Abstract: [Purposes] The unification of the global height datum relies on high-precision global gravity field models,yet existing models are often insufficient in both accuracy and spatial resolution. [Methods] To address this limitation,this study extends GRACE/GOCE satellite gravity field models by integrating the high-degree model EGM2008 and the residual terrain model (RTM),thereby constructing a combined gravity field model to compensate for their truncation errors.Using this combined model and GNSS/leveling data from Brazil,the vertical datum parameters for the region are determined. [Findings] Spectral analysis reveals that the satellite gravity models exhibit lower geoid degree errors and higher signal-to-noise ratios up to approximately degree 200.Validation with GNSS/leveling data shows that the accuracy of all combined models surpasses that of the individual GRACE/GOCE models and EGM2008.Among them,the GMMG2021S-EGM2008-RTM model demonstrates the optimal performance,improving accuracy by 40.7%compared to the Tongji-GMMG2021S model and by 11.3%compared to the EGM2008 model.The final calculation yields a gravity potential value of 62 636 849.27 m²·s^-2 for the Brazilian height datum.The corresponding potential difference and vertical deviation from the global datum are approximately 4.13 m²·s^-2 and 42.2 cm,respectively,indicating that the Brazilian height datum is about 42.2 cm above the global datum. [Conclusions] This research demonstrates that the spectral combination method effectively enhances model resolution and accuracy,providing a valuable reference for global height datum unification.

Key words: unification of height datum, GRACE/GOCE gravity field models, EGM2008, RTM, combined gravity field model