Modeling Scintillation Impacts on L Band SAR Image Formation Using the SAR Scintillation Simulator (SAR-SS)

摘要

Ionospheric impacts on synthetic aperture radar (SAR) can be categorized into two types. The first type consists of effects caused by the ionospheric background such as refraction, polarization rotation, group delay, and phase advance. These effects can be largely mitigated for an L-band SAR if a suitable ionospheric model is employed during SAR processing. The second type consists of effects caused by small-scale ionospheric structures which cause scintillation, i.e. random fluctuations in the amplitude and phase of the SAR signal. Signal fluctuations which decorrelate across the synthetic aperture of the radar reduce the effective resolution of a SAR image, and alter critical differential phase relationships between images collected during satellite revisits that are required by InSAR and change detection applications. In this paper we present a phase screen model called the SAR Scintillation Simulator (SAR-SS) for predicting the impact of small-scale ionospheric structure on SAR image formation. SAR-SS consists of a phase screen generator and a propagator. The screen generator creates a 2D random realization of spatial phase fluctuations resulting from the traversal of small-scale field-aligned irregularities in the ionosphere. It accounts for the motion of the radar platform, -the drift of the ionospheric irregularities, and the oblique angle of propagation, all of which determine the scale sizes of the irregularities sampled by the radar beam. The propagator solves the 3D parabolic wave equation (PWE) using the split-step technique to compute the ionospheric transfer function for two-way propagation. This ionospheric transfer function is used to modulate the SAR signal due to terrestrial features in order to assess the ionospheric impact on SAR image formation. We compare simulated and observed PALSAR imagery over Brazil, and our preliminary findings show that SAR-SS can reproduce the essential features of azimuthal streaking and contrast degradation caused by small-scale structure in the ionosphere.