DETECTION OF BUILDING HEIGHT AND COLLAPSE MODE FROM THE MEASUREMENT OF SHADOW LENGTH IN OPTICAL IMAGES AND LAYOVER IN SAR INTENSITY IMAGES

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Visual interpretation of optical satellite images is widely used to detect building damages after recent earthquakes in the world. However, since optical satellites images are acquired from the vertical direction, they can observe only roofs of buildings. Building damages such as mid-story collapse are often overlooked because the upper surfaces of buildings do not change so much. This paper proposes the method to detect this kind of building collapses from the change in building heights, estimated from the shadow lengths in optical images measured before and after an earthquake. Boumerdes city, Algeria, is selected as a case study site where many buildings were collapsed in the 2003 Boumerdes Earthquake. Two QuickBird images, taken before and two days after the earthquake, were employed. Based on the measurement of shadow lengths, some mid-story collapses were successfully detected. The measurement of building heights was also carried out using layover effects in SAR intensity images. The tests for TerraSAR-X images in Tokyo Metropolitan area showed good level of accuracy in building height measurement. These methods may provide useful information in detecting building damages, as well as from texture information.