An algorithm of the Monte Carlo method is described which allows evaluation of the effective emissivities of isothermal and nonisothermal specular-diffuse black-body cavities for use in radiometry, photometry and optical pyrometry. The calculation provides estimates of normal spectral effective emissivity for black-body cavities, formed by cone surfaces and a cylinder. It does this for an isothermal cavity and for a cavity having an arbitrary variation of temperature along the cavity length.
The precision blackbody sources developed at the All-Russian Institute for Optical and Physical Measurements (Moscow, Russia) and their characteristics are analyzed. The precision high-temperature graphite blackbody BB22p, large-area high-temperature pyrolytic graphite blackbody BB3200pg, middle-temperature graphite blackbody BB2000, low-temperature blackbody BB300, and gallium fixed-point blackbody BB29gl and their characteristics are described.
An algorithm based on the Monte Carlo method is described that permits the precise calculation of radiant emission characteristics of nonisothermal blackbody cavities for use as standard sources in radiometry, photometry, and radiation thermometry. The algorithm is realized for convex axisymmetric specular-diffuse cavities formed by three conical surfaces. The numerical experiments provide estimates of normal effective emissivities of cylindrical blackbody cavities with flat or conical bottoms for various axisymmetric temperature distributions on the cavity walls.
Radiometry based on black bodies remains one of the fundamental fields of radiometry. Black bodies are widely used as standard sources in radiometry of noncoherent optical radiation from the ultraviolet to the far-infrared spectral regions. Outstanding progress in radiometry has been made in the last decade due to development of high-precision cryogenic radiometers, which have made it possible to decrease the measurement uncertainty to 0,01 %. New technology and optical physics call for significant improvement in the accuracy of black-body-based radiometry and the practical realization of spectral radiance and irradiance scales having an accuracy of 0,1 %. However, the accuracy of black-body-based radiometry is now limited by the accuracy of thermodynamic temperature measurements of a radiating cavity. For example, the uncertainty of spectral radiance and spectral irradiance scales is from 0,5 % to 1 % in the UV due to uncertainties in pyrometric measurements. The required uncertainty of modern black-body-based radiometry is about 0,1 %. This can be achieved by using the latest advances in the field of high-precision radiometric instrumentation, such as absolute radiometers, large-area high-temperature black bodies and synchrotrons.
Near-ambient-temperature black-body sources are routinely used for calibration 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 usually determined by reference to a measured temperature and a calculated effective emissivity. The temperature is measured with one or more contact thermometers positioned close to the emitting black-body surface. In this case traceability to the International System of Units (SI) is to the kelvin through the ITS-90. This paper describes an alternative, more direct method based on the use of absolutely calibrated filter radiometers. These filter radiometers form part of a new facility called AMBER (Absolute Measurements of Black-body Emitted Radiance) which has been designed to determine the radiance 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 µm) and a resolution of 0.001 % (0.3 mK). The facility obtains its traceability to the SI directly through radiometric standards in the form of a cryogenic radiometer rather than through the ITS-90.
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