1. Content Overview
Remote sensing technology began to be used in geological disaster investigation as early as the late 1970s. Countries that have developed well abroad include Japan, the United States, the European Union, etc. Japan used remote sensing images to compile a national 1:50,000 geological disaster distribution map; European countries have systematically summarized remote sensing technology methods based on remote sensing surveys of a large number of landslides and debris flows, and pointed out the identification of different scales, different brightness or Contrast the spatial resolution of remote sensing images required for landslides and debris flows. The remote sensing survey of geological disasters in my country started in the early 1980s. It started late but developed rapidly. It gradually developed in serving large-scale projects in mountainous areas and expanded to railway and highway route selection, mountainous towns and other areas ( Feng Dongxia et al., 2002). Since the launch of the land and resources survey, digital geological hazard technology has been used to complete special remote sensing surveys of nearly 40×104 km2 of geological hazards in the Three Gorges reservoir area of ??the Yangtze River, along the Qinghai-Tibet Railway, the Himalayas, eastern Sichuan and other places; in 2005 Remote sensing technology has been widely used in the 1:50,000 detailed geological disaster survey of nearly 40×104 km2 in 127 counties in areas with serious geological hazards such as the loess area, southwest region, Hunan, Hubei and Guangxi regions deployed since 2015, and was conducted with SPOT 5 data. Regional coverage, key areas are covered with high-resolution data above 1m.
Since 2008, there have been the “5·12” Wenchuan earthquake disaster, the “6·5” mountain collapse disaster in Jiwei Mountain, Wulong Iron Mine Township, Chongqing, and the “4·14” Yushu earthquake disaster. Remote sensing technology has played a very important role in emergency investigations of geological disasters such as the "6·28" Guanling landslide disaster and the "8·7" huge debris flow disaster in Zhouqu County, Gansu. In particular, the "Aerial Remote Sensing Survey of Secondary Geological Disasters" project completed in the "5.12" Wenchuan earthquake-stricken area used the most advanced domestic aerial remote sensing technology equipment and methods to carry out the largest multi-platform, multi-sensor, and multi-sensor survey to date. The data processing system's aerial remote sensing emergency disaster investigation provided high-definition disaster area images and disaster interpretation information to the State Council Earthquake Relief Headquarters, relevant national ministries and commissions, and disaster-stricken local governments in the shortest possible time; the first post-earthquake disaster area aviation information was obtained Remote sensing images and high-precision digital aerial remote sensing images along the Yingxiu Town-Wenchuan line were praised by comrades from the earthquake relief frontline headquarters as a "great contribution" to earthquake relief. The results directly serve the relevant national earthquake emergency and disaster relief departments, provide 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 Pingping, 2009; Zhao Yingshi et al., 2003).
The characteristics of remote sensing survey and monitoring technology for geological disasters are as follows:
1) The distribution of geological disasters such as landslides is usually scattered and the cause mechanisms are complex. However, remote sensing technology can monitor large-scale areas and regions from high altitudes. Detect the whole picture of the individual, obtain the macroscopic characteristic information of the area and the individual, and conduct a comprehensive investigation and research.
2) Most geological disaster bodies are located in areas with very inconvenient transportation and communication. Remote sensing technology is not limited by ground conditions. Remote sensing technology can be used in areas with harsh natural conditions, such as deserts, swamps, mountains, etc. Replace humans in data collection and detection.
3) Traditional geological disaster investigation methods have relatively slow data collection speeds and high labor costs. Remote sensing detection can collect data from the same area periodically and repeatedly, so that all geological hazards can be obtained in a timely manner. The latest data on various natural phenomena in the region. According to the changes in data, the natural phenomena in the area are dynamically monitored and the changes in ground things are dynamically reflected.
2. Application scope and application examples
1. Remote sensing investigation and monitoring of geological disasters in the Himalayas
The Himalayas are the most serious geological disaster areas in my country First, at the beginning of the 20th century, the Aerospace Remoteness Center carried out geological disaster investigation and monitoring in the Himalayas. Using remote sensing technology, it finally interpreted 175 landslides, 361 mudslides, and 17 collapses within the 170,000 km2 area of ??the Himalayas. Severe sections, 13 outburst glaciers terminal lakes, and two outburst barrier lakes, detailed analysis of the regional environmental characteristics of the development of geological disasters, regional geological characteristics of the development of geological disasters, distribution characteristics of geological disasters, landslide areas, and debris flow areas As well as the development patterns of collapse areas, etc.; it focuses on evaluating the distribution of major geological disaster hazards in the region and the areas that may be affected. Research has found that major geological disaster hazards in the Himalayas include river dammed lake outburst hazards, glacial lake outburst hazards, landslide hazards, and debris flow hazards. Among them, river dammed lake outburst hazards and glacial lake outburst hazard areas are at risk. The area is wide (Figure 1), and the degree of disaster hazard is high.
Figure 1 Evaluation chart of hidden dangers of Qu Dian Cuo, Zhi Xi Cuo, Jin Cuo and Fright Cuo collapse
2. Emergency Remote Sensing Survey of the Wenchuan Earthquake
“5 ·After the 12" Wenchuan earthquake, the aerial remote sensing emergency disaster survey was carried out, and 43,000km2 of high-definition aerial remote sensing images were obtained in 14 severely affected counties and cities including Beichuan. , house damage and other disasters, as well as secondary disasters such as landslides and barrier lakes, the remote sensing survey finally interpreted 7226 landslides, 147 barrier lakes, and 1423 disaster-damaged roads caused by the earthquake; delineated dangerous places There are 264 villages and towns (Figure 2) and 1,732 potentially dangerous roads. The results directly serve the relevant national earthquake emergency and disaster relief departments, provide 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 Pingping, 2009; Tong Liqiang, 2008).
Figure 2 Remote sensing assessment of potential hazards of secondary geological disasters in Beichuan County
3. Remote sensing investigation and monitoring of Zhouqu debris flow
The evening of August 7, 2010 Around 11 o'clock, a heavy rainstorm suddenly fell in the mountainous area in the northeastern part of Zhouqu County, Gansu Province. The rainfall reached 97mm and lasted for more than 40 minutes. It triggered a huge flash flood geological disaster in the two ditches of Sanyanyu and Luojiayu, and mudslides entered Zhouqu County. And poured into the Bailong River, forming a barrier lake, causing huge losses and major difficulties to people's lives, property, production and life.
Debris flows mainly occur in the Sanyanyu and Luojiayu river basins in the north of Zhouqu County. Both river basins are first-class tributaries on the left bank of the Bailong River and are shaped like a "ladle".
(1) Remote sensing interpretation of debris flow characteristics (Figure 3)
Sanyanyu Debris Flow: The average width of the debris flow area is 80m. After exiting the ditch and entering Sanyanyu, due to the topography It becomes flat and wide, and the channel ratio decreases from 144‰ to 88‰, thus forming a surface flow with a length of 1.6km and an average width of 260m, and forming a 5-2m thick debris accumulation; after entering the county town, due to the construction of buildings Due to the impact, the debris flow contracted and narrowed to a width of 50m, and then entered the Bailong River after running for 320m. The debris flow visible circulation area has a flow area of ??0.35 km2, the length of the visible circulation area in Dayugou is 3.2km, and the visible circulation area in Xiaoyugou is 1.2km; the surface flow accumulation area and scouring accumulation area have an area of ??0.41km2, a length of about 2km, and the widest It is 350m away and has an average width of 200m. According to media reports, it is estimated that the average sedimentation thickness in this area is about 1m, and the estimated debris accumulation volume is 41×104 m3.
Luojiayu Debris Flow: The average width of the debris flow area is 15m. After exiting the ditch entrance and entering Luojiayu, the terrain becomes flat and wide, and the channel ratio decreases from 224‰ to 110‰. The debris flow The affected area becomes wider (100m), and debris accumulation gradually forms. After running for 800m, it reaches the vicinity of Luojiayu. Due to the reduction of debris material, the width of the debris flow becomes narrower (40m), and returns to the river channel. After running for 1.6km, the affected area becomes wider (100m). Pass through Chengguan Town and enter Bailongjiang River.
The visible flow area of ??the debris flow above the Luojiayu ditch mouth is 0.09km2, 6.2km long; the debris flow area below the Luojiayu ditch mouth is 0.16km2, 2.5km long, the widest part is 160m, the average width is 70m, based on the average thickness Calculated at 1m, the debris accumulation volume is 16×104 m3.
Figure 3 Remote sensing interpretation of debris flow characteristics
Figure 4 Remote sensing image of debris flow disaster
Bailongjiang debris flow debris deposition zone: area 0.16km2, length 2.2km , it is reported that the maximum thickness of the clastic sedimentation zone is 10m. Calculated based on the average thickness of 4m, the clastic accumulation volume is 64×104 m3. The main contributor of debris is the Sanyanyu debris flow. Based on the calculation that the Luojiayu debris flow accounts for 1/4 and the Sanyanyu debris flow accounts for 3/4, the debris accumulation volume of the Sanyanyu debris flow in the Bailong River is 48×104 m3. The debris accumulation volume of the Luojiayu debris flow in the Bailong River is 16×104 m3.
To sum up, the total amount of debris accumulation formed by the Sanyanyu debris flow is 89×104 m3, which is a giant scale; the total amount of debris accumulation formed by the Luojiayu debris flow is 32×104 m3, for large scale.
(2) Interpretation of debris flow disaster (Figure 4)
The "8·7" huge debris flow disaster in Zhouqu County buried and destroyed 232 bungalows (less than 3 floors), 22 buildings, and the death toll is estimated to be close to 2,000. The disaster caused by this debris flow is a major geological disaster.
(3) Remote sensing interpretation evaluation of the Sanyanyu gully debris flow control project
In 1999, the Sanyanyu gully completed a debris flow control project designed according to the standard of once in 50 years. , mainly based on interception and drainage engineering, combining interception and drainage, coupled with biological measures. The Sanyanyu Debris Flow Comprehensive Control Project mainly includes: 4 ditch-fixing and slope-stabilizing dams; 4 mortar stone bank protection dams; 11 sand-retaining dams (Figure 5), with a dam height of 8 to 18 m, of which there are 2 main dams at the mouth of the main ditch. Dams, 5 sand check dams in Dayugou, 4 sand check dams in Xiaoyugu; and 24 anti-scouring sills with a height of 0.5 m.
Based on post-disaster image analysis, the sand barrage project played a certain role in reducing the severity of this disaster. As shown in Figure 6, a large amount of debris was intercepted upstream of each sand barrage; the debris flow in Xiaoyu Valley was small in scale, and the sand barrage at the mouth of the ditch was not damaged. As shown in Figure 7, the debris flow overturned the dam. Most of the debris was intercepted. The treatment project has played a role in reducing peak flow and sediment outflow. < /p>
Figure 7 Quick Bird image after the debris flow at the intersection of Dayugou and Xiaoyugou
Figure 8 Satellite remote sensing image before the Guanling landslide disaster
Figure 9 Digital aerial photography after the Guanling landslide
4. Remote sensing investigation and monitoring of the severe geological disaster of the Guanling landslide
Guanling County, Guizhou at 14:30 on June 28, 2010 Landslides were triggered by continuous heavy rainfall in the Yongwo Group of Dazhai Village, Gangwu Town, also known as the "6·28" geological disaster in Guanling. This landslide resulted in 99 people from 37 households missing or buried. It was a rare landslide debris flow compound disaster (Figure 8, Figure 9).
(1) Interpretation of landslide terrain and disaster area characteristics
The mountain where the landslide occurred is a "boot-shaped terrain" with steep upwards and gentle downwards, and the landslide area is located exactly where the steep and gentle changes occur. transition zone. The average slope of the terrain in the landslide area is 31°, the average slope of the terrain behind the landslide is 46°, the elevation of the trailing edge of the landslide is 1160m, and the elevation of the shear exit is 1000m. The channel ratio in the debris flow area dropped to 175‰ (Fig. 10).
Figure 10 Erdaoyan-Yongwo topographic profile
After comparing the images before and after the landslide disaster, the traces of the landslide disaster are very clear. As shown in Figure 11, the disaster can be divided into landslide area, scraping area, debris accumulation area, late debris flow accumulation area, and bank collapse area. The area of ??the disaster affected area is 186,775 m2.
The landslide slid from south to north to west. After running 450m, it violently collided with a small hillside where the Yongwo Village Group of Dazhai Village is located. After deflecting 80°, it transformed into a high-speed debris flow generally heading west, and shoveled the debris flow along the ditch. The surface accumulation body eventually formed a rare landslide debris flow disaster. Combining the existing terrain and geological environment data, it was interpreted that the area affected by the Yongwo landslide disaster in Dazhai was 186,775m2.
Figure 11 Interpretation map of Guanling Dazhai-Yongwo landslide disaster area
Figure 12 Topographic profile of Guanling Dazhai-Yongwo landslide disaster area
Figure 13 Topographic changes in the Guanling Dazhai-Yongwo landslide disaster area
(2) Calculation of landslide scale (Figure 12, Figure 13)
Scale of landslide body: length of landslide body 370m, with an average width of 166m, a landslide area of ??72,500m2, a maximum landslide thickness of 55m, and a landslide volume of approximately 117.6×104 m3. It is a medium-sized landslide.
Scale of debris accumulation: 960m in length, 110m in average width, 114275 m2 in area, 40m in maximum thickness, and 174.7×104 m3 in volume.
(3) Disaster Interpretation and Assessment
According to the comparison of images before and after the landslide, about 80% of the landslide area is sloping farmland, with an area of ??about 90 acres; the debris accumulation area is about 70% is cultivated land, with an area of ??about 120 acres; 16 houses were buried in Dazhai Village (group), 17 houses were buried in Yongwo Village (group), and 1 house was buried along the road in the lower part. As shown in the interpretation diagram, four bank collapses developed in the lower part near the reservoir; due to the impact of bank collapse, cracks developed behind two residential houses, posing safety risks. According to local conditions, due to the migrant workers, it is estimated that 3 to 5 people live in each house. According to the lowest estimate, the number of people buried is about 34×3, which is 102 people. Based on this, this disaster is determined to be a major disaster.
3. Promotion of transformation methods
Conference exchanges, technical training and technical consultation.
Technical support unit: China Land and Resources Airborne Geophysical Exploration and Remote Sensing Center
Contact person: Ge Xiaoli
Correspondence address: Aerospace Remote Center, No. 31 Xueyuan Road, Haidian District, Beijing Institute of Remote Sensing Methods and Technology
Postcode: 100083
Telephone: 010-62060051
E-mail: gxiaoli@sohu.com