Image multispectral sensing

• US 5,479,258 A
• Filed: 10/12/1994
• Issued: 12/26/1995
• Est. Priority Date: 12/28/1992
• Status: Expired due to Term

• Current Assignee: Pacific Advanced Technology, Inc. (PAT Industries, Inc.)
• Original Assignee: PAT Industries
• Inventors: Morris, George M., Hinnrichs, Michele
• Primary Examiner(s): McGraw, Vincent P.
• Assistant Examiner(s): HANTIS, KAREN
• Application Number:
  US08/320,776
• Time in Patent Office: 440 Days
• Field of Search: 356/326, 356/328, 356/330-334, 356/300, 250/226
• US Class Current: 356/326
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/2823 Imaging spectrometer

Abstract

A spectrophotometer useful for spectral analysis of light emanating from one or more targets within an image is described. The apparatus comprises a diffractive lens having an optical axis, a planar array of photodetector elements (pixels), a means for changing the distance between the photodetector array and the diffractive lens along the optical axis and a signal processor. If either the photodetector array or the lens is moved along the optical axis, different wavelengths of light from each target within the image come into and out of focus on particular photodetector elements in the plane of the photodetector array generating sequential images corresponding to different wavelengths. By tracking each pixel'"'"'s output in the photodetector array as a function of lens position relative to the photodetector array, the spectral composition of each target within the image is generated. Background (non-target) radiation will generally appear as a broad spectrum while light emanating from targets will have a fine spectral signature which is easily differentiated from the background. The sequential images from the photodetector array are processed so that only discrete spectral components are retained for each photodetector array position. Each target'"'"'s spectrum is built up from sequential images and may be compared with a library of known target signatures for purposes of recognition.

Claims

1. An apparatus for measuring the spectral composition of an image comprising:

(a) a diffractive element for dispersing spectral components of an image and directing said spectral components into a volume having a cross-sectional area A and a length L;

(b) a photodetector array comprising a planar surface having a plurality of discrete light detectors deployed thereupon, said photodetector array having an area substantially equal to A; and

(c) means for changing the distance between said diffractive element with respect to said photodetector array in the direction of L;

(d) means for measuring and storing the distance between said diffractive element and said photodetector array;

(e) means for measuring and storing the intensity of spectral components of the image which impinge upon said photodetector array;

and wherein said spectral composition of said image is determined by computing the intensity of the spectral components impinging upon said photodetector array as a function of the distance between the diffractive element and the photodetector array.

2. The apparatus of claim 1 wherein said diffractive element is a diffractive lens.

3. The apparatus of claim 1 wherein said diffractive element is a diffractive mirror.