Moving transmitter correlation interferometer geolocation

• US 7,268,728 B1
• Filed: 10/13/2005
• Issued: 09/11/2007
• Est. Priority Date: 10/13/2005
• 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.
• Primary Examiner(s): Issing; Gregory C.
• Application Number:
  US11/249,922
• Time in Patent Office: 698 Days
• Field of Search: 342/424, 342/451
• US Class Current: 342/424
• CPC Class Codes: G01S 3/74 Multi-channel systems specially adapted for direction-finding, i.e. having a single antenna system capable of giving simultaneous indications of the directions of different signals systems in which the directions of different signals are determined sequentially and displayed simultaneously G01S3/04, G01S3/14
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 7/4021 of receivers

Abstract

A Moving Transmitter Correlation Interferometer Geo-Location (MT-CIGL) system is disclosed that permits locating both moving and stationary transmitters from moving DF equipment. A conjugate gradient based search routine is utilized which solves for the location of moving and stationary transmitters at the start of each measurement sequence and then solves for the velocity and direction of motion of the moving transmitter. This information is used to track the moving transmitter. Received signals are sampled, digitized and stored in covariance matrices. They are then summed and normalized using an equation that has velocity terms that are set to zero to minimize extraneous correlation peaks, and a maximum correlation peak is developed. A conjugate gradient search routine is used to find the correlation peak of the summed data. The value of the peak is then analyzed to see if it is above or below a predetermined value. If the peak value is above the predetermined value the transmitter is stationary and the located correlation peak is the location of the transmitter. If the peak value is below the predetermined value the transmitter is moving and the peak does not indicate the correct location of the transmitter. Another conjugate gradient search routine is performed using the previous erroneous peak as the starting point for the search to identify the actual location of the moving transmitter at the beginning of a search sequence. That location is then processed through the same equation, but without the velocity terms set to zero, to calculate the velocity and direction of motion of the transmitter. This information can then be used to plot a track for the moving transmitter.

Claims

1. A method for locating a transmitter from which an electromagnetic signal is being received using a plurality of antennas and a plurality of receivers mounted on a moving platform, and indicating the geolocation and track of movement of the transmitter, and the geolocation of the transmitter when the transmitter is not moving, the method comprising the steps of:

(a) storing a plurality of sets of digitized samples of the electromagnetic signal received with the antennas and receivers;

(b) processing the plurality of digitized signal sample sets of step (a) to obtain a like plurality of signal array vectors;

(c) performing a first analysis of the digitized signal sample sets and their signal array vectors to locate a distinctive point having a peak value that may indicate the geolocation of the source of the electromagnetic signal, the first analysis being performed using an equation that has velocity terms but setting the velocity terms equal to zero;

(d) analyzing the peak value of the distinctive point from the first analysis to determine if the transmitter is moving or not moving, and when it is indicated that the transmitter is not moving that distinctive point identifies the geolocation of the transmitter;

(e) performing a second analysis of the digitized signal sample sets and their signal array vectors when it is determined in step (d) that the transmitter is moving, using the equation mentioned in step (c) with the velocity terms not set equal to zero, and using the distinctive point located in step (c) as the starting point of the second analysis, the result of the second analysis yielding the initial geolocation of the moving transmitter at the start of formation of the signal sample sets in step (a), a velocity vector and a direction vector of the moving transmitter; and

(f) calculating a track of movement of the moving transmitter using the geolocation determined in step (e), the velocity vector and the direction vector determined in step (e).

2. The method for locating a transmitter of claim 1 further comprising the step of:

(g) summing and normalizing the sets of digitized samples of the electromagnetic signal and their signal array vectors to produce a normalized summation set of the digitized signals that has the distinctive point having a peak value that may indicate the geolocation of the source of the electromagnetic signal, the summing reducing extraneous peaks in the sets of digitized samples of the electromagnetic signal and their signal array vectors and developing a distinctive, maximum peak that may be the distinctive point, and the first analysis is performed on the normalized summation set of the digitized signals.

3. The method for locating a transmitter of claim 2 wherein the peak value analysis step (d) comprises the steps of:

(h) determining an empirical value; and

(i) comparing the peak value of the distinctive point from the first analysis with the empirical value and if the peak value is greater than the empirical value the transmitter is not moving, and if the peak value is less than the empirical value the transmitter is moving.

4. The method for locating a transmitter of claim 3 wherein the received electromagnetic signal is subject to electromagnetic scattering perturbations caused by the platform on which the antennas and receivers are mounted, and wherein calibration testing of the receivers and antennas while mounted on the platform is performed and a plurality of array calibration vectors from the testing are derived and stored, and further comprising the step of:

(j) correlating each of the plurality of signal array vectors from step (b) with the stored array calibration vectors to obtain corrected geolocation based correlation data that is substantially unaffected by the perturbations and are used in the summing and normalizing performed in step (g).

5. The method for locating a transmitter of claim 4 wherein step (a) further comprises the steps of:

(k) digitizing the signals received with the plurality of antennas and receivers; and

(l) sampling the digitized signals at the Nyquist rate and storing the samples in the plurality of covariance matrices.

6. The method for locating a transmitter of claim 5 further comprising the step of:

(n) performing an eigenvalue decomposition on the digitized signal samples stored in the plurality of covariant matrices to obtain the signal array vectors of step (b).

7. The method for locating a transmitter of claim 6 further comprising the step of:

(o) periodically repeating steps (a) through (n).

8. The method for locating a transmitter of claim 3 wherein the moving platform on which the antennas and receivers are mounted performs turns as the signal from the moving transmitter is being received in order to increase the accuracy of:

(i) the determination of the initial geolocation of the moving transmitter at the start of formation of the signal sample sets, for use in calculating a track of movement of the moving transmitter in step (f), (ii) the velocity vector, and (ii) the direction vector of the moving transmitter determined by the second analysis in step (e).

9. The method for locating a transmitter of claim 1 wherein the peak value analysis step (d) comprises the steps of:

(g) determining an empirical value; and

(h) comparing the peak value of the distinctive point from the first analysis with the empirical value and if the peak value is greater than the empirical value the transmitter is not moving, and if the peak value is less than the empirical value the transmitter is moving.

10. The method for locating a transmitter of claim 9 wherein the received electromagnetic signal is subject to electromagnetic scattering perturbations caused by the platform on which the antennas and receivers are mounted, and wherein calibration testing of the receivers and antennas while mounted on the platform is performed and a plurality of array calibration vectors from the testing are derived and stored, and further comprising the step of:

(i) correlating each of the plurality of signal array vectors from step (b) with the stored array calibration vectors to obtain corrected geolocation based correlation data that is substantially unaffected by the perturbations.

11. The method for locating a transmitter of claim 10 wherein the moving platform on which the antennas and receivers are mounted performs turns as the signal from the moving transmitter is being received in order to increase the accuracy of:

(i) the determination of the initial geolocation of the moving transmitter at the start of formation of the signal sample sets, for use in calculating a track of movement of the moving transmitter in step (f), (ii) the velocity vector, and (ii) the direction vector of the moving transmitter determined by the second analysis in step (e).

12. The method for locating a transmitter of claim 1 wherein the received electromagnetic signal is subject to electromagnetic scattering perturbations caused by the platform on which the antennas and receivers are mounted, and wherein calibration testing of the receivers and antennas while mounted on the platform is performed and a plurality of array calibration vectors from the testing are derived and stored, and further comprising the step of:

(g) correlating each of the plurality of signal array vectors from step (b) with the stored array calibration vectors to obtain corrected geolocation based correlation data that is substantially unaffected by the perturbations.

13. The method for locating a transmitter of claim 12 wherein step (a) further comprises the steps of:

(h) digitizing the signals received with the plurality of antennas and receivers; and

(i) sampling the digitized signals at the Nyquist rate and storing the samples in a plurality of covariance matrices.

14. The method for locating a transmitter of claim 1 wherein step (a) further comprises the steps of:

(g) digitizing the signals received with the plurality of antennas and receivers; and

(h) sampling the digitized signals at the Nyquist rate and storing the samples in a plurality of covariance matrices.

15. The method for locating a transmitter of claim 14 further comprising the step of:

(i) performing an eigenvalue decomposition on the digitized signal samples stored in the plurality of covariant matrices to obtain the signal array vectors of step (b).

16. The method for locating a transmitter of claim 15 wherein the moving platform on which the antennas and receivers are mounted performs turns as the signal from the moving transmitter is being received in order to increase the accuracy of:

(i) the determination of the initial geolocation of the moving transmitter at the start of formation of the signal sample sets, for use in calculating a track of movement of the moving transmitter in step (f), (ii) the velocity vector, and (ii) the direction vector of the moving transmitter determined by the second analysis in step (e).

17. The method for locating a transmitter of claim 1 further comprising the step of:

(g) performing an eigenvalue decomposition on the digitized signal samples stored in the plurality of covariant matrices to obtain the signal array vectors of step (b).

18. The method for locating a transmitter of claim 17 further comprising the step of:

(h) summing and normalizing the sets of digitized samples of the electromagnetic signal and their signal array vectors to produce a normalized summation set of the digitized signals that has the distinctive point having a peak value that may indicate the geolocation of the source of the electromagnetic signal, the summing reducing extraneous peaks in the sets of digitized samples of the electromagnetic signal and their signal array vectors and developing a distinctive, maximum peak that may be the distinctive point, and the first analysis is performed on the normalized summation set of the digitized signals.

19. The method for locating a transmitter of claim 1 wherein the moving platform on which the antennas and receivers are mounted performs turns as the signal from the moving transmitter is being received in order to increase the accuracy of:

(i) the determination of the initial geolocation of the moving transmitter at the start of formation of the signal sample sets, for use in calculating a track of movement of the moving transmitter in step (f), (ii) the velocity vector, and (ii) the direction vector of the moving transmitter determined by the second analysis in step (e).

20. The method for locating a transmitter of claim 1 further comprising the step of:

(g) periodically repeating steps (a) through (f).