Abstract
Excavation of a subway station and rail crossover cavern in downtown Los Angeles, California, USA, induced over 1.8 cm of surface settlement between June 2018 and February 2019 as measured by a ground-based monitoring system. Point measurements of surface deformation above the excavation were extracted by applying Interferometric Synthetic Aperture Radar (InSAR) time-series analyses to data from multiple sensors with different wavelengths. These sensors include C-band Sentinel-1, X-band COSMO-SkyMed, and L-band Uninhabited Aerial Vehicle SAR (UAVSAR). The InSAR time-series point measurements were interpolated to continuous distribution surfaces, weighted by distance, and entered into the Minimum-Acceleration (MinA) algorithm to calculate 3D displacement values. This dataset, composed of satellite and airborne SAR data from X, C, and L band sensors, revealed previously unidentified deformation surrounding the 2nd Street and Broadway Subway Station and the adjacent rail crossover cavern, with maximum vertical and horizontal deformations reaching 2.5 cm and 1.7 cm, respectively. In addition, the analysis shows that airborne SAR data with alternative viewing geometries to traditional polar-orbiting SAR satellites can be used to constrain horizontal displacements in the North-South direction while maintaining agreement with ground-based data.
Highlights
The increasingly extensive archives of SAR data collected by various sensors on spaceborne and airborne platforms offer a variety of wavelengths and distinct viewing geometries from which surface deformation measurements can be made
Calculated 3D deformations from all Interferometric Synthetic Aperture Radar (InSAR) datasets reveal the temporal and spatial extents of subsidence related to excavation activities (Figure 6)
Calculated horizontal displacements are consistent with a subsidence event, where horizontal motions centered around the vertical settlement are directed towards each other
Summary
The increasingly extensive archives of SAR data collected by various sensors on spaceborne and airborne platforms offer a variety of wavelengths and distinct viewing geometries from which surface deformation measurements can be made. SAR platforms, i.e., from different line of sight (LOS) vectors, can improve our ability to resolve the East, North, and Up components of the observed surface displacements [7]. This combination is necessary for comparison to ground-based datasets and overcomes one of the main limitations of InSAR, in which a dataset from one track can measure displacements only in a single LOS projection. Successes in extracting 2D displacements were carried out by combining both left and right-looking acquisitions from
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