| 摘要 |
A system for detecting and isolating incoming acoustic waves is disclosed, the system including means for transmitting a random noise signal which will intersect the incoming waves. Cross modulation products, particularly the first order sum and difference frequencies, occurring in the volume where the incoming low frequency and transmitted high frequency signals meet and intersect are propagated back toward a receiver where the modulated noise signals are correlated with the transmitted noise signal to isolate the lower frequency incoming signal. The interaction between the transmitted and incoming signals takes place at a plurality of volumetric segments which are located at various distances from the transmitter. By correlating the modulated return signals, which are received at selected intervals, with properly delayed replicas of the transmitted signal, the interaction, or cross modulation products, at any selected range can be isolated in the receiver. By summing these isolated signals, the incoming frequency can be detected, the overall system acting as a virtual receiving array.
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