Zenith Tropospheric Delay Modeling Errors in SLR-Derived Geodetic Parameters: Analysis Using ERA5 Hourly Data

Summary Satellite Laser Ranging (SLR)-derived geodetic parameters are critical for geophysical studies. These key parameters are sensitive to errors in tropospheric delay modeling. The Mendes and Pavlis (MP) model, the current standard for zenith tropospheric delay (ZTD) correction in SLR data processing, employs simplifications that potentially introduce systematic errors into SLR-derived products. In this study, we assess the magnitude and temporal characteristics of ZTD errors by comparing ZTD estimates from the MP model and vertical integration method utilizing ERA5 reanalysis data with high time resolution of 1 hour. Our analysis reveals that the modeling discrepancies between the MP model and vertical integration method exhibit a millimeter-level mean offset and seasonal variations, which are absorbed into the estimated geodetic parameters and account for a nonnegligible portion of their seasonal variability. The implementation of vertical integration method reduces the annual amplitude of station coordinates by 5.6%, 10.4%, and 14.4% in the E, N, and U components, respectively. For geocenter coordinates, annual signals of the Z component are reduced by 21.4% when using vertically integrated ZTD. The application of vertical integration method also yields a shift of +0.08 ppb in the terrestrial scale and reduces 28.5% of the annual scale variation. These results demonstrate that ZTD errors can distort the seasonal and interannual analyses of SLR-derived geodetic parameters. Adoption of more accurate tropospheric modeling is essential for improving the reliability of SLR-based geophysical investigations.