SWIR

SWIR — short-wave infrared — covers wavelengths from about 0.9 to 1.7 micrometers, just beyond what the eye and standard silicon cameras can see. Unlike thermal imaging, which detects heat that objects emit, SWIR works mostly with reflected light: at night, natural radiance from the upper atmosphere, called airglow, floods the SWIR band with photons that reflect off terrain and vehicles much like moonlight in the visible band. The result is an image that looks like a black-and-white photograph of the scene rather than a heat map, with recognizable shadows and textures.

The band has tactical properties that drive adoption. Many laser designators, target markers, and covert illuminators operate at SWIR wavelengths invisible to image intensifiers and the eye, so SWIR cameras are the sensor that sees them. SWIR also penetrates haze and smoke better than visible light, and it makes certain materials — camouflage paints, fabrics, disturbed earth — look conspicuously different from their visible appearance.

The enabling technology is the indium-gallium-arsenide focal plane array, historically expensive but falling in price as commercial machine-vision demand grows. In defense use, SWIR now appears in targeting pods, gimbals, and helmet systems, typically fused with thermal and intensified channels rather than replacing them.