Calibration of the Satellite Gravity Gradients for GOCE and Analysis on Its Drag Free Control System

GOCE is the first modern satellite, which carried a gravity gradiometer measuring the earth gravity filed with high accuracy by the differential measurements of the accelerometers. Its along track is in a drag-free status and the accelerometers are off-center mounted. These characteristics make GOCE a significant difference from the standard satellite-satellite tracking (SST) technique. In this paper, the problem of non-strictness in the common mode acceleration calibration of GOCE is pointed out first and, then the schemes to calibrate six accelerometers individually to separate the bias parameters are presented. The precise kinematic orbit of GOCE is used in the accelerometer calibration and drag-free control system evaluation by the dynamics method. Some fundamental results are achieved. Firstly, although the neutral atmosphere density at the altitude of GOCE orbit is higher than that of GRACE satellites with two to three orders of magnitude, the residual non-conservative force of the GOCE satellite along the track is one order of magnitude lower than the corresponding component of the GRACE satellites, which shows the compensation effect of the drag-free control system fully. Secondly, it can be concluded that the drag-free control system has a significant effect on the determination of GOCE's velocity by comparing the orbital velocity interpolated from the position and integrated with the orbit dynamics. Thirdly, the non-conservative force acting on GOCE satellite is analyzed and the accelerometer calibration parameters are estimated and evaluated. The possible developments on the preprocessing of the satellite gravity gradients with the accelerometer calibration results are also discussed in this paper. © 2018, Surveying and Mapping Press. All right reserved.