Analysis of Gradient-Induced Distortion in Dual Beam ATI Systems for Vector Surface Current Mapping

摘要

This paper summarizes an analysis of gradient-induced distortions in the vector surface current estimates generated by dual-beam, along-track interferometric SAR systems. In such systems, interferograms from two squinted beams, one squinted forward of broadside and the other aft, are combined to measure the full surface current vector with only a single aircraft pass. However, in the presence of significant current gradients, an effect akin to velocity-bunching can cause distortion in the measured current estimates. Up to a point, these distortions can be removed by a straightforward, spatial remapping of the interferogram pixels based upon their phase values. However, there is a critical current gradient beyond which the true surface current field is not recoverable. In addition, the along-track component of the surface current introduces unequal azimuthal displacements in the fore- and aft-squinted interferograms. As a result, when along-track currents are present, the two interferograms will not be spatially registered. If appreciable along-track current gradients are also present, the resulting current vector estimates in and around the gradient region will undergo further distortion. These effects are explored through an approximate, linear analysis as well as through a full interferometric SAR model, using the current gradients present in rivers as an example.