International Collaborations

1.  Validation of combined gravity model EGM2020

Chair: Srinivas Bettadpur (USA)

Affiliation: IAG commission 2

Status: Active (2017-2021)


The main objective of this working group is to validate EGM2020 and preliminary versions of it, to identify potential deficiencies and propose model improvements in different regions of the world. For this independent external validation, a full arsenal of validation methods and external independent data sources shall be applied. This includes validation against GPS/levelling observations, regional data bases of gravity field functions, other global and regional gravity field models, orbit tests to assess mainly the long wavelengths of the field as well as the spectral transition from satellite to terrestrial data, assessment in the frame of mean dynamic ocean topography computations, correlation analysis with topographic potential and isostatic potential models, etc. Potential deficiencies in the preliminary versions of the model shall be identified, in order to improve the model until its final release in 2020. Additionally, the plausibility and consistency of the uncertainty estimates (variance-covariance information) provided together with the model shall be assessed

2.  Forward gravity field modelling of known mass distributions

Chair: D. Tsoulis (Greece)

Affiliation: IAG commissions 2, 3 and GGOS

Status: Proposed (2019-2023)


·         Examine new theoretical developments (numerical, analytical or spectral) in expressing the gravity signal of ideal geometric distributions

·         Perform validation studies of precise terrain effects over rugged mountainous topography

·         Compute the gravity effect of structures in the Earth's interior and embed this effort in the frame of a Synthetic Reference Earth Model

3.  High-resolution harmonic series of gravitational and topographic potential fields

Chair: S. Claessens (Australia)

Affiliation: IAG commission 2 and GGOS

Status: Proposed (2019-2023)


·         Develop and compare combined full least-squares, block-diagonal least-squares and quadrature approaches to very high-degree and order spherical, spheroidal and ellipsoidal harmonic analysis.

·         Develop and compare methods to compute high-resolution harmonic potential models using ellipsoidal geometry, either in terms of spherical, spheroidal or ellipsoidal harmonic series.

·         Study the divergence effect of ultra-high degree spherical, spheroidal and ellipsoidal harmonic series inside the Brillouin sphere/spheroid/ellipsoid.

·         Study efficient methods for ultra-high degree and order harmonic analysis (the forward harmonic transform) for a variety of data types and boundary surfaces, as well as harmonic synthesis (the reverse harmonic transform) of various quantities.

4.  Regional sea level and vertical land motion

Chair: Roelof Rietbroek (Germany)

Co-Chair: Riccardo Riva (Netherlands)

Affiliation: IAG commissions 2, 4, IAG sub commission 2.6, GGOS and Inter-Commission Committee on “Geodesy for Climate Research”

Status: Proposed


·         Encourage the use of geodetic datasets for multi-disciplinary studies related to sea-level

·         Communicate the need for a consistent treatment of observations and models of sea
level change and vertical land motion to non-geodetic scientific communities.

·         Advance the science of regional and global sea-level research by identifying open
questions and gathering state-of-the-art work.

·         Communicate and coordinate activities with other relevant working groups (specifically:
Geodesy for the Cryosphere), in particular on the topic of vertical land motion.

5.  IAG sub-commission 2.4e: Gravity and geoid in the Asia-Pacific

Chair: Cheinway Hwang (Taiwan, ROC)

Co-Chair: Wenbin Shen (Mainland China)

Affiliation: IAG commission 2

Status: Proposed (2019-2023)


a)    Gravity and related Data

·         Share available gravity data

·         Share available DEMs along common borders

·         Combine resources for terrestrial gravity surveys along common borders

·         Promote regional airborne gravity surveys

·         Determine improved coastal gravity anomalies from satellite altimetry

b)   Gravimetric geoid and hybrid geoid quality control

·         Share GNSS/levelling and vertical deflection data for geoid quality control

·         Promoteregional GNSS/levelingand vertical deflection campaigns

·         Connect regional vertical datums

c)      Education & Research

·         Organize meetings and workshops toimprove modeling and evaluation techniques of gravimetric quasi/geoids, and to promote their application to height modernization and vertical datum connection.

·         Propose technical sessions in scientific and professional conferences

·         Propose matters of common concern/interest.