Takashi Shibata, Nagoya University, Nagoya, Japan, Koichi Shiraishi, Fukuoka University, Fukuoka, Japan, Masataka Shiobara, National Inst Polar Research, Tokyo, Japan, Suginori Iwasaki, National Defense Academy, Kanagawa, Japan and Toshiaki Takano, Chiba University, Department of Electrical and Electronics Engineering, Chiba, Japan