Bosai Solution ID : JBP00119

Utilization of satellite SAR data -Estimation of subsurface
conditions based on ground surface deformation obtainedby satellite SAR－Estimation of subsurface deformation by inverse analysis using finite element
method (FEM)

HazardEarthquake Land Slide

Solution Purpose
Prevention & Mitigation

Solution Theme
Research & Investigation Risk Assessment Disaster Prevention Plan Infrastructure Technology
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Technology Subject
Technical Research & Development Feasibility Study Hazard Simulation Risk Monitoring Mitigation Plan
Dam & Reservoir Sabo Road Railways Airport Information Analysis & Judgement

Advantages
Using ranging data obtained by Synthetic Aperture Radar (SAR) -equipped satellites, ground surface
deformation can be measured. In addition, by combining inverse analysis technology, we can estimate
the subsurface strain conditions that cause land surface deformation. This is useful for analyzinglandslides, embankment deformation, and surface subsidence.

Solution Illustrated
Interferometric SAR analysis is a method of studying the deformation of the earth's surface using
satellite SAR. Each time a satellite passes through the same orbit, the phase of the radio wave reflectedfrom the earth's surface is measured. If the ground surface is rising, for example, the distance from thesatellite changes and a phase difference is generated. From this phase difference, the amount of
deformation of the ground surface is determined.
The obtained deformation of the ground surface is regarded as the deformation of the top surface of theanalytical model, and changes in the strain distribution inside the model and areas of reduced stiffness
are estimated by inverse analysis.

Note: Figure modified from the phase diagram, "What is Interferometric SAR/SAR Interferogram?" available from Geospatial
Information Authority of Japan's website: https://www.gsi.go.jp/uchusokuchi/sar_mechanism.html

Background
Deformation of the earth's surface can be detected using satellite SAR. However, estimating the cause of
the deformation requires the strain distribution in the ground that caused the deformation, which canbe obtained by inverse analysis using a 3D FEM with a Kalman filter.

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Exposition of the Solution
Once surface deformation is obtained, Geolab's inverse analysis software, Geo-Inverse, using the FEM
allows investigation of changes in physical properties and strain occurred in the subsurface.
To evaluate the performance of the inverse analysis, the model shown in Figure 1 is prepared. Assume aregion of volume shrinkage inside the model (red in Fig. 1). Figure 2 shows the deformation of theground surface caused by this shrinkage strain.
This is the ground surface deformation obtained from satellite SAR measurements. An inverse analysis isperformed with this deformation as a known and the area and magnitude of the strain changes as anunknown.
Figure 3 shows the shrinkage area obtained from the inverse analysis. Figure 4 compares themeasurement and identification results, which are on a straight line with a slope of 1, indicating theaccurate reproducibility of measurement results by the identification results.

left side：Fig. 1 Mountain and shrinkage area (indicated by red).
right side：Fig. 2 Ground surface displacement contour obtained by inverse analysis.

left side：Fig. 3 Shrinkage contour obtained by inverse analysis.
right side：Fig. 4 Correlation between measurements and results obtained by inverse analysis.

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In Figs. 3 and 4, warmer colors indicate greater changes.

Achievements of Examples
Geolab is currently working on case studies on landslides.

Corporate Profile
Geoscience Research Laboratory
JM Bldg.4F, 3-1-6 Yamatohigashi, Yamato, kanagawa, 242-0017, Japan Tel. : +81-46-200-2281
 E-mail : chisouken@geolab.jp
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