Radiometric calibration of airborne SAR imagery

A method to compute a fully calibrated airborne synthetic aperture radar (SAR) image is presented. In a first step the data is processed taking motion compensation errors into account by using the reflectivity displacement method (RDM). This paper focuses on the second step, namely the rigorous determination of the backscattering coefficient σ⁰ and γ. To determine the exact local area and the local incidence angle, high precision flight path data, a high resolution digital elevation model (DEM), as well as sensor and processor characteristics need to be considered. Radiometric distortions due to the antenna diagram, to the reciprocal value of the third power of the slant range, and to the sine of the local incidence angle are also corrected, by taking into account aircraft displacements and terrain height variations. Magnitude data of the E-SAR system of the German Aerospace Research Establishment (DLR) collected over a hilly region in Switzerland are used to demonstrate the calibration technique.