Refining gravity anomaly data of coastal areas by combining XGM2019e-2159 and SRTM/GEBCO_2024 residual terrain model with forward modeling method

Abstract. As one of the Earth's fundamental physical fields, the gravity field model’s accuracy is considerably constrained in areas with sparse coverage or data gaps. In coastal areas, satellite altimetry data are affected by land contamination and errors from tidal models, while shipborne gravity measurements fail to obtain valid gravity data in nearshore regions. Therefore, gravity field models’ accuracy in coastal areas is relatively lower. Additionally, due to the truncation of global gravity field models at specific degrees, truncation errors prevent the acquisition of high-precision gravity anomaly (GA) information. In response to this problem, this study introduces detailed land topography and ocean bathymetry data, and adopts a gravity forward modeling method based on the residual terrain model (RTM) to reduce the truncation error of the gravity field model in the target coastal area. Thus, high-precision GA information can be obtained in the coastal area. First, the high-resolution terrestrial digital elevation model SRTM V4.1 is merged with the marine bathymetry model GEBCO_2024, and then combined with the reference topography model Earth2014 to construct the RTM. The RTM is then discretized into regular grid prisms, and the GA generated by the RTM at target points is computed in the spatial domain using the prism integration method to refine the XGM2019e-2159 gravity anomaly (XGM-GA) model. For computational points located in coastal areas, the rock-equivalent topography (RET) method is employed to avoid distinguishing between the different densities of land and ocean prisms during the calculation process. Based on this, a mass center offset correction is proposed to address the errors caused by prism position shifts in the RET method. To validate the feasibility of this method, this study focuses on a selected region along the U.S. West Coast (125° W–122° W, 39° N–42° N) and refines the XGM-GA model. Measured GA data from NGS99 serve as the reference for validating the experimental results. The research results show that after applying the RTM method, the root mean square error between the modeled GA and the measured GA decreased from 14.55 mGal to 8.19 mGal over the entire study area, and from 14.98 mGal to 8.19 mGal in the coastal area. The power spectral density analysis conducted at the end of this study shows that the power spectral density of the high-frequency band of the XGM-GA model significantly increased after applying the RTM method. All the above results prove the feasibility of the RTM gravity forward modeling method in improving the accuracy of the gravity anomaly model.