汶川地震山地灾害遥感快速提取及其分布特点分析

The Extraction of Mountain Hazard Induced by Wenchuan Earthquake and Analysis of Its Distributing Characteristic

针对泥石流滑坡灾害体特有的物质组成与活动特点,通过比较分析其在不同遥感影像的光谱特征差异,选择ETM+影像作为主要数据源,提取湿度指数与绿度指数,利用ETM+的穗帽变换、影像差值增强、密度分割和掩膜技术建立了泥石流滑坡山地灾害快速提取模型,并用于汶川地震。通过灾害体的提取,分析了本次地震山地次生灾害的分布规律,利用空间叠加进行了成因的分析。本次地震山地灾害具有如下特点:(1)沿主要地表破裂带分布;(2)山地灾害主要出现在8度—9度地震烈度区,随着烈度的降低,山地灾害的总面积也相应的减少;(3)山地灾害主要发生在海拔高度1000—2500m的地带;(4)主要发生在坡度20°—50°之间的边坡上;(5)地震及余震期间以崩塌滑坡滚石为主,后期以泥石流滑坡为主;(6)具有河流左右两岸呈不对称分布等特点。结果表明,利用ETM+影像建立基于湿度指数与绿度指数的快速提取模型,对于大规模泥石流滑坡提取效果较好,进行大区域山地灾害的遥感快速提取是可行的。

The deadly Wenchuan Earthquake hit Wengchuan,a small city southwest of Sichuan Province,China,with a magnitude of 8.0,at 14∶28 local time of May 12.It shook more than half of China and brought devastation to more than fifty counties.The earthquake has not only caused numerous personnel casualties and destroyed kinds of facility directly,but also induced a lot of mountain hazards,and superimposed the hazards more severely.The extraction of earthquake-induced moutain hazards using remote sensing images has important significance for earthquake relief,assessment of bearing capacity of disaster area and reconstruction work after earthquake.The extraction of disaster area is realized by a method combination of information enhancement,information fusion and visual interpretation.According to the active characteristic and material combination of debris flows and landslides,we compare and analyze the spectral feature difference of different images and take ETM+ image as main data source.Debris flows and landslides have two distinct properties of higher water content and lower vegetation cover.The reflective features on remote sensing images are soil moisture and vegetation coverage,which can be reflected by wetness index and green index.After the extraction of wetness index and green index,tasseled cap transformation,image difference reinforcement,density slide and mask technology are used to build the quick extraction model for debris flows and landslides.The model is used to extract mountain hazards induced by Wenchuan earthquake.The distribution rule and feature of geo-hazard and genesis are analyzed by spatial overlay.Mountain hazards induced by the earthquake distribute mainly along Longmenshan Mountain earthquake zones and rivers on both hillsides.They have the following characteristics: 1.The types of mountain hazards are diverse,including collapses,landslides,rockfalls,imprisoned lakes,debris flows and so on.2.The relation is closed between the strong level of the action and the intensity of the earthquake.The mountain hazards are mainly present in the earthquake intensity area from 8 degree to 11 degree.With the intensity reduced,the gross area of geo-hazard decreased.3.The mountain hazards mainly occurred in areas 1000m to 2500m altitude.4.The gradient of the slop of generating geo-hazard mainly varied in the range from 20 to 50 degree.5.In quantity by collapseds,landslides,rockfalls primarily during aftershock and landslides,debris flows primarily during anaphase.6.Pair of ecological environment destruction is enormous.