US3740704A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Sonic detection method and apparatus
Assignee: United States Department of the Navy
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Filing: 1968-10-28
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Granted: 1973-06-19
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Expires: 1988-10-28
Abstract
Abstract A sonic detection system installed adjacent the upstream side of a bridge for detecting and indicating the intrusion of swimmers into an adjacent guarded volume of water. The system utilizes the interference signal attributable to multiple signal reflection paths and Doppler frequency shifts therein to enable the detection of both swimmers floating with the primary current and those moving relative to the primary current. The system includes a directional, continuous wave sound projector and a matched directional receiver which are submerged and are arranged in spaced relation normally of the primary current to have their beam pattern axes intersect at a point upstream of the bridge for establishing the guarded volume. Fixed filters and an adjustable filter are included along with a display which is adjustable for the prevailing ambient conditions to provide indications that the overall response and/or certain received signal frequency spectra have increased above generally randomly varying ambient levels.
Inventors
- 👤 H Suter
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 04:41
CPC Classifications
G; G01; G01S; G01S15/00; G01S15/02; G01S15/50; G01S15/52; G01S15/523
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
208 words
A method of detecting the appoach of an energy reflective object moving through a body of water having a current of variable velocity comprising the steps of: continually ensonifying a guarded volume of water within the body of water with a single tone acoustic signal to produce a reflected interference signal; receiving the interference signal reflected from the guarded volume; processing the received interference signal both to extract a plurality of fixed groups of Doppler shift frequency spectra of successive frequencies in a plurality of contiguous bandwidths of fixed center frequencies defining in composite a predetermined range of frequency spectra corresponding to a range of Doppler velocities encompassing the variable velocity of the current and to extract a variable group of Doppler shift frequency spectra in a narrow bandwidth of selectively adjustable center frequency within the predetermined range; selecting for extraction a variable group of Doppler shift spectra having frequencies greater than an amplitude peaked variable group of spectra having a maximum composite signal level and having a composite group signal level under prevailing ambient conditions which is less than that of the amplitude peaked variable group; and detecting group signal level increases above preset threshold levels for each of the fixed and selected variable groups of spectra.
Claim 2
Independent Claim
208 words
A method of detecting the appoach of an energy reflective object moving through a body of water having a current of variable velocity comprising the steps of: continually ensonifying a guarded volume of water within the body of water with a single tone acoustic signal to produce a reflected interference signal; receiving the interference signal reflected from the guarded volume; processing the received interference signal both to extract a plurality of fixed groups of Doppler shift frequency spectra of successive frequencies in a plurality of contiguous bandwidths of fixed center frequencies defining in composite a predetermined range of frequency spectra corresponding to a range of Doppler velocities encompassing the variable velocity of the current and to extract a variable group of Doppler shift frequency spectra in a narrow bandwidth of selectively adjustable center frequency within the predetermined range; selecting for extraction a variable group of Doppler shift spectra having frequencies greater than an amplitude peaked variable group of spectra having a maximum composite signal level and having a composite group signal level under prevailing ambient conditions which is less than that of the amplitude peaked variable group; and detecting group signal level increases above preset threshold levels for each of the fixed and selected variable groups of spectra.
Claim 3
Dependent Claim
95 words
A method according to claim 1 wherein the step of selecting includes the steps of: detecting a maximum composite group signal level of a first variable group of spectra encompassing those spectra of maximum amplitude which correspond to the prevailing ambient velocity of the current; detecting a minimum composite group signal level of a second variable group of spectra having greater frequencies than the the first group; and selecting for extraction a third variable group of spectra having both frequencies and a composite group signal level intermediate those of the first and second variable groups.
Claim 4
Dependent Claim
26 words
A method according to claim 2 further comprising the step of: establishing the guarded volume of water remotely of a location of receiving the interference signal.
Claim 5
Dependent Claim
40 words
A method according to claim 2 further comprising the step of: establishing the preset threshold level for each of the fixed and the third variable groups of spectra above the composite group signal level thereof which prevails under ambient conditions.
Claim 6
Dependent Claim
102 words
A method according to claim 1 further comprising the steps of: positioning within the body of water and in fixed relation to a bottom boundary of the water both a narrow beam directional projector for projecting the acoustic signal and a narrow beam directional receiver for receiving the interference signal at spaced locations along a line extending transversely of the prevailing direction of the current; and orienting the projector and receiver to have respective beam pattern axes intersecting remotely upstream along the bisector of the projector-receiver spacing which bisector is aligned with the direction of the current, forming thereby the guarded volume.
Claim 7
Dependent Claim
39 words
A method according to claim 5 wherein the steps of positioning comprises the step of: spacing the projector from the receiver a distance of at least 10 feet along the line extending perpendicularly of the direction of the current.
Claim 8
Dependent Claim
38 words
A method according to claim 6 wherein said step of continually ensonifying includes the step of: continually ensonifying the guarded volume with a single tone acoustic signal having a frequency in the range between audible and 150 KHz.
Claim 9
Dependent Claim
162 words
Detection apparatus comprising: array means including projector means for ensonifying a guarded volume of water with an acoustic signal and receiver means for receiving reflections of said acoustic signal and providing a receiver output signal; detector means connected to said receiver means for receiving said receiver output signal and providing a detector output signal indicative of Doppler shift spectra in said receiver output signal; a plurality of fixed bandpass filters connected to receive said detector output signal for providing filtered output signals of respective frequency bands collectively forming a predeteRmined frequency range encompassing Doppler shift spectra attributable to moving acoustic signal reflective media; an adjustable, narrow bandpass filter connected to receive said detector output signal for providing a filtered output signal and having adjusting means for shifting its bandpass characteristics and center frequency over a predetermined range; and indicator means for indicating signal level increases in the filtered output signals of each of said adjustable bandpass filter and said fixed bandpass filters.
Claim 10
Dependent Claim
162 words
Detection apparatus comprising: array means including projector means for ensonifying a guarded volume of water with an acoustic signal and receiver means for receiving reflections of said acoustic signal and providing a receiver output signal; detector means connected to said receiver means for receiving said receiver output signal and providing a detector output signal indicative of Doppler shift spectra in said receiver output signal; a plurality of fixed bandpass filters connected to receive said detector output signal for providing filtered output signals of respective frequency bands collectively forming a predeteRmined frequency range encompassing Doppler shift spectra attributable to moving acoustic signal reflective media; an adjustable, narrow bandpass filter connected to receive said detector output signal for providing a filtered output signal and having adjusting means for shifting its bandpass characteristics and center frequency over a predetermined range; and indicator means for indicating signal level increases in the filtered output signals of each of said adjustable bandpass filter and said fixed bandpass filters.
Claim 11
Dependent Claim
36 words
Detection apparatus according to claim 8 wherein: said projector means includes a projector and oscillator means connected to said projector for providing thereto a continuous wave, single tone, signal for projection to ensonify the guarded volume.
Claim 12
Dependent Claim
41 words
Apparatus according to claim 8 further comprising: circuit means connected between said oscillator means and said receiver means for continuously applying an electrical sample of said single tone signal for addition to the said electrical output signal of said receiver means.
Claim 13
Dependent Claim
42 words
Apparatus according to claim 8 wherein: said projector means and said receiver means comprise a narrow beam directional projector and a matched narrow beam directional receiver arranged in spaced relation to form a guarded volume spaced from said projector and said receiver.
Claim 14
Dependent Claim
53 words
Apparatus according to claim 11 wherein: said transducer and said receiver are spaced apart along a line extending transversely of a prevailing current in a guarded volume and have their beam axes orineted to intersect at an upstream point on a current-flow direction aligned bisector of the spacing between said projector and receiver.
Claim 15
Dependent Claim
32 words
Apparatus according to claim 12 wherein: said projector means includes oscillator means providing a continuous wave, single tone signal for projection having a frequency in the range between audible and 150 KHz.
Claim 16
Dependent Claim
27 words
Apparatus according to claim 12 wherein: said projector and said receiver each comprise a concave parabolic signal reflector and a spherical transducer fixed at the focus thereof.
Claim 17
Dependent Claim
90 words
Apparatus according to claim 12 wherein: said projector means includes an oscillator providing a continuous wave single tone electrical signal, a coupling transformer having a primary winding connected to receive said electrical signal and having a grounded, center tapped secondary winding connected to said projector and a potentiometer having a movable wiper arm connected across said secondary winding of said coupling transformer; and said apparatus further comprises circuit means for applying the electrical signal appearing at said wiper arm to said receiver means for addition to said receiver output signal.
Claim 18
Dependent Claim
58 words
Apparatus according to claim 12 further comprising: variable gain amplifier means for amplifying said detector output signal applied to said filters including an automatic gain control loop for adjusting the gain of said amplifier to compensate for changes in the prevailing signal level of the detector output signal gradually occurring over a period of at least ten minutes.
Claim 19
Dependent Claim
120 words
Apparatus according to claim 12 wherein said display means comprises: a plurality of control means each including an input attenuator having adjusting means and being connected to receive said filtered output signal from a respective one of said fixed and adjustable filters for providing a respective filtered attenuated signal each said control means further including threshold responsive alarm driving means connected to receive said filtered attenuated signal for providing an alarm signal; a plurality of meter means each connected to receive a respective said filtered attenuated signal; and a plurality of indicator means each connected to said control means for receiving a respective alarm signal and being responsive thereto for indicating that said filtered attenuated signal exceeds a threshold level.
Claim 20
Dependent Claim
77 words
Apparatus according to claim 17 wherein said plurality of said indicator means further comprises: a plurality of visual alarms each connected to a respective alarm driving means to receive said alarm signal for providing a visual indication; OR gate means connected to each of said alarm driving means for receiving said alarm signals and providing an OR gate output signal; and audible alarm means connected to receive said OR gate output signal for emitting an audible alarm.
Claim 21
Dependent Claim
64 words
Apparatus according to claim 18 further comrpising: a resistor connected at one end to receive the output signal of said detector means; a charging capacitor connected to the other end of said resistor for integrating said signal over a period of at least 1 second; and a meter connected to said charging capacitor for indicating the level of the signal appearing across said capacitor.
References Cited (Backward Citations)
US3121856A
Cited
US3383678A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-06-18 | 1976-12-18 | 1977-06-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-06-18 | 1980-12-18 | 1981-06-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-06-18 | 1984-12-18 | 1985-06-19 | $7700.00 | Window Closed / Lapsed |