Bright Singularities: Polarimetric Calibration of Spaceborne PolSAR Systems

In this letter, we present a new algorithm for the polarimetric calibration of spaceborne imaging radar systems. The technique combines two features: first, a new method for estimation of distortion matrices without the need for assumptions of small coupling or reciprocity; and second, it employs a factorized polar decomposition, which allows separate estimation of Faraday rotation from system distortion matrices in low-frequency spaceborne systems. We highlight a source of residual error in the procedure called hidden rotators, but show how to mitigate such errors to obtain fully calibrated data for arbitrary Faraday rotation. We illustrate using simulated data from the L-band ALOS-2 satellite.