Change detection of landslides and debris in south Taiwan after "Morakot" typhoon based on HJ-1-B Satellite images

The 0908 typhoon “Morakot” heavily attacked Taiwan. It brought strong rainfall which not only caused water level rise in several reservoirs and rivers, but also triggered a large number of landslides, debris flow, collapse and other geological disasters. All of these changes resulted in flooding, and for the worst, several villages were buried. In this paper, using NDVI(Normal Differential Vegetation Index) subtractive method, together with a combined symbol coding method of the least related bands, changes in south Taiwan after “Morakot”, mainly geological disasters and hydrology changes were detected based on HJ-1-B (Environment and Disaster Monitoring Satellites Constellation 1) remote sensing data. Kobayashi Jiasian Township Xiaolin village which was wholly buried in the debris flow disaster and its vicinity were chosen for the study area. The areas where geological disasters and hydrology (including reservoirs and rivers) changes occurred were fast detected, and then the results were analyzed quantitatively. The results showed that NDVI subtractive method could well detect the number and size of landslides and debris, also the enlarged area of reservoirs and rivers. According to the accuracy testing, NDVI subtractive method was proved to be a fast and effective approach for monitoring and assessment of typhooninduced changes.