Abstract
Identifying Persistent Scatterers (PSs) is one of the key processing steps of the Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) technique. The number, density, and reliability of identified PSs directly affect the monitoring accuracy of land subsidence, especially in higher density urban environments. As a result of the side-looking viewing geometry of SAR, the layover effect poses a major challenge to the PS identification. This research proposes joint modeling of the PS-InSAR technique and RELAX algorithm for SAR tomography (PS-InSAR+RELAX) to detect single and double scatterers and to improve the identification and reliability of PSs. It has been demonstrated that RELAX improves separation of the scatterers when compared to two other spectral analysis methods for SAR tomography, Beam-Forming (BF) and Singular Value Decomposition (SVD). RELAX exhibits the least noise when the number of baseline changes from 15 to 30, and it can separate the scatterers at a lower Normal-Slant-Range (NSR) height than the two other methods. As RELAX can better identify, separate, and then filter out layover scatterers, the number and density of PSs identified by PS-InSAR+RELAX is reduced and visually simplified, suggesting that the method can effectively reduce the influence of the layover effect on the PS identification. Also, the PSs identified by PS-InSAR+RELAX are more coherent than those identified by the traditional PS-InSAR technique. The proposed technique has been applied to Sentinel-1A data acquired from 2014 to 2016, to monitor land subsidence in the city of Beijing, China. When evaluated against the leveling measurements, PS-InSAR+RELAX performs better than the traditional PS-InSAR technique, with the correlation coefficients (r) of r = 0.98 and r = 0.95, respectively.
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 in synergy with construction engineering in urban areas
We propose an innovative joint approach in which the Persistent Scatterers (PSs)-Interferometric Synthetic Aperture Radar (InSAR) technique is combined with the spectral analysis method RELAX (PS-InSAR+RELAX) to improve the PS identification and, the accuracy of land subsidence monitoring
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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 in synergy with construction engineering in urban areas. To ensure sustainable urban development and the safety of people’s lives and property, land subsidence monitoring has become an ongoing process in Beijing, China. Land subsidence monitoring relied on conventional methods, which were point-based and time-consuming approaches. With the development of the Interferometric Synthetic Aperture Radar (InSAR) techniques and their capabilities to measure large-scale ground movement with an accuracy of millimeters, land subsidence monitoring has become advanced and convenient. Various PS-InSAR based methods have been developed and successfully used in urban areas, as high-rise buildings can be identified as PSs. The number, density, and reliability of identified PSs improve the deformation time series and deformation velocity estimated over the identified PSs and improve the accuracy of displacement measurements [5].
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