Split-field and internally filtered imaging polorimeter development and testing
Heisey, Peter H.
Cooper, Alfred W.
Crittenden, Eugene C.
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A 'split-field' infrared optical system has been designed and constructed to provide simultaneous image pairs in a single frame of an infrared (IR) imager, differing only in the direction of linear polarization. The optical train is afocal, allowing its use with a variety of infrared imaging devices. The system can operate in both long-wave IR (8-12 micrometers) and mid-wave IR (3-5 micrometers) with interchangeable polarizing splitter plates. previous work at the Naval Academic Center for Infrared Technology (NACIT) at the Naval Postgraduate School has demonstrated that significant image improvement in infrared image contrast can be obtained by use of polarization filtering, especially for targets at sea through suppression of polarized sea background emission in the long wave, or of polarized reflection in the midwave. That work utilized digital subtraction of sequential image pairs with orthogonal polarizations, but suffered from inability to obtain simultaneous images and also from problems due to reflections from external polarization filters. Both of these problems are eliminated with the new split-field technique. Preliminary tests of this system with an AGA-780 imager were carried out in a field experiment using an Arleigh Burke DDG class ship as target at varying distances at sea. For comparison, images were also taken in successive pairs in time with the AGA-780 viewing the scene directly ( without the split-field adjunct) with interchangeable internal polarizing filters in a rotatable filter wheel. Subjective and numerical analysis of the data from the field experiment demonstrated good image quality and contrast improvement, and potential for future utility
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