Surface Condition Surveys in Ice Covered Waters using Acoustic Reverberation

Abstract

Acoustic reverberation time is investigated, by scale-model experiments, for its suitability as a readily-measured index of the physical surface conditions in ice-covered waters. As such, it is envisioned as the basis of expedient survey techniques for such potential applications as trapped oil detection or ice road condition monitoring. The scaled experiments, to establish feasibility, are conducted in a small tank with naturally grown ice cover, anechoic-lined side walls, and a hard bottom, imitating thereby a horizontally-extended underwater environment, like an ice-covered sea. An impulsive source generates sound up through low ultrasonic frequencies (to 90 kHz), wavelengths of which are suitability short relative to the tank dimensions that near-ideal diffuse-field reverberant conditions are surmised to prevail; decay time of the impulse (“reverberation time”) is extracted from a hydrophone signal. Results suggest high sensitivity of the reverberation time to ice coverage (vs. absence), and somewhat lower sensitivity, albeit still promising for survey techniques, to other such features as variations in ice thickness, or the presence of trapped oil; this is suggestive of likely feasibility of the proposed survey techniques at full scale.