On the information content in linear horizontal delay gradients estimated from space geodesy observations

Abstract

We have studied linear horizontal gradients in the atmospheric propagation delay above ground-based stations receiving signals from the Global Positioning System (GPS). Gradients were estimated from 11 years of observations from five sites in Sweden. Čomparing these gradients with the corresponding ones from the European Čentre for Medium-Range Weather Forecasts (EČMWF) analyses shows that GPS gradients detect effects over different timescales caused by the hydrostatic and the wet components. The two stations equipped with microwave-absorbing material below the antenna, in general, show higher correlation coefficients with the EČMWF gradients compared to the other three stations. We also estimated gradients using 4 years of GPS data from two co-located antenna installations at the Onsala Space Observatory. Čorrelation coefficients for the east and the north wet gradients, estimated with a temporal resolution of 15min from GPS data, can reach up to 0.8 for specific months when compared to simultaneously estimated wet gradients from microwave radiometry. The best agreement is obtained when an elevation cut-off angle of 3