Wide area change detection with satellite imagery for locating underground nuclear testing

With the advent of high resolution optical imagery from commercial earth observation satellites, the use of remote sensing data for verification of nuclear non-proliferation agreements is becoming increasingly attractive. Non-governmental organizations are routinely publishing high-quality imagery of sensitive nuclear installations round the world, and verification authorities, such as the IAEA or CTBTO, will also want to make use, directly or indirectly, of this additional open source of information. Exact location of the sites of underground nuclear explosions is a task eminently suited to satellite imagery. Here both moderate resolutions for detecting signals in very large testing ranges as well as high resolution images for exact interpretation play important roles. We describe in our paper a particularly sensitive change detection procedure for bitemporal, multispectral satellite imagery which can be used to locate the spall zone of underground nuclear explosions with commercial satellite imagery. The method is based on the multivariate alteration detection (MAD) technique of Nielsen et al. Linear combinations of the spectral channels in two images of the same scene are chosen so as to minimize their positive correlation. This leads to a series of difference images, the so-called MAD components, which are mutually orthogonal (uncorrelated) and ordered according to decreasing variance in their pixel intensities. The case studies demonstrate the usefulness of combined seismic and satellite image analysis for CTBT verification. The LANDSAT imagery, when used in change detection mode, is suited to locate signals of the typical dimensions of a spall zone in very large scenes. Higher resolution data, if available, can then be consulted to aid in the interpretation of the change signal. When obtained independently by satellite remote sensing, the pinpointing of a nuclear test site serves as a so-called seismic master event location for relative determinations of possible future explosions at the test site. The observation of a possibly significant change in satellite imagery, in conjunction with a seismic signal, can be used to trigger and to guide on-site inspections by the CTBT control authority. Additional studies are underway or are planned with historical data from the Chinese test site at Lop Nor, Semipalatinsk in the former Soviet Union and the Nevada test site