GB2238121A - Apparatus for locating 2 sonobuoy - Google Patents

Apparatus for locating 2 sonobuoy Download PDF

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Publication number
GB2238121A
GB2238121A GB9022784A GB9022784A GB2238121A GB 2238121 A GB2238121 A GB 2238121A GB 9022784 A GB9022784 A GB 9022784A GB 9022784 A GB9022784 A GB 9022784A GB 2238121 A GB2238121 A GB 2238121A
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GB
United Kingdom
Prior art keywords
sonobuoy
water
laser
acoustic noise
signals
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB9022784A
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GB2238121B (en
GB9022784D0 (en
Inventor
John Arthur Glasgow
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BAE Systems Electronics Ltd
Original Assignee
GEC Marconi Ltd
Marconi Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by GEC Marconi Ltd, Marconi Co Ltd filed Critical GEC Marconi Ltd
Publication of GB9022784D0 publication Critical patent/GB9022784D0/en
Publication of GB2238121A publication Critical patent/GB2238121A/en
Application granted granted Critical
Publication of GB2238121B publication Critical patent/GB2238121B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S5/00Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/18Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
    • G01S5/30Determining absolute distances from a plurality of spaced points of known location

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

The apparatus comprises a pulsed laser 2 which provides acoustic noise signals at known points A in a body of water. The acoustic noise signals are detected at the sonobuoy 5. The time delay between transmission and detection is used to derive the distance from the points and hence the position of the sonobuoy 5 can be derived. <IMAGE>

Description

Sonobuoy Location This invention relates to a device for locating a sonobuoy at sea.
Sonobuoys are often used to locate submarines or other vessels by passive sonar, that is, the sonobuoy detects noise produced by the vessel. They can be deployed in areas where a submarine is thought to be by a parachute drop from an aircraft. The detected noise is transmitted back to the aircraft by a radio link where it is interpreted. A problem in the past has been to determine from time to time the position of these sonobuoys for it is necessary to relate the bearing of the submarine to the sonobuoys so that ultimate accurate location of a target submarine can be ensured.
Previously the location of the sonobuoys has been achieved by overflying them at intervals, noting their position from the aircraft and hence deriving the actual position of the buoys. However, this can interfere with other operations to be carried out by the aircraft.
Moreover the aircraft may have to return to overfly an area several times to locate several sonobuoys According to the present invention there is provided apparatus to locate a sonobuoy in an expanse of water comprising: processing means for receiving and processing signals received from the sonobuoy; and a laser for producing at least two light pulses for illuminating two spatially separated known points on the surface of the water such that the light pulses produce two spatially separate acoustic noise signals in the water which are detected by the sonobuoy to produce second signals which are transmitted to the processing means which calculates from the second signals and the position of the known points the position of the sonobuoy.
By locating the sonobuoy by producing acoustic noise signals in the water, it is not necessary to overfly the sonobuoy for the acoustic noise signals can be produced some distance away. Since the acoustic noise signals propogate in all directions in the water, the same acoustic noise signals may be used to locate other sonobuoys.
The acoustic noise signals are produced by the rapid heating effect of the laser beam on the water causing rapid expansion of the water and a similar shock wave effect as that produced by a small explosion.
Conveniently, the position is determined from the round trip pulse delay times. This delay is the duration between the transmission and reception of a pulse.
According to a second embodiment of the invention, the processing means determines the position of the sonobuoy by utilising the difference between the pulse repetition frequency of the laser and the frequency of the acoustic noise signals detected by the sonobuoy.
Such an arrangement enables any Doppler shift in the frequency on reception by the sonobuoy to be incorporated into the calculation of the bearing of a sonobuoy, from for example a straight line of eruptions in the water.
The range of the sonobuoy may be found by the round trip time, that is the duration between the transmission and reception of a pulse.
Advantageously the laser is pulsed such that the pulse repetition frequency is detectible by a sensor at the sonobuoy and is within the passband of the sonobuoy's sonar. The power level of the laser can therefore be kept to a minimum and each separate pulse can be precisely timed and arranged to ensure the pulses will add coherently in the sonobuoy receiver to give correspondingly larger signal and the resulting signal transmitted to the aircraft by radio.
Advantageously, the laser may be steered and pulsed so as to impinge the water surface at different positions. Such an arrangement would be advantageous where the apparatus was to be used on a helicopter which could then locate the sonobuoy whilst hovering.
The present invention will now be described by way of example only and with reference to the Figures in which: Figure 1 illustrates diagrammatically a first embodiment of the invention; and Figure 2 illustrates diagrammatically a second embodiment of the invention.
Referring to Figure 1, an overflying aircraft 1 has a laser source 2 mounted on its under side. Pulsed laser light 2A is directed towards known positions on the sea surface 3.
A small area A of the sea surface is illuminated by one of the pulses. This causes rapid expansion of the water causing shock waves 4 to emanate from A. They are detected at a distance d by a detector 5 mounted on a sonobuoy 6. This is the same detector that detects noise from any submarines present in the area. An antenna 8 is mounted on the sonobuoy 6 and is in radio communication with a receiver 9 on the aircraft 1. Information as to the time of arrival of the shock wave 4 is instantaneously transmitted to the aircraft, where it is processed by a processor 10.
The round trip time between initiation of the pulsing of the laser 2 and receiving a response signal from the sonobuoy 5 is recorded by activating a counter within the aircraft. The counter is deactivated when the response signal is received. As the velocity of propagation of the laser energy and the radio signal is approximately 200,000 times faster than sound in water, the laser beam and radio signal propagation delays may be neglected for range measurement. Hence distance d can be computed, that is, the distance from A at which the sonobuoy is located. A locus of positions is thus accorded to the sonobuoy. On transmission of further pulses from laser source 2 when aircraft 1 is at a different position, a short time interval after the first pulse, th same process is repeated.A triangulation technique, using two signals or a "cocked hat" technique using three signals is then used to unambiguously locate the position of the sonobuoy 5. Calculation is performed by the processor 10.
An alternative embodiment, in which location is performed by a different method, will now be described with reference to Figure 2. By transmitting a sequence of pulses in a straight line L at times T1, T2 etc and arranging for the resulting sequence of eruptions T1', T21 etc to be uniformly spaced along the straight line on the sea surface, the bearing 0 of the sonobuoy relative to the line may be determined. This is achieved by using the difference in the perceived frequency (pl) of the pulses as received at the sonobuoy S compared to the actual Pulse Repetition Frequency of the laser (p2). The use of this technique is not a major complication for the signal processing, as it is normal with sonobuoys to use frequency measurement techniques for target analysis and to observe Doppler shifts and other signal frequency variations and characteristics.
The use of two such sequences of noise sources set in different directions will enable unambiguous location of a sonobuoy relative to the two lines. The variation of the perceived frequency (pl) with the bearing of the sonobuoy from the line L may be derived on the following basis in which a fixed pulse repetition frequency of a laser (p2) and a uniform linear sequence of eruptions in the water is employed.
The pulse repetition frequency of the laser is p2 and the velocity of sound in water is c. The spacing of the eruptions in the water is less than c/p2. For convenience the spacing of the eruptions in the water is c/Np2 where N is typically 2 and need not be integer.
At a remote point broadside to the line the received frequency will be p2 as all the path lengths, and hence propagation delays, will be the same. However, at a point ahead and on the line of eruptions the time between adjacent pairs of eruptions, that is the perceived frequency will be: P1 = NP2 N+l By analogy at a point behind and on the line of the eruptions, the period between pulses will be: P1 - NP2 N-l A sonobuoy positioned in between these two extremes of directions at angle 0 to the line L will receive an intermediate frequency wherein the relationship between the angle 0 and the received frequency is: P1 = NP2 N - cos 0 Hence the co-ordinates of a sonobuoy may be found directly.
Of course variation could be made without departing from the scope of the invention, in that the processors could be mounted on the sonobuoys, their position determined in-situ and this position communicated to the overflying aircraft.
The aircraft may simultaneously determine the positions of a number of sonobuoys as the radio return from each will be distinguishable thus allowing separate delays from the noise sources to be determined.
In alternative embodiments of the invention the laser light pulses may be arranged to impinge on the water surface in a predetermined pattern, the range and direction of the sonobuoy may be determined by the timings of the sequence of acoustic noise signals received by the sonobuoy.
The processing means could then compare these received signals with predetermined sets of reference time delay waveforms for that predetermined pattern.
Each time delay waveform corresponding to alternative sonobuoy positions. The sonobuoy could therefore be located by waveform matching.
With suitable signal processing the pattern could be produced randomly offering less chance of the submarines being alerted to the presence of a detection system for the acoustic noise signals would appear random to the submariners and attributed to natural phenomena.

Claims (8)

1. Apparatus to locate a sonobuoy in an expanse of water comprising: processing means for receiving and processing signals received from the sonobuoy; and a laser for producing at least two light pulses for illuminating two spatially separated known points on the surface of the water such that the light pulses produce two spatially separate acoustic noise signals in the water which are detected by the sonobuoy to produce second signals which are transmitted to the processing means which calculates from the second signals and the position of the known points the position of the sonobuoy.
2. Apparatus as claimed in claim 1 wherein the position is located from the calculated round trip pulse delay times.
3. Apparatus as claimed in claim 1 wherein the processing means determines the position of the sonobuoy by utilising the difference between the pulse repetition frequency of the laser and the frequency of the acoustic noise signals detected by the sonobuoy.
4. Apparatus according to Claim 2 or 3 wherein the pulse repetition frequency of the laser is tuned so that the signal received at the sonobuoy is within the pass-band of a sensor mounted on the sonobuoy.
5. Apparatus according to any preceding claim wherein the laser is steered and pulsed so as to impinge the water surface at different positions.
6. Apparatus substantially as herein described and with reference to and as illustrated by Figures 1 or 2.
7. A method of locating a sonobuoy comprising the steps of generating in the water two separate acoustic noise signals, at known positions and at known times with a laser beam, detecting the acoustic noise signals arriving at the sonobuoy, and determining the position of the sonobuoy by calculating its distance from the source of each acoustic noise signal.
8. A method of locating a sonobuoy substantially as herein described with reference to and illustrated by Figures 1 or 2.
GB9022784A 1989-10-21 1990-10-19 Sonobuoy location Expired - Fee Related GB2238121B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB898923750A GB8923750D0 (en) 1989-10-21 1989-10-21 Sonobuoy location

Publications (3)

Publication Number Publication Date
GB9022784D0 GB9022784D0 (en) 1990-12-05
GB2238121A true GB2238121A (en) 1991-05-22
GB2238121B GB2238121B (en) 1994-02-09

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GB898923750A Pending GB8923750D0 (en) 1989-10-21 1989-10-21 Sonobuoy location
GB9022784A Expired - Fee Related GB2238121B (en) 1989-10-21 1990-10-19 Sonobuoy location

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GB898923750A Pending GB8923750D0 (en) 1989-10-21 1989-10-21 Sonobuoy location

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2568975C1 (en) * 2014-07-24 2015-11-20 Российская Федерация, От Имени Которой Выступает Министерство Промышленности И Торговли Российской Федерации Laser-acoustic system for detecting underground objects

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1211052A (en) * 1967-12-05 1970-11-04 Krupp Gmbh Apparatus for locating underwater sound-emitting objects
GB1580393A (en) * 1976-03-29 1980-12-03 Cyr R Underwater transponder arrangement and a metho of calibrating the same

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1211052A (en) * 1967-12-05 1970-11-04 Krupp Gmbh Apparatus for locating underwater sound-emitting objects
GB1580393A (en) * 1976-03-29 1980-12-03 Cyr R Underwater transponder arrangement and a metho of calibrating the same

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2568975C1 (en) * 2014-07-24 2015-11-20 Российская Федерация, От Имени Которой Выступает Министерство Промышленности И Торговли Российской Федерации Laser-acoustic system for detecting underground objects

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Publication number Publication date
GB2238121B (en) 1994-02-09
GB8923750D0 (en) 1990-04-25
GB9022784D0 (en) 1990-12-05

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PCNP Patent ceased through non-payment of renewal fee

Effective date: 19951019