The Tropospheric Products of the International GPS Service

The International GPS Service (IGS) produces several tropospheric products that are based on combined contributions from several IGS Analysis Centers. These products contain time series of total zenith delay from a large subset of the IGS network of ground-based GPS receivers. The IGS has recently adapted a new method for the derivation of the combined tropospheric products. In this paper we describe this method and assess its benefits. Each product consists of time series of total zenith troposphere delay at 5 minute intervals from a set of IGS ground sites. Total zenith delay values are estimated with the precise point positioning approach, using the IGS combined GPS orbit and clock solutions, and Rinex files generated by each site. Presently there are two types of IGS tropospheric products: "Final", and "near real time (nrt)". The Final product is based on the IGS "Final", and most precise combined GPS orbit and clock products, and on daily Rinex files, and has a latency of approximately 10 days after the data is collected. The NRT product is based on the IGS ultra-rapid GPS orbit and clock products, and on hourly Rinex files. The latency is up to three hours after data has been collected. We compare this new approach for generating the IGS combined tropospheric products with the previous approach, which was based on explicit combination of total zenith delay contributions from the Analysis Centers. The new combination approach enables the IGS to rapidly generate high accuracy and high reliability total zenith delay time series for many hundreds of sites, increasing the utility of the products to weather modelers, climatologists, and GPS analysts. We discuss issues of accuracy, quality control, and utility of the new products.