Comparison of the inversion periods for MidIR and LWIR polarimetric and conventional thermal imagery

We report the results of a diurnal study in which radiometrically calibrated polarimetric and conventional thermal imagery are recorded in the MidIR and LWIR to identify and compare the respective time periods in which minimum target contrast is achieved. The MidIR polarimetric sensor is based on a division-of-aperture approach and has a 640x512 InSb focal-plane array, while the LWIR polarimetric sensor uses a spinning achromatic retarder to perform the polarimetric filtering and has a 324x256 microbolometer focal-plane array. The images used in this study include the S0 and S1 Stokes images of a scene containing a military vehicle and the natural background. In addition, relevant meteorological parameters measured during the test period include air temperature, ambient loading in the LWIR, relative humidity, cloud cover, height, and density. The data shows that the chief factors affecting polarimetric contrast in both wavebands are the amount of thermal emission from the objects in the scene and the abundance of MidIR and LWIR sources in the optical background. In particular, it has been observed that the MidIR polarimetric contrast was positively correlated to the presence of MidIR sources in the optical background, while the LWIR polarimetric contrast was negatively correlated to the presence of LWIR sources in the optical background.