Understanding Infrared Thermography Reading 7 Part 2 of 2.pdf

The reference emitter technique works well when the target is at a different
temperature than the background, such as in the case of a steam inlet valve
whose body is at system operating temperature, while the applied emissivity
reference is at the same temperature as the target.
The reflective emissivity technique works well for smooth surfaces such as an
electrical connection. The reflective emissivity technique is independent of
target temperature, although the temperature of the target must remain
constant throughout the measurement.
A third, field-type method for estimating the effective emissivity of a specific
target under specific conditions, is described in Section 3.3.3 and is illustrated
in Appendix C, Plate 5.
Charlie Chong/ Fion Zhang