Infrared imaging system for enhancing the perception of a scene by a vehicle operator

• US 5,534,694 A
• Filed: 09/06/1994
• Issued: 07/09/1996
• Est. Priority Date: 06/04/1992
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: Eby, Edward D., Ball, Gary E.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US08/300,895
• Time in Patent Office: 672 Days
• Field of Search: 250/330, 250/334, 250/339, 250/226, 250/339.14, 340/945, 340/953, 340/705, 358/113, 358/103, 348/342, 359/614, 359/634
• US Class Current: 250/330
• CPC Class Codes: G01J 1/0488 with spectral filtering
• CPC Class Codes: G01J 1/26 adapted for automatic variation of the measured or reference value regulation of light intensity G05D25/00
• CPC Class Codes: G01J 2001/0276 Protection
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 5/0816 using attenuators
• CPC Class Codes: H04N 23/11 for generating image signals from visible and infrared light wavelengths
• 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 thermal or infrared imaging system that is particularly useful to enhance a vehicle operator'"'"'s perception of surrounding scene features under vision-impaired conditions, e.g., rain, fog, smoke, and the like. Scene radiation is passed to an imaging sensor through a wavelength-selective attenuator that operates to pass radiation in a first wavelength range substantially without attenuation and to pass radiation in a second wavelength range with controllable attenuation. This permits maximum sensitivity to objects in the scene that radiate in the fist wavelength range and controllable sensitivity to objects that radiate in the second wavelength range, whereby the sensor may be prevented from becoming overloaded or saturated by radiation in the second wavelength range while continuing to produce useable image signals of objects in the scene that radiate in the first wavelength range.

Claims

1. An aircraft infrared imaging landing aid system for enhancing the perception of a scene by an operator comprising:

an infrared imaging sensor;

an optical system for receiving infrared radiation from a scene and forming an infrared image of the scene on said sensor;

a readout coupled to said sensor for outputting electrical signals representative of the infrared image of the scene on said sensor;

a display for receiving the electrical signals from said readout and producing a visible image viewable by said operator, said visible image being representative of the infrared image of the scene on said sensor; and

a wavelength-selective attenuator between the scene and said sensor for controllably attenuating a selected wavelength range of the infrared radiation received from the scene.

2. The infrared imaging system according to claim 1, further comprising an attenuator control, responsive to said sensor and operative on said attenuator, for controlling the attenuation by said attenuator in response to the intensity of the infrared radiation from the scene on said sensor.

3. The infrared imaging system according to claim 1, wherein the optical system includes bandpass means for passing to said attenuator only the infrared radiation having wavelengths between 1 μ

m and 5 μ

m, and wherein the selected wavelength range is between 1 μ

m and 3 μ

m.

4. The infrared imaging system according to claim 1, wherein the wavelength-selective attenuator comprises:

a wavelength selective beam splitter for splitting the infrared radiation from the scene into a first beam and a second beam, wherein the infrared radiation in said selected wavelength range is directed along said first beam and the remainder of the infrared radiation is directed along said second beam;

a controllable attenuator located in said first beam; and

a beam combiner for combining said first beam and said second beam into a combined beam and directing said combined beam towards said sensor.

5. The infrared imaging system according to claim 4, wherein the controllable attenuator comprises a variable transmissivity neutral density filter wheel pair.

6. The infrared imaging system according to claim 4, wherein the controllable attenuator comprises a pair of rotatable polarized wheels.

7. The infrared imaging system according to claim 4, wherein the beam splitter comprises a dichroic cube that reflects the infrared radiation in said selected wavelength range and transmits the remainder of the infrared radiation.

8. An aircraft infrared landing aid system for imaging infrared radiation having wavelengths within a selected wavelength range, comprising:

an infrared sensor;

a display, responsive to said sensor, for producing a visible image viewable by an aircraft operator; and

means, disposed between said focusing means and said sensor, for controllably attenuating said infrared radiation having wavelengths within a subrange of said selected wavelength range.

9. The system according to claim 8, said system further including bandpass means for allowing only infrared radiation having wavelengths between 1 μ

m and 5 μ

m to be focused onto said sensor, and wherein said attenuating means controllably attenuates said infrared radiation having wavelengths between 1 μ

m and 3 μ

m.

10. The system according to claim 8, wherein the attenuating means comprises:

a dichroic cube for splitting the infrared radiation from said focusing means into a first beam and a second beam, wherein the infrared radiation having wavelengths within said subrange is directed along said first beam and the remainder of the infrared radiation is directed along said second beam;

a controllable attenuator for attenuating said first beam; and

a beam combiner for combining said attenuated first beam and said second beam into a combined beam, said combined beam being directed towards said sensor.

11. The system according to claim 10, further comprising an attenuator control, responsive to said sensor and operative on said controllable attenuator, for controlling the attenuation of said first beam in response to the intensity of said infrared radiation sensed by said sensor.

12. An imaging system for enhancing the perception of a scene by a vehicle operator, comprising:

means for imaging electromagnetic radiation having wavelengths within a wavelength band;

means for focusing the electromagnetic radiation from said scene onto said imaging means; and

means, disposed in front of said imaging means, for controllably varying the intensity of said electromagnetic radiation having wavelengths within a subband of said wavelength band, said varying means including means for splitting said electromagnetic radiation from said focusing means into first and second beams, said first beam consisting of said electromagnetic radiation having wavelengths within said subband, said second beam including at least some of the remainder of said electromagnetic radiation;

a controllable attenuator for controlling the intensity of said first beam; and

combining means for combining an output of said attenuator with said second beam to provide a combined beam, said combined beam being directed towards said imaging means.

13. The iamging system according to claim 12, wherein the focusing means focuses only electromagnetic radiation having wavelengths between 1 μ

m and 5 μ

m onto said sensor, whereby said wavelength band is between 1 μ

m and 5 μ

m, and wherein said varying means controllably varies the intensity of said electromagnetic radiation having wavelengths between 1 μ

m and 3 μ

m, whereby said subband is between 1 μ

m and 3 μ

m.

14. The imaging system according to claim 12, wherein said controllable attenuator includes a variable transmissivity neutral density filter wheel pair.

15. The imaging system according to claim 12, wherein said controllable attenuator includes a pair of rotatable polarized wheels.

16. The imaging system according to claim 12, wherein the splitting means includes a dichroic cube that reflects said electromagnetic radiation having wavelengths within said subband and transmits said remainder of electromagnetic radiation, whereby said first beam is formed from said reflected radiation and said second beam is formed from said transmitted radiation.

17. The imaging system according to claim 12, further comprising an attenuator control, responsive to said imaging means and operative on said controllable attenuator, for controlling the attenuation by said attenuator in response to the intensity of said electromagnetic radiation imaged by said imaging means.