Abstract
Acoustic data from the Canada Basin Acoustic Propagation Experiment are discussed. These recordings were obtained under seasonally varying sea ice to the north of Alaska during a period of 154 days. They contain signals from sources that were deployed at ranges of 17.5, 29.6, and 237.8 km and ambient sounds from marine mammals and ice-related events. After the area was covered with ice, the amplitude of receptions from the most distant source gradually decreased as scattering features on the underside of the ice developed during fracturing, drifting, ridging, and rafting events. Improvements are presented for an Arctic acoustic model that is based on the parabolic equation method, and the approach is applied to a problem in which variable ice thickness acts as a loss mechanism by scattering energy out of the waveguide. Some of the recordings have a harmonic signature that is believed to be associated with the resonances of ice floes rubbing together, but variations in the harmonics over short time scales cannot be explained in terms of the resonances of an isolated floe. This behavior may be related to the coupling of vibrations at contact points that vary during the relative motions of floes.
Highlights
Changing conditions in the Arctic, such as diminishing sea ice[1], is one of the factors that recently led to a renewed interest in Arctic acoustics and motivated the Canada Basin Acoustic Propagation Experiment (CANAPE)
It is not practical to run this model at high frequencies, but it is usually sufficient to test the accuracy of a parabolic equation model at low frequencies since (a) continuous horizontal variations in the properties of the medium become more gradual on the scale of a wavelength as frequency increases and (b) horizontal variations associated with a sloping interface do not scale with frequency
Applications to CANAPE data motivated improvements to the Arctic parabolic equation model that are useful at higher frequencies than had been considered previously
Summary
Changing conditions in the Arctic, such as diminishing sea ice[1], is one of the factors that recently led to a renewed interest in Arctic acoustics and motivated the Canada Basin Acoustic Propagation Experiment (CANAPE). An improved approach for handling variations in ice thickness is presented for the Arctic parabolic equation[5], which was not available during previous studies in Arctic acoustics[6,7,8,9,10,11,12,13]. Applying this model for parameter ranges relevant to CANAPE led to a better understanding of the requirements for obtaining stable solutions
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