Temporal And Spatial Differentiation Of Dynamic Evolution Of Tidal Network In Central Jiangsu Coastal Areas Supported By Multi-source Long-term Sequence Remote Sensing Images

As the most active geomorphic unit on the tidal flat,the tidal creek is the main channel for controlling the exchange of matter and energy between tidal flats,salt marshes and the outer seas.The central coastal area of Jiangsu is the region with the most abundant tidal flat resources in China.The tidal creeks on the flat is fully developed and frequently changed.Under the combined effects of periodic tidal erosion,storm surge disasters,human activities and sea level rise,the tidal network grows rapidly,the shape of the tidal creek is sensitive and variable,which poses a certain threat to the comprehensive utilization of seawater such as coastal dams,sea gates,reclamation areas and artificial breeding.Under the background of intensified human activities,it is necessary to clarify the dynamic evolution law of tidal network and the tidal flat stability in temporal and spatial differentiation in the coastal areas of central Jiangsu,which is especially necessary for the future coastal zone construction in Jiangsu.Based on remote sensing technology and GIS technology,this research using Sentinel-2A,Landsat-8 OLI and HJ-1A/B and other remote sensing image data,constructed a dataset of the tidal ditch system in the central Jiangsu coast and the dynamic evolution process of the tidal network and the time and space differentiation of tidal flat are analyzed.The main contents and conclusions of the study are as follows:(1)Tidal network extraction method.Based on multi-source long-term sequence remote sensing image data(Sentinel-2A,Landsat-8 OLI,GF-1 and HJ-1A/B),the support vector machine supervised classification algorithm and the fuzzy C-means classification and multi-scale Hessian matrix level set segmentation algorithm are used to extract the tidal channel system from the collected optical images.Constructing the Data Collection of the tidal network in the Central Coast of Jiangsu Province in 2009-2018.The data set is composed of tidal network extraction results based on 45 scene HJ-1A/B image data,6 scenes Sentinel-2A image data,12 scenes GF-1 image data and 8 scenes Landsat-8 OLI image data.(2)Calculation of average displacement of tidal network and temporal evolution of tidal network.Introducing a Buffer-Overlay-Statistics algorithm to calculate the average displacement of the tidal network in the region.From the two scales of interannual and seasonal changes,the temporal development trend of the tidal channel system in the region is analyzed,and studied the response law of the tidal system to cofferdam activity.The results show that during the period of 2009-2018,the offset distance of the tidal network in the study area showed a downward trend,and its displacement is greatly affected by the cofferdam activity.When the cofferdam activity is stopped,the displacement of the tidal network in the area decreases and tends to stabilize.In addition,the tidal network in the study area has a large displacement from May to November of each year,with an average displacement of 440 m.The displacement is small in January to April and December,and the average offset is less than 200m.(3)Spatial evolution of tidal network and tidal flat stability.Through the oscillation of the local tidal network and the evolution of each main channel,the evolution law of the tidal channel system in the region is analyzed.Revealing the general spatial differentiation of tidal channel system by frequency superposition analysis of tidal data sets,and the stability of the tidal flat is divided by the activity degree of the tidal network in the region.The results show that the oscillation of the tidal network in the region is zonal.In general,the overall displacement of the tidal creek in the northwestern part of Tiaozini is the largest,followed by the southwest area of Tiaozini,and the displacement of the eastern part of Tiaozini is smaller.In the tidal flat area near the south of Tiaozini,the average displacement of the tidal creek is the smallest,and the tidal network is the most stable.In the region,Xi Dagang has the largest swing and has a clear trend of moving to the southeast,the swing of the SiShenggang is second,and the law of the swing in the channel is different.Followed by the Dongdagang channel,its swing is small in space,but it has changed a lot in shape,the Gao Nigang channel is relatively stable,but its channel width is constantly expanding.According to the results of the tidal network superposition in 2009-2018,the research divide the entire study area into stable tidal flats,basic stable tidal flats and unstable tidal flats,the proportion of this three types of tidal flats to the total tidal flat area is 28.26%,14.51%and 57.23%.