John P Fay

US Patent:

43887112, Jun 14, 1983

Filed:

Jul 28, 1981

Appl. No.:

6/287959

Inventors:

John W. Fay - Old Lyme CT

Assignee:

The United States of America as represented by the Secretary of the Navy - Washington DC

International Classification:

G01S 380

US Classification:

367135

Abstract:

An apparatus for rejection of turbulence induced flow noise for towed hydhone arrays. Two adjacent hydrophones in the array are spaced less than flow noise coherence distance apart forming a flow noise cancelling module. The inverted acoustic/flow noise signal from the lead hydrophone of the pair is split, one side passing to the final stage of signal processing while the other side, filtered, amplified and inverted, is added to the combined signal from the lag hydrophone which has been filtered and amplified. The acoustic signal components cancel leaving only the lead hydrophone flow noise plus the lag hydrophone flow noise which has been shifted by a factor dependent upon tow vessel speed and hydrophone spacing. This flow noise signal is then combined in an adder-inverter with the delayed feedback from the output stage of this same adder-inverter, cancelling the lag hydrophone flow noise leaving only the flow noise of the lead hydrophone which is then combined with the acoustic signal plus flow noise output of the lead hydrophone. The flow noise components cancel yielding only the signal of interest, free of flow noise and undistorted by minor phase shifts.