The Coherent Pixels Technique (CPT): An Advanced DInSAR Technique for Nonlinear Deformation Monitoring

Abstract

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.

Advances in space-borne SAR interferometry and its application to ground deformation monitoring

“…Improvements were made in terms of linear and nonlinear deformation extraction and robustness with DEM error, thus allowing DEM refining and APS removal. Blanco-Sanchez (Blanco-Sanchez et al, 2008) refined this approach and detailed the main steps, such as interferogram set selection, coherent pixels selection, and linear and nonlinear blocks for a full deformation retrieval. The related algorithms consist of Delaunay triangulation and Minimum Spanning Tree for the best combination of interferogram selection, Conjugate Gradient Method (CGM) for Phase Unwrapping, and multi-layer for reliable estimation of linear deformation.…”

A New Detection Algorithm for Coherent Scatterers in SAR Data

“…With these setting parameters, an overlap of 75% between two consecutive sublook spectra is obtained using N = 5 sublooks, compared with an overlap of 96% when using N = 30 sublooks. Nevertheless, it is important to remark that the correlation among the sublooks is known and included in the coherence matrix M [see (7)], and the GLRTA detector uses this correlation information for whitening the clutter before the detection.…”

“…Normally, considering the revisit time of current spaceborne platforms, a time span larger than several months or even one year is necessary for the identification of permanent scatterers (PSs), as a stack on the order of 20-30 images is necessary for a good PS detection performance. A second possibility to detect temporally stable targets is known as coherence stability [6], [7]. This approach instead uses the estimated coherence maps from the multilooked interferograms, which can be related to the standard deviation of the interferometric phase, and selects only pixels with enough phase quality.…”

A robust regression-based linear model adjustment method for SAR interferogram stacking techniques

“…Second, atmospheric inhomogeneities will introduce uncertain phase delays, which may decrease the accuracy of deformation measurements. To overcome such problems, a series of new methods that measure ground deformation based on a stack of differential interferograms have been developed in recent years Rocca 2000, 2001;Berardino et al 2002;Mora, Mallorqui, and Broquetas 2003;Hooper, Segall, and Zebker 2007;Blanco-Sanchez et al 2008). Such methods, referred to as interferogram stacking techniques, are capable of obtaining deformation time series with millimetre accuracy.…”