1. a School of Human Environmental Science, Ochanomizu University, 2‐1‐1, Otsuka, Bunkyo‐ku, Tokyo 112‐8610 Japan; e‐mail: mieko@ns.is.ocha.ac.jp
2. b Remote Sensing Technology Center of Japan, 1‐9‐9, Roppongi, Minato‐ku, Tokyo 106‐0032 Japan; e‐mail: sugimura@restec.or.jp; tanaka@restec.or.jp
3. c Department of Civil Engineering, University of Tokyo, 7‐3‐1, Hongo, Bunkyo‐ku, Tokyo 113‐8656 Japan; e‐mail: tamai@hydra.t.u-tokyo.ac.jp