| With the development of information technology,remote sensing technology and the application of remote sensing image water conservancy,the application of multi-band remote sensing image to water area extraction and water depth inversion has become one of the hot research topics.However,the research of water area extraction and water depth inversion not only provides scientific basis for safe operation and economic operation of reservoir area,while promotes the wide application of remote sensing technology in water conservancy field and speeds up the pace of intelligent water conservancy monitoring and measurement.Therefore,This paper adopts the method of water area extraction to discuss and study the inversion model of water depth with the example of the reach of Haibowan Reservoir in Inner Mongolia and the main contents and conclusions are as follows:1)For the research of water depth inversion model in the reservoir area: the method of statistical correlation is used to study the water depth inversion model in the still water area of Wuhai Lake while the method of using the same pixel data to represent the water depth is improved by statistical correlation analysis on the problem of single point measurement depth value on behalf of the remote sensing as yuan corresponding depth.Therefore,the inversion factors of water depth are selected while 15 groups of double band models with linear,quadratic and exponential forms and 5 groups of multi-band models with different numbers of inversion factors are established based on the correlation between the water depth value and the combination of different bands.Moreover,five better inversion models were selected while the model accuracy was tested by the sample of the unattended data points,which was compared with the results of the test showing that the band of remote sensing image with the largest water depth response in the study area is the red band of B4 in the middle band of Landsat-8 while the optimal inversion model of water depth in Haibowan reservoir is a multi-band inversion model established by 12 inversion factors.The average absolute error is 0.68 m,which accounts for 13.59% of the average water depth.However,the inversion error of the optimal model is within the acceptable range of remote sensing bathymetry,and it can be applied to practice to a certain extent combined with the characteristics of short period and low cost of remote sensing.In this study,the inversion effect of shallow water depth or deeper water depth is poor through residual map analysis.And it is concluded that sediment and land have negative effects on the inversion depth while the inversion error in the area where many factors are superimposed increases through the error qualitative analysis.2)In addition,the advantages and disadvantages of different water extraction methods are studied in the area of water area extraction in reservoir area.The single band threshold method and the multi-band spectral relationship method are not suitable for the study area by visual discrimination combined with false color synthesis map,which have poor results in small water bodies,turbid water bodies and mixed pixels with many phenomena of non-water bodies being extracted as water bodies.Moreover,the fast threshold determination method based on the image values of multiple mixed pixels is proposed in the process of threshold determination while the threshold value determined by this method used to extract water information is relatively complete,which can reduce the workload of threshold determination.The extraction results of normalized differential water body index(NDWI),improved normalized differential water body index(MNDWI)while the revised normalized differential water body index(RNDWI)and new water body index(NWI)in the study area were compared.However,the applicability of the four water body index methods was evaluated by using the pseudo-color composite map according to the water characteristics of the study area and the key visual discriminant area of the affected features.With the using the water area extraction method that suitable for the study area,the area of the water area was extracted from 1999 to 2016 while the changes of the area of the study area before and after the establishment of the database were analyzed,indicating that the improved normalized differential water body index method is suitable for the extraction of water area in the study area.The advantage of MNDWI is that it is effective in the shallow water area and the small water area,such as the shallow water area and the small water body area,where the sediment content is large enough to be applied to the water body of this research area very well.However,the study area can be divided into two sections according to the past year's wobble.The 16 km from the dam site to the upstream of the dam is a wandering channel while the 16~40km section from the upstream of the dam is a canyon section.The wandering reach swung from side to side with over 1 km the maximum swinging spoke while the total water area of the canyon section did not change much before the reservoir was built.The main reason of affecting the channel deformation in this period was the influence of the flow characteristics of the curved channel.The variation of water area is mainly due to the dam's blocking and storing upstream water before and after the construction of the reservoir,resulting in the increase of the area of the upper section of the river,which is about 7 times that of the original river course while the area of the lower section of the river does not change much.The main reason for the change of water area in this period is the elevation of water level in front of dam caused by the construction of dam.The increase of water area in the study area will not only effectively improve the ecological environment in the desert confluence area,but also form a unique natural landscape on both sides that integrates with Yellow River,the desert and the wetland,cultivating the rapid development of the local tourism economy.It has a positive effect on the establishment of reservoir capacity curve,reservoir operation and operation,sedimentation in lake reservoir area,sediment researchto study of water depth inversion and area extraction of water area.The foundation for dynamic monitoring of water regime information in reservoir area is laid.The resolution of remote sensing image largely limits accuracy of retrieval of water depth and extraction of water area.With the development of remote sensing technology,its accuracy will continue to improve and promote the application of remote sensing technology in a wider field. |
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