| Under the background of the intensified urbanization in our country,the demand for urban construction land continues to increase,and the existing land scale can not meet the needs of high-quality urban development.Therefore," cutting mountains and building cities"," filling ditches to create land" have become one of the feasible solutions to the development of land space currently.The "Flat Mountain Valley filling" project in Yan ’an New District has changed the geomorphic form and structure of the loess gully area,resulting in numerous high-fill areas.Meanwhile,due to the various geomorphic types,the terrain is uneven and the thickness of the loess varies,coupled with the adverse geological effects of strong site collapsibility,it is bound to cause different degrees of land subsidence.Synthetic Aperture Radar Interferometry(InSAR)can be used to conduct large area,allday,all-weather and centimeter-level or even millimeter-level high-precision monitoring of the region.In this paper,multi-source remote sensing technology based on time-series InSAR technology is used to monitor the long-term sequence of surface deformation information before and after the construction of Yan’an New District in detail,and GACOS data is introduced to correct the atmospheric error of InSAR process,so as to improve the monitoring accuracy of surface deformation.Using optical remote sensing image classification technology to explore the relationship between land use type and land subsidence,finally summarized and analyzed the influence of different factors on the land subsidence phenomenon in the study area.The main work of this paper are as follows:(1)To solve the problem of atmospheric influence in InSAR processing,GAOCS products are used in this paper for atmospheric correction.The test shows that the standard deviation of atmospheric phase and the standard deviation of average sedimentation rate are reduced after atmospheric correction in the whole study area.Therefore,atmospheric correction based on GACOS data is effective,and the overall accuracy can be improved by15%-20%.(2)PS-InSAR and SBAS-InSAR technologies were used to monitor the land subsidence in Yan ’an New District.The results of InSAR monitoring of two different time series showed that the land subsidence in Yan ’an New District was serious and unevenly distributed,with three large linear distribution settlement funnels and four small settlement funnels gathering areas.The areas with serious subsiding phenomena are Qiao Gou area,Gao Jia Gou area and the eastern boundary slope protection of the new District.The surface deformation rate of Yan’an New Area ranges from-72mm/yr to 29mm/yr during the whole study period.Since 2015,the spatial location of surface subsidence in Yan ’an New Area has gradually extended toward the northeast.The distribution area of subsidence area has shown an increasing trend in the early stage,and then has slowly decreased since 2018.The maximum subsidence rate and average subsidence rate in the three time periods decreased gradually with time.The maximum subsidence rate decreased from 71.94mm/yr in 2015-2018 to 53.68mm/yr in 2019-2022,and the average annual subsidence rate in the study area decreased from 5.81mm/yr to3.42mm/yr.Since 2018,with the reduction of surface engineering,the settlement rate began to slow down gradually and the settlement phenomenon improved,which indicates that the settlement in the study area is closely related to engineering construction.(3)In order to analyze and study the relationship between land subsidence,ground construction,land cover and land use change in Yan ’an New District,this paper uses Landsat remote sensing image to classify the land surface,and introduces confusion matrix to verify the accuracy of classification results.The results show that: Among the four main land use types(mountain,green land,residential land,and construction land),the land subsidence of mountain is relatively light,and the land subsidence of the other three types has different degrees of severity.The settlement of residential land is the most serious and the area of settlement is the widest.The land use transfer matrix was constructed,and the corresponding analysis method was applied to detect the land settlement characteristics of different land use transfer situations.It was concluded that the seventh type of land use transfer(engineering construction land → residential land)had a strong correlation with the highest level of land settlement.The cumulative settlement in most areas was more than 200 mm,and the settlement phenomenon was the most serious.(4)Based on the InSAR subsidence monitoring data and the classification results of remote sensing images,the subsidence genetic mechanism of loess geological types was studied.As the loess in Yan ’an New District has strong collapsibility characteristics,largescale land development and urban construction lead to the destruction of the original structure of the loess,the reduction of structural strength,and the strength of cementation and connection between particles are significantly weakened.Meanwhile,affected by high filling projects,the settlement rate of Yan ’an New Area increases significantly with the increase of the thickness of the filled loess.The land settlement of different degree after land construction is largely controlled by the filling and compaction process of loess with different thickness. |
