Setting the correct emissivity

Appendix C is a listing of various targets and their approximate generic emissivities. Emissivities are shown for various temperatures and in several spectral bands. Where not otherwise indicated, temperatures should be assumed to be 25°C. 

These values can be used as a guide when absolute temperature values are not critical. When measurement accuracy is important, however, it is always better to directly determine the actual effective emissivity of the surface to be measured using the actual instrument to be used in the measurement. This is because emissivity varies with surface characteristics and measurement spectral band, and will often vary among samples of the same material. 

Several methods may be used to quickly estimate target effective emissivity. The following steps outline one way to determine the emissivity setting needed for a particular target material using the instrument intended to be used for the measurement  

Prepare a sample of the material large enough to contain several spot sizes or IFOVs of the instrument. A 10 cm x 10 cm (4 in. x 4 in.) sample is a good choice. 

Spray one half of the target sample with flat black (light absorbing) paint, or cover it with black masking tape or some other substance of known high emissivity. 

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