An analysis of the accuracy of zenith tropospheric delay calculated from ECMWF/NCEP data over Asian area

The tropospheric delay is an important error source for the satellite navigation and positioning, and the numerical forecast data derived from meteorological instruments can be used to calculate the tropospheric delay. In this study, the zenith tropospheric delay (ZTD) observed from 49 Global Positioning System (GPS) sites distributed in Asian area is used to assess the effectiveness and accuracy of ZTD calculated with the data from the European Center for Medium-Range Weather Forecasts (ECMWF) and the United States National Centers for Environmental Prediction (NCEP). The practicability of ECMWF/NCEP data in Asian area and the relation between the resolution and the accuracy for the ECMWF data are also studied. The results are: (1) relative to GPS observed ZTD (GPS ZTD), the bias and rms for the ECMWF data are -1.0 cm and 2.7 cm respectively, which are better than that for the NCEP data and can be used for ZTD study and application with high accuracy; the bias and rms for the NCEP forecast data are 2.4 cm and 6.8 cm, which are sufficient for the tropospheric delay correction in the real-time GNSS navigation and positioning. (2) The bias and rms show a seasonal variation, which generally show larger values in summer months and smaller values in winter months; however, the relation between the bias and rms and the latitude is not obvious, but the rms decreases with increasing altitude. In addition, the daily bias and rms at eastern Asian area in summer and at southern in winter have a relatively larger variation. (3) The resolutions of 2.5 degree and 0.5 degree ECMWF data are compared; the rms for the latter is decreased by 1 similar to 5 mm than the former. These results provide a reference for the effectiveness and accuracy of the ECMWF/NCEP data used for calculating the tropospheric delay in the space geodesy, navigation and positioning, and INSAR, etc.