Abstract: A low frequency detection system including the use of the sloping characteristics of the underwater near shore, the tapered section of ocean above the near shore, and an acoustic array. The acoustic array comprises a plurality of detectors that extend into the earth and are near the shore and tapered media. Low frequency sound energy in the range of from about 1 to about 100 Hz is coupled into the earth at discrete positions along the interface between the ocean and the sloping underwater shore. The maximum energy density for each frequency occurs at different ocean depths and the acoustic detectors are positioned to receive the optimum earth radiated beam at selected frequencies. The system involves locating tuned elements of an array in different arrangements and using a plurality of arrays and moving or stationary sound sources for active target detection and underwater earth mapping.

Abstract: A capacitor goniometer type tilt compensator is provided for the bi-directional elements in a transducer array in which each pair of bi-directional transducers is tilt or twist compensated to make image lobe cancellation possible. This is done by a specialized capacitor goniometer type compensator at each pair of bi-directional transducers which modifies their outputs in accordance with the deflection angle from the local vertical so as to obtain an output signal substantially the same as would be obtained by a single, properly oriented bi-directional transducer.