BPSGGOS Joint Working Group on

Towards a consistent set of parameters

for the definition of a new GRS

Chair: Urs Marti

Terms of Reference

The Geodetic Reference System 1980 GRS80 is still the conventional system for most applications in Geodesy and other Earth sciences. It was defined through the four parameters a (semi-major axis), J2 (Dynamical Form Factor), GM (geocentric Gravitational Constant) and ω (Angular Rotation Velocity). It represents the scientific status of the 1970ies and in its concept, the tidal systems and relativistic theories are not considered. Since its adaptation, various inconsistencies have been introduced into geodetic standards and applications, such as new values for GM or a in the IERS conventions. In 2015, a conventional value for the gravitational potential at sea level W0 was adopted in an IAG resolution, which is in contradiction to the definition of GRS80.
This WG will publish a new set of defining parameters for a modern GRS based on todays knowledge and calculate all the necessary derived parameters in a consistent way. It will study the necessity to work towards an IAG resolution to replace GRS80 as the conventional system and provide transformation procedures between the two systems. It will study as well the necessity to define and adopt a conventional global gravity field model for standard applications in geodesy, navigation and related topics.
This JWG is assigned to the GGOS Bureau of Products and Standards (BPS) and works together with representatives of IAG Commissions 1 and 2, the Inter-Commission-Committee on Theory (ICCT), the International Gravity Field Service (IGFS), the International Earth Rotation and Reference Systems Service (IERS) and the Committee on Essential Geodetic Variables (EGV).
This JWG will focus its activities on the coordination of the geometric reference frame, the global height system, the global gravity network and their temporal changes. The application of Earth orientation parameters and tidal models and the underlying standard and reference models has to be brought into consistency.

Objectives and activities

The main objectives and activities of this working group are:

  • Calculate consistent parameters of a new mean Earth ellipsoid and derived quantities
  • Study the necessity to replace the global reference system GRS80 as the conventional system
  • Advance the realization of a conventional global reference gravity field model (combined and satellite only)
  • Assist the working group for establishing the International Height Reference System (IHRS) in the realization
  • Integrating and combining the global gravity network with other techniques
  • Study the influence of earth orientation parameters, tidal models and relativistic effects on the realization of a consistent global reference frame in geometry, height and gravity
  • Foster the free exchange of geodetic data and products


Urs Marti (Switzerland), Chair
Detlef Angermann (Germany), Chair of GGOS BPS, IERS
Richard Gross (USA) IAG Vice President, Committee on EGV
Ilya Oshchepkov (Russia), GRS, Gravity Networks and Height Systems
Christopher Kotsakis (Greece), Commission 1
Jonas Ågren (Sweden), Commission 2
Ulrich Meyer (Switzerland) COST-G
Riccardo Barzaghi (Italy), IGFS
Jaakko Mäkinen (Finland), Tidal Systems
Pavel Novak (Czech Republic), ICCT
Laura Sánchez (Germany), IHRF
Hartmut Wziontek (Germany), IGRF
John Nolton (USA), GRS
Robert Heinkelmann (Germany), IAU
Sergei Kopeikin (USA), relativistic effects
Erricos Pavlis (USA), ILRS

(last update 09.2020)