COMPARING THE HIGHER ORDER IONOSPHERIC REFRACTION EFFECTS ON GPS PRECISE POINT POSITIONING ACCURACIES IN DIFFERENT REGIONS AND SEASONS - A CASE STUDY OF TAIWAN REGION

Abstract

The precise point positioning (PPP) accuracy can reach centimeter level using global positioning system (GPS) dual-frequency data. However, centimeter level accuracy is insufficient for high accuracy applications, such as control surveying, deformation monitoring, etc. To improve the accuracy of PPP, higher order ionospheric refraction effects must be taken into account. The purpose of this research is to investigate the effects on PPP accuracies caused by higher order ionospheric refraction errors. The first step is to estimate the higher order ionospheric refraction terms of GPS dual-frequency data. And then, correcting the GPS RINEX file accordingly. At last, evaluating the accuracy of PPP accuracies after higher order ionospheric refraction errors are corrected. There are two programs applied in this paper: RINEX_HO and gLAB(global navigation satellite system-LABoratory). RINEX_HO, developed by São Paulo State University in Brazil, can estimate higher order ionospheric refraction terms and produce a corresponding corrected observation file. gLAB, developed by gAGE(Research group of Astronomy and GEomatics Technical University of Catalonia in Spain), can perform precise point positioning and calculate position errors. The following data sets of Taiwan region are tested, including the GPS observation data provided by Civil-NET, precise ephemeris and other data from international global navigation satellite system service (IGS). And the period of these data are a few days before and after the spring equinox, summer solstice, autumn equinox and winter solstice of year 2014. The detailed theory, experiment methods and preliminary result will be presented in this paper.