Determination of Emissivity
With each lot of AERI Blackbody cavities that are painted (with Chemglaze Z306 flat black), six witness samples are coated at the same time. These samples are cured along with the cavities. The witness samples are painted in a fixture that mimics the geometry of the blackbody cone.
The witness samples are sent to Labsphere for reflectance measurements, from 2 to 17µ. Labsphere maintains reflectance traceability back to the National Physical Laboratory in England. Emissivity is (1-Reflectance). Labsphere measures the absolute reflectance of the witness samples to better than ±1%. This translates to a cavity emissivy uncertainty of ±0.0008.
Another ±1% uncertainty has been added to account for the variation in the application of the paint. This accounts for variations within a blackbody and between blackbody and witness samples. This value was chosen based on experience.
The cavity enhancement factor for the AERI Blackbodies is calculated to be 12.76, using the analysis of C. L. Sydnor which is presented in JPL Technical Report No. 32-1463. An uncertainty of 10% has been added to this factor. This translates to a cavity emissivity uncertainty of ±0.0004.
The AERI Blackbody Cavity emissivity is determined to be 0.996.