oa The Permanent Scatterers Technique to Measure Slow Earth Motion from Space

The Permanent Scatterers technique uses data from satellite mounted Synthetic　Aperture Radars like ERS1, ERS2, ENVISAT and Radarsat to extract the location of　scatterers that have strong and stable signature so that they will not be corrupted by　clutter. Then, it is possible to determine the spatial position of the PS with a sub - metric precision and their progressive motion (one measurement per month, approximately) with sub - millimetric precision. The spatial density of the PS decreases from several hundred /km2 in towns to just a few in agricultural environment. However, a metal pipe can be sufficient to make a PS, and detect an illegal well from the seasonal subsidence. If the PS density is high enough, an estimate is possible of the Atmospheric Phase Screen that rotates the radar signals, initiating the bootstrap process that finally yields relative motions and locations. The minimum length of the data series necessary to estimate PS is about 10 - 15 takes. Applications go from building stability analyses and collapse predictions, subsidence analysis, pre seismic motion analysis, landslides studies. More than 2800 images have been processed in more than 60 sites around the world. Data from Tokyo and the Isu province in Japan will be shown.