Coherent geolocation system

• US 20050275588A1
• Filed: 05/25/2004
• Published: 12/15/2005
• Est. Priority Date: 05/25/2004
• Status: Active Grant

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Carroll, Melvin, Adler, Henry, Schiffmiller, Richard
• Granted Patent: US 7,315,280 B2
• Time in Patent Office: Days
• US Class Current: 342/387
• CPC Class Codes: G01S 2205/03 Airborne
• CPC Class Codes: G01S 5/0249 Determining position using measurements made by a non-stationary device other than the device whose position is being determined

Abstract

A coherent TOA system is provided for rapidly ascertaining the position of a pulse train emitter such as a radar. Techniques are provided to estimate the underlying repetition interval of the emitter and to do the TOA processing knowing which of the particular pulses is being detected at a collector, thus surmounting the effect of gaps in the received pulse stream. The subject system is preferable to conventional time-difference-of-arrival geolocation systems which require that each of the collecting platforms measure the same pulse from the emitter, and also to non-coherent TOA systems whose accuracy is less than that achievable with the subject coherent system for the same amount of data.

Claims

1. A method for ascertaining the location of a pulse train emitter, comprising the steps of

collecting pulses from the emitter at a collector at a plurality of locations;

measuring the time of arrival of collected pulses at the plurality of locations using a coherent processing technique; and

,

determining from the measured times of arrival of the collected pulses the location of the pulse train emitter.

2. The method of claim 1, wherein the coherent processing includes estimating the pulse repetition interval of the emitter so that accurate times of arrival can be measured.

3. The method of claim 2, wherein the coherent processing includes identifying the pulse number of a pulse received at the collector.

4. The method of claim 3, wherein the coherent processing includes ascertaining the time of emission of the first pulse, the number of pulse repetition intervals from the first pulse and the identity of the pulse number of a collected pulse, thus to minimize the effect of gaps in receipt of emitted pulses at a collector.

5. The method of claim 1, wherein the collecting step includes a collector moving to spaced-apart locations.

6. The method of claim 1, wherein the location determining step includes hypothesizing an emitter location, for a set of emitted pulses generating expected times of arrival of corresponding pulses at the plurality of locations, comparing measured times of arrival with the expected times of arrival, and identifying the hypothesized emitter location as the actual emitter location when the error between actual and hypothesized times of arrival is less than a predetermined threshold.

7. The method of claim 1, wherein the location determining step includes detecting a set of inter-pulse intervals between two different collector locations and determining from the set of inter-pulse intervals the location of the emitter.

8. A method of improving the accuracy of the geolocation of a pulse train emitter, comprising the steps of

coherently determining the times of arrival of pulses from the emitter at a plurality of different collector locations;

and,

determining emitter location from the coherently determined times of arrival of the pulses at the plurality of different collector locations.

9. The method of claim 8, wherein the steps of coherently determining the times of arrival of pulses from the emitter include the step of determining an underlying pulse repetition interval for the pulses emitted by the emitter.

10. The method of claim 9, wherein the step of coherently determining the times of arrival of the pulses includes ascertaining at a collector location the number of the pulse in the pulse train arriving at the collector.

11. The method of claim 8, wherein the location determining step includes analyzing an ensemble of times of arrival of pulses at different locations.

12. The method of claim 11, wherein the ensemble of times of arrival is the result of collectors at widely spaced-apart locations, thus to establish a long measurement baseline.

13. A method of enhancing the accuracy of a time-of-arrival-based geolocation system for determining the location of a pulse train emitter, comprising the steps of

detecting the times of arrival of emitted pulses at collector locations which are widely spaced apart using coherent processing;

and,

determining emitter location from an ensemble of times of arrival from the spaced-apart collector locations.

14. The method of claim 13, wherein the collector is located at an aircraft flying along a flight path and further including identifying the location of the collector as the aircraft travels the flight path, the coherent processing making possible data collection over a long flight path to establish a long baseline for enhanced accuracy.

15. A system for ascertaining the location of a pulse train emitter, comprising

a collector for collecting pulses from the emitter, said collector positioned at a plurality of locations;

a detector for measuring the time of arrival of said collected pulses at said plurality of locations using a coherent processing technique; and

,

a processing unit for determining from the measured times of arrival of the collected pulses the location of said pulse train emitter.

16. The system of claim 15, wherein the coherent processing of said detector includes an estimator for estimating the pulse repetition interval of the emitter so that accurate times of arrival can be measured.

17. The system of claim 16, wherein the coherent processing of said detector includes a pulse number identifier for identifying the pulse number of a pulse received at said collector.

18. The system of claim 17, wherein said coherent processing includes a unit for ascertaining the time of emission of a first pulse in said pulse train arriving at said collector at a collector-location, the number of pulse repetition intervals from said first pulse and the pulse number of a pulse arriving at said collector after said first pulse, thus to permit minimizing the effect of gaps in receipt of emitted pulses at said collector.

19. The system of claim 15, wherein said processing unit determines the location of said pulse train emitter using a pattern of inter-pulse intervals of pulses received at different collector locations based on times of arrival of said received pulses.