Polarization imaging focuses on degrees of linear polarization (DoLP) and angles of polarization (AoP). This paper introduces a polarization imaging set which employs a LWIR polarization imaging system along with a set of cooperative self-made target panels to acquire polarized radiation. The sampling flowchart is given and the process of polarization acquisition demonstrated. The experiment shows that larger the observation angle, stronger DoLP signal and weaker radiance lowers the contrast of polarization image.
Equivalent extinction ratio and polarization orientation are two significant parameters representing the performance of a polarized pixel in an integrated micropolarizer array camera. With manufacturing and integrating errors of the micropolarizer array, equivalent extinction ratios are nonuniform and polarization orientations of polarized pixels deviate from their nominal values. Measuring the equivalent extinction ratio and the polarization orientation of each polarized pixel by rotating a polarizer at a tiny step is extremely time-consuming and even inaccurate. Therefore, this paper proposes a calibration method for the equivalent extinction ratio and the polarization orientation of each polarized pixel. Its principle is derived by theorizing the relationship between an orientation of a linearly polarized incident light and its digital output of a polarized pixel. In experiment, this derived principle is applied to an integrated micropolarizer array camera. Experimental result proves that calibrated equivalent extinction ratios generally vary from 4.5 to 10, with a mean of 7.939 and a standard variation of 1.053.
Integrating microgrid polarimeters on focal plane array (FPA) of an infrared detector causes non-uniformity of polarization response. In order to reduce the effect of polarization non-uniformity, this paper constructs an experimental setup for capturing raw flat-field images and proposes a procedure for acquiring non-uniform calibration (NUC) matrix and calibrating raw polarization images. The proposed procedure takes the incident radiation as a polarization vector and offers a calibration matrix for each pixel. Both our matrix calibration and two-point calibration are applied to our mid-wavelength infrared (MWIR) polarization imaging system with integrated microgrid polarimeters. Compared with two point calibration, our matrix calibration reduces non-uniformity by 30~40% under condition of flat-field data test with polarization. The ourdoor scene observation experiment indicates that our calibration can effectively reduce polarization non-uniformity and improve the image quality of our MWIR polarization imaging system.