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Abstract

A signal processor for continuous wave (CW) sonars of the type using a doppler filter bank for target detection, in which improved detection capability under reverberation limited conditions and particularly at relatively low doppler values is accomplished by introduction of an adaptive filter providing a notch filter characteristic centered on the mean frequency of the reverberation spectrum and of width and depth continuously automatically adjusted to conform at least approximately to the inverse of the reverberation spectrum. For effecting this adjustment the notch filter is made voltage variable and is enclosed within an automatic notch control (ANC) loop in which the notch control voltage is derived by comparison of signal level on one doppler filter on which appears reverberation plus noise against signal level on another on which appears noise only, to thus derive a control signal providing a measure of reverberation level. The ANC loop thus controlled operates in conjunction with associated automatic gain control (AGC) and automatic frequency control (AFC) loops, to 'prewhiten' or flatten the reverberation and noise spectra in a manner such that each of the matched filters in the doppler bank may contribute equally to its output.

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First Claim