Bistatic Doppler underwater intrusion detection sonar
First Claim
1. A bistatic sonar system for detecting intrusion into a predetermined zone of a body of water, said system comprising:
- a source of a reference frequency;
fixed, continuous wave transmitter means, responsive to said reference frequency, for insonification of said zone with acoustic energy at a predetermined frequency;
fixed receiver means including hydrophone means, separately disposed from said transmitter means, for receiving acoustic signals from said zone and providing corresponding electrical signals as an output;
automatic gain controlled amplifier means, responsive to said hydrophone means, for amplifying target return signals with a gain that is varied in response to slowing changing background noise;
up and down Doppler resolver means, responsive to said reference frequency and to the output of said amplifer means, for providing target signal containing up Doppler and down Doppler sideband frequencies;
signal processing means, responsive to said up Doppler and down Doppler sideband frequencies, for effecting filtering and detection of signals at a plurality of fixed bandpass frequencies within said sideband frequencies and for repetitively providing a multiple bit binary word representative of samples of a plurality of detected return signal conditions including energy, spectral slope, and stroke content;
logic means, responsive to predetermined combinations of rates of occurrence of word bit binary levels, for generating a utilization initiating signal; and
utilization means, responsive to said utilization initiating signal, for effecting a predetermined utilization function.
1 Assignment
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Accused Products
Abstract
A bistatic, Doppler sonar that having a plurality of receiver channels det intrusion in an insonified water zone processes return signals in a plurality of discrete up Doppler and down Doppler frequencies to effect short and long term averaging of return energy and short and long term averaging of return energy slope prior to sampling and comparison to generate a multiple bit binary word that is periodically updated and read out in parallel form to detection logic. The detection logic utilizes parallel sets of shift register memories and comparators to detect when rates of occurrence of energy, slope, and stroke conditions exceed predetermined rates, and utilizes a plurality of levels of coincidence gates to detect predetermined combinations of such conditions that will produce an alarm initiating signal.
34 Citations
13 Claims
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1. A bistatic sonar system for detecting intrusion into a predetermined zone of a body of water, said system comprising:
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a source of a reference frequency; fixed, continuous wave transmitter means, responsive to said reference frequency, for insonification of said zone with acoustic energy at a predetermined frequency; fixed receiver means including hydrophone means, separately disposed from said transmitter means, for receiving acoustic signals from said zone and providing corresponding electrical signals as an output; automatic gain controlled amplifier means, responsive to said hydrophone means, for amplifying target return signals with a gain that is varied in response to slowing changing background noise; up and down Doppler resolver means, responsive to said reference frequency and to the output of said amplifer means, for providing target signal containing up Doppler and down Doppler sideband frequencies; signal processing means, responsive to said up Doppler and down Doppler sideband frequencies, for effecting filtering and detection of signals at a plurality of fixed bandpass frequencies within said sideband frequencies and for repetitively providing a multiple bit binary word representative of samples of a plurality of detected return signal conditions including energy, spectral slope, and stroke content; logic means, responsive to predetermined combinations of rates of occurrence of word bit binary levels, for generating a utilization initiating signal; and utilization means, responsive to said utilization initiating signal, for effecting a predetermined utilization function. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A bistatic, Doppler sonar system including a projector for insonifying a water zone with continuous wave acoustic energy centered at a predetermined carrier frequency, a multiple channel receiver for receiving return signals from said zone at frequencies including said carrier frequency and Doppler shifted sidebands thereof and operative to form alarm initiating signals when the return signals include detected energy, time, and frequency characteristics representative of an intrusion into said zone, each receiver channel comprising:
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a hydrophone; an automatic gain controlled preamplifier connected to amplify outputs of said hydrophone; resolver means, responsive to direct and quadrature forms of said carrier frequency and to said return signals, for providing outputs representative of up Doppler and down Doppler frequencies; pluralities of first and second filter and detector units for detecting return signals at corresponding pluralities of discrete up Doppler and down Doppler frequencies, respectively; a plurality of first and second short term averagers connected to provide short term averages of the return signals detected by said first and second sets of filter and detector units, respectively; a plurality of first and second long term averagers connected to provide long term averages of the return signals detected by said first and second sets of filter and detector units, respectively; first and second slope computing means, responsive to a portion of said short term averages of said first and second short term averagers, respectively, for providing first and second slope representing signals; first and second additional long term averagers for providing long term averages of each of said slope representing signals; first and second multiplexers for respectively sampling said long and short term averages to form first and second series of samples representative thereof; a comparator for comparing said samples of said first and second series to provide a series of binary data bits representative thereof; a recirculating memory for converting said series into a periodically recirculating multiple bit binary word, and for periodic reading out of said word in parallel bit form; first, second, third, fourth and fifth pluralities of parallel accumulator and comparator means, responsive to said periodic parallel bit readout, for providing a plurality of outputs each representative of presence or absence of a predetermined frequency of occurrence of a predetermined return signal condition corresponding to presence or absence of an intrusion; a plurality of coincidence gate means, responsive to predetermined combinations of said accumulator and comparator means outputs to provide an intrusion signal. - View Dependent Claims (11, 12, 13)
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Specification