2002a), "Sound from a light aircraft for underwater acoustics experiments?" Acta Acustica united with Acustica 88

Abstract: A research programme is being conducted off the coast, north of La Jolla, southern California, USA, in which a single-engine, propeller-driven light aircraft acts as the source of sound in underwater acoustics experiments. Receivers are located in the atmosphere (a microphone about 1 m above the sea surface), in the 15 m deep water column (a vertical array of eight hydrophones) and in the very-fine-sand sediment (a hydrophone and shear sensor, or bender, buried about 75 cm beneath the sea floor). Propeller noise from the aircraft, exhibiting a characteristic sequence of harmonics extending from approximately 80 Hz to 1 kHz, has been clearly detected simultaneously in all three media. A technique has been developed for measuring the low-frequency sound speed in the sediment from the Doppler shift of the propeller signature on a single buried hydrophone. Other types of otherwise difficult measurement, for instance, the low-frequency acoustic attenuation in a sediment, appear to be feasible by exploiting the high mobility of an aircraft as a sound source. 1