METHOD OF SEARCHING FOR A THERMAL TARGET

• US 20090321636A1
• Filed: 06/25/2009
• Published: 12/31/2009
• Est. Priority Date: 06/26/2008
• Status: Active Grant

• Current Assignee: Lynntech Incorporated
• Original Assignee: Lynntech Incorporated
• Inventors: Lusher, John, Ragucci, Anthony J.
• Granted Patent: US 8,373,127 B2
• Time in Patent Office: Days
• US Class Current: 250/330
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 23/90 Arrangement of cameras or camera modules, e.g. multiple cameras in TV studios or sports stadiums
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response
• CPC Class Codes: H04N 5/262 Studio circuits, e.g. for mixing, switching-over, change of character of image, other special effects ; Cameras specially adapted for the electronic generation of special effects
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

In one embodiment, an efficient method is presented for aerial searching for a small thermal target in a search area, such as a single person in open water, using two thermal imagers or “cameras” coupled with a computer which presents data from the system to a human user for inspection. One of the two thermal imagers has a very wide field of view (WFOV) fixed forward of or below the aircraft. The other, narrow field-of-view (NFOV) imager has a high zoom capability but its field of view can be reoriented to geo-point to a location on command. The WFOV thermal imager collects images rapidly so that no individual image is blurred due to changes in the field of view (FOV) on the time-scale of the image capture. The images are geo-registered using information from a global positioning receiver as well as the current altitude, roll, pitch, yaw, and velocity of the aircraft. As the aircraft moves and the FOV in the WFOV thermal imager changes, the computer averages the amplitude of the thermal radiation detected from each geo-registered position on the water below using the captured images continuously and in real time. The signal from a thermal target in the water is integrated while the background is relatively suppressed, enhancing the signal-to-noise ratio for the target as the square root of the number of images collected in which the target appears. A target which is much smaller than the area covered by a single pixel or that even has a thermal contrast below the noise equivalent temperature difference of the WFOV thermal imager can be detected. Thermal anomalies which have a signal commensurate in amplitude and spatial extent to the object of the search are selected by the system and their coordinates are relayed to the NFOV thermal imager. The NFOV thermal imager zooms into these locations sequentially and presents the image information to the human user who can then either reject or verify that the subject being imaged is the object of the search.

Claims

1. A system for searching for a thermal target, comprising:

a wide field-of-view thermal imager disposed on an aerial platform and configured for directing toward a search area and geo-registering thermal signals across a field of view of the wide field-of-view thermal imager;

a narrow field-of-view thermal-imaging video imager configured to geo-point and zoom to a field of view that is less than or equal to 10% of the wide field-of-view; and

a computer connected to both the wide field-of-view thermal imager and the narrow field-of-view thermal imager, wherein the computer is configured to geo-register and time-integrate the amplitude of the thermal signals emanating from each sector in the search area imaged by the wide field-of-view thermal imager, identify one or more sectors of interest having an average thermal signal that is at least three standard deviations above a local mean thermal signal, and direct the narrow field-of-view thermal imager to geo-point to the sector of interest and display a thermal image associated with the sector of interest to a user.

2. The system of claim 1, wherein the wide field-of-view thermal imager is rigidly mounted to the aerial platform and geo-registration of the field of view is accomplished through software.

3. The system of claim 1, wherein the wide field-of-view thermal imager is movably mounted on a gimbal for counteracting the aerial platform'"'"'s buffeting motion to hold the WFOV imager at a substantially constant orientation relative to the Earth.

4. The system of claim 1, wherein the wide field-of-view thermal imager and the narrow field-of-view thermal imager are both configured to detect thermal radiation in either the mid-wave or long-wave infrared region of the electromagnetic spectrum.

5. The system of claim 1, further comprising:

avionics on the aerial platform, wherein the avionics are configured to provide real-time position and orientation data.

6. The system of claim 1, further comprising:

at least one sensor internal to either or both of the thermal imagers, wherein the at least one sensor provides real-time geo-registration data.

7. The system of claim 1, wherein the wide field-of-view thermal imager is configured to acquire video at a frame rate high enough to avoid blurring due to aerial platform motion.

8. The system of claim 1, wherein computer is configured to geo-register the thermal signals from the wide field-of-view thermal imager and geo-point the narrow field-of-view thermal imager based on a flat map of only latitude and longitude coordinates, or to a visual image of the search area covered.

9. The system of claim 1, wherein the computer is a component of either of the WFOV or narrow field-of-view thermal imagers.

10. The system of claim 1, wherein the computer is a sub-component or card within the computer component of either of the wide field-of-view or narrow field-of-view thermal imagers.

11. The system of claim 1, wherein the user is a human being or automatic target recognition software.

12. The system of claim 1, wherein the narrow field-of-view thermal imager can automatically detect, further magnify, and track the most intense thermal anomaly in the narrow sector it has been directed to image, thereby increasing the visual impact of that object to the user without requiring user intervention.

13. The system of claim 1, wherein the orientation of the centerline of the wide field-of-view thermal imager relative to the vertical is 45°

or less in order to minimize spatial resolution non-uniformity or curvature of the wide field-of-view thermal imager'"'"'s visual field due to perspective or optical aberration.

14. The system of claim 1, wherein a background image is subtracted from each video frame collected by the wide field-of-view thermal imager to correct for non-uniformity in the focal point array sensitivity, fixed pattern noise, or environmental effects influencing the output from the wide field-of-view thermal imager.

15. The system of claim 1, wherein the wide field-of-view thermal imager has a field of view of 45°

or greater for directing ahead of or directly below the aerial platform to the search area.

16. A method for searching for a thermal target from an aerial platform, comprising:

identifying a search area and a plurality of sectors within the search area;

tracking movement of the aerial platform over the search area;

directing a wide field-of-view infrared imager toward the search area, the wide field-of-view infrared imager including a focal plane array having a plurality of pixels, wherein the plurality of pixels includes one or more pixel responsive to heat emitted by each of the plurality of sectors that pass within a field of view of the wide field-of-view infrared imager as the sectors pass beneath the aerial platform;

tracking each of the plurality of sectors as images of the sectors pass across successive pixels in the focal plane array and integrating thermal signals associated with each sector at successive pixels over a period of time;

identifying a sector having an average thermal signal which exceeds the average thermal signal of the surrounding sectors; and

directing a narrow field-of-view infrared imager to image the identified sector at a higher resolution than imaged by the wide field-of-view infrared imager to assess whether the identified sector contains the object of the search.

17. The method of claim 16, further comprising:

determining an average thermal signal within a spectral range of the wide field-of-view infrared imager by averaging the thermal signals determined at each successive pixel as the sector passes across the field of view of the wide field-of-view infrared imager.

18. The method of claim 16, further comprising:

ranking the probability that each of a plurality of identified sectors contains the object of the search; and

displaying a plurality of identified sectors to a user based on the probability ranking.

19. The method of claim 18, wherein the probability of each sector containing the object of the search is based on the deviation between the average of the thermal signals and the local mean field, the physical size of the anomaly, and whether or not the peak thermal signal for the sector is greater than or less than a background thermal signal.

20. The method of claim 16, further comprising:

using the narrow field-of-view thermal imager to automatically detect, magnify and track the most intense thermal anomaly in the sector that the narrow field-of-view thermal imager is imaging.

21. The method of claim 16, further comprising:

subtracting a background image from each image collected by the wide field-of-view thermal imager to correct for non-uniformity in the focal point array sensitivity, fixed pattern noise, or environmental effects influencing output from the wide field-of-view thermal imager.

22. A method for searching for a thermal target, comprising:

directing a wide field-of-view thermal imager disposed on a moving platform toward a selected search area;

geo-registering an image in a field of view of the wide field-of-view thermal imager;

averaging the amplitude of a thermal signal emanating from each sector in the search area imaged by the wide field-of-view thermal imager;

identifying one or more sectors of interest as any sector having an average signal that is at least three standard deviations above a local mean;

directing a narrow field-of-view thermal imager disposed on the moving platform configured to geo-point to the sector of interest, zoom to a field of view that is equal to or less than 10% of the field of view of the wide field-of-view thermal imager; and

displaying the sector of interest to a user.

23. The method of claim 22, wherein the moving platform is an aerial platform and the search area is the surface of a body of water.

24. The method of claim 22, wherein the moving platform is an aerial platform and the search area is the surface of a land mass.

25. The method of claim 22, wherein the moving platform is supported on land or water and the search area is in the sky or horizon.

26. The method of claim 22, wherein the moving platform stays in one location but can be rotationally re-oriented.

27. The method of claim 22, wherein the wide field-of-view thermal imager is stationary and for which the field of view does not change but the narrow field-of-view thermal imager can be re-oriented.

28. The method of claim 22, wherein the imaging components are sensitive to targets emitting radiation in any wavelength range of the electromagnetic spectrum.