Emissivity - Teledyne FLIR A68 Series User Manual

The IR absorbing material is thermally isolated by suspending it within a vacuum,
however it is still sensitive to changes in the camera body temperature.
When the camera operating temperature changes, the FLIR A68/A38 series shutterless
operation automatically compensates for the corresponding responsivity changes in the
microbolometer pixel array (non-uniformity correction (NUC)). The NUC is factory
calibrated across the working temperature range of the camera in free-running mode
at 30fps.
However, if the thermo-mechanical environment of the camera changes from the
factory calibration environment (for example, one side is exposed to heat or surface
mounting conditions) the sensor fixed pattern noise (FPN) correction can be enabled to
correct for these differences. If the camera temperature changes, or improved image
quality is required, FPN correction can be recalculated to ensure optimal response.

Emissivity

Emissivity is a measure of a material's ability to emit infrared energy. It is measured
on a scale from 0.00 to 1.00. Typically, the closer a material's emissivity rating is to
1.00 (that is. 100%), the more that material tends to absorb reflected or ambient
infrared energy and emit only its own infrared radiation. Most organic materials (for
example, plants and animals), have an emissivity rating of 0.95.
Substances with very low emissivity ratings, like highly polished metals, tend to be
very reflective of ambient infrared energy and less effective at emitting their own
electromagnetic waves. For example, an object with an emissivity of 0.5, half the
image pixel value is the result of the ambient temperature of the surrounding
environment being reflected. Therefore, an understanding of target environments
containing objects with emissivities of less than 0.7 is required to accurately analyze
image scenes.
24 • Introduction to Microbolometers FLIR A68/A38 Series IR Camera User's Manual