Paul W. Jameson
Richard N. Brown
BBN, 70 Fawcett St., Cambridge, MA 02138
Most ship-mounted planar hydrophone array systems employ stiff structures for isolation from local noise. One type of structure is a plate (``window''), which isolates the hydrophones from high wave-number turbulence on the outer surface. Most arrays also use a heavy steel plate behind the array to achieve isolation from the inner surface. These plates support bending waves, which can be induced by TBL forces. Even though these waves are subsonic over the frequency region of interest, the noise stress can enter the array output through an aliasing lobe when the array is steered. This noise increase is frequency dependent, and increases with frequency after a critical value. This talk will indicate how this noise contaminates the array response and discuss the interplay of element spacing, steering, and frequency performance of the array.