Abstract: A method for optimizing the design of finite noise barriers by using an extension of the Biot-Tolstoy rigorous closed form impulse solution for diffraction of an acoustic pressure pulse by an infinite rigid wedge. An initial finite barrier is defined and then a calculation made of the impulse signal transmitted on one side of the barrier and received on the other side by adapting the Biot-Tolstoy solution to a digital computer. The integrals of the acoustic pressure impulse are calculated for each source/receiver path for each segment of the barrier. The integrals are then compared and the segments are adjusted and new calculations made until all integral contributions are equal. The integrals are then digitally Fourier transformed to determine attenuation at the desired frequencies. After comparison with the desired attenuation, all segments are proportionately adjusted and the entire computational process reiterated until the optimal attenuation is achieved.

Abstract: An acoustical deverberator for eliminating the reverberation from a sound gnal originating with a transient sound source in shallow water. The sound signal is received by a single hydrophone and autocorrelated to determine the time differences between the direct signal and the bottom surface reflected signals. Together with the surface and bottom reflection coefficients and known depths of the hydrophone and water, the time differences are used to determine corrections which are applied to the received sound signal. The result is a clean sound signal free from interfering reverberation.

Abstract: A surface acoustic signal defader for optimizing the signal received from derwater sound scattered from the ocean surface. The bandwidth of the underwater sound source is monitored and the frequency of maximum signal strength is identified. When the maximum signal strength frequency fades a predetermined amount, reception is switched to the signal of maximum anti-correlation. This process is continuous such that when the new frequency fades the anti-correlation process will determine the optimum frequency for the new fading condition, thus resulting in optimum reception of surface scattered underwater sound.

Abstract: A plurality of processing channels each receive one of a number of direct d secondary signal energy rays. Each channel includes an A/D converter and computer the logic of which is controlled by a Fast Fourier Transform (FFT) algorithm to produce a plurality of data outputs each containing the amplitude and phase information of selected frequencies present in the channel input. To enhance signal detection and minimize signal strength fluctuations, each of the selected frequency outputs of each channel FFT is compared with each identical frequency output of other channel FFT's. Phase compensation means such as a shift register adjusts the phase relationship between all identical FFT outputs to permit their amplitudes to be constructively added. The individual subtotals so produced are totalled to provide an output representing the combined strength of the multi-path signal energy.