The Quantitative Capabilities of HEM Inversion for the Sea Ice Case

Abstract

Semi-empirical methods are routinely used for Helicopter Electromagnetic (HEM) sea ice thickness mapping. Although these methods yield sufficiently accurate thickness data, it is of interest to determine whether formal one-dimensional (1D) geophysical inversion could yield improved results. If both the thickness and the ice conductivity could be mapped, the results could be used to estimate glaciological parameters such as the age of the sea ice. Sea ice conductivity data could also be potentially used to estimate the strength of the ice sheet, which would be valuable information for planning of icebreaking operations. By investigating synthetic and field data we show that, in the case of level sea ice of thickness up to 2 m, the accuracy of our HEM system is not high enough to sense the small conductivity variations arising from the age of the ice. Sea ice conductivity has a stronger influence on the measured HEM responses in areas of thick, deformed sea ice (pressure ridges), where bulk conductivity is higher as a result of the large seawater-filled porosity. Synthetic three-dimensional HEM data generated for pressure ridge models has shown that the 1D interpretation methods conventionally used for interpretation of sea ice thickness overestimate the true bulk conductivity at 3D features.