Analysis of the GRACE Gravity Sensor System

The performance of the current GRACE gravity field models significantly exceeds the performance of all other models available before GRACE. However, the performance of these new models is still significantly below the predicted performance. This degradation in performance has a strong effect on the geophysical exploitation of the GRACE mission. There are two possible causes for the degraded performance:

It is possible that the analysis models are simply not sophisticated enough for fully exploiting the information content of the gravity field sensor system. There could also be deficiencies in the accuracy and the consistency of the used geophysical reduction models or the gravity field determination algorithms. The second possible explanation is that the accuracy of individual elements or of the interaction of the individual elements of the gravity field sensor system is suboptimal or that inadequate signal processing methods have been used.

The purpose of this investigation is a thorough analysis of this second complex. The gravity field sensor system consists of the K-Band distance measurements, the star sensor data for the orientation in inertial space, the accelerometer data and the GPS phase and code data. The Jet Propulsion Laboratory in Pasadena is entrusted with the operational GRACE data processing. In this talk the results of the review of the applied processing strategies from the level of raw instrument data (level 1a) to the level of gravity field determination input data (level 1b) will be presented. Possible alternatives to the official processing strategy will be discussed and occurring differences will be evaluated in terms of the expected impact on the derived gravity field models.