Phase Center Variation Modeling of ICESat GPS Antenna for Precision Orbit Determination

Abstract

For precision orbit determination (POD), the precise location of the phase center of the on-board GPS antenna must be modeled. The phase center of a GPS antenna varies as a function of the azimuth and elevation angle of incoming signal. There are two methods to model the phase center variation. One is to measure the phase center variation with ground test in anechoic chamber. The other is to calibrate the phase center location based on onorbit measured GPS data. There are again two method to calibrate the phase center location using the on-orbit data. One is called direct method and the other method is called residual method. In the research described in this paper, the residual method was applied to ICESat precision orbit determination. Since ICESat POD at Center for Space Research uses doubledifferencing approach, the resulting residuals were converted into zero-differenced residuals. The quality of the resulting orbit solution was assessed by measurement residual RMS, SLR residual RMS and orbit overlap analysis. Orbit solution with phase center variation model developed in this research showed noticeable improvement.