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3. CONCLUSION With the aim of carrying out a development of satellite SAR-based external deformation measurement of rockfill dams, this paper focused on nineteen rockfill dams in Japan. A total of 135 scenes of satellite SAR data was used over a period of nearly two years from late 2014 to early 2016 for study. External deformations of nineteen rockfill dams were measured by satellite SAR and compared with existing GPS or electro-optical survey data. The average RMSE of nineteen rockfill dams between SAR and existing geodetic measurements was about 5 mm. As earthquake induced settlement up to several centimeters was also well measured by satellite SAR data, satellite SAR data is useful both in normal times and after earthquakes. In order to conduct accurate external deformation measurements using satellite SAR data, it is important for us to pay attention to factors that cause reduction of the accuracy such as ground surface vegetation. Because we find that the satellite SAR based external deformation measurement of rockfill dams is accurate and useful, we will continue our research to put our research results into practical use. ACKNOWLEDGEMENTS This research has been supported by the Strategic Innovation Promotion Program (SIP) of the Cabinet Office, Government of Japan. We would like to thank to dam management offices in Japan which provided valuable data for our research. REFERENCES [1] EMADARI L., MOTAGH M., HAGHIGHI M.H. Characterizing post- construction settlement of the Masjed-Soleyman embankment dam, Southwest Iran, using TerraSAR-X SpotLight radar imagery, Engineering Structures, 143, pp.261–273, 2017. [2] GRAZANIC G., LIER O., EKSTROM I., LARSEN Y., LAUKNES T.R. Adopting remote sensing dam surveillance, 82nd Annual Meeting of ICOLD, pp. 688-697, 2014. [3] HANSSEN R. Detecting instabilities in dams using satellite radar interferometry, 81st Annual Meeting of ICOLD, 2013. [4] LAZECKY M., BAKON M., PERISSIN D., PAPCO J., GAMSE S. Analysis of dam displacements by spaceborne SAR interferometry, 85th annual meeting of ICOLD, 2017. 816