Improving Sea Surface Height Reconstruction by Simultaneous Ku- and Ka-Band Near-Nadir Single-Pass Interferometric SAR Altimeter

Wide-swath near-nadir interferometric altimetry (IA) is a newly developed technology for sea surface height (SSH) measurement. However, the absence of actual measurement data makes this novel SSH mapping technique difficult to verify and apply for wide-swath interferometric altimeters. To verify the designed performance of the scheduled wide-swath single-pass interferometric altimeter in the "Guanlan Mission," an airborne campaign was carried out off the coast of Rizhao, China, on November 16, 2020. An airborne dual-frequency interferometric radar altimeter system (ADIRAS) with a single-pass mode was utilized for SSH measurement as the first flight. Two pioneering and fundamental works have been conducted: an intensive altimetry error analysis according to the ADIRAS parameter settings along the incident direction, an effective SSH reconstruction approach based on a multichannel likelihood (ML) function, and detailed validation procedures through airborne campaigns illustrated in this study. The results indicated that the difference between the wave-induced sea surface elevation (WSSE) variances derived by the ML approach and GNSS buoy was 2 cm(2), which was smaller than the results of the single band on Ku (11 cm(2)) and Ka (6 cm(2)). Moreover, the estimated significant wave height (SWH) bias of joint bands was 10 cm, which was also superior to that of Ku (39 cm) and Ka (24 cm). Both simulated data and real airborne dual-frequency InSAR data were employed in this study for cross validation of the proposed method. This approach represents an effective technique for SSH reconstruction of future spaceborne/airborne interferometric altimeters.