| 摘要 |
Various types of rivercraft propelled by motor, poling, sculling or paddling are found to generate broadband noise having a superimposed low frequency sinusoidal modulation. To detect the presence of such craft, a hydrophone, tethered in a river from a moored subsurface float is connected to a concealed transmitter located on the bank. The detected audio signal is demodulated and filtered. When classification criteria have been satisfied, a gate opens allowing the demodulation information to be processed by a logic circuit, which, if satisfied, causes the hydroacoustic signal to be transmitted over an RF link to a remote receiver station.
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