Measuring Cold Object Temperatures Using Infrared Cameras

For cold targets a LWIR or VLWIR camera is superior to MWIR. Data and calculations in support of this position are given in this paper.

Many infrared scenes involve temperatures that fall below the temperatures measured in typical test configurations. Some examples are described below, which demonstrates the importance of cold temperature targets.

Winter or Arctic Scenes - Cold weather infrared scenes have been modeled by NVESD as part of their key 3rd Gen FLIR initiative.

Upper Atmospheric Targets - In the upper atmosphere, including altitudes common for aircraft, backgrounds are cold and targets can attain like temperatures.

Cold Sky - Infrared imagery is important for tactical missile imaging systems and for imaging of toxic fumes; and such imagery must contend with the cold atmosphere.

Long Ranges - When measuring distant targets of known temperature, a decrease in the apparent temperature of the target as a function of distance is noticeable. This effect is caused by absorption of infrared light by the air between the camera and the target, the so-called air path. The effect of the air path is particularly noticeable with infrared cameras operating in the MWIR band. This is because carbon dioxide in the atmosphere absorbs infrared light strongly in the 4.2 to 4.4 micron band.

Low Emissivity - Targets with low emissivity, which includes aerospace metals such as aluminum and titanium, exhibit low apparent temperatures, and further, can reflect the cold sky and give apparent temperatures much lower than the true value.