Covariance constrained difference inversion of time lapse electrical resistivity tomography data
ABSTRACTHydrogeophysics has become a major field of research in the past two decades, and time lapse electrical resistivity tomography (ERT) is one of the most popular techniques to monitor passive and active processes in shallow subsurface reservoirs. Time lapse inversion schemes have been developed to refine inversion results, but they mostly still rely on a spatial regularization procedure based on the standard smoothness constraint. We have applied a covariance based regularization operator to the time lapse ERT inverse problem. We first evaluated the method for surface and crosshole ERT with two synthetic cases and compared the results with the smoothness constrained inversion (SCI) These tests showed that the covariance constrained inversion (CCI) better images the target in terms of shape and amplitude. Although more important in low sensitivity zones, we have observed improvements everywhere in the tomograms. Those synthetic examples also show that an error made in the range or in the type of the.