利用TM卫星数据监测泥石流

Monitoring Debris Flow by means of Satellite Image

地质灾害分布范围广 ,应用卫星图像监测地质灾害是一种可行的方法 .泥石流沟小流域面积一般达到平方公里的数量级 ,可以由卫星图像观察到 .TM数据有 7个波段 ,各个波段图像的标准差是不同的 .我们计算了泥石流沟各波段的标准差 ,按大小排成一个序列 ,发现地理条件相同 ,标准差序列也相同 .在一定尺度范围内 ,各泥石流沟的标准差序列和周围不一致 ,表示该沟处于特殊的发育阶段 ,有爆发泥石流的危险 .应用上述方法 ,对甘肃主要泥石流分布区的典型泥石流沟进行了分析 ,认为这是监测泥石流的可行方法 .

Nearly a half part of Gansu Province is covered by loess. Water and other forces cut the loess plateau and deep valleys are formed. A great number of geological hazards happen in these areas. One of them is debris flow. In China, there is about 0.65×10 6 km 2 land suffered by debris flow, accounting for 7% of the territory. There is 4.0×10 8 m 3 debris flow recorded every year. When debris flow happens, a lot of soil, sand and rock mixed water rushes out of a valley, destroying village and town, road and railway, factories and buildings, persons and livestock. Because the hazards are distributed very wide, satellite image is the best way to monitor the hazards. The basin of debris flow valley is one sq. km or more in average, so it can be seen in satellite image. Suppose the value of each pixel of an image is x i, i=1, 2, 3…n, then the average number =∑x i/n. The pixel numbers of each debris-flow valley are about 10 000～60 000. TM data has 7 bands with different standard deviation. For a valley the standard deviation can be calculated and a sequence of standard deviation for each band can be made. It can be seen that the standard deviation of Band 5 is the largest and that of Band 6 is the least for Dongjiangshui Valley of Wudu County, Gansu Province. The character sequence of the Dongjian-gshui debris flow is 5731426.The standarddeviation is17.40 for of Band 1, 11.99 for Band 2,19.10 for Band 3, 17.03 for Band 4, 29.09 for Band 5, 10.27 for Band 6 and 20.18 for Band 7. The standard deviation sequences of the image for some places in Gansu, Sichuan, Guizhou Provinces are also computed. It is found that if the natural condition is similar, the sequence will be the same. Then the standard deviation sequences of the main debris-flow valleys in Gansu Province are computed as shown in Table 3. The sequence is the same in a certain area as shown in Figure 3.A different sequence in the certain area (the legend mark is ) means the debris flow valley may be in danger.So a change of image sequence for a debris flow valley may be used as a symbol to monitor a debris flow.