Germany), Philippe Lamothe (Geodetic Survey
Canada), Vicente Navarro (ESA), Carey Noll (CDDIS/NASA, US until 2021), Mirko
Reguzzoni (Politecnico Milan, Italy), Jim Riley (UNAVCO, US), Dan Roman (NGS, US),
Laurent Soudarin (CLS, France), Daniela Thaller (BKG, Germany), Yusuke Yokota (GGOS
Japan)
Associated Members
Godfred Amponsah (NGS, US), Sandra Blevins (CDDIS/NASA, US), Roelf Botha (SARAO,
South Africa), Francine Coloma (NOAA CORS, US), Allison Craddock (JPL/NASA, US),Michael Craymer (Canadian Geodetic Networks, Canada), Theresa Damiani (NOAA CORS,
US), Patrick Michael (CDDIS/NASA, US), Basara Miyahara (GGOS, Japan), Mike Pearlman(Harvard Smithsonian – Center for Astrophysics, US), Nacho Romero (ESA), Christian
Schwatke (TU Munich, Germany), Martin Sehnal (GGOS, BEV, Austria), Lori Tyahla(CDDIS/NASA, US)
Motivation and purpose
Data publications with digital object identifiers (DOI) are best practice for FAIR sharing data.
Originally developed with the purpose of providing permanent access to (static) datasets
described in scholarly literature, DOI today are more and more assigned to dynamic data too.
These DOIs are providing a citable and traceable reference of various types of sources (data,
software, samples, equipment) and means of rewarding the originators and institutions. As aresult of international groups, like the Coalition on Publishing Data in the Earth, Space andEnvironmental Sciences (COPDESS1) and the Enabling FAIR Data project2, data withassigned DOIs are fully citable in scholarly literature and many journals require the data
underlying a publication to be publicly available. Initial metrics for data citation allows data
providers to demonstrate the value of the data collected by institutes and individual scientists.
This is especially relevant for geodesy, because geodesy researchers are often much more
involved in operational aspects and data provision than researchers in other fields might be.
Therefore, compared to other scientific disciplines, geodesy researchers appear to be12

https://copdess.org
https://copdess.org/enabling-fair-data-project/

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producing less ‘countable scientific’ output. Consequently, geodesy data and equipment
require a structured and well-documented mechanism which will enable citability, scientificrecognition and reward that can be provided by assigning DOI to data and data products.
While this is easy for static data, like for global of regional gravitational models or GNSS
campaign data, most geodetic data are large (mainly due to the large number of files with hightemporal resolution), dynamic (real time data acquisition and provision), and highly granular.
Geodetic services of the International Association for Geodesy (IAG) are international key
player for geodetic data provision and distribution and their operating institutions and funding
agencies increasingly require the provision of tangible data use and access statistics. Credit
through citation was a major reason for the Global Geodetic Observing System (GGOS) toestablish a ‘Working Group on Digital Object Identifiers (DOIs) for Geodetic Data Sets’3(GGOS DOI WG) in October 2019. This Working Group is designated to establish bestpractices and advocate for the consistent implementation of DOIs across all IAG Services andin the greater geodetic community.
Objectives
The main objectives and activities of this working group are(1) To identify what the community needs from consistent usage of DOIs for data to being able todiscover, permanently cite and access data, and acknowledge the data providers;(2) develop recommendations for DOI minting strategies for different geodetic data types andgranularity across IAG Services (static, dynamic, observational data, data products,
combination products, networks);(3) to develop recommendations for a consistent method for data citation across all IAG Services,to support data providers, and to provide quantitative support detailing the use of geodetic
datasets and other resources;(4) to develop recommendations for connecting metadata standards for data discovery (e.g.
DataCite, ISO19115) with community metadata standards (e.g. GeodesyML, Sitelogs).

Activities and Actions• Physical kickoff meeting during AGU2019, 3-5 video conferences per year.
• Regular presentations of the group’s activities during national and international conferences
and workshops (AGU, EGU, GGOS Days, IAG GA, IVS GM, UAW, etc., see also the publications
section below)• Creation of a Zenodo Community where presentations and documents are collected andpublished with DOI4
• Collection of data products and already existing and planned DOI activities for IAG services andgeodetic data centers (living document).
• Outside the box: exploration of DOI minting and citation practices from other communities inthe Earth sciences for potential adoption for geodetic data sets: e.g. network DOIs, persistentidentifier for instruments, DOI citation recommendations for data compilations andhierarchical data products.
• Introduction to different persistent identifiers (PID) and agreement on their importance formaking data findable, accessible, interoperable and reusable (FAIR, Wilkinson et al., 2016).
PIDs allow, e.g., to uniquely identify published data, scholarly literature and code (via DOIs),
persons (via ORCID), institutions and funding agencies (via ROR – the registry of researchorganizations) via machine-actionable links that should be included in the metadata. PIDs
3
4

https://ggos.org/about/org/co/dois-geodetic-data-sets/
https://zenodo.org/communities/ggos-doi-wg/

Global Geodetic Observing System (GGOS)

within machine-actionable metadata (e.g. DataCite, GeodesyML) are key elements forconnecting data with articles, software and other research outcome as well as to institutions,funding agencies, researchers, and instruments.
• Discussions on the objects, DOIs are assigned to, i.e. data products vs. data files or continuous
time series from individual stations and development of recommendations for metadata
properties.

Outcomes• Support for the development of a DOI Service for the International Service for theInternational Service for the Geoid (IGS) in collaboration with GFZ Data Services (start July2020). As part of this collaboration, regional geoid models are successively assigned with DOI
and collected in the dedicated ‘IGS datacenter’ of the catalogue of GFZ Data Services5 withdirect links to ISG’s Geoid Repository6 Recently also official models (e.g. Slovenia, Costa Rica,
Austria) provided by federal agencies, have been assigned with DOI. This is a clear sign that
DOI are increasingly attractive beyond the academics.
• DOIs for data products or data files? One of the first recommendation of the GGOS DOI WG isthat DOIs for product ’types’ (e.g. Precise Science Orbits, IAG final products) or observational
networks (e.g., GNSS networks) are preferred to DOIs for individual data files. These DOIs for
growing time series mainly serve for citation purposes and not for identifying individual data
streams (similar to DOIs for seismic networks, e.g. Evans et al. 2015).
• DOIs for rapid or ultra-rapid products? These are existing for different geodetic techniques
and are outdated very soon (precisely within days or few weeks when the next better productis available). However, they are occasionally used in research articles (and could be cited if
assigned with a DOI). Due to the requirement that DOI-referenced data have to be available
persistently, the group agrees to support DOIs for rapid and ultra-rapid products only if thedata are archived for the long term by the datacenter. A datacenter that is not planning toarchive rapid or ultra-rapid products should not assign DOIs to them (e.g. AIUB and GFZ haveassigned DOIs to their rapid and ultra-rapid IGS products, while ESA is not using DOIs for theseproducts, because of their ‘rolling archive’)• Development of a concept for assigning DOI to hierarchical products and its implementation
for the use case ICGEM/ COST-G (Combination Service for Time-variable Gravity Fields):
monthly GRACE time series7: Individual monthly field solutions are produced by a number ofInternational Analysis Centers and are later combined to the COST-G combination productwhich represents a „best fit model’. The connection between the original solutions and the
combination product is done via the “related identifier” property of the DataCite Schema: the
DOI metadata of the original solutions from the Analysis Center includes a reference (using the“related identifier” property) to the combination Product using the DataCite relation type „Is
Part Of’ (i.e., they have contributed to the COST-G combination product). The metadata of the
combination product includes the citation of all original products from the Analysis Centers
using the relation type „Is Derived From’. The adoption of this concept for ITRF2020 has been
agreed by the IERS CB (May 2021) and in currently being implemented.

5

https://dataservices.gfz-potsdam.de/portal/?fq=datacentre_facet:%22DOIDB.ISG%20%20ISG%20International%20Service%20for%20the%20Geoid%22
6
https://www.isgeoid.polimi.it/Geoid/geoid_rep.html
7Monthly GRACE series: https://doi.org/10.5880/ICGEM.COST-G.001, Monthly GRACE-FO series:
https://doi.org/10.5880/ICGEM.COST-G.002)

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DOIs for GNSS data: One task of the current project FAIR GNSS8, funded by the Belgian Science
Policy Office (BELSPO), is to apply the FAIR Principles (Wilkinson et al, 2016) to GNSS Data andto develop a DOI service for the European and Belgian GNSS data collections managed by theRoyal Observatory Belgium. This was the opportunity begin with the development of metadata
recommendations for the use case GNSS data. Moreover, GNSS data represents a good use
case for geodetic data in general: DOIs for GNSS campaign data are examples for static
products; IAG orbit and clock products are good examples for DOIs for dynamic data with new
DOI versions only required when there are changes in the data processing routine; DOIs for
GNSS networks are also already used (e.g. by UNAVCO, AIUB, GFZ, INGV), however: GNSS
stations are not always organized as networks and some stations may be part of several
networks. We have therefore accepted the necessity to assign DOI for the (ongoing) timeseries measured with one GNSS station. Tangible results of our discussions resulted in the:• ‘Metadata Recommendations for geodetic data: GNSS’: a guide to recommended metadata
properties and sub-properties relevant for GNSS data for DataCite and geodesyML schemas
with examples on how to provide the information (e.g. separating first and last names, adding
ORCID and ROR identifier whenever possible). This document is currently in discussion with the
GGOS DOI WG and a first version expected to be released after IUGG2023. It includes a general
introduction to DOIs and their application for geodetic data, followed by recommendations forthe provision of specific metadata properties DataCite, GeodesyML metadata with examples.
The document was developed for the GNSS use case, but already with a more general focus
allowing an easily extension to apply for other geodetic datasets. Guiding principles for therecommendations were (1) maximum automatization: for metadata properties fromGeodesyML/ Sitelogs mapped into DataCite metadata, (2) following the FAIR Principles andintegration of PIDs in the metadata, (3) compliance with the General Data Protection
Regulation (GDPR).
• DOI assignment to GGOS Documents: documents, like the GGOS Strategic Plan, GGOS
implementation plan, IAG Travaux will be published with DOI from 2023 on (collaboration with
GFZ).

Ongoing discussions and future plans
Ongoing discussions focus on the revision of the metadata recommendations and its extension
to metadata s for other geodetic techniques. Our activities will further include
recommendations of controlled vocabularies describing geodetic datasets (to be used inmetadata for stations and data, ideally the same vocabularies to facilitate cross-references
between stations, sensory, data and networks). These vocabularies should be registered via a
vocabulary registration service (e.g. Research Vocabularies Australia9) and provided inmachine-actionable format (RDF) following the SKOS10 guidelines for the semantic web.
Moreover, we will explore the potential implementation of the concept of the “Persistent
Identification of Instruments Working Group11” of the Research Data Alliance (RDA12) for
using PIDs for instruments and explore the required harmonization of DOI-related metadatafrom different data centers for similar products.

8

https://fair-gnss.oma.be/https://ardc.edu.au/services/research-vocabularies-australia/
10
https://www.w3.org/2004/02/skos/
11
Persistent Identification of Instruments Working Group: https://www.rd-alliance.org/groups/persistentidentification-instruments-wg
12
RDA = Research Data Alliance (https://www.rd-alliance.org/)
9

Global Geodetic Observing System (GGOS)

References
Evans, P. L., A. Strollo, A. Clark, T. Ahern, R. Newman, J. F. Clinton, H. Pedersen, and C. Pequegnat(2015). Why seismic networks need digital object identifiers, Eos, 96, https://doi.org/10.1029/2015EO036971
Wilkinson, M., Dumontier, M., Aalbersberg, I. et al. The FAIR Guiding Principles for scientific data
management and stewardship. Sci Data 3, 160018 (2016). https://doi.org/10.1038/sdata.2016.18

Selected publications and conference presentations related to the WG
Journal Articles
Ince, E. S., Barthelmes, F., Reißland, S., Elger, K., Förste, C., Flechtner, F., Schuh, H. (2019). ICGEM – 15
years of successful collection and distribution of global gravitational models, associated services and futureplans. - Earth System Science Data, 11, 647-674. https://doi.org/10.5194/essd-11-647-2019
Coetzer, G., Botha, R., Schollar, C., Elger, K. (2022): An Institutional Research Data Repository and DigitalObject Identifiers for SARAO Radio Astronomy, Fundamental Astronomy, and Geodesy Datasets. - Bulletin of
the American Astronomical Society, 54, 2. https://doi.org/10.3847/25c2cfeb.66ee866c
Reguzzoni, M., Carrion, D., De Gaetani, C. I., Albertella, A., Rossi, L., Sona, G., Batsukh, K., Toro Herrera,
J. F., Elger, K., Barzaghi, R., Sansó, F. (2021). Open access to regional geoid models: the International Service
for the Geoid. - Earth System Science Data, 13, 4, 1653-1666. https://doi.org/10.5194/essd-13-1653-2021
Presentations at conferences and workshops
Blevins, S. M., Tyahla, L., Michael, B. P., Noll, C. E. (2020). IN046-06 - DOIs for geodetic data and derived
product collections at the NASA GSFC CDDIS. AGU 2020 Fall Meeting (Online 2020).
Bruyninx, C., De Bodt, S., Fabian, A., Legrand, J., Miglio, A., Moyaert, A., Oset Garcia, P., & Van
Nieuwerburgh, I. (2022) Towards FAIR GNSS data. Splinter Meeting 3 at EUREF 2022 Symposium 02 June,
2022 (online) with invited talk by Elger, K. presenting the GGOS DOI WG(https://euref2022.eu/)
Bruyninx, C., De Bodt, S., Fabian, A., Legrand, J., Miglio, A., Oset Garcia, P., & Van Nieuwerburgh, I.
(2022). FAIR-GNSS webinar - Putting the FAIR principles into practice: the journey of a GNSS data repository.
Royal Observatory of Belgium (ROB). https://doi.org/10.24414/ROB-FAIRGNSS-PRESENTATION
Bruyninx, C., De Bodt, S., Legrand, J., Fabian, A., Miglio, A., Oset Garcia, P., Van Nieuwerburgh, I. (2022).
Moving towards FAIR GNSS data: putting principles into practice" (poster) at BNCGG study day “Belgian
contributions to Earth Sciences in a Changing World”, Brussels, 4/11/2022
Bruyninx, C., Fabian, A., Legrand, J., & Miglio, A. (2020). GNSS Station Metadata Revisited in Response to
Evolving Needs. Copernicus GmbH. https://doi.org/10.5194/egusphere-egu2020-18634
Bruyninx, C., Miglio, A., Fabian, A. Legrand, J. (2021) Introduction to FAIR data Towards FAIR GNSS
data. Splinter meeting “Towards FAIR GNSS data” at EUREF 2021 Symposium, online, 27/05/2021
Coetzer, G., Botha, R., Elger, K. (2023) Digital Object Identifiers and Metadata for VLBI Datasets andProducts. Poster presented at Bologna VLBI: Life begins at 40! (22-26 May 2023, Bologna),
https://doi.org/10.5281/zenodo.8022888
Coetzer, G., Botha, R., Scholar, C., & Elger, K. (2021). Digital Object Identifiers for SARAO’s Radio
Astronomy, Fundamental Astronomy and Geodesy Datasets. Poster presented at the 9th conference on Library
and Information Services in Astronomy (LISA IX),14 to 18 June 2021, https://doi.org/10.5281/Zenodo.4889095
Coetzer, G., Takagi, Y. Elger, K. (2021) Digital Object Identifiers for the IVS. Proceedings 12th IVS General
Meeting 2021, URL: https://ivscc.gsfc.nasa.gov/publications/gm2022/44_coetzer_etal.pdf
Craddock, A., Elger, K., Sehnal, M., Fridez, P. (2019). DOIs for Geodetic Datasets. Unified Analysis
Workshop, October 2-4, 2019, Paris, France.
De Bodt, S. (2021). Towards FAIR GNSS data (Splinter Meeting) at EUREF 2021 Symposium, online,
27/05/2021
Elger, K. & GGOS DOI Working Group. (2022). Some backgrounds about DOI minting. GGOS Days 2022,
Munich, Germany, 14-15 November 202,2 https://doi.org/10.5281/zenodo.7354892 (Video)
Elger, K. (2020). G022-02 - What are the benefits for assigning DOI to Geodetic data? First ideas of the
GGOS DOI Working Group - Abstracts, AGU 2020 Fall Meeting (Online 2020, Video).
Elger, K. and the GGOS DOI WG (2020). Report from the GGOS Working Group on DOI for geodetic data.
Oral presentation during the GGOS Days 2020 (October 5-7, 2020, online)
Elger, K., Coetzer, G., Botha, R., GGOS DOI Working (2020): Why do Geodetic Data need DOIs? First
ideas of the GGOS DOI Working Group - Abstracts, EGU General Assembly 2020 (Online 2020).
https://doi.org/10.5194/egusphere-egu2020-17861
Elger, K., GGOS DOI WG (2021). News from the GGOS DOI Working Group - Abstracts, EGU General
Assembly 2021 (Online 2021). https://doi.org/10.5194/egusphere-egu21-15081 (PICO presentation)
Elger, K., GGOS DOI WG (2023). The world of DOIs for geodetic data – metadata recommendations andstatus report of the GGOS DOI Working Group. EGU General Assembly 2023, Vienna, Austria, 23–28 April
2023. EGU23-6384, https://doi.org/10.5194/egusphere-egu23-6384

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Elger, K., GGOS DOI Working Group (2022): News from the GGOS DOI Working Group - Abstracts, ,EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10982,
https://doi.org/10.5194/egusphere-egu22-10982 (presentation slides)
Elger, K., Miglio, A., & Bruyninx, C. (2023). Why do Geodetic Data need DOIs? An introduction to data
publications and the GGOS DOI Working Group. Invited talk at the 335 Section Forum at the Jet Propulsory
Laboratory (JPL), Pasadena, CA, US (March 9), https://doi.org/10.5281/Zenodo.8022958
Elger, K., Miglio, A., Bruyninx, C., Thaller, D., & GGOS DOI Working Group. (2022). Concepts for DOI
minting for Geodetic Datasets. Unified Analysis Workshop 2022 (UAW 2022), Thessaloniki, Greece, 21-23
October 2022, https://doi.org/10.5281/zenodo.7239190
Miglio, A., Bruyninx, C., Fabian, A., Legrand, J., Pottiaux, E., Van Nieuwerburgh, I., & Moreels, D. (2020).
Towards FAIR GNSS data: challenges and open problems. EGU General Assembly 2020 (Online 2020).
https://doi.org/10.5194/egusphere-egu2020-18398
Miglio, A., Fabian, A., Bruyninx, C., De Bodt, S., Legrand, J., Oset Garcia, P., and Van Nieuwerburgh, I.
(2022) Proposed metadata standards for FAIR access to GNSS data, EGU General Assembly 2022, Vienna,
Austria, 23–27 May 2022, EGU22-11968, https://doi.org/10.5194/egusphere-egu22-11968
Sehnal, M., Craddock, A. B., Elger, K. (2020). GGOS Coordinating Office – Recent Achievements andActivities. - Abstracts, AGU 2020 Fall Meeting (Online 2020).
Sehnal, M., Craddock, A., Elger, K. (2020). GGOS Coordinating Office – Recent Achievements andActivities - Abstracts, EGU General Assembly 2020 (Online 2020), https://doi.org/10.5194/egusphere-egu20206540

Global Geodetic Observing System (GGOS)

GGOS Affiliate: GGOS Japan
Chair: Toshimichi Otsubo (Japan)
Secretary: Basara Miyahara (Japan)
This multi-institution entity was initially established as GGOS Working Group of Japan in
2013, later approved as GGOS Affiliate in 2017 and renamed as GGOS Japan in 2019. The
purpose was to strengthen collaboration among Japan’s geodetic stations and colleagues and tofoster Japanese space geodetic activities internationally. It is reaching the 10-year anniversary
in 2023.
In recent years, GGOS Japan has constantly hosted its own annual meetings for broad range ofspace geodetic research and activities where additional English-spoken sessions were recently
arranged with the DACH (2022) and Iberoatlantic (2023) colleagues. It also organises smallersize meetings on specific topics such as data DOI minting (2019) and co-location local tie(2020). It was remarkable that Japanese institutes were nicely collaborated to conduct local tie
campaigns for the ITRF2020 project. A new aspect of GGOS Japan is to co-organise existing
domestic meetings in the field of VLBI and SLR in 2020 where GGOS Japan core members
are often given an opportunity of invited talks. GGOS Japan has updated the terms of referencein 2021 so that co-hosting or supporting related meetings can be accommodated as one of its
roles. It should be noted that in accordance with the renewal of GGOS website the webpagesof GGOS Japan were largely updated, utilizing the GGOS Cloud function. GGOS Japan has
adopted its logo in 2022, often shown in the presentation slides, the leaflets and the stickers.
GGOS Japan is a loose organization of public sectors and university members. It does not havemembership qualification, but its core members are selected. As of May 2023, they are:
Chair: Toshimichi Otsubo (Hitotsubashi University)
Secretary: Basara Miyahara (Geospatial Information Authority of Japan)
Outreach: Shinobu Kurihara (Geospatial Information Authority of Japan)
Data DOI WG Lead: Yusuke Yokota (University of Tokyo)
Technique Representatives:
VLBI: Kensuke Kokado (Geospatial Information Authority of Japan)
SLR: Yuto Nakamura (Japan Coast Guard)
GNSS: Hiroshi Takiguchi (Japan Aerospace Exploration Agency)
DORIS: Yuichi Aoyama (National Institute of Polar Research)
Gravity: Koji Matsuo (Geospatial Information Authority of Japan)
These members have actively involved in session planning of annual JpGU meetings and annual
Geodetic Society of Japan meetings, where “GGOS” is always seen as (a part of) a session
name. Likewise, we should make every effort to utilize the “GGOS” keyword for budget
hunting, aiming at future GGOS Core sites in Japan or Antarctica. Encouraging geodetic
technology development is also in our scope - in addition to high precision and high operability,
we are aware that we should significantly reduce costs per geodetic facility envisaging a denser
global geodetic network in the future.

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GGOS Affiliate: GGOS D-A-CH
Chair: Hansjörg Kutterer (Germany)
GGOS D-A-CH is the GGOS affiliate of the so-called D-A-CH region representing thosecountries in Central Europe with significant German-speaking populations: Germany (D),Austria (A), Switzerland (CH). GGOS D-A-CH is based on a joint initiative of the national
geodetic commissions DGK, ÖGK and SGK in 2020. It was approved by GGOS CB on May
19, 2021, as the second regional GGOS affiliate after GGOS Japan.
GGOS D-A-CH was initiated by the members and guests of the Geodesy department of DGK
and the respective members of ÖGK and SGK. There is a long-term and outstanding traditionof cooperation within these commissions both contributing to and benefitting from activities inmathematical, physical and space geodesy. GGOS D-A-CH was established as basis and forum
for GGOS-related activities in the D-A-CH region and in particular as a stimulator andincubator for GGOS-related coordinated research. The publication “Geodesy 2023” by J.
Müller and R. Pail (https://geodaesie.info/zfv/zfv-archiv/zfv-147-jahrgang/zfv-20224/geodesy-2030), with contributions from a multitude of scientists in the D-A-CH region, serves
as scientific guideline. It addresses the grand challenges of Earth sciences and the respective
contributions of Geodesy reflecting the scientific innovations and technological developmentsof the present decade and beyond.
GGOS D-A-CH comprises university members and members from the public sector.
Qualification for membership is based on an expression of interest. As of June 2023, there are
the following participations:
Coordination group: Johannes Böhm (Austria), Johannes Bouman (Germany), Susanne Glaser(Germany), Adrian Jäggi (Switzerland), Roland Pail (Germany), Markus Rothacher(Switzerland), Harald Schuh (Germany)Group of member institutions:• Universities: Technical University Berlin, University Bern, University Bonn, Technical
University Dresden, Leibniz University Hannover, Karlsruhe Institute of Technology,
Technical University Munich, University Stuttgart, Technical University Vienna, ETH
Zurich• Research institutions and national agencies: Federal Office of Metrology and Surveying(BEV, Austria), Federal Agency for Cartography and Geodesy (BKG, Germany), GFZ
German Research Centre for Geosciences (GFZ, Germany)
Members of GGOS D-A-CH have actively been involved in the preparation of scientificmeetings and conferences. In May 2022, a round-table discussion was organized under theumbrella of the German Research Foundation (DFG) in order to prepare a joint research
proposal. Regular presentation and reporting is organized within the GGOS CB meetings, theannual GGOS Days and the annual gatherings of the national geodetic commission. In addition,
regular meetings with GGOS Japan took place for mutual exchange. Finally, the IAG

Global Geodetic Observing System (GGOS)

Symposium G06 “Monitoring and Understanding the Dynamic Earth with Geodetic
Observations” within the 28th General Assembly of the IUGG in Berlin 2023 was co-organized
and co-convened.

GGOS Science Panel
Chair: Kosuke Heki (Japan) Comm. 2
Members:
Original members in this term 2019-2023• M. Rothacher (Switzerland) Comm.1• G. Blewitt (USA) Comm. 1• T. Gruber (Germany) Comm. 2• J. Chen (USA) Comm. 3• J. Ferrandiz (Spain) Comm. 3• J. Wickert (Germany) Comm. 4• P. Wielgosz (Poland) Comm. 4• Y. Tanaka (Japan) ICCT• M. Crespi (Italy) ICCT• M. Sideris (Canada) FA (UHS)• P. Lognonne (France) FA (Geohazards)• D. Chambers (USA) FA(Sea level)*• E. Forootan (UK/Germany) FA (Geod. Space Weather)Members representing new organizations added in 2021
• J. Muller (Germany) QuGe
• M. Van Camp (Belgium) QuGe
• P. Sakic (Germany) ICCM
• K. Tadokoro (Japan) ICCM
• A. Klos (Poland) ICCC
• C. Blackwood (USA) ICCC
*FA dissolved
Two new members from each of the three newly organized organizations within IAG havebeen added in 2021. This made the number of members of the GGOS Science Panel increase
from 14 to 20.
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 2019-2023 period, this
support included participation in Consortium, Coordinating Board, and Executive Committee

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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 2019-2023 period, GGOS sessions
have been organized at:
•
•
•
•
•
•
•
•

2019 American Geophysical Union Fall Meeting in San Francisco
2020 American Geophysical Union Fall Meeting (virtual conference)2020 European Geosciences Union General Assembly (virtual conference)
2021 European Geosciences Union General Assembly (virtual conference)
2021 American Geophysical Union Fall Meeting (virtual conference)
2022 European Geosciences Union General Assembly (virtual conference)
2022 American Geophysical Union Fall Meeting (hybrid conference)
2023 European Geosciences Union General Assembly (hybrid conference)

Owing to the COVID19 pandemic, most international conferences from 2020 until 2022 springwere held as virtual (on-line) meetings. The 2022 December American Geophysical Union(AGU) and 2023 April European Geoscience Union (EGU) meetings were held as hybrid
meetings. As a future session, the Science Panel proposed a GGOS session in the 2023
December AGU Fall Meeting (hybrid meeting in San Francisco). AGU and EGU intend to keep
the meetings hybrid in future (2024-), but the on-site aspect will become major.
Starting in 2021, the Science Panel cooperated in the effort to renew the GGOS website, being
led by the GGOS Coordinating Office and the GGOS Bureau of Products and Standards,
specifically in reviewing the GGOS product page descriptions. The pages are now complete
and are visited frequently by researchers.
Unified Analysis Workshops (UAW) are co-organized by GGOS and International Earth
Rotation and Reference Systems Service (IERS). The 2022 Workshop was the 6th in a series
of workshops that are held every two years for the purpose of discussing issues that arecommon 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. The 2022 Workshop was held as a hybrid meeting in Thessaloniki, Greece, 2123 October. There, the discussion focused on the data analysis especially on ITRF2020.
Objectives and Planned Efforts for 2023-2027 and Beyond
During the next four years 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:••••American Geophysical Union (AGU), Fall Meetings
Asia Oceania Geosciences Society (AOGS), Annual Meetings (optional)
European Geosciences Union (EGU), General Assemblies
International Association of Geodesy, General and Scientific Assemblies**GGOS sessions in IUGG/IAG are mainly organized by GGOS-EC members rather thanthe Science PanelGlobal Geodetic Observing System (GGOS)The Strategic Plan Workshop was held in Munich, Germany during 16-17 November 2022
following the GGOS Days. There, future roles expected for the Science Panel were briefly
discussed.
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. Activities related to EGV will continue in thecommittee on EGV established in 2019, which includes the whole Science Panel members.

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GGOS Bureau of Networks and Observations
Prepared by Michael Pearlman, Erricos C. Pavlis, Frank Lemoine, Daniela Thaller, Benjamin
Männel, Roland Pail, C.K. Shum, Nick Brown, Sandra Blevins, Ryan Hippenstiel
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:
•
•
•
•
•

•

Director (Mike Pearlman/CfA USA)
Secretary (Claudia Carabajal/SSAI NASA USA)
Analysis Specialist (Erricos Pavlis/UMBC USA)
IERS Representative (Ryan Hippenstiel/ NOAA USA)
Representatives from each of the member Services:o IGS (Allison Craddock/JPL CalTech USA, Markus Bradke/ GFZ Germanyo ILRS (Frank Lemoine /NASA USA, Clement Courde/OCA, France)o IDS (Jérôme Saunier/IGN France, Guilhem Moreaux, CLS France)o IVS (Hayo Hase/BKG Germany, Dirk Behrend/NASA USA)o IGFS (Riccardo Barzaghi/PM Italy, George Vergos/UT Greece)o PSMSL (Elizabeth Bradshaw/BODC UK, Lesley Rickards/ BODC UK)
Representatives from each of the member Standing Committees:o PLATO (Daniela Thaller/BKG Germany, Benjamin Maennel/GFZ Germany)o Data and Information Systems (Nick Brown/GA Australia, Sandra
Blevins/NASA/USA)o Satellite Missions (Roland Pail/TUM Germany, C.K. Shum/OSU USA)o IERS WG on Survey Ties and Co-location (Ryan Hippenstiel/ NOAA USA)

Purpose and Scope• Advocate for new and increased network participation, encouraging formation of newpartnerships to develop new sites and co-location sites•

Hold annual meetings of the Services and Standing Committees/Working Groups toshare and discuss status plans, progress;•

Give talks and posters at public meetings to help familiarize the community withGGOS activities;•

Encourage integration of ground observation networks within the GGOS affiliatedNetwork;•

Work with the UN GGIM and its affiliates to develop a plan for the implementation of
the IAG geodetic network to satisfy the IAG requirement for the ITRF

Global Geodetic Observing System (GGOS)

Activities• Participated and gave talks/posters on the BN&O and the ILRS at the AGU, EGU,
IAG, JpGU-AGU, etc.
• The BN&O has been advocating for enhanced network infrastructure for Latin
America, and participated and gave talks on the GGOS Bureau of Networks andObservations at;
o IUGG meeting “Implementation of the Global Reference Frame (GGRF) in
Latin America” in in Buenos Aires, September 16 - 20, 2019;o SIRGAS meeting in Rio de Janeiro, November 12 – 14, 2019;o Unified Analysis Workshop in Paris, October 2 – 4, 2019;•••

Met with representative from existing and planned stations in Latin America to discuss
strategies, station details, equipment, etc.
Supported new and vulnerable stations and analysis centers with letters of support anddocumentation;
New SLR and VGOS stations have recently become active and others are scheduled to
become active over the next few years; we have been disappointed by the schedule
delays in many stations so we are now taking a closer look at deployment schedules totry to figure out what is realistic and what kind performance we can reasonably
expect; from that we can estimate the expected quality of our data products including
the Reference Frame.

•

Worked with the IGFS define the gravity field measurement configuration at GGOS
network core and co-location sites; encourage the cooperation of the IGS and DORIS
with PSMSL to enhance the geodetic link of the tide gauges to the reference frame;•

A Memorandum of Cooperation had been established with ROSCOSMOS and the
ILRS to enhance cooperation and data diagnosis issues: this may provide a vehicle forbroader cooperation; the Russians have been regular participants in ILRS activities,
we believe that are desirous of formally joining the GGOS network; Unfortunately thecurrent situation with Ukraine has put a significant hold on much of this activity;•

The GGOS “Site Requirements for GGOS Core Sites” document (with the IAG
Services) should be updated to include the requirements for the gravity field with theguidance of the IGFS;

Outcomes and Future Plans• Continue the tasks above;•

Bureau Call for Participation in the “Global Geodetic Core Network: Foundation for
Monitoring the Earth System”; work with new potential groups interested inparticipating; discussions are underway with the Russian SLR network; they
participate in ILRS and VLBI activities, but have yet to join the GGOS network; closewith the Russians;•

Project network status 5 and 10 years ahead to anticipate data product quality
especially the ITRF;•

Work with the IAG and the UN GGIM to develop a plan for the IAG Network tosatisfy the ITRF requirements;•

The Standing Committees/Working Groups will each continue their tasks (see below)

Websites:

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https://ggos.org/about/org/bureau/bno/
Presentations and Posters
Pearlman, et al., Update on the Activities of the GGOS Bureau of Networks and Observation,
AGU Fall virtual meeting, December 14, 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 andPlans of the Bureau of Networks and Observations”, Abstract No. EGU2019-6181, presented
at the European Geosciences Union General Assembly, Vienna, Austria, April 07-12, 2019.
Pearlman et al., Status and Plans for the GGOS Bureau of Networks and Observations, IUGG
Meeting, Montreal Convention Center, July 15, 2019.
Pearlman, M., GGOS Bureau of Networks and Observations, presented at the IUGG,
Implementation of the Global Reference Frame (GGRF) in Latin America, Buenos Aires,
Argentina, September 16 – 20, 2019.
Pearlman, M., C. Noll, and E. Pavlis, GGOS Bureau of networks and Observations, GGOS
Days 2019, October 5 – 7, 2019.
Pearlman, M. and Noll, C., GGOS Bureau of Networks and Observations, GGOS Days 2019
Meeting, Rio de Janiero, Brazil, November 13 – 14, 2019.
Pearlman, M., et al., Current Activities and Plans of the Bureau of Networks andObservations” (poster), AGU Fall virtual meeting, December 1 – 17, 2020.
Pearlman, M., et al., “GGOS Bureau of Networks and Observations: Network Status andRelated Activities” (poster), IAG Symposium 2021 Beijing, China, June 28 – July 2, 2021.
Pearlman, M., et al., “An Update on the GGOS Bureau of Networks and Observations”,
EGU General Assembly, Vienna, Austria, May 23 – 27, 2022.
Presentations on the BN&O at each annual GGOS Coordinating Board meeting and GGOS
Days Meeting.

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 May 2023):• AIUB, Switzerland: R. Dach, F. Andritsch (left AIUB)• BKG, Germany: D. Thaller, H. Hellmers• DGFI-TU Munich, Germany: M. Bloßfeld, A. Kehm
• ETH Zürich, Switzerland: M. Rothacher, B. Soja, M. Schartner, I. Herrera Pinzón (now at
AIUB)• GFZ/TU Berlin, Germany: B. Männel, S. Glaser• IfE University Hannover, Germany: J. Müller, L. Biskupek• IGN, France: D. Coulot, A. Pollet

Global Geodetic Observing System (GGOS)

•
•
•
•
•

JPL, USA: R. Gross
NASA GSFC/JCET, USA: E. Pavlis
NMA, Norway: E. Mysen, G. Hjelle
TU Vienna, Austria: J. Böhm, H. Wolf
University Wrozlaw, Poland: K. Sosnica, J. Najder

Purpose and Scope
•
•
•
•
•
•

Develop optimal methods of deploying next generation stations, and estimate the dependenceof reference frame products on ground station architectures
Estimate improvement in the reference frame products as co-located and core stations areadded to the network
Estimate the dependence of the reference frame products on the quality and number of the siteties, the space ties, and potential atmospheric 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 are added,
e.g., use co-locations on GNSS and LEO satellites, add special co-location satellites (GRASP,E-GRASP/Eratosthenes, NanoX, GENESIS, etc.)
Estimate the improvement in the reference frame products as new observation types andconcepts are added, e.g., inter-satellite links

Achievements during the reporting time span:
•
•
•
•
•
•
•
•
•

•
•
•
•
•
•
•

Several projects related to simulation studies became funded and even extended to a second
phase at various institutions (e.g., GFZ, DGFI-TUM, TU Vienna, University Wrozlaw, IfE
Hannover)
Several geodetic software packages have been augmented by the capability to carry out
realistic simulation scenarios (e.g., VieVS, DOGS, Bernese, Geodyn, EPOS-OC)
Simulations of optimal locations for an additional VGOS station were carried out, with special
focus on its contribution to EOP determination (Schartner et al., 2020). A location in SouthAmerica is most beneficial.
Studies on integration of VGOS and S/X-legacy network for VLBI were carried out.
Optimized scheduling methods for VGOS were investigated.
Simulations and analysis of VLBI tracking data of Galileo satellites are carried out to assess
the possibilities for improving dUT (Wolf et al. 2021).
The benefit of using a local time transfer system for short VLBI baseline analysis wasdemonstrated.
Studies for combined GNSS-Rapid and VLBI Intensives showed that improved ERPs withlow latency can be derived (Hellmers et al., 2019).
Studies on the quality of GNSS-based scale by adding LEOs to an integrated processing or byusing Galileo data were carried out. A correction to the satellite antenna phase center offset(PCO) in nadir direction of approx. -200mm was found for GPS (Huang et al., 2021; Huang etal., 2022).
Studies on the potential of SLR Short baseline observations (e.g. at Wettzell) for monitoring
the terrestrial local ties were carried out in order to identify technique-specific systematic error
sources.
Studies on the impact of adding the LLR data in infra-red to reference frame products werecarried out by IfE, Uni Hannover.
Studies on future GNSS constellations were carried out (Glaser et al., 2020).
Consistent estimation of TRF+CRF+EOP started along with the VLBI reprocessing activities
related to ITRF2020 generation.
Studies related to alternative parameterization of EOPs from 24-h VLBI sessions started, inorder to be consistent with estimation intervals by the other space-geodetic techniques.
PLATO members are involved in the GENESIS science team and supports the mission withrealistic simulations and contributed to the GENESIS white paper (Delva et al., 2023)
Presentations were given at IAG Assembly (July 2019), annual conferences of EGU and AGU

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514

as well as meetings of IAG Services.

Future Plans
•
•

•
•

Improved analysis methods for reference frame products will be developed with the focus ofincluding 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 dedicatedsatellite mission as co-location in space. Therefore, we recommend to strive by all means for asatellite mission dedicated to co-location in space. The acceptance of the GENESIS mission
by ESA’s ministerial conference in November 2022 was a first achievement in this context.
A coordinated analysis campaign with exchanged simulated observations was re-started in
May 2021 in order to get an estimate about the comparability of the simulation studies.
Simulations of network projections will be carried out if new potential stations come up.

Publications
•
•

•

•
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•
•

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•

•

Biskupek, L. and Müller, J. and Torre, J-M. (2021): Benefit of New High-Precision LLR Data for theDetermination of Relativistic Parameters. Universe, 7, 34 DOI: 10.3390/universe7020034
Delva, P., Altamimi, Z., Blazquez, A., Blossfeld, M., Böhm, J., Bonnefond, P., Boy, J.-P., Bruinsma, S.,
Bury, G., Chatzinikos, M., Couhert, A., Courde, C., Dach, R., Dehant, V., Dell’Agnello, S., Elgered, G.,
Enderle, W., Exertier, P., Glaser, S., Haas, R., Huang, W., Hugentobler, U., Jäggi, A., Karatekin, O.,
Lemoine, F. G., Le Poncin-Lafitte, C., Lunz, S., Männel, B., Mercier, F., Métivier, L., Meyssignac, B.,
Müller, J., Nothnagel, A., Perosanz, F., Rietbroek, R., Rothacher, M., Schuh, H., Sert, H., Sosnica, K.,
Testani, P., Ventura-Traveset, J., Wautelet, G., Zajdel, R. (2023): GENESIS: co-location of geodetic
techniques in space. - Earth Planets and Space, 75, 5. https://doi.org/10.1186/s40623-022-01752-w
Dill, R., H. Dobslaw, H. Hellmers, A. Kehm, M. Bloßfeld, M. Thomas, F. Seitz, D. Thaller, E.
Schönemann, U. Hugentobler (2020): Evaluating Processing Choices for the Geodetic Estimation ofEarth Orientation Parameters with Numerical Models of Global Geophysical Fluids. J Geophys Res
Solid Earth 125(9):e2020JB02,002. https://doi.org/10.1029/2020JB020025
Glaser S, König R, Neumayer K H, Balidakis K, Schuh H (2019) Future SLR station networks in theframework of simulated multi-technique terrestrial reference frames, Journal of Geodesy
doi:10.1007/s00190-019-01256-8
Glaser S, König R, Neumayer K H, Nilsson T, Heinkelmann R, Flechtner F, Schuh H (2019) On theimpact of local ties on the datum realization of global terrestrial reference frames, Journal of Geodesy,
doi:10.1007/s00190-018-1189-0
Glaser S, Michalak G, Männel B, König R, Neumayer K H, Schuh H (2020) Reference system origin
and scale realization within the future GNSS constellation “Kepler”, Journal of Geodesy, doi:
10.1007/s00190-020-01441-0
Glaser S, Michalak G, Männel B, König R, Neumayer K H, Schuh H (2020c) Future GNSS
Infrastructure for Improved Geodetic Reference Frames, IEEE Xplore, doi:
10.23919/ENC48637.2020.9317460
Hellmers, H., D. Thaller, M. Bloßfeld, A. Kehm, A. Girdiuk (2019): Combination of VLBI Intensive
Sessions with GNSS for generating Low-latency Earth Rotation Parameters. Advances in Geosciences,
50:49-56. Doi: 10.519/adgeo-50-49-2019
Huang W., Männel B., Brack A., Schuh H. (2021) Two methods to determine scale-independent GPS
PCOs and GNSS-based terrestrial scale: comparison and cross-check. GPS Solut 25, 4.
https://doi.org/10.1007/s10291-020-01035-5
Huang, W., Männel, B., Brack, A., Maorong, G., Schuh, H. (2022) Estimation of GPS transmitter
antenna phase center offsets by integrating space-based GPS observations, Advances in Space
Research, 69(7), https://doi.org/10.1016/j.asr.2022.01.004
Kehm A., Bloßfeld M., König P., Seitz F. (2019): Future TRFs and GGOS – where to put the next SLR
station? Advances in Geosciences, 50, 17–25, DOI 10.5194/adgeo-50-17-2019
Kehm A., Hellmers H., Bloßfeld M., Dill R., Angermann D., Seitz F., Hugentobler U., Dobslaw H.,
Thomas M., Thaller D., Böhm J., Schönemann E., Mayer V., Springer T., Otten M., Bruni S., Enderle
W. (2023): Combination strategy for consistent final, rapid and predicted Earth rotation parameters.
Journal of Geodesy, 97(3), DOI 10.1007/s00190-022-01695-w
Lengert, L., D. Thaller, C. Flohrer, H. Hellmers, A. Girdiuk (2022): On the improvement of combined
EOP series by adding 24-hours VLBI to VLBI Intensive and GNSS data. In: Proceedings of the IAG

Global Geodetic Observing System (GGOS)

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Scientific Assembly 2021, Beijing / virtual. IAG Symposia Series
Michalak G, Glaser S, Neumayer K H, König R (2021) Precise orbit and Earth parameter determination
supported by LEO satellites, inter-satellite links and synchronized clocks of a future GNSS, Advancesin Space Research, doi:10.1016/j.asr.2021.03.008
Pinzón, I.H., Rothacher, M. (2020). Co-location of Space Geodetic Techniques: Studies on IntraTechnique Short Baselines. In: Freymueller, J.T., Sánchez, L. (eds) Beyond 100: The Next Century inGeodesy. International Association of Geodesy Symposia, vol 152. Springer, Cham.
https://doi.org/10.1007/1345_2020_95
Herrera Pinzón, I., Rothacher, M. and Riepl, S. Differencing strategies for SLR observations at theWettzell observatory. J Geod 96, 4 (2022). https://doi.org/10.1007/s00190-021-01588-4
M. Schartner, J. Böhm, A. Nothnagel (2020): Optimal antenna locations of the VLBI Global Observing
System for the estimation of Earth orientation parameters. Earth Planets and Space, 72 (2020), 87; S. 1
– 14
Singh, V.V., Biskupek, L., Müller, J., Zhang, M. (2021): Impact of non-tidal station loading in LLR.
Advances in Space Research DOI: 10.1016/j.asr.2021.03.018

GGOS Standing Committee on Satellite Missions (CSM)
Chair: Roland Pail (Germany)
Vice-Chair: C.K. Shum (USA)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 other documentation. CSM
traditionally has about one meeting per year, although the pandemic has precluded and will likely
prohibit in the near future any such meetings. Therefore, the main work is and will accomplished via
email exchanges. Additional members will be added in the near future.
Purpose and Scope
The Committee on Satellite Missions (CSM) has been set-up as an international panel of experts, with
consultants of national and international space agencies.
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 andspace-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 Earth observation.
They are the key for monitoring change processes in the Earth system on a global scale with hightemporal and spatial resolution. Therefore, beyond purely scientific objectives they meet a number ofsocietal 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 the availability of satellite infrastructure, to propose andto advocate new missions or mission concepts, especially in case that a gap in the infrastructure is
identified.
Activities
Improve coordination and information exchange with the missions for better ground-based network
response to mission requirements and space-segment adequacy for the realization of GGOS goals,
including:•••

Advocate, coordinate, and exchange information with satellite missions as part of the GGOS
space infrastructure, for a better ground-based network response to mission requirements andspace-segment adequacy for the realization of the GGOS goals;
Assess current and near-future satellite mission infrastructures and their relevance towards
achieving GGOS 2020 goals;
Support proposals for new mission concepts and advocate for needed missions;Report of the IAG Vol. 43 ─ Travaux de l’AIG 2019-2023

516

•
•

Interfacing and outreach with other components of the Bureau; especially with the groundnetworks component, the GGOS Performance Simulations and Architectural Trade Offs
(PLATO) activities, as well as with the Bureau of Standards and Products.
Advocate the realization of future gravity field missions: Future gravity satellite constellation
MAGIC (double-pair mission). Decision on funding of polar pair (P1) by NASA/DLR;
decision on Phase B of inclined pair (P2) at ESA Ministerial Conference in November 2022

Future Activities and Objectives• Continue the planned activities, i.e., updating the two central lists, supporting future satellite
missions, etc.;• Work with the Coordinating Office to set up and maintain a Satellite Missions Committee
section on the GGOS website;• Evaluate the contribution of current and near-term satellite missions to the GGOS 2020 goals;• Work with GGOS Executive Committee, Focus Areas, and data product development
activities (e.g., ITRF) to advocate for new missions to support GGOS goals;• Support the Executive Committee and the Science Committee in the GGOS Interface withspace agencies;• Finalize and publish (outreach) of Science and User Requirements Documents for future
gravity field missions.
• Advocate and support national and international space agencies in their processes towards
future gravity missions, by providing/exchange available technical information, and propose
to support/participate in missions studies towards their realization;• Communicate with Chinese IAG colleagues to seek advice and collaborations to advocate forpossible availability of Chinese gravity mission data to the scientific community,
Continue exchange with PLATO on joint interests and possible collaborations; set up a moreformal procedure of collaboration; discuss needs and run simulations to study the impact of
future satellite missions, identify gaps for fulfilling the GGOS goals, etc.;• Investigate possible collaborations with commercial satellite companies, e.g., Spire Global, Inc.,
PlanetIQ, GeoOptics, with launched Cubesat constellations, on GGOS research andapplications including GNSS occultation, and bistatic radar reflectometry.
WebsiteWebsite will be built or improved.
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.
Schlaak, M; Pail, R; Jensen, L; Eicker, A: Closed loop simulations on recoverability of climate trends
in next generation gravity missions. Geophysical Journal International 232 (2), 2022, 1083-1098.
Zahzam, Nassim; Christophe, Bruno; Lebat, Vincent; Hardy, Emilie; Huynh, Phuong-Anh; Marquet,
Noémie; Blanchard, Cédric; Bidel, Yannick; Bresson, Alexandre; Abrykosov, Petro; Gruber, Thomas;
Pail, Roland; Daras, Ilias; Carraz, Olivier: Hybrid Electrostatic–Atomic Accelerometer for FutureSpace Gravity Missions. Remote Sensing 14 (14), 2022, 3273.
Purkhauser, Anna F.; Pail, Roland: Triple-Pair Constellation Configurations for Temporal Gravity
Field Retrieval. Remote Sensing 12 (5), 2020.
Purkhauser, Anna F; Siemes, Christian; Pail, Roland: Consistent quantification of the impact of key
mission design parameters on the performance of next-generation gravity missions. GeophysicalGlobal Geodetic Observing System (GGOS)

Journal International 221 (2), 2020, 1190-1210
Hauk, Markus; Pail, Roland: Gravity Field Recovery Using High-Precision, High–Low Inter-Satellite
Links. Remote Sensing 11 (5), 2019
Pail, R.; Bamber, J.; Biancale, R.; Bingham, R.; Braitenberg, C.; Eicker, A.; Flechtner, F.; Gruber, T.;
Güntner, A.; Heinzel, G.; Horwath, M.; Longuevergne, L.; Müller, J.; Panet, I.; Savenije, H.;
Seneviratne, S.; Sneeuw, N.; van, Dam T.; Wouters, B.: Mass variation observing system by high low
inter-satellite links (MOBILE) – a new concept for sustained observation of mass transport fromspace. Journal of Geodetic Science 9 (1), 2019, 48—58

GGOS Standing Committee on Data and Information Systems
Chair: Nicholas Brown (GA Austria)
Vice-Chair: Sandra Blevins (NASA USA)
Purpose and Scope
The Committee on Data and Information had two GGOS objective areas:• Development and implementation of a portal;• Development and implementation of a metadata scheme
Near term Metadata activity (NASA CDDIS)
CDDIS continues to add new data and derived product collections and further populate collectionlevel metadata stored in the Earth Observation System Data and Information System (EOSDIS)
Common Metadata Repository (CMR). CDDIS is an EOSDIS Distributed Active Archive Centers(DAACs) and thus utilizes the EOSDIS infrastructure to manage collection and granule level metadata
describing CDDIS archive holdings; these metadata include 120 published DOIs representing DORIS,
GNSS, and SLR data and derived product collections archived at the CDDIS archive. Since the AGU
Fall Meeting 2019 the CDDIS actively participates in the GGOS DOI Working Group, sharing NASA
Earth Science Data and Information System (ESDIS) DOI methods and best practices with the greater
Geodesy community.
Longer-Term Metadata activity (Nick Brown/Geoscience Australia)
Development of a Geodesy Markup Language (GeodesyML), for the GNSS community; potential for
expansion to the other space geodesy techniques and GGOS. The current study is identifying metadata
standards and requirements, assessing critical gaps and the how these might be filled, what changes
are needed in the current standards, and who are the key people who should work on it (morecomprehensive scheme). The schema that would be used by its elements for standardized metadata
communication, archiving, and retrieval. First applications would be the automated distribution of upto-date station configuration and operational information, data archives and catalogues, and procedures
and central bureau communication. One particular plan of great interest is a site metadata schema
underway within the IGS Data Center Working Group. This work is being done in collaboration with
the IGS, UNAVCO, SIO, CDDIS, and other GNSS data centers. The current activity is toward ameans of exchange of IGS site log metadata utilizing machine-to-machine methods, such as XML andweb services, but it is expected that this will be expanded to the other Services to help manage site
related metadata and to other data related products and information. Schema for the metadata should
follow international standards, like ISO 19xxx or DIF, but should be extendable for technique-specificinformation, which would then be accessible through the GGOS Portal.
This work has been put on hold due to the unavailability of Nicholas Brown and Sandra Blevins
departure from CDDIS. Sandra Blevins has been replaced by Taylor Yates from NASA/CDDIS;
Discussion has been initiated with the IGS on a possible path forward in Nick’s activity.

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Activities and Actions
Activities underway at CDDIS:
1. Complete collection level metadata related to CDDIS data and derived product holdings in the
EOSDIS Common Metadata Repository (CMR)
2. Continue to re-ingest CDDIS data and derived product holdings in order to extract granulelevel metadata linked to these new collection level records
Activities underway in Geodesy Markup Language (GeodesyML) System
1. Review and document the metadata and standards requirements of precise positioning users in
expected high use sectors (e.g. precision agriculture, intelligent transport, marine, locationbased services etc.).
2. Assess and document the critical gaps in standards which restrict how Findable Accessible
Interoperable and Reusable (FAIR) precise positioning data is for the expected high use
sectors.
3. Record use cases of standards being applied well and the benefits it provides to users.
4. Review the “use cases” of geodetic data developed by Geoscience Australia and the IGS Data
Center Working Group.
(https://drive.google.com/drive/folders/1L792ImLktAiAbmhX9WZhvHrXB3BMD00G?usp=sharing) and document what work and time would be required to ensure these use cases can be
met in international standards. This could be:• Identify which gaps can be filled by GeodesyML• Identify which components of GeodesyML would be better, handled by / integrated with,existing standards (such as TimeSeriesML, SensorML, Observations and Measurements)
where possible.
• Identify which components of already existing international geospatial infrastructure canbe approached (such as the European Inspire initiative)• Advise on who we should engage with from the OGC/ISO community to facilitate achange to a standard to meet our requirements.
5. Work with Project Partners to develop and test other use cases (e.g. integration of geodetic
data with geophysics data (e.g. tilt meters), Intelligent Transport Sector data, mobile
applications). Then, document what work and time would be required to ensure these use
cases can be met in international standards.
6. Provide advice on how to best engage with the right communities to learn from theirexperiences, test their tools and influence the development of required standards.
Future Activities and Objectives
1. Working with the IGS Infrastructure Committee, complete the development of the metadata
system for GNSS (IAG) and then expand its role to the other IAG Services (IVS, ILRS, IDS,
IGFS, etc.).

IERS Working Group on Site Survey and Co-location
JWG 1.2.2 : Methodology for surveying geodetic instrument reference points
Chair:
Ryan Hippenstiel (USA)Vice-chair : Sten Bergstrand (Sweden)Global Geodetic Observing System (GGOS)

Members• Zuheir Altamimi (IGN, France)• Sten Bergstrand (BIPM, France)• Steven Breidenbach (NOAA/NGS, USA)• Benjamin Erickson (NOAA/NGS, USA)
• Cornelia Eschelbach (Frankfurt Univ. of Applied Sciences, Germany)• Kendall Fancher (NOAA/NGS, USA)
• Charles Geoghegan (NOAA/NGS, USA)
• Dionne Hansen (LINZ, New Zealand)• Ryan Hippenstiel (NOAA/NGS, USA)
• Christopher Holst (Technische Universität München, Germany)• Michael Lösler (Frankfurt Univ. of Applied Sciences, Germany)• Kevin Jordan (NOAA/NGS, USA)
• Saho Matsumoto (GSI, Japan)• Jack McCubbine (GA, Australia)• Damien Pesce (IGN, France)• Anna Riddell (GA, Australia)• Owen Smallfield (LINZ, New Zealand)• Jerome Saunier (IGN, France)• Elena Martínez Sánchez, (Observatorio de Yebes, Spain)• Daniela Thaller, (BKG, Germany)• Bart Thomas (GA, Australia)• Agnes Weinhuber (Technische Universität München, Germany)
Correspondent Members• Xavier Collilieux (IGN, France)• Mike Pearlman (Harvard/GGOS, USA)
• Robert Heinkelmannm, (GFZ, Germany)

Overview
Areas of work of the Working Group on Site Survey and Co-location are standards anddocumentation (guidelines, survey reports, etc.), coordination (share know-how and join efforts
between survey teams), research (investigate discrepancies between space geodesy and tie
vectors, alignment of tie vectors into a global frame), and cooperation. Our group has a new setof terms and has received confirmation of new participants in the group. We would continue
to encourage participation from any agency or community that is conducting research,
improving protocols, or completing field surveys of local ties as sites with various space
geodesy techniques present. Our group has continued to share improved protocols,
technologies, and instrumentation to provide the most accurate tie measurements possible forall sites around the world. We reminded participants to share their contributions of local tie
data for inclusion into ITRF2020 and many were submitted.
Activities and publications during the period 2019–2023
Improvements have been made to standardize report and data submissions of local tie surveys
to provide consistency across all agencies. Survey data has recently been reported with new
standards in place.
The group is continuing to explore methodologies to measure and quantify antenna
deformation. Research and continued field tests using laser scanning and terrestrial inSAR havebeen discussed. In addition, a comparison of two approaches to quantifying deformation effects

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at Onsala will be undertaken. Members completed and documented work researching sitedependent GNSS antenna calibrations to account for systematic errors and biases. Personnel at
Yebes are studying data collected from both a laser scanner and UAV, detailing differences insolutions at various temperatures and times of day.
Measurements were collected at the Zeppelin Observatory (Svalbard, Norway) andHartebeesthoeck has been reprocessed (Muller et al., 2020). The latter was assisted by updatingof local software to allow estimating VLBI and SLR references points from raw survey data
into one single processing.
A tie survey at Yarragadee was completed in June of 2021, the results of which were developed
into a presentation shared with working group members and participants of the Unified Analysis
Workshop in 2022. In addition, Geoscience Australia (GA) recently completed a tie survey at
Hobart with survey results and reporting forthcoming. GA continues to look at cooperation
with universities to improve resources available and the efficiency of surveys.
Colleagues from Frankfurt Univ. of Applied Sciences, BKG and NLS submitted the results andfurther processing of tie surveys at Wettzell and Metsähovi for publication in the IAG 2021
conference proceedings.
IGN contributed local tie surveys at Malé, Crozet, Futuna, and Grasse, including new SAR
reflectors and additional work processing with fully automated determination of the SLR
telescope reference point at Côte d’Azur. This work (Barneoud, et al., 2023) was presented at
REFAG2022. IGN also completed an updated of the COMP3D software which now includes
full integration of axis determination and increased ability to input data. This software wasused to process a 2021 survey of Ny-Ålesund (Brandal).
The US National Geodetic Survey conducted an IERS local site survey at the National Radio
Astronomy Observatory in Maui (GNSS and SLR), the Table Mountain GeophysicalObservatory in Colorado (new GNSS, gravity), Midway Naval Research Laboratory's OTF in
Virginia (GNSS and SLR), and the International Earth Rotation and Reference Systems Service(IERS) Mauna Kea site (VLBA). Surveys were paused in the spring of 2020 due to the COVID
pandemic and partially resumed in the fall of 2021. In addition, surveys investigating lines ofsight and detailing the calibration piers for the SLR were performed at Goddard Geophysicaland Astronomical Observatory (GGAO) in 2021 and 2022. A survey at KPGO - Kōkeʻe Park
Geophysical Observatory was completed in May of 2023 and the final results and report will
be released soon.
NGS fully implemented the use of an absolute laser tracking system (Leica AT402) into allcompleted tie surveys, enhancing precision of terrestrial observations. Progress was made ontechnical memorandum documenting current NGS procedures which will be released whendevelopments are complete.
NGS has developed deflection of vertical (DoV) measurement capabilities utilizing a robotic
total station and camera, and will continue testing equipment for deployment on upcoming local
tie surveys. It is being called the TSACS (Total Station Astrogeodetic Control System), andthe procedures and specifications were shared with researchers from Frankfurt who built andtested a similar system.
Collaboration among the group members has increased with information sharing leading tosoftware, hardware, processing, and field protocols improvements. As an example, GSI Japan

Global Geodetic Observing System (GGOS)

and Land Information New Zealand held a recent workshop with positioning staff. Saho
presented about a local tie survey at Ishioka. In addition, GSI also released a video detailingthe Ishioka site which highlighting co-location work.
Within the joint project GeoMetre, members determined the reference point of an SLR
telescope at Wettzell, the Satellite Observing System Wettzell (SOS-W), using applied closerange photogrammetry instead of a polar measurement system.
Close range photogrammetry was also used to investigate on the deformation behaviour of thereceiving unit of the Onsala Twin Telescope (OTT-N), as well as the 20 m Radio Telescope
Wettzell (RTW) and the Twin Telescope Wettzell (TTW-2) in joint measurement campaigns
of Frankfurt Univ. of Applied Sciences and Bochum Univ. of Applied Sciences. The signal pathvariations of these radio telescopes were derived using the common approach as well as spatial
ray tracing. The results were reported to the IVS. Since VGOS-antennas are designed forbroadband reception, the impact of frequency-dependent illumination functions onto theobtained signal path variations was studied in detail.
There is also a general interest from all members about moving towards locating InSAR targets
and including them in tie surveys when co-located with other techniques. Some field results
were captured in Collilieux et. al. 2022 as listed below.
Overall, the group has been active in this period, increasing the vectors used from ITRF2014 to
ITRF2020, and decreasing the number of vectors with a discrepancy of greater than 5 mm.
(Altamimi, 2023).

References
Altamimi, Z., P. Rebischung, X. Collilieux, L. Métivier and K. Chanard (2023) ITRF2020: An
augmented reference frame refining the modeling of nonlinear station motions, J Geod.
10.1007/s00190-023-01738-w
Barneoud, J., C. Courde, J. Beilin, M. Germerie-Guizouarn, D. Pesce, M. Vidal, X. Collilieux
and N. Maurice (2023) Automatic determination of the SLR reference point at Côte d’Azur
multi-technique geodetic Observatory, REFAG 2022 proceedings, in review
Bergstrand, S., Jarlemark, P., Herbertsson, M. (2020). Quantifying errors in GNSS antenna
calibrations: Towards in situ phase center corrections, J Geod. 94. 10.1007/s00190-020-014330
Collilieux, X., Courde, C., Fruneau, B., Aimar, M., Schmidt, G., Delprat, I., Defresne, M.-A.,
Pesce, D., Bergerault, F., Wöppelmann, G. (2022). Validation of a Corner Reflector installation
at Côte d’Azur multi-technique geodetic Observatory. Advances in Space Research. 70.
10.1016/j.asr.2022.04.050
Eschelbach, C., Lösler, M. (2022), A Feasibility Study for Accelerated Reference Point
Determination Using Close Range Photogrammetry. 5th Joint International Symposium on
Deformation Monitoring (JISDM), 20-22 June 2022, Polytechnic University of Valencia(UPV), Valencia, Spain, 2022. 10.4995/JISDM2022.2022.13417

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Eschelbach, C., Lösler, M., Haas, R., Greiwe (2020) A.: Untersuchung vonHauptreflektordeformationen an VGOS-Teleskopen mittels UAS. In: Wunderlich, T.A. (eds.):
Ingenieurvermessung 20: Beiträge zum 19. Internationalen Ingenieurvermessungskurs,
Wichmann, 411-424, ISBN: 978-3-87907-672-7
Eschelbach, C., Lösler, M., Haas, R., Fath, H. (2019) Extension and Optimization of the Local
Geodetic Network at the Onsala Space Observatory. In: Proceedings of the 10th IVS General
Meeting, Svalbard, 27-31, NASA/CP-2019-219039
Fancher, K., Hippenstiel, R. (2019) US National Geodetic Survey - Recent and Planned Local
Site Survey Activites. Proceedings of the Unified Analysis Workshop 2019.
http://ggos.org/media/filer_public/ff/67/
ff679767-62ec-4065-acfc3394ae85d573/uaw_sitesurvey_1- hippenstiel_usnationalgeodeticsurvey.pdf
Lösler, M., Eschelbach, C., Mähler, S. et al. (2023) Operator-software impact in local tie
networks. Appl Geomat 15, 77-95. 10.1007/s12518-022-00477-5
Lösler, M., Kronschnabl, G., Plötz, C., Neidhardt, A., Eschelbach, C. (2023)
Frequenzabhängige Modellierung von Signalwegvariationen an VLBI-Radioteleskopen. zfv,
148(3), 177-187. 10.12902/zfv-0429-2023
Lösler, M., Eschelbach, C., Greiwe, A., Brechtken, R., Plötz, C., Kronschnabl, G., Neidhardt,
A. (2022) Ray Tracing-Based Delay Model for Compensating Gravitational Deformations of
VLBI Radio Telescopes. Journal of Geodetic Science, 12(1), 165-184. 10.1515/jogs-2022-0141
Lösler, M., Eschelbach, C., Klügel, T. (2022) Close Range Photogrammetry for High-Precision
Reference Point Determination: A Proof of Concept at Satellite Observing System Wettzell. In:
Freymueller, J. T., Sánchez, L. (eds.): Geodesy for a Sustainable Earth, Scientific Assembly of
the International Association of Geodesy (IAG), Springer, Berlin, 2022,
doi:10.1007/1345_2022_141
Lösler, M., Eschelbach, C., Klügel, T., Riepl, S. (2021) ILRS Reference Point Determination
using Close Range Photogrammetry. Applied Sciences, 11(6), 2785. 10.3390/app11062785
Lösler M., Eschelbach C., Riepl S., Schüler T. (2019) A Modified Approach for ProcessIntegrated Reference Point Determination. Proceedings of the 24th European VLBI Group forGeodesy and Astrometry Working Meeting, 17-19 March 2019, Las Palmas de Gran Canaria,
Spain, Haas, R., Garcia-Espada, S., López Fernández, J. A. (eds.): 172-176.
10.7419/162.08.2019
Lösler, M., Haas, R., Eschelbach, C., Greiwe, A. (2019) Gravitational Deformation of RingFocus Antennas for VGOS – First Investigations at the Onsala Twin Telescopes Project.
J Geod, 93(10), 2069-2087. 10.1007/s00190-019-01302-5
Mähler, S., Klügel, T., Lösler, M., Schüler, T., Plötz, C. (2019) Permanent Reference Point
Monitoring of the TWIN Radio Telescopes at the Geodetic Observatory Wettzell. In:
Proceedings of the 10th IVS General Meeting, Svalbard, 251-255. NASA/CP-2019-219039
Pesce, D., Saunier J. (2019) IGN Recent and Planned Local Site Survey Activities &Contribution to the EURAMET GeoMetre Project. Proceedings of the Unified Analysis

Global Geodetic Observing System (GGOS)

Workshop 2019. http://ggos.org/ media/filer_public/9f/b6/9fb60a43-3d60-4218-9f4889ac81073b79/ uaw_sitesurvey_2-saunier_ignrecentactivities.pdf
Pollinger et al., (2023) 18SIB01 Geometre, Large-scale dimensional measurements for
geodesy,
final
publishable
report,available
onlineathttps://www.ptb.de/empir2018/fileadmin/documents/empir/GeoMetre/18SIB01_GeoMetre_P
ublishable_Summary_M30_v1_ACCEPTED.pdf
Varenius, E., Haas, R., Nilsson, T. (2021) Short-baseline interferometry local-tie experiments
at the Onsala Space Observatory. J Geod 95, 54, 10.1007/s00190-021-01509-5Co-location
surveyonlinereports
https://www.ngs.noaa.gov/corbin/iss/:

http://itrf.ign.fr/local_surveys.php

and• Erickson, B., Breidenbach, S., Jordan, K. Maui co-location survey, June 2019
• Jordan, K., Hippenstiel, R., Erickson, B., Fancher, K. Stafford co-location survey, October
2019• Jordan, K., Hippenstiel, R., Fancher, K. Table Mountain co-location survey, October 2019
• Jordan, K., Hippenstiel, R., May, J. Mauna Kea co-location survey, May 2020
• Muller J.-M., Pesce D., Collilieux X., 2014 Hartebeesthoek co-location survey reprocessing
report, dec 2020
• IGN: Malé, Sep 2021
• IGN: Crozet• IGN: Futuna, Summer 2022
• IGN: Grasse, yearly, most recently Mar 2023

https://www.euramet.org/research-innovation/search-research-projects/details/project/largescale-dimensional-measurements-for-geodesy/Report of the IAG Vol. 43 ─ Travaux de l’AIG 2019-2023

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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 Modeling”, Chair: Maik Thomas(Germany)
Committee “Definition of Essential Geodetic Variables (EGV)”, Chair: Richard
Gross (USA)Working Group “Towards a consistent set of parameters for the definition of a new
GRS”, Chair: Urs Marti (Switzerland)

The Bureau of Products and Standards (BPS) is chaired and operated by the Technical
University of Munich (TUM). The BPS staff members are Detlef Angermann, Thomas Gruber,Michael Gerstl, Urs Hugentobler and Laura Sánchez (all from TUM), as well as Robert
Heinkelmann (GFZ German Research Centre for Geosciences Potsdam) and Peter
Steigenberger (German Aerospace Centre (DLR), Oberpfaffenhofen). The Bureau comprises
the staff members, the chairs of the associated GGOS components as well as representatives of
the IAG Services and other entities involved in standards and geodetic products. The present
status of the associated 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: June 2023)

Global Geodetic Observing System (GGOS)

Overview
The Bureau of Products and Standards (BPS) is a key component of IAG’s Global Geodetic
Observing System (GGOS). It supports GGOS in its goal to obtain consistent products
describing the geometry, rotation and gravity field of the Earth as well as the temporal changesof these quantities in mm-accuracy. In order to fully benefit from the ongoing technologicalimprovements of the geodetic observing systems, it is essential that the analysis of the precise
observations is based on the definition and application of common standards and conventions.
This is an important requirement for reliably monitoring global change phenomena (e.g., global
sea level rise, ice melting, global water cycle) and for providing the metrological basis for an
improved understanding of the Earth system. Figure X.1 illustrates the integration of different
observation types to determine consistent geodetic parameters as the basis for studies of the
Earth system, the interactions among its sub-components and the connection to outer space.

Fig. X.1: The integration of the “three pillars” Earth’s geometry, rotation and gravity fieldrequires unified standards to obtain consistent geodetic products as the basis for Earthsystem research and for precisely quantifying global change phenomena.
The mission of the BPS is:••••

to serve as coordinating point for the homogenization of IAG standards and products;
to keep track of the adopted geodetic standards and conventions across all componentsof the IAG;
to motivate the development of new and integrated geodetic products, needed for
Earth sciences and society;to describe and promote geodetic products (see GGOS website, www.ggos.org).

To accomplish these BPS tasks, a close interaction between the BPS and the IAG Services, theIERS Conventions Center and other entities involved in standards and conventions such as the
IAU Commission A3 “Fundamental Standards”, the International Organization forstandardization (ISO/TC 211), the Committee on Data for Science and Technology(CODATA), the United Nation Global Geospatial Information Management (UN-GGIM)
Subcommittee on Geodesy (SCoG) Working Group “Data Sharing and Development of
Geodetic Standards”, and the newly established UN Global Geodetic Centre of Excellence(UN-GGCE) has been established.

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526

Objectives
The objectives of the BPS are divided into two major topics:•

Standards: A key objective is the compilation of an inventory regarding standards,
constants, resolutions and conventions adopted by IAG and its components. This
includes an assessment of the present status, the identification of gaps and shortcomings
concerning geodetic standards and the generation of the IAG products, as well as theprovision of recommendations. It is obvious that such an inventory needs to be regularly
updated, since the IAG standards and products are continuously evolving. The BPS shallalso propose the adoption of new standards where necessary and propagate standards
and conventions to the wider scientific community promoting their use. In this context,
the BPS recommends the development of a new Geodetic Reference System GRS20XX
based on the best estimates of the major parameters related to a geocentric level
ellipsoid.

•

Products: The BPS shall take over a coordinating role regarding the homogenization ofstandards and geodetic products. The present status regarding IAG Service products
shall be evaluated, including analysis and combination procedures, accuracy assessmentwith respect to GGOS requirements, documentation and metadata information for IAG
products. The Bureau shall initiate steps to identify user needs and requirements for
geodetic products and shall contribute to develop new and integrated products. The BPS
shall also contribute to the development of the GGOS Portal (as central access point forgeodetic products), to ensure interoperability with IAG Service data products andexternal portals (e.g., GEO, EOSDIS, EPOS, GFZ Data Services).

Activities
The BPS Implementation Plan 2020 – 2022 gives an overview and schedule of the BPS tasks(see Figure X.2). The activities of the BPS are divided into three main categories: Coordination
activities, specific tasks of the BPS, and outreach activities. Currently, GGOS is developing arefined strategy and new implementation plans for its components for the term 2023 – 2026.
Updating of the BPS inventory
In 2019 and 2020, the second version of the inventory has been prepared for publication in the
Geodesist’s Handbook 2020 (Angermann et al., 2020). In this updated version of the inventory
the general structure of the original document published in the Geodesist’s Handbook 2016 islargely kept, whereas the contents of the individual sections has been updated to take into
account the latest developments.
The updates in the field of standards and conventions comprise the newly released ISO
standards by ISO/TC211 covering geographic information and geomatics, the activities of the
GGRF Working Group “Data Sharing and Development of Geodetic Standards” within the UNGGIM Subcommittee on Geodesy, the update of the IERS Conventions initiated by the IERS
Conventions Center, and the recently adopted resolutions by IAG, IUGG and IAU that are
relevant for geodetic standards and products. In the framework of the update of the IERS
Conventions, the director of the BPS has been nominated as Chapter Expert for Chapter 1“General definitions and numerical standards”.

Global Geodetic Observing System (GGOS)

Fig. X.2: Overview and schedule of BPS activities. Please note that some changes regarding
the schedule of meetings and workshops were necessary due to the pandemic situation.
Product-based review of standards and conventions
The second version of the inventory also provides an update regarding IAG products,
addressing the following major topics (see Angermann et al., 2020):•

Celestial reference systems and frames•

Terrestrial reference systems and frames•

Earth orientation parameters•

GNSS satellite orbits•

Gravity and geoid•

Height systems and their realizations

New versions of IERS products have been released for the celestial and terrestrial reference
frame as well as for the EOP, namely ICRF3, ITRF2014 and EOP 14C04. Although a significant
progress has been achieved compared to previous realizations, there are still some deficiencies
and open problems that are addressed in this inventory. Recommendations are provided for eachproduct to further improve their accuracy and consistency. Concerning GNSS satellite orbits,
the modelling has been improved and some missing information has been provided by thesatellite operators, but there are still some remaining deficiencies. A remarkable progress has
been achieved in the field of gravity and geoid related data and products, including thedevelopment of a dedicated data and products portal based on online applications for thecreation of metadata for gravity and geoid data. Also the latest developments and achievementsin the field of height systems and their realizations are reported (for details see the Report of
the GGOS Focus Area “Unified Height System”).

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Description and representation of geodetic products
In cooperation with the IAG Services, other data providers and contributing experts as well as
the GGOS Coordinating Office and the members of the GGOS Science Panel, user-friendly
product descriptions have been generated and implemented at the GGOS website(www.ggos.org).
The geodetic products are classified into two categories:•

Geodetic themes: Reference frames, geometry, Earth orientation, gravity field,
positioning and applications.

•

Earth system components and space: Outer and near space, atmosphere, hydrosphere,
oceans, cryosphere, solid Earth.

Until now, about 23 product descriptions are displayed at the GGOS website. Table X.2
provides a list of these product descriptions along with so-called “appetizer questions” for eachparticular product. With such an information portal, GGOS contributes to advertise data science
products to other disciplines and to make geodesy more visible in the geoscientific communityand beyond (Angermann et al., 2022a). The product descriptions have been reviewed by themembers of the GGOS Science Panel, coordinated by its chair Kosuke Heki, and have been
implemented at the GGOS website by Martin Sehnal, the Director of the GGOS Coordinating
Office. All the above mentioned contributions are gratefully acknowledged by the BPS.
Table X.2: List of product descriptions that are currently displayed at the GGOS website(www.ggos.org), including an “appetizer question” for each particular product.

Global Geodetic Observing System (GGOS)

BPS contributions to the updating of the IERS conventions
In the framework of the Unified Analysis Workshop (Thessaloniki, Greece, October 21-23,2022), a dedicated session on standards, conventions, and formats has been organized by the
BPS and the IERS Conventions Center. In this session, an overview about the status of the IERS
Conventions update was given, followed by presentations on particular topics such as numericalstandards, nutation issues, high-frequency EOPs, relativistic effects, etc.
In this context, the focus of the BPS is on the updating of Chapter 1 of the IERS Conventions“General definitions and numerical standards”. One issue was the treatment of the permanenttide in heights as specified in the definition of the International Height Reference System(IHRS), which prescribes the IHRF coordinates in the mean-tide system to support
oceanographic and hydrographic modeling. Section 1.1 “Permanent Tide” of the IERS
Conventions will be updated accordingly to refer to these IHRS developments. Furthermore,
the present status concerning numerical standards (Section 1.2 of the IERS Conventions) has
been addressed. Several updates have been proposed that will be incorporated to reflect thelatest changes in the field of standards and conventions (Angermann et al., 2022b). As outcomeof the Unified Analysis Workshop 2022, two recommendations on numerical standards havebeen endorsed:•

REC-1: The BPS recommends that the used numerical standards including time andtide systems must be clearly and consistently documented for all geodetic products(IAG/GGOS)•

REC-2: The BPS recommends that the necessity of a new Geodetic Reference System(GRS) should be further clarified (WG: Urs Marti)

GGOS Days 2022 and Strategic Plan Workshop 2022 in Munich
The GGOS Days 2022 (Nov. 15-16) and the Strategic Plan Workshop (Nov. 16-17) took placein the city center of Munich, hosted at the representative facilities of the Bavarian Academy of
Sciences and Humanities (BAdW).

Fig. X.3: On-site participants of the GGOS Days 2022.
The GGOS Days 2022 were organized by the German Geodetic Commission (DGK), theTechnical University of Munich (TUM) and GGOS. In total 111 interested people from many
countries around the world participated in this hybrid conference, 33 of them in-person and 78
virtually. Further information is available at the GGOS website (https://ggos.org/event/ggos-

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days-2022/). This website also provides links to download the presentations, videos and photosof the conference.
Directly after the GGOS Days 2022, the GGOS Strategic Plan Workshop was convened at thesame venue. About 20 invited IAG representatives participated in this workshop to discuss the
future direction and goals of GGOS. Besides about 15 in-person participants, a few colleagues
attended remotely. The discussions were based on the results of a community survey to develop
a new strategy for GGOS.

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 andconventions used for the generation of IAG products. In: Drewes H, Kuglitsch F, Adám
J, Rozsa S (Eds.) The Geodesist's Handbook 2020, Journal of Geodesy,
https://doi.org/10.1007/s00190-020-01434-z, 2020.

•

Angermann D., Gruber T., Gerstl M., Heinkelmann R., Hugentobler U., Sánchez L.,
Steigenberger P., Gross R., Heki K., Marti U., Schuh H., Sehnal M., Thomas M.: GGOS
Bureau of Products and Standards: Description and promotion of geodetic products}.
In: Freymueller J., Sánchez L. (Eds.), IAG Symposia, doi 10.1007/1345_2022_144,2022a.

•

Angermann D., Gruber T., Gerstl M., Heinkelmann R., Hugentobler U., Sánchez L.,
Steigenberger P.: GGOS of Products and Standards (BPS): BPS Activities onStandards}. Unified Analysis Workshop 2022, Thessaloniki, Greece,
10.5281/zenodo.7291721, 2022b.

GGOS Committee on Earth System Modeling
Chair: Maik Thomas (Germany)Role
The GGOS Committee on “Earth System Modeling” tends to promote the development ofphysically consistent modular Earth system modeling tools that are simultaneously applicable
to all geodetic parameter types (i.e., Earth rotation, gravity field and surface geometry) andobservation techniques. Hereby, the committee contributes to:•

The interpretation of geodetic monitoring data and, thus, to a deeper understanding ofprocesses responsible for the observed variations;•

The establishment of a link between the geodetic products delivered by GGOS andnumerical process models;•

A consistent combination and integration of observed geodetic parameters derived fromvarious monitoring systems and techniques;•

The utilization of geodetic products for the interdisciplinary scientific community.

Global Geodetic Observing System (GGOS)

Objectives
The long-term goal is the development of a physically consistent modular numerical Earthsystem model for homogeneous processing, interpretation and prediction of geodetic
parameters with interfaces allowing the introduction of constraints provided by geodetic timeseries of global surface processes, rotation parameters and gravity variations. This ultimate goal
implicates the following objectives:•

Development of Earth system model components considering interactions andrelationships between surface deformation, Earth rotation and gravity field variations aswell as interactions and physical fluxes between relevant compartments of the Earthsystem;•Promotion of homogeneous processing of geodetic monitoring data (de-aliasing,
reduction) by process modeling to improve analyses of geodetic parameter sets;•

Contributions to the interpretation of geodetic parameters derived from different
observation techniques by developing strategies to separate underlying physicalprocesses;•

Contributions to the integration of geodetic observations based on different techniques
in order to promote validation and consistency tests of various geodetic products.

Activities
The activities of the committee mainly concentrated on systematic comparisons of different
stand-alone and coupled model approaches as well as on the further development and evaluationof model interfaces for dynamical coupling and algorithms for data assimilation.
•

Implementation of interfaces to geodetic monitoring data based on Kalman and particle
filter approaches in order to constrain and improve stand-alone model approaches andto prove consistency of various geodetic monitoring products;•

Implementation and evaluation of various numerical approaches with different
complexities for the consideration of self-attraction and loading in ocean generalcirculation models;•Feasibility studies regarding the coupling of neural networks with traditional data
assimilation techniques and application of the combined approach in stand-alone
models. Application of neural networks for downscaling purposes.

•

Discussion and estimation of consequences of upcoming hardware developments for
CPU intensive model simulations (high-performance computing vs. exascalemodeling).

•

Feasibility studies for the provision of error and uncertainty estimates of model
predictions of geodetic parameters (Earth rotation, gravity field, surface deformation)
due to imperfect model physics, initialization, and external forcing.

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Fig. X.4: Simulated mass anomalies in a modular system model approach.
Selected publications:•

Bagge, M., Klemann, V., Steinberger, B., Latinovic, M., Thomas, M.: Glacial-isostatic
adjustment models using geodynamically constrained 3D Earth structures.
Geochemistry Geophysics Geosystems (G3), 22, 11, e2021GC009853, 2021.

•

Boergens, E., Dobslaw, H., Dill, R., Thomas, M., Dahle, C., Flechtner, F.: Modelling
spatial covariances for terrestrial water storage variations verified with synthetic
GRACE-FO data. GEM - International Journal on Geomathematics, 11, 24, 2020.

•

Huang, P., Sulzbach, R., Tanaka, Y., Klemann, V., Dobslaw, H., Martinec, Z.,
Thomas, M.: Anelasticity and lateral heterogeneities in Earth's upper mantle: impact
on surface displacements, self‐attraction and loading and ocean tide dynamics. Journalof Geophysical Research: Solid Earth, 126, 9, e2021JB022332, 2021.

•

Irrgang, C., Dill, R., Boergens, E., Saynisch-Wagner, J., Thomas, M.: Self-validating
deep learning for recovering terrestrial water storage from gravity and altimetry
measurements. Geophysical Research Letters, 47, 17, e2020GL089258, 2020.

•

Irrgang, C., Boers, N., Sonnewald, M., Barnes, E. A., Kadow, C., Staneva, J.,
Saynisch-Wagner, J.: Towards neural Earth system modelling by integrating artificial
intelligence in Earth system science. Nature Machine Intelligence, 3, 667-674, 2021.

•

Schachtschneider, R., Saynisch-Wagner, J., Klemann, V., Bagge, M., Thomas, M.: Anapproach for constraining mantle viscosities through assimilation of palaeo sea level
data into a glacial isostatic adjustment model. Nonlinear Processes in Geophysics, 29,
1, 53-75, 2022.

Global Geodetic Observing System (GGOS)

Committee on Essential Geodetic Variables
Chair: Richard Gross (USA)The GGOS BPS Committee on Essential Geodetic Variables was established in 2018 in orderto define a list of Essential Geodetic Variables and to assign requirements to them. 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 listof EGVs has been determined, requirements can be assigned to them. Examples of 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 to derive requirementson the observing systems that are used to observe the EGVs. And the list of EGVs can serve as
the basis for a gap analysis to identify observations needed to fully characterize the geodetic
properties of the Earth. During GGOS Days 2017 it was agreed that a Committee within the
GGOS Bureau of Products and Standards should be established in order to define the list of
Essential Geodetic Variables and to assign requirements to them. This Committee wassubsequently established in 2018 and consists of representatives of the IAG Services,
Commissions, Inter-Commission Committees, and GGOS Focus Areas.
Tasks
The tasks of the Committee on Essential Geodetic Variables are to:•Develop criteria for choosing from the set of all geodetic variables those that areconsidered essential•

Develop a scheme for classifying EGVs•

Within each class, define a list of EGVs•

Assign requirements to each EGV•Document each EGV including its requirements, techniques by which it is observed,
and point-of-contact for further information about the EGV•

Perform a gap analysis to identify potential new EGVs•

Define a list of geodetic products that depend on each EGV•Assign requirements to the EGV-dependent products•

Hold workshops to engage the geodetic community in the process of defining EGVs,
determining their dependent products, and assigning requirements to them

Activities•

A meeting of the Committee on Essential Geodetic Variables was held on 14 July
2019 in Montreal in conjunction with the 27th General Assembly of the IUGG. At themeeting, defining characteristics of essential geodetic variables were discussed.

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Working Group “Towards a consistent set of parameters for the definition of a new
GRS"
Chair: Urs Marti (Switzerland)Members: Detlef Angermann (Germany), Richard Gross (USA), Ilya Oshchepkov (Russia),
Christopher Kotsakis (Greece), Jonas Ågren (Sweden), Ulrich Meyer (Switzerland),
Riccardo Barzaghi (Italy), Jaakko Mäkinen (Finland), Pavel Novak (Czech Republic),
Laura Sánchez (Germany), Hartmut Wziontek (Germany), John Nolton (USA), Robert
Heinkelmann (Germany), Sergei Kopeikin (USA), Erricos Pavlis (USA), ILRS
Objectives and Activities
The main task of this WG is to define a consistent set of parameters and formulas for thedefinition of a new conventional Global Reference System (GRS). This includes the geometry(size and shape of a reference ellipsoid), the gravity field (normal gravity field of this ellipsoid),
physical heights, terrestrial time and Earth rotation.
This new definition becomes necessary because since the introduction of GRS80 (Moritz, 1980)
the knowledge in Geodesy has improved a lot (e.g. GNSS, gravity space missions) and the useof the parameters became inaccurate and inconsistent over time. The problem of the permanent
Earth Tide was not yet a topic at the epoch of the definition of GRS80. A new set of parameters
was published by Groten in 2004 but was not widely introduced in Geodesy. Another source ofparameters are the IERS conventions, which do not strictly apply GRS80.
The acceptance of the IAG Resolution No. 1 in 2015 which defines the potential at sea level(W0) even increases the inconsistency in the geodetic parameters of the conventional GRS (inGRS80, W0 is a derived quantity).
The new set of parameters is based on the four fundamental parameters: W0 (Potential at
Reference Level), J2 (dynamic form factor, “flattening”), GM (geocentric gravitational
constant) and ω (angular velocity of the Earth). All these quantities are well observed andmonitored by various geodetic space techniques. (This implies that the semi major axis of theellipsoid will be a derived parameter).
Most of the defining parameters change with time. This includes seasonal variations and longterm trends. These changes are important and must be considered for the consistency with the
ITRF (e.g. ellipsoidal heights). Nevertheless, in order to keep things simple for the user, thistime variability will not be treated in the published definition of a new GRS. All quantities will
be fixed to the epoch 2010.0. This is the epoch at which the W0 of the IAG resolution No. 1 isdefined.
All calculations will be done in the zero-tide system. Only at the very end, conversion formulas
to mean tide and tide-free will be given for all quantities. In order to keep things simple, somevery minor terms in this conversion will be neglected.
Results
A draft of the paper with the calculation of the parameters is available. It follows more or lessthe structure of the papers by Moritz (1980) and Groten (2004). However, it is not ready to be
published to a broader community, since it has not been thoroughly discussed yet and is not ina state of general agreement of the WG members. Therefore, this WG should be continued insome form.
The calculation of a new set of parameters is one thing. The main problem will be to convince
the users to adopt such a system as a new global reference. Many users don’t see the necessity

Global Geodetic Observing System (GGOS)

to replace GRS80, as they just see it as a conventional model for the conversion of geocentric
coordinates or for the calculation of gravity anomalies. Main concerns are the danger ofconfusion and the necessity to update many software packages. This discussion has still to belead and arguments for and against such a change are still evaluated.
Another question to be answered is the necessity to define a conventional global gravity fieldmodel. For many applications (e.g. global height system, reference for local geoid
determination), the assignment of such a standard model has some advantages. For different
application we would need a low-resolution satellite-only model and a high-resolution
combined model.
The progress of the work has been presented in October 2022 at the Unified Analysis Workshop(UAW) in Thessaloniki by D. Angermann and regularly at the GGOS days.

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Focus Area “Unified Height System”
Lead: Laura Sánchez (Germany)
With contributions from: H.A. Abd-Elmotaal (Egypt), J. Ågren (Sweden), H. Denker(Germany), R. Forsberg (Denmark), A. Gómez (Argentina), V.N. Grigoriadis (Greece), T.
Gruber (Germany), G. Guimarães (Brazil), J. Huang (Canada), T. Jiang (China), Q. Liu(Germany), J. Mäkinnen (Finland), U. Marti (Switzerland), K. Matsuo (Japan), P. Novák(Czech Republic), D. Smith (USA), M. Varga (Croatia), G. Vergos (Greece), M. Véronneau(Canada), Y. Wang (USA), K. Ahlgren (USA), R. Winefield (New Zealand), M. Amos (New
Zealand), D. Avalos (Mexico), M. Bilker-Koivula (Finnland), D. Blitzkow (Brazil), S. Claessens(Australia), X. Collilieux (France), M. Filmer (Australia), A.C.O.C. Matos (Brazil), J.
McCubbine (Australia), R. Pail (Germany), D. Roman (USA), H. Teitsson (Faroes), C. Tocho(Argentina), E. Antokoletz (Argentina), H. Wziontek (Germany).
The GGOS Focus Area “Unified Height System” (GGOS-FA-UHS, formerly Theme 1) wasestablished at the 2010 GGOS Planning Meeting (February 1 - 3, Miami, Florida, USA) to leadand coordinate the efforts required for the establishment of a global unified height system thatserves as a basis for the standardisation of height systems worldwide. Starting point was theresults delivered by the IAG Inter-Commission Project 1.2 Vertical Reference Frames (IAGICP1.2-VRF), which was operative from 2003 to 2011. During the 2011-2015 term, different
discussions focussed on the best possible definition of a global unified vertical reference system
resulted in the IAG resolution for the Definition and realisation of an International Height
Reference System (IHRS) that was approved during the 2015 General Assembly of theInternational Union of Geodesy and Geophysics (IUGG) in Prague, Czech Republic. In the term
2015-2019, actions dedicated to investigate the best strategy for the realisation of the IHRS
(i.e., the establishment of the International Height Reference Frame – IHRF) were undertaken.
In particular, a preliminary station selection for the IHRF reference network was achieved anddifferent computation procedures for the determination of potential values as IHRS coordinates
were evaluated. For the present term, 2019-2023, the objectives of the GGOS-FA-UHS are (i)to compile detailed standards, conventions, and guidelines to support a consistent determinationof the IHRF at global, regional and national levels; (ii) to coordinate with regional/national
experts in gravity field modelling the computation of a first IHRF solution; and (iii) to design
an operational infrastructure that ensures the long-term sustainability and reliability of the
IHRS/IHRF. This infrastructure should operate under the responsibility of the International
Gravity Field Service (IGFS).
Networking within the IAG
The implementation of a global reference system for physical heights as the IHRS is a big
challenge and requires the support of a wide scientific community. Thus, the installation of the
IHRS/IHRF is only possible within a global and structured organisation like the IAG. Presently,
following entities are contributing to achieve the goals of the GGO-FA-UHS:- GGOS-FA-UHS and IGFS working group Implementation of the International Height
Reference Frame (IHRF), chairs L Sánchez (Germany) and R Barzaghi (Italy).
- ICCT joint study group Geoid/quasi-geoid modelling for realization of the geopotential
height datum, chairs: J Huang (Canada), YM Wang (USA).
- IAG SC 2.2: Methodology for geoid and physical height systems, chairs: G. Vergos(Greece), Rossen S. Grebenitcharsky (Saudi Arabia).
- IAG Commission 2.2 working group Error assessment of the 1 cm geoid experiment,
chairs: T Jiang (China), V Grigoriadis (Greece).

Global Geodetic Observing System (GGOS)-

IAG Commission 2 joint working group On the realization of the International Gravity
Reference Frame, chairs: H. Wziontek (Germany), S. Bonvalot (France)
GGOS-BPS working group Towards a consistent set of parameters for a new GRS, chair
U Martí (Switzerland)International Gravity Field Service – IGFS, chair: R, Barzaghi (Italy), vice-chair: G.
Vergos (Greece).

Advances in the establishment of the IHRF
To move forwards in the realisation of the IHRS, we currently concentrate on four primary
aspects: (1) specific standards and conventions that ensure consistency between the IHRS
definition and the IHRF coordinates; (2) a global reference network for the IHRF; (3) thedetermination of IHRF coordinates at the reference stations; and (4) an operational
infrastructure to guarantee a reliable and long-term sustainability of the IHRS/IHRF. (see adetailed discussion of these four aspects in Sánchez et al. 2021).
Standards and conventions for the IHRS/IHRF
The IHRS is a gravity potential-based reference system: the vertical coordinates aregeopotential numbers [C(P) = W0 − W(P)] referring to an equipotential surface of the Earth's
gravity field realised by the IAG conventional value W0 = 62 636 853.4 m2s-2. The spatialreference of the position P for the potential W(P) = W(X) is given by the coordinates X referringto the ITRS/ITRF. Geopotential numbers are defined as the primary vertical coordinate as they
can be converted to any type of physical heights (orthometric or normal heights). As thereference value W0 is constant and conventionally adopted, the IHRS essentially materialises
the combination of a geometric component given by the coordinate vector X in the ITRS/ITRF
and a physical component given by the determination of potential values W at X. To becompatible with the ITRF, the accuracy of the IHRF geopotential numbers and their variation
with time should be at least 310-2 m2s-2 (equivalent to  3 mm in height) and 310-3 m2s2 -1
a ( 0.3 mm a-1), respectively. However, for the moment, the goal is to reach 110-1 m2s-2(about 1 cm) in the static component.
The most pragmatic way to determine potential values W(P) would be to introduce the ITRF
coordinates of any point into the harmonic expansion equation representing a global gravity
model (GGM) of high degree (up to degree 2190 or higher). These models could provide
potential values with accuracies of around 0.2 m2s−2 (equivalent to 2 cm in height) in regionswith flat and moderate terrains when dense and consistent gravity data are used in thecomputation of the GGM. If no regional gravity data are available to be included in the GGM,
the best possible mean accuracy offered by these models would be around 2.0 m2s−2 (0.2 m),
or even worse (up to 10 m2s−2 or 1 m) in regions with strong topography gradients. To
increase this accuracy, the values W(P) could be determined from gravity field observables
applying appropriate modelling strategies, which in general correspond to geoid or quasi-geoid
computation methods. In the geoid/quasi-geoid computation, the primary functional to be
determined is the disturbing potential T = W – U. If the disturbing potential T(P) is known, thedetermination of station potential values W(P) is straightforward. However, the determinationof the disturbing potential relies not only on the available gravity data but also on the gravity
field modelling approaches. This includes different methods for the handling of terrain effects,
the filtering and combination of surface gravity data, the treatment of long-wavelength errors,
the mathematical formulations to invert and to integrate gravity and terrain observations, etc.
Since there are so many parameter choices when handling the gravity and terrain data, theobtained potential values inevitably vary from computation to computation. Thus, different

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groups can generate quite different results from the same input data, see Fig. 1. Nevertheless,to define only one standard procedure for the computation of potential values is unsuitable asdifferent data availability and different data quality exist around the world, and additionally,
regions with different characteristics require particular approaches (e.g. modification of kernel
functions, size of integration caps, geophysical reductions like GIA, etc.). On the other hand, acentralised computation of the IHRF coordinates (like in the ITRF) also poses a problem dueto the restricted accessibility to terrestrial gravity data.
In order to get as similar and compatible results as possible, we complied a set of basic standards
covering general constants, reference ellipsoid, mass centre convention, zero-degree correction
to realise the vertical datum defined by the conventional W0 value, standardised formulas forthe conversion of potential coordinates between different permanent tide systems, and astandardised procedure to recover potential values from existing regional/national geoid or
quasi-geoid models. The latter is of particular importance as (1) the regional geoid/quasi-geoid
models include surface gravity data sets that are not always available for the determination of
GGM, (2) the regional models can assimilate new regional/local gravity surveys very quickly,and (3) national/regional experts on gravity field modelling have the best possible knowledge
about the local conditions (topography, data distribution, geophysical corrections, validation
data, etc.) to be considered in the computation of the geoid/quasi-geoid, or more precisely, inthe determination of the disturbing potential T in their countries/regions.

Fig. 1 Comparison of potential values obtained from different approaches using the same input
gravity data: Standard deviation of the differences between C(P) from gravity field modellingand from levelling varies from 0.12 m2s-2 (~1.2 cm) to 0.78 m2s-2 (7.8 cm).

Global reference network of the IHRF
The main criteria for the selection of IHRF reference stations were defined as:- GNSS continuously operating reference stations to detect reference frame deformations(with preference for stations belonging to the ITRF and the regional reference frames
like SIRGAS, EPN, APREF, etc.);- Co-location with fundamental geodetic observatories to ensure a consistent connection
between geometric coordinates, potential and gravity values, and reference clocks;

Global Geodetic Observing System (GGOS)-

Co-location with reference stations of the International Gravity Reference Frame(IGRF) to integrate the gravity and physical height reference frames;
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).

Based on this criteria, a preliminary station selection for the IHRF was initiated in 2016. This
selection was based on a global network with worldwide distribution, including a core network(to ensure sustainability and long-term stability of the reference frame) and regional/national
densifications (to provide local accessibility to the global frame). The core network includes
fundamental geodetic observatories, ITRF sites with more than two space geodetic techniques,
IGRF reference stations and selected IGS reference stations to ensure a global coverage as
homogeneous as possible. During 2017-2018, regional and national experts were asked toevaluate 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, the first approximation to the IHRF
reference network was completed in 2019. This network comprises about 170 stations (Fig. 2)
and currently, it is regularly refined in agreement with changes/updates of other geodetic
reference frames (ITRF and IGRF and their densifications).

Fig. 2 IHRF core network (as of June 2023)

Determination of IHRF coordinates
A key activity in this regard was the evaluation of different methodologies for the determinationof potential values as IHRS/IHRF reference coordinates within the so-called Colorado
experiment. This experiment aimed at computing geoid, quasi-geoid and potential values using

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the same input data and the own methodologies of colleagues involved in the gravity fieldmodelling. About 40 colleagues grouped in fourteen international computation groups
contributed to this initiative. The Colorado experiment started at the IAG/IASPEI Scientific
Assembly (Aug 2017, Kobe). First results were discussed at the GGHS2018 Symposium (Sep
2018, Copenhagen). A second computation was ready for the EGU2019 (Apr 2019, Vienna)and some refinements (third computation) were delivered in Jun 2019. The results wereextensively discussed at the IUGG2019, Symposium G02: Static Gravity Field and Height
Systems (July 2019, Montreal).
The input gravity and topographic data, the GNSS/levelling validation data, and the 14 geoid
and quasi-geoid models produced within the Colorado experiment are available from theInternational
Service
for
the
Geoid
(https://www.isgeoid.polimi.it/Projects/colorado_experiment.html) and can be used as a basis
to evaluate any geoid computation method or software anywhere.
Based on the efforts of the previous term 2015-2019, in particular, the outcomes of the Colorado
experiment, we classified the computation of potential values in three main scenarios:a) Regions without (or with very few) surface gravity data,- The only option to determine potential values is the use of GGM of high resolution- Expected mean accuracy values around the 4.0 m2s−2 (40.0 cm in terms of height)
level or even worse in regions with strong topography gradients- It could be improved for instance to the .0 m2s−2 (10.0 cm) level if new and bettersurface gravity data are included in the GGMs.
- To avoid multiple potential values provided by different GGM-HRs at the same
point, it is necessary to select one GGM-HR as reference model.
b) Regions with some surface gravity data, but with poor data coverage or unknown data
quality,- The reliability of the existing (quasi-)geoid models is poor
- Additional gravity surveys around the IHRF stations would help to increase theaccuracy of the geopotential numbers computed at those specific stations.
c) Regions with good surface gravity data coverage and quality.
- Potential values may be inferred from precise geoid/quasi-geoid regional models.
Using this classification, we started in the beginning of 2021 the computation of a first solution
for the IHRF. As an initial action, a short description of the “step by step” to infer IHRF
potential values from local/regional geoid/quasi-geoid models was prepared. It is based on the
IHRS paper published by Sánchez et al. (2021) and was distributed to the members of theworking group Implementation of the International Height Reference Frame (IHRF), so thatthey can compute potential values at the IHRF stations located in their countries using theirpresent/latest geoid/quasi-geoid models. This activity is supported by about 40 colleagues from
Canada, Mexico, USA, Germany, Italy, Switzerland, Austria, Sweden, Finland, Australia,
Japan, China, South America, Russia, and Africa. Complementary, the ISG and the IGFS areevaluating the quality and documentation of the different regional models available at the Geoid
Repository of ISG in order to identify which models can be used to infer potential values. Thisaction is useful for the IHRF computation in areas underrepresented in the working group.
Simultaneously, we are computing potential values for all the IHRF stations (Fig. 2) using GGM
extended with topography-based synthetic gravity signals, reaching resolutions up to degree ~80000 … ~ 90000. As mentioned, this would be the only option available in those regions
where no geoid/quasi-geoid models are available. At the end, we will have different potential
values for the same points. The agreement of the different GGM and the models stored by ISG

Global Geodetic Observing System (GGOS)

with the own computations performed by the colleagues of the working group will allow us todecide which GGM+topography models perform better. The results of these computations will
be presented at the next IUGG2023 General Assembly in Berlin, Germany.
Special Issue of the Journal of Geodesy on “Reference System in Physical Geodesy”
Based on the advances for the establishment of the IHSR/IHRF and the International Terrestrial
Gravity Reference System and Frame (ITGRS/ITGRF), a special issue on Reference Systems
in Physical Geodesy of the Journal of Geodesy has been completed. With the 18 papers in thisspecial issue, important issues related to the establishment of the IHRF and ITGRF as well as
to the improvement of accurate geoid modelling and the long-term stability of absolute gravity
observations have been addressed. We are grateful to all authors for the efforts. A large numberof international colleagues served as reviewers for the manuscripts, a laborious and timeconsuming task. We thank them all for their important and diligent work. Finally, we would
like to thank the Editor-in-Chief, Jürgen Kusche, for his generous and indispensable support in
the editorial process, from the development of the special issue to its final publication. The
papers included in this special issue are (papers contributing to this report are marked in fett):
Antokoletz ED, Wziontek H, Tocho CN et al. (2020) Gravity reference at the Argentinean–
German Geodetic Observatory (AGGO) by co-location of superconducting and absolutegravity measurements, J Geod 94, 81, https://doi.org/10.1007/s00190-020-01402-7.
Bilker-Koivula M, Mäkinen J, Ruotsalainen H, et al. (2021) Forty-three years of absolutegravity observations of the Fennoscandian postglacial rebound in Finland, J Geod 95, 24,
https://doi.org/10.1007/s00190-020-01470-9.
Claessens SJ, Filmer MS (2020) Towards an International Height Reference System:
insights from the Colorado experiment using AUSGeoid computation methods, J
Geod 94, 52, https://doi.org/10.1007/s00190-020-01379-3.
Grigoriadis VN, Vergos GS, Barzaghi R et al (2021) Collocation and FFT-based geoid
estimation within the Colorado 1 cm geoid experiment, J Geod 9, 52,
https://doi.org/10.1007/s00190-021-01507-7.
Işık MS, Erol B, Erol S, Sakil FF (2021) High-resolution geoid modeling using leastsquares modification of stokes and hotine formulas in Colorado, J Geod 95, 49,
https://doi.org/10.1007/s00190-021-01501-z.
Liu Q, Schmidt M, Sánchez L, Willberg M (2020) Regional gravity field refinement for(quasi-) geoid determination based on spherical radial basis functions in Colorado,
J Geod 94, 10, https://doi.org/10.1007/s00190-020-01431-2.
Mäkinen J (2021) The permanent tide and the International Height Reference Frame
IHRF, J Geod 95, 106, https://doi.org/10.1007/s00190-021-01541-5.
Oja T, Mäkinen J, Bilker-Koivula M, et al. (2021) Absolute gravity observations in Estonia
from 1995 to 2017, J Geod 95, 131, https://doi.org/10.1007/s00190-021-01580-y.
Pálinkáš V, Wziontek H, Vaľko M, et al. (2021) Evaluation of comparisons of absolutegravimeters using correlated quantities: reprocessing and analyses of recent comparisons,
J Geod 95, 21, https://doi.org/10.1007/s00190-020-01435-y.
Sánchez L, Ågren J, Huang J, Wang YM, Mäkinen J, Pail R, Barzaghi R, Vergos GS,
Ahlgren K, Liu Q (2021) Strategy for the realisation of the International Height
Reference System (IHRS), J Geod, 95, 3, https://doi.org/10.1007/s00190-021-01481-0.
Scherneck HG, Rajner M, Engfeldt A (2020) Superconducting gravimeter and seismometer
shedding light on FG5’s offsets, trends and noise: what observations at Onsala Space
Observatory can tell us, J Geod 94, 80, https://doi.org/10.1007/s00190-020-01409-0.

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Schilling M, Wodey É, Timmen L. et al. (2020) Gravity field modelling for the Hannover
10 m atom interferometer, J Geod 94, 122, https://doi.org/10.1007/s00190-020-01451-y.
Van Westrum D, Ahlgren K, Hirt C, Guillaume S (2021) A Geoid Slope Validation Survey(2017) in the rugged terrain of Colorado, USA, J Geod 95, 9,https://doi.org/10.1007/s00190-020-01463-8.
Varga M, Pitoňák M, Novák P, Bašić T (2021) Contribution of GRAV-D airborne gravity
to improvement of regional gravimetric geoid modelling in Colorado, USA, J Geod95, 53, https://doi.org/10.1007/s00190-021-01494-9.
Wang YM, Li X, Ahlgren K, Krcmaric J (2020) Colorado geoid modeling at the US
National Geodetic Survey, J Geod 94, 106, https://doi.org/10.1007/s00190-020-01429w.
Wang YM, Sánchez L, Ågren J, Huang J, Forsberg R, Abd-Elmotaal HA, Barzaghi R, Bašić
T, Carrion D, Claessens S, Erol B, Erol S, Filmer M, Grigoriadis VN, Isik MS, Jiang T,
Koç Ö, Li X, Ahlgren K, Krcmaric J, Liu Q, Matsuo K, Natsiopoulos DA, Novák P, Pail
R, Pitoňák M, Schmidt M, Varga M, Vergos GS, Véronneau M, Willberg M, Zingerle P(2021) Colorado geoid computation experiment – Overview and summary, J Geod,
95, 12, https://doi.org/10.1007/s00190-021-01567-9.
Willberg M, Zingerle P, Pail R (2020) Integration of airborne gravimetry data filtering
into residual least-squares collocation: example from the 1 cm geoid experiment, J
Geod 94, 75, https://doi.org/10.1007/s00190-020-01396-2.
Wziontek H, Bonvalot S, Falk R, Gabalda G, Mäkinen J, Pálinkáš V, Rülke A, Vitushkin L(2021) Status of the International Gravity Reference System and Frame, J Geod 95, 7,
https://doi.org/10.1007/s00190-020-01438-9.

Operational infrastructure to ensure the long-term sustainability of the IHRS/IHRF
An IHRS/IHRF objective is to support the monitoring and analysis of Earth’s system changes.
The more accurate the IHRS/IHRF is, the more phenomena can be identified and modelled.
Thus, the IHRS/IHRF must provide vertical coordinates and their changes with time asaccurately as possible. As many global change phenomena occur at different scales, the global
frame should be extended to regional and local levels to guarantee consistency in theobservation, detection, and modelling of their effects. From this perspective, we are proposing
the establishment of an operational infrastructure within the IGFS that takes care ofa) Maintenance of the IHRF reference network in accordance with the GGOS-BNO andthe coordinators of the reference networks for the ITRF, IGRF and their regional
densifications. This activity should be faced by the IHRF reference network
coordination (see blue boxes in Fig. 3).
b) Maintenance of a catalogue with the conventions and standards needed for the IHRF.
This should consider a harmonisation with the conventions and standards kept by the
GGOS-BPO, the IERS Conventions (for the determination of the ITRF), and thestandards applied in the IGRF and the global gravity field modelling. This task should
be carried out by the IHRF conventions’ coordination (see pink boxes in Fig. 3).
c) The national/regional agencies/entities contributing to the realisation of the IHRF in
their regions may be declared as IHRF national/regional computation centres (dark bluebox in Fig. 3). The input data would then be provided by existing IAG gravity field
services and local data centres; e.g., GGM are provided by ICGEM and surface gravity
data are provided by the Bureau Gravimétrique International (BGI) andGlobal Geodetic Observing System (GGOS)

refined/complemented with gravity data available at local data centres. In a similar way,
one can proceed with digital elevation models (see violet box in Fig. 3).
d) In an ideal data flow scheme, the national/regional IHRF computation centres would
provide the IGFS with the following products (cyan box in Fig. 3): potential values at
the IHRF reference stations; vertical datum unification parameters (to transform theexisting local height systems to the IHRF); mean gravity anomalies or disturbances(without violating data confidentiality but contributing to the determination of improved
GGMs); and regional geoid/quasi-geoid models of high resolution. The mean gravity
anomalies (or disturbances) and the geoid/quasi-geoid models would be then managed
by BGI and ISG. For the combination of the regional/national solutions, validation,
storage, management, and servicing of potential values at IHRF stations and vertical
datum parameters, the IGFS would have to establish a new element, which could becalled IHRF product centre (see magenta boxes in Fig. 3).

Fig. 3 Proposal for an IHRF operational infrastructure within the IGFS

The IHRF operational infrastructure within the IGFS will be managed by the IHRF
Coordination Centre. Presently, we are preparing the terms of reference for this centre forapproval by the IAG Executive Committee. With this centre established in the IGFS, we candeclare the objectives of the GGOS-FA-UHS accomplished and this FA will be
decommissioned at the IUGG2023 General Assembly.

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GGOS Geohazards Focus Area

Introduction: The concept of GNSS Tsunami Early Warning Systems (GTEWS) was borne of
the societal suffering inflicted by the Great Indian Ocean Earthquake and Tsunami of Boxing
Day 2004. We learned that the existing sparse regional IGS network of GPS receivers could
have provided warning of the impending tsunami within 15 minutes of the initial fault zone
rupture that produced the tsunami, many hours in advance of the seismological warning.
GTEWS related research was further advanced by the Japanese GEONET realtime network
measurements of the 2011 Tohoku Oki earthquake. Analysis of the GEONEt GNSS data
demonstrated that an accurate tsunami prediction could be generated within 5 minutes of theinitial fault rupture using the existing infrastructure. The GEONET data also demonstrated that
ionospheric Total Electron Content measurements could also provide images of thedevelopment and propagation of the tsunami beginning within ten minutes of initial ocean
uplift.

https://www.dropbox.com/sh/fg20mtydg136vx6/AABNr2kSnMo429nCxEHhBDfoa?dl=0
Activities During 2015-2019: These significant demonstrations of GNSS based Tsunami
Disaster Early Warning prompted the GGOS encourage the 2015 General Assembly adoptionof Resolution #4 calling for the IUGG membership to support the development of a GNSS
augmentation to Tsunami Warning Systems within the Indo-Pacific. On April, 2016 the GGOS
issued its Call for Participation in the GNSS Augmentation for Tsunami Early Warning(GATEW) working group in support of Resolution #4. The GATEW working group now
includes 18 institutions from 12 nations with substantial experience and roles in thedevelopment of geodetic applications to disaster risk reduction. The GGOS Geohazards
collaborated with the Association of Pacific Rim Universities (APEC), NASA and the IUGG
Commision on Geophysical Risk and Sustainability (GRC) to conduct the GTEWS 2017
workshop to explore the feasibility and utility of GTEWS.
Activities during 2019-2023: The GTEWS 2017 workshop report was published by the APRU
in 2019 and subsequently UNDRR in 2020 as a contributing paper to its Global Assessment
Report of 2019. The work shop report reviews the scientific and programmatic developmentsof GTEWS, endorses the development of an Indo-Pacific GTEWS and provides specificrecommendations to insure a strong Indo-Pacific GTEWS program. The first recommendation
was the formation of a "GNSS Shield Consortium” to apply the GTEWS 2017 recommendation
for the establishment of an Indo-Pacific GTEWS program in support of the UNDRR Sendai
Framework for Disaster Risk Reduction.

Global Geodetic Observing System (GGOS)

Scientific development of the GTEWS 2017 was significantly slowed by the COVID 19
pandemic that restricted international collaboration. Despite these restrictions the IGS, GRC
and the GGOS/Geohazards FA worked with GEO to develop the Geodesy for Sendai
framework to develop collaborations for the application of GNSS to goals of the Sendai
Framework of the UNDRR. Geodesy4Sendai was codified in the GEO Work Programme of2020-2022 and 2023 to 2O25. within the Geodesy for Sendai Framework. The GRC applied
was granted $10K by the IUGG to support the organization of the GTEWS Coordinating
Committee as recommended by the GTEWS 2017 workshop.
Activities during 2023: The implementation of GTEWS continued as recommended by the
IUGG Resolution #4 within the individual programs of Indian, Japanese, Chilean, and US
agencies. Unfortunately, as noted by the GTEWS 2017 workshop report, a reticence persists
among several Indo-Pacific nations to engage in the sharing of real time GNSS essential for therealization operation of an Indo-Pacific GTEWS. The GGOS Geohazards recognizes that
GTEWS for the Indo-Pacific will require significant international collaboration between
institutions and agencies. Our activities work to implement this important need for international
collaboration.
The GGOS Geohazards. the IGS and the GRC have joined in support of the UN ICG Working
Group task force on “Applications of GNSS for Disaster Risk Reduction” (Geodesy4DRR).
The IGS published Stop 5 of the Tour de l’IGS that focussed upon GNSS Applications to theSouth Pacific Disaster Risk Reduction. Stop 5 included a report by the
GRC/GGOS_Geohazards recommendation on the formulation of GTEWS_Oceania. The
GTEWS_Oceania concept recognizes the need to develop a South Pacific real time GNSS
network in support GTEWS as well as numerous other GNSS applications to environmental
hazard risk reduction. The GRC and the GATEW working group members as well as the IGC
Geodesy4DRR task force are engaging the member nations of the Oceania region in theformulation of GTEWS_Oceania. GTEWS_Oceania is holding monthly meetings to resolve adevelopment plan for the GTEWS network.
Future Activities:
Following the GTEWS 2017 workshop report, the objective is to establish a governing council
to determine data policy, identify resources, and establish a development plan to establish a
GTEWS_Oceania network and analysis capability. It is too early to resolve the success of the
GTEWS_Oceania Initiative but there is a growing participation by the nations of Oceania.
A draft Charter (Terms of Reference) is under review and implementation plans are being
developed by a growing number of participating nations. The Oceania region has a significant
number of GNSS receivers of varying quality and varying communications capability.
Resources will be needed to upgrade these receiver stations and provide the regional broadband
communications as well analysis systems. Discussions are underway to apply the $10K
IUGG/GRC grant as a matching grant to further develop further resources for
GTEWS_Oceania.

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GGOS Focus Area ‘Geodetic Space Weather Research’
Chair: Michael Schmidt (Germany)
Vice-Chair: Ehsan Forootan (Denmark)Introduction
Space weather is a very up-to-date and interdisciplinary field of research. It describes physicalprocesses in the near-Earth space mainly caused by the Sun’s radiation of energy. The
manifestations of space weather are multiple, e.g. variations of the Earth’s magnetic field,
variations of the upper atmosphere consisting of the compartments magnetosphere, ionosphere,
plasmasphere, and thermosphere, also known as the MIPT system (due to coupling processes),
as well as solar wind, i.e. the permanent emission of electrons and photons including theinterplanetary magnetic field (IMF), i.e. the component of the solar magnetic field that isdragged out from the solar corona by the solar wind flow. The magnetosphere is the part of thenear-Earth space, in which the total magnetic field is dominated by the Earth’s magnetic fieldand not by the IMF. It is well-known that the pressure of the solar wind compresses the magnetic
field on the day side of the Earth and stretches it into a long tail on the night side.
Activities
The GGOS Focus Area on Geodetic Space Weather Research (FA-GSWR) has been installed
in 2017. At the FA-GSWR splinter meeting during the IUGG 2019 General Assembly inMontreal, it was decided to extend the scientific content of the FA-GSWR by themagnetosphere and the plasmasphere such that it now deals with the complete MIPT systemand the mutual couplings. As shown in Fig. 1, the scientific structure of the FA-GSWR can bevisualised now as a double tetrahedron.

Fig. 1: Structure of the FA-GSWR including the plasmasphere and the magnetosphere: the yellowcoloured parts are related to geodetic applications such as Precise Orbit Determination (POD) andPrecise Point Positioning (PPP); the blue-coloured parts are related to solar phenomena especially tospace weather.

Global Geodetic Observing System (GGOS)

The most important task of the FA-GSWR is the development of a concept for the combined
evaluation of measurements from solar and geodetic satellite missions, as well as magnetic field
information under the consideration of the physical coupling processes. Although rather
challenging, this concept plays the most important role to reach the main objectives of the FAGSWR, namely the development of an(1) improved electron density model of the ionosphere including the plasmasphere and an(2) improved model of the neutral density in the thermosphere.

In a study, members of the FA-GSWR proposed that both the electron density and the neutral
density should be interpreted as so-called Essential Geodetic Variables (EGV); consequently,
the developed improved models should finally be provided as GGOS products to potential
users.
To approach these goals, an IAG GGOS Joint Study Group (JSG) and three IAG GGOS Joint
Working Groups (JWG) have been established within the FA-GSWR. These IAG GGOS
groups are entitled as
JSG 1: Coupling processes between magnetosphere, thermosphere, and ionosphere(implemented within the IAG ICCT and joint with GGOS)JWG 1: Electron density modelling (joint with IAG Commission 4)
JWG 2: Improvement of thermosphere models (joint with IAG Commission 4)
JWG 3: Improved understanding of space weather events and their monitoring by satellite
missions (joint with IAG Commission 4).
Their achievements in the last 4 years will be presented in more details in what follows.
The special issue ‘Observing and Modelling Ionosphere and Thermosphere using in situ andRemote Sensing Techniques’ of the journal ‘Remote Sensing’ was initiated by members of the
FA-GSWR. The deadline for manuscript submission was December 31, 2020.
WebsiteWe have significantly updated the GGOS web pages about the FA-GSWR(https://ggos.org/about/org/fa/geodetic-space-weather-research/)byincludingmore
information about space weather in general, but also more detailed information about the workin the JSG and the 3 JWGs. Furthermore, we added on the GGOS web page ‘Geodetic Products’
information about ionosphere and thermosphere products.
2nd IAG Commission 4 ‘Positioning and Applications’ Symposium
Due to the Corona pandemic many of the planned activities at conferences and workshops did
not work out during the reporting period and had to be postponed. One example is the 2nd IAG
Commission 4 Symposium, which was originally scheduled for September 2020. It finally took
place from September 5th to 8th, 2022, at Wissenschaftsetage Potsdam. The Symposium
website (https://www.iag-commission4-symposium2022.net/) created by Copernicus GmbHwill be available at least for a five-year timeframe. The scientific program of the symposiumincluded altogether nine sessions. Some of them were arranged according to the IAG
Commission 4 structure, and others were dedicated to the special topics of the FA-GSWR,
namely (1) to Atmospheric Remote Sensing of the Ionosphere and (2) to the topics of the FA
itself. The corresponding presentations and posters are part of the open access Symposium
Proceedings and can be downloaded from https://zenodo.org/communities/iag-comm4-symp2022/.

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Apart from the scientific programme, a Joint Splinter Meeting of the IAG Sub-Commission 4.3
and the FA-GSWR took place; furthermore, an IAG, FA-GSWR and IAGA (International
Association of Geomagnetism and Aeronomy) Splinter Meeting on the specific topic of “Space
Weather Research” took place at the end of the symposium. During this meeting it was
discussed how a joint inter-association study group on space weather topics within the IUGG
can be established. Since there are already examples of this type of joint study group within the
IAG, we planned to create a list of objectives for such a joint inter-association study group thatwould combine the activities of IAG and IAGA. A further discussion is now scheduled for the
IUGG 2023 General Assembly, which will be held in Berlin from July 11 to 20, 2023. One of
the goals of such a study group will be to develop a roadmap for the establishment ofinternational space weather data centres and space weather services for scientific purposes.
While space weather services, including warning systems for the public, must be installed by
the governments of countries such as Germany, i.e., they are national institutions, the question
here, for example, is how measurements from different scientific fields such as geodesy andsolar physics can be combined to enable reliable prediction of space weather events. To solvethese and other problems in space weather research, it is necessary to form an international teamthat brings together as much experience as possible.
Other issues
Many papers related to the scientific content of the JSG 1 and the JWG1 to JWG3 have been
written in the last years. Significant progress has also been made in third-party funded national and international projects; the work within these projects is often strongly coupled with theobjectives of individual groups of FA-GSWR.
On the next pages an overview of the scientific work of the JWGs of the FA-GSWR within thelast four years, i.e. the reporting period 2019 to 2023, is provided.
JSG 1 (JSG T.27): Coupling processes between magnetosphere, thermosphere andionosphere
Chair: Andres Calabia (China)
Vice-Chair: Munawar Shah (Pakistan)
Research Coordinator: Binod Adhikari (Nepal)(Led by ICCT; joint with GGOS, Focus Area on Geodetic Space Weather Research andCommission 4, Sub-Commission 4.3)
Members
Christine Amory-Mazaudier (France, Italy)
Astrid Maute (USA)Yury Yasyukevich (Russia)
Gang Lu (USA)
Anoruo Chukwuma (Nigeria)
Oluwaseyi Emmanuel Jimoh (Nigeria)
Munawar Shah (Pakistan)
Binod Adhikari (Nepal)

Andres Calabia (China)
Piyush M. Mehta (USA)LiangLiang Yuan (Germany)
Naomi Maruyama (USA)Toyese Tunde Ayorinde (Brazil)
Charles Owolabi (Nigeria)
Emmanuel Abiodun Ariyibi (Nigeria)
Olawale S. Bolaji (Australia)

Since this study group is part of the Inter-Commission Committee on Theory (ICCT), the midterm report of JSG 1 (JSG T.27) can be found in the ICCT Section of this report and is notrepeated here.

Global Geodetic Observing System (GGOS)JWG 1: Electron density modelling
Chair: Fabricio dos Santos Prol (Germany)
Vice-Chair: Alberto Garcia-Rigo (Spain)(Led by GGOS; joint with Commission 4, Sub-Commission 4.3)
Members
A. Goss (Germany)
A. Smirnov (Germany)
B. Nava (Italy)
D. Themens (United Kingdom)
F. Arikan (Turkey)
G. Jerez (Brazil)
G. Seemala (India)
H. Lyu (Spain)
J. Norberg (Finland)
K. Alazo (Italy)

M. Hoque (Germany)
M. Muella (Brazil)
Mir-Reza Razin (Iran)
O. Arikan (Turkey)
S. Jin (China)
S. Karatay (Turkey)
S. Yildiz (Turkey)
T. Gerzen (Germany)
T. Kodikara (Germany)
Y. Migoya-Orue' (Italy)

Activities during the period 2019-2023
The objective of JWG 1 Electron density modelling is to evaluate and improve establishedmethods of 3D electron density estimation in terms of electron density, peak height, Total
Electron Content (TEC), or other derived products that can be effectively used for GNSS
positioning or studying perturbed conditions due to representative space weather events. Figure
2 shows the main steps planned in the group. The steps were achieved through the realizationof three main points:• Development of a database, where the methods from the group members were evaluatedusing a common ground in terms of reference data. Besides ionosonde measurements, wehave gathered in-situ data from C/NOFS, DMSP, GRACE and SWARM missions.
Electron density profiles from Incoherent Scatter Radar and GNSS radio-occultation(RO) were also included in the analysis, as well as TEC measurements from altimeters
and other LEO satellites with receivers for precise orbit determination.
• Pragmatic assessment of established methods for 3D electron density was performed todefine their accuracy related to specific parameters of high importance for Space Weather
and Geodesy.
• Papers were published indicating the space weather conditions and expected errors of themethods.
The first two years (2019-2021) of the project development were devoted to establishing a fairdatabase for our evaluations, selecting proper instruments and pre-processing techniques to thedataset. The remaining two years (2021-2023) were for the model developments andevaluations. A few campaigns were created to carry out a pragmatic model evaluation between
the members. We have chosen 4 geomagnetic storms as basis for the analysis in case of
disturbed days.
The following activities have been conducted based on the created dataset or within the groupcooperation. A direct comparison between several models was investigated by Kodikara et al.
(2021). We have conducted a few cross-validations between the electron density measurements
provided by the instruments used in the dataset (Smirnov et al. 2021). We have also checked

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the feasibility of using ionosonde observations to evaluate established TEC models (Jerez et al.
2021). A high-resolution global-scale tomography was developed and evaluated by Prol et al.
(2021b). A new climatological model was developed and evaluated by Hoque et al. (2022).
Swarm in-situ measurements were used to improve ionospheric forecast of the Coupled
Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) (Fernandez-Gomez et al.,2022). A novel technique was developed to estimate differential code bias (DCB) based onreceivers dedicated to LEO-POD (Hernández-Pajares et al., 2023). A new method wasdeveloped to extract electron density RO retrievals based on truncated measurements of thetopside ionosphere (Hoque et al., 2023). A novel neural network model of Earth’s topside
ionosphere was developed (Smirnov et al., 2023).
A crucial problem identified in the current ionospheric models was the lack of a correct
description of the topside ionosphere and plasmasphere. We understand now that empiricalmodelling of electron density needs to be essentially improved above the F2 layer peak (hmF2)
for a better characterization of the topside TEC (Prol et al. 2019), which can contribute from
10% to 60% to the ground-based TEC measurements. In this regard, a few studies of the groupwere devoted to better characterise the upper part of the ionized atmosphere. Recent advancesfrom Prol et al. (2021a) and Prol and Hoque (2021) have shown that great improvements on thetopside ionosphere and plasmasphere can be obtained in comparison to typical models,
especially during disturbed conditions of storm events. Prol and Hoque (2022) have also
investigated the performance of tomography techniques to reconstruct the plasmasphere.
Despite limited accuracy, it was feasible to propose a new method to develop further
investigations of the region. Prol et al. (2022) have further discovered a way to combine theionosphere and plasmasphere trough empirical relations.

Fig. 2. Steps involved in the group of electron density modelling comprehend: 1) data gathering ofelectron density measurements; 2) data transformation into 3D grids; 3) evaluation of relevant
parameters for the community, such as in terms of GNSS positioning. Positioning results are obtainedby a high-accurate ionospheric model (see Prol et al., 2018 for details).

Global Geodetic Observing System (GGOS)

The activities of the group have been disseminated trough several conferences. A remarkable
example is shown in Prol (2022), who addressed the current challenges and opportunities for
3D ionospheric imaging. In the future, it is expected to provide a simulated case scenario to be
used as basis for a fair data evaluation. A first dataset, which is simulated considering the fullenvironment of the ionosphere and plasmasphere, is complete. An upcoming publication willshow details of the simulated dataset (Prol et al., 2023). This dataset not only incorporate TEC
measurements from typical ground-based GNSS receivers and POD receivers, but also
incorporate upcoming LEO-PNT mega-constellations. As we advance with the group goals,
more complex dynamics are planned to be incorporated in the simulations of the ionosphereand plasmasphere.
Publications
Fernandez-Gomez, I., Kodikara, T., Borries, C., Forootan, E., Goss, A., Schmidt, M.,
Codrescu, M. V. (2022) Improving estimates of the ionosphere during geomagnetic storm
conditions through assimilation of thermospheric mass density. Earth Planets Space 74, 121.
https://doi.org/10.1186/s40623-022-01678-3
Hernández-Pajares, M.; Olivares-Pulido, G.; Hoque, M.M.; Prol, F.S.; Yuan, L.; Notarpietro,R.; Graffigna, V. (2023) Topside Ionospheric Tomography Exclusively Based on LEO POD
GPS Carrier Phases: Application to Autonomous LEO DCB Estimation. Remote Sens. 15,
390. https://doi.org/10.3390/rs15020390
Hoque, M. M., Jakowski, N., Prol, F. S. (2022) A new climatological electron density model
for supporting space weather services, J. Space Weather Space Clim., 12, 1.
https://doi.org/10.1051/swsc/2021044
Hoque, M. M.; Yuan, L.; Prol, F. S.; Hernández-Pajares, M.; Notarpietro, R.; Jakowski, N.;
Olivares Pulido, G.; Von Engeln, A.; Marquardt, C. (2023) A New Method of Electron
Density Retrieval from MetOp-A’s Truncated Radio Occultation Measurements. Remote
Sens. 15, 1424. https://doi.org/10.3390/rs15051424
Jerez G. O., Hernández-Pajares M., Prol F. S., Alves D. B. M., Monico J. F. G. (2020)
Assessment of Global Ionospheric Maps Performance by Means of Ionosonde Data. Remote
Sens., 12, 3452. https://doi.org/10.3390/rs12203452
Kodikara T., Zhang K., Pedatella N. M., Borries C. (2021) The impact of solar activity on
forecasting the upper atmosphere via assimilation of electron density data. Space Weather, 19,e2020SW002660. https://doi.org/10.1029/2020SW002660
Prol F. S., Camargo P. O., Hernández-Pajares M., Muella M. T. A. H. (2018) A new method
for ionospheric tomography and its assessment by ionosonde electron density, GPS TEC, andsingle-frequency PPP. IEEE Transactions on Geoscience and Remote Sensing, 57, 25712582.
Prol F. S., Themens D. R., Hernández-Pajares M., Camargo P. O., Muella M. T. A. H. (2019)
Linear Vary-Chap Topside Electron Density Model with Topside Sounder and RadioOccultation Data. Surv Geophys., 40, 277–293. https://doi.org/10.1007/s10712-019-09521-3
Prol F.S., Hoque M.M. (2021) Topside Ionosphere and Plasmasphere Modelling Using GNSSRadio Occultation and POD Data. Remote Sens., 13, 1559.
https://doi.org/10.3390/rs13081559
Prol F.S., Hoque, M.M., Ferreira A. A. (2021a) Plasmasphere and topside ionospherereconstruction using METOP satellite data during geomagnetic storms. J. Space Weather
Space Clim., 11, 5. https://doi.org/10.1051/swsc/202007

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Prol, F.S., Kodikara, T., Hoque, M.M., Borries, C. (2021b). Global-scale ionospherictomography during the March 17, 2015 geomagnetic storm. Space Weather, 19,e2021SW002889. https://doi.org/10.1029/2021SW002889
Prol, F. S. Hoque, M. M. (2022) A Tomographic Method for the Reconstruction of the
Plasmasphere Based on COSMIC/ FORMOSAT-3 Data. IEEE Journal of Selected Topics inApplied Earth Observations and Remote Sensing, 15, 2197-2208.
https://doi.org/10.1109/JSTARS.2022.3155926.
Prol F. S. (2022) Challenges of Global-Scale Ionospheric Tomography using GNSS: A brief
overview. 2022 3rd URSI Atlantic and Asia Pacific Radio Science Meeting (AT-AP-RASC),
Gran Canaria, Spain, pp. 1-4. https://doi.org/10.23919/AT-AP-RASC54737.2022.9814251.
Prol, F.S., Smirnov, A.G., Hoque, M.M., Shprits, Y. Y. Combined model of topside
ionosphere and plasmasphere derived from radio-occultation and Van Allen Probes data. Sci
Rep., 12, 9732 (2022). https://doi.org/10.1038/s41598-022-13302-1
Prol, F.S., Smirnov, A.G., Kaasalainen, S., Hoque, M. M., Bhuiyan, M. Z. H., Menzione, F.
(2023) The potential of LEO-PNT mega-constellations for ionospheric 3D imaging: A
simulation study. IEEE Journal of Selected Topics in Applied Earth Observations and Remote
Sensing, Under Review.
Smirnov, A., Shprits, Y., Zhelavskaya, I., Lühr, H., Xiong, C., Goss, A., et al. (2021).
Intercalibration of the plasma density measurements in Earth’s topside ionosphere. Journal ofGeophysical Research: Space Physics, 126, e2021JA029334.
https://doi.org/10.1029/2021JA029334
Smirnov, A., Shprits, Y., Prol, F., Lühr, H., Berrendorf, M., Zhelavskaya, I. Xiong, C. (2023)
A novel neural network model of Earth’s topside ionosphere. Sci Rep., 13, 1303.
https://doi.org/10.1038/s41598-023-28034-z

JWG 2: Improvement of thermosphere models
Chair: Christian Siemes (The Netherlands)
Vice-Chair: Kristin Vielberg (Germany)(Led by GGOS; joint with IAG Commission 4, Sub-Commission 4.3 and ICCC)
Members
Armin Corbin (Germany)
Ehsan Forootan (Denkmark)Mona Kosary (Iran)
Lea Zeitler (Germany)
Christopher McCullough (USA)
Sandro Krauss (Austria)
Natalia Hladczuk (The Netherlands)

Saniya Behzadpour (Austria)
Aleš Bezděk (Czech Republic)
Sean Bruinsma (France)
Michael Schmidt (Germany)
Barbara Süsser-Rechberger (Austria)
Peter Nagel (USA)Andres Calabia (Spain)

Activities during the period 2019-2023
This working group was founded in November 2019. Since accurate observations of thethermospheric neutral density are the basis for thermosphere models, we formulate the objective
to improve thermosphere models through providing relevant space geodetic observations andincreasing consistency between datasets by advancing processing methods. Thus, we assembled

Global Geodetic Observing System (GGOS)

a group of scientists with a focus on the processing of thermospheric neutral densities fromaccelerometers, GNSS and satellite laser ranging observations. Additionally, we attracted groupmembers with expertise in data assimilation of mass densities into models.
Our first ongoing activity is the review of space geodetic observations and state-of-the-art
processing methods. We started with a comparison of accelerometer-derived mass densities,
since our working group has a large expertise in this area. Figure 3 provides an overview of theprocessing from accelerometer measurements to thermospheric mass densities including thevariety of models used in the intermediate steps. In a living document, we assessed the models
used by five different institutes in the processing of the densities, which paves the way to decide
on a standard processing algorithm in the future.

Fig. 3: Processing of measured accelerations to thermospheric mass density including required
background models

Besides the theoretical model comparison, we initiated a data comparison. During our groupmeetings, we agreed on the comparison of GRACE A datasets because this covered all solar
and geomagnetic activity and different eclipse conditions. The datasets used in the comparison
are listed in Error! Reference source not found.. Initially, the Technical University of Graz,
the University of Bonn, and the Delft University of Technology contributed their datasets.
Later, also the Zentrum für angewandte Raumfahrttechnologie und Mikrogravitation (ZARM)
of the Universität Bremen used the datasets for their comparisons.
A key result of the comparison was that the neutral density observations show scale differencesof 10 – 60% as demonstrated in Figure 4. The differences need to be interpreted in light of thethermosphere model accuracy of 20 – 30% (Bruinsma et al., 2022). The selected approach of athorough comparison of observational datasets is therefore a prerequisite for improving thethermosphere models. We identified significant differences in all processing steps, in particular
the accelerometer data calibration, radiation pressure modelling, and the aerodynamic force
coefficient modelling. Accurately modelling the aerodynamic force coefficient modelling is oneof the hardest challenges (Mehta et al., 2022). Though the source of the differences between
the datasets is presently not fully understood, identifying the differences was an important
activity that provided valuable impulses to improve the modelling capabilities of the involved
institutions. In addition to the accelerometer-derived datasets, we also performed a comparisonof the Swarm C POD-derived density datasets for 2015 from TU Graz and TU Delft. It was
found that the TU Graz density datasets show larger variations in comparison to the TU Delft
ones. The TU Graz density dataset reaches low values, indicating that this dataset has some

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554

room for improvement. Finally, an overview of SLR-derived density observations was provided
by guest speaker Mathis Bloßfeld from TU Munich.
Table 1: GRACE A datasets used for comparison

DatasetTU GrazUni Bonn

TU Delft

Calibrated accelerations

✓

✓

✓

Observed aerodynamic accelerations

✓

✓

✓

Aerodynamic force coefficients

✓

✓

✓

Neutral density observations

✓

✓

✓

Modelled neutral density (along orbit)

✓

✓

✓

Orbit (position and velocity)

✓

✓

✓

Radiation pressure acceleration

✓

✓

✓

Shadow function

✓

✓

✓

F10.7 index

✓

✓

✓

Kp index✓✓✓

ap index✓✓✓

Period2002-04-05–
2017-06-29

2002-08-01 2002-04-01––
2009-12-31 2009-12-31

Fig. 4: Comparison of neutral density observations

Beyond the joined activities of the working group, our group members published the following
research papers relevant to improving thermospheric densities.
Publications
Bandikova, B., McCullough, C., Kruizinga, G. L., Save, H., and B. Christophe. “GRACE
Accelerometer Data Transplant.” Advances in Space Research. 2019, 64 (3), pages 623-644.
doi: 10.1016/j.asr.2019.05.021
Behzadpour, S., Mayer‐Gürr, T., and S. Krauss (2021). GRACE Follow‐On accelerometerdata recovery. Journal of Geophysical Research: Solid Earth, 126, e2020JB021297.
https://doi.org/10.1029/2020JB021297

Global Geodetic Observing System (GGOS)

Bruinsma, S., C. Siemes, J. T. Emmert, and M. G. Mlynczak, 2022. Description andcomparison of 21st century thermosphere data. Advances in Space Research.
Https://doi.org/10.1016/j.asr.2022.09.038.
Corbin, A., Kusche, J. (2022). Improving the estimation of thermospheric neutral density via
two-step assimilation of in situ neutral density into a numerical model. Earth Planets Space
74, 183. https://doi.org/10.1186/s40623-022-01733-z.
Forootan, E., S. Farzaneh, C. Lück, and K. Vielberg (2019). Estimating and predicting
corrections for empirical thermospheric models. Geophysical Journal International 218(1),479-493. doi:10.1093/gji/ggz163
Forootan, E., Farzaneh, S., Kosary, M., Schmidt, M., and M. Schumacher (2021), A
simultaneous Calibration and Data Assimilation (C/DA) to improve NRLMSISE00 using
Thermospheric Neutral Density (TND) from space-borne accelerometer measurements.
Geophysical Journal International, 224 (2), pages 1096-1115, doi.10.1093/gji/ggaa507
Forootan, E., Kosary, M., Farzaneh, S., Kodikara, T., Vielberg, K., Fernandez-Gomez, I.,
Borries C., Schumacher, M. (2022). Forecasting global and multi-level thermospheric neutral
density and ionospheric electron content by tuning models against satellite-based
accelerometer measurements. Sci Rep 12, 2095 (2022). https://doi.org/10.1038/s41598-02205952-y.
Forootan, E. (2023). ESA’s multi-level global thermosphere data products consistent with
Swarm and GRACE(-FO). Retrieved from https://earth.esa.int/
451 eogateway/activities/swarm-disc-pre-study-5-2
Krauss S., S. Behzadpour, M. Temmer and C. Lhotka (2020). Exploring Thermospheric
Variations Triggered by Severe Geomagnetic Storm on 26 August 2018 Using GRACE
Follow‐On Data. Journal of Geophysical Research: Space Physics, 125, e2019JA027731.
https://doi.org/10.1029/2019JA027731.
Mehta, P. M., S. N. Paul, N. H. Crisp, P. L. Sheridan, C. Siemes, G. March, and S. Bruinsma,
2022. Satellite drag coefficient modeling for thermosphere science and mission operations.
Advances in Space Research. 10.1016/j.asr.2022.05.064.
Palmroth, M., Grandin, M., Sarris, T., Doornbos, E., Tourgaidis, S., Aikio, A., Buchert, S.,
Clilverd, M. A., Dandouras, I., Heelis, R., Hoffmann, A., Ivchenko, N., Kervalishvili, G.,
Knudsen, D. J., Kotova, A., Liu, H.-L., Malaspina, D. M., March, G., Marchaudon, A.,
Marghitu, O., Matsuo, T., Miloch, W. J., Moretto-Jorgensen, T., Mpaloukidis, D., Olsen, N.,
Papadakis, K., Pfaff, R., Pirnaris, P., Siemes, C., Stolle, C., Suni, J., van den IJssel, J.,
Verronen, P. T., Visser, P. and M. Yamauch (2021). Lower-thermosphere–ionosphere (LTI)
quantities: current status of measuring techniques and models. Annales Geophysicae, 39 (1),pages 189-237. Copernicus GmbH.
Siemes, C., Borries, C. Bruinsma, S. Fernandez-Gomez, I. Hładczuk, N. van den IJssel, J.
Kodikara, T. Vielberg, K. Visser P. (2023) New Thermosphere Neutral Mass Density andCrosswind Datasets from CHAMP, GRACE, and GRACE-FO. Journal of Space Weather andSpace Climate. https://doi.org/10.1051/swsc/2023014
van den IJssel, J., Doornbos, E., Iorfida, E., March, G., Siemes, C., and O. Montenbruck(2020). Thermosphere densities derived from Swarm GPS observations. Advances in Space
Research, 65 (7), pages 1758-1771.
Vielberg, K. and J. Kusche (2020). Extended forward and inverse modeling of radiationpressure accelerations for LEO satellites. Journal of Geodesy, 94 (43).
https://doi.org/10.1007/s00190-020-01368-6

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Verbanac G., Bandic M., Krauß S. Influence of the solar wind high-speed streams on thethermospheric neutral density during the declining phase of solar cycle 23. , 15 Jun 2022, In:
Advances in Space Research. 69, 12, p. 4335-4350 16 p.
Zeitler L., Corbin A., Vielberg K., Rudenko S., Löcher A., Blossfeld M., Schmidt M., Kusche
J. (2021). Scale Factors of the Thermospheric Density: A Comparison of Satellite Laser
Ranging and Accelerometer Solutions. Journal of Geophysical research-Space Physics,
126(12),Number: e2021JA029708, doi.org/10.1029/2021JA029708.

JWG 3: Improved understanding of space weather events and their monitoring bysatellite missions
Chair: Haixia Lyu (China, 2021 – 2023), Alberto Garcia-Rigo (Spain, 2019 – 2021)
Vice-Chair: Benedikt Soja (Switzerland)(Joint with IAG Commission 4, Sub-Commission 4.3)
Members
Anna Belehaki (Greece)
Anthony J. Mannucci (USA)
Enric Monte-Monero (Spain)
Rami Qahwaji (UK)
Xiaoqing Pi (USA)

Denise Dettmering (Germany)
Consuelo Cid (Spain)
Jens Berdermann (Germany)
Pietro Zucca (The Netherlands)
Jinsil Lee (Republic of Korea)

Activities during the period 2019-2023
JWG3 aims at gaining a better understanding of space weather events and their effect on Earth’s
atmosphere and near-Earth environment. In particular, by analysing the correlation between
Space Weather data from different sources (including observations from spacecraft and radio
telescopes) and perturbed ionospheric/plasmaspheric conditions derived from different space
geodetic techniques (e.g. GNSS, DORIS, RO, VLBI, satellite altimetry) and identifying themain parameters that could be useful to improve their real time determination and their forecasts
in extreme conditions.
For this purpose, a multidisciplinary team has been assembled. In fact, the members of the WG
provide access to complementary models as well as operational products/services linked toionospheric Total Electron Content determination, ionospheric electron density, geomagnetic
disturbances from the Sun to Earth, DORIS ionospheric products, Traveling IonosphericDisturbances (TIDs) and scintillations, solar flare detection/prediction, EUV flux-rate, CMEs
and SEPs, solar corona electron density, dimming and coronal holes, solar wind, polar
depletions, among others. Combination of such measurements and estimates can pave the way
for a better understanding of space weather events.
At first, an online survey form to gather feedback from JWG 3 members was carried out to havea better understanding of the complementarity within the team, which was helpful to identify
the existing background in both geodetic and space weather domains.
Particularly, we identified potential useful data sources to broaden our analysis, as well as theexisting models and operational products/services being provided or accessible by themembers. Furthermore, applications that could impact positively to end users were listed,Global Geodetic Observing System (GGOS)

complementing the initial considered ones. In addition, it was a way to interchange ideas on theobjectives and expectations of what the JWG should be.
At first, a set of three historical representative space weather events were selected. Given thesewere coincident with the ones selected within JWG 1, we have finally extended the events tobe analysed adding a fourth case which was also considered by JWG 1. Thus, we will analysestorm-related periods in 2013, 2015, 2017 and 2018. Also note that the connection between
both joint working groups was considered a key objective from the beginning.

Fig 4: Capture of the online survey form

We are currently working on the correlation between SW products and perturbed ionosphericelectron density/Total Electron Content, jointly with JWG 1. We have been compiling and/or
generating data and plots from different sources (see few plots below) that could be linked tothe selected events useful to understand perturbed conditions and features found within JWG 1
analysis. The possibility to provide insights of these correlations could be helpful for JWG 1
and may also be highlighted through their website and database, as part of the coordination
process, we are conducting with them. We also keep in mind that for the monitoring andprediction of space weather events and their impact on geodetic measurements, low latency
data availability would be of great importance, ideally in real time (RT) or near real time (NRT),
also to enable triggering alerts.

Fig. 5: Left: Shock interaction with the interplanetary magnetic field of SEP events associated toeastern events (Garcia-Rigo et al., 2016). Right: Radio source geometry and coronagraph images for
VLBI experiment to assess the electron density of the solar corona (Soja et al., 2014)

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The conducted analyses and the combination of measurements and estimates, derived fromspace geodetic techniques and from solar spacecraft missions, shall lead us to a better
understanding of the main parameters that could be useful to improve real time determination
as well as predictions derived from geodetic techniques, in case of extreme solar weather
conditions. In fact, there is the interest within the team on how well models can reproducechanges during storms, understanding the interactions with the solar wind and magnetosphere,
and how correlation of data from different available techniques could be key in this regard.

Fig. 6: Left: (from top to bottom) the LDi and LCi geomagnetic indices, and the geomagneticallyinduced current measured at a substation in the northwest of Spain by REE during the period from 16
to 20 March 2015. Colored areas in panels correspond to the five-level scale introduced to help
decision makers in an operational environment (Cid et al., 2020). Right: Superposed plot of the GOES
X-ray flux (red) and the amplitude of GQD recorded at UAH receiver (green) from 6 to 14 UT on 6
September 2017 (Guerrero, Cid et al., 2021).

Fig. 7: Left: Detected solar flares prior to St. Patrick’s day 2015 Geomagnetic Storm by means of
SISTED detector, which relies on GNSS-based ionosphere monitoring (Garcia-Rigo et al., 2017;
Borries et al. 2020). Right: UPC-IonSAT ionospheric TEC GIMs perturbed conditions during St.
Patrick’s day 2015.

To foster interdisciplinary cooperation, the Session AS52 “Ionospheric Space Weather
Monitoring and Forecasting” at the Asia Oceania Geosciences Society (AOGS) 2023 from July
30 to August 4, 2023, was initiated and 19 abstracts were attracted; see Figure 8. Researchers
from Geodesy and Space Physics will meet and exchange knowledge during this event.

Global Geodetic Observing System (GGOS)

Fig. 8: AOGS 2023 Session AS52 News released by the PITHIA-NRF project website

Among the fruitful research indicated in the publications, a new 3D ionosphere model based on
characterizing shape function is constructed (Lyu et al. 2023), which deepens our understandingof the spatial variability of the ionosphere, thus with better prediction of the ionospheric state.
This model will be further refined and shared with the JWG1 for assessment in order to facilitate
the collaboration between JWG1 and JWG3.
It is worth mentioning that the newly built Chashan Broadband Solar millimeter spectrometer(CBS) has begun its routine observation from 35 to 40 GHz since 2020 and the first solar flareobservation was reported by Yan et al. (2022). The CBS provides a new data source for space
weather events and more synergy will be done in the future.

Fig. 9: Overview of the X2.2 flare observed by GOES, NoRP, and CBS on 2022 April 20 (Yan et al.,
2022)

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In a collaboration between IAG Sub-Commission 4.3 Working Group 4.3.2. “Ionosphere
Prediction” and this FA-GSWR JWG 3, predictions of global ionospheric maps (GIMs) havebeen investigated. ETH Zurich provided predictions of one-day ahead forecasts that were thencompared with those of other institutions. Three different types of predictions were computed,
with one of them including data related to space weather and geomagnetic activity (“auxiliarydata”). Comparisons of the results for quiet days in terms of ionospheric activity are given in
Fig. 10, whereas the results for storm days are depicted in Fig. 11. The model that included
auxiliary data did not result in improved predictive performance during quiet days, but delivered
the best performance during the storm days.

Fig. 10: One day ahead forecast errors of UPC (red), HUN (blue), DLR (orange), ETH models (shadesof green; the model with space weather data is in dark green) and COM(black) with respect to IGS
final maps on quiet days of 210 and 211 in 2022.

Fig. 11: One day ahead forecast errors of UPC (red), HUN (blue), DLR (orange), ETH models (shadesof green; the model with space weather data is in dark green) and COM (black) and COM(black) withrespect to IGS final maps on storm days of 104 and 105 in 2022.

Global Geodetic Observing System (GGOS)

In several publications and presentations by Natras et al. (2022a, b, c, d, e, f, 2023), space
weather and geomagnetic data were used as input to machine learning models to predict VTECat different latitudes. As shown in Fig. 12, in certain cases significant feature importance isattributed to the solar and geomagnetic data. This means that they have an impact on theprediction of VTEC. The physical relationship between VTEC and these parameters does nothave to be exactly known as the machine learning algorithms learn the relationship between
these variables.

Fig. 12: Relative importance of input variables to VTEC forecast estimated from the Random Forestmodels. Results are presented for 1 h forecast with non-differenced data (first row) and differenced
data (second row), and for 24 h forecast with non-differenced data (third row) and differenced data
(fourth row) for high-latitude (left), mid-latitude (middle) and low-latitude (right) VTEC (Natras et al.,2022a).

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In Awadaljeed et al. (2022), solar flux data from the Soil Moisture and Ocean Salinity (SMOS)
mission was considered for improving predictions of ionospheric VTEC. The inclusion of thehighly resolved solar flux data generally had a positive impact on the predictive performance,
when included as input to most types of machine learning algorithms (Fig. 13). The work waspresented at the “SMOS for Space Weather” workshop organised by ESA and shows how
missions that were not originally intended for space weather monitoring can still make animportant contribution.

Fig. 13: VTEC prediction errors (in terms of Mean Absolute Error, MAE) of different machinelearning algorithms. Blue bars indicate models that have only been trained on VTEC data. Orange bars
represent models that include solar flux data from SMOS (Awadeljeed et al., 2022).

Additional next steps include the possibility to conduct extensive simulations, combining
different datasets and testing different algorithms, carry out comparisons and validation against
external data, as well as deriving impact on end user’ applications (such as in the case of HF
communications, GNSS positioning and EGNOS performance degradation, influence onground and space-based infrastructures, etc.).
Publications
Abed, A. K., Qahwaji, R., Abed, A. (2021). The automated prediction of solar flares from
SDO images using deep learning. Advances in Space Research, 67(8), 2544-2557.
Aroca-Farrerons, J., Hernández-Pajares, M., Lyu, H. (2022), Can the GEC be used as Space
Weather index? Oral presentation in the 21st International Beacon Satellite Symposium,
Boston, USA: 1-5 August 2022
Awadaljeed M., Kłopotek G., Soja B. (2022): "Exploring SMOS Solar Flux Data for Data
Fusion with Machine Learning in the CAMALIOT Project"; Talk: 1st workshop on SMOS forSpace Weather, ESA-ESRIN, Frascati, Italy; 2022-11-14.
Awadaljeed M., Kłopotek G., Soja B. (2022): "VTEC estimates in the VGOS era: Quality
assessment of VTEC derived with the use of the next-generation VLBI system"; Talk: 12th
IVS General Meeting, online; 2022-03-28 – 2022-04-01; in: "Abstract book IVS General
Meeting 2022", p. 52.
Berdermann, J., Kriegel, M., Banys, D., Heymann, F., Hoque, M. M., Wilken, V., Borries, C.,
Heßelbarth, A. and Jakowski, N. (2018), Ionospheric response to the X9.3 Flare on 6

Global Geodetic Observing System (GGOS)

September 2017 and its implication for navigation services over Europe, Space Weather,
Volume 16, Issue 10, Pages 1604-1615, https://doi.org/10.1029/2018SW001933.
Bloßfeld M., Zeitlhöfler J., Rudenko S., Dettmering D. (2020), Observation-Based Attitude
Realization for Accurate Jason Satellite Orbits and Its Impact on Geodetic and Altimetry
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Garcia-Rigo A., Soja B. (2020), New GGOS JWG3 on Improved understanding of space
weather events and their monitoring, EGU General Assembly Conference Abstracts (p. 2049)
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understanding of space weather events and their monitoring, EGU General Assembly 2021,
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for risk estimation in space launch operations. J. Space Weather Space Clim., 6 (27), A28,
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weather station at the University of Alcala. J. Space Weather Space Clim., Volume 11, 2021,
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and Geoeffectiveness. Solar Physics, 296(3), 1-18.
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to September-2017 geomagnetic storm and December-2019 annular solar eclipse over Sri
Lankan region. Acta Astronautica, 180, 575-587.
Kauristie K., Andries J., Beck P., Berdermann J., Berghmans D., Cesaroni C., De Donder E.,
de Patoul J., Dierckxsens M., Doornbos E., Gibbs M., 2021. Space weather services for civil
aviation—challenges and solutions. Remote Sensing, 13(18), p.3685.

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Kihara W., Munakata K., Kato C., Kataoka R., Kadokura A., Miyake S., Kozai M., KuwabaraT., Tokumaru M., Mendonça R.R.S., Echer E. et als. (2021). A peculiar ICME event inAugust 2018 observed with the Global Muon Detector Network. Space Weather, 19(3),e2020SW002531.
Lyu H., Hernández-Pajares M., Monte-Moreno E., Zhang H., Li M. (2023), Modeling
Ionospheric Electron Density: Global 3D semivariogram characteristics and Kriging
interpolation of shape function, Oral presentation in the 28th IUGG General Assembly,
Berlin, Germany: 11-20 July 2023.
Mannucci A. et al. (2020), Chapman Conference on Scientific Challenges Pertaining to Space
Weather Forecasting Including Extremes: Recommendations for the Community,
Recommendations from the Chapman Conference on Scientific Challenges Pertaining toSpace Weather Forecasting Including Extremes, 11-15 February 2019, Pasadena, CA, USA.
https://doi.org/10.5281/zenodo.3986940
Mao S., Kłopotek G., Awadaljeed M., Soja B. (2023): "Machine learning for global modelingof the ionosphere based on multi-GNSS data"; Talk: European Geosciences Union General
Assembly 2023, Vienna, Austria; 2023-04-23 – 2023-04-28; EGU23-9260,
https://doi.org/10.5194/egusphere-egu23-9260
McGranaghan, R., Riley, P., Forsyth, C., Camporeale, E., Gjerloev, J., Lynch, K., Mannucci
A., Skone S., Zhang B., Hatch S., Bloch, T. (2021). The opportunity and challenge forprogress toward meso-and substorm-scale understanding and modeling of the coupledgeospace system. 43rd COSPAR Scientific Assembly. Held 28 January-4 February, 43, 1172.
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Transactions on Geoscience and Remote Sensing, doi: 10.1109/TGRS.2021.3060107.
Natras R., Soja B., Schmidt M. (2022c): "Uncertainty Quantification for Ionosphere
Forecasting with Machine Learning"; Talk: International Workshop on GNSS Ionosphere(IWGI2022), Neustrelitz, Germany; 2022-09-26 – 2022-09-26.
Natras R., Soja B., Schmidt M. (2022d): "Interpretable Machine Learning for Ionosphere
Forecasting with Uncertainty Quantification"; Talk: 1st Workshop on Data Science for GNSS
Remote Sensing, Potsdam, Germany; 2022-06-13 – 2022-06-15.
Natras R., Soja B., Schmidt M. (2022e): "Machine Learning Ensemble Approach for
Ionosphere and Space Weather Forecasting with Uncertainty Quantification"; Talk: 3rd URSI
Atlantic Radio Science Meeting, URSI AT-AP-RASC 2022, Gran Canaria, Spain; 2022-05-29– 2022-06-03.
Natras R., Soja B., Schmidt M., Dominique M., Türkmen A. (2022f): "Machine Learning
Approach for Forecasting Space Weather Effects in the Ionosphere with Uncertainty
Quantification"; Talk: European Geosciences Union General Assembly 2022, Vienna,
Austria; 2022-05-23 – 2022-05-27; EGU22-5408, https://doi.org/10.5194/egusphere-egu225408
Natras R., Soja B., Schmidt M. (2022a): "Ensemble Machine Learning of Random Forest,
AdaBoost and XGBoost for Vertical Total Electron Content Forecasting"; Remote Sensing
14(15):3547 https://doi.org/10.3390/rs14153547
Natras R., Soja B., Schmidt M. (2022b): "Machine Learning Ensemble Approach for
Ionosphere and Space Weather Forecasting with Uncertainty Quantification"; In: "2022 3rd
URSI Atlantic and Asia Pacific Radio Science Meeting (AT-AP-RASC)", pp. 1-4,
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Global Geodetic Observing System (GGOS)

Natras R., Soja B., Schmidt M. (2023): "Uncertainty Quantification for Machine Learningbased Ionosphere and Space Weather Forecasting"; Space Weather, submitted.
Pi, X., Mannucci, A. J., Verkhoglyadova, O. (2021). Polar Topside TEC Enhancement
Revealed by Jason‐2 Measurements. Earth and Space Science, 8(3), e2020EA001429.
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(geb. Wenzel), Daniela, Wilken, Volker (2019), Solar Radio Burst events on September 6,2017 and its impact on GNSS signal frequencies. Space Weather. Wiley. Volume17, Issue 6,
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Ionosphere Based on a Comparison of Real-Time Solar Wind Data with the Best-Fitting
Historical Storm Event. Atmosphere, 12(12), 1684.
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Delayed Ionospheric Response to Solar EUV. Journal of Geophysical Research: Space
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27‐day solar rotation period analyzed with GOLD and IGS TEC data. Journal of GeophysicalResearch: Space Physics, 126(2), e2020JA028861.
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Lie Zhu, Xiaoqing Pi et al. (2021), Challenges in Specifying and Predicting Space Weather,
Space Weather 19, no. 2 (2021): e2019SW002404.
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baseline interferometry. Nature communications, 5(1), pp. 1-9.
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forecasts: the case of the Solar Wind driven autoregression model for Ionospheric Forecast(SWIF). Advances in Space Research.
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Geophysicae (Vol. 39, No. 4, pp. 641-655). Copernicus GmbH.
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2, pp. 341-355). Copernicus GmbH.
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Advances in Space Research, 69(6), 2460-2476.
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Evaluation of Total Electron Content Prediction Using Three Ionosphere‐Thermosphere
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Zhai, C., Chen, Y., Cheng, X., Yin, X. (2023). Spatiotemporal Evolution and Drivers of theFour Ionospheric Storms over the American Sector during the August 2018 Geomagnetic
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7, A13

Global Geodetic Observing System (GGOS)

Focus Area “Artificial Intelligence for Geodesy” (AI4G)
Chair: Prof. Dr. Benedikt Soja (ETH Zurich, Switzerland)
Vice-Chair: Dr. Maria Kaselimi (National Technical University of Athens, Greece)
With contributions from:Dr. Milad Asgarimehr (GFZ Potsdam, Germany)
Dr. Lei Liu (University of Colorado Boulder, USA)
Dr. Alexander Sun (University of Texas at Austin, USA)
Dr. Saniya Behzadpour (ETH Zurich, Switzerland)
Dr. Sadegh Modiri (BKG, Germany)
Dr. Justyna Śliwińska (Polish Academy of Sciences, Poland)
On May 12, 2023, the GGOS Coordinating Board accepted the proposal to establish a new
GGOS Focus Area on Artificial Intelligence for Geodesy (AI4G). The establishment thus falls
barely into the IAG period 2019-2023. As the Focus Area and its Joint Study Groups are
currently in the phase of implementation, the report will not include a description of alreadycompleted activities, but rather on the goals, objectives, and planned activities of the Focus
Area.
The Focus Area will utilize methods from the field of Artificial Intelligence (AI), including
machine learning techniques, to improve geodetic observations and products.
Introduction
The field of artificial intelligence has seen rapid progress in recent years, with breakthroughs
in areas such as natural language processing, computer vision, and deep learning. This progresshas led to the development of new AI applications and technologies and has the potential totransform a wide range of industries and fields.
AI has become increasingly important in science, with applications in fields such as physics,
biology, chemistry, and astronomy. It has become well-established in the neighboring
disciplines of geodesy, including climate and weather prediction, space sciences, and remotesensing, helping to improve our understanding and prediction of complex natural phenomena.
In general, AI can help scientists analyze complex data, identify patterns and relationships, anddevelop new hypotheses, ultimately accelerating the pace of scientific discovery.
Geodesy has seen a significant increase in observational data in recent years, for example
in the case of Global Navigation Satellite Systems (GNSS) and InSAR missions. Furthermore,
auxiliary data used in the analysis of space-geodetic data such as meteorological orenvironmental models have seen a significant increase in spatio-temporal resolution.
Traditional data processing and analysis techniques that rely largely on human input are notwell suited to harvest such rich data sets to their full potential.
Recent advances in the development of machine learning algorithms, in particular efficient
implementations of deep neural networks, together with a significant increase in computing
power, have the potential to facilitate:•
the automation of data processing,•the detection of anomalies in time series and image data,•
their classification into different categories,•
modeling complex spatio-temporal data,•and creating enhanced derivate products in geodesy.
For these reasons, there has been a strong increase in research related to AI and machinelearning in geodesy, covering various problems, including those mentioned above in relation to568

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geometric space-geodetic techniques, gravity field, and earth orientation parameters, among
other topics.
Objectives(1)
Develop improved geodetic products based on AI and machine learning
The Focus Area aims to explore the potential of AI and machine learning methods in improving
the quality and accuracy of geodetic observations and products. The objective is to develop new
approaches and methods that can help extract valuable information from large and complex
geodetic datasets and use this information to create more accurate and reliable products.
Depending on the application, improved geodetic products could have a higher accuracy,
resolution, as well as better performance in in real-time or prediction scenarios. This will often
involve assimilating data from different sources.
To achieve the above objective, it is important to identify the most relevant and suitable
geodetic and auxiliary datasets that can be used for training and validating machine learningalgorithms. This will involve selecting datasets that have the right spatio-temporal resolution,accuracy, and other relevant characteristics that can help improve geodetic products.
The Focus Area will also work on designing appropriate machine learning methods that caneffectively improve the quality of geodetic data. This will involve exploring different machinelearning algorithms, such as deep neural networks, and developing new techniques that can beused to analyze geodetic data.
(2)
Evaluate improved geodetic products based on AI and machine learning:
Thorough quality assessment is essential for increasing trust in the products produced with theuse of AI, especially considering the “black box” nature of deep learning algorithms.
The Focus Area will compare the performance of different machine learning methods withtraditional data analysis approaches. This will involve identifying the strengths andlimitations of each approach and determining the most appropriate method for a given
application.
AI4G will pay particular attention to the accuracy, precision, and reliability of the results
produced by machine learning algorithms. This will involve developing new techniques forerror assessment and uncertainty quantification, and identifying potential sources of errors
in the results.
Implementation
To achieve the objectives mentioned above, AI4G plans to implement at least three joint study
groups, tackling specific topics related to the use of AI in geodetic observations and products.
Concretely, we plan to establish study groups that will focus on GNSS remote sensing, gravity
field and mass change determination, and Earth orientation parameter prediction.
JSG 1: AI for GNSS Remote Sensing
Chair: Dr. Milad Asgarimehr (GFZ Potsdam, Germany)
Vice-chair: Dr. Lei Liu (University of Colorado Boulder, USA)The first study group will focus on GNSS remote sensing and will investigate topics such as
ionosphere and troposphere modeling and prediction, as well as the retrieval of wind speed, soil
moisture, and other environmental variables through GNSS reflectometry.
JSG 2: AI for Gravity Field and Mass Change
Chair: Dr. Alexander Sun (University of Texas at Austin, USA)
Vice-chair: Dr. Saniya Behzadpour (ETH Zurich, Switzerland)Global Geodetic Observing System (GGOS)

The second study group will address the application of AI to improve the determination of thegravity field and the related mass change. The topics that will be covered include the fusion ofgravity data with hydrological models, the downscaling of mass anomalies, bridging the gap
between GRACE and GRACE-FO missions, and the improved processing of satellite
gravimetry data.
JSG 3: AI for Earth Orientation Parameter Prediction
Chair: Dr. Sadegh Modiri (BKG, Germany)
Vice-chair: Dr. Justyna Śliwińska (Polish Academy of Sciences, Poland)
The third study group will explore the use of AI for predicting Earth orientation parameters.
This group will build on the successful Second Earth Orientation Parameter Prediction
Comparison Campaign organized by the International Earth Rotation and Reference Systems
Service (IERS) and will continue to investigate machine learning for the prediction of Earthorientation parameters and effective angular momentum.
In addition to organizing joint study groups, AI4G also aims to facilitate collaboration beyond
these study groups. The goal is to ensure that the methodological progress achieved in thesestudy groups benefits the wider geodetic community. To this end, we plan to organize events
such as workshops or summer schools in addition to sessions at scientific conferences todisseminate the findings of the joint study groups. The progress of the Focus Area will be
documented on a dedicated website and advertised on social media.
The AI4G will collaborate closely with existing components of the International Associationof Geodesy (IAG), in particular the working and study groups of its commissions andcommittees, as well as other relevant organizations, including the International
Telecommunication Union (ITU) and its Focus Group on AI for Natural Disaster Management(FG-AI4NDM). In the case of IAG, the concrete ties will be defined when the working andstudy groups for the next four-year term are established following the IUGG General Assembly
2023 conference.