Integrated adjustment of LEO and GPS with PANDA in precision orbit determination

The paper examined the integrated adjustment of GPS (Global Positioning System) and LEO (Low Earth Orbiter) data for Precision Orbit Determination (POD). The GPS observations from the LEOs and fiducial ground stations, space-borne accelerometer data and star camera data are adjusted at the observation level with the SLR (Satellite Laser Ranging) and KBR (K-Band Ranging) data included in the processing with zero weight to obtain their measurement residuals. Six modes of experiments are designed according to whether to use ground station data, to use LEO data and to fix ambiguities or not. On the one hand, the results from their comparisons illuminate that the accuracy of GPS orbits gains much profit from the integrated adjustment. With the decreasing of the number of ground stations, the contribution to GPS orbit quality by adding three LEOs without ambiguity fixing is even larger than that by fixing ambiguity with the ground stations only. Moreover, if the ambiguities are also fixed in the integrated adjustment, the GPS orbit accuracy will be improved further. On the other hand, the results reveal that although the absolute accuracy of LEO orbits in the integrated adjustment is not enhanced as obviously as that of the GPS orbits, the improvement is still perceptible. Furthermore, integrated adjustment is able to improve the relative accuracy of twin GRACE satellites to some extent. However, this contribution is not as much as that through ambiguity fixing between GRACE satellites.