A survey of infrared polarization in the outdoors

This paper provides a summary of the principles that combine to create the infrared polarization signature of an object viewed in the outdoor environment. The primary variables discussed here include polarized emission and reflection from the source (object of interest). Because the observed polarization signature arises from a combination of mutually orthogonally polarized emitted and reflected radiance components, the background radiance is an important variable to consider in many infrared imaging situations. Examples are shown of polarization spectra calculated for a smooth dielectric surface viewed under atmospheric conditions ranging clear and dry to cloudy. As long as the object of interest is radiometrically warmer than the background (sky in this case), the observed radiance is partially p-polarized, but the degree of polarization varies with the magnitude of the reflected radiance.