| The Jiangsu coastline possesses a unique underwater radiating sandbar,with tidal flat resources accounting for a quarter of the country’s total.Due to the combined influence of natural factors and human economic activities,the ecological environment of the Jiangsu coast is facing unprecedented challenges.In order to understand and protect the coastal zone,a comprehensive understanding of coastal information is needed,and research on the coastline and intertidal zone can provide a basis for comprehensively understanding the process of coastal zone changes and the transformation of resource environments.The coastline represents the evolution of the resource and environmental ecosystem of the coastal zone under the influence of climate change,sea level change,and land-sea interaction,and is a concentrated manifestation of human impact and changes to the natural environment.The morphology and terrain changes of the intertidal zone are directly related to the changes in the coastline.The identification and analysis of the characteristics and changes of the coastline and intertidal zone help to reveal the process of land-sea interaction.Based on ground observations,drone measurements,and multi-source remote sensing data,this study analyzed the spectral characteristics of typical landforms to address the water content of the muddy tidal flats and the large difference in suspended sediment concentration near the shore in Jiangsu.It constructed an algorithm that can separate water,land and tidal flats in any tidal condition(exposed or submerged tidal flats)for extracting the coastline.To capture the dynamic changes of the intertidal zone,a change detection method is employed to identify its morphology.The use of spaceborne lidar replaces in-situ elevation observations,and a random forest feature selection method is utilized to identify the topography of the intertidal zone.Through the analysis of the coastline,intertidal zone morphology,and topographic changes in Jiangsu,the study reveals the characteristics of coastal zone changes and explores the processes and patterns of coastal zone transition,providing a basis for the study of coastal zone resource development and ecological conservation.The conclusions obtained are as follows:1)A mudflat coastline extraction algorithm was constructed.In this study,a new coastline extraction method was proposed specifically for muddy coastlines in Jiangsu.The method combines the Improved Spectral Water Index(IWI)with the Otsu algorithm.The extracted coastlines achieved an accuracy of over 81% when compared to validation shorelines under three different scenarios,and the accuracy within a three-pixel range exceeded 91%.Apart from IWI,the response of various indices to water bodies varied significantly under different tidal and sediment concentration conditions.The sensitivity of an index can be defined as its susceptibility to tidal and turbidity effects when identifying water bodies.The sensitivity,ranked from low to high,can be ordered as follows: IWI,MNDWI(the modified normalized difference water index),RNDWI(revised normalized difference water index),EWI(enhanced water index),AWEI(automated water extraction index),and NDWI(normalized difference water index).The validation results of accuracy are ranked in the opposite order to the sensitivity ranking.2)The morphology and changes of the intertidal zone in Jiangsu were identified.In this study,taking advantage of the low sensitivity of the Improved Spectral Water Index(IWI)to suspended sediment water bodies,the intertidal zones extracted based on the IWI index and the coefficient of variation(CV)for the years 1990,2000,2010,and 2022 were found to be close to existing research results.The vegetation area of the intertidal zone extracted based on the maximum Normalized Difference Vegetation Index(NDVI)values were compared to the UAV images,and the accuracy was high with an average error of 0.12.Analysis of the morphological changes in the intertidal zone revealed that,overall,the intertidal zone in Jiangsu is gradually accreting towards the sea with a decreasing area,but the rate of decrease is slowing down,with the change rate decreasing from 78.6 km~2/10 years to 23.3 km~2/10 years.The non-vegetation area of the intertidal zone showed a continuous decreasing trend from 1990 to 2022,with a total reduction of 1313.84 km~2,mainly occurring in the coastal areas of Yancheng and Nantong.The radiation sandbar region showed a growth trend,but the magnitude was much smaller than the overall decreasing trend.From 1990 to 2000,the vegetation area along the Jiangsu coast decreased by a total of 204.57 km~2,primarily in the northern and central regions of Jiangsu,with a slight increase in the southern region.From 2000 to 2010,the vegetation area decreased by a total of 161.82 km~2,with a slight increase in the northern region of Jiangsu and a predominant decreasing trend in the central and southern regions.From 2010 to 2022,the vegetation area along the coast remained relatively stable,with decreases primarily occurring in the northern region and increases primarily occurring in the central region.3)The terrain and changes of the intertidal zone in Jiangsu were identified.In this study,ICESat-2 data was used instead of in-situ elevation data,and a terrain recognition method for intertidal zone was constructed based on random forest feature selection.Feature importance analysis revealed that the added features of TP(time phase)and NDWI(normalized difference water index)in the random forest were highly important,and the inclusion of these features improved the accuracy of the model.The terrain recognition results of the intertidal zone were compared with UAV Li DAR data,and the accuracy of the mudflat terrain was 0.20 m.Based on slope and coefficient of variation(CV)analysis of the terrain changes over multiple years,the results indicate that the intertidal zone topography in Jiangsu experienced minor and gradual accretion from 2019 to 2022.The east-west variation of the intertidal zone topography(perpendicular to the shoreline)showed similar patterns,with an increasing magnitude of topographical changes.However,the north-south variation exhibited less similarity in terms of topographical changes.The area with the fastest growth rate of intertidal zone terrain is in the southwest of the radiation shoal and the island dam survey at the mouth of the Sheyang River,while the area with the fastest decline rate is mainly in the middle of the radiation shoal.There is small change in terrain from Doulong Port to Liangduo Dam,while overall the terrain from Jianggang Port to Changsha Port has a slight downward trend.The suspended sediment concentration in the Jiangsu Sea area is high,and the exchange of land and sea materials is frequent due to tidal effects.From the perspective of the vertical shoreline direction,the sedimentation trend is greater in the area near the high tide line.This study presents methods for coastline extraction,intertidal zone morphology identification,and topography recognition in Jiangsu.The research findings contribute to the accurate quantification of the spatiotemporal evolution characteristics of the Jiangsu coastal zone.They provide a basis for the integrated spatial monitoring and rational utilization and management of the Jiangsu coastal zone. |
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