Radiant energy – Infrared-to-visible imaging – Including means for scanning field of view
Reexamination Certificate
1999-10-12
2001-10-30
Dang, Hung Xuan (Department: 2873)
Radiant energy
Infrared-to-visible imaging
Including means for scanning field of view
C250S330000, C250S335000
Reexamination Certificate
active
06310345
ABSTRACT:
BACKGROUND OF THE INVENTION
Infrared polarimetry is a technique for acquiring and processing emissive and scattered radiation in the infrared bands and, as such, has applications in astronomy, space exploration, materials characterization, plasma diagnostics, biological measurements and characterization of military targets. In the military, exemplar applications of polarization information occur in enhancement of the discrimination of targets from clutter and enhancement of feature identification. These enhancements reduce false alarm rates in both human and automatic target recognition and enable improvements in target classification, counter-measure rejection and defeat of camouflage.
However, infrared polarimetry is still in a rather immature state of development. Hence it is not used in any existing or planned military system, even though some research has indicated that infrared polarization imagery can provide surface orientation information, distinction between flat plates and cylinders and discrimination between tanks and heated flat plate decoys, all based on differences in polarization signatures of the various items. It has been discovered further that polarization imagery is possible with relatively cool objects.
Much of the difficulties encountered both in military and peaceful applications of the nascent infrared polarimetry are due to significant limitations in the extant instrumentation. One such limitation is the polarization aberrations introduced by the instrument itself. In addition, optical components of the instruments introduce some change in the polarization state of the infrared radiation as the radiation propagates through the instrument. Optical coatings, scattering and birefringence effects also may cause unintended changes in the polarization state that perturb the intended polarization changes wrought about by the polarizers and retarders.
SUMMARY OF THE INVENTION
The polarization-resolving infrared imager for filtering and processing polarized infrared radiation as described in detail hereinbelow utilizes the detector configurations of either a first-generation infrared imaging detector device having 60 (rows)×1 (column) of detector elements (pixels) or a second-generation infrared imaging detector device having at least 240 (rows)×4 (columns) of detector elements (pixels).
In the embodiment using a first-generation infrared imaging detector device, prior to being incident on the detector device, the incoming infrared radiation impinges on a polarization filter that is stepped through three polarization positions (e.g. 0, 45 and 90 degrees) to separate the radiation into portions that are, respectively, at 0, 45 and 90 degrees of polarized radiation. The polarization filter, which is physically separate from the detector device, transmits the three portions of polarized radiation to be detected by the detector device and processed by suitable video electronics to produce various image combinations.
In the embodiment using a second-generation infrared imaging detector device which is the preferred embodiment of the invention, polarization-filtering wire grids are integrated onto the detector elements. Three of the four detector elements in each row of the second-generation infrared imaging detector device have coupled thereto polarization elements to filter or select radiation portions of horizontal polarization, vertical polarization and 45-degree polarization, respectively. The fourth detector element in the row remains clear to detect the total infrared radiation with no polarization distinction. This pattern of selecting the three polarization orientations is repeated at each succeeding row of detector elements. Using a scan mirror of sufficient sweep in conjunction with the detector device and the polarization-filtering grid results in one frame of the scene representing horizontal polarization, one frame representing vertical polarization and one frame representing 45-degree polarization, all with one sweep of the scan mirror in real-time scenario. This provides near simultaneous infrared scene information at different polarizations.
REFERENCES:
patent: 5369276 (1994-11-01), Antesberger
An article entitled “Infrared Polarimetric Sensors for Missile Weapon Systems” by Huey F. Anderson, presented at the “Workshop on Infrared and Millimeter Wave Polarimetry” and published in Apr. 1996 in the proceedings as Special Report RD-MG-96-8. This article was also made releasable to the NATO.
Anderson Huey F.
Pittman William C.
Westrich Richard G.
Bush Freddie M.
Chang Hay Kyung
Dang Hung Xuan
The United States of America as represented by the Secretary of
Tischer Arthur H.
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