A unified approach lo change analysis and despeckle of multitemporal ERS-1

Local-statistics speckle filtering has been extended to multitemporal SAR data by exploiting the space-varying temporal correlation of speckle noise between two images of the same scene taken at different times. A nonlinear transformation aimed at decorrelating the data across time while retaining the multiplicative noise model is defined from the pixel geometric mean and ratio of a couple of spatially overlapped observations. The average temporal correlation coefficient is estimated from the scatter-plots of local standard deviation to local mean calculated on transformed couples of images, through an unsupervised clustering procedure. The images are filtered in the transformed domain and reversely transformed to yield despeckled observations in which seasonal changes are preserved, or even highlighted, and texture analysis is expedited. Tests on SAR images from repeat-pass ERS-1 are presented to corroborate the underlying assumptions.