A Zenith Tropospheric Delay Interpolation Method Considering Elevation

Zenith Tropospheric Delay (ZTD) plays a crucial role in navigation and water vapor retrieval. The Global Navigation Satellite System (GNSS), as a reliable technology to obtain high-precision ZTD, usually adopts interpolation or fitting to improve the spatial coverage of ZTD. In this paper, a High-related ZTD interpolation model (HRZ) was proposed to overcome the shortcomings of traditional interpolation methods, such as low fitting accuracy, limited applicability, and neglect of height considerations. This method assumes that the Zenith Hydrostatic Delay (ZHD) and Zenith Wet Delay (ZWD) of Radiosonde (RS) stations and GNSS stations share identical proportionality coefficients. By applying the proportionality coefficients of RS to the GNSS ZTD data, the GNSS ZTD can be separated into ZHD and ZWD components. This separation allows for the realization of ZTD interpolation by vertical correction of elevation and spherical harmonic fitting of the designated elevation plane, respectively, at any position of GNSS. The HRZ model was established and evaluated based on the data from 200 GNSS stations and 12 RS stations provided by the Nevada Geodetic Laboratory (NGL) in the western United States in 2021. The results demonstrated that the average Root Mean Square Error (RMSE) of the ZTD deviation of the HRZ model was 12.3 mm, and the accuracy exhibited improvements of 11.5% and 88.5%, respectively, compared with 13.9 mm and 107.4 mm of polynomial interpolation and spherical harmonic interpolation. Furthermore, the HRZ model demonstrated impressive precision in fitting ZTD values, with almost all the fitted ZTD values falling within a range of less than 20 mm. This level of accuracy met the threshold value required for ZTD in water vapor inversion applications.