3.3. Landslide mapping and statistics
An inventory of landslides for these two catchmentswas constructed
by automated classification using SPOT 4 multispectral images, with
pixel resolution of 12.5, taken before and after typhoons by the Center
for Space and Remote Sensing Research, Taiwan. The SPOT 4
multispectral images used in this study have mean cloud cover of less
than 8%. The interpreted landslide types include rock fall, soil slips, and
flow slides. The mapped landslides include both source area and
depositional zone, hence landslide mapping in this study does not
discriminate between source areas and deposit zones. After the
preliminary interpretation of landslides by satellite images, a recheck
is undertaken by stereoscopic interpretation of multi-temporal 1:5000
aerial photographs taken after 1999 Chi-Chi earthquake and 2004
Mindulle typhoon by the Aerial Survey Office of Forestry Bureau of
Taiwan in order to detect the errors of interpretations. Finally, the
landslides are traced on the topographymap produced by a 40mdigital
terrain model of Taiwan and field investigations. In the 12.5 m SPOT 4
3.3. Landslide mapping and statisticsAn inventory of landslides for these two catchmentswas constructedby automated classification using SPOT 4 multispectral images, withpixel resolution of 12.5, taken before and after typhoons by the Centerfor Space and Remote Sensing Research, Taiwan. The SPOT 4multispectral images used in this study have mean cloud cover of lessthan 8%. The interpreted landslide types include rock fall, soil slips, andflow slides. The mapped landslides include both source area anddepositional zone, hence landslide mapping in this study does notdiscriminate between source areas and deposit zones. After thepreliminary interpretation of landslides by satellite images, a recheckis undertaken by stereoscopic interpretation of multi-temporal 1:5000aerial photographs taken after 1999 Chi-Chi earthquake and 2004Mindulle typhoon by the Aerial Survey Office of Forestry Bureau ofTaiwan in order to detect the errors of interpretations. Finally, thelandslides are traced on the topographymap produced by a 40mdigitalterrain model of Taiwan and field investigations. In the 12.5 m SPOT 4
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