DefinePK

Abstract

In differential GPS or DGPS, it is generally considered that the ionospheric correction is the same for both reference and unknown target (or mobile or user) receivers. However, it is clear that the ray paths from the satellite to the two receivers will generally traverse the ionosphere at slightly different elevations. Any horizontal ionospheric gradient present would also introduce errors into the DGPS correction. These two effects have been investigated in the present work in order to obtain a more accurate ionospheric correction for DGPS and have been found to be roughly comparable showing that they are both important. To accomplish this, the differential delay between the two paths for different elevations and azimuths has been done using an analytical ray tracing program. By performing ray-tracing calculations with and without a linear horizontal ionosphere gradient, the effects of elevation angle and horizontal gradient have been separated and a ratio of these effects has been determined for different elevations and horizontal ionosphere gradients. Empirical models have been introduced to model these variations based on the ray-tracing results.