ACAP - Global Gravity Field Modelling From Orbit Data Based on the Acceleration Approach

The main purpose of the ACAP project was to compute a global gravity field based on precise orbit information using the so-called acceleration approach. This method is based on Newton's second law of gravitation, which states that the acceleration of a mass is related to the forces acting on it.

Short Description

Transferred to a satellite this means that all forces acting on it cause accelerations. These accelerations cannot be observed directly, but they can be calculated from orbit positions by means of numerical differentiation. Beside some minor forces, like air drag, solar radiation pressure or gravity fields of the Moon, the Sun and other planets, the main force in this context is the Earth's gravity field.

Different simulations were carried out to test the method and find the best configuration for estimating the gravity field. Additionally different widely used numerical differentiators were tested to find the most appropriate method to derive the necessary accelerations. We tested Newton-Gregory inter- polation, Taylor-MacLaurin differentiation and polynomial approxi- mation.

The investigations revealed that Newton-Gregory and Taylor-MacLaurin are only a special case of a polynomial approximation. Furthermore, using a polynomial provides far more flexibility in terms of degree, used epochs and degree of freedom. Based on these findings real data from ESA's GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission was used to produce the gravity field solution shown in the illustration below.

The investigations showed that the acceleration approach is capable of producing competitive gravity field solutions, compared to current high-end models based on satellite and/or terrestrial data, especially in low degrees.

Project Partners


Graz University of Technology, Institute of Theoretical Geodesy and Satellite Geodesy - Torsten Mayer-Gürr

Contact Address

Graz University of Technology
Institute of Theoretical Geodesy and Satellite Geodesy
Torsten Mayer-Gürr
Steyrergasse 30
A-8010 Graz
Tel.: +43 (316) 873 - 6359