1. a Division of Geodetic Science, School of Earth Sciences, The Ohio State University , 275 Mendenhall Laboratory, 125 South Oval Mall, Columbus, OH, 43210, USA
2. b Byrd Polar Research Center, The Ohio State University , 1090 Carmack Road, Columbus, OH, 43210, USA
3. c Department of Geography , University of California , 1255 Bunche Hall, Los Angeles, CA, 90095, USA