Tetsuo Motoba, Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States, Yusuke Ebihara, Kyoto University, Research Institute for Sustainable Humanosphere, Kyoto, Japan, Akira Kadokura, NIPR National Institute of Polar Research, Tachikawa, Tokyo, Japan and Yasunobu Ogawa, NIPR National Institute of Polar Research, Tokyo, Japan