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Remote Sens. 2018, 10(8), 1318; https://doi.org/10.3390/rs10081318

Coherence Difference Analysis of Sentinel-1 SAR Interferogram to Identify Earthquake-Induced Disasters in Urban Areas

1
Graduate Institute of Applied Geology, National Central University, Taoyuan 32001, Taiwan
2
Center for Space and Remote Sensing Research, National Central University, Taoyuan 32001, Taiwan
3
Department of Natural Resources and Environmental Studies, National Dong Hwa University, Shoufeng, Hualien 97401, Taiwan
4
Department of Geography, National Taiwan University, Taipei 10617, Taiwan
*
Author to whom correspondence should be addressed.
Received: 16 June 2018 / Revised: 13 August 2018 / Accepted: 16 August 2018 / Published: 20 August 2018
(This article belongs to the Special Issue Applications of Sentinel Satellite for Geohazards Prevention)
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Abstract

This study proposes a workflow that enables the accurate identification of earthquake-induced damage zones by using coherence image pairs of the Sentinel-1 satellite before and after an earthquake event. The workflow uses interferometric synthetic aperture radar (InSAR) processing to account for coherence variations between coseismic and preseismic image pairs. The coherence difference between two image pairs is useful information to detect specific disasters in a regional-scale area after an earthquake event. To remove background effects such as the atmospheric effect and ordinal surface changes, this study employs the two-step threshold method to develop the coseismic coherence difference (CCD) map for our analyses. Thirty-four Sentinel-1 images between January 2015 and February 2016 were collected to process 30 preseismic image pairs and two coseismic image pairs for assessing multiple types of disasters in Tainan City of southwestern Taiwan, where severe damages were observed after the Meinong earthquake event. The coseismic unwrapping phases were further calculated to estimate the surface displacement in east-west and vertical directions. Results in the CCD map agree well with the observations from post-earthquake field surveys. The workflow can accurately identify earthquake-induced land subsidence and surface displacements, even for areas with insufficient geological data or for areas that had been excluded from the liquefaction potential map. In addition, the CCD details the distribution of building damages and structure failures, which might be useful information for emergency actions applied to regional-scale problems. The conversion of 2D surface displacement reveals the complex behavior of geological activities during the earthquake. In the foothill area of Tainan City, the opposite surface displacements in local areas might be influenced by the axis activities of the Kuanmiao syncline. View Full-Text
Keywords: InSAR; coseismic coherence difference; liquefaction; Meinong earthquake; surface displacement InSAR; coseismic coherence difference; liquefaction; Meinong earthquake; surface displacement
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Lu, C.-H.; Ni, C.-F.; Chang, C.-P.; Yen, J.-Y.; Chuang, R.Y. Coherence Difference Analysis of Sentinel-1 SAR Interferogram to Identify Earthquake-Induced Disasters in Urban Areas. Remote Sens. 2018, 10, 1318.

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