1. a Norwegian Defence Research Establishment (FFI), Division for Electronics, PO Box 25, NO‐2027 Kjeller, Norway
2. b University of Oslo (UiO), PO Box 1032 Blindern, NO‐0315 Oslo, Norway
3. c Norwegian Polar Institute (NPI), PO Box 399, Polar Environmental Centre, NO‐9296 Tromsø, Norway