Monitoring Of Water Extent And Variation Analysis Of The Poyang Lake Using GF-1 Remote Sensing Data

As an indicator of the regional environment,lake is an essential part of the ecosystem.Poyang Lake,as the largest freshwater lake in China,has a significant high water level dynamic change,water extent of Poyang Lake is a key factor for the ecological environment.The largest water area of Poyang Lake was 3522.73 km2 in July 24,2016.The water area was the smallest in January 31,2014,as the water area was 987.58km2.The largest water area was 3.6 times larger than the minimum area.In recent years,the high water level and low water level phenomenon of Poyang Lake have higher appearances frequency and longer duration.Based on the real time and dynamic characteristics of RS and GIS,it is meaningful to timely monitor the water coverage information of Poyang Lake in a large scale.(1)Using the water area range of the highest water level as the research area of Poyang Lake.After image preprocessing,this paper compared the extraction results of support vector machine(SVM)classification method,single band threshold method and normalized difference water index(NDWI)method and verified the accuracy,water extents of Poyang Lake area were finally extracted by NDWI.(2)The results showed periodic variation of water extent of Poyang Lake in Jun 2013-Dec 2016.Water area began to rise faster from April to June,and reached peak in July and August.Water area gradually declined in September,until January of the following year and reached the minimum.The lake water area frequently fluctuated in April and November.The seasonal variation of Poyang Lake was roughly same,but every year had unique changes.During the dry season in winter 2015,Poyang Lake had abnormal high water level and water area was 2249.31km2,which was 1.6,1.9,and 1.5 times of same period in 2013,2014,and 2016.(3)According to the water extraction of Poyang Lake area and the water level data of 4 hydrological stations,this paper built the linear,logarithmic,exponential,and quadratic polynomial models between the lake's area and water level.The results showed the quadratic polynomial model in Duchang hydrological station was optimal model for water extent and water level.(4)The analysis showed that the main water area and the dish-shaped sublakes surrounding of Poyang Lake covered by water in the long term,the change of water area in Poyang Lake wetland was obvious.The highest frequency of water cover appeared in 2016.The dish-shaped sublakes had higher frequency of water cover in autumn,but the main water area had higher frequency of water cover in spring.