Study On Water Extraction And Application In Mianyang City Based On Landsat Image

In this paper,Mianyang City,Sichuan Province was used as the research area,and Landsat images and DEM data were used as data sources.Different methods were used to extract water in the study area,and the most suitable water extraction method for the study area was found through comparison.On the basis of water extraction,the spatial and temporal distribution characteristics of the water body were analyzed,and the spatial distribution pattern of the water body in Mianyang City and the characteristics of the secular variation of the Fujiang and Wudu reservoirs were revealed,with a view to making a scientific reference for the protection and planning of the local water body,which will reduce the blindness of water resource utilization and planning.The main research contents and results of this article are as follows:(1)Through comparison among the application effects of single-band threshold method,water index method(Normalized Difference Water Index(NDWI)?Modified Normalized Difference Water Index(MNDWI)?Enhanced Water Index(EWI),automatic extraction water index method(AWEI)),spectral relationship method,DEM river network extraction and object-oriented methods in the study area,it was found that traditional water extraction methods such as single-band threshold method,water index method,and spectral relationship method were only suitable for water information extraction with flat terrain or open water areas;DEM river network extraction was only suitable for the extraction of river network in mountainous areas,and could not extract water information such as lakes and ponds in mountain areas;the object-oriented extraction method was relatively effective,but the discontinuous phenomenon of mountain rivers can appear;through comparative analysis of the above methods,combined with the characteristics of the complex terrain and broken waters in Mianyang City,an extraction method based on the combination of DEM river network extraction and object-oriented extraction was explored.(2)After repeated experiments,the water extraction segmentation scale of the fused Landsat8 image was set to 30 and the merged scale was set to 60.though analyzing the spectral characteristics of the objects and the combined effect of the spectral band,the water extraction model was established,which,in combination of DEM river network extraction,was used to accurately extract the water information in the study area;the layered random sampling method was used to evaluate the accuracy of the extraction results of several water extraction methods in combination with the confusion matrix and Kappa coefficient;the results show that the method based on the combination of DEM river network extraction and object-oriented method has the highest accuracy;the overall accuracy of the extraction results reaches 91.88%;and the total Kappa coefficient is 0.8374.(3)The spatial analysis function of GIS software was used to analyze the distribution of waters in the study area and the influence of terrain such as slope and elevation on the water distribution,and a hierarchical study of the local water distribution was carried out in combination with the terrain level index and landscape separation index;the results showed that the total landscape separation of Mianyang City was 3.7747,and the topographic index was between[0.236,3.033].The water bodies are densely distributed in areas such as Santai County,Mianyang City,Jiangyou City,Zitong County,Yanting County,and Anzhou District with lower elevation(H?1000m)and flat terrain(S?15°);they are sparsely distributed in areas with high elevations(1000<H?3500)and steep terrain(S>15°)while no water was found;in Pingchuan County and some parts of Beichuan Qiang Autonomous County,in the4th-level topographic index area with elevations above 3500m.(4)By comparing the water extraction results of the mother river Fujiang in Mianyang City in 2009 and 2018,it was concluded that Mianyang City,a pilot city of a water-saving society,has better water resources protection,and in the process of urban development,the water shortage caused by the uneven distribution of water resources in Mianyang City was partly relieved by the Wudu Reservoir;during the ten years from2009 to 2018,the net increase of waters of the Fujiang River is 580.31hm~2,of which171.73hm~2 was transferred out and 751.84hm~2 was transferred in.