This invention relates to a security system, and more particularly but not exclusively relates to a security system for guarding one or more localities partly or wholly surrounded by water.

Fish farms located in natural bodies of water (for example at sea, or in sea lochs, fjords, lochs, lakes and the like) are liable to surface and/or submarine attack by predators (eg seals) , poachers, and vandals. Guard may be mounted on a fish farm by personnel patrolling on the farm, on surrounding water, or on adjacent land. However, by reason of the need for 24 hour per day, 7 day per week protection, combined with exposure and remoteness, use of guard personnel is expensive. Moreover, attacks on the farm stock by seals are particularly difficult for personnel to detect.

Proposals have been made for automatic security systems for fish farms, but such systems are complex and expensive, relying on military-type radar and sonar systems.

It is therefore an object of the invention to provide a

security system which obviates or mitigates the above- mentioned disadvantages.

According to a first aspect of the present invention there is provided a security system comprising an array of one or more vibration sensors and/or hydrophones discriminating per se or by operative association with distinct discriminator means between detected signals of different causative origins, and decision means responsive to the amplitude and/or duration of discriminated signals to initiate one or more predetermined security operations of a nature dependent on the specific detected signal or a specific combination of detected signals.

According to a second aspect of the present invention there is provided a fish farm security system comprising a detection array including hydrophones having dispositions and frequency spectral sensitivities for the discriminatory detection of various types of intruder, response means coupled to the array to respond to various individual detected signals or to predetermined combinations thereof, and a plurality of security devices and/or arrangements selectively controlled by said response means in accordance with a pre-programmed internal decision as to the significance of detected signals, at least one said security device or arrangement being directly or indirectly controlled via a broadcast link, and at least one said security device or arrangement comprising an underwater sound producer constructed or adapted to scare predators intruding on the fish farm.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings wherein:-

Fig. 1 is a block schematic diagram of one embodiment of a security system in accordance with the invention; and

Figs. 2, 3 and 4 are schematic diagrams of certain parts of the system of Fig. 1 showing these parts in greater detail.

Referring first to Fig. 1, the embodiment of the security system schematically illustrated therein comprises a detection section 10, a control and signal processing section 12, and a signalling and warning section 14.

The detection section 10 comprises an array of vibration sensors and hydrophones. The vibration sensors are formed by varying lengths 16, 18, 20 and 22 of piezo-electric cable. The cable lengths 16, 18 and 20 each have a respective hydrophone 24, 26 and 28 connected to one end. Each hydrophone may comprise a length of co-axial cable having an inter-electrode di-electric of radially polarised polyvinylidene di-fluoride, and former-wound into a helix of overall cylindrical or other shape having dimensions suited to the intended spectrum of acoustic sensitivity. These different combinations of piezo-electric cable and hydrophone serve to detect various characteristic vibrations and/or sounds indicative of the approach or proximity of people, creatures, or objects to the array.

When the security system of Fig. 1 is applied to the guarding of a fish farm located in a natural body of water, the detection array 10 of piezo-electric cables 16, 18 and 20 and hydrophones 24, 26 and 28 will be distributed at

selected depths in the water around the fish pens, and the phoneless length 22 of piezo-electric cable will be laid out on adjacent land (if any). The cable length and the frequency spectral sensitivities of the hydrophones, together with their spatial distribution, are chosen to enhance selective response of individual detectors respectively to seals, other water-borne predators, swimmers, divers, boats and other craft, whether on the surface or submerged. In circumstances where pressure wave detection is preferred, piezo-electric cables of selected lengths will be primarily or exclusively employed. However, tests have shown that in the context of protection of fish farms, acoustic sensing provides the most efficient detection, thereby making the length of piezo-electric cable immaterial; it is the hydrophones and the length of hydrophone which now determines which sounds are heard. The detection equipment cable and hydrophone preferably extends to a depth of 10-20 feet underwater. The seal scarer cable and transducer (see below) preferably extends to one metre below the bottom of the farm nets.

The cables 16-20 are individually connected to the control and signal processing section 12 by screened connector cables 30 leading to respective signal discriminators 32 within the control section 12. (One or more hydrophones (not shown) may be individually connected by respective screened connector cables directly to respective discriminators within the control section 12, without intervening lengths of piezo-electric cable) . Each discriminator 32 will filter its own respective signals received from the detection array 10, according to the respective detection requirement, and may comprise a respective filter having a substantially predetermined frequency pass spectrum and forming a distinct discriminator means discriminating the respective detected signals from

other signals of different causative origins.

The control and signal processing section 12 is enclosed within a weatherproof equipment enclosure 13 which is fitted with tamper detectors (such as door-operated switches) to give alarm signals to an alarm annunciator module 34 within the control section 12 upon detection of tampering or attempted tampering.

The discriminators 32 feed the alarm annunciator module 34 within the control section 12. The discriminators 32 are preset to filter all signals received but act only on signals coming within the preset parameters, and will respond according to the amplitude and/or duration of discriminated signals to initiate a predetermined security operation of a nature dependent on the specific detected signal (or possibly in conjunction with further circuitry, dependent on a specific combination of detected signals); for example, "immediate alarm" for a strong signal, "wait" for a weak signal, "monitor" for a signal partly within parameters. A control/timer module 36 is coupled to the alarm annunciator module 34 to restrict the response of the boat detection signalling circuit to 'unworked' hours only (eg 5.30 pm to 7.30 am) to allow legitimate access to the protected zone without triggering false alarms. An automatic re-set module 38 automatically re-sets the system after a predetermined set time interval has elapsed following an alarm.

The alarm annunciator module 34 feeds an intrusion level decision module 40 (schematically detailed in Fig. 2) which employs programmable diode logic to give predetermined outputs upon various combinations of alarm inputs, and thus initiate appropriate alarm(s) and/or other security function(s) relevant to the level and degree of persistence of

intrusion or attack, and the environmental and physical location of each individual fish farm or other locality being guarded by the security system. Specific examples will be given later, following the description of further parts of the security system.

For the operation of alarms, warning devices and other security devices remote from the control and signal processing section 12, a multiple-channel VHF transmitter 42 is coupled to the intrusion level decision module 40 via a block, selector 44 (schematically detailed in Fig. 3), which employs programmable diode logic to give predetermined outputs upon various combinations of inputs from the intrusion level decision module 40 and thus control appropriate alarm(s) and/or other security function(s), according to the security system user's requirements. The transmitter 42 has four channels in the illustrated embodiment, individually controlling switch contacts within the block selector 44. (However, any number of channels can be employed according to circumstantial requirements.) Details of the remote equipment controlled by the transmitter 42 will be given below, one such set of equipment comprising floodlights and/or stroboscopes which respond only to the boat detection circuit and which are effective only at night and are accordingly enabled during hours of darkness and/or 'unworked' hours and disabled during daylight hours and/or during working hours when authorised personnel are legitimately present in the fish farm, by means of a timer 46 within the block selector 44. The timer 46 will time the 'lights on' duration in relation to main alarm timing 'alarmed time', eg 10 seconds, 20 seconds, 30 seconds, or other suitable period in dependence on the circumstances and preselected performance parameters. The result is that if a boat stayed within the protected area ^• covered by the detecion array 10,

this would give an on/off/on lighting effect.

The transmitter 42 broadcasts via an aerial 48 (shown as a single collective aerial in Fig. 1 and as four individual aerials in Fig. 3). Use of radio links to control outlying equipment eliminates the risk of nets being entangled with the cables otherwise necessary to transmit control signals. (Although the block selector 44 is shown separate from the intrusion level decision module 40 in Fig.l, the circuitry of the block selector 44 could be incorporated into and combined with the circuitry of the intrusion level decision module 40).

Also included within the control section 12, for the communication of alarms to selected persons, is a VHF/UHF pager transmitter 50 which broadcasts via an aerial 52 to a pocket pager 53 carried by a person to be notified in the event of an alarm or warning signal.

Local alarms and warning devices in the control and signal processing section 12 include a local audible alarm 54 operated by the intrusion level decision module 40, and a wire-controlled (as distinct from radio-controlled) seal scarer 56 powered from a generator 58 (schematically illustrated in greater detail in Fig. 4) producing a random frequency for a period of random duration when initiated by the module 40. The seal scarer 56 comprises an underwater loudspeaker or like transducer producing predator-disturbing sounds from the power delivered by the generator 58. The generator 58 comprises a random time pulse generator 58T and a random frequency generator 58F. The random nature of the output from the scarer 56 diminishes the risk of habituation and loss of fear by the seals.

The control and signal processing section 12 is powered by an internal rechargeable 12-volt battery pack 60 outputting through a power supply unit 62. The battery pack 60 preferably has a capacity sufficient for 168 hours (1 week) of normal use without intermediate recharging, but may alternatively have any other suitable capacity. A nearby wind- driven generator 64 recharges the battery 60 through a voltage regulator 66. A power failure or an excessively low power level is detected by a power failure/low power warning module 68 coupled to the power supply unit 62, and operates to actuate the pager transmitter 50, together with a low power warning indicator 70 mounted on the enclosure 13.

Various remote units forming part of the signalling and warning section 14 of the security system are employed in combinations and with distributions that are appropriate to the circumstances and security demands. Shown in Fig. 1 by way of example are four such remote units, each radio controlled by one of the four channels of the transmitter 42. One such remote unit 100 comprises a weatherproof enclosure 102 housing an appropriately tuned VHF receiver 104 controlling a random generator 106 (equivalent to the generator 58) which powers a seal scarer 108. The unit 100 further includes a battery pack 110, a power supply unit 112, a low power warning unit 114, a low power warning indicator 116. A local windmill generator 118 feeds the battery pack 110 through a regulator 120. The unit 100 is self-contained, and suitable for use on fish pens adjacent the pen on which the enclosure 13 is mounted.

A smaller remote radio-operated seal scarer unit 200 consists of a VHF receiver 202, a 'random' generator 204, and a seal scarer 206 comprising an underwater loudspeaker or like transducer producing predator-disturbing sounds from the power delivered by the 'random' generator 204.

Another form of remote radio-controlled unit 300 may consist of a VHF receiver 302 and a closed-circuit television system (CCTV) 304.

A further form of. remote radio-controlled unit 400 functions to provide optical deterrence of human or animal intruders by providing a VHF receiver 402 to control an array 404 of floodlights and/or stroboscopes.

Examples of remote units activated in response to specific warnings received, from the detectors of the detection section 10, are given below:-

Seal detected: the local seal scarer 56 is activated and the remote scarers 108, 206 are triggered through the block selector 44 and the relevant VHF transmissions.

Boat detected: the local audible alarm 54 and the VHF/UHF pager transmitter 52 are activated, and the remote CCTV 304 is triggered into operation through the block selector 44 and the relevant VHF transmission.

Diver detected: the local seal scarer 56, the local audible alarm 54 and the VHF/UHF pager transmitter 50 are activated, and the remote seal scarers 108, 206 are triggered through the block selector 44 and the relevant VHF transmissions.

Land approach detected (only applicable where the main control equipment is land-based) : the local audible alarm 54 and the VHF/UHF pager transmitter 50 are activated, and the remote CCTV 304 is triggered through the block selector 44 and the relevant VHF transmission.

The block selector 44 is further illustrated in Fig. 3 where -different functions are allocated to the four blocks or channels in comparison to Fig. 1 to demonstrate that any number of remotely sited security devices or other devices can be triggered or controlled from one trigger block or control unit, or that any combination of warning devices or other devices can be triggered or controlled from one trigger block or control unit. As shown in Fig. 3, the VHF trigger block transmission 42A will trigger the remote seal scarers 108, 206, whilst the VHF block transmission 42B will trigger the CCTV 304 and lights and horns if required.

The random frequency generator module 58 of Fig. 4 will activate the local seal scarer 56 and energise its underwater loudspeaker or like transducer for a randomly selected duration and at a randomly selected frequency as aforedescribed; the random time pulse generator 58T has a minimum of four different durations, and the random frequency generator 58F has a minimum of four frequency outputs. There is therefore a minimum of sixteen responses (variations on durations and frequency) . (Variations of duration and/or frequency may be continuously variable rather than step-variable, and may be truly random or pseudo-random) .

In use, the weatherproofed equipment enclosure 13 (not shown in constructional detail) is bolted to a walkway of a fish farm. The box-like unit sits on a main support of mild steel construction having four legs each being of 1" tubular construction with angle iron jointing bars. The support is protected by a protective coating. The turbine generator mast and main VHF/UHF aerial are each about eight feet tall and are bolted onto the main support legs. The box-like unit bolts onto a wooden base which rests across the main support, the base being bolted to the angle iron jointing

bars .

The box-like unit is of glass-reinforced fibreglass and has an anti-tamper protection lid, the lid being secured by spring clips and locked with a padlock. All cabling to the system will be run through and be protected by plastic conduits. Underwater cable is used below the water line.

The above described embodiment of security system has been designed to give the user early detection and warning of possible attack on sea based fish farms. The fish farm security system provides the following functions:-

(1) The system will detect and warn of any approach to the fish farm by any boat or craft on the surface or submerged.

(2) The system will detect and warn of any approach to the fish farm by any diver.

(3) The system will detect and warn of any approach to the fish farm by any seal(s) .

(4) The system will detect and warn of any approach to the fish farm by any unauthorised person whether by water or on shore adjacent to the fish farm.

(5) The system has full anti-tamper protection.

(6) The system is self-contained for use in remote areas with minimum maintenance.

(7) The system will give a stepped level of warning, dependent on the level of intrusion/threat of intrusion to

the fish farm.

(8) The system is inter-connected by the use of radio links to avoid line cables tangling nets.

(9) The system is of modular construction to ensure its adaptability to the requirements of each individual fish farm.

(10) The system will give audible and visual warnings both on the surface (remote and local) and underwater.

(11) The system will operate sonic scarers with a random duration and at a random frequency to alleviate the possibility of seals becoming accustomed to the underwater warning.

(12) The system is capable of automatically re-setting itself after a pre-set time interval has elapsed.

(13) The system is housed in weatherproof containers to protect it from the harsh environment expected at a fish farm.

(14) The system can be sea-based at the fish farm or land- based adjacent to the fish farm.

(15) The system will monitor its own power supplies and warn of impending or actual power failure.

As well as being applicable to guarding of fish farms, the security system in accordance with the invention (or subsystems thereof) can also be applied in other situations; for example:-

(a) detection of seals or other underwater mammals: the equipment could be used for automatic herding of sea life into or out of a particular area such as an area subject to oil spillage.

(b) boat detection (civil and military): the boat detection equipment can detect a surface or submerged boat at a distance of up to 25 miles, and this could be useful for the security of oil rigs, fishing boats, harbour entrances, and military sea-based bombing ranges.

(c) diver detection (civil and military) : applicable to the security of oil rigs and harbour entrances.

While certain modifications and variations have been described above, the invention is not restricted thereto and other modifications and variations can be adopted without departing from the scope of the invention as defined in the appended claims.