Characterization of Atmospheric Propagation Errors for DGPS

A GPS reference station network has been setup in an area of 25-km radius. The objective is to develop a real-time model of the atmospheric propagation errors in this region. In this paper, GPS L1-L2 carrier phase measurements are analyzed to assess the size of the residual tropospheric and ionospheric errors in DGPS. Meteorological sensors were collocated with each of the receivers. The analysis is based on precise estimates of the residual single and double difference propagation delays obtained from GPS carrier phase data. These propagation delays are examined in relation to geomagnetic events, weather fronts, and other atmospheric data to determine their correlations. This research is motivated by the goal of reducing the atmospheric error in DGPS. We intend to explore the feasibility of mitigating the error in real-time by fitting a model to the residuals measured over the region covered by the network of GPS stations. Reducing the atmospheric error would also help in resolving the carrier phase integer ambiguities. Recent studies have shown that the integer ambiguities may be resolved with GPS L1-L2 measurements from a single epoch provided that the errors in the double differences are kept small [1]. The analysis presented here is an attempt to characterize the size of these errors.