Comparsion of Absolute Radiometric Transponder Calibration Strategies

Spaceborne synthetic aperture radars (SAR) are systems capable of acquiring high-resolution earth-observation data independent on time of day and weather. These SAR systems have to be calibrated before first use and at regular intervals. For these radiometric calibrations active targets with known backscatter, so called transponders, serve as an external reference. For determining the frequency-dependent radar cross section (RCS) of these transponders, different measurement methods are available. This paper gives an overview of four different strategies with a following uncertainty analysis according to the Guide to the expression of uncertainty in measurement (GUM). After comparison with respect to accuracy and feasibility, a recommendation for the best absolute radiometric transponder calibration method is given.