RADIOMETRIC SLOPE CORRECTION OF SYNTHETIC-APERTURE RADAR IMAGES

The brightness in a SAR image is affected by topographic height variat ions due to 1) the projection between ground and image coordinates, an d 2) variations in backscattering coefficient with the local scatterin g geometry, This paper derives a new equation for 1), i.e., the radiom etric slope correction, based on a calibration equation which is invar iant under a coordinate transformation. An algorithm is described to o btain the slope correction from a SAR interferogram, which also enable s retrieval of the full scattering geometry, Since the SAR image and i nterferogram are derived from the same data set, there is no need to m atch the image with the calibration data, There is also no need for ph ase unwrapping since the algorithm only uses the fringe frequencies, A maximum-likelihood estimator for the fringe frequency is analyzed and the algorithm is illustrated by processing ERS-1 SAR data, The exampl e demonstrates that the spatial resolution and calibration error are a dequate for most applications.