Infrared concealed object detection enhanced with closed-loop control of illumination by.mmw energy

• US 8,896,701 B2
• Filed: 02/23/2010
• Issued: 11/25/2014
• Est. Priority Date: 02/23/2010
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Brown, Kenneth W., Sar, David R., Gallivan, James R., Phillips, Wilkie M.
• Primary Examiner(s): Le, Thao X
• Assistant Examiner(s): LE, LONG HUYNH
• Application Number:
  US12/711,062
• Publication Number:
  US 20110205367A1
• Time in Patent Office: 1,736 Days
• Field of Search: 348/160, 348/164, 280/735, 396/14, 340/567, 250/330, 250/338.1, 342/22, 342/52, 374/130, 382/124
• US Class Current: 348/164
• CPC Class Codes: H04N 23/56 provided with illuminating means
• 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

An active infrared sensor may include an imaging infrared sensor to provide an output signal conveying time-sequential infrared images of a scene which includes a subject, a beam generator to generate a millimeter wave energy beam, and a processor. An initial infrared image of the scene may be stored in a memory. After storing the initial infrared image, the beam generator may illuminate the subject with the millimeter wave energy beam. A temperature change across the subject due to the millimeter wave energy beam may be estimated based on the output signal and the stored initial infrared image. The beam generator may stop illuminating the subject when a highest temperature change across the subject is at least equal to a predetermined temperature change limit.

Claims

1. An active infrared sensor apparatus comprising:

an imaging infrared sensor configured to output time-sequential images of a scene which includes a subject;

a beam generator configured to generate a millimeter wave energy beam; and

a processor configured to;

store a first infrared image of the scene from the imaging infrared sensor in a memory, the first infrared image identifying an initial temperature distribution within the subject prior to illumination of the subject with the millimeter wave energy beam;

cause the beam generator to illuminate the subject with the millimeter wave energy beam to thereby create an altered temperature distribution within the subject;

obtain a second infrared image of the scene from the imaging infrared sensor, the second infrared image identifying the altered temperature distribution within the subject due to the millimeter wave energy beam;

identify differences between the first and second infrared images to determine how the millimeter wave energy beam changes the temperature distribution within the subject; and

cause the beam generator to stop illuminating the subject when a highest temperature change across the subject caused by the millimeter wave energy beam equals or exceeds a predetermined temperature change limit.

2. The apparatus of claim 1, wherein the processor is further configured to store the second infrared image at approximately the same time as causing the beam generator to stop illuminating the subject.

3. The apparatus of claim 2, wherein the processor is further configured to:

determine a highest temperature change rate across the subject;

when the highest temperature change rate is less than a predetermined minimum rate, cause the millimeter wave energy beam'"'"'s power to increase; and

when the highest temperature change rate is greater than a predetermined maximum rate, cause the millimeter wave energy beam'"'"'s power to decrease.

4. The apparatus of claim 3, wherein:

in a covert mode of operation, the temperature change limit, the minimum rate, and the maximum rate are set to first respective values, and

in an aggressive mode of operation, the temperature change limit, the minimum rate, and the maximum rate are set to second respective values, each second respective value greater than the corresponding first respective value.

5. The apparatus of claim 4, wherein:

the first respective values of the temperature change limit, the minimum rate, and the maximum rate are set such that heating caused by the millimeter wave energy beam is at most barely perceptible to the subject, and

the second respective values of the temperature change limit, the minimum rate, and the maximum rate are set such that the heating caused by the millimeter wave energy beam is easily perceptible but not discomforting to the subject.

6. The apparatus of claim 1, further comprising a pointing mechanism;

wherein the processor is further configured to control the pointing mechanism to cause the millimeter wave energy beam and the imaging infrared sensor to track the subject from prior to storing the first infrared image until after storing the second infrared image.

7. The apparatus of claim 1, wherein the processor is further configured, after causing the beam generator to stop illuminating the subject, to store a third infrared image of the scene after waiting a predetermined time interval.

8. The apparatus of claim 7, further comprising a pointing mechanism;

wherein the processor is further configured to;

cause the millimeter wave energy beam to track the subject from prior to storing the first infrared image until after storing the second infrared image, and

cause the imaging infrared sensor to track the subject from prior to storing the first infrared image until after storing the third infrared image.

9. The apparatus of claim 1, wherein the processor is further configured, when the subject has been illuminated for a predetermined maximum illumination period, to store the second infrared image and cause the beam generator to stop illuminating the subject.

19. The apparatus of claim 1, wherein the processor is further configured to automatically recognize the subject as one of a targeted object and a benign object.

10. A method for capturing infrared images, comprising:

storing a first infrared image of a scene from an imaging infrared sensor, the first infrared image identifying an initial temperature distribution within a subject in the scene prior to illumination of the subject with a millimeter wave energy beam;

illuminating the subject with the millimeter wave energy beam to thereby create an altered temperature distribution within the subject;

obtaining a second infrared image of the scene from the imaging infrared sensor, the second infrared image identifying the altered temperature distribution within the subject due to the millimeter wave energy beam;

identifying differences between the first and second infrared images to determine how the millimeter wave energy beam changes the temperature distribution within the subject; and

discontinuing illuminating the subject when a highest temperature change across the subject caused by the millimeter wave energy beam equals or exceeds a predetermined temperature change limit.

11. The method of claim 10, further comprising:

storing the second infrared image at approximately the same time as discontinuing illuminating the subject.

12. The method of claim 11, further comprising:

determining a highest temperature change rate across the subject;

when the highest temperature change rate is less than a minimum rate, increasing the millimeter wave energy beam'"'"'s power; and

when the highest temperature change rate is greater than a maximum rate, decreasing the millimeter wave energy beam'"'"'s power.

13. The method of claim 12, further comprising:

selecting one of a covert mode or operation and an aggressive mode of operation;

when the covert mode of operation is selected, setting the maximum temperature change limit, the minimum rate, and the minimum rate to respective first values; and

when the aggressive mode of operation is selected, setting the maximum temperature change limit, the minimum rate, and the minimum rate to respective second values, each second respective value greater than the corresponding first respective value.

14. The method of claim 13, wherein:

the first respective values of the temperature change limit, the minimum rate, and the maximum rate are set such that heating caused by the millimeter wave energy beam is at most barely perceptible to the subject, and

the second respective values of the temperature change limit, the minimum rate, and the maximum rate are set such that the heating caused by the millimeter wave energy beam is easily perceptible but not discomforting to the subject.

15. The method of claim 10, further comprising:

tracking the subject with the millimeter wave energy beam and the imaging infrared sensor from prior to storing the first infrared image until after storing the second infrared image.

16. The method of claim 10, further comprising:

after discontinuing illuminating the subject, storing a third infrared image of the scene after waiting a predetermined time interval.

17. The method of claim 16, further comprising:

tracking the subject with the millimeter wave energy beam from prior to storing the first infrared image until after storing the second infrared image; and

tracking the subject with the imaging infrared sensor from prior to storing the first infrared image until after storing the third infrared image.

18. The method of claim 10, further comprising:

when the subject has been illuminated for a predetermined maximum illumination period, storing the second infrared image and discontinuing illuminating the subject.

20. The method of claim 10, further comprising:

automatically recognizing the subject as one of a targeted object and a benign object.

21. A non-transitory computer readable medium embodying a computer program, the computer program comprising computer readable program code for:

storing a first infrared image of a scene, the first infrared image identifying an initial temperature distribution within a subject in the scene prior to illumination of the subject with a millimeter wave energy beam;

initiating the illumination of the subject with the millimeter wave energy beam to thereby create an altered temperature distribution within the subject;

obtaining a second infrared image of the scene, the second infrared image identifying the altered temperature distribution within the subject due to the millimeter wave energy beam;

identifying differences between the first and second infrared images to determine how the millimeter wave energy beam changes the temperature distribution within the subject; and

discontinuing illuminating the subject when a highest temperature change across the subject caused by the millimeter wave energy beam equals or exceeds a predetermined temperature change limit.