GB2525893A

GB2525893A - Detection system for underwater signals

Info

Publication number: GB2525893A
Application number: GB1408076.6A
Authority: GB
Inventors: Terence Ivan Mason
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-05-07
Filing date: 2014-05-07
Publication date: 2015-11-11
Also published as: GB201408076D0

Abstract

A buoy comprises at least one hydrophone 12, 14 to convert acoustic radiation received from an active acoustic transmitter into electronic signals, and an analysis package 16 to send messages to a remote receiver when triggered by electronic signals corresponding to anticipated acoustic signals from such a transmitter. The system can feature a global position system 24 (GPS) to determine the location of the buoy. The buoy can be programmed to identify specific acoustic signals remotely through a modem or locally through a control port. In use multiple buoys can be spaced apart according to the depth and acoustic transmissivity of the water. Three of the devices can be used to give an accurate location of the transmissions, which can be the pings from a downed aircrafts black box or people banging on the hull or fuselage of a submerged vessel or aircraft.

Description

Detection system for underwater signals [0001] This invention relates to a method and apparatus for detecting underwater acoustic signals and to an alerting system when underwater acoustic signals of interest are detected.

[0002] Recent losses of aircraft and ferries have indicated the need for a system rapidly to detect underwater acoustic signals and to alert would be rescuers of the presence of signals that are of relevance in their search for survivors and wreckage.

[0003] Existing systems are limited to dipping sonar-buoys with hydrophones or submersibles with hydrophones. The capital costs of aircraft or helicopters equipped with hydrophones or of submersibles similarly equipped means that searchers cannot search large areas of ocean at any one time, and therefore deployment is often limited to places where other information suggests that there is a probability of finding a target. In addition such equipment is often deployed one at a time, so that triangulation information to secure a fix on a potential target is absent, limiting the speed of response.

[0004] Acoustic signals of interest may come from an acoustic transmitter on an aircraft black box, trapped persons banging on the hull of a submerged or partially submerged vessel of aircraft.

[0005] The present invention provides a low cost identification and signalling system with individual detectors which may deployed in relatively large numbers over an expanse of sea. It thus provides a system whereby acoustic transmissions originating under water can be identified, triangulated and the source pinpointed with a high degree of accuracy.

[0006] According to the present invention in a first aspect a buoy comprises at least one hydrophone to convert received acoustic radiation from an active acoustic transmitter into electronic signals, and an analysis package to send messages to a remote receiver when triggered by electronic signals apparently corresponding to anticipated acoustic signals from such a transmitter.

[0007] According to a second aspect of the invention a method of locating an active underwater acoustic transmitter comprising deploying on a water mass one or more such buoys.

[0008] The invention provides an electronic buoy which can be tuned to detect acoustic transmissions of interest and to transmit a radio signal to a satellite, aircraft or ship when signals falling within the parameters given to the device are detected. In this way too the need for continual monitoring is obviated as transmission will only occur when a signal of interest is identified by the device. This can be transmitted immediately or downloaded subsequently. In many present system, the outputs of hydrophones need to be continuously monitored with the risk that a lapse of concentration on the part of the monitor leads to a vital signal being missed.

[0009] It is possible to have two types of device. A low cost one that can be deployed in large numbers just to find possible signals of interest, and more sophisticated specifically tuned devices to be deployed to the an area in to identify the direction from which the signal is coming. Three of the more sophisticated devices could be used to give an accurate location for the transmissions.

[0010] By virtue of sending and receiving signals via a satellite system which is being monitored remotely, say on land, the devices can be deployed from aircraft, helicopters ships and the like without the need for special equipment on board. This is quite unlike existing detection systems for the identification, for example of aircraft black boxes.

[0011] The acoustic signals are typically in the frequency range 100Hz to 1 MHz for active acoustic transmitters, say attached to aircraft black boxes, but to identify the presence of survivors of a sinking of a ship or an aircraft banging on the hull of the vessel concerned a much lower threshold is needed.

[0012] Received acoustic signals are converted by a hydrophone to electrical signals which are then processed by the circuits in an electronic package, using a combination of hardware and software, to determine whether a specified sought after sound is present. If it is, then measurements pertaining to the specific sound can be made. These may include the level, frequency and duration of the sound. A number of signal events may be saved for later communication, together with the time and the location of the buoy.

[0013] To provide accurate location and time of day the buoy is equipped with a Global Navigation Satellite System receiver, typically using the GPS network.

[0014] To communicate the results of the signal processing to the operator, the buoy is equipped with a satellite modem to send and receive short data messages, typically using the Iridium Short Burst Data Service. This route may also be used in reverse to change some operating feature.

[0015] Multiple hydrophones on a buoy can be used to provide bearing information for an acoustic source using established beam4orming techniques. Greater accuracy can be obtained by combining measurements mentioned above from several buoys spaced at suitable intervals.

[0016] Electrical power for the buoy is obtained from an internal battery pack. To permit a reasonable operating duration, the majority of the electrical circuits may be shut down most of the time, waking at pre-determined intervals.

[0017] The buoy contains sufficient signal processing ability to determine the likelihood of the specified signal being present. It is not necessary for the acoustic signals to be continuously monitored by a human operator.

[0018] The buoy communicates the results of its acoustic analysis via a satellite link. The results can be sent anywhere in the world. Many such buoys can be deployed, only those with useful results send back data.

[0019] By combining the results from several buoys it is possible to determine the location of the acoustic source.

[0020] The buoy can be configured or programmed prior to deployment by downloading the necessary settings either via a computer link or fitting a plug-in sub-unit.

[0021] At the end of a deployment, the buoy can be commanded to send its exact position to facilitate collection, or to place itself in an inert state.

[0022] In order that the invention may be more fully understood, the following description, by way of example only, refers to the accompanying drawing which shows a block diagram of an analysis system of a buoy according to the invention.

[0023] A buoy 10 has two hydrophones 12 and 14 to convert received acoustic waves into electronic signals which are fed to an electronic package 16.

(Although two hydrophones are illustrated in practice at least one is need and more than two can be used). The package can either be pre-programmed through the Control and Programming port 18, pre4itting of a module, or adjusted before deployment or by a remote signal through received though antenna 22 and the modem 20, to filter out all signals bar those at the specific frequency or frequency band of interest. In the case of a buoy being deployed to identify a specific black box the frequency setting will be very specific, on the other hand if it is to identify banging on the hull of a vessel by trapped survivors, the setting might be to a relatively broad band lowish frequencies.

[0024] Received acoustic signals are converted by the hydrophones 12 and 14 to electrical signals which are then processed by the circuits in the electronic package 16, using a combination of hardware and software, to determine whether a specified sought after sound is present. If it is, then measurements pertaining to the specific sound can be made. These may include the level, frequency and duration of the sound. A number of signal events may be saved for later communication, together with the time and the location of the buoy.

[0025] To provide accurate location and time of day the buoy is equipped with a Global Navigation Satellite System receiver 24, typically using the GPS network.

[0026] To communicate the results of the signal processing to the operator, the buoy is equipped with a satellite modem to send and receive shod data messages, typically using the Iridium Short Burst Data Service. This route may also be used in reverse to change some operating feature.

[0027] The multiple hydrophones (two 12 and 14 are shown but more could be used) are used to provide bearing information for an acoustic source using

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established beam-forming techniques. Greater accuracy can be obtained by combining measurements mentioned above from several such buoys spaced at suitable intervals.

[0028] Electrical power for the buoy 10 is obtained from an internal battery pack 26. To permit a reasonable operating duration, the majority of the electrical circuits are shut down most of the time, waking at pre-determined intervals.

[0029] The buoy contains sufficient signal processing ability to determine the likelihood of the specified signal being present. It is not necessary for the acoustic signals to be continuously monitored by a human operator.

[0030] The buoy communicates the results of its acoustic analysis via a satellite link through the modem 20 and antenna 22. The results can be sent anywhere in the world. Many such buoys can be deployed, only those with useful results send back data.

[0031] By combining the results from several buoys it is possible to determine the more accurately the location of the acoustic source.

[0032] The buoy can be configured or programmed prior to deployment by downloading the necessary settings either via a computer link or fitting a plug-in sub-unit.

[0033] In relatively shallow water say down to l000m depth, on an initial search buoys according to the invention may deployed at 10Km intervals, if the depth increases or the frequency or the acoustic transmissivity of the water concerned is low, then the deployment interval will need to be reduced. One a potential "hit" is achieved then further buoys would be deployed closer to the origin of the sound to pin point its exact origin.