Calibration of spaceborne linearly polarized low frequency SAR using polarimetric selective radar calibrators

Abstract

Spaceborne synthetic aperture radar (SAR) systems operating at lower frequencies, such as P-band, are significantly affected by Faraday rotation (FR) effects. This paper presents a novel algorithm for measuring system errors (channel imbalance and cross-talk) in the presence of Faraday rotation for spaceborne polarimetric SAR data. It uses four polarimetric selective calibrators (four polarimetric active radar calibrators [PARCs] or possibly two PARCs and two gridded trihedrals). Theoretical analysis and simulations demonstrate that the optimized calibration scheme puts tight constraints on the accuracy of the associated Faraday rotationif the cross-talk is to be accurately measured. There are also strong constraints on the allowable signal-to-noise ratio and average polarimetric noise associated with the calibration devices. The analysis suggests that, unless the calibration sites are at the magnetic equator, independent measurements of total electron content (TEC) from a direct ground-satellite line-of-sight dual-frequency system are also needed.