Range finding array camera

• US 5,200,793 A
• Filed: 02/20/1992
• Issued: 04/06/1993
• Est. Priority Date: 10/24/1990
• Status: Expired due to Fees

• Current Assignee: Kaman Aerospace Corporation (Kaman Corporation)
• Original Assignee: Kaman Aerospace Corporation (Kaman Corporation)
• Inventors: Pflibsen, Kent, Ulich, Bobby L.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US07/839,746
• Time in Patent Office: 411 Days
• Field of Search: 356/5, 356/152, 358/96
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/89 for mapping or imaging

Abstract

An electro-optical camera system is presented. In accordance with the present invention, a light source (e.g. laser) is modulated by an electro-optic modulator (such as a Pockels cell) and transmitted out through an optical system toward a static target scene. The light backscattered from the target scene is then focused by the same optics back through the same Pockels cell onto a two-dimensional array camera such as a CCD or a CID (charge-couple device or charge injection device). A computer determines the frequency modulation period of each pixel in the array as the frequency of the electro-optic modulator is varied. This period is inversely proportional to the range of the target in the direction defined by the pixel location. Thus, all three spatial coordinates (two angles and a range) of each target area sensed by each pixel are determined. The computer will display the array of range data using a suitable output device such as a video display unit or a printer.

Claims

1. An electro-optical camera system comprising:

light source means;

light beam modulating means in communication with said light source means for modulating light received from said light source means;

optical focusing means for directing said modulated light through a medium and at a target and for receiving light backscattered from said target and directing said backscattered light through said light beam modulating means wherein said light beam modulating means modulates said backscattered light;

photodetector means having a plurality of pixels, said photodetector means for receiving said backscattered light from said light beam modulating means and detecting at least three intensity levels associated with a period of modulation back through said light beam modulating means for each of said pixels;

frequency modulating means for varying the frequency of modulation of said light beam modulating means; and

computer means for determining the frequency modulation period at each of said pixels as the frequency of modulation of said light beam modulating means is varied wherein range data of the target is determined.

2. The camera of claim 1 including:

output means for displaying said range data.

3. The camera of claim 1 wherein:

said range data defines a three dimensional image.

4. The camera of claim 1 wherein:

said light source comprises a laser.

5. The camera of claim 1 including:

beamsplitter means;

wave plate means in communication with said beamsplitter means; and

wherein said beamsplitter means and said wave plate means are optically positioned between said light source means and said light beam modulating means and wherein light from said light source means is transmitted through said beamsplitter means and said wave plate means and wherein said backscattered light is transmitted through said beamsplitter means and said wave plate means to said photodetector means.

6. The camera of claim 5 wherein:

said wave plate means rotates the polarization of the transmitted light by 45 degrees on each pass.

7. The camera of claim 5 wherein:

said beamsplitter means comprises a polarizing beam splitter.

8. The camera of claim 5 including:

a beam expander optically positioned between said light source means and said beamsplitter means.

9. The camera of claim 5 including:

bandpass filter means optically positioned between said photodetector means and said beamsplitter means.

10. The camera of claim 1 wherein:

said light beam modulating means modulates light sinusoidally.

11. The camera of claim 1 wherein:

said photodetector means comprises a two dimensional array camera.

12. The camera of claim 1 wherein:

said optical focusing means comprises an objective lens.

13. The camera of claim 11 including:

video amplifier means for amplifying video signals from said two dimensional camera, said video amplifier means communicating with said photodetector means; and

video digitizer means for digitizing said amplified video signals, said video digitizer means communicating between said video amplifier means and said computer means.

14. The camera of claim 1 wherein:

said frequency modulating means comprises a variable radio frequency oscillator.

15. The camera of claim 26 wherein:

said computer means fits the illuminance of each pixel using the equation;

space="preserve" listing-type="equation"><

I.sub.w (i,j)>

=I.sub.O (i,j)+I.sub.l (i,j).cos(ω

.sub.RF.2Rn/c)(1)

where

I_w (i,j) is the instantaneous illuminance of the pixel at row i and column j in the said photodetector means;

<

I_w (i,j)>

is the time averaged value of I_w (i,j);

I_O (i,j) and I_l (i,j) are constants;

ω

_RF is the light beam modulating means frequency;

n is the index of refraction of the medium;

c is the speed of light in a vacuum; and

R is the range from the camera to the target.

16. The camera of claim 15 wherein:

said light beam modulating means modulates light received from said light source means by cos (ω

_RF t) and modulates backscattered light by cos (ω

_RF (t-τ

)) where;

τ

=2Rn/c; and

t=time in seconds;

17. The camera of claim 16 wherein:

said computer means applies a least squares curve fitting algorithm to previously measured pixel illuminance data for at least three known values of modulator frequency to determine Io, I_l and τ

.

18. The camera of claim 17 wherein:

each of said range values is determined by;

space="preserve" listing-type="equation">R(i,j)=(c/2n)τ

(i,j).

19. The camera of claim 1 wherein:

said light beam modulating means comprises electro-optic modulator.

20. The camera of claim 19 wherein:

said electro-optic modulator comprises a Pockels cell means.

21. The camera of claim 1 including:

light source beam splitter means optically positioned between said light source means and said light beam modulating means, said light source beam splitter means producing an array of beams for illuminating selected areas of a target scene.

26. The camera of claim 1 wherein:

said range data comprises a plurality of range values, each one of said range values corresponding to one of said pixels.

22. A method for providing range data of a target using an electro-optical camera system including the steps of:

generating a light beam;

modulating the light beam using a light beam modulator;

directing the modulating light beam through a medium and at a target;

receiving light backscattered from the target and directing the backscattered light back through said light beam modulator wherein the received backscattered light is modulated;

detecting at least three intensity levels associated with a period of modulation back through said light beam modulator for each of a plurality of pixels; and

converting said period associated with said intensity levels at each of said pixels into range data of the target.

23. The method of claim 22 including the step of:

converting said range data to a three dimensional image of the target.

24. An apparatus for providing range data of a target using an electro-optical camera system including:

means for generating a light beam;

means for modulating the light beam using a light beam modulator;

means for directing the modulated light beam through a medium and at a target;

means for receiving light backscattered from the target and directing the backscattered light back through said light beam modulator wherein the received backscattered light is modulated;

means for detecting at least three intensity levels associated with a period of modulation back through said light beam modulator for each of a plurality of pixels; and

means for converting said period associated with said intensity levels at each of said pixels into range data of the target.

25. The apparatus of claim 24 including:

means for converting said range data to a three dimensional image of the target.