Towards a consistent set of parameters for the definition of a new GRS

In the last few years, a consistent set of parameters for a consistent GRS was developed. The goal is to replace GRS80 as the official conventional system. This change becomes more and more necessary because since the introduction of GRS80, the knowledge in geodesy has improved significantly (e.g. GNSS, gravity space missions), the IERS conventions have changed several times and the use of the parameters became inaccurate and inconsistent over time. 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.

The new set of parameters is based on the four fundamental parameters: W₀ (potential at reference level), J2 (dynamic form factor), GM (geocentric gravitational constant) and ω (angular velocity of the Earth). All these quantities are well observed and monitored by various geodetic space techniques. Most of the defining parameters change with time. This includes seasonal variations and long-term trends.

The main problem is the discussion if the replacement of GRS80 as the conventional system is really necessary. Many users do not see the advantage to replace it, as it is seen just as a conventional model for the conversion of geocentric coordinates or for the calculation of gravity anomalies. However, the working group is in favor of working towards an IAG resolution that defines a new GRS. The main goal is not to increase accuracy, but to bring back consistency into geodetic applications.