Polarization filtering for window self-emission due to aero-thermal heating

Abstract

In flight vehicles subject to extreme aero-thermal heating of the optical window, the optical system is configured to look through an off-axis segment of the optical window and a polarizer is positioned in the optical path between the off-axis segment and the detector. The polarizer comprises at least one filter pixel that imparts a linear polarization of a certain angular value to filter the incident radiation as a function of its polarization. In the case of a sheet polarizer, the entire polarizer is aligned to the plane of incidence. The sheet polarizer preferentially filters the target radiation to increase the SNR at the detector. In the case of a microgrid polarizer, at least one and preferably multiple filter pixels in each sub-array aligned to the plane of incidence. The microgrid polarizer can produce data products including a radiance image, an AoLP image and a DoLP image, only the AoLP image removes the self-emitted window radiance and an gradient caused by non-uniform aero-thermal heating.