A Practical Approach To Creating A Landslide Database Using Taiwan SPOT Mosaci
5. Discussion and Conclusion
By conventional stereoscopic photo-interpretation, 1680 photographs are interpreted by 4 well-trained personnel using tow weeks. In total, 40 work-days are used to do the interpretation, 4076 landslides with 234,059,976 m2 are identified. After 60 more work-days of data transfer, cleaning, and digitization, a landslide database of Nantou County is created ( Figure 5).
The well -trained geologist spends only tow days in front of the computer, a landslide database of the Nantou County is created ( Figure 6). On the other hand, the well-trained GIS specialist work s out a first result with three days. The result is a 269 pseudo-landslides, which is proved with 70% of errors. Source of the mistakes are due to only considering the tonal feature, over looking to the features of a landslide, including the location, shape, and trend of the long-axis. A second result was worked out after two more days. 708 places of landslides are recognized ( Figure 7). There are only 5% of errors. Some large-scaled landslides are overlooked. Nevertheless, a third time of work generates an interesting result. A total of 1650 landslides are delineated ( Figure 8). Errors are more than 70%. Errors are originated from the hesitating and uncertainty of the training background of the GIS specialist. The northeastern part of the study area is cloudy are. Tens of shadows and artificial features are mistaken as landslides. Omission of the large-scaled landslides in the southeastern part is still there. This gives an important indication of the problem that results of good quality can only be obtained by professional people in landslide geology.
The comparison of results by geologist and GIS specialist and the API result concludes that the training in geology seams more critical than the acquaintance of computer skills. It is also proved that the Simi-automated approach is an efficient and effective approach , which can be further applied for the generation of a landslide database of the whole Taiwan by using the Taiwan SPOT mosaic.
Figure 1 Index map of the coverage of aerial photographs of Nantou County, Taiwan
Figure 2 SPOT ISO clas of Don -Pu Area of Nantou County. The dark areas are classified as landslide area.
Figure 3 An enlargement of SPOT mosaic of the upper-stream area of Chen-Yo-lan Stream in Nantou County. Landslides in white tone are conspicuous.
Figure 4 Color aerial photographs in the catchment area of Shi-Men Reservoir. A landslide in white tone is readily shown.
Figure 5. Landslides interpreted from 1260 aerial photographs. 4076 landslides with Max /Min /Avg Size of 5150m, 10m, and 321m.
Figure 6. landslides interpreted by well trained geologist from SPOT mosaic, 755 landslides with Max/Min/Avg size of 2000m, 32m, and 250m.
Figure 7. Landslides interpreted by well-trained GIS specialist from SPOT mosaic 708 landslides are identified. Large-scaled landslides are overlooked.
Figure 8. Landslides interpreted by well-trained GIS specialist from SPOT mosaic 1650 pseudeo-landslides are identified.
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