Automatic detection of change direction of multi-temporal ERS-2 SAR images using two-threshold EM and MRF algorithms

An algorithm of two-threshold expectation maximum (EM) and Markov random field (MRF) is developed to detect the change in direction in urban surfaces from multi-temporal synthetic aperture radar (SAR) images. The difference in the SAR images demonstrates a variation in backscattering caused by the surface change over all image pixels. Two thresholds are derived by the EM iterative process and are applied to change the direction of three classes: enhanced scattering, reduced scattering and unchanged regimes. Initializing from the EM result, the iterated conditional modes (ICM) algorithm of the MRF is then applied to analyse the detection of contexture change in the urban area. As an example.. two images of ERS-2 SAR in 1996 and 2002 over Shanghai City are studied.