Filtering of multichannel SAR images

An explicit form of the linear multichannel synthetic aperture radar (SAR) intensity filter, which preserves radiometry while optimally reducing speck le is derived, together with a compact expression for the theoretical gain in equivalent numbers of looks (ENLs). The filter can be applied to mixed d ata types, which is demonstrated using a combination of ERS and JERS satell ite data, and confirms the filter performance predicted by the theory. Test s indicate that a simplified form of the filter, which neglects correlation between images, gives an ENL only slightly less than optimal, while being much easier to implement. Exact analysis of the effect of estimating filter weights shows that the linear increase in ENL with the number of images pr edicted for the ideal filter does not occur. In practice, the ENL is affect ed by the window size used to estimate the weights and saturates as the num ber of images increases. An efficient recursive form of the filter is descr ibed, which is most naturally applied to multitemporal data for the practic ally important case where the current image is uncorrelated with previous i mages in a data sequence.