System and method for direction finding and geolocation of emitters based on line-of-bearing intersections

• US 8,723,730 B2
• Filed: 07/27/2011
• Issued: 05/13/2014
• Est. Priority Date: 07/27/2011
• Status: Active Grant

• Current Assignee: Harris Global Communications, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: Exelis Incorporated (L3Harris Technologies, Inc.)
• Inventors: Lu, Ning Hsing, Chan, Chi Chiu, Shi, Qun
• Primary Examiner(s): Liu, Harry
• Application Number:
  US13/191,696
• Publication Number:
  US 20130027251A1
• Time in Patent Office: 1,021 Days
• Field of Search: 342/464
• US Class Current: 342/464
• CPC Class Codes: G01S 3/34 the separate antennas comprising one directional antenna and one non-directional antenna, e.g. combination of loop and open antennas producing a reversed cardioid directivity characteristic
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders

Abstract

According to an embodiment of the present invention an emitter geolocation technique determines the geolocation of a radio frequency (RF) emitter using pair-wise line-of-bearing intersections that are derived from signal-to-noise ratios of transmitted signals received at a sensor. The technique may be employed with ground based vehicle or small unmanned air vehicles (UAV), and obtains reliable geolocation estimates of radio frequency (RF) emitters of interest.

Claims

1. A system for locating an emitter comprising:

a plurality of antennas including a first antenna with a first radiation pattern and a second different antenna with a second radiation pattern different from the first radiation pattern, wherein the first and second radiation patterns provide a received signal gain with respect to signals received from said emitter;

a receiver to receive signals from each of said plurality of antennas transmitted by said emitter and obtain received signal strength measurements of said received signals at a plurality of different locations; and

a processor to process said received signal strength measurements to locate said emitter, wherein said processor includes;

a location module to;

process said received signal strength measurements and determine lines-of-bearing to said emitter based on a combination of received signal strength measurements of a signal received by each of said first antenna and said second antenna at said plurality of different locations; and

determine a location of said emitter based on intersections of said lines-of-bearing to said emitter at said plurality of different locations.

2. The system of claim 1, wherein said received signal strength measurements include signal-to-noise ratio measurements of said signals received at said plurality of antennas.

3. The system of claim 2, wherein said location module determines a maximum signal-to-noise ratio from said signal-to-noise ratio measurements and determines a line-of-bearing to said emitter based on said maximum signal-to-noise ratio.

4. The system of claim 2, wherein said location module:

groups said received signal strength measurements into at least two clusters;

determines a maximum signal-to-noise ratio from said signal-to-noise ratio measurements within each cluster; and

determines a line-of-bearing to said emitter based on each of said maximum signal-to-noise ratios.

5. The system of claim 1, wherein said location module determines said location by solving a set of simultaneous equations relating to said lines-of-bearing, wherein said set of simultaneous equations include unknown variables representing coordinates of said location of said emitter.

6. The system of claim 5, wherein said set of simultaneous equations includes:

7. The system of claim 5, wherein said location module computes a line-of-bearing from each of said plurality of different locations within to said emitter.

8. The system of claim 7, wherein said location module computes a plurality of line-of-bearing intersections that approximate said location of said emitter using line-of-bearing pairs.

9. The system of claim 8, wherein said location module filters said plurality of line-of-bearing intersections by comparing each individual line-of-bearing intersection to filtering criteria, wherein when said individual line-of-bearing intersection does not meet said filtering criteria said individual line-of-bearing intersection is discarded.

10. The system of claim 8, wherein said location module determines one or more arithmetic median value based geolocation centroids from selected ones of said plurality of line-of-bearing intersections.

11. The system of claim 10, wherein said one or more geolocation centroids are determined using the set of equations:

x_C=median(x₁,x₂ . . . x_M)

y_C=median (y₁,y₂ . . . y_M)

and wherein x_C, y_C represent coordinates of said geolocation centroid, and M represents a quantity of said line-of-bearing intersections.

12. The system of claim 10, wherein said location module computes a root-mean-square error of said one or more geolocation centroids.

13. The system of claim 12, wherein said location module computes said root-mean-square error of said one or more geolocation centroids using the set of equations:

14. The system of claim 13, wherein said location module filters said one or more geolocation centroids by comparing a ratio of Std_R and Std_I to an error threshold, wherein when said ratio does not pass said error threshold a geolocation centroid used as a basis for said root-mean-square error computation is discarded.

15. The system of claim 1, wherein said signals transmitted by said emitter include radio frequency signals.

16. The system of claim 1, wherein said receiver is mounted on a mobile platform that traverses a pre-planned path to obtain said received signal strength measurements at said plurality of locations.

17. The system of claim 16, wherein said mobile platform includes a terrain based vehicle or an unmanned aerial vehicle.

18. The system of claim 1, further including a plurality of receivers each mounted on a stationary platform at a corresponding one of said plurality of locations to obtain said received signal strength measurements.

19. The system of claim 1, wherein said first antenna comprises an omni-directional antenna and said second antenna comprises a directional antenna.

20. A method for locating an emitter comprising:

(a) receiving signals transmitted by said emitter via each of a plurality of antennas including a first antenna with a first radiation pattern and a second different antenna with a second radiation pattern different from the first radiation pattern, wherein the first and second radiation patterns provide a received signal gain with respect to signals received from said emitter, and obtaining received signal strength measurements of said received signals at a plurality of different locations; and

(b) processing said received signal strength measurements, via a processor, and determining lines-of-bearing to said emitter based on a combination of received signal strength measurements of a signal received by each of said first antenna and said second antenna at said plurality of different locations to determine a location of said emitter based on intersections of said lines-of-bearing to said emitter at said plurality of different locations.

21. The method of claim 20, wherein step (b) further includes:

(b.1) determining said location using signal-to-noise ratio measurements of said signals received at said plurality of antennas.

22. The method of claim 21, wherein step (b.1) further includes:

(b.1.1) determining a maximum signal-to-noise ratio from said signal-to-noise ratio measurements; and

(b.1.2) determining a line-of-bearing to said emitter based on said maximum signal-to-noise ratio.

23. The method of claim 21, wherein step (b.1) further includes:

(b.1.1) grouping said received signal strength measurements into at least two clusters;

(b.1.2) determining a maximum signal-to-noise ratio from said signal-to-noise ratio measurements within each cluster; and

(b.1.3) determining a line-of-bearing to said emitter based on each of said maximum signal-to-noise ratios.

24. The method of claim 20, wherein step (b) further includes:

(b.1) determining said location by solving a set of simultaneous equations relating to said lines-of-bearing, wherein said set of simultaneous equations include unknown variables representing coordinates of said location of said emitter.

25. The method of claim 24, wherein said set of simultaneous equations includes:

26. The method of claim 24, wherein step (b.1) further includes:

(b.1.1) computing a line-of-bearing from each of said plurality of different locations to said emitter.

27. The method of claim 26, wherein step (b.1) further includes:

(b.1.2) computing a plurality of line-of-bearing intersections that approximate said location of said emitter using line-of-bearing pairs.

28. The method of claim 27, wherein step (b) further includes:

(b.2) filtering said plurality of line-of-bearing intersections by comparing each individual line-of-bearing intersection to filtering criteria, wherein when said individual line-of-bearing intersection does not meet said filtering criteria said individual line-of-bearing intersection is discarded.

29. The method of claim 27, wherein step (b) further includes:

(b.2) determining one or more arithmetic median value based geolocation centroids from selected ones of said plurality of line-of-bearing intersections.

30. The method of claim 29, wherein said one or more geolocation centroids are determined using the set of equations:

x_C=median(x₁,x₂ . . . x_M)

y_C=median (y₁,y₂ . . . y_M)

and wherein x_C, y_C represent coordinates of said geolocation centroid, and M represents a quantity of said line-of-bearing intersections.

31. The method of claim 30, wherein step (b) further includes:

(b.3) computing a root-mean-square error of said one or more geolocation centroids.

32. The method of claim 31, wherein step (b.3) computes said root-mean-square error of said one or more geolocation centroids using the set of equations:

33. The method of claim 32, wherein step (b) further includes:

(b.4) filtering said one or more geolocation centroids by comparing a ratio of Std_R and Std_I to an error threshold, wherein when said ratio does not pass said error threshold a geolocation centroid used as a basis for said root-mean-square error computation is discarded.

34. The method of claim 20, wherein said first antenna comprises an omni-directional antenna and aid second antenna comprises a directional antenna.

35. A program product apparatus comprising a non-transitory computer readable memory device with computer program logic recorded thereon for locating an emitter, wherein a receiver receives signals transmitted by said emitter via each of a plurality of antennas including a first antenna with a first radiation pattern and a second different antenna with a second radiation pattern different from the first radiation pattern to obtain received signal strength measurements of said received signals at a plurality of different locations, said program product apparatus further comprising:

a location module to process said received signal strength measurements of signals transmitted by said emitter and obtained at a plurality of different locations, and determine lines-of-bearing to said emitter based on a combination of received signal strength measurements of a signal received by each of said first antenna and said second antenna at said plurality of different locations to determine a location of said emitter based on intersections of aid lines-of-bearing to said emitter at said plurality of different locations.

36. The apparatus of claim 35, wherein said received signal strength measurements include signal-to-noise ratio measurements of said signals received at said plurality of antennas.

37. The apparatus of claim 36, wherein said location module determines a maximum signal-to-noise ratio from said signal-to-noise ratio measurements and determines a line-of-bearing to said emitter based on said maximum signal-to-noise ratio.

38. The apparatus of claim 36, wherein said location module:

groups said received signal strength measurements into at least two clusters;

determines a maximum signal-to-noise ratio from said signal-to-noise ratio measurements within each cluster; and

determines a line-of-bearing to said emitter based on each of said maximum signal-to-noise ratios.

39. The apparatus of claim 35, wherein said location module determines said location by solving a set of simultaneous equations relating to said lines-of-bearing, wherein said set of simultaneous equations include unknown variables representing coordinates of said location of said emitter.

40. The apparatus of claim 39, wherein said set of simultaneous equations includes:

41. The apparatus of claim 39, wherein said location module computes a line-of-bearing from each of said plurality of different locations to said emitter.

42. The apparatus of claim 41, wherein said location module computes a plurality of line-of-bearing intersections that approximate said location of said emitter using line-of-bearing pairs.

43. The apparatus of claim 42, wherein said location module filters said plurality of line-of-bearing intersections by comparing each individual line-of-bearing intersection to filtering criteria, wherein when said individual line-of-bearing intersection does not meet said filtering criteria said individual line-of-bearing intersection is discarded.

44. The apparatus of claim 42, wherein said location module determines one or more arithmetic median value based geolocation centroids from selected ones of said plurality of line-of-bearing intersections.

45. The apparatus of claim 44, wherein said one or more geolocation centroids are determined using the set of equations:

x_C=median(x₁,x₂ . . . x_M)

y_C=median (y₁,y₂ . . . y_M)

and wherein x_C, y_C represent coordinates of said geolocation centroid, and M represents a quantity of said line-of-bearing intersections.

46. The apparatus of claim 44, wherein said location module computes a root-mean-square error of said one or more geolocation centroids.

47. The apparatus of claim 46, wherein said location module computes said root-mean-square error of said one or more geolocation centroids using the set of equations:

48. The apparatus of claim 47, wherein said location module filters said one or more geolocation centroids by comparing a ratio of Std_R and Std_I to an error threshold, wherein when said ratio does not pass said error threshold a geolocation centroid used as a basis for said root-mean-square error computation is discarded.

49. The apparatus of claim 35, wherein said first antenna comprises an omni-directional antenna and said second antenna comprises a directional antenna.