Airborne surveillance method and system

• US 4,910,526 A
• Filed: 05/18/1987
• Issued: 03/20/1990
• Est. Priority Date: 05/18/1987
• Status: Expired due to Fees

• Current Assignee: Avion Systems, Inc.
• Original Assignee: Avion Systems, Inc.
• Inventors: Donnangelo, Nicholas C., Abaunza, John T., Aiken, John G.
• Primary Examiner(s): Moskowitz, Nelson
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US07/050,716
• Time in Patent Office: 1,037 Days
• Field of Search: 342/455, 342/32, 342/37, 342/46, 342/29, 342/30, 342/36, 342/42
• US Class Current: 342/455
• CPC Class Codes: G01S 13/781 Secondary Surveillance Radar [SSR] in general
• CPC Class Codes: G01S 13/933 of aircraft or spacecraft
• CPC Class Codes: G01S 3/48 the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured

Abstract

An airborne surveillance method and system allows an observer aircraft to determine the position and change of position of a multiplicity of target aircraft and thus allows analysis of collision threats from these aircraft. The system uses a phase comparison direction finding antenna to determine direction of nearby ground based SSRs and all target aircraft of interest. The system further makes use of all other available data including Mode C transponder generated altitude information of the target aircraft, the altitude of the observer aircraft, the received signal strength of both the SSR beam and the received transponder signal, the time difference of arrival between the SSR interrogation signal and the response from the target aircraft, and a variety of other factors to determine the position of the target aircraft. The system compensates for the attitude of the observer aircraft and performs optimal Kalman filtering on the input data set to produce an estimate on target position based upon prior estimates and upon information contained in the data set while making estimates of the error magnitude of each measurement and compensating for these errors. The covariance matrix Q of the Kalman filter is adaptively vaired so as to optimize the estimate of the degree of correlation between various input values.

Claims

1. In an environment having at least one rotating interrogation signal source, a method of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer object located remotely from said interrogation signal source, the positions of the observer object, target object and interrogation signal source forming a geometrical arrangement, comprising:

(a) determining the direction of said interrogation signal source by direction finding on said interrogation signal to develop source direction data;

(b) determining the direction to a said target object by direction finding on a transponder signal produced by said transponder to develop target direction data;

(c) assembling additional available data relevant to relative positions of said objects and/or said interrogation signal source, said additional data being selected to form a data set best suited to develop a present position estimate of said target object in the present geometrical arrangement;

(d) developing a present position estimate of said target object based on said direction data and said data set of additional data; and

(e) developing a present position value of said target object by using a past position value to modify the present position estimate including varying the degree of modification based on a value associated with said present position value;

said steps (d) and (e) performing the continuous tracking of target object position through geometrical arrangements where the target object position is not readily observable from a single interrogation signal source to allow full time tracking of said target object even when transmitting responses to interrogation signals from only a single interrogation signal source independent of said geometrical arrangement.

2. The method of claim 1 further comprising:

assembling said direction data and said data set of additional data into vector data packets;

said step (d) of developing utilizing said data packets to develop said present position data.

3. The method of claim 1 further comprising:

estimating the error in said direction data and said additional available data to develop error data associated with said data;

developing a current position error estimate using said error data;

said step (e) of developing using said current position error estimate as said value associated with said present position value to determine the relative weight to give said present position value.

4. The method of claim 1 further comprising:

determining the degree of accuracy of each element of said direction data and said additional available data in determining position of said target object and developing an error estimate associated with each said data element;

said step (d) of developing utilizing said error estimates in determining the weight to be attributed to each said data element in developing said present position estimate.

5. The method of claim 4 wherein said step (e) of developing utilizes said current position error estimate as said value associated with said present position value to determine the weight to give said present position estimate in determining said present position value.

6. The method of claim 1 wherein said target and observer objects are aircraft.

7. The method of claim 4 wherein said target and observer objects are aircraft.

8. The method of claim 6 wherein said rotating interrogation signal source is an air traffic control secondary surveillance radar (SSR).

9. The method of claim 5 wherein said process is iteratively performed.

10. The method of claim 5 wherein said step (b) of determining includes direction finding only on said transponder signals received by said observer aircraft level received within a predetermined time after receipt of said interrogation signal.

11. The method of claim 5 wherein said step (e) of developing utilizes optimal Kalman filtering.

12. The method of claim 11 wherein said Kalman filtering is adaptive.

13. The method of claim 12 wherein a covariance matrix Q of said Kalman filter is varied adaptively.

14. In an environment having at least one rotating interrogation signal source, a method of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer object comprising:

(a) determining the position of the observer object with respect to said interrogation signal source;

(b) determining the direction of said target object by direction finding on said transponder to develop a target direction vector;

(c) determining the speed of rotation of said interrogation signal source;

(d) calculating the angle theta swept by said interrogation signal between said observer object and target object from the speed of rotation of said interrogation signal source;

(e) determining the vertical altitude of said target object from a transmission developed from the target aircraft transponder;

said altitude of said target aircraft, angle theta and direction to the target aircraft from the observer aircraft forming elements of data;

(f) determining the degree of accuracy of each element of said data and developing an error estimate associated with each said data element;

(g) developing an estimate of the present position of said target aircraft relative to said observer aircraft from the altitude of said target aircraft, the angle theta and the direction to said target aircraft from said observer aircraft;

said step (g) of developing utilizing said error estimates in determining the weight to be attributed to each said data element in developing said present position estimate;

(h) developing a present position value of said target object by using a past position value to modify the present position estimate including varying the degree of modification based on a value associated with said present position value.

15. The method of claim 14 wherein said step (h) of developing utilizes said current position error estimate as said value associated with said present position value is determining the relative weight to give said present position estimate in determining said present position value.

16. The method of claim 14 wherein said target and observer objects are aircraft.

17. The method of claim 15 wherein said target and observer objects are aircraft.

18. The method of claim 14 wherein said step (h) of developing is performed by optimal Kalman filtering wherein a covariance matrix Q of said Kalman filter is varied adaptively.

19. In an environment having at least one rotating interrogation signal source, a method of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer object comprising:

(a) determining the time difference of arrival between receipt of the interrogation signal by said observer object and receipt of an interrogation response generated by the transponder of the target object;

(b) calculating Kappa, the sum of the distance from the interrogation signal source to the target object and the distance between said observer object and said target object minus the distance between the interrogation signal source and the observer object from said time difference of arrival;

(c) establishing an observer aircraft plane of the observer object;

(d) determining the direction of said target object by direction finding on said transponder to develop a target direction vector;

(e) determining the intersections of an ellipsoid described by Kappa and a plane containing said target direction vector normal to said observer aircraft plane to form first and second target object current solutions;

(f) developing a present position value by using a past position value of each said solution to modify its associated target object current solution to determine first and second present position values of said target aircraft;

(g) monitoring said first and second solutions to detect improper divergence and discarding the one of said first and second solutions determined to be clearly erroneous thereby allowing tracking of said target object even when transmitting responses without attitude information in response to interrogation signals from a single interrogation signal source.

20. A method of tracking from an observer aircraft the position of at least one target aircraft transmitting a response to an interrogation radar signal from an interrogation radar positioned remotely from said observer aircraft comprising:

(a) selecting various data criteria relevant to the position of said target aircraft including criteria obtained from the target aircraft'"'"'s response to the interrogation radar signal;

(b) accumulating measured data values from each said data criteria;

(c) estimating the error of each of said data values to develop data value error estimates;

(d) developing a present position estimate of said target object and an associated position error estimate from said data values and data value error estimates; and

(e) developing a present position value of said target aircraft by using a past position value of the position of said target aircraft to modify the present position estimate including varying the degree of modification based on the position error estimate to optimize the developed position value.

21. The method of claim 20 wherein each said position values has an error estimate associated therewith.

22. The method of claim 20 wherein said steps (d) and (e) are performed by optimal filtering.

23. The method of claim 22 wherein said error estimates are used as covariance matrix elements in said steps (d) and (e) of developing.

24. The method of claim 20 wherein the position of the observer aircraft, each said target aircraft and each said interrogation radar form a geometrical arrangement;

said method performing the continuous tracking of target aircraft position through geometrical arrangements where the target aircraft position is not readily observable from a single interrogation radar to allow full time tracking of said target aircraft, independent of said geometrical arrangement.

25. The method of claim 20 wherein said step (c) adaptively varies the estimate of the error of at least one data value based on a varying condition to form its associated data value error estimate thereby further optimizing the present position value.

26. The method of claim 25 wherein said error estimates are used as covariance matrix elements in said steps (d) and (e) of developing.