Comparison of the Inversion Periods for Mid-wave IR (MidIR) and Long- wave IR (LWIR) Polarimetric and Conventional Thermal Imagery

摘要

We report the results of a diurnal study that recorded radiometrically calibrated polarimetric and conventional thermal imagery in the mid-wave IR (MidIR) and long-wave IR (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 640 512 indium antimonide (InSb) focal-plane array (FPA), while the LWIR polarimetric sensor uses a spinning achromatic retarder to perform polarimetric filtering and has a 324 x 256 microbolometer FPA. The images used in this study include the S0 and S1 Stokes images of a scene containing a military vehicle and the natural background. 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 show 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, we 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.