The Coherent Pixels Technique (CPT):: An advanced DInSAR technique for nonlinear deformation monitoring

This paper shows the potential applicability of orbital Synthetic Aperture Radar (SAR) Differential Interferometry (DInSAR) with multiple images for terrain deformation episodes monitoring. This paper is focused on the Coherent Pixels Technique (CPT) developed at the Remote Sensing Laboratory (RSLab) of the Universitat Politecnica de Catalunya (UPC). CPT is able to extract from a stack of differential interferograms the deformation evolution over vast areas during wide spans of time. The former is achieved thanks to the coverage provided by current SAR satellites, like ESA's ERS or ENVISAT, while the latter due to the large archive of images acquired since 1992. An interferogram is formed by the complex product of two SAR images (one complex conjugate) and its phase contains information relative to topography, terrain deformation and atmospheric conditions among others. The goal of differential interferometric processing is to retrieve and separate the different contributions. The processing scheme is composed of three main steps: firstly, the generation of the best interferogram set among all the available images of the zone under study; secondly, the selection of the pixels with reliable phase within the employed interferograms and, thirdly, their phase analysis to calculate, as the main result, their deformation time series within the observation period. In this paper, the Coherent Pixels Technique (CPT) is presented in detail as well as the result of its application in different scenarios. Results reveal its practical utility for detecting and reproducing deformation episodes, providing a valuable tool to the scientific community for the understanding of considerable geological process and to monitor the impact of underground human activity.