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For infrared calibrations beyond 2 pm, DoD support enabled NIST to build the Low Background Infrared (LBIR) facility, consisting of two cryogenic chambers and two absolute cryogenic radiometers, for the calibrations of cryogenic blackbodies from facilities of DoD and its missile defense contractors [31,32].
The question was simple enough to answer, as blackbodies are always constructed from good absorbers.
At NIST these blackbodies are used to calibrate standard platinum resistance thermometers (SPRTs) to cover the temperature range from 15 [degrees]C to 170 [degrees]C and standard gold-platinum thermocouples to cover the range from 400 [degrees]C to 900 [degrees]C.
Laboratory blackbodies are specialized objects always made from relatively good emitters of radiation over the frequency range of interest, as well illustrated by the facts (see references within [8-12]).
The calibration methods used by the participating organizations included blackbodies or radiating panels to irradiate the sensors, and the heat-flux at the sensor was calculated by radiometric principles or reference standard calorimeters.
Max Planck recognized that blackbodies were complex devices, as the data provided for his analysis had been obtained by some of the premier experimentalists in Germany [11-13].
Since laboratory blackbodies must be Lambertian emitters [11, p.
That is why he advocated that optically thick gases could emit as blackbodies.
Conversely, it is known that laboratory blackbodies constructed from graphite, or soot (carbon black, lampblack), can reach rather high emissivities over certain frequencies [18-21].
The LLT facility, with variable-temperature water- and oil-bath blackbodies and cesium and sodium heat-pipe blackbodies, has been developed for calibration of pyrometers and sources in the temperature range from 288 K to 1223 K (140-142).
One could compute the spectral radiance of these blackbodies, but only as well as you knew what their temperatures actual were.
Experimental blackbodies of the 19th century were manufactured using either graphite, or soot [7], precisely because such carbon surfaces were not transparent and exceeded all others in being devoid of reflection.