GB2133149A - Detecting device - Google Patents

Abstract

A device for detecting the presence of an aircraft or other object includes at least one transducer (14) for detecting sound or electromagnetic radiation from the object, and a housing such as a buoy (11, 12) for a filter for selecting certain signals generated by the transducer, an amplifier, a SELCALL encoder and a transmitter. These enable an encoded radio-frequency signal to be transmitted identifying the device which has been operated due to the detection of the presence of an object. The transducer 14 may receive signals from a microphone or from a heat-sensing fly's eye lens system. Geophones 16 may be provided underwater. <IMAGE>

Description

SPECIFICATION Detecting device This invention relates to a device for detecting the presence of an object in the proximity of the device. The invention is primarily concerned with the detection of aircraft passing the device, but the detection of other objects such as, for example, motor vehicles, ships, human beings is also envisaged.

It is an object of the present invention to provide an improved device for this purpose which may be constructed, in the main, readily and easily from readily available components using well known and well developed techniques.

The present invention consists in a device for detecting the presence of an aircraft or other object which includes at least one transducer for detecting sound or electromagnetic radiation from the object, a filter for selecting certain signals generated by the transducer, and an amplifier, SELCALL encoder and transmitter, to enable an encoded radio-frequency signal to be transmitted identifying the device which has been operated due to the detection of the presence of an object.

When it is desired to receive early warning of the approach of an aircraft across a stretch of water, a number of devices arranged to float upon the water are installed at a number of positions which are carefully noted.

Each device may conveniently be mounted in a buoy, such as a Dan Buoy 123-16 having a weight at the end of a line for stability, and adapted to be dropped in position by means of a parachute. Each device includes a number of transducers connected through filters to an amplifier, a transmit switch, a SELCALL encoder, and a normally quiescent radio transmitter (so as to preserve battery life), having an aerial mounted upon the buoy.

The transducers include a microphone able to detect an aircraft within a range of, say, 2 to one mile, an infra-red detector, an ultra-violet detector, a pyro-electric detector and a radio receiver. The efficacy of the transducers may be improved with the aid of a fly's eye lens and a multi-facetted mirror. It is thought that it may be possible to achieve a useful detection range of 3-5 miles.

The filters are chosen so as to reject unwanted signals caused by the ambient conditions, such as the noise of the sea and wind and radiation from the sun and moon, but to pass very selectively signals over certain ranges of signals from its associated transducer characteristic of an aircraft to be detected. It may even be possible to pass only signals caused by certain types of aircraft.

When a filter passes a signal to the amplifier indicating the presence of an aircraft, or an aircraft of the type to be detected, the transmit switch is operated, the transmitter is switched on and the SELCALL encoder causes a signal to be transmitted with a coded identification of that particular detector which has been operated.

At some remote location, on a ship or on land,the transmitted signal is received by a conventional HF or VHF receiver fitted with a SELCALL decoder to permit the conversion of the received signal into an identification of the buoy in operation. This can then be related to the known positions of the buoys to give an indication of the position of the detected aircraft. If desired, the identification of the buoy may be shown on a LED display, and/or may be used to indicate further action or warning. In some cases, if two buoys respond in turn then an indication of the approximate direction of the aircraft can be obtained.

Although the invention has been described with references to devices installed in the sea for detecting aircraft, it will be appreciated that the device may equally well be adapted for installation upon land or suspended from balloons or parachutes and the transducers and filters may be designed so as to detect objects other than aircraft or in addition to them.

In the accompanying drawings:- Figure 1 is a general diagrammatic view of one form of detecting device installed in water, and Figure 2 is a block diagram of the electronic components of the detecting device.

In carrying the invention into effect according to one convenient mode by way of example, figure 1 shows a detecting device in the form of a buoy having a generally cylindrical body 11 with a flotation collar 1 2 at the top. On top of the body is mounted an HF aerial 13 upon which is mounted a dismountable transducer head 14 and a VHF aerial 15.

The bottom of the body 11 is connected to a line connected to a number of hydrophones 1 6 originally housed in a dispenser 1 7 until the device is installed, the dispenser 1 7 being connected to a further dispenser 1 8 for an anchor 1 9 again housed in the dispenser until the device is installed in the water.

As shown in Figure 2, the body 11 includes a processor 21 arranged to receive and process signals from the various sensors to identify and confirm a genuine detection. Signal averaging and noise reduction techniques together with coincidence detection are used to give a high probability of detection together with a low false alarm rate.

When a genuine detection has been confirmed, the processor operates a transmission switch 22 to operate a transmitter 23 which generates correctly modulated signals with the aid of a SELCALL encoder 24. When these signals are received, for example by a receiver 26 located on a ship and connected to a SELCALL decoder 25, the output of the decoder 25 can be used to identify which detector has operated and thus where the detection has taken place.

One of the sensors includes a wide band aerial 31 and RF amplifier 32 whose output is fed to a conditioning unit 33 which generates characteristic data (e.g. frequency, repetition rate, signal strength, duration, for input to the processor 21. Depending upon the application, the e/m spectrum can include ratio-altimeter, TACAN, HF and VHF communications, radar etc.

In order to detect heat radiation from the aircraft, a fly's eye lens system 41 is provided in conjunction with a multi-facetted mirror system and a multi-element pyro electric detector, which enables the processor to identify single source signals or multi-source signals, and to distinguish between moving and stationary heat sources. The output from the sensor is fed via an amplifier/ multiplexer 42 and converter 43 to the processor 21.

Another of the sensors includes a microphone 51 whose output is passed through amplifiers and filters 52 and an analogue to digital converter 53 to provide another input for the processor 21. The detected signals can then be analysed to eliminate background noise due to sea, wind, storms etc., and to differentiate between aircraft noise and other sound sources such as birds.

Low power consumption technology (such as CMOS processors) is used to keep battery drain to a minimum.

Various additional facilities may be provided. A SELCALL receiver may be installed in the detector to permit remote interrogation of such unit. This can be used to request information upon the detected signals. The facility may also be available to change the transmit frequency to prevent jamming.

As shown in Figure 1, hydrophones 16 may be provided with appropriate audio-conditioning circuits to enable the presence of sea-going craft to be detected.

A flux gate compass may be used in conjunction with information from the fly's eye detector to derive information upon the heading of the detected intruder.

Use of a library of noise signatures may be used to identify the type of intruder.

Solar cells may be used to extend the useful deployed life of the detectors.

A self-destruction feature could be provided to prevent acquisition by the enemy.

Directional microphones may be provided to give additional information upon aircraft heading when used in conjunction with a flux gate compass. Doppler information for the filtered signal, and rate of change of heading could be processed to give data on target range and speed.

In a land based environment, seismic detectors could be used to provide information upon movements of troops and vehicles.

In a sea based system it is believed that, for example, for an area with a radius of 200 miles 600 buoys would be required at intervals of two miles and that it should be possible to install these at a rate of seventeen buoys per hour from a surface craft having a speed of 30 knots. Use of three craft would enable a complete defensive ring to be placed in two or three days. It is hoped that the operative range of two miles could be increased.

Claims (6)

1. A device for detecting the presence of an aircraft or other object which includes at least one transducer for detecting sound or electromagnetic radiation from the object, a filter for selecting certain signals generated by the transducer, and a processor, SELCALL encoder and transmitter, to enable an encoded radio-frequency signal to be transmitted to a remote location.

2. A device as claimed in claim 1, wherein the components are mounted in and upon a buoy to permit the device to be installed in water.

3. A device as claimed in claim 1 or 2, which includes a wide band aerial and RF amplifier whose output is fed to a conditioning unit to generate characteristic data which is then fed to the processor.

4. A device as claimed in claim 1,2 or 3, which includes means for detecting heat radiation including a fly's eye lens system, a multi-facetted mirror system and a multi-element pyro electric detector to provide a signal for the processor to distinguish between single and multi-source signals and between moving and stationary heat sources.

5. A device as claimed in any one of claims 1 to 4, which includes a microphone whose output is amplified and filtered and then converted to digital form for feeding to the processor.

6. A device for detecting the presence of an object, substantially as described with reference to the accompanying drawings.