Ocean Surface Currents Measurement From GEO-LEO Bistatic Along-Track Interferometric SAR: Methods and Optimization

Spaceborne synthetic aperture radar (SAR) along-track interferometry (ATI) serves as a primary approach to measure the total surface current vector (TSCV) of the ocean. However, single-spaceborne SAR systems are constrained by limited observation perspectives, leading to challenges in measuring 2-D TSCV. To address the 2-D TSCV inversion issue, a bistatic SAR that utilizes geosynchronous SAR (GEO SAR) as the radiation source and low Earth orbit SARs (LEO SARs) as passive receivers is proposed. This bistatic SAR configuration outperforms existing bistatic SAR ATI systems in terms of cost efficiency as well as intersatellite synchronization simplicity. For the GEO-LEO SAR system, we develop new interferometric signal models and processing methods to enable 1-D and 2-D TSCV estimation. Second, to enhance measurement performance, a system configuration optimization algorithm that considers both imaging and ATI performances is applied. Optimization results demonstrate that a larger GEO SAR elevation angle improves estimation accuracy. Finally, based on the currently operating L-band GEO SAR system LSAR4-01, optimization and full-link ATI simulations are conducted, verifying the effectiveness of the optimization algorithm and highlighting the potential design of LEO SAR orbits for high-accuracy ATI observations. Simulations achieve an imaging resolution of <100 m and a 2-D TSCV inversion bias of 0.1 m/s. The influence of errors on simulation accuracy is also discussed in depth.