Precision geolocation system and method using a long baseline interferometer antenna system

• US 20060114157A1
• Filed: 08/11/2005
• Published: 06/01/2006
• Est. Priority Date: 08/11/2004
• Status: Active Grant

• Current Assignee: Sierra Nevada Corporation
• Original Assignee: Sierra Nevada Corporation
• Inventors: Kolanek, James, Carlsen, Eric
• Granted Patent: US 7,286,085 B2
• Time in Patent Office: Days
• US Class Current: 342/424
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders

Abstract

A long baseline interferometer antenna system and method for determining the location of an emitter. The long baseline interferometer antenna system comprises a first antenna, a second antenna, an inertial navigation system, an antenna baseline measurement system, a multi-channel receiver and a processor. The first and second antenna elements are positioned on a platform and are both configured to receive signals from the emitter. The first and second antenna elements form a long baseline antenna pair. The inertial navigation system measures the platform position and attitude; and the antenna baseline measurement system measures the antenna baseline vector between the first and second antenna elements. The multi-channel receiver measures the differential phase between antenna pairs, and the processor computes the emitter location. Additional antenna elements can be included and some can be configured as squinted beam pair and make use of amplitude difference of arrival measurements.

Claims

1. A long baseline interferometer antenna system for determining the location of an emitter, the long baseline interferometer antenna system comprising:

a first antenna element positioned on a platform, the first antenna element being configured to receive signals from the emitter;

a second antenna element positioned on the platform, the second antenna element being configured to receive signals from the emitter, the first and second antenna elements forming a long baseline antenna pair;

an inertial navigation system for providing measurements of the platform position and the platform attitude; and

an antenna baseline measurement system for providing measurements of the antenna baseline vector between the first antenna element and the second antenna element,

a multi-channel receiver for measuring the differential phase between pairs of antennas; and

a processor for processing the information to determine the location of the emitter.

2. The long baseline interferometer antenna system of claim 1, wherein the first and second antenna elements are configured as a squinted beam pair, and wherein the multi-channel receiver is capable of measuring the differential amplitude between the signals received by the first and second antenna elements.

3. The long baseline interferometer antenna system of claim 1, further comprising a third antenna element positioned near the first antenna element, the third antenna element being configured to receive signals from the emitter, the first and third antenna elements forming a short baseline antenna pair.

4. The long baseline interferometer antenna system of claim 3, wherein the first and third antenna elements are configured as a squinted beam pair, and wherein the multi-channel receiver is capable of measuring the differential amplitude between the signals received by the first and third antenna elements.

5. The long baseline interferometer antenna system of claim 1, further comprising

a third antenna element positioned on the platform;

and

a fourth antenna element positioned on the platform, the third and fourth antenna elements being configured to receive signals from the emitter,

wherein the platform is an aircraft having a nose section, a tail section, a first wing and a second wing, and the first antenna element is positioned on the nose section, the second antenna element is positioned on the first wing, the third antenna element is positioned on the tail section, and the fourth antenna element is positioned on the second wing, such that any two of the first, second, third and fourth antenna elements form a long baseline antenna pair.

6. The long baseline interferometer antenna system of claim 5, further comprising

a fifth antenna element positioned on the platform near the first antenna element, the first and fifth antenna elements forming a short baseline antenna pair;

and

a sixth antenna element positioned on the platform near the second antenna element, the second and sixth antenna elements forming a short baseline antenna pair; and

a seventh antenna element positioned on the platform near the third antenna element, the third and seventh antenna elements forming a short baseline antenna pair; and

an eighth antenna element positioned on the platform near the fourth antenna element, the fourth and eighth antenna elements forming a short baseline antenna pair, the fifth, sixth, seventh and eighth antenna elements being configured to receive signals from the emitter.

8. The long baseline interferometer antenna system of claim 1, wherein the antenna baseline measurement system comprises:

a first navigation system antenna located in close proximity to the first interferometer antenna;

a second navigation system antenna located in close proximity to the second interferometer antenna;

an accurate measurement of the offset vector between the first navigation system antenna and the first interferometer antenna; and

an accurate measurement of the offset vector between the second navigation system antenna and the second interferometer antenna.

9. The long baseline interferometer antenna system of claim 8, wherein the first and second navigation system antennas are GPS antennas.

10. The long baseline interferometer antenna system of claim 8, wherein the antenna baseline measurement system further comprises:

a first inertial measurement unit located in close proximity to the first interferometer antenna and the first navigation system antenna; and

a second inertial measurement unit located in close proximity to the second interferometer antenna and the second navigation system antenna.

11. A geo-location method for determining the location of an emitter using a long baseline interferometer antenna system including a first antenna element and a second antenna element mounted on a platform, the first and second antenna elements forming a long baseline antenna pair, the method comprising:

moving the platform along a measurement path;

collecting a series of sets of signal observations from the first and second antenna elements while the platform is moving along the measurement path, each set of signal observations being collected at a particular observation time;

processing the signal observations to provide differential phase measurements between the signal observations of the first and second antenna elements;

collecting platform position and attitude measurements using an inertial navigation system;

interpolating the platform position and attitude measurements to the observation times;

collecting measurements of an antenna baseline vector for the long baseline antenna pair using an antenna baseline measurement system;

interpolating the measurements of the antenna baseline vector to the observation times;

performing a coarse precision emitter location estimate using amplitude difference of arrival measurements; and

performing a fine precision emitter location estimate using phase difference of arrival measurements.

12. The geo-location method of claim 11, further comprising:

collecting a series of signal observations from a third antenna element at the observation times while the platform is moving along the measurement path, the third antenna element being located near the first antenna element, the first and third antenna elements forming a short baseline antenna pair; and

processing the signal observations to provide differential phase measurements between the signal observations of the first and third antenna elements.

13. The geo-location method of claim 12, wherein the step of performing coarse precision emitter location estimate comprises:

generating an initial emitter location estimate; and

generating a coarse emitter location estimate using the initial emitter location estimate.

14. The geo-location method of claim 13, wherein the step of generating an initial emitter location estimate comprises:

measuring the amplitude difference of arrival for the short baseline antenna pair;

measuring the amplitude difference of arrival for the long baseline antenna pair;

estimating the amplitude difference of arrival for the short baseline antenna pair, and for the long baseline antenna pair for several proposed emitter locations; and

calculating the initial emitter location estimate to minimize the difference between the measured amplitude difference of arrivals and the estimated amplitude difference of arrivals at the several proposed emitter locations.

15. The geo-location method of claim 14, wherein the step of generating a coarse emitter location estimate comprises:

starting at the initial emitter location estimate; and

methodically progressing through a plurality of emitter location estimates to find the coarse emitter location estimate, the coarse emitter location estimate being the location estimate of the plurality of emitter location estimates that minimizes the difference between the measured values of the amplitude difference of arrival and the estimated values of the amplitude difference of arrival for the location estimate.

16. The geo-location method of claim 12, further comprising:

performing medium precision emitter location estimate using phase difference of arrival measurements.

17. The geo-location method of claim 16, wherein the step of performing medium precision emitter location estimate comprises:

measuring the phase difference of arrival for the short baseline antenna pair; and

starting at the coarse emitter location estimate; and

methodically progressing through a plurality of emitter location estimates to find the medium emitter location estimate, the medium emitter location estimate being the location estimate of the plurality of emitter location estimates that minimizes the difference between the measured values of the phase difference of arrival for the short baseline antenna pair and the estimated values of the phase difference of arrival for the short baseline antenna pair at the location estimate.

18. The geo-location method of claim 16, wherein the step of performing fine precision emitter location estimate comprises:

measuring the phase difference of arrival for the long baseline antenna pair;

starting at the medium precision emitter location estimate; and

methodically progressing through a plurality of emitter location estimates to find the fine emitter location estimate, the fine emitter location estimate being the location estimate of the plurality of emitter location estimates that minimizes the difference between the measured values of the phase difference of arrival for the long baseline antenna pair and the estimated values of the phase difference of arrival for the long baseline antenna pair at the location estimate.

19. The geo-location method of claim 12, further comprising:

calibrating the geo-location method to reduce the effect of measurement bias errors.

20. The geo-location method of claim 19, wherein the step of calibrating, comprises:

computing the difference between consecutive phase measurements to compute first difference measurements; and

computing the emitter location using the first difference measurements.

21. The geo-location method of claim 19, wherein the step of calibrating, comprises:

solving for the receiver phase bias scalar;

computing the emitter location using the solved value of the receiver phase bias scalar.

22. The geo-location method of claim 19, wherein the step of calibrating, comprises:

solving for the true antenna baseline vector and the antenna baseline bias vector;

computing the emitter location using the solved value of the true antenna baseline vector and the antenna baseline bias vector.

23. The geo-location method of claim 19, wherein the step of calibrating, comprises:

calculating the location of a known emitter using the geo-location method, the known emitter having a known emitter location;

determining the phase bias and the antenna baseline bias from the difference between the calculated location of the known emitter and the known emitter location.