The Images Interpretation And Information Extraction Of The Potential Debris Flows By Remote Sensing Way In The Worst Disaster Of Wenchuan

There were many disastrous debris flows in Wenchuan earthquake areas in2010,especially the debris flows caused by heavy rainfall conditions in Wenjiagou ofQingping Town of Mianzhu City and Hongchungou of Yingxiu Town of WenchuanCounty.The outbreaks of debris flows caused huge economic losses and casualties,and seriously restricted the economic construction and development. Wenchuanearthquake caused massive landslides and collapse, which piled into loose material.The loose material and lots of new landslides caused by heavy rainfall conditionsmake the frequency and scale of debris flow of the strong earthquake areas increase.Many studies show that the Wenchuan earthquake zone has entered a new activeperiod, and debris flows will be more frequent in the next5to10years in this region.Therefore, to carry out the information extraction the potential debris flows of theWenchuan earthquake zone, prevent and forecast disaster scientifically, areparticularly important to people’s safety and economic development.In this paper, the high spatial resolution aerial imageries and1:50000topographic maps were used as data sources and a virtual three-dimensional scene ofthe study area was established by using GIS technology. Based on remote sensinginterpretation signs, the topography, the conditions of geological environment and thesurrounding surface features, the author interpreted and extracted the collapse,landslides, mudslides information of the study area. Then, on the basis of the knownactive debris flow characteristics and previous results, combined with the analytichierarchy process and GIS spatial analysis function, debris flow risk value range wasobtained. At last, the average of the risk value of the various active debris flow was calculated by using the grid as a unit. The lowest average was used as a standard todetermine the potential debris flow, by this way, to extract the thirty-four potentialdebris flow gullies in the study area.The main research results obtained in the study are as follows:(1)Production of3D visualization image of dynamic analysis the remote sensingimages geological interpretation. The author extracted contour lines on the basis of thedigital topographic map to construct DEM and produced the3D visualization ofimage dynamic analysis map of remote sensing images geological disastersinterpreted by using aerial imagery on May14,2008and the TM data of July2008and May2004.The three-dimensional visualization of the image not onlyhighlighted the spatial characteristics of geological disasters (collapse, landslide,debris flow), but also dynamically observed multi-angle, multi-scale, and visualize thetopography information to help the extraction and analysis of landslides, avalanches,landslides and other geological disasters.(2)Remote sensing interpretation and information extraction of the collapse,landslide and activities debris flows in the study area. Based on collapse, landslideRemote sensing interpretation signs and field trips, the author used high spatialresolution aerial imageries and three-dimensional visualization of dynamic analysismap to determine there were53landslides,1575collapses,76.58km2disaster areasand14active debris flow of49.49km2. The collapse, landslide distributed in theMinjiang River and its tributaries, mainly in Yingxiu and Yinxing town, and thecollapse had mass in the study area.(3)The debris flow risk value was obtained using grid as a unit. This paperconsidered landslide distribution characteristics, debris flow forming conditions andregular and the results of previous studies, selected the terrain elevation, hillside slope,aspect, the stratum lithology, to the fault distance, the earthquake damage, thedistance from the river, the maximum rainfall, land use types, population density as10factors to analyze the debris flow development characteristics of the study area,then used the analytic hierarchy process to obtained the risk value of the study area.(4)The extraction of potential debris flow. Base on the average, the active debrisflow risk value was calculated using watershed as a unit. The average was used asstandard to analysis the potential debris flow risk. Then maximum, average andminimum risk value of the active debris flow was used to re-class the debris flow ofthe study area. Based on the analysis of debris flow conditions, combined with the dynamicanalysis of aerial imagery and3D visualization of geological disasters map, thepotential debris flow of the study area were RS interpreted. The result was comparedwith Hongchungou debris flow in2010, and then its reliability was proved.