Evaluation of Blackbody Cavity Emissivity in the Infrared Using Total Integrated Scatter Measurements

Abstract

Deviations from ideal blackbody (BB) behavior can be characterized by a BB's effective emissivity. The cavity emissivity is most often obtained through a model, given a particular set of input parameters associated with the BB cavity geometry and surface optical properties. It can also be measured directly (radiance) or indirectly (reflectance). A study of BB cavity emissivity using the reflectance method is presented. Several types and designs of blackbody cavities, including those from fixedpoint and water bath BBs, using our infrared total integrated scatter (ITIS) instrument for emissivity evaluation are examined. The emissivity is characterized as a function of position on the output aperture, as well as a function of output angle. The measurements have revealed emissivity values, both significantly greater than, and in confirmation of, modeling predictions. For instance, the emissivities of three fixed point BB cavity designs were found to vary significantly despite modeling predictions in the design process of similar behavior. Also, other BB cavities that exhibited poor emissivity performance were re-painted and re-machined, in one case more than once, before the predicted performance was achieved.

NIST Radiance Temperature and Infrared Spectral Radiance Scales at Near-Ambient Temperatures

“…1, the effective emissivity of each cavity is determined in three independent ways. The first is based on reflectometric measurements (as reported at this conference [14]); the values obtained as summarized in Table 1 are found to be very close to the design targets as well as to the prediction of Monte Carlo [15] modeling, our second method. Finally, we have validated these emissivity values by comparing independent primary sources, as shown later in this article.…”

Characterizing the NRC Blackbody Sources for Radiation Thermometry from 150 °C to 962 °C

“…We are currently evaluating the feasibility of setting up a system at NRC for the direct determination of blackbody cavity emissivity, following the NIST methodology [11]. Because at least a portion of the apparent temperature differences may be due to the influence of changes in room temperature on the output of the RT1550, we will repeat the comparison measurements once we receive delivery of the RT1550 that we have purchased from NIST.…”

Design and Evaluation of Large-Aperture Gallium Fixed-Point Blackbody

“…The emissivity of the BB cavity was also evaluated using our infrared total integrated scatter (ITIS) system [10]. The ITIS system consists of infrared laser sources (10.6 µm wavelength in this case), a diffuse gold infrared integrating sphere, pyroelectric and MCT detectors, and a motion control system for manipulating both the .…”

“…The ring spike at a radius of about 6 mm can be explained by an imperfection in the machined cone. Additional details can be found in the companion paper of [10].…”