Abstract
Abstract. Layover occurs as a consequence of the slant range scale distortion in Synthetic Aperture Radar (SAR) data and it is commonly observed in the images acquired over urban areas. There may be two or more Persistent Scatterers (PSs) in one pixel. Moreover, these PSs do not have amplitude stability and spatial coherence. The threshold method used in the Persistent Scatterer Interferometric (PSI) SAR technique cannot identify the PS with two scatterers in urban, the accuracy of urban land subsidence is reduced. To solve this problem, we used Fast Fourier Transform (FFT) convert PSs in frequency domain during PS identification process of PSI, by observing their characteristics in the frequency domain, the layover scatterers can be identified and separated. The results of simulation experiment show that by analyzing the peak distribution characteristics of PSs in the elevation direction under the relatively even space baseline, PSI with FFT can identify single scatterers and layover scatterers. After separating the layover scatterers, the reliability of PSs identification are improved. For the real data experiment, we use 31 Sentinel-1A IW images covering Beijing from 2014 to 2016 as data sources. The results show that the proposed method can effectively identify layover scatterers which cannot be identified by the threshold method in urban, reducing the effect of layover scatterers, improving the accuracy of urban land subsidence monitoring.
Highlights
Land subsidence is a geological phenomenon caused by natural physical and chemical processes or by human activities such as over-exploitation of subsurface fluids and solid minerals and construction engineering primarily in urban
The basic model is as follows Eq (1): φx,i = φdef,x,i + φa,x,i + φorb,x,i + φε,x,i + nx,i where φx,i is the phase of the xth Persistent Scatterers (PSs) point in the ith interferogram, φdef,x,i is the phase related to the deformation along Line of Sight (LOS), φa,x,i is the phase caused by the atmospheric phase, φorb,x,i is the orbit error phase, φε,x,i is DEM error phase, nx,i is the thermal noise of the system
The Persistent Scatterer Interferometric (PSI) and the Fast Fourier Transform (FFT)+PSI are applied to Sentinel-1A IW images from October 2014 to September 2016 respectively, and the land subsidence information in Beijing is obtained, as shown in Fig. 5
Summary
Land subsidence is a geological phenomenon caused by natural physical and chemical processes or by human activities such as over-exploitation of subsurface fluids and solid minerals and construction engineering primarily in urban. Land subsidence has been discovered in more than 150 regions and cities over the world. Beijing is one of the areas where land subsidence is relatively serious in China (Chen et al., 2015). Excessive exploitation of groundwater is the main cause of land subsidence in Beijing (Wang et al, 2005). Five large land subsidence areas have been formed in Changping District, Chaoyang District, Shunyi District and Tongzhou District. The potential threatens of urban land subsidence mainly include damage to buildings, railways, roads and bridges. To ensure sustainable urban development and to improve the residental environment and safety
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