The optimal selection of orbital parameters in the future ImprovedGRACE satellite gravity measurement mission in China is carried out by using the combined model of cumulative geoid height errors influenced by the intersatellite rangerate error of interferometric laser ranging system, orbital position and velocity errors of GPS receiver and nonconservative force error of accelerometer based on the improved semianalytic method. The simulated results show as follows.Firstly, at degree 300, cumulative geoid height error is 3.993×10 -1 m at 350 km orbital altitude, the accuracies are improved respectively 8.770 times and 77.145 times at 300 km and 250 km compared with that at 350 km orbital altitudes, and the accuracies are decreased respectively 8.718 times and 75.307 times at 400 km and 450 km compared with that at 350 km orbital altitudes.Secondly, cumulative geoid height error is 3.993
×10-1 cm as using 50 km intersatellite range, and the accuracies are reduced respectively 1.259 times and 1.395 times using 110 km and 220 km compared with that using 50 km intersatellite ranges.Finally, the optimal designs of average orbital altitude 350 km and mean intersatellite range 50 km are suggested in the future first ImprovedGRACE gravity satellite in China.
The tropospheric refraction in the position of a GPS receiver is computed with fitting the tropospheric refraction of CORS, but the accuracy which is estimated with the available tropospheric model is low. The tropospheric refraction is gained by fitting its grids in CORS, so the accuracy can be improved. Taking the data of WUHN as an example, it is shown that the accuracy of U is better than that with estimating by tropospheric model, and is similar with the results of parameter estimation.This way is easy for the tropospheric refraction because it has been provided before computing the results of the GPS receiver.