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 along-track observations from a single satellite are sparse. To enhance research capabilities for mesoscale ocean phenomena, fusing observations from multiple satellites is the most effective technical approach. The HY-2C/D satellites are China's first inclined-orbit altimetry satellites. Their orbital configuration is similar to that of the internationally advanced Jason series satellites, making them particularly suitable as data sources for sea surface height anomaly (SSHA) fusion. Building upon the internationally advanced operational MIOST SSHA fusion product, this study integrates HY-2C/D satellite data to generate a fused SSHA product that incorporates observations from all currently operating satellite radar altimeters, thereby expanding the application scope of the HY-2C/D satellites. The study first calculated the SSHA for the HY-2C/D satellites and performed cross-calibration, including self-cross-calibration and mutual cross-calibration using the Jason-3 satellite as the reference standard, to correct their systematic biases. Subsequently, the Optimal Interpolation (OI) method was employed, using the MIOST SSHA field as the background field, to generate a fused SSHA field for a region (10°×10°) in the South China Sea. In constructing the most critical variance-covariance matrix for the OI method, its diagonal elements were derived from the standard deviations obtained from the HY-2C/D self-cross-calibration, while the correlation scales were determined based on the SSHA power spectrum to construct the covariance matrix elements. Finally, this paper conducted both qualitative and quantitative validation of the fusion results. The qualitative analysis was primarily based on geographical distribution maps of SSHA before and after fusion; a comparison reveals that additional eddies were identified in the fused product. Quantitative analysis utilized tidal gauge data from China's independent Wanshan Calibration Site as validation data. The assessment of the SSHA fields before and after fusion demonstrated the contribution of HY-2C/D data in improving the accuracy of multi-source data fusion.