Correlation interferometer geolocation

• US 20060087475A1
• Filed: 02/06/2004
• Published: 04/27/2006
• Est. Priority Date: 03/20/2003
• 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: Struckman, Keith A.
• Granted Patent: US 7,233,285 B2
• Time in Patent Office: Days
• US Class Current: 342/451
• 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
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial

Abstract

Correlation Interferometer Geo Location (CIGL) uses DF antenna array movement on an aircraft while taking a Plurality of sets of transinitted signal Measurements. Each measurement set is stored as data in a covariance matrix, and the matrices are each decomposed to yield measured array vectors. Using an array manifold table developed during calibration of the CIGI. system, and containing testing array vectors, the measured array vectors are each correlated to testing array vectors to develop a correlation Surface that includes compensation for perturbations Such as aircraft induced electromagnetic scattering, All the correlation surfaces are summed and normalized, with the resultant summation undergoing conjugate gradient processing to more accurately geo-locate the transmitter. Improved accuracy with fewer antennas and polarization independence are also achieved.

Claims

1. A method for receiving electromagnetic radiation with a plurality of antennas and a plurality of receivers, which received electromagnetic radiation is subject to electromagnetic scattering perturbations, and producing an output that is substantially unaffected by the perturbations and indicates the geolocation of the source of the electromagnetic radiation, the method comprising the steps of:

(a) forming a plurality of covariance matrices from a like plurality of sets of samples of the received electromagnetic radiation received with the plurality of antennas and receivers, each matrix yielding a measured array vector;

(b) correlating each of the plurality of measured array vectors yielded in step (a) with testing array vectors previously stored during calibration of the receivers and antennas, and retrieving geolocation information associated with correlated, stored testing array vectors, the plurality of geolocation information retrieved being substantially unaffected by the perturbations;

(c) summing the plurality of retrieved geolocation information obtained during correlation in step (b) to produce a summation set of geolocation data that has a distinctive point that indicates the geolocation of the source of the electromagnetic radiation; and

(d) searching the summation set of geolocation data to identify the distinctive point that indicates the geolocation of the source of the electromagnetic radiation.

2. The method for receiving electromagnetic radiation of claim 1 wherein the receiver is moving and the source of electromagnetic radiation is fixed.

3. The method for receiving electromagnetic radiation of claim 2 wherein the testing array vectors and their associated geolocation information are generated when the source of electromagnetic radiation is at a fixed position and the receiver is moved over a predetermined path, and the location of the source and the receiver are both known during, testing so accurate geolocation information can be calculated for the source of electromagnetic radiation and stored with each testing array vector.

4. The method for receiving electromagnetic radiation of claim 3 wherein the search ing performed in step (d) consists of multiple conjugate gradient searches performed on the summation set of geolocation data to clearly identify the distinctive point that indicates the geolocation of the source of the electromagnetic radiation.

5. The method for receiving electromagnetic radiation of claim 4 wherein by summing the sets of geolocation data retrieved during step (b) extraneous correlation peaks therein are minimized and a maximum correlation peal is developed at the distinctive point to clearly indicate the geo-location of the source of the electromagnetic radiation.

6. The method for receiving electromagnetic radiation of claim 5 wherein the sets of samples of step (a) are produced by sampling the received electromagnetic radiation for a portion of each second of time and for a plurality of sequential seconds.

7. The method for receiving electromagnetic radiation of claim 6 wherein the method is independent of the polarization of the electromagnetic radiation.

8. The method for receiving electromagnetic radiation of claim 1 wherein the testing array vectors and their associated geolocation information are generated when the source of electromagnetic radiation is at a fixed position and the receiver is moved over a predetermined path, and the location of the source and the receiver are both known during testing so accurate geolocation information can be calculated for the source of electromagnetic radiation and stored with each testing array vector.

9. The method for receiving electromagnetic radiation of claim 8 wherein the searching performed in step (d) consists of multiple conjugate gradient searches performed on the summation set of geolocation data to clearly identify the distinctive point that indicates the geolocation of the source of the electromagnetic radiation.

10. The method for receiving electromagnetic radiation of claim 9 wherein the receiver is moving and the source of electromagnetic radiation is fixed.

11. The method for receiving electromagnetic radiation of claim 1 wherein the searching preformed in step (d) consists of multiple conjugate gradient searches performed on the summation set of geolocation data to clearly identify the distinctive point that indicates the geolocation of the source of the electromagnetic radiation.

12. The method for receiving electromagnetic radiation of claim 11 wherein the receiver is moving and the source of electromagnetic radiation is fixed.

13. The method for receiving electromagnetic radiation of claim 12 wherein the testing array vectors and their associated geolocation information are generated when the source of electromagnetic radiation is at a fixed position and the receiver moves over a predetermined path, and the location of the source and the receiver are both known during testing so accurate geolocation information can be calculated for the source of electromagnetic radiation and stored with each testing array vector.

14. The method for receiving electromagnetic radiation of claim 13 wherein the sets of samples of step (a) are produced by sampling the received electromagnetic radiation for a portion of each second of time and for a plurality of sequential seconds.

15. A method for receiving electromagnetic radiation sent by a transmitter at a fixed location with a plurality of antennas and a plurality of receivers on a moving platform, which received electromagnetic radiation is subject to environmental perturbations caused by the platform, and producing an output that is substantially unaffected by the perturbations and indicates the geolocation of the transmitter, the method comprising the steps of:

(a) forming a plurality of covariance matrices from a like plurality of sets of samples of the electromagnetic radiation received by the plurality of antennas and receivers, the sampling being performed for a portion of each second of time and for a plurality of sequential seconds;

(b) decomposing all matrices to yield a plurality of measured array vectors;

(c) correlating each of the measured array vectors produced is step (b) with testing array vectors previously stored during calibration of the receiver and antennas, and retrieving geolocation information associated with a stored testing array vector that most closely matches each of the plurality of measured array vectors, the plurality of geolocation information retrieved being substantially unaffected by the perturbations;

(d) summing the plurality of retrieved geolocation information obtained during correlation in step (c) to produce a summation set of geolocation data that has a distinctive point that indicates the geolocation of the transmitter; and

(e) performing multiple conjugate gradient searches on the summation set of geolocation data to identify the distinctive point that indicates the geolocation of the transmitter.

16. The method for receiving electromagnetic radiation of claim 15 wherein the testing array vectors and their associated geolocation information are generated when the source of electromagnetic radiation is at a fixed position and the receiver is moved over a predetermined path, and the location of the source and the receiver are both known during testing so accurate geolocation information can be calculated for the source of electromagnetic radiation and stored with each testing array vectors.

17. A method for calibrating apparatus used for receiving electromagnetic radiation using a plurality of antennas and a plurality of receivers located on a moving platform, and indicating the geo-location of the source of the electromagnetic radiation while being substantially unaffected by perturbations caused by the platform, the calibration method comprising the steps of:

(a) moving the platform over a predetermined path while the source of electromagnetic radiation is at a fixed position, and the location of the source and the platform are both known during calibration so geo-location information can be calculated for the source of electromagnetic radiation at each location of the platform;

(b) forming a plurality of covariance matrices from sets of samples of the received electromagnetic radiation, each matrix yielding a testing array vector;

(c) calculating the correct geo-location of the source of electromagnetic radiation with respect to the platform for each testing array vector, based on the known position of the platform and source; and

(d) storing each testing array vector and the associated calculated geo-location of the source of electromagnetic radiation in a correlation table for later use with the receiving apparatus to indicate the geo-location of other sources of electromagnetic radiation the geo-location of which is initially unknown.

18. The method for calibrating apparatus for receiving electromagnetic radiation in accordance with claim 17 further comprising the steps of:

(e) forming a plurality of covariance matrices from sets of signal samples derived from signals received from an unknown source of electromagnetic radiation, each matrix yielding a measured array vector that is affected by perturbations caused by the platform; and

(f) correlating the measured array vectors against the stored testing array vectors to find a closest match;

where the geo-location information stored with the testing array vector that is a closest match to the measured array vector indicates the corrected geo-location of the source of electromagnetic radiation substantially unaffected by perturbations caused by the platform.

19. A computer readable medium containing executable instructions for processing electromagnetic signals received by a plurality of antennas and a plurality of receivers and producing an output that is substantially unaffected by perturbations caused by a platform on which the antennas and receivers are mounted, and indicating the geo-location of the source of the electromagnetic signals, the executable program instructions comprising program instructions for:

(a) forming a plurality of covariance matrices from a like plurality of sets of samples of the received electromagnetic radiation received with the plurality of antennas and receivers, each matrix yielding a measured array vector;

(b) correlating each of the plurality of measured array vectors yielded in step (a) with testing array vectors previously stored during calibration of the receivers and antennas, and retrieving geo-location information associated with correlated, stored testing array vectors, the plurality of geo-location information retrieved being substantially unaffected by the perturbations;

(c) summing the plurality of retrieved geo-location information obtained during correlation in step (b) to produce a summation set of geo-location data that has a distinctive point that indicates the geo-location of the source of the electromagnetic radiation; and

(d) searching the summation set of geo-location data to identify the distinctive point that indicates the geo-location of the source of the electromagnetic radiation.