An infrared target and background projection system.

Abstract

A major difficulty in determining how well an infrared sensor will perform under actual operating conditions is that testing is often unfeasible due to expense and destructive nature of the tests. These devices are generally tested in a laboratory using a simulator to represent the target. In presenting a scenario to a sensor, there are three distinct areas which must be addressed--the optical system which projects the scene to the detector, the target simulator, and the background simulator. It was determined that the optical system currently in use projected an acceptable scene except in those scenarios where the target was at high altitude against a low radiance background. The mirrors act as room temperature graybody sources which combine to introduce enough unwanted radiation into the projected beam to significantly increase the apparent background temperature. Several single mirror collimators were designed for use in these situations. In designing target models, an important consideration is how the radiation seen by the sensor changes as the target-sensor separation distance changes. At long range, the target appears to the sensor to be a "point" source with radiation that is a sum of all the component radiances of the target. A procedure for representing long-range targets as an equivalent blackbody of equal in-band radiation is described. As the target-sensor distances closes, the individual temperature regions become resolved at the detector. A multi-engine simulator was designed which, when used with the JAWS apparatus, will project the appearance of hot engines and the cooler fuselage. The two most significants improvements designed deal with the problem of projecting the background. The first design is a coldsource which allows projection of colder than room temperature backgrounds to the detector. This is done by limiting the amount of room radiation which can enter the optical train to that necessary to achieve the lower temperature. The next improvement was the use of large sheets of polyethylene of varying thickness to attenuate the radiation projected. By using large sheets, the entire background can be moved, eliminating the frame rate problems inherent in most projector technologies.