Remote Sensing Monitoring Of Tidal Flat Changes Near The Radial Sand Ridges In Jiangsu Coastal Zone

The dynamic change rule of tidal flat can be obtained macroscopically with remote sensing method.However,the complex topography,frequent erosion and siltation and the asynchronism of tidal level in the Radial Sand Ridges(RSR)of Jiangsu Province have increased the difficulty of large-scale remote sensing monitoring of tidal flat.In this study,the object-oriented method was used to construct the classification rules to realize the batch extraction of waterlines,and the tidal flat boundary was determined based on the outermost boundary of the waterlines sequence.Subsequently,the extent of tidal flats from 1985 to 2017 in the study area were extracted and the statistical analysis of temporal and spatial variation of tidal flats was implemented.Meanwhile,based on the method of post-classification comparison,erosion and deposition characteristics of tidal flats were studied.The main conclusions were as follows:(1)From 1985 to 2017,the tidal flat stocks in the study area showed a decreasing trend.In 32 years,the area decreased by about 1 600.25 km~2,a decrease of 39.15%.The area of tidal flat reduced by reclamation accounted for 87.70%of the total area of tidal flat reduced.After 2005,the main land types of reclaimed tidal flats changed from saltmarshes to barren mudflat.(2)Obvious differences in tidal flat variation characteristics among different sections of the RSR were found.Tidal flats in the north bank were found with the greatest change.The decrease area of tidal flat was 69.51%,accounting for 52.65%of the total reduction area of tidal flat in the RSR.The reduction of 87.24%of the change area of tidal flats was caused by reclamation.Tidal flat reclaimed was the main reason for the erosion characteristics of the tidal flat in the northern bank.The inner part of the RSR was the area with the largest tidal flat stock and the smallest change.This region showed the alternating characteristics of silting and erosion,which was mainly reflected by ocean hydrodynamics.The area of tidal flat in the middle bank decreased by 38.92%,accounting for 25.20%of the total reduction area of the tidal flat in radial sandbanks.The change of low tide flat in the middle bank was characterized by alternation of silting and erosion,which was affected by both reclamation and marine dynamic factors.The decrease area of tidal flat in the south bank was 62.60%,accounting for 25.20%of the total reduction area of tidal flat in the RSR,next only to the north bank.Due to reclamation,78.29%of the tidal flat area in the south bank was lost.Under the combined action of reclamation and marine hydrodynamics,artificial shoreline in part of the south bank was already close to the low tide line,and the erosion characteristic of tidal flat was obvious.In summary,by using multi-source satellite images data,the extraction method and temporal-spatial dynamic changes of tidal flat were studied,which could improve the extraction methods of tidal flat and promote the scientific planning and sustainable development of the tidal flat resources in the RSR region of Jiangsu Province.