Bassett, C., and A. Lavery, T. Maksym, and J. Wilkinson, Laboratory measurements of high-frequency, broadband acoustic scattering of growing sea ice and oil beneath sea ice, Proc. Mtgs. Acoust., 21, 070008 (2014).
This figure roughly shows the experimental setup for laboratory experiments related to detecting crude oil spills under sea ice. In the experiments frazil ice, pancake ice, and congelation were grown and oil was released under the ice. High-frequency, broadband sonars were used to quantify the changes in acoustic backscatter when crude oil was present. The lines in the upper right-hand corners of the subplots are matched filter data from the experiments under congelation ice. The two peaks in the right plots are due to the presense of the oil and multiple interfaces (water/oil and oil/ice). The presence of the oil can also be inferred from frequency spectra.
The morphology of sea ice during the early stages of growth is strongly dependent on environmental conditions. Under calm conditions, congelation ice forms through downward growth of ice crystals from the water surface. Under turbulent conditions (surface waves), rapid freezing of ice crystals occurs in the upper water column (frazil ice), eventually consolidating into pancake ice through repeated collisions and agglomeration of the loose frazil crystals. It is expected that high-frequency scattering from the basal layer of the ice varies for different sea ice types and can reveal structural information that governs the behavior of the ice and its interactions with the environment. Broadband scattering measurements of sea ice are presented beginning with ice-free conditions and through initial stages of growth in laboratory experiments for both congelation and frazil ice. With increased interest in drilling for hydrocarbon resources in the Arctic and the associated environmental concerns of an oil spill in ice-covered waters, improved methods for detection of crude oil both under or frozen within sea ice are needed. Acoustic scattering data are presented demonstrating how the scattering changes when crude oil is spilled beneath the ice.
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