Abstract:

An aerial, remote sensor has been devised to detect underwater sound through an ice layer by optically measuring the resulting vibration velocity on the ice surface, using a laser Doppler vibrometer. The laser was focused on an ice block approximately 8 in. wide by 12 in. long and 3.5 in. thick floating in a tank of water 16 in. deep. A submerged transducer was used to generate underwater acoustic signals to provide ice surface vibrations for the sensor to detect. Although acoustic attenuation through the ice was not an issue for this test, laser alignment was crucial. Since sensor reliability depends on receiving laser reflections from the ice surface, the laser was steered nearly perpendicularly onto the ice surface that had both smooth and rough features. The broadband optical sensor provides a remote sensing capability for measuring ice surface vibrations in response to underwater acoustic signals such as from marine mammals, passive or active sonar, and from underwater acoustic communication systems. The results of this landmark experiment will be presented, which demonstrate the feasibility for detecting underwater sound through an ice layer by probing the ice surface with a laser vibrometer, paving the way for in‐air sensing in arctic regions.