The assimilation of multi-GNSS Zenith Total Delays and Horizontal Delay Gradients

Abstract:

Radio signals which are transmitted by the multi-GNSS constellation and received by a ground-based station allow the estimation of the zenith total delay (ZTD) and horizontal delay gradients. We developed operators to assimilate these multi-GNSS tropospheric data in a variational data assimilation framework. In this presentation we analyse our latest impact trials using simulated and real observations from selected globally distributed stations. In our experiments we use numerical weather model data from the Global Forecast System. In the Observation System Simulation Experiment (OSSE) we extract ZTDs and horizontal delay gradients from the operational analysis, add noise to mimic observation errors, and assimilate these simulated observations into the 24h forecast valid at the same time. The impact is measured in terms of the refractivity profiles surrounding the considered station. In the Observation System Experiment (OSE) the simulated observations are replaced by real observations. In either case, the OSSE and OSE, we find that the assimilation of the horizontal delay gradients on top of the ZTD has a weak positve impact.