Impact of atmospheric delay reduction using KARAT on GPS/PPP analysis

Abstract

We have been developing a state-of-art tool to estimate the atmospheric path delays by ray-tracing through meso-scale analysis (MANAL data) data, which is operationally used for numerical weather prediction by Japan Meteorological Agency (JMA). The tools, which we have named "KAshima RAytracing Tools (KARAT)", are capable of calculating total slant delays and ray-bending angles considering real atmospheric phenomena. The KARAT can estimate atmospheric slant delays by an analytical 2-D ray-propagation model by Thayer and a 3-D Eikonal solver. The biases of slant delay estimates between the Thayer model and the modern mapping functions, which are ranging from 18 to 90 mm, are considered to be a deficiency of the mapping functions. We compared PPP solutions using KARAT with that using the Global Mapping Function (GMF) and Vienna Mapping Function 1 (VMF1) for GPS sites of the GEONET (GPS Earth Observation Network System) operated by Geographical Survey Institute (GSI). In our comparison 57 stations of GEONET during the year of 2008 were processed. The KARAT solutions are slightly better than the solutions using VMF1 and GMF with linear gradient model for horizontal and height positions. Our results imply that KARAT is a useful tool for an efficient reduction of atmospheric path delays in radio based space geodetic techniques such as GNSS and VLBI. © Springer-Verlag Berlin Heidelberg 2012.