The Height Anomaly Computation for West Sichuan Province Using FFT

Because of the rugged topography in the west Sichuan province, it is very difficult to carry out the conventional surveying there. If the GPS technique is used to provide the control of photography. the geodetic field work will be much easier and more economical. But the GPS given ellipsoidal heights must be converted to normal heights. So a quasi-geoid with high resolution is needed in this area. In this paper, a 5'×5' gridded quasi-geoid has been computed over a 14°×12årea in west Sichuan by using FFT method which employed the planar-approximated Stokes integral. The Molodensky first-oder approximate term has been also considered in the computation. Comparing the results with some astrogravimetric levelling and GPS levelling, We found that they are about 1 meter in accuracy. Furthermore, the study shows that the results including the contribution of residual gravity anomalies are 20 percent more accurate than geopotantial model only derived quasi-geoid and another 20 percent improvement can be obtained by considering the Molodensky first-oder approximate term using a 0.5'×0.5' DTM.