Study On Extraction And Dynamic Change Of Lake Area In Nanchang City Based On Landsat TM/OLI Image

Lakes are more sensitive to changes in the surrounding environment and can truly reflect the regional climate evolution and social economic activities.In recent 30years,with the development of society and economy,Nanchang has carried out large-scale urban construction and the urban ecological environment has suffered a considerable degree of damage.Therefore,timely and accurate grasping of the changes in the area of lakes in Nanchang is particularly important.The emergence of water extraction technology and remote sensing dynamic monitoring technology provide technical support for the study of the dynamic changes of lakes.In this paper,Landsat TM/OLI satellite imagery is used as the data source.Based on the analysis of the spectral features of typical features in Nanchang City,three commonly used water extraction methods,NDVI,NDWI and MNDWI,have been improved.Two types of water extraction methods,namely the new combination water index(NCWI)and the empirical normalized difference water index(ENDWI),were obtained to suppress the information of buildings and bare ground.Taking ENDWI as the best extraction model of lake water in Nanchang city,the lake distribution map and lake area change map of Nanchang city from 1989 to 2015 were made.Then the change of lake area in Nanchang city from 27 years was analyzed.The results are as follows:(1)Compared with the NDVI,NDWI and MNDWI water extraction methods,NCWI and ENDWI have better inhibition effects on buildings and bare land information.The contrast between water and buildings reached 0.50 and 0.51respectively,and the contrast between water and bare land reached 0.86 and 0.93respectively.(2)For Landsat TM images,the overall classification accuracy,Kappa coefficient,mapping accuracy and user accuracy of the water extracted by the ENDWI among the five water body extraction methods were the highest,and the misclassification error and leakage error were the lowest.For Landsat OLI images,the ENDWI has the highest mapping accuracy for water extraction and the lowest leakage error.The overall classification accuracy,Kappa coefficient,and user accuracy are slightly lower than those for NDVI and NDWI,and the misclassification error is slightly higher than NDVI and NDWI.(3)From 1989 to 2015,the total area of lakes in Nanchang City showed a linear decrease,with a total reduction of 1.719 km~2.Among the 14 lakes in Nanchang urban area,there are 3 expansive lakes,namely Qianhu Lake,Yao Lake and Nantang Lake respectively.There are 3 atrophic or disappearing lakes which are Zhujia Lake,Tiexian Lake and Qingshan Lake respectively.There are 8 atrophic lakes,namely Kongmu Lake,Diezi Lake,Huangjia Lake,Libu Lake,the Xianshi Lake,the Old City of Four Lakes,Aixi Lake and Xiang Lake.(4)From 1989 to 2015,the change of lake area in Nanchang City was the result of the joint action of climate factors and social and economic factors.From the perspective of impact degree,the influence of social and economic factors was stronger than that of climate.Among them,the main driving forces for the area change of the Yao Lake are the annual precipitation,annual precipitation,and annual evaporation.In addition to the Yao Lake,the changes in the total area of other lakes in Nanchang City are related to social and economic factors.