4-Dimensional Imaging from Interferometric Synthetic Aperture Radar

Acquisition of a series of spaceborne interferometric synthetic aperture radar (InSAR) scenes permits imaging of a surface in four dimensions, that is the several mm-level temporal evolution of the three dimensional structure of the ground surface. The spatio-temporal variations of a surface measured at mm accuracies not only reveals activity on the surface but also can indicate movement below the surface. To generate these multitemporal images, we use motion compensation techniques to precisely register multiple acquisitions, correct each radar scene for phase variations due to topographic features, and then generate many radar interferograms. Linear inversion methods then extract the temporal change of each point in the images over time, where we use singular value decomposition of an overdetermined system to filter the results for a stable solution. While our focus has been on naturally occurring phenomena such as natural hazards, aquifer modeling, and energy production, man-made subsurface activity such as tunneling and mining can readily be seen in precise surface deformation images. Here we present our imaging methodology and several examples of surface deformation time series demonstrating our ability to track cm-level surface change over time.