An airborne electromagnetic system on a fixed wing aircraft for sea ice thickness mapping

Abstract

An experimental campaign has been performed in 1991–1994 in the Baltic Sea, a brackish water basin, to test the ability of an airborne electromagnetic (AEM) system, mounted to a fixed wing aircraft (Twin Otter), to map sea ice thickness. Measurements are made with a vertical coplanar configuration of coils mounted on wing tips. The EM frequency is 3.1 kHz. A laser profilometer was integrated into the system for high frequency surface topography mapping. Test profiles were performed along 1–2 km long lines calibrated for ground truth. In good mapping conditions the thickness accuracy is ± 0.2 m for undeformed ice but worse for deformed ice with variable geometry. The raw horizontal resolution is 100 m. Analytical half-space EM models described well the overall ice thickness distribution. A 3D model was used for extraction of more detailed ice geometry. For unconsolidated deformed ice a nonzero electric conductivity must be assumed. The penetration length, which depends on the ice conductivity distribution, gives up to 70 m for fully resistive ice. The system is feasible for polar seas since the conductivity contrast between sea ice and sea water is much higher there than in the Baltic. The Twin Otter offers a wide operation area because the measurement ground speed is 90–120 knots and maximum flight duration is 6–8 hours.