Understanding the Significance of Radiometric Calibration for Synthetic Aperture Radar Imagery

In applications such as target recognition, quantitative use of the information present in synthetic aperture radar (SAR) imagery is pivotal for detecting and classifying the scattering centers of the target(s). This paper presents an investigation of the various forms for radiometric calibration in SAR imagery. For the cases of point and extended targets, respectively, the radar cross section (sigma) and the backscatter coefficient (sigma(o)) are studied. Other forms of the backscatter coefficient, including the radar brightness (beta(o)) and (gamma(o)) are also examined, and their relevance to sigma(o) is presented. A real-world SAR chip from a single-channel Radarsat-2 image for ground-truthed vehicle targets is used to demonstrate the applicability of the radiometric calibrations. It is concluded that the beta(o) calibration gives the most accurate result, in contrast to sigma(o) and gamma(o) because it is not dependent on the sea-level geoid model typically used to approximate the local incidence angles.