Detection of major changes in satellite images

In this paper the problem of detecting changes between two photographs of the same scene taken at different dates is addressed. Considering that both images are already accurately registered our problem reduces to a) detect changes between corresponding pixels, and b) determine whether these changes are a clue of a major change in the scene. The solution of a) involves the use of spectral invariant features, since we consider the general situation of comparing photographs coming from different spectral channels. The answer to b) implies the computation of an absolute threshold above which a region of the image will be detected as having "meaningful changes". In order to do that, we apply a recently introduced method yielding accurate false alarm rates for each detection. We show that this method permits to help significantly photo-interprets in their search for major changes in a scene. This will be illustrated by a striking application, the detection of the explosion of the AZF chemical plant in Toulouse (France) in September 2001.