SAR Imaging through the Earth's Ionosphere
Final rept. 15 Apr 2010-30 Sep 2013
NORTH CAROLINA STATE UNIV AT RALEIGH
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Spaceborne imaging of the Earths surface by synthetic aperture radars SAR may be adversely affected by the ionosphere. Image distortions are due to mismatches between the actual radar signals that are subject to temporal dispersion and Faraday rotation in the ionospheric plasma, and their ungarbled form assumed by the SAR signal processing algorithm known as the matched filter. To mitigate the distortions, we propose to probe the terrain and hence the ionosphere on two distinct carrier frequencies. Subsequently, we analyze the resulting two images and accurately evaluate their relative displacement by applying an area-based image registration algorithm. This, in turn, translates into an accurate estimate of the total electron content and its along-the-track gradient in the ionosphere. The latter are the parameters of the plasma that are responsible for the dispersion-induced mismatches between the signal and the filter. In addition to that, image autocorrelation analysis allows us to evaluate the parameters that control the Faraday rotation. Knowing all those parameters, we can correct the matched filter and thus improve the quality of the image. We also analyze the linearized scattering off the target for both isotropic and anisotropic case.
- Atmospheric Physics
- Active and Passive Radar Detection and Equipment