Two adaptive filters for speckle reduction in SAR images by using the variance ratio

This paper presents some experimental results on the properties of image speckle along with two adaptive filters that are useful for speckle reduction. An investigation of available SIR-B digital image data over Australia shows that speckle is non-while Gaussian noise and fits a multiplicative noise model in which the noise, uncorrelated with signal, has a mean of 1 and a constant standard deviation. The non-uniform spectrum can be represented by an empirical formula. Based on these results, two adaptive filters have been designed, a moving average filter and a combined moving median filter. In both of these, variance ratios are used to govern the filter parameters. The filters have been applied to some SIR-B image segments, showing good results in both smoothing speckle and maintaining edges.