Rabasar: A Fast Ratio Based Multi-Temporal Sar Despeckling

In this paper, a generic method is proposed to reduce speckle in multi-temporal stacks of SAR images. The method is based on the computation of a "super-image", with a large number of looks, by temporal averaging. Then, ratio images are formed by dividing each image of the multi-temporal stack by the "super-image". In the absence of changes of the radiometry, the temporal fluctuations of the intensity at a given spatial location are due to the speckle phenomenon. In areas affected by temporal changes, fluctuations cannot be ascribed to speckle only but also to radiometric changes. The overall effect of the division by the "super-image" is the spatial stationarity improvement: ratio images are much more homogeneous than the original images. Therefore, filtering these ratio images with a speckle-reduction method is more effective, in terms of speckle suppression, than filtering the original multi-temporal stack. After denoising of the ratio image, the despeckled multi-temporal stack is obtained by multiplication with the "super-image". Results are presented and analyzed both on synthetic and real SAR data and show the interest of the proposed approach.