Integrated adjustment of LEO and GPS in precision orbit determination

At present, usually only the ground stations are used for the precise orbit determination (POD) of GPS satellites. The precise orbits of Low Earth Orbiters (LEO) are determined with GPS orbits and clocks fixed. The integrated adjustment of LEO and GPS for POD that is first reported in (Zhu et al., 2004),which means the orbits of GPS satellites and LEOs are determined simultaneously, is introduced here. At first, the contribution of LEOs to GPS POD is illuminated. On the one hand, the data from 43, 32 and 21 ground stations besides three LEOs are used. In the case of 21 ground stations plus three LEOs, about 5.0 cmaccuracy from IGS final orbit can be achieved with only one day's data. On the other hand, the data from one, two and three LEOs besides 43 stations are employed. It is shown that the improvement can reach 31% when only one LEO is added to 43 ground stations. These achievements are mainly attributed to the strengthened geometry afterLEOsare included. Then, the improvement of LEO orbits in the integrated adjustment is presented. When 43 ground stations are used, the improvement can get to 17% and 32% without accelerometer data for CHAMPand GRACE, respectively. So it is demonstrated that the LEO orbit accuracy is improved simultaneously with the GPS orbits in the integrated adjustment.