Research On Land Subsidence Monitoring In Xi’an With InSAR Technology And High Resolution Data

Interferometric Synthetic Aperture Radar(InSAR) is a new space-to-earth observing technology emerged in the late sixties of the twentieth century and gradually developed since then. Because of its wide range of measurement, high spatial resolution, sustainable monitoring, and high efficiency, it has become a widely used method of subsidence measurement. It can provide more effective reference data for subsidence evaluating and the determination of relevant control measures than the traditional geotechnical survey and conventional geodetic survey(such as leveling and GPS).In recent years, InSAR technology is developing towards higher resolution and higher precision just like other remote sensing technologies. A series of high resolution satellites‘ launch, high resolution DEM acquisition means‘ development provides a vast source of data for radar interferometry, as well as leads to the expectation of better measurement results.For this purpose, this paper carried out a series of research and analysis on the application of high resolution SAR data and DEM data in urban area land subsidence monitoring, based on InSAR technology‘s hardware development, and achieved the following results:1. The DEM error problem in high resolution SAR data processing is discussed. Topographic phase simulation and correction method using 20 m resolution DSM data obtained through Mapping Satellite is tested, and it is found that the SRTM DEM is more suitable for conventional D-InSAR to simulate and correct topographic phase as external elevation data. For the use of high resolution DSM data, the corresponding coregistration, geocoding and other models and methods should be studied, otherwise, the coregistration and geocoding error will introduce new DEM error.2. The main technical parameters of StaMPS technology were analyzed, and we came to a conclusion that the selection of ―weed_standard_dev‖ should seek a balance among the PS point number, precision, and the computational efficiency, and take into account the regional deformation characteristics, and the parameter ―unwrap_grid_size‖ should be set similar to the image pixel size and external DEM resolution. Then the values of other important parameters in the process of TerraSAR-X data processing are suggested.3. Take the land deformation monitoring of ―Yuhuazhai‖, the subsidence center of Xi‘an city as an example, PS-InSAR monitoring technology is studied. PS points with stable scattering characteristics are selected by amplitude dispersion thresholding and interferometric phase analysis, which ensured the reliability of phase information. According to the temporal and spatial characteristics of the error term phase, look-angle error, atmosphere phase and other error terms are evaluated and removed by filtering and iterative estimation. The accuracy of the unwrapped phase is guaranteed by pre-filtering before phase unwrapping, and the true value of the phase is recovered by 3D phase unwrapping method. Finally, the annual average subsidence rate of the region is acquired.4. The ground subsidence of Xi’an city was monitored using PS-SBAS technology, and the annual average rate and deformation time series result of Xi‘an land subsidence is gained. The accuracy of InSAR monitoring result is verified by GPS and leveling data. The correctness of the interference measurement results is verified preliminarily, and the annual rate accuracy of the deformation is of the millimeter grade.