Effect of Earth's rotation and range foldover on space based performance

A space based radar (SBR) by virtue of its motion generates a Doppler frequency component to the clutter return from any point on the Earth as a function of the SBR - Earth geometry. The effect of Earth's rotation around its own axis also adds an additional component to this Doppler frequency. The overall effect of the Earth's rotation on the Doppler turns out to be two correction factors in terms of a crab angle affecting the azimuth angle, and a crab magnitude scaling the Doppler magnitude of the clutter patch, interestingly both factors depend only on the SBR orbit inclination and its latitude and not on the specific location of the clutter patch of interest. Further, it is shown that the crab angle has maximum effect for an SBR on a polar orbit that is above the equator. The crab magnitude on the other hand peaks for an SBR on an equatorial orbit. It is also shown that Earth's rotation together with range foldover phenomenon significantly degrade the clutter suppression performance of adaptive processing algorithms. Detailed derivations of these results are presented in this paper.