以四川省北川县唐家山地区为研究区,利用2006-11-10的SPOT卫星影像数据,依据NDVI和地形信息进行耕地识别,辅以少量的人工修正,快速获取灾前耕地分布信息.应用2008-05-14的FORMOSAT-Ⅱ卫星影像数据和2008-06-04的ALOS卫星影像数据,采用人机交互解译快速获取地震诱发的崩塌滑坡、堰塞湖等次生灾害信息.灾前耕地分布信息叠加地震次生灾害数据及影像,进行变化检测,实现耕地损毁的快速评估.结果表明,研究区内崩塌滑坡、堰塞湖等次生灾害严重,崩塌滑坡533处,面积1408.20hm2,堰塞湖水面面积已达604.69 hm2.共毁坏耕地86.88 hm2,耕地毁坏率8.84%.崩塌滑坡、被毁耕地分布与断裂带分布一致,断裂破碎带内耕地毁坏率达18.74%,占研究区被毁耕地面积的74.53%.
Themain suffering area of theWenchuanEarthquake locates in themountainous area ofwestern Sichuan, an\nareawhich is very prone tomountain hazards such as landslides and debris flows because of themountains and deep valleys, complex geological structure aswell aswelldeveloped fault zones there. The Wenchuan Earthquake had directly in ducedmassive secondary disasters such as collapse and landslideswhich destructed large area of farmlands. At the same tmie, theWenchuan Earthquake also induced more than 30 barrier lakesmaking some farmlands be inundated and destructed. In order tomake a scientific evaluation of the disaster situation and provide scientific basis for reconstruction and rational settlementofpeople in the suffering area, it isnecessary to acquire the information of the destructed farmlands. In this paper, satellite remote sensing data aswellas appropriate information extractionmethodswere used to acquire the distribution information of farmlands before theWenchuan Earthquake and information of collapse, landslides, barrier lakes after Wenchuan Earthquake based on information such as landform features inmountainous area, landuse information and miagery characteristics of seasonal aspect. Spatial analysiswas applied to evaluate the farmland loss to provide reference for the reconstruction planning.In this paper, Tangjiashan area ofBeichuan countywas taken as a case study area for evaluating the farmland loss caused by secondarydisasters. NDVIwasderived from the SPOT mi age data of November 10th, 2007.Based on NDVI and landform information, the farmlandswere identified and the distribution information of farmlandswas obtained. Manual correctionswere then used to elmi inate possible errors in the previous farmland identification. The FORMOSAT-II miage of May 14th, 2008 and the ALOS miage of June 4th, 2008 were used to acquire the information of these secondary disasters such as collapse, landslides aswellasbarrier lakes induced by theWenchuanEarthquake based onman-computer interac-tive interpretation. Based onGIS technology, the rapid evaluation of farmland destructionwas carried outaccording to the comprehensive analyses of farmland distribution before theWenchuan Earthquake and the distribution information of these secondary disasters induced by theWenchuan Earthquake. Then the temporal and spatial characteristics of farmland loss were analyzed. The results show that the secondary disasters such as collapse, landslides aswellasbarrier lakeswere very serious in the study area. Therewere 533 sites ofcollapse and landslides which had a total area of1408.20 hm2, aswell as barrier lakeswith an area of604.69 hm2in the study area. The area of the farm lands destructed by secondary disasters were 86.88 hm2accounting for 8.84% of the total farmland area. The distribution of collapse, landslides and destructed farmlandswas consistentwith the distribution of fault zone. And the destruction rate of the farmland on the fault zonewas 18.74%, accounting for 74. 53% of the farmlands destructed in the study area.The secondary disaster induced by the main shock had seriously destructed the farmlandswhile the aftershocks furthered the destruction. With the adventof rain season, the secondary disasterwillstillbe ofgreatthreats to the farmlands so it isnecessary to strengthen the dynamicmo-nitoring of the farmland in the study area.As there is good forest coverage in this area, suitable seasonal aspectswith vegetation indexwere used to extract the distribution information of farmlandsbefore the Wenchuan Earthquake with the assistof landform information. In the FORMOSAT-II and ALOS mi agery the distribution information ofcollapse and landslides induced by the earthquakewas quickly extracted by visual interpretation according to the hue,shape in formation in the miagery, landform features and refer- ence to the satellite mi agery before the earthquake aswel,l then the farmland loss information was acquired using GIS.However, the rapid acquirementof the collapse and landslides information by automated classification needs further study.