Land Subsidence Monitoring In Transition Zone And Its Relationship With Coastline Changes

The land-ocean transitional zone is where the ocean and the land meet.Its environmental evolution is directly related to the living space,quality of life and the sustainable development of society.Therefore,the land-ocean transitional zone has become a research hotspot in recent years.With the continuous development of high intensity,land subsidence of a large-scale has occurred in the land-ocean transitional zone.Time-series InSAR technology has great advantages and broad prospects in deformation monitoring,and has been widely used in surface deformation monitoring in many fields,including the land-ocean transitional zone.This paper uses the improved time series InSAR technology to monitor the land subsidence in the Pearl River Estuary and Hangzhou Bay land-ocean transitional zone.Analyzes the results of subsidence,and discusses the relationship between land subsidence and coastline changes.The specific research contents are as follows:Using the DS-InSAR method based on KS test and eigendecomposition algorithm,the subsidence information of the Pearl River Estuary from 2015 to 2018 were obtained;and using the SBAS-InSAR technology with non-local mean filtering,the subsidence information of the Hangzhou Bay from 2015 to 2019 were obtained.The results suggest that land subsidence in the Pearl River Estuary and Hangzhou Bay is widespread and unevenly distributed with large differences.The northwest and southeast are the main subsidence areas in the Pearl River Estuary,with a maximum sedimentation rate greater than 25 mm/year.The subsidence of Hangzhou Bay is mainly distributed along the north central coastal belt,the reclamation area of tidal flats in the west,the industrial parks of towns in the south and along the road and river,with a maximum sedimentation rate greater than-70 mm/yr.The analysis shows that human activities,such as reclamation,infrastructure construction and industrial park construction,are the main causes of land subsidence.The coastline changes corresponding to SAR images were extracted by remote sensing method,and the relationship between them was analyzed in combination with InSAR settlement results.The results show that the land subsidence in the land-ocean transitional zone is closely related to coastline changes.Land subsidence is obvious in the area where the coastline changes drastically.Changes in coastline are often accompanied by changes in the Submarine topography,which leads to the variation in estuary dynamic field and change in sedimentary pattern,which may lead to the occurrence of land subsidence in areas where the coastline changes.In addition,human reclamation leads to the continuous advance of the coastline to the sea,and the reclamation area contains loose sediments with strong compressibility,which is prone to self-consolidation and cause land subsidence.