Crossed orbit interferometry - Theory and experimental results from SIR-B

Crossed orbit interferometry, which can perform measurements with only one antenna making two images of a scene during two separate passes and can operate even if the orbits are not parallel, is discussed and tested using SIR-B data. It is found that a Doppler refocusing of the SAR azimuth correlation, involving a resampling of one of the imgages in the cross-track direction, is necessary to remove the linear shift of the scene. The refocusing process also involves a terrain dependent resampling in the azimuth direction. A method for finding tie points to guide the resampling is discussed and a coarse altitude map derived only from the tie points is presented. Spatial heterodyned interferograms that contain the effects of the crossed orbit geometry are presented and a theoretical model is developed to explain them. The model is extended to calculate altitudes from the interferograms, and a final altitude map is presented.