Application of remote sensing techniques and in situ instrumentation for multi-scale assessment of levees

Abstract

In situ instrumentation, including extensometers and global positioning systems (GPS), was also employed to measure the displacement of some locations in two levee sections, the London Avenue Canal levee and the V-line levee. A comparison of displacement is made between the in situ measurements and the results obtained from InSAR techniques. The comparison shows a good agreement in displacement trends, thus indicating the potential of remote sensing techniques to monitor the displacement of entire levee systems.

The failure of flood-control infrastructure, such as levees, due to a natural or manmade hazard can have significant repercussions, sometimes with dramatic and unanticipated consequences on human life, property, and the country’s economy. Thus, the integrity of a levee is an important issue that needs to be assessed frequently. This can be achieved by long-term monitoring of the subsidence of the levee to identify potential weak sections and prioritize maintenance efforts. Remote sensing techniques appear to be a promising option to conduct this widespread monitoring and have been used by the geoscience community for many years for estimating land surface displacement. However, the application of remote sensing techniques to monitor the deformation of levees is still limited because of the difficulty in processing radar image data on low coherence areas, such as the surface of grass-covered levees. In the civil engineering community to date, there have only been limited applications of remote sensing techniques to estimate the long-term displacement of a target.

This thesis presents the application of the interferometric synthetic aperture radar (InSAR), a remote sensing technique, to monitor the displacement of the New Orleans area and its levee system from 2002 to 2005 and 2009 to 2014. The input data for the time period 2002-2005 are radar images taken by Canada's first commercial Earth observation satellite (Radarsat-1). The input data for the time period 2009-2014 are from the German Space Agency’s X-band satellite (TerraSAR-X). Three analysis methods of InSAR were employed to estimate the displacement of the ground surface: Interferometric Point Target Analysis (IPTA), Differential InSAR (D-InSAR), and N Small Baseline Subsets (NSBAS). A step by step procedure of analysis for performing these methods is presented. The analysis results are then presented and discussed to investigate the advantages and disadvantages of each method in estimating the displacement of the ground surface, especially the displacement of levees. In addition, the accuracy of the analysis results is also investigated for each analysis method and radar sensor combination.