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[STT39-P06] Detection of Surface Displacement in Urban Areas by Satellite SAR Differential Interferometry
Keywords:differential interferometry, InSAR, surface displacement, ground subsidence, Sentinel
It has been widely known that the surface displacement can be detected at an order of millimeters to centimeters by the differential interferometry using satellite-borne Synthetic Aperture Radar (SAR) data. The detection of the surface displacement in the urban area by using satellite SAR differential interferometry was performed in the research.
A part of the road was collapsed on 2020/10/8 at Higashi Tsutsujigaoka 2-chome, Chofu, where the tunnel excavation work on the Tokyo Gaikan Expressway had been carried out at a depth of 47 m beneath the road. The collapsing of the road and the discrete distribution of several underground hollows found along the excavation route suggest a possible subsidence covering a certain area centered on the route. Thanks to relative short working time, low cost and wide coverage, the satellite SAR differential interferometry is said to be one of excellent tools to investigate such phenomena.
The data used in the research is of C-band SAR with about 6 cm wavelength acquired by Sentinel-1, a satellite of the European Space Agency. Sentinel-1 data has the advantages of the acquisition at every 12 days interval and of free of charge. In general, a detectable displacement amount by satellite SAR differential interferometry is said to be 1/10 of the radar wavelength, and the displacement at the order of millimeters to centimeters can be detected by C-band SAR data.
Twelve (12) scenes of Sentinel-1 spanning since July, 2020 to November, 2020 for both of northward (ascending) orbit and southward (descending) orbit were selected. Fifty six (56) interferometry pairs with observation intervals ranging from 12 days (1 cycle) to 84 days (7 cycles) were selected for both northward and southward orbits, and differential interferometry analyses was conducted to construct the displacement history through the time series analysis. Results found follow;
- On the northward orbit, the displacement away from the satellite was detected on the west side of the excavation route, and the displacement toward the satellite was detected on the east side of the route.
- On the southward orbit, opposite to the result on the northward orbit, the displacement away from the satellite was detected on the east side of the excavation route, and the displacement toward the satellite was detected on the west side of the route.
- The displacement on the northward orbit was detected for the data after 2020/9/24, while on the southward orbit it was detected for the data after 2020/9/18.
The opposite distribution patterns of the displacement on each orbit suggest the subsidence occurred around the excavation route. The shield machine passed through possible subsiding area on 2020/9/14 according to media reports, which is concordant with the observation dates of satellite SAR data that the displacement was detected.
In order to investigate the displacement pattern in detail, a 2.5-dimensional analysis was conducted by combining detected displacements from the interferometry pairs of 7/14 and 10/30 for the northward orbit and of 7/20 and 11/5 for the southward orbit. The result indicates that, in the quasi-east-west direction, eastward surface displacement occurred in the west and westward surface displacement occurred in the east of the route, with the center slightly located to the east of the excavation route. The maximum horizontal displacement of about 2 cm in both the east and west directions and a maximum subsidence amount of about 3 cm were estimated from the 2.5-dimensional analysis.
The result of the research shows that the surface displacement in the urban area can be detected at the order of millimeters to centimeters by the differential interferometry using C-band SAR data.
A part of the road was collapsed on 2020/10/8 at Higashi Tsutsujigaoka 2-chome, Chofu, where the tunnel excavation work on the Tokyo Gaikan Expressway had been carried out at a depth of 47 m beneath the road. The collapsing of the road and the discrete distribution of several underground hollows found along the excavation route suggest a possible subsidence covering a certain area centered on the route. Thanks to relative short working time, low cost and wide coverage, the satellite SAR differential interferometry is said to be one of excellent tools to investigate such phenomena.
The data used in the research is of C-band SAR with about 6 cm wavelength acquired by Sentinel-1, a satellite of the European Space Agency. Sentinel-1 data has the advantages of the acquisition at every 12 days interval and of free of charge. In general, a detectable displacement amount by satellite SAR differential interferometry is said to be 1/10 of the radar wavelength, and the displacement at the order of millimeters to centimeters can be detected by C-band SAR data.
Twelve (12) scenes of Sentinel-1 spanning since July, 2020 to November, 2020 for both of northward (ascending) orbit and southward (descending) orbit were selected. Fifty six (56) interferometry pairs with observation intervals ranging from 12 days (1 cycle) to 84 days (7 cycles) were selected for both northward and southward orbits, and differential interferometry analyses was conducted to construct the displacement history through the time series analysis. Results found follow;
- On the northward orbit, the displacement away from the satellite was detected on the west side of the excavation route, and the displacement toward the satellite was detected on the east side of the route.
- On the southward orbit, opposite to the result on the northward orbit, the displacement away from the satellite was detected on the east side of the excavation route, and the displacement toward the satellite was detected on the west side of the route.
- The displacement on the northward orbit was detected for the data after 2020/9/24, while on the southward orbit it was detected for the data after 2020/9/18.
The opposite distribution patterns of the displacement on each orbit suggest the subsidence occurred around the excavation route. The shield machine passed through possible subsiding area on 2020/9/14 according to media reports, which is concordant with the observation dates of satellite SAR data that the displacement was detected.
In order to investigate the displacement pattern in detail, a 2.5-dimensional analysis was conducted by combining detected displacements from the interferometry pairs of 7/14 and 10/30 for the northward orbit and of 7/20 and 11/5 for the southward orbit. The result indicates that, in the quasi-east-west direction, eastward surface displacement occurred in the west and westward surface displacement occurred in the east of the route, with the center slightly located to the east of the excavation route. The maximum horizontal displacement of about 2 cm in both the east and west directions and a maximum subsidence amount of about 3 cm were estimated from the 2.5-dimensional analysis.
The result of the research shows that the surface displacement in the urban area can be detected at the order of millimeters to centimeters by the differential interferometry using C-band SAR data.