Remote Sensing Monitoring Research On The Change Of The Coastline Of Sheyang River Estuary

The shoreline is a tracing line of sea water and the land formed by years' average spring tides.In muddy coast area,shoreline's position changes which caused by varieties of reasons such as the hydrodynamic action,geological disasters,the rising sea levels suffered from global warming,natural conditions transform,land reclamations,marine engineering constructions and human activities,have a significant impact on coastal ecology,environment and social economy.Comparing to the traditional methods for monitoring shorelines which are not only time-consuming,laborious,but also difficult to operate,the existing technical one,using multi-source remote sensing data to obtain information is very convenient and efficient,has become an important method for muddy coast shoreline's extraction.However,there're some difficulties in accurately extracting shoreline from remote sensing data.In this paper,we select Sheyang estuary's shore,in the middle of Jiangsu coast as the study area.We collect ZY-3,SPOT,Landsat,HJ-1A,HJ-1B and other multi-source remote sensing data,the measured tide data,the typical sectional elevation measurement data as data source and take advantage of GIS and remote sensing combined technology,and adopt different extraction methods to get information about a variety of shoreline phases.Then we conduct space analyses of dynamic changes based on these,aiming at understanding the dynamic changes of erosion and sedimentation about muddy coast,and providing technical and data support to ensure rational development and utilization of space resources at the coastal zone.The main work and achievements are as follows:1.Waterline extractionWe extract instantaneous waterline of the study area automatically by using density split method,unsupervised and supervised classification combined,tri-bands gradient differences water index(TGDWI),and make applicability analysis of three methods.The results show that:for density split method applied to images,their gray values are significantly different,resulting in better interpretation;for images containing high concentration of sediment in coastal water,TGDWI can better differentiate water from land.It's highly important to do pre-processing and post-processing of images which can enhance the continuity of waterline extraction,and improve the degree of automation.2.Artificial shoreline classification and remote sensing extractionArtificial shoreline in the study area is divided into five categories,namely the aquaculture ponds causeway coast,coast ports,constructive causeway coast,river embankment coast and road embankment coast.Given five kinds of artificial shoreline remote sensing interpretation signs,we combine density split method with the method of human and computer interactive interpretation to achieve the extraction of artificial shorelines.3.Based on tide projections and GIS space analysis superimpose shorelineWe use T_Tide to calculate the measured tide sites curve and compute the tide level at imaging time,and the average tide of the spring tide.We estimate the mean high spring tide line,taking it as the natural shoreline of the study area.By base of GIS topological analysis superimposed with natural shoreline and artificial shoreline,we obtain sensing shoreline in study area.4.Characteristics and reasons of Sheyang Estuary shoreline changesWith the base of shoreline extracted from remote sensing data and statistical analyses by GIS,we use the baseline method to calculate the shoreline erosion and deposition distances in the four periods of 2000?2004,2000?2008,2008?2012,2008?2015,as well as shoreline change and types,which mirror Sheyang River characteristics' spatial and temporal variations.The results showed that:(1)In 2000?2015,the total length of shoreline in study area in 2015 is 61.98 km,9.79 km longer than 2000,with an average annual growth of 0.30%;(2)The study area is in a transition area of erosion and deposition,with erosion as dominance in general.In 2000?2015,annual deposition rate is 58.76 m/a and annual erosion rate is 89.89 m/a,scouring and silting magnitude are large;(3)In 2000?2015,artificial coast in the study area has continued to grow,and it has been increased by 33.64 km in 15 years.Aquaculture ponds causeway coast is the main type of artificial coast in artificial shoreline types.According to the reasons of the coastline change,from 2000 to 2015,the shoreline changes in the study area are influenced by both natural factors and human factors.Storm surge is the main natural factor,the main artificial factors are the reclamations for aquaculture and harbor constructions.