TWO-COLOR HORIZON SENSOR

• US 3,657,549 A
• Filed: 05/21/1970
• Issued: 04/18/1972
• Est. Priority Date: 05/21/1970
• Status: Expired due to Term

• Current Assignee: Harold H. Seward, Ian G. Mcwilliams, Low George M Deputy Administrator of The National Aeronautics and Space, Mark Gorstein, N/a,
• Original Assignee: Harold H. Seward, Ian G. Mcwilliams, Low George M Deputy Administrator of The National Aeronautics and Space, Mark Gorstein, N/a,
• Inventors: McWilliams, Ian G., N/a,, Low, George M. Deputy Administrator of the National Aeronautics and Space, Seward, Harold H., Gorstein, Mark
• Primary Examiner(s): Borchelt, Archie R.
• Application Number:
  US05/039,344
• Time in Patent Office: 698 Days
• Field of Search: 250/209,226,83.3UV 352/203
• US Class Current: 250/208.5
• CPC Class Codes: G01S 3/7868 using horizon sensors

Abstract

A radiant energy sensor which may be employed to detect discrete radiant energy wavelength bands from a selected portion of a radiating body such as the horizon. As radiant energy from various portions of the body is detected, the energy is analyzed according to its color characteristics by means of a double monochrometer. A combination lens-prism system is used to refract the radiant energy according to its wavelength. Photo detectors in the double monochrometer respond to two selected wavelength bands of the radiant energy and are connected to a difference amplifier to determine the null output of the two detectors. The null condition is adjusted to correspond with the discrete wavelength bands to be sensed.

Claims

1. Apparatus for sensing discrete radiant energies from a radiating body comprising:

sampling means for capturing radiant energy from a selected portion of the radiating body;

wavelength dispersive refracting means for separating the captured radiant energy in a detection plane according to the wavelength of the radiant energy; and

detecting means at selected locations in the detection plane for sensing the radiation at two selected wavelength bands.

2. Apparatus for sensing discrete radiant energies according to claim 1 wherein:

the detecting means includes two sensors at separate locations in the detection plane and a differential comparator connected to the output of the sensors to process the difference signal in a signal channel.

3. Apparatus for sensing discrete radiant energies according to claim 2 wherein:

the comparator has a null condition at a preselected ratio of the energies sensed by the sensors at the locations in the detection plane.

4. AppaRatus according to claim 1 for sensing discrete radiant energies from a body radiating light energy wherein:

the sampling means includes an optical lens and an aperture plate.

5. Apparatus according to claim 4 wherein:

the optical lens is an objective lens having a given image plane and optical axis; and

the aperture plate is positioned in the image plane of the objective lens with an aperture in the plate centered on the optical axis of the lens.

6. Apparatus according to claim 1 for sensing discrete energies in the light spectrum wherein:

the refracting means includes a dispersyn having a lens portion and a prism portion in a single optical element having the form of a peripheral portion of a convex lens.

7. Apparatus according to claim 6 wherein:

the sampling means includes an optical aperture plate; and

the refracting means includes a first dispersyn positioned with the focal plane of the convex lens at the aperture plate, thereby collimating the light beamed from the aperture.

8. Apparatus according to claim 7 wherein:

the refracting means further includes a second dispersyn positioned in the collimated light beam from the first dispersyn and having a focal plane at the detection plane.

9. Apparatus for sensing a preselected altitude from atmospheric radiation near the horizon comprising:

image forming means for generating an optical image of a portion of the horizon color profile in an image plane;

wavelength dispersive refracting means for separating the optical image according to the wavelengths in the color profile portion at a detection plane; and

detecting means in the detection plane for sensing the ratio of the color intensities at two bands of selected wavelengths.

10. Apparatus according to claim 9 wherein:

the detecting means includes photodetectors positioned at locations in the detection plane corresponding to the selected wavelengths.

11. Apparatus according to claim 10 wherein:

two photodetectors are positioned in the detection plane; and

the detecting means also includes a comparator having two signal inputs connected to the respective photodetectors.

12. Apparatus according to claim 10 wherein:

the photodetectors are two silicon photodiodes and the one photodiode is positioned at a location in the detection plane corresponding to wavelengths in the band of 430 nanometers to 490 nanometers.

13. Apparatus according to claim 12 wherein:

the other photodiode is positioned at a location in the detection plane corresponding to wavelengths in the band of 340 nanometers to 380 nanometers.

14. Apparatus according to claim 9 wherein:

the refracting means includes two dispersyns, each dispersyn having a convex lens portion and a prism portion, the dispersyns being positioned between the image plane and the detection plane with the refraction angles of the prism portions being additive.

15. Apparatus according to claim 14 wherein:

the dispersyns are positioned between the image plane and the detection plane with the focal planes of the respective lens portions located respectively in the image plane and the detection plane.

16. A method of sensing the ratio of discrete wavelength bands in a portion of a colored field comprising:

forming an optical image of the portion of the colored field;

wavelength dispersive refracting the light from the optical image to form a refraction pattern of the colors in the field portion; and

detecting the intensity of two refraction pattern at the discrete wavelength bands.

17. The method of sensing according to claim 16 including:

comparing the intensities of the refraction pattern detected at the discrete wavelength bands.

18. The method of sensing according to claim 16 wherein:

the step of refracting includes refracting the light from the optical image successively through two prisms.

19. The method of sensing according to claim 18 wherein:

the step oF refracting additionally includes collimating the light passing between the two prisms.

20. The method of sensing according to claim 18 wherein:

the step of refracting additionally includes focussing the light from the optical image after successively refracting the light.

21. The method of sensing according to claim 16 wherein:

the step of forming a single image includes focussing an image of the earth horizon in an aperture plate.

22. The method of claim 21 for sensing the earth-horizon wherein:

the step of detecting includes selecting two discrete wavelength bands from a known combination of wavelength bands in the earth-horizon color profile.

23. The method of claim 22 for sensing the earth-horizon including:

referencing the ratio of the detected intensities with the known combination of the two wavelength bands in the earth-horizon.

24. The method of claim 22 wherein:

the step of selecting includes selecting the known combination from a stable combination of wavelength bands in the earth-horizon color profile.

25. The method of claim 24 wherein:

the step of selecting includes selecting the wavelength bands from the range extending from 340 nanometers to 490 nanometers.