KEYWORDS: Polarization, Polarimetry, Signal to noise ratio, Prototyping, Sensors, Chemical analysis, Humidity, Chemical detection, Coating, Titanium dioxide
We report on the development of a prototype polarization tag based system for detecting chemical vapors. The system primarily consists of two components, a chemically sensitive tag that experiences a change in its optical polarization properties when exposed to a specific chemical of interest, and an optical imaging polarimeter that is used to measure the polarization properties of the tags. Although the system concept could be extended to other chemicals, for the initial system prototype presented here the tags were developed to be sensitive to hydrogen fluoride (HF) vapors. HF is used in many industrial processes but is highly toxic and thus monitoring for its presence and concentration is often of interest for personnel and environmental safety. The tags are periodic multilayer structures that are produced using standard photolithographic processes. The polarimetric imager has been designed to measure the degree of linear polarization reflected from the tags in the short wave infrared. By monitoring the change in the reflected polarization signature from the tags, the polarimeter can be used to determine if the tag was exposed to HF gas. In this paper, a review of the system development effort and preliminary test results are presented and discussed, as well as our plan for future work.
Image registration is a digital image processing technique that takes two or more of images of a scene in different coordinate
systems and transforms them into a single coordinate system. Image registration is a necessary step in
many advanced image processing techniques, such as multi-frame super-resolution. For that reason, registration
accuracy is very crucial. While image registration is usually performed on images, one can perform the registration
using metric images as well. This paper will present registration methods and their accuracies for various noise
levels for the case of pure translational image motion. Registration techniques will be applied to the images
themselves as well as to phase congruency images, gradient images, and edge-detected images. This study will also
investigate registration of under-sampled images. Noise-free images are degraded using three types of noise:
additive Gaussian noise, fixed-pattern noise along the column direction, and a combination of these two. The
registration error is quantified for two registration algorithms with three different images as a function of the
signal-to-noise ratio. A test on the usefulness of the image registration and registration accuracy performed on the
intensity images of the Stokes imaging polarimeter. The Stokes images calculated before and after registration of
the intensity images are compared to each other to show the improvement.
Nighttime active SWIR imaging has resolution, size, weight, and power consumption advantages over passive MWIR and LWIR imagers for applications involving target identification. We propose that the target discrimination capability of active SWIR systems can be extended further by exerting polarization control over the illumination source and imager, i.e. through active polarization imaging. In this work, we construct a partial Mueller matrix imager and use laboratory derived signatures to uniquely identify target materials in outdoor scenes. This paper includes a description of the camera and laser systems as well as discussion of the reduction and analysis techniques used for material identification.
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