Mitigation of image artifacts in LWIR microgrid polarimeter images
2007
Microgrid polarimeters, also known as division of focal plane (DoFP) polarimeters, are composed of an integrated
array of micropolarizing elements that immediately precedes the FPA. The result of the DoFP device is that
neighboring pixels sense different polarization states. The measurements made at each pixel can be combined to
estimate the Stokes vector at every reconstruction point in a scene. DoFP devices have the advantage that they
are mechanically rugged and inherently optically aligned. However, they suffer from the severe disadvantage
that the neighboring pixels that make up the Stokes vector estimates have different instantaneous fields of view
(IFOV). This IFOV error leads to spatial differencing that causes false polarization signatures, especially in
regions of the image where the scene changes rapidly in space. Furthermore, when the polarimeter is operating
in the LWIR, the FPA has inherent response problems such as nonuniformity and dead pixels that make the
false polarization problem that much worse. In this paper, we present methods that use spatial information from
the scene to mitigate two of the biggest problems that confront DoFP devices. The first is a polarimetric dead
pixel replacement (DPR) scheme, and the second is a reconstruction method that chooses the most appropriate
polarimetric interpolation scheme for each particular pixel in the image based on the scene properties. We have
found that these two methods can greatly improve both the visual appearance of polarization products as well
as the accuracy of the polarization estimates, and can be implemented with minimal computational cost.
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