Research On Surface Deformation Monitoring And Related Factors Of Typical Cities In The Yangtze River Delta

The Yangtze River Delta,as a typical coastal zone with the most active economic development in China,is experiencing urban expansion at an unprecedented speed and scale.However,uncontrolled urban expansion will have certain impacts on society,ecology and economy.The coastal zone is affected by the interaction of the ocean,land and rivers at the same time,and the ecological environment is very fragile.In addition,human activities,including infrastructure construction,underground resource extraction,soft soil consolidation and compaction,exacerbated surface deformation in the region,threatening the ecological environment and human production and life.Therefore,it is of great significance to reveal the spatiotemporal distribution and deformation mechanism of surface deformation in the Yangtze River Delta region in a timely and accurate manner.Synthetic Aperture Radar(SAR)is a high-resolution imaging radar.As an active microwave sensor,it has the ability to obtain data all-weather and all-day,and the data quality is not affected by weather conditions and cloud cover.SAR can obtain highresolution radar images similar to optical images even under complex weather conditions.Interferometric SAR(InSAR)can extract vertical surface deformation variables by using the coherent information of multi-phase complex radar images of remote sensing satellites.Two common long-term surface deformation monitoring techniques include the Permanent Scatterers(PS)method and the Small Baseline Subsets(SBAS)method.In view of the short monitoring period and small scope of existing surface deformation research,and the lack of quantitative research on the driving factors of surface deformation,this paper takes the Yangtze River Delta as the research area and Sentinel-1 image as the data source,combining PS-InSAR and SBAS-InSAR to extract ground deformation information;based on time series ground deformation monitoring and series spatial pattern analysis methods to reveal the evolution law of surface deformation;use generalized additive model(GAM)and grey relational analysis(GRA)to Identify the driving factors of surface deformation;and further expand the application of InSAR technology in surface deformation.The main conclusions of this paper are as follows:(1)PS-InSAR and SBAS-InSAR technology can be combined with each other to improve surface deformation monitoring and detection capabilities.The PS points obtained based on the PS-InSAR are basically located in the region under deformation and with high coherence.The PS points with sufficient number and uniform density,which can meet the selection requirements of ground control points(GCP)in SBAS.The standard deviation of the average deformation rate accuracy is basically within 2mm/year,and the standard deviation of the accuracy of Hangzhou and Jiaxing is even less than1mm/year.(2)Typical cities in the Yangtze River Delta have both subsidence and uplift in 2019-2020,and the overall distribution is normal.The rate and scope of regional subsidence are basically larger than the rate and scope of regional uplift,though there are certain regional differences in specific cities.Many cities show a state of overall stable or slight subsidence and partial uplift,such as Shanghai,Yangzhou,Jiaxing,Huzhou,Shaoxing,Hefei,Wuhu,Ma’anshan and Wuxi.Some cities have areas with significant uplift rates,such as Zhenjiang,Wuxi and Changzhou.(3)The trend of the cumulative amount of time series deformation of each typical city in the Yangtze River Delta from 2019 to 2020 cannot be fully expressed by the same mathematical expression.Some urban areas are linearly deformed,such as subsidence areas in Nanjing and Taizhou,and uplift areas in Hefei and Suzhou.In addition,there may be a time node after which the cumulative deformation volume trend changes.For example,in the uplift interest area selected by Huzhou,its cumulative deformation curve first continued to decline to July 2019,then gradually increased to July of the following year,and then continued to decline.(4)The deformation field of the Yangtze River Delta has a high degree of spatial autocorrelation and is strongly concentrated.The values of Global Moran’s I for all cities are positive,with the values of z-score are above 2.58.The various clusters of Local Moran’s I show that the centers of Hangzhou,Jiaxing,Changzhou and Ningbo,have relatively large deformation areas,of which the subsidence area and the uplift area each account for about 1/3 of the central city.(5)There are regional differences in the correlation factors of deformation field,and the correlation between subsidence and uplift is not exactly the same.In this paper,the correlation between subsidence and uplift of each factor is ranked with the help of GAM and GRA methods,and the strong correlation is obtained,because it is socio-economic factor and geographical environment factor.