Underwater Signal Discrimination System.
DEPARTMENT OF THE NAVY WASHINGTON DC
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In an underwater-target detection apparatus of the echo-ranging type wherein a receiver signal, resulting from transmission of search pulses, comprises reverberation and at times a target echo, said reverberation presenting a frequency spectrum of greater bandwidth than said target echo and presenting an amplitude-modulaton envelope generally including pulses of character similar to said search pulses, and said target echo occurring at an unpredictable frequency within a comparatively wide frequency band substanially centered upon the reverberation mean frequency, a receiver circuit for effecting discrimination of target echoes from reverberation, said receiver cicuit comprising first filter means having a rejection notch characteristic centered upon the reverberation mean frequency, and of comparatively limited bandwidth substantially matching that of the major energy portion of said reverberation, for converting said receiver signal to a modified signal with strong attenuation of reverberation in only a correspondingly limited central portion of its frequency spectrum and without substantially affecting target echoes occurring at frequencies outside of said rejection notch demodulator means for deriving from said modified signal a unipolar signal corresponding to the modulaton envelope of said modified signal and second filter means having a bandpass response characteristic with upper cutoff frequency substantially equal to half said limited bandwidth of the first filter means rejection notch, for isolating, from said unipolar signal, only such signal pulses as correspond to target echoes. Author
- Acoustic Detection and Detectors