Abstract
Combining pre-disaster optical and post-disaster synthetic aperture radar (SAR) satellite data is essential for the timely damage investigation because the availability of data in a disaster area is usually limited. This article proposes a novel method to assess damage in urban areas by analyzing combined pre-disaster very high resolution (VHR) optical data and post-disaster polarimetric SAR (PolSAR) data, which has rarely been used in previous research because the two data have extremely different characteristics. To overcome these differences and effectively compare VHR optical data and PolSAR data, a technique to simulate polarization orientation angles (POAs) in built-up areas was developed using building orientations extracted from VHR optical data. The POA is an intrinsic parameter of PolSAR data and has a physical relationship with building orientation. A damage level indicator was also proposed, based on the consideration of diminished homogeneity of POA values by damaged buildings. The indicator is the difference between directional dispersions of the pre and post-disaster POA values. Damage assessment in urban areas was conducted by using the indicator calculated with the simulated pre-disaster POAs from VHR optical data and the derived post-disaster PolSAR POAs. The proposed method was validated on the case study of the 2011 tsunami in Japan using pre-disaster KOMPSAT-2 data and post-disaster ALOS/PALSAR-1 data. The experimental results demonstrated that the proposed method accurately simulated the POAs with a root mean square error (RMSE) value of 2.761° and successfully measured the level of damage in built-up areas. The proposed method can facilitate efficient and fast damage assessment in built-up areas by comparing pre-disaster VHR optical data and post-disaster PolSAR data.
Highlights
Remote sensing techniques have been developed during the past few decades to detect damage induced by natural disasters
We focused on the polarization orientation angle (POA) because it has a physical relationship with building orientation [20,21,22], which can be estimated using very high resolution (VHR) optical data
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Summary
Remote sensing techniques have been developed during the past few decades to detect damage induced by natural disasters. The common method to detect disaster-induced damage is based on the change detection technique whereby the data remotely sensed, before and after the disaster, are compared. It is necessary to acquire data shortly after a disaster. In this situation, a SAR is superior to an optical sensor due to its relative insensitivity to the weather and illumination conditions. Several studies have investigated disaster-induced damage using pre and post-disaster SAR data [1,2,3,4,5,6]. Damage investigation has been improved using fully polarimetric SAR (PolSAR) data because it allows more efficient results with its additional polarization scattering mechanism compared to a single polarization mode [5,6]
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