1. a Radar Systems and Remote Sensing Laboratory, Department of Electrical Engineering and Computer Science , University of Kansas , 2291 Irving Hill Road, Lawrence, Kansas, 66045-2969, U.S.A
2. b Byrd Polar Research Center, The Ohio State University , 108 Scott Hall, 1090 Carmack Road, Columbus, OH, 43210-1002, U.S.A
3. c U.S. Army Cold Regions Research and Engineering Laboratory , 72 Lyme Road, Hanover, NH, 03755-1290, U.S.A
4. d Wave Scattering Research Center, Department of Electrical Engineering , The University of Texas , 416 Yates Street, Arlington, TX, 76019-0016, U.S.A