基于洪水过程的农业洪灾变化遥感快速评估模型及其应用

洪涝灾情的准确测度需要同时兼顾淹没区的面积大小和淹水时长信息。利用淹没区内由水和作物等多种地物所组成的"复合水体"不同于水体的波谱时间变化特性,将不同洪灾时期的水体指数和植被指数进行信息复合,以有效凸显水体和洪涝淹没区之间的影像差异,据此进行了灾初期、峰期和中后期等3个时次受淹范围的有效识别。在此基础上,根据洪涝灾情随着淹没时长而加重以及灾区内淹水时长非均匀分布的特性,建立基于淹没时长的受淹面积不等权参与的洪灾扩展动态度指数(Variation Index of Flood,VIF)和区域灾情比较指数(Comparison Index of Flood Disaster,CIFD)两种模型,并将模型应用于鄱阳湖区2016年夏季农业洪涝灾害的时空变化遥感监测。结果显示,应用上述两种模型不仅可以准确获取鄱阳湖区本次农业洪涝灾情的演变趋势,而且能够方便地对比分析区域内不同地方的受灾程度。鄱阳湖区在2016年6月23日~7月25日期间的洪涝灾情具有由弱增强再趋弱的特征,其VIF指数由初始阶段(6月23日~7月9日)的3.75降至后续阶段(7月9日~7月23日)的1.29;鄱阳县是研究区内受灾最严重的区域,其CIFD指数值居于研究区内各受灾县市之首,该县受灾总面积以及多次被淹的灾区面积均高于其他县市。

FAST ASSESSMET MODEL OF FLOOD HAZARDS BASED ON FLOODING PROCESS AND REMOTE SENSING DATA: A CASE STUDY IN POYANG LAKE REGION

Extent of inundation is a key factor in flood damage assessment.In the previous research on flood damage assessment,flooded regions were often assigned weight coefficients corresponding to the submerged acreage,which actually implied that equal weighting of flooded acreage factor was used in flood damage assessment.However,extent of inundation usually changed during a flood event.For example,one spot may be submerged at the beginning of flooding and then may become non-flooded soon afterwards,while other areas may be submerged for the whole period of a flooding event.Therefore,these areas should be assigned time-weighted inundated acreage to take into account of their differences in inundation duration.Based on this fact,Variation Index of Flood (VIF) and Comparison Index of Flood Disaster (CIFD) were proposed to monitor the spatiotemporal characteristics of 2016 summer flood in the Poyang Lake regions.In order to acquire the actual acreage factor,the extent of inundation from 23rd to June 25th of July was mapped using GPS-based field investigation and remote sensing data before and after the flooding,including multi-temporal Landsat 8OLI,GF-1 WFV and Google earth imagery.To resolve the difficulty in remote sensing distinction between water body and the flooded area,image fusion was applied to integrate information from Normalized Difference Vegetation Index,Modified Normalized Difference Water Index (MNDWI) of the Landsat 8OLI in the early stage of the flood event and Normalized Difference Water Index (NDVI) in the latter stage.By doing so,the color differences between water body and the flooded area in the satellite images can be enlarged to have an effective discrimination of these areas.This study revealed that:1) A total area of 33 329.28 hm2 was covered by flood excluding the original extent of the water in the study area.And 81％ of flooded land area occurred in counties of Poyang,Yongxiu,Yugan,Duchang,Xinjian,Xingzi and Jinxian,located in the lake region;2) VIF tnder decreased from 3.75 in early stage to 1.29 in later stage,implying that the flood damage diminish quickly during that flood event;3) The most severe flood damage was in Poyang County with the CIFD index of 1.954,the largest among all other counties;4) Although the proposed method needs further testing,our investigation demonstrated the feasibility and the usefulness of the combined use of VIF and CIFD models and the image fusion processing technique to integrate NDVI,NDWI and MNDWI at the differentflooding stages in the flood damage assessment procedure.