Comparison of Scene Contrast Temperature in MWIR and LWIR

One of the primary activities in emissive infrared imager design is the trade on whether to use midwave infrared (MWIR) or longwave infrared (LWIR) in the application. Applications include target acquisition (both target search and target identification), threat warning, aircraft detection, and pilotage. There has been a great deal of work in the characterization of MWIR versus LWIR target signatures. There has been much less work in the characterization of scene (sometimes called background) contrast. The scene contrast of the background can be just as important in the performance of the sensor in an application. A few examples are: 1) a high scene contrast with high clutter contrast can make target search much more difficult, 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 flying performance of a rotorcraft pilotage system. This paper discusses the differences observed in scene contrast between mid-wave infrared (MWIR) and long-wave infrared (LWIR) bands. This provides a scene contrast characterization for emissive infrared applications. Radiometrically calibrated imagery is acquired with MWIR and LWIR cameras in various environments and the measured MWIR and LWIR scene contrast is compared. The radiometric comparison is performed in terms of the standard deviation of the scene equivalent blackbody temperature. Comparisons are provided under different conditions such as rural versus urban and day versus night. This comparison enables the infrared system designer with the means to perform detailed engineering trades.