Passive optical system for background suppression in starring imagers
First Claim
1. A passive optical system for background suppression in staring array imagers, said system comprising:
- a dual focus objective lens and polarizing means for providing a linearly polarized image in a first focal image plane and an opposite linearly polarized image in a second focal image plane;
a detector array positioned in said first focal image plane closest to said objective lens for receiving a sharp focused linearly polarized image of a high spatial frequency feature target and low spatial frequency background therein and an unsharp defocused opposite linearly polarized image in said second focal image plane which contains a blurred image of said high spatial frequency feature target and an image that contains a faithful reproduction of said low spatial frequency background as in said sharp focused linearly polarized image in said first focal image plane, said focused and defocused images received in each pixel site of said detector array;
difference sensing means for sensing said focused and defocused images at each pixel site to provide output signals proportional to the difference between said focused and defocused opposite linearly polarized images; and
means for electronically processing said output signals from each of said pixel sites to algebraically subtract said backgrounds and produce an enhanced contrast target signal for said staring array imager.
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Abstract
A dual focus objective lens and opposite linear polarizers associated therewith for providing a linearly polarized image at a first focal image plane and an opposite linearly polarized image at a second focal plane. A detector array is positioned at the first focal image plane which is closest to the objective lens. Each pixel site of the detector array has two halves with opposite polarities in each half wherein each half looks at opposite planes of polarization in the two image planes. One plane of polarization receives a focused linearly polarized image of the high spatial frequency target and low spatial frequency background and the other plane of polarization receives a slightly defocused image which contains a defocused image of the high spatial frequency target but a rather faithful reproduction of the low spatial frequency background. The two outputs from each half of the pixel sites are algebraically subtracted by processing electronics leaving a high contrast target image.
44 Citations
19 Claims
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1. A passive optical system for background suppression in staring array imagers, said system comprising:
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a dual focus objective lens and polarizing means for providing a linearly polarized image in a first focal image plane and an opposite linearly polarized image in a second focal image plane; a detector array positioned in said first focal image plane closest to said objective lens for receiving a sharp focused linearly polarized image of a high spatial frequency feature target and low spatial frequency background therein and an unsharp defocused opposite linearly polarized image in said second focal image plane which contains a blurred image of said high spatial frequency feature target and an image that contains a faithful reproduction of said low spatial frequency background as in said sharp focused linearly polarized image in said first focal image plane, said focused and defocused images received in each pixel site of said detector array; difference sensing means for sensing said focused and defocused images at each pixel site to provide output signals proportional to the difference between said focused and defocused opposite linearly polarized images; and means for electronically processing said output signals from each of said pixel sites to algebraically subtract said backgrounds and produce an enhanced contrast target signal for said staring array imager. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification