GB2440777A

GB2440777A - Moving object identification

Info

Publication number: GB2440777A
Application number: GB9907676A
Authority: GB
Inventors: Roger Sean Fitzpatrick
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1998-04-30
Filing date: 1999-04-01
Publication date: 2008-02-13
Anticipated expiration: 2019-04-01
Also published as: GB9809369D0; GB2440777B; GB9907676D0

Abstract

A system for identifying friendly aircraft or the like operates either in an entirely passive manner or in an active manner. In the passive mode, both the aircraft 1 and ground-based surveillance radar 2 have a store 14 and 23 containing information as to the expected locations of the aircraft at specific times. The aircraft autopilot 11 controls the aircraft 1 so that it follows a specific path at a specific time. The radar 2 identifies the aircraft 1 as a recognised or friendly aircraft if it is at the correct locations at the correct times. In the active mode, the radar 2 emits interrogation signals I at specified times and the aircraft emits response signals R at specified times. The aircraft is recognised if the response signals are received at the correct times.

Description

244O77 Moving Object Identification This invention relates to systems

and methods for identifying moving objects.

Known systems for identifying moving objects, such as used, for example, by airborne and seaborne vehicles, respond automatically to a remote, coded RF interrogation signal emitted by a surveillance system by emitting an RF signal embedding a vehicle identification code and optionally other three-dimensional position, intention, or other codes.

Emission of such an automatic response signal is a disadvantage, in the case of military operations, because it reveals the presence of the responding vehicle to a hostile surveillance system. It also enables any other vehicle capable of receiving and reproducing the original vehicle's emitted response code to spoot that is, to disguise itself as a friendly vehicle.

There is also a problem in non-military operations because a proliferation of responding vehicles can saturate the system with large numbers of interrogations and responses. Overlapping interrogations or responses can also interfere with each other to produce phenomena known as garble.

It is an object of the present invention to provide an alternative moving object identification system and method.

According to one aspect of the present invention there is provided a system for identifying a moving object, the system including a movement guidance system associated with the object and containing infonnation as to the planned position of the object at different moments in time and surveillance equipment remote from the object, the surveillance equipment including means for detecting the position of objects, a store containing information as to the planned position of one or more recognised objects at different moments in time, and means for comparing the position of a detected object at a moment in time with the stored position or positions associated with that moment so as to identify whether the detected object is a recognised object.

The object may be an aircraft and the movement guidance system may be an autopilot. The movement guidance system and the surveillance equipment are preferably both arranged to receive timing signals from a common source, such as a satellite navigation system. The information as to planned position preferably includes information about a range of positions within which the object is expected to be located at particular moments in time.

The system preferably includes means associated with the object for detecting that the object is not, or will not be, at the planned position or within the range of positions at a predetermined time, said detecting means being arranged to emit a signal to the surveillance equipment identifying the object if it detects that the object is not or will not be at the planned position or within the range of positions at the predetermined time. The detecting means may be arranged to emit said signal autonomously or only in response to an interrogating signal from the surveillance equipment.

According to another aspect of the present invention there is provided a method for identifying a moving object, the method including the steps of providing guidance information to the object as to the position at which the object should be located at different moments in time, surveying the object remotely to detect the position of the object, and comparing the detected position of the object with information as to planned position of one or more recognised objects at different moments in time so as to identify whether the detected object is a recognised object.

According to a further aspect of the present invention there is provided a system for identifying an object including interrogation means, response means associated with said object, and common timing signal generating means, the interrogation and response means being arranged to generate interrogation and response signals only at defined times dependent on said common timing signal generating means.

According to a fourth aspect of the present invention there is provided a method of identifying an object including the steps of generating a common timing signal, generating an interrogation signal at a defined time referenced to said common timing signal, and monitoring for a response from said object to determine whether said response is generated at a second defined time referenced to said common timing signal.

A system and method for identifying an aircraft, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the system; Figure 2 is a schematic diagram of the system in greater detail; Figure 3 is a perspective view of the system with the aircraft deviating from its planned path; Figure 4 illustrates interrogation emissions; and Figure 5 illustrates response emissions With reference first to Figures 1 and 2, the system comprises an aircraft 1 and surveillance equipment 2 in the form of a radar. The aircraft 1 flies along a path 10 passing within the range of the radar 2.

The aircraft 1 has an autopilot 11 connected to receive position information from navigation equipment 12 and to provide control outputs to a flight control system 13, which appropriately controls the aircraft flight control surfaces, propulsion system and the like, so that the aircraft flies along the programmed path 10 at the programmed time. More particularly, the autopilot 11 is connected to a store 14 containing information as to the planned position of the aircraft 1 at different moments in time; this is defined in terms of a series of points A to E along the flight path 10. The aircraft 1 also includes a receiver 15 of common timing signals, such as from a GPS or GNSS satellite 16. The receiver 15 provides time output signals of high accuracy to the navigation equipment 12. The receiver 15 may also supply position information from the satellite 16 to the navigation equipment 12. The aircraft I also includes a transponder 17 connected to the navigation equipment 12, the operation of which will be described later.

The surveillance radar 2 includes a conventional radar transmitter/receiver 20, which provides outputs representative of the position of targets detected by the radar to a processor 21. The radar 2 also includes an additional transmitter/receiver 20' and a processor 21'. The radar 2 includes a receiver 22 of common timing signals from the satellite 16 and provides timing signals to the processor 21'. The radar also includes a store 23 containing information as to the position of recognised aircraft at different moments in time. More particularly, the position information identifies boxes, or 3-D gates, F to J defining a range of positions at which an aircraft could be located at particular times to be identified as a recognised or friendly aircraft. The information in the store 23 includes the information in the store 14 of the aircraft 1, and may also include different information in respect of other aircraft. The radar 2 also includes a transponder 27 connected with the processor 21'.

In normal operation, the autopilot 11 of the aircraft 1 controls the aircraft by appropriately steering it in three dimensions and controlling its velocity by means of its drag and propulsion capabilities to fly along the path 10 so that it arrives at the points A to E at the progranimed times. The radar processor 21' identifies an aircraft and compares its identified position at different times with those in the store 23. Providing the positions are within the boundaries of the gates F to J, the processor 21' provides an output to a utilization unit 24, such as a display, indicating that the aircraft is recognized as one with which the system is familiar.

Should a hostile aircraft enter the range of the radar 2 and take a different flight path, it will not be recognized and an alarm will be generated by the utilization unit 24 warning of a hostile target. Even if the hostile aircraft should attempt to follow the path of a recognised aircraft, such as, in pursuit of a recognised aircraft, the hostile aircraft will still be identified as such because the time at which it reaches the programmed gates F to J will be different from the programmed times. Although it is only necessary for the system to have one gate, by using more than one, it makes it less likely that any other aircraft would be able to emulate a recognised aircraft. The size of the gates is chosen to be sufficiently large to give sufficient margin for deviation by a recognised aircraft whilst being small enough to minimize the chance of a hostile aircraft following closely enough to come within the gate. The size of the gates could be increased in adverse weather conditions.

The arrangement described above is entirely passive in that it does not require the emission of any interrogating or response signal by the moving object or the surveillance equipment. This makes it impossible for a hostile aircraft or the like to jam the system or to copy response signals.

It can, however, be an advantage for the system to be capable of operating actively, such as when the moving object is unable to follow the programmed path. An aircraft, for example may have to deviate from the programmed path to avoid collision, to evade hostile action or because of damage. Figure 3 shows such a situation where the aircraft 1' has turned left away from the path 10 onto a new path 10', which passes through only the first two gates F and G at the correct times.

In such a situation, the aircraft navigation system 12 may be arranged to monitor deviation from the programmed path 10 aiid to initiate an active mode at a point P. Similarly, the response of the surveillance equipment 2 when it identifies a target but fails to recognise it at any moment may be to emit an interrogation signal at an agreed time, as shown in Figure 4. In this example, the agreed time lies between times t3 to t4, so the radar 2 emits an interrogation signal I within this window w1. The aircraft I similarly only responds to the signal I received within this window and rejects the other signals shown in Figure 4.

A system in which the interrogation and response signals are generated at defined times can itself provide sufficient security in some cases without the need for the interrogating party to know the expected position of the responding party. The defined times can be in some jittered pattern known to both parties by reference to a common, external timing signal, such as GPS/GNSS or pseudolites.

When a correct interrogation signal is received from the ground transponder 27, the aircraft transponder 17 generates a coded response signal R, indicative of the aircraft identification, as shown in Figure 5. This signal R is emitted within a prearranged response window W2 between times t5 and t6, which is recognised by the radar 2. Thus, even if hostile forces were able to intercept the response signal and copy it, this would not be recognised unless it were generated within the correct time window. The transmission of the interrogating and response signals is made in accordance with an agreed schedule of one or more windows, which schedule is part of the agreed plan for that aircraft and is either unique to that aircraft or is related to its present position. In its active mode, either or both -the surveillance equipment's interrogations or the aircraft's identification responses may include codes varying the future agreed schedule of windows.

The transponder 17 could be arranged also tO generate codes indicative of future flight plan gates. The transponder 17 need not necessarily respond to interrogation signals but could instead emit its identification signals autonomously. The emitted codes may be encrypted and could be used only once for each emission according to a sequence agreed with the surveillance equipment.

During its passage, the identification system of the aircraft may detect interrogation by surveillance equipment to which it is desirable to return an identifying response but which is not a party to the aircraft's agreed plan. In this case, recourse may be made to a general area schedule of windows known to all participants in the identification system such that valid interrogations arise only during agreed general area interrogation windows, and valid responses are similarly made during agreed general area response windows.

It will be appreciated that the invention is not confined to aircraft but could be used to identify any moving object, such as a marine vessel or a land vehicle. The invention could also be used to identify a person carrying a transponder arranged to provide responses at a precision-defined times in response to precision-defined interrogation signals at staggered intervals.

Claims

CLAIMS

1. A system for identifying a moving object, wherein the system includes a movement guidance system associated with the object arid containing information as to the planned position of the object at different moments in time and surveillance equipment remote from the object, and wherein the surveillance equipment includes means for detecting the position of objects, a store containing information as to the planned position of one or more recognised objects at different moments in time, and means for comparing the position of a detected object at a moment in time with the stored position or positions associated with that moment so as to identify whether the detected object is a recognised object.

2. A system according to Claim I, wherein the object is an aircraft.

3. A system according to Claim I or 2, wherein the movement guidance system is an autopilot.

4. A system according to any one of the preceding claims, wherein the movement guidance system and the surveillance equipment are both arranged to receive timing signals from a common source.

5. A system according to Claim 4, wherein the common source is a satellite navigation system.

6. A system according to any one of the preceding claims, wherein the information as to planned positions includes information about a range of positions within which the object is expected to be located at particular moments in time.

7. A system according to any one of the preceding claims, including means associated with the object for detecting that the object is not or will not be at the planned position or within the range of positions at a predetermined time.

8. A system according to Claim 7, wherein said detecting means is arranged to emit a signal to the surveillance equipment identifying the object if it detects that the object is not or will not be at the planned position or within the range of positions at the predetermined time.

9. A system according to Claim 8, wherein said detecting means is arranged to emit said signal autonomously.

10. A system according to Claim 8, wherein said detecting means is arranged to emit said signal only in response to an interrogating signal from the surveillance equipment.

11. A method for identifying a moving object, the method including the steps of providing guidance information to the object as to the position at which the object should be located at different moments in time, surveying the object remotely to detect the position of the object, and comparing the detected position of the object with information as to planned position of one or more recognised objects at different moments in time so as to identify whether the detected object is a recognised object.

12. A system for identifying an object including interrogation means, response means associated with said object, and common timing signal generating means, the interrogation and response means being arranged to generate interrogation and response signals only at defined times dependent on said common timing signal generating means.

13. A method of identifying an object including the steps of generating a common timing signal, generating an interrogation signal at a defined time referenced to said common timing signal, and monitoring for a response from said object to determine whether said response is generated at a second defined time referenced to said common timing signal.

14. A system for identifying a moving object substantially as hereinbefore described with reference to the accompanying drawings.

15. A method for identifying a moving object substantially as hereinbefore described with reference to the accompanying drawings.

16. Any novel and inventive feature or combination of features as hereinbefore described.

Amendments to the claims have been filed as follows 1. A system for identifying a moving object, wherein the system includes a movement guidance system associated with the object and containing information as to the plaimed position of the object at different moments in time and surveillance equipment remote from the object, and wherein the surveillance equipment includes means for detecting the position of objects, a store containing information as to the planned position of one or more recognised objects at different moments in time, and means for comparing the position of a detected object at a moment in time with the stored position or positions associated with that moment so as to identify whether the detected object is a recognised object.

2. A system according to Claim 1, wherein the object is an aircraft.

3. A system according to Claim 1 or 2, wherein the movement guidance system is an autopilot.

4. A system according to any one of the preceding claims, wherein the movement guidance system and the surveillance equipment are both arranged to receive timing signals from a common source.

5. A system according to Claim 4, wherein the common source is a satellite navigation system.

6. A system according to any one of the preceding claims, wherein the information as to plarmed positions includes information about a range of positions within which the object is expected to be located at particular moments in time.

7. A system according to any one of the preceding claims, including object detecting means associated with the object for detecting that the object is not or will not be at the planned position or within the range of positions at a predetennined time.

8. A system according to Claim 7, wherein said object detecting means is arranged to emit a signal to the surveillance equipment identifying the object if it detects that the object is not or will not be at the planned position or within the range of positions at the predetermined time. - 9. A system according to Claim 8, wherein said object detecting means is arranged to emit said signal autonomously.

10. A system according to Claim 8, wherein said object detecting means is arranged to emit said signal only in response to an interrogating signal from the surveillance equipment.

11. A method for identifying a moving object, the method including the steps of providing guidance information to the object as to the position at which the object should be located at different moments in time, surveying the object remotely to detect the position of the object, and comparing the detected position of the object with information as to plarmed position of one or more recognised objects at different moments in time so as to identify whether the detected object is a recognised object.

12. A system for identifying a moving object substantially as hereinbefore described with reference to the accompanying drawings.

13. A method for identifying a moving object substantially as hereinbefore described with reference to the accompanying drawings.