Active thermal imaging and passive thermal imaging are two distinct infrared thermal imaging technologies, differing in energy source adoption and operating principles.

An active thermal imaging system generally requires an external energy source, such as an infrared laser or other light sources, to stimulate the target surface and generate heat.

The system measures temperature variations on the target surface induced by external excitation. After being stimulated, the surface temperature of the target rises due to energy absorption, generating a thermal image that displays the contour and temperature distribution of the object.

Active thermal imaging is commonly deployed for target detection under low-light conditions, such as nighttime and dimly lit scenarios.

Passive thermal imaging requires no external energy source. Instead, it detects inherent infrared radiation naturally emitted by the target itself.

Temperature discrepancies across an object lead to differences in its emitted infrared radiation. A passive thermal imaging system captures the intensity and spatial distribution of such infrared radiation to construct a thermal map that reflects the object’s temperature profile.

Widely adopted in night vision devices, search & rescue operations, surveillance and military sectors, passive thermal imaging operates without supplementary lighting, making it suitable for dim environments or total darkness.

In short, active thermal imaging relies on an external energy source for operation, while passive thermal imaging works based on intrinsic thermal radiation emitted by the target object.