Investigations of skeletal layer microstructure in the context of remote sensing of oil in sea ice

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ABSTRACT (2017-159)The Arctic Oil Spill Response Technology – Joint Industry Program (JIP) funded a controlled basin experiment in November 2014 to assess the relative capabilities of a variety of oil in ice remote sensing techniques. An 80-cm sheet of level salt-water ice was grown in the Test Basin facility at the US Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, New Hampshire. The basin ice was representative of natural level sea ice grown under quiescent conditions. This created a controlled baseline environment to compare different sensors with a manageable number of variables. The sensor testing spanned a two-month ice growth phase and a one-month decay/melt period. The detailed physical and electrical properties of the lab-grown ice sheet were monitored over the course of the experiment.Analysis of preliminary sensor data revealed that the skeletal layer--the soft, porous band of new ice crystals at the growing ice water interface--plays a significant role in the process of incorporation of oil into the ice sheet, with oil infiltration occurring between the small lamellae structures. In addition, the underwater sensors, particularly acoustic sensors, appeared to be very sensitive to skeletal layer properties, especially the surface roughness of the ice/water interface and the density of the skeletal layer.Preliminary X-ray micro-computed tomography (micro-CT) data collected as part of the experiment demonstrated a qualitative scale dependence of sensor response to the skeletal layer microstructure. We used a cold-hardened Bruker SkyScan 1173 micro-CT scanner, housed in a −10 °C cold room, to generate full 3-dimensional x-ray images of the sea ice samples. We have demonstrated that the system is capable of distinguishing areas of void space, brine, ice, and oil at 40 micron resolution. The micro-CT scans were used to characterize the skeletal layer of the ice, including measuring density, thickness, orientation and spacing of the lamellae at 39 – 71 micron voxel resolution.Characterizing the ice structure with high resolution micro-CT imaging may resolve some of the ambiguity in the sensor measurements and lead to improved accuracy of the numerical models that predict sensor performance in different oil and ice scenarios.