Tropospheric refractivity and zenith path delays from least-squares collocation of meteorological and GNSS data

Precise positioning requires an accurate a priori troposphere model to enhance the solution quality. several empirical models are available, but they not properly characterize the state of troposphere, especially in severe weather conditions. another possible solution is to use regional troposphere models based on real-time or near-real time measurements. in this study, we present the total refractivity and zenith total delay (ztd) models based on a numerical weather prediction (nwp) model, global navigation satellite system (gnss) data and ground-based meteorological observations. we reconstruct the total refractivity profiles over the western part of switzerland and the total refractivity profiles as well as ztds over poland using the least-squares collocation software comedie (collocation of meteorological data for interpretation and estimation of tropospheric pathdelays) developed at eth zürich. in these two case studies, profiles of the total refractivity and ztds are calculated from different data sets. for switzerland, the data set with the best agreement with the reference radiosonde (rs) measurements is the combination of ground-based meteorological observations and gnss ztds. introducing the horizontal gradients does not improve the vertical interpolation, and results in slightly larger biases and standard deviations. for poland, the data set based on meteorological parameters from the nwp weather research and forecasting (wrf) model and from a combination of the nwp model and gnss ztds shows the best agreement with the reference rs data. in terms of ztd, the combined nwp-gnss observations and gnss-only data set exhibit the best accuracy with an average bias (from all stations) of 3.7 mm and average standard deviations of 17.0 mm w.r.t. the reference gnss stations.