GB2240847A - Sonar surveillance system for shallow water - Google Patents
Sonar surveillance system for shallow water Download PDFInfo
- Publication number
- GB2240847A GB2240847A GB9102718A GB9102718A GB2240847A GB 2240847 A GB2240847 A GB 2240847A GB 9102718 A GB9102718 A GB 9102718A GB 9102718 A GB9102718 A GB 9102718A GB 2240847 A GB2240847 A GB 2240847A
- Authority
- GB
- United Kingdom
- Prior art keywords
- sensors
- sonar
- barrier
- detection system
- underwater detection
- 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
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO 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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/003—Transmission of data between radar, sonar or lidar systems and remote stations
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO 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
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
- G01S15/04—Systems determining presence of a target
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO 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
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/87—Combinations of sonar systems
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/16—Actuation by interference with mechanical vibrations in air or other fluid
- G08B13/1609—Actuation by interference with mechanical vibrations in air or other fluid using active vibration detection systems
Landscapes
- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
Abstract
A surveillance sonar system for detection particularly of swimmers comprises a number of sonar emitters/receivers 23 operating at a frequency which is high enough such that the signals are low range, leading to a signal/reverberation ratio insensitive to array dimensions and a requirement for only low bandwidth. Such a system is produced by locating a series of sonar detectors, both active and passive, to produce overlapping beams giving an insonified barrier at the minimum response range around a sensitive target 21. A continuous region extending along the length of the barrier is formed within each point is covered by at least two emitters. Coherent processing of the received sonar signals is then used. The overlapping beams could be produced by bottom located sonars 23 with upwardly directed beams or by sonars 24 sited on platforms in mid-water depth with horizontal beams. The spatial diversity thus produced by overlapping beams reduces the possibility of false alarms. The barrier sonars are sequenced such that there is minimum mutual interference. The system also preferably includes the use of a second tier detector arrangement provided by a high resolution sonar located on a boat which is directed to the general area in which barrier penetration is detected. <IMAGE>
Description
A Surveillance System for use in Shallow Water The invention relates te underwater surveillance detectors for use
particularly to provide security in harbour installations where there are
high ambient noise levels.
In underwater areas of high noise use of conventional optical or sonar
detection Eystems is unsatisfactory. the underwater swimmer, suitably equipped can present a serious threat to prime targets in harbour
environments for example. Such environments pose surveillance problem associated with murky shallow water and the distracting influence of normal
dockyard activities. Poor underwater visibility places an emphasis on use
of sonar for swinmer detection and when using such a detection arrangement
operation of ships' sonar during maintenance tests or normal depth sounding
activities adds to the difficulties of detecting intruders.
Active sonar arrangements could overcome sane of the abate noise difficulties hcwever use of active transmissions in shallow water leads to problems
associated with reverberation and severe signal fluctuation due to inultipath trananission.
The object of the invention is to provide an underwater detection system
capable of detecting swiMmers in shallow murky water.
The invention provides an underwater detection system for use in shallow
water comprising:
a plurality of spaced short detection range sonar transmitter/receiver
sensors arranged to provide an insonified barrier of overlapping beams such
that a continuous region is formed extending along the barrier wherein each point in the barrier region is insonified by at least two sensors;
a control unit connected to the sensors such that ultrasound energy is
transmitted sequentially by respective sensors with a time interval between
successive transmissions so as to avoid interference and false response in
adjacent sensors; and
means to receive signals detected by the sensors, to coherently process
spatially diverse information fran adjacent sensors, and to provide an
indication of the position where the insonified barrier has been penetrated.
Coherent processing of the sonar information provides a system with good performance against multipath interference in shallow water and low sensitivity to interference fram ships' wakes and their sonars.
We choose suitably high frequency such that the sonar range is limited by propagation loss or by propagation anomaly e.g. knawn velocity gradient.
typically the frequency is greater than 300 kiz. Active correlation in the invention combats both interference fran ship's sonars and fluctuation in signal strength and reverberation due to xltipath transmission.
By using short range sonar sensors the system reliability under varying sea state conditions can be high with low sensitivity of the signal/ reverberation ratio to array dimensions and signal bandwidth. In addition relatively siFçle signal processing techniques can be employed leading to system simplicity and cost effectiveness. The inherent performance stability makes the invention suitable for use in an autcmated system. Advantageously therefore the means receiving the signals include a threshold level detector effective such that an alarm or other warning signal is produced when a sensor signal exceeds a predetermined threshold level.
Since the system is insensitive to sensorbeamwidth it is preferable to employ wide-beamwidth sensors such that economy in numbers can be achieved.
Advantageously the system includes one or more passive sonar sensors and a passive receiver responsive to noise originated by a target whereby an object penetrating the insonified barrier can be classified. Classification means may include correlation detectors. The e processing against multipath is due to the inherent diversity action (in frequency and time) of a correlation receiver. This diversity may be combined with spatial diversity provided by the distributed sensors.
The system may also include one or more magnetic sensors. The magnetic sensors may also be connected to the passive receiver. Advantageously the signals may be connected from sensors to receivers by optical fibres.
Advantageously, for locating a swimmer the system includes a boat equipped with a high resolution sonar, preferably a sector scanning sonar, for intercepting the swimmer once penetration of the insonified barrier has been detected. Advantageously the system includes a radio link to transfer information fran the sonar barrier to the boat.
The disposition and type of sensors employed will generally be optimised in dependence on the degree of security required, the sea bed topograpoy and the water depth. The sensors may be located on the sea-bed and directed;uplrardly such that their beams overlap. Alternatively the sensors may besupportedat mid-water depth with their beams directed borizontally so as to provide an insonified barrier.
The invention will now be described with reference to the aocwpasying Drawings of which:
Figure 1 graphically illustrates the dependence of signal/surface reverberation ratio on range to array depth ratio for a sonar system;
Figures 2a - 2d show planviews of four sonar security barrier arrangements to protect a ship or installation close to a shore; and
Figure 3 is a schematic diagram of a sonar system configuration.
As can be seen in Figure 1 there is a significant change in performance of a sonar array at the point 11 when signal to reverberation ratio is plotted against range to array depth. Area A on the graph corresponds to operation where the sensitivity of the signal/reverberation ratio to array dimensions and signal bandwidth is low and array depth presents the major controlling influence. In area B, on the other hand, the sensitivity to array dimensions and signal bandwidth is almost as great as the sensitivity to array depth.
Obviously, if long ranges are essential then area B is the only choice, demanding narrow acoustic beaowidths and wide signal bandwidths to achieve the necessary performance, In the surveillance role a large number of beams would then be required to provide any appreciable coverage and the requirement for such a large number of beams increases the overall oarrplexity and vulnerability to false alarm and false target responses.
Another point about operation in area B is the sensitivity between signal/reverberation ratio and range, where it can be seen fran the slope of the graph that a small change in signal/reverberation corresponds to a considerable change in range. This inpies that a complex system of signal processing and beam forming would be required to retain stability and consistency of performance under varying sea state conditions.
Operation in area B, therefore, although promising long detection ranges under reverberation limited conditions, does demand appreciable if not completely unmanageable equipment complexity for really extensive surveillance coverage, particularly when, for example, a system of autariatic detection is required. In area A, it can be seen that provided a short detection range is acceptable, there is considerably less sensitivity between the signal/reverberation ratio and range, and it is much easier to achieve a stable performance and set a detection threshold for an automatic detection scheme.Also the reduced sensitivity to array dimensions or beam width and signal bandwidth means that, despite the shorter ranger surveillance coverage may be achieved with fewer judiciously placed wide beams, and therefore much less complex equipment. Also, environmental conditions often present an ultimate limit to the detection range and no amount of clever signal processing can retrieve the situation. In the present invention, which aims to provide an automatic surveillance facility in shallow water over a relatively extensive area, short range sensors operating in area A are selected. As will be described below, once an intrusion into a protected area has been identified the invention may use a longer range sonar operating in area B to accurately locate the intruder.
Thus a frequency typically greater than 300 kHzr is chosen such that the sonar range is limited by propagation loss or propagation anomaly, e.g. velocity gradient in the selected site.
Figure 2 shows four possible sonar security barriers for protecting a sensitive site area 21 (shown shaded) adjacent to a shore. Sites rea,uiring surveillance coverage can differ widely in detailed area of coverage, water depths and sea bed topography so there will be a range of appropriate patterns of sensor placement. The barriers are formed such that adjacent sensor beams overlap to provide spatial diversity in the received sonar signals.
Figure 2a shows an arrangement of security surveillance applicable to protecting a site where the sea water 22 is particularly shallow and a high degree of security is required. Sonar transmitter/receivers 231 and 232 are located on the sea bed and upwardly directed so as to form two respective rows of overlapping beams. mis forms a dense insonified area or barrier around the site 21. Tne e barrier is placed a minimum distance from the site 21 consistent with providing adequate time for response to intrusion through the
barrier so as to minimise the number of sensors required.
In Figures 2b and 2c fewer sensors 24 and 25 respectively are employed. The
sensors are mounted at approximately mid-water depth, pointing borizontally to produce a barrier of overlapping beams. As sbcwTb each of the sensors 24
bas an identical b-i directed around the line of the insonified barrier. In
Figure 2c, sensors 252 are each arranged to provide relatively narrow forward
and backward beams along the line of the barrier wbile inner sensors 251
provide outwardly directed relatively wide beams towards respective outer
sensors 252 to cover the areas of low sensitivity in the beam patterns of the
252 sensors.
Figure 2d shows an arrangement particularly suitable for a sea bed shelving
away from the area 21 to be protected. The sensors 26 producing relatively
wide angle beams are arranged either on the sea bed or atmiwater depth with beams directed borizontally and outwardly in the direction of increasing
water depth. In this manner the number of sensors is reduced to a minintm while providing an increasing depth coverage with range to match the sea bed
topography.
As shown in the Figure 2 arrangements the sonar detection range of the sensors
indicated by the dashed lines is only of importance in terms of sensor spacing
and hence the total number required for a given unbroken surveillance coverage. In concept each sensor can be siie and the numbers required do not represent a particular problenb and the really critical performance
requirement, that of providing a timely warning of approaching intruders, is solely dependent on spacing of theline of sensors from the boundary of the sensitive area.This scheme therefore relieves the pressure on the sonar detection performance, which in shallow water is fraught with problems
including velocity gradient effects which represent virtually an inssursountable limit, and diverts the emphasis on to the physical placement
of the sensors and lengths of signal and supply cables fran tbese sensors to
the shore-based equipment; technical problems that are caoparatively easy to
solve.
As can be seen fran the sensor placeeent patterns of sches 2(a) to 2(d) there
are varying degrees of overlap of the beams and it is in these overlap regions
that spatial diversity is achieved. By inonifying a target in the overlap region using sensors separated in space, the propagation paths to and fran the target possess detailed features that are independent and an averaging process will then yield improved signal/reverberation performance. It is to be noted that this improvedperform2nce is a consequence of spaced d sensors and cannot be achieved by the nwllti-beam single array sensors.Thus, the mu1tiple, short range, less complex sensor system, if so arranged, has the added advantage of being able to provide spatial diversity.
Bavingncw achieved very good signal/reverberation performance by adopting a short range sensor schemewith inherent spatial diversity characteristics it now remains to note that interpolation and tracking techniques applied to the sensor responses can provide further enhancements to the target detection process.
Finally, bearing in mind the finite speed of sound in water and that each sensor transmission has to be sequenced in such a way that interference and false responses are avoided in adjacent sensors, a further advantage of the short sensor is that the shorter listening intervals involved keep the overall sequence time to a minimum The insonified barriers described above lead to a high probability of detection of an intruder whilst the intruder is within the barrier. Upon detection the system can be arranged to sound an alarm and, based on the location of the particular barrier segment crossed, a boat can be sent out equipped with a high resolution sector scanning sonar to intercept the intruder.Thus the invention operates advantageously as a 2-tier detection system: the first tier insonified barrier indicating penetration and the second tier boat-monitor sonar being used tto intercept the swimmer. Once located by weans of the second tier boat sonar, scare charges or towed electrically energised electrodes can be used to bring the swimmer to the surface.
A typical system configuration is shown in Figure 3. An array 31 of active and passive sonar sensors is situated along the required barrier position 32 to suit the local erwironeent as in one of the arrangements shown for tampl in Figure 2. One or more magnetic sensors may be included in the barrier.
Underwater cables 33 connect power and received signals between groups of sensors 31 and respective shore boxes 34. Depending on the detailed application the sensors can be conventional underwater transducers, or fibre optic versions which have the advantage of simplifying the cableways to the shore. The shore boxes 34 are each connected to a console 35 housing the display 36, a recorder 37, the processing electronics 38 and a radio link 391t392 to the boat 310. The e processing electronics includes a transmitter 311, a sequencer 312, an active correlation receiver 313, a passive receiver 314, been interpolation 315, thresholding 316, tracking 317 and classification logic 318 embracing both active and passive nodes.The display 36 has facilities to show sensor and beam positions in relation to an overall area plan, beam intruder alarm indications including tracks, and sonar A scans both sequenced and selected. The recording facility 37 is included to enable alarm trips to be checked and to provide training for boat operators. The e radio unit 391 in the console transmits the display information to the boat operator enabling a high resolution sonar 319 on the boat to be accurately directed to the barrier crossing. The application of an active correlation technique cats interference from ship's sonars and fluctuations in echo strength and reverberation due to multipath.The processing against multipath is due to the inherent diversity receiver action (in frequency and time) of a correlation receiver and this is combined with the spatial diversity provided by the distributed array of sensors.
According to more specific requirements in terms of cost, canolexity and degree of protection alternative features can be made available such as choice of detection threshold dependant on threat status and extent of operator participation.
A critical feature of an automatic alarm system is the false alarm rate. If there are too few alarms it might be argued that security procedures would then lack adequate rehearsal and refinement. On the other hand if there are too many then a genuine alarm might be ignored. By operating the sensors in the way described above an extrettely low statistical false alarm rate can be achieved and unwanted responses to targets such as boat traffic and shoals of fish, when within the bounded protected area, can be eliminated. There remains, of course, the problem of boat traffic, fish, debris etc. crossing the sonar beams constituting the barrier. The characteristics of this sort of target are quite different to that of an intruder.A boat will possess a wake, a passive signature, a radar response, and a crossing velocity different from those associated with the more covert operation. Fish shoals have a particular signature and travel along a somewhat erratic path. It is characteristics like these, and others, that will feature in the echo consistency, tracking and classification logic referred to above.Now, although present day computing technology can cope with such a task, classification algorithms will need updating and further development as knowledge of the whole range of targets (both wanted and unwanted) and the environment improves. Itis means that early versions of any type of autanatic intruder detection system will require sane limited form of operator intervention to counter the unknown or unexpected responsive: hence the recording system referred to above. Thus the system nust be equipped with the facility to readily expand the classification logic as required and it is then expected that operator interaction will steadily decrease.In addition, as the sonar system and its display is simply part of an overall security system it should not be regarded in isolation but as an additional source of information to be combined with standard procedures involving visual sightings, radar displays and known timetabled events. This will relieve, to sane extent, pressure on early versions of classification logic but this does not exclude the need to progressively develop more advanced comçuting algorithms because it is recognised that an intruder might well exploit standard activities to mask his approach.
A further consideration with regard to the computing algorithms used is the inherent spatial and time diversity action of the short range overlapping sonar beams of the proposed system. Initially the thresholding of rapidly sequenced beams will suffice but further improvements in performance can be gained by storing successive A scan responses. With the majority of electronics housed in the console and shore boxes, the off-shore sensor electronics should consist of no more than receiver pre-ampIffication, line termination, and transmitter matching circuitry. Such simplicity confers advantages in terms of compactness, reliability and flexibility of sensor installation arrangements.Sensors can be located in a variety of ways depending on seabed topography and composition, ranging fram custat-built bottom located platforms, or mini-towers/tripods with adjustable legs to tethered buoyant platforms with adjustable risers. Problems associated with the softer seabed can be countered by using either some form of pile construction or distributed loading to encourage ccwFaction. This last wethodhasalready been used successfully by adopting a large diameter for the heavy sinker weight of a buoyant platform and this idea can be extended to lighter weight applications using loading pads, rafts or a wide expanse of close knit mesh.
The present surveillance system provides a warning time of intruder approach determined solely by the range at which a sonar barrier is located from the sensitive area. Sonar detection performance then simply determines sensor separations and hence the number of sensors in a barrier, and what would otherwise have been an ipoossible sonar detection range requirement is converted into the reasonably easily satisfied need to mount sensors at that warning range and convey signals and power via cabling to the shore.
It is notable that the area within the barrier can support local boat traffic without triggering an alarm.
The barrier is segmented to provide target track information and a boat equipped with high resolution sonar completes the final phase to accurately locate the intruder.
Finally, it must be emphasised that there are swinr and water depths for which 100% successful sonar operation cannot be guaranteed and in these cases mechanical devices must be used swimmer either into a favourable water depth or out of the water completely.
Claims (13)
1. An underwater detection system for use in shallow water comprising: a plurality of spaced short detection range sonar transmitter/receiver sensors arranged to provide an insonified barrier of overlapping beams such that a continuous region is formed extending along the barrier wherein each point in the barrier region is insonified by at least two sensors; a control unit connected to the sensors such that ultrasound energy is transmitted sequentially by respective sensors with a time interval between successive transmissions so as to avoid interference and false response in adjacent sensors; and means to receive signals detected by the sensors, to coherently process spatially diverse information from adjacent sensors, and to provide an indication of the position where the insonified barrier has been penetrated.
2. An underwater detection system as claimed in claim 1 wherein the means receiving the signals includes a threshold level detector effective such that an alarm or other warning signal is produced when a sensor signal exceeds a predetermined threshold level.
3. An underwater detection system as claimed in claim 1 or 2 wherein the sensors have wide beamwidth.
4. An underwater detection system as claimed in any one preceding claim wherein the system includes one or more passive sonar sensors connected to a passive receiver and responsive to noise originated by a target whereby an object penetrating the insonified barrier can be classified.
5. An underwater detection system as claimed in claim 4 wherein the classification means includes correlation detectors.
6. An underwater detection system as claimed in any one preceding claim wherein there is included one or more magnetic sensors.
7. An underwater detection system as claimed in claim 6 wherein the magnetic sensors are connected to the passive receiver.
8. An underwater detection system as claimed in any one preceding claim wherein the signals may be connected from sensors to receivers by optical fibres.
9. An underwater detection system for locating a swimmer underwater as claimed in any one preceding claim wherein the system includes a boat equipped with a high resolution sonar for intercepting the swimner once penetration of the insonified barrier has been detected.
10. An underwater detection system for locating a swimmer underwater as claimed in claim 9 wherein the high resolution sonar is a sector scanning sonar.
11. An underwater detection system as claimed in claim 9 or 10 wherein the system includes a radio link to transfer information from the sonar barrier to the boat.
12. An underwater detection system as claimed in any one preceding claim wherein the sensors are located on thesea-bedand directed upwardly such that their beams overlap.
13. An underwater detection system as claimed in any one of claims 1 to 11 wherein the sensors are supported at mid-water depth with their beams directed horizontally so as to provide an insonified barrier.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB909002948A GB9002948D0 (en) | 1990-02-09 | 1990-02-09 | Swimmer surveillance system |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9102718D0 GB9102718D0 (en) | 1991-03-27 |
| GB2240847A true GB2240847A (en) | 1991-08-14 |
| GB2240847B GB2240847B (en) | 1994-03-09 |
Family
ID=10670715
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB909002948A Pending GB9002948D0 (en) | 1990-02-09 | 1990-02-09 | Swimmer surveillance system |
| GB9102718A Expired - Lifetime GB2240847B (en) | 1990-02-09 | 1991-02-08 | A surveillance system for use in shallow water |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB909002948A Pending GB9002948D0 (en) | 1990-02-09 | 1990-02-09 | Swimmer surveillance system |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB9002948D0 (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2897442A1 (en) * | 2006-02-13 | 2007-08-17 | Marc Brussieux | Intrusion detection device for e.g. coastal area, has coordination unit to coordinate detection unit with information so that detection axis is pointed towards intruder, and control unit to control pointing of axis on position of intruder |
| WO2017131980A1 (en) * | 2016-01-25 | 2017-08-03 | Microsoft Technology Licensing, Llc | Intrusion detection for submerged datacenters |
| US9913409B2 (en) | 2015-06-26 | 2018-03-06 | Microsoft Technology Licensing, Llc | Intrusion detection for submerged datacenters |
| FR3060761A1 (en) * | 2016-12-20 | 2018-06-22 | Thales | OPTIMIZED SYSTEM FOR THE ACOUSTIC DETECTION OF VARIOUS UNDERWATER THREATS ON A SENSITIVE AREA |
| FR3060762A1 (en) * | 2016-12-20 | 2018-06-22 | Thales | MODULAR DISTRIBUTED SYSTEM FOR THE ACOUSTIC DETECTION OF UNDERWATER THREATS ON A SENSITIVE AREA |
| US10524395B2 (en) | 2015-06-26 | 2019-12-31 | Microsoft Technology Licensing, Llc | Artificial reef datacenter |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1205660A (en) * | 1968-01-02 | 1970-09-16 | Bendix Corp | Fish counting device using sound waves |
| GB2042173A (en) * | 1979-02-05 | 1980-09-17 | Bendix Corp | Ultrasonic fish counting system |
| GB2111679A (en) * | 1981-10-20 | 1983-07-06 | Standard Telephones Cables Ltd | Sonar intruder detectors |
-
1990
- 1990-02-09 GB GB909002948A patent/GB9002948D0/en active Pending
-
1991
- 1991-02-08 GB GB9102718A patent/GB2240847B/en not_active Expired - Lifetime
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1205660A (en) * | 1968-01-02 | 1970-09-16 | Bendix Corp | Fish counting device using sound waves |
| GB2042173A (en) * | 1979-02-05 | 1980-09-17 | Bendix Corp | Ultrasonic fish counting system |
| US4225951A (en) * | 1979-02-05 | 1980-09-30 | The Bendix Corporation | Fish counter with scanning transducer |
| GB2111679A (en) * | 1981-10-20 | 1983-07-06 | Standard Telephones Cables Ltd | Sonar intruder detectors |
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2897442A1 (en) * | 2006-02-13 | 2007-08-17 | Marc Brussieux | Intrusion detection device for e.g. coastal area, has coordination unit to coordinate detection unit with information so that detection axis is pointed towards intruder, and control unit to control pointing of axis on position of intruder |
| US9913409B2 (en) | 2015-06-26 | 2018-03-06 | Microsoft Technology Licensing, Llc | Intrusion detection for submerged datacenters |
| US10524395B2 (en) | 2015-06-26 | 2019-12-31 | Microsoft Technology Licensing, Llc | Artificial reef datacenter |
| WO2017131980A1 (en) * | 2016-01-25 | 2017-08-03 | Microsoft Technology Licensing, Llc | Intrusion detection for submerged datacenters |
| WO2018115127A1 (en) * | 2016-12-20 | 2018-06-28 | Thales | Optimised acoustic detection system for detecting various underwater threats in a sensitive zone |
| WO2018115125A1 (en) * | 2016-12-20 | 2018-06-28 | Thales | Modular distributed system for the acoustic detection of underwater threats in a sensitive zone |
| FR3060762A1 (en) * | 2016-12-20 | 2018-06-22 | Thales | MODULAR DISTRIBUTED SYSTEM FOR THE ACOUSTIC DETECTION OF UNDERWATER THREATS ON A SENSITIVE AREA |
| FR3060761A1 (en) * | 2016-12-20 | 2018-06-22 | Thales | OPTIMIZED SYSTEM FOR THE ACOUSTIC DETECTION OF VARIOUS UNDERWATER THREATS ON A SENSITIVE AREA |
| US11333755B2 (en) | 2016-12-20 | 2022-05-17 | Thales | Optimised acoustic detection system for detecting various underwater threats in a sensitive zone |
| IL267486B1 (en) * | 2016-12-20 | 2023-03-01 | Thales Sa | Optimised acoustic detection system for detecting various underwater threats in a sensitive zone |
| IL267474B1 (en) * | 2016-12-20 | 2023-03-01 | Thales Sa | Modular distributed system for the acoustic detection of underwater threats in a sensitive zone |
| IL267474B2 (en) * | 2016-12-20 | 2023-07-01 | Thales Sa | Modular distributed system for the acoustic detection of underwater threats in a sensitive zone |
| IL267486B2 (en) * | 2016-12-20 | 2023-07-01 | Thales Sa | Optimised acoustic detection system for detecting various underwater threats in a sensitive zone |
| US11796674B2 (en) | 2016-12-20 | 2023-10-24 | Thales | Modular distributed system for the acoustic detection of underwater threats in a sensitive zone |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9002948D0 (en) | 1990-04-04 |
| GB9102718D0 (en) | 1991-03-27 |
| GB2240847B (en) | 1994-03-09 |
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