NWP for PPP

Precise positioning requires an accurate a priori troposphere model to enhance the solution quality. Several empirical models are available, but they may 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. We present  a high-resolution model of troposphere based on a spatial high-resolution (4 km × 4 km) Numerical Weather Prediction (NWP) Weather Research and Forecasting (WRF) and Global Navigation Satellite System (GNSS). We reconstruct the total refractivity profiles as well as zenith total delay (ZTD) over Poland using the least-squares collocation software COMEDIE (Collocation of Meteorological Data for Interpretation and Estimation of Tropospheric Pathdelays) developed at ETH Zürich.

Fig.1. Comparison of ZTD from GNSS station KRAW (top) and REDZ (bottom) with ZTDs from COMEDIE from 3 different data sets: ‘WRF only’, ‘WRF/GNSS’  and ‘GNSS only’ with corresponding residuals of ZTD_GNSS − ZTD_COMEDIE (mm) for all data sets (bottom).

We can conclude that the best troposphere models based on collocation can be obtained from the combination of NWP and GNSS data. Using NWP-only data biases the troposphere delays in particular due to the overestimation of the humidity after rainfalls. Using GNSS-only data provides substantially larger differences of the total refractivity with respect to the RS measurements. Whereas, using a NWP/AWS-GNSS combination results in the smallest biases and the smallest residuals with respect to both, RS and GNSS data. We recommend to use these models as an a priori model of the troposphere for positioning.

References

Wilgan K, Hurter F, Geiger A, Rohm W, Bosy J (2016) Tropospheric refractivity and zenith path delays from least-squares collocation of meteorological and GNSS data. J Geod (online). doi: 10.1007/s00190-016-0942-5