| Water is an important surface covering with functions such as climate regulation,drinking water and irrigation,and is closely related to human production and life.The emergence and development of satellite remote sensing technology has provided an efficient means to study water bodies.Based on Landsat-8 and GF-2 image data,this paper explores water extraction methods,and analyzes the dynamic changes of the top ten lakes in the Yunnan-Guizhou Plateau from 2011 to 2020,and explores the area changes of lakes in the Yunnan-Guizhou Plateau in the past decade and its relationship with climatic factors and human activities.The main research contents include:(1)Based on the Landsat-8 image,the reflection characteristics of the water body on the Landsat-8 image were analyzed.The results showed that the water body in the visible light to mid-infrared band,with the increase of the wavelength,the reflectivity gradually decreased,and in the near-infrared and mid-infrared bands.In the infrared band,the reflectivity of water bodies is significantly lower than that of other ground objects.Therefore,drawing on the existing principles and ideas of water body index construction,the visible light bands in the Landsat-8 data are taken as one group,corresponding to the second,third and fourth bands of the image data;the near-infrared and mid-infrared bands are taken as another group,corresponding to For the fifth and sixth bands of the image data,the water body index model is constructed by using the difference between the two sets of data.Based on Landsat-8 image data,water extraction experiments were conducted in Hefei,Ankang and Kangding areas with a total of 3 scene data and 5 different scenarios.The results show that the model can not only suppress the influence of clouds,shadows,bare soil,bright-colored ground objects and buildings on water extraction,but also can extract water containing a large number of cyanobacteria well,and the threshold is stable,and the kappa coefficient is better than 96.85 %,the overall accuracy is as high as 99.69%,and the overall error is less than 8.92%.Compared with other water body indices,the extraction accuracy of the multi-band combined water body index constructed in this paper is significantly improved.(2)In view of the problem that the existing water body index is difficult to deal with the problem of “salt and pepper” phenomenon when water bodies are extracted from remote sensing images with complex environment and high spatial resolution,this paper analyzes the spectral information of surface cover based on GF-2 images,and constructs a A comprehensive water index(CWI),in order to verify the performance of the comprehensive water index,firstly,the water body is extracted by image segmentation combined with the water body index and the accuracy is verified;secondly,in order to make full use of the spectral information and the advantages of the classifier,the spectral information of the segmented homogeneous object and the water body index are combined as the input data of the classifier,and the water body is extracted and the accuracy is verified;finally,the applicability of the comprehensive water body index in the World View-2 image and the GF-1 image is verified.The test results show that:(1)the newly constructed comprehensive water body index can effectively suppress the influence of shadows,buildings,roads,vegetation,bare soil and other surface coverage during water body extraction,and the accuracy is significantly improved;(2)the water body is extracted by image segmentation combined with the water body index.The information can effectively inhibit the occurrence of salt and pepper phenomenon;(3)The classifier combined with the water body index can effectively improve the water body extraction accuracy;(4)The comprehensive water body index is also applicable to the Worldview-2 image and the GF-1 image.In summary,the comprehensive water body index constructed in this paper can effectively extract water body information,and can be used for the extraction of rivers and lakes and the investigation of pond aquaculture area,etc.It is a high-precision water body extraction method.(3)Using the Landsat-7 and Landsat-8 image data to extract the top ten lakes in the Yunnan-Guizhou Plateau from 2011 to 2020,and analyze their dynamic changes,the results show that:(1)During 2011-2020,the lake area showed a trend of decreasing first and then increasing,the lake area of the Yunnan-Guizhou Plateau has a minimum value in 2015 and a maximum value in 2019.The lake area in 2020 is comparable to that in 2019.Most of the changes in the area of a single lake also showed a trend of first decreasing and then increasing.The year when the minimum area of a single lake appeared was different,but mostly around 2015.Lakes with deeper lakes have smaller area changes,and lakes with shallower lakes have larger changes in area;(2)From 2011 to 2020,the temperature of the Yunnan-Guizhou Plateau showed a gradual increase trend,and the annual average temperature of each station increased with the increase of latitude.Gradually decreases.The lake area on the Yunnan-Guizhou Plateau shows an opposite trend to the annual average temperature.The reason is that within a certain range,the temperature increases,the evaporation increases,and the lake water consumption increases,resulting in a decrease in the lake area.(3)From 2011 to 2020,the average annual precipitation on the Yunnan-Guizhou Plateau showed an overall increasing trend,and there was no significant correlation between the annual average precipitation on the Yunnan-Guizhou Plateau and the total area of lakes on the Yunnan-Guizhou Plateau.As far as a single lake is concerned,not all lake areas have a positive correlation with precipitation.The lake areas of Dianchi Lake,Erhai Lake,Yilong Lake and Caohai Lake have a positive correlation with precipitation.Among them,Dianchi Lake area and precipitation are positively correlated.The correlation coefficient between them is0.33.There was a negative correlation between the area of other lakes and precipitation,and the correlation coefficients between lake area and precipitation in Chenghai,Lugu Lake and Qilu Lake were all greater than 0.5.It can be seen that precipitation is also one of the meteorological factors affecting the lake area,but because the change of lake area is not only dominated by meteorological factors,the correlation between the two is negatively correlated.(4)Analyze the impact of human activities on lake area.For individual lakes,human activities are the main factor affecting the area change. |
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