Enhanced and New Possible Functionalities of ATI-SAR through Multibaseline Acquisition and Modern Spectral Estimation Techniques

A brief discussion of some open problems of the conventional single-baseline along-track interferometric (ATI) technique for ocean sensing is given. A survey of previous research on advanced multibaseline ATI concepts is presented, stressing how multibaseline acquisition coupled with proper processing has great potential for improving the performance of ATI. Extended operation in critical conditions, reliable velocity extraction, enhanced imaging resolution and sensitivity can be obtained. In particular, a robust multibaseline velocity estimation technique is presented. It exploits the multibaseline Doppler resolution capability to produce estimates of ocean surface velocity that are robust to possible bimodal spectra of speckle, arising when both advancing and receding Bragg waves contribute to radar scattering. Bias and inflated variance for unexpected dual Bragg components in conventional ATI are analyzed. Three methods are proposed to process multibaseline data for robust estimation, based on Fourier transform, on adaptive Capon’s filtering, or on super-resolution MUSIC spectral estimation. Performance is analyzed in detail by both simulation and the statistical Cramér-Rao bounding technique. Results show that this multibaseline technique may be effective to produce accurate estimates in absence of detailed local wind information. A vision of integration with other advanced ATI techniques is finally hinted.