Two-color infrared full-Stokes imaging polarimeter development

Infrared polarization imaging shows great potential to improve system performance in a variety of tactical applications. Previous IR polarization imaging has highlighted the possible utility of polarization as a way to easily separate manmade objects from natural backgrounds. If the polarization signatures are indeed robust across a wide variety of tactical imaging conditions, polarization stands to significantly improve our ability to automatically detect and cue targets. Man-in-the-loop applications stand to benefit as well: in search scenarios both the time to detect and false alarm rate could be substantially reduced. The possible benefits of polarization imaging require a more complete study of target and background phenomenology before polarization imaging can seriously be considered as a candidate tactical sensor. In order to accurately quantify the target and background signatures and to address questions such as optimal waveband and choice of Stokes vector components sensed, the U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) is developing a breadboard infrared (IR) polarization imaging capability. This paper covers the sensor design, choice of polarization elements, problems with their fabrication, alignment, calibration and use. Different polarization sensing approaches are compared and their tactical utility is addressed. Sample imagery is then presented.