Ecological Flow Assessment Method Based On Remote Sensing Image Automatic Extraction Of River Water Surface Width

Global warming and the rapid development of the global economy have increased the evaporation of river water or was used in large quantities,resulting in a decrease in global river runoff.China also proposed in the "Water Pollution Prevention and Control Action Plan" to ensure the ecological flow and restore the river ecology.In the supervision of ecological flow,how to scientifically determine the ecological flow and how to evaluate whether a certain river currently meets the standard is an urgent problem that needs to be solved.Satellite remote sensing is not limited to limited ground monitoring site data,and has the advantages of rapid,large-scale,and dynamic monitoring.This paper selects five representative rivers with typical cross-sections as the study area,namely the Tangmazhai cross-section of the Taizi River,the Huayuankou cross-section of the Yellow River,the Zhoukou cross-section of the Shaying River,the Punan cross-section of the Jiulong River,and Sanggan which can represent different river types in different basins.Section of Heshixiali.Obtain the hydrological data of the study area,as well as the Gao Fen series(GF1,GF1B,GF1C,GF1D,GF2 and GF6),Sentinel-2,Landsat series of remote sensing cloudless images from January 2018 to December 2018.This article realizes remote sensing The method of automatically extracting the water surface width of the river section,and batch-processed cloud-free images from January 2018 to December2018,obtained the temporal and spatial changes of the water surface width in the study area over time,and found that it can be obtained on a monthly basis The width of the water surface.At the same time,a method is proposed to evaluate whether the ecological flow is up to standard using the water surface width index extracted by remote sensing: the relationship constructed by historical hydrological data is used to obtain the monthly minimum river water surface width of the section,and the water surface width extracted by remote sensing is compared with the minimum water surface width.The width of the water surface of the river is used to judge whether the ecological flow meets the standard,and then calculate the ecological flow guarantee rate of the section within one year.The main research results obtained in this paper are:(1)According to the classification of different small and medium-sized rivers,a method for automatically extracting the water surface width of the river section with strong applicability is realized by remote sensing,and a set of operational processing procedures is formed.This method has good accuracy,and the error of extracting water surface width is within 1 pixel.At the same time,it is analyzed that this method has good fault tolerance for flares,thin ice,and thin cloud shadows,and will not affect the extraction of river water surface width.effect.(2)In the case of extreme lack of hydrological data,a model based on high-resolution images that automatically extracts the width of the water surface and solves the minimum ecological flow is proposed,and demonstration applications are carried out on five typical sections,forming a model suitable for non-rectangular sections Minimum water surface width-minimum water level-minimum ecological flow monitoring technology system,and at the same time,explore the scope of application of this method in major cross-section rivers across the country.(3)Monitoring and evaluating the ecological flow guarantee degree of a certain river section through automatic batch extraction of water surface width.It is found that in 2018,except for the Yellow River Huayuankou section with a rectangular cross-section,which cannot be evaluated for the degree of ecological flow protection,the protection rate of the Tangmazhai section of the Taizi River is 100%,the Zhoukou section of the Shaying River,the Punan section of the Jiulong River,and the Shixia of the Sanggan River.The guarantee rate of the cross-section in all areas has not reached 100%.It is necessary to strengthen the remote sensing monitoring of the river where the cross-section is located,and to track the ecological flow.