Reflective chopper for infrared imaging systems

• US 5,051,591 A
• Filed: 01/10/1991
• Issued: 09/24/1991
• Est. Priority Date: 07/28/1989
• Status: Expired due to Fees

• Current Assignee: Raytheon TI Systems, Inc. (Rtx Corporation)
• Original Assignee: Texas Instruments, Inc.
• Inventors: McKenney, Samuel R., Trotta, Patrick A.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US07/639,401
• Time in Patent Office: 257 Days
• Field of Search: 250/350, 250/351, 250/347, 250/342, 250/334, 250/332, 250/330
• US Class Current: 250/351
• CPC Class Codes: G01J 5/0805 Means for chopping radiation
• CPC Class Codes: H04N 23/20 for generating image signals from infrared radiation only
• 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

A chopper, in an infrared imaging system, is used to scatter infrared radiation from a viewed scene. This scattered radiation is detected with an infrared detector and used to produce a reference signal, which represents the uniform average radiance of the scene. This reference signal may be substracted from a signal representing the unscattered radiation emitted by the scene, to produce a signal that represents only radiance differences and that is an optimal signal for amplification.

Claims

1. A method for producing an image of a scene, using an infrared imaging system, comprising the steps of:

detecting the actual infrared radiation from said scene to form a biased signal representing the radiances of objects within said scene;

scattering the infrared radiation emitted by said scene by placing an array of tubes having reflective inner surfaces across said actual radiation, such that rays of said radiation pass through said tubes at angles that are deviated from their normal path by said reflective inner surfaces;

detecting said scattered radiation to form a reference signal;

subtracting said reference signal from said biased signal to obtain an unbiased signal representing radiance differences emitted by said scene; and

displaying an image generated in response to said unbiased signal.

2. The method of claim 1, wherein said scattering step causes a uniform average radiance of said scene to be irradiated upon an infrared detector.

3. The method of claim 1, wherein said scattering step further comprises arranging said tubes so that they are adjacent to each other and their axis is generally parallel to said rays.

4. The method of claim 1, wherein said scattering step comprises moving said array of tubes through sequential portions of a beam of radiation emitted by said scene.

5. The method of claim 1, wherein said scattering step comprises rotating a spiral shaped arrangement of said array of tubes across a beam of said radiation emitted by said scene.

6. The method of claim 5, wherein said rotating of said spiral comprises covering an infrared detector array line by line.

7. The method of claim 1, and further comprising the step of synchronizing said steps of producing signals.

8. A method for use in an infrared imaging system having an infrared detector, of generating a reference signal representing background radiance of a scene, comprising the steps of:

scattering the infrared radiation emitted by said scene by passing portions of said radiation in parallel through a number of passageways having reflective inner surfaces, such that rays of said radiation leave said passageways at angles that are deviated from their normal path, and the average radiance emitted by said scene is irradiated on said detector;

detecting said scattered radiation with said infrared detector; and

generating a reference signal representing the uniform average radiance of said scene, using said scattered radiation.

9. The method of claim 8, wherein said scattering step further comprises arranging said passageways so that they are adjacent to each other and their axis is generally parallel to said rays.

10. The method of claim 8, wherein said detector has an array of receiving elements, and said scattering step comprises moving an arrangement of said passageways with respect to the receiving portion of said detector such that said radiation reaches said detector line by line of said detector.

11. The method of claim 8, wherein said scattering step comprises rotating a spiral shaped arrangement of said passageways of across a beam of said radiation emitted by said scene.

12. The method of claim 11, wherein said infrared detector has an array of receiving elements, and said rotating of said spiral shaped arrangement of passageways comprises covering said infrared detector array line by line.

13. An apparatus for producing an image of a scene, using an infrared imaging system, comprising:

optics for focusing radiation emitted by said scene on an infrared detector;

a chopper placed between said optics and an infrared detector, for scattering the infrared radiation emitted by said scene, wherein said chopper has an arrangement of tubes with reflective inner surfaces, the axis of each tube being placed generally parallel to the axis of said focused radiation;

a detector for detecting said scattered radiation, at a first time, to form a biased signal representing the radiance of objects in said scene, and at a second time, to form a reference signal in response to the output of said chopper;

electronics for receiving said signals and for subtracting said reference signal from said biased signal to obtain an unbiased signal representing radiance differences emitted by said scene; and

a display for displaying an image generated in response to said unbiased signal.

14. The apparatus of claim 13, wherein said chopper produces radiation representing the average radiance, but not the radiance differences emitted by said scene.

15. The apparatus of claim 13, wherein said the tubes of said arrangement of tubes are closely adjacent such that the solid portions of the front of said chopper are minimized.

16. The apparatus of claim 15, wherein said arrangement of tubes comprises a honeycomb pattern of adjacent tubes.

17. The apparatus of claim 13, wherein said arrangement of tubes forms a single spiral shape.

18. The apparatus of claim 13, wherein said arrangement of tubes forms a double spiral shape.

19. The apparatus of claim 13, and further comprising a means for synchronizing the motion of said arrangement of tubes with said electronics.

20. A chopper for use with an infrared imaging system having an infrared detector, comprising:

an arrangement of passageways generally parallel to each other, each having an inner surface that is reflective to infrared radiation; and

an actuating device for moving said arrangement of tubes in front of said infrared detector, such that the axis of said tubes is generally perpendicular to the receiving face of said detector.

21. The apparatus of claim 20, wherein said passageways have a honeycomb relationship to each other.

22. The apparatus of claim 20, wherein said arrangement of passageways has a leading edge and said actuating device moves said arrangement of passageways with respect to said detector such that said detector is covered sequentially by said leading edge.

23. The apparatus of claim 22, wherein said leading edge is curved and said actuating device rotates said arrangement of passageways.

24. The apparatus of claim 20, wherein said arrangement of passageways has a spiral shape.

25. The apparatus of claim 20, wherein the diameter of each of said passageways is less than one fourth the diameter of a beam of radiation entering said arrangement of passageways.

26. A method of generating a reference signal for use with an infrared imaging system, comprising the steps of:

receiving infrared radiation emitted by a scene into an array of passageways;

reflecting said radiation from the inner surfaces of said passageways as said radiation passes through said passageways; and

permitting said reflected radiation to emerge from said passageways with substantially the same average intensity as upon entry to said passageways, but in a substantially unmodulated form.

27. The method of claim 26, wherein said receiving step comprises receiving said infrared radiation into a spiral shaped array of passageways, and further comprising the step of rotating said spiral shaped array of passageways.