The detection of deformation on vegetated dikes using InSAR

Abstract

Almost four million people in the Netherlands who live below sea level are protected by 17000 km of dikes against the water. Since deformation can be an indicator of a developing failure mechanism, information about this parameter can help authorities to detect weak spots in the dutch water defense structures.
In this research, Radar Interferometry (InSAR) is used to estimate deformation time series on the vegetated part of the dike. Using Point Scatterers (PS), it is already possible to estimate deformation time series with mm precision on objects with a coherent reflection over time. Apart from objects, also surfaces provide a reflection of the radar signal. These so-called Distributed Scatterers (DS), which can for instance be found on dikes, are often strongly affected by temporal decorrelation. Although conventional approaches to detect and estimate these DS do not work, there may still be coherent information for interferograms with small temporal baselines. In this research project, a methodology is presented to detect coherent DS on the vegetated part of a dike and to estimate their deformation time series.
To do so, the phases of PS are subtracted from the DS on the vegetated part of the dike to reduce the phase noise due to different states of the atmosphere. The estimated coherence matrix is then used to only select coherent interferograms which are used to unwrap the phases with respect to PS. Using data obtained from the TerraSAR-X (X-band) and Radarsat-2 (C-band) satellites, it was shown that DS could be detected on some parts of the grass-covered inner slope of the Marken dike.