Equivalent system model for the calibration of polarimetric SAR under Faraday rotation conditions

Abstract

An equivalent system model (ESM) that can be used to calibrate a SAR system affected by both the effect of system errors and the Faraday rotation (FR) is proposed. This ESM contains only system-distortion-like parameters but includes a distortion matrix (DM) that is identical to the original, which contains the effects of both the system errors and the Faraday rotation angle (FRA). With this model, the conventional distributed-target-based (DT-based) algorithms which have not taken FR effect into account are readily applicable. The conditions on FRA for the successful application of DT-based algorithms are studied, and the results suggest that reliable estimates can be obtained for a well-designed system whose true system crosstalk level is lower than $-20$ dB provided that the mean FRA at the calibration site is within ${\pm~15^{\circ}}$ and that the FRA can be suitably modeled as Gaussian. Thus, the requirements on the crosstalk level or the FRA that are commonly employed in other calibration methods designed for data affected by FR are relaxed.