Accuracy Analysis of ZTD and ZWD Calculated from MERRA-2 Reanalysis Data over China

  Objectives  Tropospheric delay is one of the main errors in high-precision positioning and navigation, and it is a key parameter in the process of retrieving precipitable water vapor from global navigation satellite system (GNSS) signals. The latest generation of atmospheric reanalysis data of National Aeronautics and Space Administration, MERRA-2, can be used to calculate high-resolution tropospheric delay products. However, there is no literature on the accuracy of the zenith tropospheric delay(ZTD) and zenith wet delay(ZWD) calculated from MERRA-2 data. Therefore, the purpose is to evaluate ZTD and ZWD calculated from MERRA-2 reanalysis data over China.

  Methods  Based on the data of ZTD products from 214 GNSS stations of the crustal movement observation network of China (CMONOC) and 87 radiosonde stations data in 2015, the accuracy and performance of ZTD/ZWD derived from MERRA-2 data in China is evaluated.

  Results  The results show that the ZTD calculated from MERRA-2 data with the annual bias and root mean square error(RMSE)of 0.32 cm and 1.21 cm when compared with CMOMOC-derived ZTD, respectively; the bias and RMSE have obvious seasonality, which generally show relative lower accuracy in summer and higher accuracy in winter.In terms of spatial distribution, the variation trend of bias with latitude and elevation is not obvious, but the RMSE generally shows a decreasing trend with the increase of latitude and elevation. The ZWD and ZTD calculated from MERRA-2 data has the annual bias of 0.37 cm and 0.53 cm compared with radiosonde profiles, respectively; while those of RMSE are 1.44 cm and 1.61 cm, respectively. The bias and RMSE of ZWD and ZTD calculated from MERRA-2 data also have the temporal and spatial variation characteristics, which has similar feature with the tested result of CMONOC GNSS ZTD products.

  Conclusions  Therefore, the ZTD and ZWD calculated from MERRA-2 reanalysis data over China have significant accuracy and stability, which can be used as a data source to establish high-precision and resolution tropospheric correction model and high-precision GNSS water vapor detection in China.