First Simultaneous Inversion of Sea-Surface Velocity and Height Based on PIE-1 SAR Constellation

Sea-surface velocity (SSV) and sea-surface height (SSH) are among the most crucial parameters in an oceanic dynamic environment. Using spaceborne interferometric synthetic aperture radar (InSAR) to obtain high-resolution, large-scale survey area, high observation frequency, and high-precision ocean dynamic parameters is advantageous. However, the hybrid baseline InSAR phase data include components from both SSV and SSH, making it challenging to distinguish them and affecting inversion accuracy without additional information. The PIE-1 constellation, the world's first four-satellite distributed InSAR system, was successfully launched into orbit on March 30, 2023. This constellation can form multiple interferometric pairs by combining two satellites, enabling the potential to extract SSV and SSH from hybrid phase signals simultaneously. In this study, two pioneering and fundamental works were conducted: 1) an integrated current-height inversion model was developed based on the multichannel likelihood (ML) function, with error analysis performed according to PIE-1 parameters and 2) the detailed data processing scheme for the first simultaneous inversion of SSV and SSH based on spaceborne InSAR data was presented. The inversion results were compared to Doppler centroid analysis (DCA)-derived Doppler velocity and reference data from the ESA's Copernicus Marine Service (CMEMS). Both qualitative and quantitative comparisons validated the effectiveness and accuracy of the inversion results. This approach represents an effective technique for simultaneous inversion of SSV and SSH in future multibaseline spaceborne/airborne InSAR systems.