The Integration of GNSS/Leveling Data with Global Geopotential Models to Define the Height Reference System in Several Regions of Vietnam

observations and precise leveling benchmarks to adjust global geopotential models to the Vietnamese height datum (VN-2000). We selected 18 first-order leveling benchmarks in the Red River Delta, computing the actual geoid height anomaly N_TC from GNSS ellipsoidal heights (h) and orthometric heights (H). Geoid undulations N_G were computed from five global models (EGM2008, EIGEN-6C4, GECO, SGG-UGM-2, XGM2019e_2159). Differences between N_TC and N_G were minimized using a 3D Molodensky transformation and a second-degree polynomial fit. Results show that XGM2019e_2159 had the smallest initial residuals, consistent with previous findings. After adjustment, all models achieve comparable accuracy (RMSE ≈ 0.04–0.07 m) on independent check points. The adjusted XGM2019e_2159 yields the best performance (RMSE ≈ 0.047 m). This demonstrates that high-degree global models, when transformed to the VN-2000 datum, provide an effective solution for GNSS-based height determination in Vietnam.