Landslide Surface Deformation Detected by Synthetic Aperture Radar (SAR) Interferometry in Shizu Area on the Southern Foot of Mt. Gassan, Japan
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L-band (22.36 cm in wavelength) radars such as ALOS (Advanced Land Observing Satellite)/PALSAR (Phased Array type L-band Synthetic Aperture Radar) are suitable for observing landslide surface deformation in Japan. In this study, we produced InSAR (SAR interferometry) images using PALSAR data and observed the fringes produced; after subtracting orbital and topographic fringes, the resulted fringe indicated a 2 × 1 km landslide surface deformation on the southern foot of Mt. Gassan (stratovolcano, 1,994 m in elevation) in Japan; this landslide is actually a reactivated old landslide. According to a previous study, slide surfaces can be identified both in the deposits and in the underlying mudstone, which has a maximum depth of 160 m from the ground surface. The InSAR image indicated surface deformation at more than half of the L-band wavelength along the LoS (line of sight). Because of the good coherence (0.4–0.6) of the obtained InSAR image, we unwrapped the phase of the InSAR image and obtained a continuous phase. We found that the detected landslide deformation could be separated into two sections: a fluvial erosion-affected section and an upper slope section. In the former section, repeated surface deformation between 0 and 7 cm along the LoS implies the deformation by many sub-slide surfaces. In the latter section, surface deformation along LoS uniformly increased from 2.5 cm at the upper scarp to 13.5 cm at the foot of the slopes; this implies that one large rigid landslide block controls surface deformation. An on-site GPS survey of the fluvial erosion-affected section revealed the landslide’s surface deformation, and the measurement results from the GPS survey show good agreement with the InSAR results.
KeywordsLandslide SAR GPS InSAR
The PALSAR data used in this study were provided by JAXA. The Ministry of Economy, Trade and Industry (METI) and JAXA retain the ownership of the original SAR data. The Shinjo River Office provided in situ GPS survey result and the photograph. Prof. Hiroshi Yagi (Yamagata Univ., Japan) guided geological and geomorphologic characteristics in the field and showed overview of the recent landslide deformation there. We are thankful for them.
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