[AHW26-P03] Ground surface deformation induced by groundwater development in the central part of Saitama Prefecture, Japan, detected by ALOS/PALSAR
Keywords:Ground subsidence, Groudwater, SAR
On the other hand, analytical techniques for assessing ground deformation using interferometric synthetic aperture radar (InSAR) onboard satellites or airplanes have been achieving great results in various fields. Thus, in this research, we examined local characteristics of ground surface deformation through interferometric analysis of persistent scatterer InSAR (PSI) using ALOS/PALSAR data obtained from 2006 to 2011. The PSI method is an analytical technique that allows the calculation of rates of displacement of a target on the ground surface through the extraction of points that have stable phase characteristics over time (PS), such as buildings. As an external digital elevation model, we used digital base map with an interval of 10 m constructed and distributed freely by the Geospatial Information Authority of Japan (GSI). The synthetic aperture radar (SAR) can detect only one-dimensional displacements between the satellite and a target on the land surface in the direction of the line of sight (LOS). However, in the SAR observations, it is possible to observe the same location on the ground surface from the two directions of the ascending orbit and the descending orbit. We could calculate quasi-vertical and quasi-east–west components of a displacement rate on a plane determined by the ascending and descending LOS vectors from the two LOS displacement rates. Because a very large number of PS points were detected in this area, we thinned out the data at 200 m intervals. Tropospheric noise reduction using a numerical weather model provided by the Japan Meteorological Agency was applied. To reduce the influences of any orbital errors, a correction to flatten the phase inclination of the entire study area was applied. The average of the phases in the area where no displacement was seen was set to zero as a reference.
According to the distribution maps of quasi-vertical displacement rates from 2006 to 2011, the districts showing subsiding tendency were confirmed in the southern part of the Omiya Upland, the downstream area of the Arakawa Lowland, the southern part of the Kawagoe Upland, and some other locations. On the contrary, the districts showing stable or uplifting tendencies were confirmed in the northern part of the Omiya Upland, the midstream area of the Arakawa Lowland, the northern part of the Iruma Upland, and in the Kawagoe Upland. In the areas showing subsiding tendency, we confirmed that an increase in the amount of groundwater withdrawals from several years before and through the analysis period had been observed. Conversely, in the areas showing stable or uplifting tendencies, we were able to confirm a fixed or decreasing amount of groundwater withdrawals through the period.
In our presentation, we will examine relationships between ground deformation tendency, geological conditions, and groundwater withdrawals with the goal of helping to solve the ground subsidence problems in the urban areas.