Abstract
Abstract. Synthetic aperture radar (SAR) is an effective means of monitoring land subsidence, and differential interferometric SAR (DInSAR) is commonly used to acquire the necessary data. In particular, persistent scatterer interferometry (PSI) can be used to measure land subsidence accurately over a wide area from multi-temporal SAR images. However, the estimated displacement is obtained only in the radar line-of-sight (LOS) direction, making it necessary to develop a method for measuring three-dimensional displacements by combining multidirectional observations. Therefore, we propose herein a method for estimating three-dimensional displacement velocities by combining the results from PSI and geodetic deformation measurements, namely, Global Positioning System and leveling data. We apply the least-squares method to Kansai International Airport in Japan by using 13 ALOS-2/PALSAR-2 ascending images from 2014 to 2018 and 17 ALOS-2/PALSAR-2 descending images from 2015 to 2018. In validation, the rootmean- square errors are 14, 16, and 14 mm/year for the east–west, north–south, and vertical components, respectively, showing that combining PSI results and geodetic deformation measurements is effective for monitoring land subsidence.
Highlights
Land subsidence is a serious problem globally because of climate change and ground-water extraction, making inexpensive techniques for monitoring land subsidence highly necessary
The persistent scatterer interferometry (PSI) estimated displacement was obtained in the LOS direction only; to compare it with the leveling data we used the displacement divided by the cosine of the incident zenith angle of the radar as the vertical displacement, assuming that the horizontal displacement was zero
The accuracy of the ascending PSI compared with the leveling data was a root-mean-square error (RMSE) of 22 mm/year, and the accuracy of the descending PSI was an RMSE of 18 mm/year
Summary
Land subsidence is a serious problem globally because of climate change and ground-water extraction, making inexpensive techniques for monitoring land subsidence highly necessary. We are interested in monitoring land subsidence in and around civil infrastructure such as airports built on landfill. Synthetic aperture radar (SAR) is an effective means of doing so, and differential interferometric SAR (DInSAR) can be used to measure land subsidence over a wide area. Persistent scatterer interferometry (PSI) (Ferretti et al, 2000) extracts and exploits stable scatterers, known as persistent or permanent scatterers (PSs), to generate accurate land-subsidence maps by excluding erroneous components and extracting the actual land-subsidence components from multi-temporal SAR images. That assumption may not be applicable to civil infrastructure that is prone to three-dimensional (3D) displacement. A method is needed for measuring 3D displacements by combining multidirectional observations
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