As early as the late 1970s, remote sensing technology was applied to the investigation of geological disasters. Japan, the United States, Europe and other countries are doing better. Japan has compiled a national 1∶50000 geological hazard map using remote sensing images. Based on a large number of remote sensing investigations of landslides and debris flows in Europe, the remote sensing techniques and methods are systematically summarized, and the spatial resolution of remote sensing images needed to identify landslides and debris flows with different scales and different brightness or contrast is pointed out. The remote sensing survey of geological disasters in China began in the early 1980s, which started late, but developed rapidly. It gradually developed in the service of large-scale projects in mountainous areas, and extended to railway and highway route selection, mountainous towns and other fields (Feng Dongxia et al., 2002). Since the large-scale investigation of land and resources was carried out, the special remote sensing investigation of geological disasters in the Three Gorges reservoir area of the Yangtze River, along the Qinghai-Tibet Railway, in the Himalayas and in eastern Sichuan has been completed by using digital geological disaster technology. Since 2005, remote sensing technology has been widely used in the detailed investigation of geological disasters of1∶ 50,000 in loess area, southwest China, Hunan, Hubei and Guangxi and other areas with serious geological disasters 127 counties, and the key areas cover high-resolution data above1m.
Since 2008, the "5. 12" Wenchuan earthquake, "6.5" Jiweishan in Wulong Iron Mine Township of Chongqing, "4. 14" Yushu earthquake, "6.28" Guanling landslide, "8.7" Zhouqu County of Gansu Province and other geological disasters. Especially in the "5. 12" Wenchuan earthquake-stricken area, the project of "secondary geological disaster investigation by aerial remote sensing" was completed, and the largest multi-platform, multi-sensor and multi-data processing system aerial remote sensing emergency disaster investigation was carried out by using the most advanced aerial remote sensing technology and equipment in China, which provided high-definition disaster images and disaster interpretation information for the State Council earthquake relief headquarters, relevant state ministries and commissions and affected local governments in the shortest time. After the earthquake, the first aerial remote sensing image of the disaster area and the high-precision digital aerial remote sensing image along Yingxiu Town-Wenchuan were praised as "great contributions" to earthquake relief by the comrades of the frontline headquarters of earthquake relief. The results directly serve the relevant departments of national earthquake emergency rescue, provide an important scientific basis for directing earthquake relief, preventing secondary geological disasters and carrying out post-disaster reconstruction, and play an important role in disaster relief and post-disaster reconstruction decision-making (Wang Ping, 2009; Zhao et al., 2003).
The characteristics of remote sensing survey and monitoring technology for geological disasters are as follows:
Geological disasters such as 1) landslide are usually scattered and the genetic mechanism is complex. Remote sensing technology can detect the panorama of a large area and individuals from high altitude, obtain the macro-feature information of the panorama of the area and individuals, and conduct comprehensive investigation and research.
2) Geological disasters are mostly located in areas where traffic and communication are very inconvenient, and remote sensing technology is not limited by ground conditions. In areas with harsh natural conditions such as deserts, swamps and mountainous areas, remote sensing technology can be used instead of human collecting and detecting data.
3) The traditional means of geological disaster investigation has relatively slow data collection and high labor cost. Remote sensing detection can periodically and repeatedly collect data in the same area, so as to obtain the latest data of various natural phenomena passing through the area in time. According to the change of data, the natural phenomena in this area are dynamically monitored to dynamically reflect the changes of things on the ground.
Second, the scope of application and application examples
1. Remote sensing investigation and monitoring of geological disasters in Himalayan region
Himalayan region is one of the most serious geological disasters in China. At the beginning of the 20th century, the Space Center carried out the investigation and monitoring of geological disasters in Himalayan region. Using remote sensing technology, the Himalayan area 170,000 km2 is interpreted as 175 landslide, 36 1 debris flow gully,17 serious collapse section, 13 moraine and 2 dammed lakes, and the development of geological disasters in this area is analyzed in detail. The distribution of major geological hazards in the region and the areas that may be affected are emphatically evaluated. It is found that the main geological disasters in Himalayan region mainly include dammed lakes, glacial lakes, landslides, mudslides and other disasters, among which dammed lakes and glacial lakes have wide disaster areas (Figure 1) and great harm.
Figure 1 Assessment Diagram of Hidden Dangers of Classical Errors, Direct Learning Errors, Golden Errors and Horrible Errors
2. Wenchuan Earthquake Emergency Remote Sensing Investigation
After the "512" Wenchuan earthquake, an aerial remote sensing emergency disaster investigation was carried out. * * Obtained high-definition aerial remote sensing images of 43000km2 in Beichuan 14 severely affected counties and cities, and completed the remote sensing investigation of roads and houses damaged in Beichuan 14 severely affected counties and cities, landslides, dammed lakes and other secondary disasters. * * * Interpretation. There are 264 dangerous towns and villages (Figure 2), and there are 1732 potentially dangerous roads. The results directly serve the relevant departments of national earthquake emergency rescue, provide an important scientific basis for directing earthquake relief, preventing secondary geological disasters and carrying out post-disaster reconstruction, and play an important role in disaster relief and post-disaster reconstruction decision-making (Wang Ping, 2009; Tong, 2008).
Fig. 2 Remote Sensing Assessment of the Potential Danger of Secondary Geological Disasters in Beichuan County
3. Remote sensing investigation and monitoring of debris flow in Zhouqu.
On the night of August 7, 2065438+00 1 1, a sudden rainstorm occurred in the mountainous area in the northeast of Zhouqu County, Gansu Province, with a rainfall of 97mm, which lasted for more than 40 minutes, causing catastrophic mountain torrents in Sanyanyu and Luojiayu ravines. Debris flows into Zhouqu County and into Bailong River, forming a dammed lake, causing great losses and difficulties to people's lives, property, production and life.
Debris flow mainly occurs in Sanyanyu and Luojiayu basins in the north of Zhouqu County, both of which are first-class tributaries on the left bank of Bailong River, showing a "ladle" shape.
Remote sensing interpretation of (1) debris flow characteristics (Figure 3)
Sanyanyu Debris Flow: The average width of debris flow circulation area is 80m. After the gully outlet enters Sanyanyu, the terrain becomes flat and wide, and the river slope decreases from 1.44‰ to 88‰, forming a surface flow with a length of 1.6km and an average width of 260m, forming a debris flow accumulation with a thickness of 5-2m; After entering the county seat, due to the influence of buildings, the debris flow shrinks to 50m wide and enters Bailong River after flowing 320m m. The flow area of debris flow visual circulation area is 0.35 km2, the length of Dayugou visual circulation area is 3.2km, and the visual circulation area of Xiaoyugou is1.2 km. : The area of surface flow accumulation area and scour accumulation area is 0.4 1km2, the length is about 2km, the widest point is 350m, and the average width is 200m m.. According to media reports, it is estimated that the average deposition thickness in this area is about 1m, and the estimated debris accumulation volume is 4 1x 104m3.
Luojiayu Debris Flow: The average width of debris flow circulation area is 15m. After the gully outlet entered Luojiayu, the terrain became flat and wide, the river slope decreased from 224‰ to 1 10‰, and the area affected by debris flow widened (100m), gradually forming debris flow accumulation. After driving 800 meters, we arrive near Luojiayu. The visible flow area of debris flow above the mouth of Luojiayu gully is 0.09km2 and its length is 6.2km. The debris flow below the mouth of Luojiayu gully has an area of 0. 16 km2, a length of 2.5km, a widest point of 160m and an average width of 70m. According to the average thickness of 1m, the accumulation volume of debris is 16x 104m3.
Fig. 3 Remote sensing interpretation of debris flow characteristics
Fig. 4 Remote sensing image of debris flow disaster
Debris flow accumulation zone in Bailong River: with an area of 0. 16km2 and a length of 2.2km. It is reported that the maximum thickness of the accumulation layer is 10m. According to the average thickness of 4m, the volume of accumulation body is 64× 104 m3. The main contributor of debris flow is Sanyanyu debris flow. According to the calculation that Luojiayu debris flow accounts for 1/4 and Sanyanyu debris flow accounts for 3/4, the accumulation volume of Sanyanyu debris flow in Bailong River is 48× 104 m3, and Luojiayu debris flow in Bailong River is 16× 104 m3.
To sum up, the total debris flow accumulation formed by Sanyanyu debris flow is 89× 104 m3, which is huge. The total debris flow accumulation formed by Luojiayu debris flow is 32× 104 m3, which is relatively large.
(2) Debris flow disaster interpretation (Figure 4)
The "August 7" catastrophic mudslide disaster in Zhouqu County buried and destroyed 232 bungalows (below 3 floors) and 22 buildings, and the estimated death toll was close to 2,000. The disaster caused by this debris flow is a major geological disaster.
(3) Remote sensing interpretation and evaluation of Sanyanyugou debris flow prevention project.
1999 Sanyanyu Debris Flow Gully has completed the debris flow control project, which is designed according to the 50-year return period standard and is mainly based on interception and drainage project and combined with biological measures. The comprehensive control project of debris flow in Sanyanyu mainly includes: 4 gully-fixing and slope-stabilizing dams; 4 masonry revetment dams; 1 1 sand bar (Figure 5), with a dam height of 8 ~ 18m, in which there are 2 main dams at the mouth of the main gully, 5 sand bars in Dayugou and 4 sand bars in Xiaoyugou; And 24 0.5 m high scour barriers.
From the post-disaster image analysis, the sand dam project has a certain effect on alleviating the severity of this disaster. As shown in Figure 6, the upstream of each sandbar intercepted a large number of sundries; Xiaoyugou debris flow is small, and the gully mouth sand bar is not damaged. As shown in Figure 7, the debris flow overflowed the dam and intercepted most of the debris. The regulation project has played a role in reducing the peak flow and sediment discharge.
Fig. 5 WorldView- 1 picture of engineering treatment at the intersection of Dayugou and Xiaoyugou.
Fig. 6 photos of debris flow at the intersection of Dayugou and Xiaoyugou after flight.
Fig. 7 Fast bird image after debris flow at the intersection of Dayugou and Xiaoyugou.
Fig. 8 Satellite remote sensing image before Guanling landslide disaster.
Fig. 9 Digital aerial photograph after Guanling landslide.
4. Remote sensing investigation and monitoring of the disastrous geological disasters of Guanling landslide.
At 20 10, 14: 30, the villagers of Yongwo Formation in Dazhai Village, WU GANG Town, Guanling County, Guizhou Province, caused landslides due to continuous heavy rainfall, also known as the "6 28" catastrophic geological disaster in Guanling. The landslide * * * caused 37 households with 99 people missing or buried, which is a rare landslide and debris flow compound catastrophe (Figure 8 and Figure 9).
(1) Interpretation of Landslide Topography and Disaster Area Characteristics
The mountain where the landslide occurred is a "shoe-shaped terrain", which is steep on the top and gentle on the bottom, and the landslide area is just in the transition zone with steep and gentle changes. The average slope in the landslide area is 3 1, the average slope behind the landslide is 46, the elevation of the rear edge of the landslide is 1 160m, and the elevation of the shear outlet is 1000m. The gully ratio in the debris flow area is reduced to 175‰ (Figure 10).
Figure 10 Erdaoyan-Yongwo topographic profile
Comparing the images before and after the landslide disaster, the landslide disaster is very clear. As shown in figure 1 1, disasters can be divided into landslide area, scraping area, debris flow accumulation area, later debris flow accumulation area and bank collapse area, and the affected area is 186775m2. The landslide slides from south to north to west. After running for 450m, it collided violently with a hillside where the villagers' group of Yongwo in Dazhai Village was located. After deflecting 80, it becomes a high-speed debris flow to the west, shoveling away the surface accumulation along the ditch, and finally forming a rare landslide and debris flow disaster. Combined with the existing topographic and geological environment data, it is explained that the affected area of Yongwo landslide in Dazhai is 186775m2.
Figure 1 1 Interpretation map of Dazhai-Yongwo landslide disaster area in Guanling.
Figure 12 topographic profile of Dazhai-Yongwo landslide disaster area in Guanling.
Figure 13 topographic changes in the Dazhai-Yongwo landslide disaster area in Guanling.
(2) Calculation of landslide scale (Figure 12, Figure 13)
Landslide scale: the landslide length is 370m, the average width is 166m, the landslide area is 72500m2, the maximum landslide thickness is 55m, and the landslide volume is about117.6x104m3, so it is a medium-sized landslide.
Stacking scale: length 960m, average width 1 10m, area 1 14275 m2, maximum stacking thickness 40m, volume 174.7× 104 m3.
(3) Disaster interpretation and assessment
According to the image comparison before and after the landslide, about 80% of the landslide area is sloping farmland with an area of about 90 mu. About 70% of debris flow accumulation area is cultivated land, with an area of about 120 mu; There are 16 buried houses in Dazhai village (group), 17 buried houses in Yongwo village (group) and 1 buried houses along the highway below. As shown in the explanatory diagram, there are four bank collapses near the lower reservoir; Affected by the bank collapse, cracks appeared behind two residential buildings, posing a safety hazard. According to local conditions, due to migrant workers, it is estimated that there are 3 ~ 5 people living in each house. According to the lowest estimate, the number of people buried is about 34×3, namely 102. Based on this, this disaster is determined to be a major disaster.
Third, promote the transformation mode.
Conference exchange, technical training and technical consultation.
Technical support unit: China Land and Resources Aerogeophysical Remote Sensing Center.
Contact: Ge Xiaoli
Address: Institute of Remote Sensing Technology, Hangyao Center, No.31Xueyuan Road, Haidian District, Beijing.
Postal code: 100083
Tel: 0 10-6206005 1
E-mail :gxiaoli@sohu.com