INFRARED RADIATION

Table 6-1.-Characteristics of IR Radiation the target and the FLIR attenuates and blurs the target signal. The FLIR operator aims the limited field of view FLIR to search the scene for targets, using a search pattern and clues, such as radar targets or laser designators. The FLIR system uses thermal sensitivity, image sharpness, spectral response, contrast, and magnifi- cation to produce a visual image of the thermal scene. The operator uses training, experience, and image interpretation skills to detect and identify targets. INFRARED RADIATION The atmosphere is a poor transmitter of infrared radiation because of the absorption properties of CO2 (carbon dioxide), H2O (water), and 03 (ozone). Infrared radiation is broken into four regions, as can be seen in table 6-1. Only the first three are used with this system. Figure 6-3 shows the transmission spectrum of the atmosphere. You can see that the best transmission is between 3 µm and 5 pm, and between 8 µm and 14 µm. The range between these wavelengths is known as a window. Infrared imaging devices are designed to operate in one of these two windows, usually the 8 µm to 14 µm window. Infrared Radiation Sources All matter whose temperature is above -273°C (absolute zero) emits IR radiation. The amount of the radiation emitted is a function of heat. Theoretically, a perfect emitter is a black body with an emissivity of 1. Realistically, the best emissivity is somewhere around 0.98. The emissivity of various objects is measured on a scale of 0 to 1. Figure 6-3.-Transmission spectrum of the atmosphere. 6-3