Research On Surface Deformation In Hohhot Based On Sentinel-1 Data

Surface deformation is a geological phenomenon of regional ground height change caused by geological and human activities.With the deepening of urbanization in Hohhot,the influence of surface deformation on people’s daily life such as transportation is becoming more and more significant.The traditional methods of land subsidence monitoring include GPS measurement and trigonometric leveling.Although the accuracy is high,it is time-consuming and costly to monitor large areas.The synthetic aperture radar differential interference technology uses the relationship between the phase and space of the radar wave in the two observations to extract the three-dimensional deformation information of the surface.Because of its high precision,wide range,all-weather and low cost,it has become an important method for urban surface deformation detection.Due to the various types of urban features,complex coherence environment,and various causes of deformation,the application of synthetic aperture radar differential interferometry and its derivative technology is limited to a certain extent.How to improve the applicability of differential interferometry in urban areas has become a current research hotspot.Based on the traditional differential interference technology,this paper analyzes and optimizes its workflow,and applies it to the actual situation of Hohhot.The main contents include:1.Aiming at the application of traditional synthetic aperture radar differential interferometry in complex environment,it is easy to regard the coherence change caused by construction as noise and participate in filtering.At the same time,the error is introduced into the surrounding area,which leads to the magnitude error of deformation measurement results in the construction area and the loss of deformation details in the surrounding area.In this paper,the sum ratio of contrast saliency and coherence is adjusted by the contrast consistency peak of radar intensity image,which is used as the basis for adjusting the size of adaptive window.An improved adaptive window offset tracking method is proposed to obtain more reliable deformation results.Based on this result,the phase filtering quality map is supplemented and the construction area is removed in the filtering stage.The method proposed in this paper is evaluated in the construction area and stable area composed of simulated data,Sentinel-1 satellite data and field survey data.The experimental results show that the improved method has better anti-noise ability than the traditional method,and the accuracy is improved by about 12%.The supplementary quality map can effectively remove the large deformation area to prevent over filtering while ensuring the filtering quality,and achieve better filtering effect.2.Aiming at the viaduct area with small absolute value of deformation but sensitive to radial deformation gradient,this paper inverts the deformation of viaduct based on small baseline set interferometric synthetic aperture radar technology,calculates the deformation gradient of viaduct path,and extracts the severe deformation area of urban viaduct.Taking three viaducts with large traffic flow in Hohhot as the research object,the deformation results of the study area from July 2020 to September 2021 were obtained.Combined with the inversion results and field investigation,the causes of deformation were analyzed.The results show that there are 10 severe deformation areas in the three viaducts.The main causes of deformation include soil erosion or urban waterlogging caused by rainfall,surface construction and rail transit operation.