Temporal correlations of atmospheric mapping function errors in GPS estimation

Abstract

The developments in global satellite navigation using GPS, GLONASS, and Galileo will yield more observations at various elevation angles. The inclusion of data acquired at low elevation angles allows for geometrically stronger solutions. The vertical coordinate estimate of a GPS site is one of the parameters affected by the elevation-dependent error sources, especially the atmospheric corrections, whose proper description becomes necessary. In this work, we derive time-series of normalized propagation delays in the neutral atmosphere using ray tracing of radiosonde data, and compare these to the widely used new mapping functions (NMF) and improved mapping functions (IMF). Performance analysis of mapping functions is carried out in terms of bias and uncertainty introduced in the vertical coordinate. Simulation runs show that time-correlated mapping errors introduce vertical coordinate RMS errors as large as 4 mm for an elevation cut-off angle of 5°. When simulation results are compared with a geodetic GPS solution, the variations in the vertical coordinate due to mapping errors for an elevation cut-off of 5° are similar in magnitude to those caused by all error sources combined at 15° cut-off. This is significant for the calculation of the error budget in geodetic GPS applications. The results presented here are valid for a limited area in North Europe, but the technique is applicable to any region provided that radiosonde data are available.