MMW Enhanced Infrared Concealed Object Detection with Closed-Loop Control of Illumination Energy

• US 20110205367A1
• Filed: 02/23/2010
• Published: 08/25/2011
• Est. Priority Date: 02/23/2010
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Phillips, Wilkie M., Brown, Kenneth W., Gallivan, James R., Sar, David R.
• Granted Patent: US 8,896,701 B2
• Time in Patent Office: Days
• US Class Current: 348/164
• CPC Class Codes: H04N 23/20 for generating image signals from infrared radiation only
• 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 to provide an output signal conveying time-sequential images of a scene which includes a subject;

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

a processor coupled to the imaging infrared sensor and the beam generator, the processor for performing actions including;

storing an initial infrared image of the scene in a memory,

after storing the initial infrared image, causing the beam generator to illuminate the subject with the millimeter wave energy beam,

estimating a temperature change across the subject due to the millimeter wave energy beam based on the output signal and the stored initial infrared image, and

causing the beam generator to stop illuminating the subject when a highest temperature change across the subject is at least equal to a predetermined temperature change limit.

2. The apparatus of claim 1, the actions performed by the processor further comprising:

storing a hot infrared image at approximately the same time as causing the beam generator to stop illuminating the subject.

3. The apparatus of claim 2, the actions performed by the processor further comprising:

determining a highest temperature change rate across the subject;

when the highest temperature change rate is less than a predetermined minimum rate, causing the millimeter wave beam power to increase; and

when the highest temperature change rate is greater than a predetermined maximum rate, causing the millimeter wave beam 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 greater than the first respective values.

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 the heating caused by the millimeter wave 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 beam is easily perceptible but not discomforting to the subject.

6. The apparatus of claim 1, further comprising:

a pointing mechanism,

the actions performed by the processor further comprising;

controlling the pointing mechanism based on the output signal to cause the millimeter wave energy beam and the imaging infrared sensor to track the subject from prior to storing the initial infrared image until after storing the hot infrared image.

7. The apparatus of claim 1, the actions performed by the processor further comprising:

after causing the beam generator to stop illuminating the subject, storing a final infrared image of the scene after waiting a predetermined time interval.

8. The apparatus of claim 7, further comprising:

a pointing mechanism,

the actions performed by the processor further comprising;

causing the millimeter wave energy beam to track the subject from prior to storing the initial infrared image until after storing the hot infrared image, and

causing the imaging infrared sensor to track the subject from prior to storing the initial infrared image until after storing the final infrared image.

9. The apparatus of claim 1, the actions performed by the processor further include:

when the subject has been illuminated for a predetermined maximum illumination period, storing the hot infrared image and causing the beam generator to stop illuminating the subject.

10. A method for capturing infrared images, comprising:

storing an initial infrared image of a scene from an imaging infrared sensor;

after storing the initial infrared image, illuminating a subject within the scene with a millimeter wave energy beam;

estimating a temperature change across the subject due to the millimeter wave energy beam based on the output signal and the stored initial infrared image; and

discontinuing illuminating the subject when a highest temperature change across the subject is at least equal to a predetermined temperature change limit.

11. The method of claim 10, further comprising:

storing a hot 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 beam power; and

when the highest temperature change rate is greater than a maximum rate, decreasing the millimeter wave beam 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 greater than the respective first values.

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 the heating caused by the millimeter wave 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 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 initial infrared image until after storing the hot infrared image.

16. The method of claim 10, further comprising:

after stopping 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 initial infrared image until after storing the hot infrared image; and

tracking the subject with the imaging infrared sensor from prior to storing the initial infrared image until after storing the final infrared image.

18. The method of claim 10, further comprising:

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