The Impact of satellite geometry on DGPS positioning

Abstract

This paper investigates the effect of Satellite Geometry in the Precision of DGPS positioning, since it has an amplifying effect on other sources of errors associated with GPS positioning. DGPS positional data were acquired at three epochs of a day using Promak3 DGPS and post-processed using GNSS solution software. The temporal variations in PDOP, number of visible satellites and the standard errors in relative positioning, (which are all functions of the satellite geometry) were analysed both graphically and statistically (using statext v1.0 software) to ascertain the impact of satellite geometry on the derived positions. The graphical results indicated various temporal variations in the parameters defining a GPS-based position on the earth surface; but the statistical tests conducted show no significant differences in the means of the PDOP and standard error in relative positioning obtained in three epochs at 0.05 significant level. Also, for the short ranges, an average standard error of 0.046m, 0.043m and 0.092m were obtained at the three epochs respectively; while for the medium ranges an average standard error of 0.112m, 0.096m, and 0.123m were obtained at the three epochs respectively.it was concluded that the longer the occupation time, the better the satellite geometry and thus the higher the precision in DGPS positioning