The Three-Transponder Method: A Novel Approach for Traceable (E)RCS Calibration of SAR Transponders

Abstract

The radiometric calibration of synthetic aperture radar (SAR) systems is typically based on the known backscatter of calibration point targets such as transponders. Before a SAR calibration campaign can begin it is therefore necessary to determine the backscatter (radar cross section or RCS) of the transponder itself. Known methods suffer from unnecessarily high uncertainty contributions and therefore also affect the radiometric uncertainty of the calibrated SAR system. In this paper we present a novel calibration approach which neither requires to disassemble the amplifier path nor necessitates a separate RCS calibration target such as a corner reflector or a circular disk. Significant sources of measurement uncertainties can therefore be outright avoided. The method is not applicable to all transponders though, and a certain type of transponder design is assumed. Nevertheless, direct metrological traceability to a realization of the SI base unit "meter" can be achieved for the first time. The reduced measurement uncertainties of the novel approach will subsequently allow to reduce the radiometric measurement uncertainties of air- and spaceborne SAR sensors in the future.