Abstract:
Hydrophones embedded within conformal, towed, and free-falling arrays are subject to a noise contribution due to the turbulent boundary layer flow that exists over the array's external surface. At medium to high flow speeds, this noise can dominate the arrays output to the extent that detection and/or localization of targets is improbable. If an independent estimate of the flow noise is available, then extracting the acoustic signals of targets from the flow noise background can be accomplished using standard signal processing techniques. A new sensor, a flush mounted hybrid detector consisting of a permanent magnet, a pair of orthogonal electrodes, and a coincident hydrophone will be shown to act as a reference sensor. The magnetic field of the permanent magnet interacts with the turbulent flow to generate an electric field that is measured by the electrodes. The voltage induced in the electrodes is proportional to the strength of the turbulent boundary layer flow and is thus an independent estimate of this noise. Experimental evidence will be shown demonstrating coherence between the electrode pair and a coincident hydrophone.