Study on the Fusionand Validation of Sea Surface Height Anomaly Field based on the Radar Altimeters Onboard HY-2C/D Satellites

Spaceborne radar altimeters can provide high-precision global sea surface height (SSH) observations regularly. However, the spatial resolution from a single satellite is relatively sparse. To facilitate the study of mesoscale ocean phenomena, multi-satellite data fusion techniques are essential. The HY-2C/D satellites, operating in inclined orbits with configurations similar to the advanced Jason series (e.g., Jason-3), are particularly suitable as data sources for SSH fusion. Although multiple operational fused SSH anomaly fields (e.g., the MIOST product) exist internationally, none currently incorporate China's HY-2C/D data. This study performed cross-calibration for the HY-2C/D radar altimeters against Jason-3 to correct systematic biases and compute sea surface height anomalies (SSHA). Using the Optimal Interpolation (OI) method, we integrated HY-2C/D data into the MIOST background field to generate a fused SSH anomaly field for the South China Sea (10°×10°). In constructing the OI's critical variance-covariance matrix, the diagonal elements were derived from the standard deviations of HY-2C/D post-calibration data, while covariance terms were determined based on the power spectrum characteristics of SSHA. Validation using tide gauge data from the Wanshan Calibration Site (China's operational altimeter calibration field) demonstrated that the fusion of HY-2C and HY-2D data reduced the root-mean-square error (RMSE) of SSHA sequences relative to ground truth. This study confirms the contribution of HY-2C/D data to fused satellite altimetry products.