GB2598890A

GB2598890A - Rescue beacon

Info

Publication number: GB2598890A
Application number: GB2014133.9A
Authority: GB
Inventors: Fleck Leonard
Original assignee: LFD Ltd
Current assignee: LFD Ltd
Priority date: 2020-09-09
Filing date: 2020-09-09
Publication date: 2022-03-23
Also published as: GB202014133D0

Abstract

Rescue beacon 10 comprises infra-red (IR) light source 140, and control circuitry 120 operable to deactivate the light source or reduce the intensity of the infrared light source in response to a trigger external to the rescue beacon. The trigger may be visible light, sound associated with a rescue vehicle, or a transmitted control signal. In a further aspect, the beacon further includes light sensor 160 and the control circuitry is operated based on an output of the sensor. The beacon may feature second source of light 150 which remains active during the deactivation of the infrared light source. The circuitry may operate when the amount of light detected by the sensor increases at greater than a threshold rate or increases between successive sensor readings by a predetermined amount. In an aspect, a search and rescue system comprises a beacon with an infrared light source and an emergency vehicle having a searchlight wherein light from the searchlight deactivates the infrared light source to protect night vision equipment.

Description

Intellectual Property Office Application No G1320141339 RTM Date -8 February 2021 The following terms are registered trade marks and should be read as such wherever they occur in this document: Osram Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo Rescue Beacon

Technical Field

The present invention relates to a rescue beacon having an infra-red light, to a search and rescue system comprising the rescue beacon, and to a search and rescue process utilising the rescue beacon.

Background

At sea (and sometimes on land), a rescue beacon may be used by a person in distress, such as following a capsize of a vessel, to provide a visual indication of the location of that person to search and rescue services. The rescue beacon may emit visible light which can be seen by the naked eye, and may also emit infra-red light. At night, infra-red light can be seen from large distances (much greater than visible light) using night vision equipment, routinely carried on search-and-rescue helicopters (for example). This makes infra-red light ideal for spotting the rescue beacon at night, from a long distance away, improving the likelihood of the rescue beacon (and thus the individual to be rescued) being discovered quickly. However, at close range the infra-red light dazzles a pilot wearing night vision goggles and ruins their night vision.

Embodiments of the present invention seek to alleviate the disadvantages of the prior art and enable infra-red light bearing beacons to be used more effectively during search and rescue operations.

Summary of the Invention

According to an aspect of the present invention, there is provided a rescue beacon, comprising: an infra-red light source; a sensor, operable to detect light incident on the rescue beacon; and circuitry, operable to deactivate, or reduce the intensity of, the infra-red light source in dependence on an output of the sensor. 1.

At close quarters (less than 200 metres), helicopters (or other search and rescue vehicles such as maritime vessels) use white light spotlights/searchlights to illuminate a target for rescue. Embodiments of the present technique make use of this fact by deactivating or reducing the intensity of the infra-red light on the beacon in the presence of light from a spotlight, to avoid dazzling the pilot at close range. This requires no change in the operating procedures of the search and rescue personnel, because the infra-red light is deactivated or reduced in intensity simply by personnel being close enough to direct a spotlight onto the beacon (which would occur anyway as part of the rescue operation) Preferably, the sensor is operable to detect visible (for example white) light, and the circuitry is operable to deactivate, or reduce the intensity of, the infra-red light source in dependence on the detection of visible light. This is beneficial because search and rescue spotlights illuminate using visible (generally white) light in order to illuminate a target with light which is visible to the naked eye of search and rescue personnel.

Preferably, the circuitry is configured to deactivate the infra-red light source when an amount of (white) light (in a particular wavelength range! band detectable by the sensor) detected by the sensor exceeds a predetermined threshold. In this way, the infra-red light will not be deactivated simply by low levels of ambient light such as moonlight.

In one embodiment, the infra-red light source is deactivated completely (emits no, or substantially no, infra-red light) in response to the detection of light at the sensor. In another embodiment, the intensity of infra-red light emitted by the infra-red light source is reduced (but to a non-zero level) in response to the detection of light at the sensor to a level less likely to dazzle a user of night vision equipment. The reduced level of light emitted may for example be approximately 1/1000 of the existing output, although in other examples may only be approximately 1/100 or 1/10.

The rescue beacon may include a second light source which emits light (or the majority of its light) outside of the infra-red wavelength range, for example visible light. The visible light source may be a white light source, or a coloured light source. In this case, the second light source may remain active during the deactivation of the infra-red light source. In other words, when light is incident on the light sensor, only the first (infra-red) light source and not the second (visible) light source is deactivated or reduced in illumination. This is because the second (visible) light source does not interfere with night vision equipment (and certainly not to the same degree as the infra-red light source), and may still aid the rescue effort for those not using night vision equipment and/or when the searchlight drifts off target.

The circuitry may be configured to deactivate or reduce the illumination of the infrared light source in response to a change in output state of the sensor which indicates that the beacon has become illuminated with visible light.

A second light source may be provided, which emits its light, or the majority of its light, outside of the infra-red wavelength waveband, wherein the circuitry is configured, in response to the change in output state of the sensor, to deactivate or reduce the intensity of only the infra-red light source.

The circuitry may be configured to deactivate or reduce the illumination of the infrared light source when an amount of light detected by the sensor increases at greater than a predetermined rate or increases between successive sensor readings by at least a predetermined amount.

If the output of the sensor indicates the beacon has been illuminated with visible light for at least a predetermined duration, the circuitry may be configured to further deactivate the second light source.

Upon a detection of white visible light on the sensor, the circuitry is configured to measure a level of illumination at the sensor at a plurality of intervals, and to deactivate the second light source if the level of illumination remains above a threshold value for the plurality of measurements.

Preferably, for maritime operations, the beacon is buoyant, and while floating the light source and the light sensor are disposed above a surface of a body of water in which the beacon is floating.

Viewed from another aspect, there is provided a search and rescue system, comprising: a rescue beacon, comprising an infra-red light source, a sensor, operable to detect light incident on the rescue beacon, and circuitry, operable to deactivate or reduce the intensity of the infra-red light source in dependence on an output of the sensor; and a search and rescue vehicle having a searchlight, wherein when a beam of light from the searchlight impinges on the sensor of the rescue beacon, the circuitry of the rescue beacon is configured to deactivate the infra-red light source to protect the night vision equipment of an operator or passenger of the search and rescue vehicle.

Viewed from another aspect, there is provided a search and rescue method utilising a rescue beacon and a search and rescue vehicle, the method comprising: emitting infra-red light from an infra-red light source of the rescue beacon; illuminating the beacon with a beam of light, using a searchlight of the search and rescue vehicle; and detecting light incident on the beacon using a sensor of the beacon; and deactivating or reducing the intensity of the infra-red light source in dependence on an output of the sensor.

Viewed from another aspect, there is provided a rescue beacon, comprising: an infra-red light source; and circuitry responsive to a trigger external to the rescue beacon to deactivate or reduce the intensity of the infra-red light.

The trigger may be the incidence of visible (for example white) light at the rescue beacon, as described above. Alternatively, the trigger may be an external control signal (received from outside the rescue beacon). More generally, the external trigger may anything originating externally (separate from the beacon itself). In one example, the trigger is a sound associated with a rescue vehicle, such as the sound of an engine/propulsion system, or the sound of rotor blades of a helicopter. It will be appreciated that a manual switch on the beacon is not external to/separate from the rescue beacon. In this case, the rescue beacon may comprise a receiver, and wherein the external control signal is a deactivate signal transmitted from a search and rescue vehicle and received at the receiver.

Viewed from another aspect, there is provided a search and rescue system, comprising: a rescue beacon, comprising an infra-red light source, and circuitry, operable to deactivate or reduce the intensity of the infra-red light source in response to a trigger external to the rescue beacon; and a search and rescue vehicle providing the external trigger, the circuitry of the rescue beacon being configured to deactivate, in response to the external trigger, the infra-red light source to protect the night vision equipment of an operator or passenger of the search and rescue vehicle.

Viewed from another aspect, there is provided a search and rescue method utilising a rescue beacon and a search and rescue vehicle, the method comprising: emitting infra-red light from an infra-red light source of the rescue beacon; providing an external trigger, from the search and rescue vehicle; detecting the external trigger, at the beacon; and deactivating or reducing the intensity of the infra-red light source in dependence on the detection of the external trigger.

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings where like parts are provided with corresponding reference numerals and in which: Figure 1 schematically illustrates a rescue beacon according to a first embodiment of the invention; Figures 2A and 2B schematically illustrate a search and rescue scenario in which a rescue beacon as shown in Figure 1 is employed; Figure 3 schematically illustrates a rescue beacon according to a first embodiment of the invention; and Figures 4A and 4B schematically illustrate a search and rescue scenario in which a rescue beacon as shown in Figure 3 is employed.

Detailed Description

Referring to Figure 1, a rescue beacon 10 according to a first embodiment is shown. The rescue beacon 10 comprises a power source (battery) 110, control circuitry 120, an on/off switch 130, a first light source 140 which emits infra-red light (for example 780 to 1000nm), a second light source 150 which emits visible light (for example 380nm to 780nm), and a light sensor 160 which senses/detects light incident thereon. The light sensor may be a Silonex NSL 19M51 light dependent resistor. The first light source may be an IR diode type Osram SFH4170S, while the second light source may be aCree XP-E2. The rescue beacon comprises a waterproof housing (casing) 105, within which the battery 110 and control circuitry 120 are disposed. The switch 130, light sources 140, 150 and sensor 160 are exposed through the casing (either via watertight apertures in the casing, or (in the case of the light sources and light sensor) via a transparent portion of the casing, which would need to be (substantially) transparent at the operating wavelengths of the light source(s) and sensor). The battery 110 may be disposed towards the bottom/base of the casing, to serve as a ballast, while the rescue beacon 10 as a whole is buoyant (and thus takes the form of a buoy), such that the upper surface of the rescue beacon 10, which bears the light sources 140, 150 and the sensor 160, remains above water while the rescue beacon 10 floats in a body of water.

The second light source 150 and the sensor 160 are preferably arranged such that little or no light from the second light source 150 reaches the sensor 160. This may be achieved by way of the relative positioning and/or orientation of the second light source 150 and the sensor 160, or by providing a structure between the second light source 150 and the sensor 160 (for example a wall adjacent to or hood around the sensor 160) which blocks illumination from the second light source 150 from reaching the sensor 160 (or at least reduces the amount of illumination reaching the sensor 160 from the second light source 150).

The control circuitry 120 is electrically connected to each of the power source 110, the on/off switch 130, the first and second light sources 140, 150, and the sensor 160. The control circuitry 120 is configured, when the rescue beacon 10 is active, to cause the first and/or second light sources 140, 150 to illuminate using electrical power from the power source 110. The rescue beacon 10 is activated by the switch 130, which may either be a manual switch actuated by a user, or a hydrostatic switch which activates the rescue beacon 10 when the hydrostatic switch becomes immersed in water. In either case, the control circuitry 120 detects when the switch 130 has been switched from an 'off' state to an "on" state, and causes the first and/or second light sources to illuminate accordingly. It will be appreciated that, in some implementations, both manual and hydrostatic switches may be provided, the manual switch serving as a backup in case the hydrostatic switch fails.

In addition to activating/deactivating the first and second light sources 140, 150 based on the switch 130, the control circuitry 120 is also responsive to the state of the light sensor 160 to either activate and deactivate the first (infra-red) light source 140 or to control an illumination intensity (amount of infra-red light output) by the first light source 140 in dependence on the light sensor 160. In particular, if (visible/white) light is detected at the sensor 160, the first light source 140 may be deactivated, or its illumination intensity reduced. Preferably, the amount of visible/white light should exceed a predetermined threshold (for example 0.2 lux -lumens per square metre) in order for the first light source to be deactivated, or (substantially) reduced in intensity. In some examples, visible/white light must be detected continuously at the sensor 160 for at least a predetermined amount of time in order for the first light source 140 to be deactivated or reduced in intensity. In this way, the infra-red light source remains active until the search and rescue personnel have a reliable fix on the position of the rescue beacon 10 (rather than the first light source being deactivated by a brief sweep of a spotlight).

In one implementation, the control circuitry 120 controls the first (infra-red) light source 140 to be off (or reduced in intensity) only while (a sufficient amount of) visible/white light is incident on the sensor 160, that is, while the amount of visible/white light incident on the sensor is above a threshold. Once the amount of visible/white light incident on the sensor 160 falls below the threshold level, the controller 120 activates (or increases the intensity of) the first light source 140. It will appreciated that a degree of hysteresis may be built in, to reduce flip-flopping in the case that the level of visible/white light incident on the sensor is close to the threshold.

In another implementation, once the first light source 140 has been deactivated or reduced in intensity, it will stay in this state until the rescue beacon 10 is reset (for example by being switched off and on again manually using the switch 130, or by way of a separate reset switch, not shown).

In another implementation, once the first light source 140 has been deactivated, it remains deactivated for a predetermined duration, measured either from when deactivation took place, or from when the illumination level at the sensor 160 falls below the threshold (that is, from when the spotlight from the search and rescue vehicle is no longer incident on the rescue beacon 10). Once the predetermined duration has expired, the first light source 140 reactivates, unless at this time the illumination level at the sensor 160 remains above the threshold. The predetermined duration may for example be 10 seconds, which may be sufficient for the first light source 140 to remain deactivated even if a searchlight should briefly drift off target due to wave motion and/or motion of the rescue vehicle.

The first light source 140 and the second light source 150 may flash intermittently (and optionally, alternately) to provide greater visibility (although in alternative implementations one or both of the light sources could illuminate continuously). Within the context of the present invention, where a light source illuminates on an intermittent basis, deactivation of that light source means discontinuing its intermittent operation such that it no longer emits light at times when (if activated) it would emit light. If the light source is to be reduced in intensity (dimmed), rather than being deactivated, an intermittent light source may continue to emit light on an intermitted basis, but at a reduced intensity.

In one implementation, the rescue beacon is operable in a daylight (power saving) mode, and a night-time mode. The night-time mode corresponds substantially to that described above. In the day-time mode, both the first (infra-red) and second (visible) light sources are deactivated to save power, since neither form of illumination serves a useful purpose during daylight hours. In practice, daylight corresponds to at least a predetermined threshold level of illumination being present at the rescue beacon (and on the sensor), and in very overcast daytime conditions the rescue beacon may therefore (beneficially) operate in the night-time mode even during the day. During night-time operation, when a searchlight is incident on the rescue beacon, it is beneficial to deactivate the infra-red (first) light source in response to the detection of visible/white light, but beneficial to leave the second (visible) source active, since it does not unduly impact night vision equipment, and makes it easier to spot the rescue beacon if the searchlight from the rescue vehicle should move off it. As such, it is desirable to be able to differentiate between daylight and a searchlight, so that daylight can cause deactivation of both light sources, while the searchlight causes deactivation of only the infra-red light source (leaving the visible light source active).

In one implementation, the infra-red (first) light source is deactivated (immediately) in response to an amount of visible/white light incident on the sensor exceeding a predetermined threshold, and the second (visible) light source is subsequently deactivated if the amount of visible/white light incident on the sensor remains above this threshold for at least a predetermined duration. One way of achieving this is, in response to the initial detection of (at least a threshold amount of) visible/white light, to start a timer (for example for 30 minutes), and to sample the level of illumination at the sensor every (say) 5 minutes during this time. If all 7 samples indicate the presence of (sufficient) visible/white light (for example, above the threshold), the rescue beacon is switched to daytime operation, and the second (visible) light source is deactivated as well.

In an alternative implementation, the circuitry may differentiate between a gradual increase in illumination incident on the rescue beacon (likely to arise as day breaks), and a rapid or instantaneous increase in illumination incident on the rescue beacon (likely to arise from a searchlight from a rescue vehicle targeting the rescue beacon). In this case, if the illumination level at the sensor gradually increases to a deactivation threshold (a gradual increase being an increase per sampling period (potentially averaged over plural sampling periods) less than a predefined level), the rescue beacon will shift into daylight mode, with both light sources being deactivated. If the illumination level at the sensor rapidly increases to a or the deactivation threshold (a rapid increase being an increase per sampling period (potentially averaged over plural sampling periods) greater than a predefined level), the rescue beacon will remain in night-time mode, but the infra-red light source (only) will be deactivated (subject for example to the end conditions of the deactivated/reduced intensity state described above).

When the rescue beacon is in the daylight mode, it will either continuously or periodically compare the light level at the sensor with a threshold, and in the case the amount of light impinging on the sensor decreases below the threshold, the rescue beacon transitions into the night-time mode.

Referring now to Figures 2A and 2B, a search and rescue scenario in which the rescue beacon 10 is used, is shown. In Figure 2A, a search and rescue helicopter 20 is searching for an individual 30 lost at sea. This may be due to a man-overboard event, or due to a vessel (not shown) sinking or capsizing. The helicopter 20 is equipped with a spotlight 22, which in Figure 2A is not activated (or at least is not illuminating the rescue beacon 10). In this state, the rescue beacon 10 is emitting high intensity infra-red light over a wide area, assisting with discovery of the rescue beacon 10 for search and rescue personnel (such as a helicopter pilot, co-pilot or other crew member) equipped with night vision equipment (such as goggles). Once the helicopter 20 has used the infra-red light source as a guide to move close to the beacon 10, the search and rescue personnel will direct a beam of visible/white light from the spotlight 22 onto the beacon 10 and individual 30. The visible/white light falling on the sensor 160 of the rescue beacon thus causes the first light source 140 of the beacon to deactivate, or reduce in intensity, as shown in Figure 2B, thus not dazzling the pilot and/or helicopter crew, and enabling the rescue to be mounted more effectively while retaining the pilot's night vision.

Referring to Figure 3, a rescue beacon 10b according to a second embodiment is shown. The rescue beacon 10b comprises a power source (battery) 110b, control circuitry 120b, an on/off switch 130b, a first light source 140b which emits infra-red light, a second light source 150b which emits visible light, and a receiver 170 with antenna 171 which is able to wirelessly receive control signals transmitted from a search and rescue vehicle. Most of the structure, configuration and function of the rescue beacon 10b of the second embodiment are identical to that of the rescue beacon 10 of the first embodiment, and so the details thereof will not be repeated. Instead, the following description focuses on the differences between the first and second embodiments, and in particular on the feature of the receiver 170, and how signals received via the receiver 170 are handled by the control circuitry 120b. A waterproof housing (casing) 105b, corresponding to the housing 105 of the first embodiment, in this case exposes the antenna 171, either with the antenna extending through the housing 105b, or by way of a portion of the housing 105b which is substantially transparent to RF (radiofrequency) signals. The antenna 171 is disposed on the beacon 10b at a location which will remain above the surface of water while the beacon 10b is floating.

The control circuitry 120b is electrically connected to the receiver circuitry 170. The control circuitry 120b is responsive to signals (for example commands) received via the receiver circuitry 170 to either activate and deactivate the first (infra-red) light source 140b or to control an illumination intensity (amount of infra-red light output) by the first light source 140b. In particular, if a deactivate signal is received at the receiver circuitry 170 (via the antenna 171), the first light source 140b may be deactivated, or its illumination intensity reduced. The deactivate signal may be an RF signal transmitted from the search and rescue vehicle. In some implementations, the control circuitry 120b may also be responsive to an activate signal being received at the receiver circuitry 170 to activate the first light source 140b, or to increase its illumination intensity. This enables the pilot (or other crew member) of a search and rescue helicopter) or other vehicle to activate and deactivate the infra-red light source at will, as a rescue operation progresses. For example, the pilot may deactivate the infra red light source 140b when it is starting to dazzle, but reactivate it again if they lose sight of the rescue beacon 10b.

In one implementation, the control circuitry 120b controls the first (infra-red) light source 140b to be off (or reduced in intensity) only while a deactivate signal is being (repeatedly) received at the receiver circuitry 170. This avoids a problem whereby the pilot may prematurely deactivate the infra-red light, only to lose sight of the beacon 10b, and move out of range to reactivate it. In another implementation, once the first light source has been deactivated or reduced in intensity, it will stay in this state until the rescue beacon is reset (for example by being switched off and on again manually using the switch 130, or by way of a separate reset switch, not shown). In another implementation, once the first light source has been deactivated, it remains deactivated for a predetermined duration, measured either from when deactivation took place, or from when deactivation signals stopped being received.

Referring now to Figures 4A and 4B, a search and rescue scenario in which the rescue beacon 10 is used, is shown. In Figure 4A, a search and rescue helicopter 20b is searching for an individual 30b lost at sea. This may be due to a man-overboard event, or due to a vessel (not shown) sinking or capsizing. The helicopter 20b is equipped with a transmitter 24 for transmitting deactivation signals (and optionally activation signals), which in Figure 4A is not activated. In this state, the rescue beacon 10b is emitting high intensity infra-red light over a wide area, assisting with discovery of the rescue beacon 10b for search and rescue personnel (such as a helicopter pilot, co-pilot or other crew member) equipped with night vision equipment (such as goggles). Once the helicopter 20b has used the infra-red light source as a guide to move close to the beacon 10, the search and rescue personnel will transmit a deactivation signal from the transmitter 24 for reception by the beacon 10b. This causes the first light source 140b of the beacon 10b to deactivate, or reduce in intensity, as shown in Figure 4B, thus not dazzling the pilot and/or helicopter crew, and enabling the rescue to be mounted more effectively while retaining the pilot's night vision.

In a variation of the second embodiment, the deactivation signals may be infra-red signals (for example IR pulses), with the antenna 171 being replaced with an infra-red light sensor. These can be handled in exactly the same way as the radiofrequency (RF) signals discussed above.

It is also envisaged that the presence of a rescue vehicle could be inferred or detected in other ways, with this inference or detection causing the deactivation (or reduction in intensity of) the IR light source. For example, the antenna and 171 and receiver circuitry 170 may be replaced with an acoustic transducer (pickup/microphone), and circuitry for either (a) measuring a volume of noise and comparing it with a threshold, or (b) detecting if measured noise levels and frequencies are consistent with a vehicle propulsion system, such as the sound of rotor blades of a helicopter, or the sound of an engine of a vessel. In this case, the IR light source may be deactivated (or reduced in intensity) in response to the detection of high levels of noise and/or the detection of sounds corresponding to rotor blades, engine or other propulsion system noise.

Note that, while the first and second embodiments have been presented above as alternatives, it is envisaged that a rescue beacon could include both a light sensor, and a receiver, in which case the infra-red light source may be deactivated either in dependence on a remote (deactivation) signal being received or in dependence on spotlight illumination being directed onto the light sensor.

While an at sea environment has been illustrated above, it will be appreciated that a variant of the beacon could be used on land, for example where individuals are lost in the wilderness. Similarly, while the rescue beacon is preferably a standalone unit (which in the case of an at-sea device is required to be buoyant, and in particular to take the form of a buoy), in alternative embodiments the rescue beacon may be temporarily or permanently mounted on a vehicle such as a lifeboat, or form part of worn equipment.

Claims

Claims 1. A rescue beacon, comprising: an infra-red light source; a sensor, operable to detect light incident on the rescue beacon. and circuitry, operable to deactivate, or reduce the intensity of, the infra-red light source in dependence on an output of the sensor.
2 A rescue beacon according to claim 1, wherein the sensor is operable to detect visible light, and the circuitry is operable to deactivate, or reduce the intensity of, the infra-red light source in dependence on the detection of visible light.
3 A rescue beacon according to claim 1 or claim 2, wherein the circuitry is configured to deactivate the infra-red light source when an amount of light detected by the sensor exceeds a predetermined threshold.
4. A rescue beacon according to any preceding claim, wherein the infra-red light source is deactivated completely in response to the detection of light at the sensor.
5. A rescue beacon according to any of claims 1 to 3, wherein the intensity of infra-red light emitted by the infra-red light source is reduced in response to the detection of light at the sensor.
6. A rescue beacon according to any preceding claim, comprising a second light source which emits light, or the majority of its light, outside of the infra-red wavelength range, the second light source remaining active during the deactivation of the infra-red light source.
7 A rescue beacon according to claim 2, wherein the circuitry is configured to deactivate or reduce the illumination of the infra-red light source in response to a change in output state of the sensor which indicates that the beacon has become illuminated with visible light.
8 A rescue beacon according to claim 7, comprising a second light source which emits light, or the majority of its light, outside of the infra-red wavelength waveband, wherein the circuitry is configured, in response to the change in output state of the sensor, to deactivate or reduce the intensity of only the infra-red light source.
9 A rescue beacon according to claim 7, wherein the circuitry is configured to deactivate or reduce the illumination of the infra-red light source when an amount of light detected by the sensor increases at greater than a predetermined rate or increases between successive sensor readings by at least a predetermined amount.
10.A rescue beacon according to claim 8, wherein if the output of the sensor indicates the beacon has been illuminated with visible light for at least a predetermined duration, the circuitry is configured to further deactivate the second light source.
11.A rescue beacon according to claim 10, wherein, upon a detection of visible light on the sensor, the circuitry is configured to measure a level of illumination at the sensor at a plurality of intervals, and to deactivate the is second light source if the level of illumination remains above a threshold value for the plurality of measurements.
12.A rescue beacon according to any preceding claim, wherein the beacon is buoyant, and while floating the light source and the light sensor are disposed above a surface of a body of water in which the beacon is floating.
13.A search and rescue system, comprising: a rescue beacon, comprising an infra-red light source, a sensor, operable to detect light incident on the rescue beacon, and circuitry, operable to deactivate or reduce the intensity of the infra-red light source in dependence on an output of the sensor; and a search and rescue vehicle having a searchlight, wherein when a beam of light from the searchlight impinges on the sensor of the rescue beacon, the circuitry of the rescue beacon is configured to deactivate the infra-red light source to protect the night vision equipment of an operator or passenger of the search and rescue vehicle.
14.A search and rescue method utilising a rescue beacon and a search and rescue vehicle, the method comprising: emitting infra-red light from an infra-red light source of the rescue beacon; illuminating the beacon with a beam of light, using a searchlight of the search and rescue vehicle; detecting light incident on the beacon using a sensor of the beacon, and deactivating or reducing the intensity of the infra-red light source in dependence on an output of the sensor.
15.A rescue beacon, comprising: an infra-red light source and circuitry responsive to a trigger external to the rescue beacon to deactivate or reduce the intensity of the infra-red light.
16.A rescue beacon according to claim 15, wherein the trigger is the incidence of visible light at the rescue beacon.
17.A rescue beacon according to claim 15, wherein the trigger is a sound associated with a rescue vehicle.
18.A rescue beacon according to claim 15, wherein the trigger is an external control signal.
19.A rescue beacon according to claim 18, comprising a receiver, and wherein the external control signal is a deactivate signal transmitted from a search and rescue vehicle and received at the receiver.
20.A search and rescue system, comprising: a rescue beacon, comprising an infra-red light source, and circuitry, operable to deactivate or reduce the intensity of the infra-red light source in response to a trigger external to the rescue beacon; and a search and rescue vehicle providing the external trigger, the circuitry of the rescue beacon being configured to deactivate, in response to the external trigger, the infra-red light source to protect the night vision equipment of an operator or passenger of the search and rescue vehicle.
21.A search and rescue method utilising a rescue beacon and a search and rescue vehicle, the method comprising: emitting infra-red light from an infra-red light source of the rescue beacon; providing an external trigger, from the search and rescue vehicle; detecting the external trigger, at the beacon; and deactivating or reducing the intensity of the infra-red light source in dependence on the detection of the external trigger.