[1] Univ Alaska Fairbanks, Inst Northern Engn, Fairbanks, AK 99775 USA
[2] Univ Alaska Fairbanks, Inst Arctic Biol, Dept Biol & Wildlife, Fairbanks, AK 99775 USA
[3] bgeos, A-2100 Korneuburg, Austria
[4] Flemish Inst Technol Res VITO, Remote Sensing Unit, B-2400 Mol, Belgium