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21 May 2014 Spatial calibration of full stokes polarization imaging camera
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Objective and background: We present a new method for the calibration of Bossa Nova Technologies’ full Stokes, passive polarization imaging camera SALSA. The SALSA camera is a Division of Time Imaging Polarimeter. It uses custom made Ferroelectric Liquid Crystals mounted directly in front of the camera’s CCD. Regular calibration process based on Data Reduction Matrix calculation assumes a perfect spatial uniformity of the FLC. However, alignment of FLC molecules can be disturbed by external constraints like mechanical stress from fixture, temperature variations and humidity. This disarray of the FLC molecules alignment appears as spatial non-uniformity. With typical DRM condition numbers of 2 to 5, the influence on DOLP and DOCP variations over the field of view can get up to 10%. Spatial nonuniformity of commercially available FLC products is the limiting factor for achieving reliable performances over the whole camera’s field of view. We developed a field calibration technique based on mapping the CCD into areas of interest, then applying the DRM calculations on those individual areas. Results: First, we provide general background of the SALSA camera’s technology, its performances and limitations. Detailed analysis of commercially available FLCs is described. Particularly, the spatial non uniformity influence on the Stokes parameters. Then, the new calibration technique is presented. Several configurations and parameters are tested: even division of the CCD into square-shaped regions, the number of regions, adaptive regions. Finally, the spatial DRM “stitching” process is described, especially for live calculation and display of Stokes parameters.
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M. Vedel, S. Breugnot, and N. Lechocinski "Spatial calibration of full stokes polarization imaging camera", Proc. SPIE 9099, Polarization: Measurement, Analysis, and Remote Sensing XI, 90990I (21 May 2014);

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