Infrared radiometers and spectrometers generally use blackbodies for calibration, and with the high accuracy needs of
upcoming missions, blackbodies capable of meeting strict accuracy requirements are needed. One such mission, the
NASA climate science mission Climate Absolute Radiance and Refractivity Observatory (CLARREO), which will
measure Earth's emitted spectral radiance from orbit, has an absolute accuracy requirement of 0.1 K (3σ) at 220 K over
most of the thermal infrared. Space Dynamics Laboratory (SDL) has a blackbody design capable of meeting strict
modern accuracy requirements. This design is relatively simple to build, was developed for use on the ground or onorbit,
and is readily scalable for aperture size and required performance. These-high accuracy blackbodies are currently
in use as a ground calibration unit and with a high-altitude balloon instrument. SDL is currently building a prototype
blackbody to demonstrate the ability to achieve very high accuracy, and we expect it to have emissivity of ~0.9999 from
1.5 to 50 μm, temperature uncertainties of ~25 mK, and radiance uncertainties of ~10 mK due to temperature gradients.
The high emissivity and low thermal gradient uncertainties are achieved through cavity design, while the low
temperature uncertainty is attained by including phase change materials such as mercury, gallium, and water in the
blackbody. Blackbody temperature sensors are calibrated at the melt points of these materials, which are determined by
heating through their melt point. This allows absolute temperature calibration traceable to the SI temperature scale.