ALBERT

Description: An extensive validation of line-of-sight tropospheric Slant Total Delays (STD) from Global Navigation Satellite Systems (GNSS), ray-tracing in Numerical Weather Prediction Models (NWM) fields and microwave Water Vapour Radiometer (WVR) is presented. Ten GNSS reference stations and almost two months of data from 2013, including severe weather events, entered the comparison. Seven institutions delivered their STDs based on GNSS observations processed using five software and eleven strategies. STDs from NWM ray-tracing came from three institutions using three different NWM models. Results show generally a very good mutual agreement among all solutions from all the techniques. The mean bias (over all stations) between the GNSS solution selected as reference, which did not use post-fit residuals in STDs, and all other GNSS solutions without post-fit residuals is −0.6 mm for STDs scaled in the zenith direction, and the corresponding mean standard deviation is 3.7 mm. Standard deviations of comparisons between GNSS a NWM ray-tracing solutions are typically 10 mm ± 2 mm (scaled in the zenith direction), depending on the NWM model and the particular station considered. When comparing GNSS versus WVR STDs, standard deviations reached 12 mm ± 2 mm, as scaled in zenith direction. Moreover, the influence of adding raw GNSS post-fit residuals, as well as residuals screened out of systematic effects, to STDs was studied. It was found that adding raw post-fit residuals always led to lower quality of GNSS STDs while the situation was not that straightforward after the post-fit residuals cleaning.