Acoustic Phase Fluctuations Caused by Garrett-Munk Internal Waves.
DEFENCE RESEARCH ESTABLISHMENT PACIFIC VICTORIA (BRITISH COLUMBIA)
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Perturbed acoustic propagation is considered between a point source and an array receiver in which the perturbations are due to a Garrett-Munk internal wave field. The resultant acoustic phase fluctuations along the array are determined. Straight ray propagation is assumed, and three array orientations are considered broadside horizontal, end fire horizontal and broadside vertical. It is shown that for an acoustic frequency of 150 Hz, a range of 50 km and a horizontal broadside receiver separation distance in the array of 1 km, the rms phase difference between the two receivers at 1000 m depth in the N. Pacific is typically 5 deg, and in the Arctic it is typically 2 deg, whereas in the N. Atlantic at the same depth it is typically 50 deg. These geographical variations are due mainly to variations in the potential sound velocity gradient. Similar phase differences occur for a vertical receiver separation of 50 m. The horizontal receiver separation necessary to reduce the acoustic coherence to 0.5 for the same operating conditions is shown to be very large in the N. Pacific about 400 km and Arctic 1000 km, but only 2.3 km in the N. Atlantic. Author