WO2019073230A1

WO2019073230A1 - Aerial object monitoring system

Info

Publication number: WO2019073230A1
Application number: PCT/GB2018/052898
Authority: WO
Inventors: Carmine CLEMENTE; Domenico GAGLIONE; Christos ILIOUDIS; John J SORAGHAN; Malcom MACDONALD; Hina BACAI
Original assignee: University Of Strathclyde
Priority date: 2017-10-11
Filing date: 2018-10-10
Publication date: 2019-04-18
Also published as: GB201718885D0

Abstract

A system for detection of an aerial object (20), wherein the system comprises at least one receiver (30) configured to receive a signal transmitted by a transmitter (10), wherein the transmitter is arranged as part of a space-based or aerial signal transmitter, and wherein, when the transmitted signal interacts with the aerial object, at least one property of the received signal is indicative of a property of the aerial object.

Description

AERIAL OBJECT MONITORING SYSTEM

FIELD OF INVENTION

The present invention relates to the detection and classification of aerial objects, such as Unmanned Aerial Vehicles.

BACKGROUND OF INVENTION

Professionally owned and/or operated, large Unmanned Aerial Vehicles (UAVs) are known to be used in several military and civilian applications, for example security, search and rescue, monitoring, disaster management and crop-management.

The proliferation and use of small UAVs is growing rapidly amongst hobbyists and amateurs, in particular due to the accessibility and low cost of UAVs.

A lack of a clear regulation relating to the use and proliferation of UAVs poses a real safety issue. There is a growing concern in the Aviation Industry of the risk that small UAVs may be used in an unconventional manner, such as to intentionally or unintentionally interfere with common airport operations. Small UAVs, particularly if used in an unregulated manner, are perceived as posing a collision risk to aircraft.

There is also a growing concern relating to the potential malicious use of UAVs. The small size of UAVs may be exploited to evade detection systems, such as conventional radar systems or border surveillance systems.

Further, the potential use of UAVs as a weapon, for example as a means to transport explosives, is an area of growing concern. It is a public concern that UAVs may pose as delivery devices for weapons or explosive, chemical or radiological material.

In light of the abovementioned concerns and the risks associated with the growing proliferation and use of UAVs, there is a need to be able to detect UAVs at specific locations, such as at airports and/or borders. There is also a need to establish information relating to a detected UAV, such as speed, flight paths, or categorization of the UAV to minimise the occurrence of false alarms.

For practical reasons, any such system should be optimised in terms of size, power consumption, weight and general portability, installation efforts and costs.

It is an object of at least one embodiment of at least one aspect of the present invention to seek to address one or more problems and/or disadvantages in the prior art. SUMMARY OF INVENTION

According to a first aspect of the present invention there is provided a system for detection of an aerial object, the system comprising:

at least one receiver configured to receive a signal transmitted by at least one transmitter, such as a transmitter comprised in a space-based and/or aerial signal transmitter; and

wherein, when the transmitted signal interacts with the aerial object, the system is configured to determine at least one property of the received signal(s) that is indicative of one or more properties of the aerial object.

The transmitter may be, comprise or be comprised in a non-cooperative transmitter.

The non-cooperative transmitter may be, comprise or be comprised in a transmitter of opportunity. The non-cooperative transmitter may be, comprise or be comprised in a transmitter that was not designed for use in, or as part of, the system for detection of an aerial object and/or for use in, or as part of, a Radio Detection And Ranging (RADAR) system. That is, the non-cooperative transmitter may operate, i.e. transmit a signal, with no indication or awareness that the signal is to be used to indicate one or more properties of the aerial object. Thus, the transmitter and/or the signal transmitted by at least one transmitter and/or operations of the transmitter may not co-operate with the receiver.

The system may be configured to determine one or more, e.g. a plurality of, properties of the received signal(s) that are indicative of the one or more properties of the aerial object.

The system may be configured to determine a profile of the aerial object, the profile comprising or being formed from the at least one property of the signal(s) and/or the one or more properties of the aerial object, e.g. a plurality of properties of the signal and/or aerial object.

The system may be configured to identify the presence of the aerial object and/or classify or characterise the aerial object based on the profile.

The at least one transmitter (e.g. the space-based or aerial signal transmitter) may transmit time or clock signals such as high precision time signals, or the likes. The at least one transmitter may transmit signals that are synchronized to, or generated in relation to, at least one atomic clock.

The transmitter may be comprised in a satellite. The space-based or aerial signal transmitter may be comprised in a geostationary satellite. The space-based or aerial signal transmitter may be in a low or medium earth orbit or a polar-orbit. The space-based or aerial signal transmitter may be in a substantially geostationary orbit.

The transmitter may be part of or comprised in a satellite of a satellite navigation system. The space-based or aerial signal transmitter may be part of a Global Navigation Satellite System (GNSS), such as NAVSTAR GPS, GLOSNASS, Galileo, and/or the likes.

The at least one receiver may be configured to receive a signal transmitted by a plurality of transmitters, such as transmitters respectively comprised in respective satellites of a plurality of satellites, e.g. satellites of a satellite navigation system.

Beneficially, the use of more than one transmitter may permit detection and/or classification or characterisation of aerial objects with a small Radar Cross Section (RCS).

The aerial object may be an unmanned aerial vehicle (UAV). The aerial object may be a drone. The aerial object may operate or be operable partially or completely autonomously. The aerial object may operate or be operable partially or completely under remote control by means of a human or computer operator. The aerial object may be an aircraft suitable for commercial and/or military applications. The aerial object may be an aircraft suitable for non-commercial applications, such as for recreational use by hobbyist or amateur aerial vehicle pilot. The aerial object may be suitable for scientific applications. The aerial object may be suitable for surveillance and/or aerial photography

The aerial object may be a fixed-wing aircraft. The aerial object may be a helicopter. The aerial object may be a tricopter, quadcopter, pentacopter, hexacopter, septacopter, octacopter, nonacopter, decacopter or any other multicopter, or the likes. The aerial object may be an ornithopter. The aerial object may be an airship. The aerial object may be a projectile, missile or any other man-made object. The aerial object may comprise at least one propeller and/or rotor. The aerial object may comprise at least one engine and/or electric motor. The engine may be a piston engine, such as a single stroke or two-stroke engine, or the likes. The engine may be an internal combustion engine, such as a Wankler engine. The engine may be a jet engine or a gas turbine. The engine may be a rocket engine.

The aerial object may be powered by one or more batteries, such as Li-Ion batteries or the like. The aerial object may be powered by an internal combustion engine, comprising at least one cylinder. The aerial object may be powered by fuel, such as gasoline, or the likes. The aerial object may be powered by fuel cells. The aerial object may be capable of non-powered flight. That is, the aerial object may be capable of gliding.

The aerial object may be a Small Unmanned Aerial Vehicle (SUAV). The aerial object may weigh less than 25kg. The aerial object may weigh less than 9kg. The aerial object may have dimensions less than 0.5 metres by 2.0 metres.

The aerial object may be a Miniature Unmanned Aerial Vehicle (MUAV). The aerial object may weigh less than 20 kilograms. The aerial object may have dimensions less than 0.5 metres by 0.2 metres.

The aerial object may be a Micro Aerial Vehicle (MAV). The aerial object may weigh less than 5 kg. The aerial object may have dimensions less than 0.5 metres by 0.5 metres.

The aerial object may have a weight and/or dimensions that are within a range defined by a Civil Aviation Authority, such as the United Kingdom Civil Aviation Authority, for a class or category of aerial object.

The aerial object may be capable of operating at altitudes of between 0 and 500 metres, and more typically of between 50 and 100 metres. The aerial object may be capable of flying at speeds in the range of 5 and 50 metres/second, and more typically of between 10 and 20 metres/second. The aerial object may be capable of hovering.

The receiver may be configured to receive a plurality of signals comprising signals from more than one, e.g. two, three or more, space-based or aerial signal transmitters.

The at least one receiver may be a satellite navigation device, or a GPS receiver, or at least a receiver configured to receive satellite navigation signals and/ or the likes.

The at least one receiver may be capable of receiving a signal from the at least one transmitter. The at least one receiver may be capable of receiving a plurality of signals from the at least one transmitter. The at least one receiver may be capable of detecting and/or measuring the at least one property of the signal received directly or indirectly from the at least one transmitter. The at least one property of the signal may comprise power or phase, or a power profile or phase profile of the received signal. The at least one property of the signal may comprise power or phase, or a power profile or phase profile of the received signal. The at least one receiver may be capable of detecting and/or measuring a change in the power or phase of the signal received directly or indirectly from the at least one transmitter. The at least one receiver may be capable of logging or storing a plurality of measurements of the at least one property of the signal, e.g. the power or phase of the signal, received directly or indirectly from the at least one transmitter. The at least one receiver may be capable of logging or storing a plurality of measurements of the property of a plurality of signals e.g. the power or phase of each of a plurality of signals received from the at least one transmitter. The profile may comprise measurements of the at least one property of the signal(s) and/or the aerial object over time, e.g. a limited time, such as from the log or store of measurements. The profile may comprise the power or phase profile, which may comprise or be derived from at least one log or store of measurements of the power or phase of a received signal.

The receiver may be an RF receiver. The receiver may be capable of receiving navigation signals transmitted directly and/or indirectly from a satellite navigation system, such as the Global Navigation Satellite System (GNSS), NAVSTAR GPS, GLOSNASS, Galileo, or the likes. The receiver may be capable of receiving electromagnetic signals directly and/or indirectly from the GNSS satellites in L-band (between 1 and 2 GHz).

The at least one receiver may be configured to detect or be capable of detecting a signal transmitted by the transmitter and reflected by, or off, an aerial object. The at least one receiver may be capable of detecting a signal transmitted by the transmitter and scattered over and/or across and/or from, at least a portion of an aerial object. Beneficially, scattering, such as forward scattering, may facilitate improved reception or detection capabilities, thus extending a minimum detectable range of the aerial object, e.g. due to a higher Signal-to-Noise Ratio achievable.

The signal may be, or comprise, a continuous signal. The signal may be, or comprise, a periodic signal. The signal may be, or comprise, a microwave signal. The signal may comprise a plurality of signals. The signal may comprise data such as ranging codes, timing signals, navigation data or the likes.

The receiver may comprise at least one antenna. The receiver may comprise a plurality of antennae. The receiver may comprise an omnidirectional antenna. The receiver may comprise an omnidirectional antenna suitable for reception of signals over a 360 degree azimuth area. The receiver may comprise at least one directional antenna, wherein at least one directional antenna is configured to receive signals over a limited azimuth of interest and/or a limited elevation angle of interest.

The receiver may comprise a processing system comprising one or more processors, such as at least one microprocessor and/or microcontroller and/or Field- Programmable-Gate-Array (FPGAs) and/or Digital Signal Processor (DSPs). The processing system may further comprise at least one amplifier, digitizer, downconverter or the likes. At least a portion of the processing system may be remote from the receiver. The receiver may be connected to, or in communication with, the processing system. The processing system may be configured to process the received signal(s). The processing system may be configured to determine at least one property of the received signal(s) that is indicative of one or more properties of the aerial object.

The at least one property of the received signal(s) may comprise one or more change or feature, e.g. one or more change or feature of the signal may comprise an increase or decrease, in the power or phase of the signal. The receiver may be configured to detect and/or measure the change, such as an increase and/or decrease, in the power or phase of the signal transmitted by the at least one transmitter. The signal may be or comprise an electromagnetic signal. Beneficially, the detection and/or classification or characterisation of aerial objects with a small Radar Cross Section (RCS) may be achieved by receiving and processing a signal transmitted directly or indirectly by more than one transmitter.

The receiver may be configured to detect and/or measure an increase and/or decrease in the power or change in the phase of a received signal caused by an aerial object moving in the proximity of, and/or across, a path such as a bistatic line-of-sight between the at least one transmitter and the receiver.

The receiver may be adapted to receive and process electromagnetic signals received directly and/or indirectly from the GNSS satellites in L-band (between 1 and 2 GHz). Beneficially, by using readily available satellite signals, a system comprising such receivers may not require allocation of specific frequency bands.

That is, the receiver may be configured to detect and/or measure an electromagnetic shadow cast by an aerial object moving in the proximity of, and/or across, a path between the transmitter and the receiver. That is, the receiver may be able to detect the effect on a received signal due to the presence of an aerial object moving in the proximity of, and/or across, a path between the transmitter and the receiver.

The measurements made by the receiver as an aerial object moves in the proximity of, and/or across, a path between the transmitter and the receiver may be used to determine a property of the aerial object and/or perform a classification of the aerial object.

The receiver may be dynamically configured to receive a signal from at least one of one of a plurality of transmitters. The receiver may be dynamically configured to receive a signal from one of a plurality of transmitters to maximise or optimise detection and classification capabilities. The receiver may comprise a plurality of receivers.

The receiver may be dynamically configured to receive a signal from at least one of a plurality of a transmitters based, at least in part, on at least one of: prior information about a satellite identification code associated with a transmitter (e.g. PRN code of the GPS constellation); a geographic area of deployment of a receiver system; and an expected set of satellites whose signal can be received by the receiver at a given time.

Beneficially, the use of receivers adapted for reception of signals transmitted by a GNSS system may be small, relatively cheap and portable. As such, a system comprising such receivers may be deployed easily and stealthily, increasing its suitability for monitoring of sensitive areas. Further, due to the wide geographical coverage of satellite signals, such as GNSS signals, a system comprising such receivers may be deployed at a wide range of geographical locations, at any time (day or night) and in all weather conditions.

Beneficially, a system comprising such receivers has no requirements to transmit signals. As such, such a system may be particularly suitable for purposes of a surveillance system wherein detection of the presence of the surveillance system is undesirable.

The at least one property of the received signal may be stored, recorded or logged.

The at least one property of the received signal may be stored, recorded or logged, such that a plurality measurements of the at least one property of the received signal may constitute or be comprised in the profile.

The at least one property of the received signal may be the power or phase of the received signal.

The power or phase of the received signal may be stored, recorded or logged, such that a plurality of measurements of the power or phase of the received signal may constitute or be comprised in a power or phase profile, which may form part of the profile used to identify the presence of, or classify, the aerial object.

The plurality of measurements of the power or phase of the received signal may be separated by a defined time interval. The defined time interval may be constant.

The power or phase profile may be indicative of a property of the aerial object, such as at least one of the aerial object's shape, length, size, speed, direction of travel, altitude and/or the like. The power or phase profile may be indicative of a speed of rotation of at least one of an engine, rotor, motor, or blade or the likes. The power or phase profile may be indicative of a rate of vibration of the aerial object. Beneficially, the power or phase profile may be used to discriminate an aerial object, such as an UAV, from an unwanted target, such as a bird or larger aircraft. The benefits of such a characterisation based on mechanical and physical characteristics of the aerial object facilitate the use of a relatively high probability of false alarm at a detection stage, thus increasing the detection probability and the minimum detectable range. As such, at a classification stage false alarms can be removed obtaining also an improved false alarm rate.

The system may be adapted to classify and/or characterise the aerial object.

The detection may comprise detection and classification and/or characterisation of the aerial object.

The system may comprise, be used with, or be adapted for use with, an alarm system, a notification system, and/or a communication system. The system may be configured to automatically provide the alarm or notification upon identifying the presence of the aerial object and/or upon matching the classification of the aerial object with one or a plurality of predetermined reference classifications. The notification or alarm may comprise presenting the predetermined classification of the aerial object.

The system may comprise, be used with, or be adapted for use with, a system for at least one of: disabling, disarming, tracking, destroying, or capturing an aerial object, which may operate responsive to the identification of the presence of the aerial object and/or the classification of the aerial object.

The system may comprise, be used with, or be adapted for use with, a system for at least one of: controlling, impeding, in any way affecting or influencing the flight path, trajectory, velocity, altitude, pitch, yaw or roll of an aerial object, which may operate responsive to the identification of the presence of the aerial object and/or the classification of the aerial object.

The system may comprise at least one antenna. The at least one antenna may be an omnidirectional antenna. Beneficially, a single, omnidirectional antenna, may be located, for example, atop a building and is a low-cost system. Such an antenna may be configured and/or oriented such that nulls are located at low elevation angles. Beneficially, this may serve to mitigate the lower gain that omnidirectional antennae have compared to directional antennae. Further, by locating nulls at low elevation angles, where the likelihood of the presence of an aerial object is low, interference from ground multipath may be reduced. In another embodiment, the system may comprise a plurality of directional antennae located in close proximity to one another. The system may comprise a plurality of directional antennae located within 5 metres of one another. The system may comprise a plurality of collocated directional antennae. The system may comprise a plurality of directional antennae located on, located within, and/or attached to, a housing.

The at least one directional antenna may be suitable for reception of signals over an azimuth of interest and/or an elevation angle of interest. Each antenna of the plurality of collocated directional antenna may be configured to cover a different azimuth and/or elevation angle or range of azimuths and/or elevation angles. The azimuth and/or elevation angle of at least two of the directional antennae may be configured to overlap.

Beneficially, the implementation of a plurality of directional antennae permits a monitored area of interest to be divided into different sectors, each of which is covered by one or more antennae. The quantity of antennae implemented may be selected dependent on the radiation pattern of each antenna and a desired azimuth and elevation angle of coverage. Beneficially, since each directional antenna of the plurality of directional antennae can cover a different elevation-azimuth sector, such a configuration permits the system to localise a possible threat in the coverage area of each sector. Beneficially, such an antenna configuration may provide better detection ranges than the aforementioned single omnidirectional antenna due to the higher antenna gain and angular localisation.

The plurality of directional antennae may be connected to a common processing system. Each antenna of the plurality of directional antennae may be connected to a processing system. Each processing system may be directly or indirectly in communication with another of a plurality of processing systems. The plurality of directional antennae may be connected to a common processing system. A multichannel processing system may process signals received by a plurality of directional antennae.

In another embodiment, the system may comprise a plurality of directional antennae that are distributed, e.g. widely distributed, such as between 50 to 100 metres apart, a kilometre apart or more, in space to one another. The system may comprise a plurality of directional antennae that are distributed around a perimeter of an area, such as an enclosed area, or along at least a portion of a perimeter or border. The system may comprise a plurality of processing systems or units that are distributed, e.g. widely distributed, such as between 50 to 100 metres apart, such a kilometre apart or more.

The plurality of directional antennae may be arranged such that the azimuth and/or elevation angle of coverage of at least two of the directional antennae may be configured to not overlap or overlap partially.

Beneficially, such an arrangement may provide surveillance for an area, for example an airport or sensitive area, such as a military installation, or for a border, for example a national border.

The system may be, comprise or be comprised in a passive detection system for passively detecting and optionally also characterising aerial objects.

The system may comprise or be comprised in a hybrid system that uses both active and passive detection.

The passive detection may be provided by detecting the signal from an external or remote transmitter, e.g. the space-based and/or aerial signal transmitter, using the at least one receiver. The external or remote transmitter used for passive detection may be a transmitter sending a signal primarily used for another purpose, such as a navigation system transmitter that sends a navigation signal for use in determining position or location of the receiver.

The system may comprise an active detection system for providing the active detection. The active detection system may be or comprise a RADAR or LIDAR detection system. The active detection system may comprise at least one active transmitter, such as one or more of a RADAR or LIDAR transmitter, a microwave or other radiation source and/or the like. The active detection system may comprise at least one active detection receiver, such as one or more of a RADAR or LIDAR receiver, a microwave or other radiation receiver and/or the like. The active detection transmitter and active detection receiver may optionally be comprised in the same physical unit, device or housing.

In an example, the system may comprise a plurality of active transmitters and/or receivers. At least one of the active transmitters and/or receivers may be provided on either side of the passive receiver (e.g. the at least one receiver).

The system may be configured to activate or operate the active detection system responsive to the passive detection. For example, the system may be configured to activate the active detection system when the passive detection system determines that an aerial object is present, e.g. when the system determines that at least one property of the received signal(s) is indicative of one or more properties of the aerial object. For example, the system may be configured to activate the active detection system when the passive detection system determines that a particular type of aerial object has been detected, e.g. based on the characterization of the aerial object performed by the system based on the passive detection. The particular type of object may be predetermined or input by an operator, for example.

The system may be configured to activate or operate the active detection system for a limited period of time responsive to the passive detection. The limited period of time may be a predetermined or user input period of time, for example. The limited period of time may be in the order of seconds, e.g. between 5 and 45 seconds, or between 8 and 20 seconds, for example.

The system may be operable to provide further information regarding aerial object using the active system whenever an aerial object or a particular type of aerial object is detected using the passive system. This may reduce the number of false alarms and may increase the speed of target detection and/or classification.

According to a second aspect of the present invention there is provided a method of use of a system for detection of an aerial object, the method comprising the steps of:

providing at least one receiver configured to receive a signal transmitted by at least one transmitter, such as a transmitter arranged as part of a space-based and/or aerial signal transmitter; and

when the transmitted signal interacts with the aerial object, using at least one property of the received signal(s) to determine one or more properties of the aerial object.

The receiver may be adapted to perform the selection of a specific transmitter, for example a GNSS satellite transmitter, by exploiting prior information about, for example, a satellite identification code. The prior information may comprise, for example, at least one of the PRN code of the GPS constellation, the geographic area of deployment of the system, and the expected set of satellites whose signal can be received by the receiver in a given instant.

Beneficially, the use of such prior information may permit selection or dynamic selection of a transmitter that will maximize the detection and/or classification and/or characterisation performance. Further, since the selection process for a transmitter, for example a GNSS satellite, may require a cross-correlation with locally-stored data, for example the GNSS satellite identification sequence, the interference from transmitters may be mitigated resulting in an increase in the received signal power and/or an increase in the signal to noise ratio of the received signal.

The receiver may be configured to detect and/or measure a change in one or more of the properties of the received signal, such as an increase and/or decrease in the power and/or change in the phase of a received signal caused by an aerial object, which may be moving in the proximity of, and/or across, a path such as a bistatic line- of-sight between the at least one transmitter and the receiver. The rate at which the power of a received signal may vary in response to an aerial object moving in the proximity of, and/or across, a path such as a bistatic line-of-sight between the at least one transmitter and the receiver may be in the region of 8 decibels. The magnitude of an increase in the power of the signal as an aerial object moves in the proximity of the path may be in the region of 1 to 2 decibels. The magnitude of a decrease in the power of the signal as an aerial object into the path may be in the region of 8 decibels. Beneficially, since the magnitude of the variation in the power of the received signal is in the range of 8 decibels, a commercially available receiver or detector, such as a Constant False Alarm Rate (CFAR) detector, may be used to detect the aerial object and expensive or customised receivers are not required.

The receiver may be configured to detect and/or measure a change in one or more of the properties of the received signal, such as an increase and/or decrease in the power or a change in the phase of a received signal caused by an aerial object moving in the proximity of, and/or across, a path such as a bistatic line-of-sight between a plurality of transmitters and the receiver. Beneficially, a plurality of signals received from different satellites, either belonging to the same constellation or to different constellations, may be integrated in order to enhance the aerial object detection and/or classification capabilities of the system. The of the plurality of signals may be code or frequency multiplexed. As such, a preliminary detection may be performed using each signal. Subsequently, the resultant data derived from each signal may be integrated, thus decreasing a Probability of False Alarm of the detector.

The processing unit may be adapted to classify an aerial object by a drop in the power or change in the phase of the received signal caused by the aerial object moving across a bistatic line-of-sight between at least one transmitter and the receiver.

The processing unit may be adapted to identify the position of an aerial object immediately before and after the aerial object passes across the bistatic line-of-sight by identifying peaks in the one or more properties, e.g. power, of the received signal. Further, the processing unit may be adapted to detect that an aerial vehicle is in the proximity of the bistatic line-of-sight by means of identifying a change in the one or more properties, e.g. power, of the received signal.

The processing unit may be adapted to log or record a plurality of measurements of the one or more properties, e.g. power, of a received signal during a time interval between the peaks in the power of the received signal. The processing unit may be adapted to convert a resultant data set of power measurements to represent power as a function of distance. As such, a distinct data set representing power as a function of distance, for a length of the aerial object, may be used to classify the aerial object.

The processing unit may be adapted to distinguish an aerial object from a target of similar dimension and/or shape.

The processing unit may be adapted to process the received signal to distinguish an aerial object from a target of similar dimension and/or shape by identifying modulations or periodicities induced in the received signal by the aerial object. Such modulations or periodic or cyclical waveforms in the signal may be induced by mechanical vibrations or rotations of the aerial object, or any part of the aerial object.

The processing unit may be adapted to process the received signal to extract a phase history of the signal. As such, the processing unit may be adapted to process the received signal to distinguish an aerial object from a target of similar dimension and/or shape based on the phase history, e.g. by establishing a Doppler or micro- Doppler signature of the aerial object.

The processing unit may be adapted to recognise and/or characterise a target. The processing unit may be adapted to recognise and/or characterise a target based on one or more Doppler or micro-Doppler measurements or a Doppler or micro- Doppler signature of the aerial object. The processing unit may be adapted to recognise and/or characterise a target based on one or more Doppler or micro-Doppler measurements or a Doppler or micro-Doppler signature of the received signal.

A micro-doppler effect and/or modulation of the signal may be a Doppler effect and/or modulation of the signal generated by micro-motions of the target, as described below.

The processing unit may be adapted to recognise and/or characterise a target based on micro-motions, or detected micro-motions, of the aerial object. The processing unit may be adapted to recognise and/or characterise a target based on micro-motions of the aerial object detected in the received signal. Such micro-motions may be movements of, and/or caused or induced by, a moving part or component of the target, such as the rotors or propellers of a UAV. Such micro-motions may be distinct from a bulk translational motion of the target, such as an overall movement of the entire target.

The processing unit may be adapted to recognise and/or characterise a target based on scattering, such as forward scattering, of a signal over and/or across and/or from, at least a portion of an aerial object.

The processing unit may be adapted to recognise and/or characterise a target based on scattering, such as forward scattering, of a signal over and/or across and/or from, at least a portion of an aerial object, the scattering of the signal being detected it the received signal. As such, the aerial object may be distinguished from an aerial object that does not exhibit such vibrations or rotations, such as a bird.

The processing unit may be adapted to process the received signal to distinguish between aerial objects of significantly different dimensions, e.g. such as distinguishing between a small UAV and an aircraft, such as an aeroplane or a helicopter.

The method may comprise passively detecting and optionally also passively characterising aerial objects.

The method may comprise using both active and passive detection.

The method may comprise passively detecting the signal from the space-based and/or aerial signal transmitter using the at least one receiver.

The method may comprise an actively detecting the aerial object using a RADAR or LIDAR detection system.

The method may comprise activating, performing or operating active detection responsive to the passive detection. For example, the method may comprise activating or performing the active detection when the passive detection determines that an aerial object is present, e.g. when it has been determined that at least one property of the received signal(s) is indicative of one or more properties of the aerial object. The method may comprise activating or performing the active detection when the passive detection determines that a particular type of aerial object has been detected, e.g. based on the characterization of the aerial object using the passive detection.

The method may comprise activating or operating the active detection for a limited period of time responsive to the passive detection. According to a third aspect of the present invention there is provided a processing system for processing a received signal(s), wherein the system comprises:

at least one receiver configured to receive a signal transmitted by at least one transmitter, such as a transmitter arranged as part of a space-based and/or aerial signal transmitter; and

a processing unit,

wherein, when the transmitted signal interacts with the aerial object, the processing unit is configured to determine at least one property of the received signal(s) that is indicative of one or more properties of the aerial object.

According to a fourth aspect of the present invention there is provided a computer program product for processing a received signal(s), wherein

when at least one receiver is configured to receive a signal transmitted by at least one transmitter, such as a transmitter arranged as part of a space-based and/or aerial signal transmitter, and when the transmitted signal interacts with the aerial object,

the computer program product is configured to determine at least one property of the received signal(s) that is indicative of one or more properties of the aerial object.

It should be understood that the features defined above in accordance with any aspect of the present invention or below relating to any specific embodiment of the invention may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment of the invention.

Furthermore, the present invention is intended to cover apparatus configured to perform any feature described herein in relation to a method and/or a method of using or producing, using or manufacturing any apparatus feature described herein.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects will now be described, by way of example only, with reference to the accompanying drawings, which:

Figure 1 a representation of an embodiment of the invention;

Figure 2 data showing an example of power drop when an UAV crosses the line of sight between a transmitter and a receiver according to an embodiment of the present invention; a schematic of a GNSS Passive Bi-static Radar (PBR) and classification scheme;

a chart showing a Euclidian distance between "shadowing" from different small UAV targets according to an embodiment of the present invention;

a representation of a single omnidirectional antenna configuration according to an embodiment of the present invention;

a representation of a system comprising a directive collocated antenna configuration according to another embodiment of the present invention; and

a representation of a system comprising a directive distributed antenna configuration according to another embodiment of the present invention.

DETAILED DESCRIPTION OF DRAWINGS

Referring firstly to Figure 1 of the accompanying drawings, there is shown a representation of an embodiment. There is shown a space-based transmitter 1 that transmits a signal 4a. An aerial object 2 is located substantially in a bistatic line of sight between the space-based transmitter 1 and a receiver 3. The signal 4a interacts with the aerial object 2, resulting in a modified signal 4b. The modified signal 4b is received by the receiver wherein at least one property of the modified signal 4b is indicative of a property of the aerial object 2. The modified signal 4b may differ from the signal 4a due to an electromagnetic shadow cast by the aerial object 2 as it moves in the proximity of, and/or across, a path between the transmitter 1 and the receiver 3. Further, and as will be described in more detail below by reference to Figure 3, the modified signal 4b received by the receiver 3 may comprise signal 4a, or components or elements or a portion of signal 4a, that have been scattered over and/or across and/or from, at least a portion of the aerial object 2.

Referring to Figure 2 of the accompanying drawings there is shown exemplary data showing an example of a drop in the power of a received signal when an aerial object 2 crosses a line of sight between a transmitter 1 and a receiver 3 according to an embodiment of the present invention. In describing the data shown in Figure 2, is it first relevant to explain how the present invention incorporates the principles of forward scattering in a bi-static radar system.

The detection capability of a generic radar depends on the received power from a target (i.e. an aerial object). Instead, in a Forward Scattering Radar (FSR), that represents a particular case of bi-static radars when the bi-static angle is close to 180°, a detection is declared when a drop in the received power is recognised, wherein the drop in the received power occurs when a target crosses a bi-static line of sight, blocking part of the transmitted signal.

The power that the receiver measures from a source of opportunity (i.e. the transmitter 1 ) in the absence of a target, assuming the free space path loss model, is equal to:

_ P_TG_TG_R ²

P^rd - (4π)*/¾

where P_T is the transmitted power, G_T and G_R are the transmitter and receiver antenna gains, respectively, λ the wavelength and R_D the transmitter-receiver distance. In presence of a target, the power that the target radiates in the forward direction is equal to:

where R_T and R_R are the transmitter-target and target-receiver distances, and a_fs is the forward scattering Radar Cross Section (RCS). Thus, the received power in presence of target can be written as:

Thus, it is clear that the larger the forward scattering RCS, the smaller the received power and, hence, the more likely is it that a power drop will be detected.

An advantage of a FSR, is that it guarantees relative RCS enhancement with respect to the generic bi-static case. In fact, in this case the RCS only depends on the area and the shape of the target's silhouette. This concept is based on the Babinet's principle which affirms that in optics a perfect absorbing target diffracts the same electromagnetic wave (apart from a 180° phase shift) as an aperture of the same shape and area A of the target. Thus, assuming that the target is electromagnetically far from both the transmitter and receiver, the forward scattering RCS can be written as:

where G_FS represents the peak antenna gain of uniformly illuminated aperture whose area is equal to A . When the bi-static angle is smaller than 180°, the forward scatter RCS rolls off from a_fs following the appropriate equivalent antenna pattern. The exemplary data in figure 2 shows a relatively constant magnitude of a power of a modified signal 4b at approximately -108 decibels between acquisition times of 0 and approximately 7.5 seconds, during which time aerial object 2 is not in a bistatic line of sign between transmitter 1 and receiver 3 and a degree of forward scattering over and/or across the aerial object 2 is relatively negligible.

The data in figure 2 shows a significant increase/spike in the magnitude of the power of a modified signal 4b between approximately 7.5 seconds and 8.1 seconds. Such an increase/spike can be attributed to the effects of back-scattering of the transmitted signal 4a over/across an aerial object 2 as the aerial object 2 approaches the bi-static line of sight between the transmitter 1 and the receiver 3.

The data in figure 2 also shows a significant decrease in the magnitude of the power of a modified signal 4b between approximately 8.1 and 8.2 seconds, relative to the relatively constant magnitude of a power of a modified signal 4b at approximately - 108 decibels between acquisition times of 0 and approximately 7.5 seconds. Such a drop in the power can be attributed to the aerial object 2 crossing the bi-static line of sight between the transmitter 1 and the receiver 3, i.e. the aerial object is casting an electromagnetic shadow over the receiver. Subsequently, between approximately 8.2 and 8.5 seconds there is an ensuing increase in the magnitude of the power of a modified signal 4b as the aerial object 2 exits the bistatic line of sight between the transmitter 1 and the receiver 3.

Finally, data in figure 2 also shows a detectable increase in the magnitude of the power of a modified signal 4b between approximately 8.5 and 10 seconds, relative to the relatively constant magnitude of a power of a modified signal 4b at approximately -108 decibels between acquisition times of 0 and approximately 7.5 seconds. Such an increase can be attributed to the effects of back-scattering of the transmitted signal 4a over/across an aerial object 2 as the aerial object 2 moves away from the bi-static line of sight between the transmitter 1 and the receiver 3.

Figure 3 shows a schematic diagram exemplifying a sequence of events that embody the present invention. Transmitter 10 is a GNSS illuminator. Receiver 30 is adapted to receive a signal from the transmitter 10. Receiver 30 is, in this particular embodiment, a Surveillance System Unit. One of skill in the art would readily understand that the receiver 30 may be a satellite navigation device, or a GPS receiver or the likes, such as an RF receiver capable of receiving navigation signals transmitted directly and/or indirectly from a satellite navigation system, such as the Global Navigation Satellite System (GNSS), NAVSTAR GPS, GLOSNASS, Galileo, or the likes. Aerial object 20 is an Unmanned Aerial Vehicle (UAV). The aerial object 20 has a perpendicular-to-a-baseline length, L, wherein the baseline 25 is a line-of sight between the transmitter 10 and the receiver 30. The aerial object 20 crosses the baseline 25 with a velocity u.

Point A is a position of the aerial object 20 immediately before it commences crossing the baseline 25.

Point B is a position of the aerial object 20 immediately after it finishes crossing the baseline 25.

Graph 40 shows the power of a signal received by the receiver 30 over time. It can be seen, at section 40a, that the power of the signal remains relatively constant as the aerial object 20 is away from the baseline 25. As the aerial object 20 approaches the baseline 25, i.e. approaches point A, the power of the received signal increases due to an effect of multipath i.e. scattering of the transmitted signal over and/or across and/or from, at least a portion of the aerial object 20. The power of the received signal reaches a peak at the point A. Between points A and B, the aerial object 20 "shadows" the transmitted signal for a time interval of duration T.

Graph 50 represents the power of the received signal in the time period T, wherein a portion of the time axis t of graph 40 has been converted to a spatial axis x by using the speed of the aerial object 20 The resultant data represents a characteristic "shadowing" profile of the aerial object across its length L. The profile comprises, for example, peaks and/or troughs in the profile, The profile depends on the silhouette of the aerial object 20. As such, aerial objects with different silhouettes produce different profiles. For example, the profiles for different aerial objects 20 may comprise different numbers, magnitudes and/or relative magnitudes of peaks and/or troughs in the power, Exemplary profiles for UAV1 60a, UAV2 60b and a bird 60c clearly show differences between the shapes of the profiles.

Figure 4 is a Distance Matrix showing a Euclidian distance between "shadowing" from three different small UAV targets 70a, 70b, 70c according to an embodiment of the present invention. Such an analysis provides a clear visual representation of the differences in received signals between different types of UAVs.

Figure 5 shows a representation of a system configuration, wherein the system comprises a single antenna 110, according to an embodiment of the present invention. The antenna 1 10 is an omnidirectional antenna. Beneficially, the single, omnidirectional antenna 1 10 is located atop a building/stucture 130. Beneficially such a system is a low-cost system. Such an antenna may be configured and/or oriented such that nulls are located at low elevation angles to mitigate the lower gain that omnidirectional antennae have compared to directional antennae. A coverage area 120 of antenna 110 is shown.

Figure 6 shows a representation of a system comprising a directive collocated antenna configuration according to another embodiment of the present invention. In this embodiment, the system comprises two directional antennae 210a, 210b located in close proximity to one another, i.e. collocated. One of skill in the art would readily recognise that such a configuration may comprise more than two antennae, and that the antennae may be located on, within, and/or attached to, a housing, and/or collocated on a common building, structure or geographical location.

Each antenna 210a, 210b is suitable for reception of signals over a limited azimuth of interest and/or a limited elevation angle of interest. As such, antenna 210a is suitable for reception of signals over a sector A, and antenna 210b is suitable for reception of signals over a sector B. One of skill in the art would readily understand that in another embodiment that falls within the scope of the present invention, the sectors A, B may be configured to overlap.

Beneficially, the implementation of a two directional antennae 210a, 210b permits a monitored area of interest to be divided into different sectors A, B, each of which is covered at least one antenna 210a, 210b. One of skill in the art would readily understand that in another embodiment that falls within the scope of the present invention, a quantity of antenna may be more than two, and may be selected dependent on the radiation pattern of each antenna and a desired azimuth and elevation angle of coverage.

Beneficially, since each directional antenna 210a, 210b covers a different elevation-azimuth sector A, B, such a configuration permits the system to localise a possible threat in the coverage area of each sector A, B. Beneficially, such an antenna configuration may provide better detection ranges than the aforementioned single omnidirectional antenna due to its higher antenna gain and angular localisation. Beneficially, such an antenna configuration may provide better or enhanced angle of arrival information than the aforementioned single omnidirectional antenna due to its higher antenna gain and angular localisation.

The directional antennae 210a, 210b are connected to a common processing system 220. The processing system 220 processes signals received by the antennae 210a, 210b. Figure 7 shows a representation of a system comprising a directive distributed antenna configuration according to another embodiment of the present invention. The system comprises six directional antennae 310a-f that are distributed around a perimeter of a protected area 300. One of skill in the art would readily understand that in another embodiment that falls within the scope of the present invention, there could be more than or less than six antenna. The plurality of directional antennae is arranged such that the sectors of coverage 320a-f (i.e. the azimuth and/or elevation angle of the directional antennae) are configured to overlap.

Beneficially, such an arrangement provides surveillance for an area 300, for example an airport or sensitive area, such as a military installation, or for a border, for example a national border.

It will be appreciated that the embodiments of the invention here before described are given by way of example only and are not meant to limit the scope of thereof in any way.

Claims

CLAIMS:

1. A system for detection of an aerial object, the system comprising:

at least one receiver configured to receive a signal transmitted by at least one transmitter, such as a non-cooperative transmitter, comprised in a space-based and/or aerial signal transmitter; and

2. The system of claim 1 , wherein the at least one property of the received signal(s) comprises a power and/or phase of the received signal(s).

3. The system claim 1 or 2, wherein a plurality of measurements of the power and/or phase of the received signal(s) are stored, recorded or logged as, or used to generate, a power profile and/or phase profile.

4. The system of claim 3, wherein the power profile and/or phase profile is used to discriminate an aerial object, such as an UAV, from an unwanted target, such as a bird or larger aircraft.

5. The system of any preceding claim, wherein the space-based or aerial signal transmitter comprises or is comprised in a satellite, such as a geostationary satellite.

6. The system of claim 5, wherein the satellite is part of a Global Navigation Satellite System (GNSS), such as NAVSTAR GPS, GLOSNASS, Galileo, or the likes.

7. The system of any preceding claim, wherein the signal is a signal transmitted directly and/or indirectly from a satellite navigation system, such as the Global Navigation Satellite System (GNSS), NAVSTAR GPS, GLOSNASS or Galileo.

8. The system of any preceding claim, wherein the detection comprises detection and/or classification and/or characterisation of the aerial object.

9. The system of any preceding claim, wherein the aerial object is an unmanned aerial vehicle (UAV) or a drone, such as a Small Unmanned Aerial Vehicle (SUAV), a Miniature Unmanned Aerial Vehicle (MUAV) or a Micro Aerial Vehicle (MAV).

10. The system of any preceding claim, wherein the aerial object is one of: a fixed- wing aircraft; a helicopter or multicopter, an ornithopter, an airship; or a projectile or missile.

1 1. The system of any preceding claim, wherein the at least one transmitter transmits signals such as high precision time signals, and/or signals that are synchronized to, or generated in relation to, at least one atomic clock.

12. The system of any preceding claim, wherein the system comprises a plurality of transmitters arranged across a plurality of space-based or aerial signal transmitters.

13. The system of any preceding claim, wherein the at least one receiver is capable of detecting and/or measuring at least one property of a signal received directly or indirectly from the at least one transmitter.

14. The system of any preceding claim, wherein the at least one receiver is capable of at least one of:

detecting and/or measuring a power and/or phase the received signal(s);

detecting and/or measuring a change in the power and/or phase of the received signal(s); and

logging or storing a plurality of measurements of the power and/or phase of the received signal(s).

15. The system of any preceding claim, wherein the at least one receiver is configured to detect and/or measure an increase and/or decrease in the power and/or change in the phase of a received signal(s) caused by an aerial object moving in the proximity of, and/or across, a path such as a bistatic line-of-sight between the at least one transmitter and the at least one receiver

The system of any preceding claim, wherein the at least one receiver is capable of detecting a signal transmitted by the transmitter and scattered over and/or across and/or from, at least a portion of an aerial object.

The system of any preceding claim, wherein the signal comprises data such as ranging codes, timing signals, navigation data or the likes.

The system of any preceding claim, wherein the at least one receiver comprises a processing system comprising at least one microprocessor and/or microcontroller and/or Field-Programmable-Gate-Array and/or Digital Signal Processors (DSPs), and optionally further comprises at least one amplifier and/or digitizer and/or downconverter or the likes.

The system of any preceding claim, wherein at least a portion of the processing system is remote from the at least one receiver.

The system of any preceding claim, wherein the measurements made by the at least one receiver as an aerial object moves in the proximity of, and/or across, a path between the transmitter and the at least one receiver are used to determine a property of the aerial object and/or perform a classification of the aerial object.

The system of any preceding claim, wherein the at least one receiver is dynamically configured to receive a signal from at least one of one of a plurality of transmitters based, at least in part, on at least one of:

prior information about a satellite identification code associated with a transmitter (e.g. PRN code of the GPS constellation);

a geographic area of deployment of a receiver system; and

an expected set of satellites whose signal can be received by the at least one receiver at a given time. The system of any preceding claim, wherein the system is adapted for use with a system for at least one of: disabling, disarming, tracking, destroying, or capturing an aerial object, and/or adapted for use with a system for at least one of: controlling, impeding, in any way affecting or influencing the flight path, trajectory, velocity, altitude, pitch, yaw or roll of an aerial object.

The system of any preceding claim, wherein the system comprises at least one omnidirectional antenna and/or at least one directional antennae.

The system of any preceding claim, wherein a plurality of directional antennae are located in close proximity to one another, such as on a building, or the likes.

The system of any preceding claim, wherein a plurality of directional antenna are widely distributed, such as between 50 to 100 metres apart, such a kilometre apart or more, around a perimeter of an area or along at least a portion of a perimeter of an area or a border.

The system of any preceding claim, wherein the antennae are arranged such that the azimuth and/or elevation angle of coverage of at least two antennae is configured to overlap.

The system of any preceding claim, wherein the at least one receiver is adapted to perform a selection of a transmitter by exploiting prior information about at least one of:

a satellite identification code;

a PRN code of the GPS constellation;

a geographic area of deployment of the system; and

an expected set of satellites whose signal can be received by the at least one receiver in a given instant.

The system of any preceding claim, wherein the at least one receiver is configured to detect and/or measure an increase and/or decrease in the power and/or change in the phase of a received signal(s) caused by an aerial object moving in the proximity of, and/or across, a path such as a bistatic line-of-sight between the at least one transmitter and the at least one receiver. The system of any preceding claim, wherein the processing unit is adapted to classify an aerial object by a drop in the power and/or change in the phase of the received signal(s) caused by the aerial object moving across a bistatic line- of-sight between at least one transmitter and the at least one receiver.

The system of any preceding claim, wherein the processing unit is adapted to identify a position of an aerial object immediately before and after the aerial object passes across the bistatic line-of-sight by identifying an increase or peaks in power and/or change in the phase of the received signal(s).

The system of any preceding claim, wherein the processing unit is adapted to log or record a plurality of measurements of the power and/or phase of the received signal(s) received during a time interval between the peaks in received power.

The system of any preceding claim, wherein the processing unit is adapted to distinguish an aerial object from a target of similar dimension and/or shape by identifying modulations induced in the received signal(s) by the aerial object.

The system of any preceding claim, wherein the processing unit or a further processing unit is adapted to provide a distance matrix of data representative of the power profile and/or phase profile of an aerial object.

The system of any preceding claim, wherein the processing unit is adapted to process the received signal(s) to extract a phase history of the signal.

The system of any preceding claim, wherein the system comprises a space- based component, such as a signal transmitter.

A method of use of a system for detection of an aerial object, the method comprising the steps of:

providing at least one receiver configured to receive a signal transmitted by at least one transmitter comprised in a space-based and/or aerial signal transmitter; and when the transmitted signal interacts with the aerial object, using at least one property of the received signal(s) to determine one or more properties of the aerial object.

A processing system for processing a received signal(s), the system comprising:

at least one receiver configured to receive a signal transmitted by at least one transmitter that is comprised in a space-based and/or aerial signal transmitter, the at least one transmitter being configured to transmit a signal; and

a processing unit,

The system of claim 37, wherein the processing unit is adapted to recognise a target based on at least one of:

one or more micro-doppler measurements of the aerial object;

a micro-doppler signature of the aerial object;

one or more micro-doppler measurements of the received signal(s); and a micro-doppler signature of the received signal(s).

The system of claim 37 or 38, wherein the processing unit is adapted to recognise a target based on at least one of:

micro-motions of the aerial object;

detected micro-motions of the aerial object; and

micro-motions of the aerial object detected in the received signal.

The system of claim 37 or 38, wherein the processing unit is adapted to recognise a target based on scattering, such as forward scattering, of a signal over and/or across and/or from, at least a portion of an aerial object, the scattering of the signal being detected it the received signal.

A computer program product for processing a received signal(s), wherein: when at least one receiver is configured to receive a signal transmitted by at least one transmitter that is comprised in a space-based and/or aerial signal transmitter, and when the transmitted signal interacts with the aerial object,

the computer program product is configured to determine at least one property of the received signal(s) that is indicative of one or more properties of the aerial object