MONITORING OF 1991 EASTERN CHINA FLOODING WITH POLAR ORBITING METEOROLOGICAL SATELLITES FY-1 AND NOAA

With polar orbiting meteorological satellites FY-1 and NOAA,flooding was monitored in the areas of the Huaihe River basin and the Taihu Lake region during June and July 1991.All satellite images from FY-1 and NOAA for concerned areas before and during flooding were examined.Those of cloud-free,with small amount of cumulus or thin cirrus were selected to exam the situation.Navigation and projection were carefully performed,to ensure the projected images at different time overlap accurately with each other in 1-2 pixels.Channel 1 (CH1) and Channel 2 (CH2) data of FY-1 and NOAA satellites with wavelength of 0.58-0.68μm and 0.725-1.1μm were used to monitor the flooding.Albedo of Channel 2 and normalized vegetation index (NDVI) were adopted as indicators to identify water body from land.With histogram and man-machine interactive methods,analysis was done.In cloud-free condition,the two indicators identified the same area and scope of the water body.Totally cloud-free image in a large area is quite rare.To understand flood process,it is necessary to use more frequent images.It was investigated to distinguish water from land in partly cloudy condition.The result showed that when there is small amount of cumulus or thin cirrus,satellite images are still valuable in monitoring water body.In case of monitoring area covered with cirrus,vegetation index is useful,and while there is small amount of cumulus on land,albedo of Channel 2 can be used.Ten images from May 16 to August 18 of 1991 were examined.The results show that in the Lixiahe area,Jiangsu Province,the area submerged in total was the largest;along main stream of the Huaihe River,the Chuhe River,and around the Chaohu Lake,a large percentage of area submerged;while in the Taihu Lake area,less field submerged.Flood monitoring was performed for 87 counties in the region concerned.These counties were put in order according to the percentage of submerged area in total.This order showed the extent of disaster at one view point.