What is the difference between active IR and thermal imaging?

Active IR systems use short wavelength infrared light to illuminate an area of interest. Some of the infrared energy is reflected back to a camera and interpreted to generate an image. Thermal imaging systems use mid- or long wavelength IR energy. Thermal imagers are passive, and only sense differences in heat. These heat signatures (usually black (cold) and white (hot)) are then displayed on a monitor. Because thermal imagers operate in longer infrared wavelength regions than active IR, they do not see reflected light, and are therefore not affected by oncoming headlights, smoke, haze, dust, etc.

Keywords: Tau2, Quark2, Boson, Muon, Lepton, Tau SWIR, PathFindIR II