Emissivity measurement and temperature correction accuracy considerations

Extraction of temperatures or temperature differences with thermography is not possible without knowledge of the target emissivity. As the technology of thermography evolves, many applications from predictive maintenance through R&D projects have increasingly stringent requirements for quality temperature measurement. Today's IR cameras and software can correct for target emissivity variations on a point-by-point basis or over the entire image. One problem is how to measure emissivity, and how emissivity measurement uncertainties propagate to temperature uncertainties. This paper discusses emissivity measurement techniques, why table values are often not valid for a particular IR camera (why you must measure emissivity) and how emissivity measurement accuracy affects temperature measurement accuracy (error budget for opaque targets).