Mapping damage during the Bam (Iran) earthquake using interferometric coherence

Abstract

We use changes in the interferometric coherence to map earthquake damages that occurred in the city of Bam during the Bam earthquake on December 26, 2003. The approach presented here defines a coherence change index that can be interpreted quantitatively in terms of damages during a catastrophic event like a major earthquake. Using five differential interferometric synthetic aperture radar images we compute maps of interferometric coherence. Three coherence change images are computed from these based on different interferograms. These three damage assessments yield very similar results despite the range of times and interferometric baselines spanned. This coherence-based damage assessment also agrees closely with independent damage maps derived from other types of imagery. Using existing or planned synthetic aperture radar (SAR) satellites coherence-based damage assessments could be obtained within days after a catastrophic event, provided the necessary reference images are prepared ahead of time. As SAR sensors can operate independently of weather conditions and daylight this may present a reliable and robust means for damage assessment.