Page - 815 - in Book of Full Papers - Symposium Hydro Engineering

SAR and GPS/electro-optical survey, the results of satellite SAR based external deformation measurements agreed well with the results by GPS or electro-optical survey. In the case of Dam N in Fig. 5, which showed a relatively large and sudden settlement by the Kumamoto earthquake in April 2016, earthquake- induced settlement was well measured by satellite SAR. Table 2 shows the average RMSE on upstream, crest and downstream surfaces and all existing geodetic points of nineteen rockfill dams. Although there are some variations among the results of RMSEs in Table 2, more than half of the average RMSEs are less than 5 mm and most values are less than 10 mm. On the other hand, several RMSEs in Table 2 show more than 10 mm and the RMSE of the downstream surface of Dam N shows more than 20 mm. It is well known that deterioration in accuracy of SAR based deformation measurements occurs when ground surface is covered with vegetation [10]. Because downstream surface of Dam N has been covered with vegetation, it leads to the relatively large RMSE of downstream surface of Dam N. Table 2 shows that external deformation monitoring using satellite SAR data is generally accurate, but we must pay attention to factors that cause reduction of the accuracy such as ground surface vegetation. Table 2 RMSE of external deformations between SAR and GPS/electro-optical survey on upstream, crest and downstream surfaces *1 : Rockfill dam part of combined dam. “-“ means no existing geodetic measurement data has been obtained. All Upstream surface Crest Downstream surface A 78.5(*1) 595(*1) ASC 6 4.4 7.5 3.2 4.4 B 161 427.1 DSC 6 3.2 2.8 2.9 3.4 C 41.2 440 ASC 5 2.3 1.7 2.1 2.8 D 89.9 786 ASC 6 7.3 11.8 4.1 6.0 E 52.5(*1) 210(*1) ASC 6 2.2 1.4 2.5 2.2 F 127 723 ASC 6 6.0 3.3 4.6 7.4 G 112 510 ASC 5 4.6 4.2 2.9 5.2 H 90 565 ASC 8 10.2 4.3 5.9 14.5 I 66 348.2 ASC 5 7.9 - 11.4 4.6 J 119.5 419.5 DSC 6 6.3 6.5 5.5 6.7 K 158 520 DSC 10 6.9 - 6.0 7.0 L 127.5 366 DSC 7 4.4 - 4.6 4.2 M 83 420 ASC 8 3.3 - 3.1 3.4 N 35 244 DSC 15 14.7 7.4 8.9 23.8 O 35(*1) 330(*1) ASC 8 3.4 3.6 4.4 2.3 P 91.7 260 ASC 8 4.6 - 7.5 3.1 Q 66 445 ASC 7 2.1 1.7 2.5 1.9 R 66.5 198 ASC 7 2.0 - 1.5 2.1 S 37 500 DSC 6 4.3 5.0 3.8 3.1 RMSE (mm) Name of dam Height(m) Crest length(m) Orbit of satellite SAR Numbers of data used 815