Comparison of Scene Contrast Temperature in MWIR and LWIR

Abstract

Infrared imagers are used for many applications, these include target acquisition (both target search and target identification), threat warning, aircraft detection, and pilotage. Scene contrast temperature (SCT) describes the radiometric temperature associated with the dynamic range of an imager and is an important factor in the performance of all of these applications; it can be just as important in the performance of the sensor in an application. A few examples are: 1) a high scene contrast with clutter can increase the difficulty of target search, 2) a high scene contrast with image-based navigation can enhance the performance of location estimation, and 3) high scene contrast with mobility sensors can enhance the performance of a rotorcraft pilotage system.SCT is influenced by the range of radiance in the scene; the temperature and emissivity of each object in a scene determines this range. The range of radiance in a scene is dependent on the band in which the imager is sensitive because blackbody emission and emissivity both vary with spectrum. This work investigates the differences in SCT between the mid-wave infrared (MWIR) and long-wave infrared (LWIR) spectra in different environments and conditions. In daytime conditions, SCT is found to be greater in MWIR, and SCT is found to be higher in LWIR in nighttime conditions. Cloudy conditions during the daytime decrease SCT regardless of band, and rainy conditions are found to dramatically decrease SCT regardless of band. The effects of these spectral differences are extrapolated to imaging performance in a pilotage scenario.