Absolute measurements of black-body emitted radiance

Near-ambient-temperature black-body sources are routinely used for calibrat ion in terms of radiance of a variety of infrared instruments such as those used in remote sensing and thermal imaging. The black-body radiance is usu ally determined by reference to a measured temperature and a calculated eff ective emissivity. The temperature is measured with one or more contact the rmometers positioned close to the emitting black-body surface. In this case traceability to the International System of Units (SI) is to the kelvin th rough the ITS-90. This paper describes an alternative, more direct method b ased on the use of absolutely calibrated filter radiometers. These filter r adiometers form part of a new facility called AMBER (Absolute Measurements of Black-body Emitted Radiance) which has been designed to determine the ra diance of an ambient-temperature black body with an uncertainty of about 0. 1% (which corresponds to a radiance temperature difference of 25 mK at 4 mu m) and a resolution of 0.001% (0.3 mK). The facility obtains its traceabil ity to the SI directly through radiometric standards in the form of a cryog enic radiometer rather than through the ITS-90.