Ionospheric Polarimetric Dispersion Effect on Low-Frequency Spaceborne SAR Imaging

Ionospheric Faraday rotation (FR) introduces polarimetric distortion to trans-ionosphere signals. Spaceborne low-frequency wide-bandwidth synthetic aperture radar (SAR) signals may be distorted by FR effect because it is highly dispersive. Ionospheric polarimetric dispersion (PD) effects on spaceborne SAR imaging are modeled and analyzed. PD effect is included in polarimetric SAR system impulse response matrices. In particular, PD effects on linearly polarized and circularly polarized SAR systems are analyzed by system impulse response matrices. Theoretically, PD will introduce amplitude modulation to SAR spectrums and hence distort linearly polarized SAR imaging; for circularly polarized systems, it introduces relative image shift and phase errors between images of different channels. Numerical evaluations and simulations show that PD effects will introduce noticeable effects on future P-band wide-bandwidth SAR systems.