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Characteristics of satellite SAR images in the areas damaged by earthquakes

The 1995 Kobe and the 1994 Northridge earthquakes realized to us the importance of grasping damage distribution at an early stage for recovery activities and restoration planning. Satellite remote sensing using SAR is one of the most promising technologies for this objective. In this paper, we investigated the scattering characteristics of microwaves for the areas hit by the 1999 Kocaeli, Turkey earthquake, using satellite SAR images. From the difference in backscattered intensity and coherence from an interferometric analysis of SAR images taken at different acquisitions, we found that the backscattering in heavily damaged areas showed significant change, compared with that in minor damage areas. The relationship between building damage and difference of pre- and post-event SAR images was found to relate to the damage level. This trend in the hard-hit areas was due to the fact that the backscattered intensity and the intensity correlation of two images became low. The degree of coherence was found to be a good index to distinguish slight to moderate damage levels. Microwave reflection is considered to decrease in hard-hit areas due to the reduction of the cardinal effect. The decorrelation of phase can also occur due to the existence of collapsed buildings. Thus, the images obtained by satellite SAR may be a powerful tool for post-disaster damage assessment.