Effect of wind on space-based radar performance

This paper addresses the effect of wind on target detection performance using a space based radar platform. Forests and lakes are constantly being modulated by wind, which then affects the radar pulse returns by suitably amplitude modulating the temporal returns, thus affecting the Doppler. Billingsley has modeled the windblown autocorrelations using a real symmetric function that is the sum of a constant term and a ldquoCauchy density function typerdquo term. Using a rational system approximation on the Billingsley spectrum, it is shown that a sixth order rational model containing two damped sinusoidal terms and two exponentially decaying terms can duplicate the wind spectrum up to about -80 dB in the case of low wind speed. Each sinusoidal component in the wind spectrum generates an additional clutter Doppler component and the effect of damping is shown to generate a bundle of uncorrelated returns for each such frequency, with each uncorrelated return containing a coherent sum of signals. As a result, the degradation in performance when wind is present can be attributed to the coherent returns that can not be nulled out using standard adaptive processing techniques.