Melting/freezing curves are studied for the single-component Ga and bimetallic eutectic alloys Ga–In, Ga–Sn, Ga–Zn and Ga–Al in small-size cells. These phase-transition studies were conducted at VNIIOFI and SDL in order to design small-size fixed-point devices for metrological monitoring of temperature sensors on autonomous platforms. Our prime objective is to develop technology to improve the long-term performance of in-flight blackbody calibration sources of space-borne radiometers. The repeatability of the melting temperature of Ga and the eutectic melting temperatures of Ga–In, Ga–Sn and Ga–Zn fixed points were studied. Our results show that small cells containing Ga and some Ga-based eutectic alloys can be used as melting fixed-point standards.
High-temperature fixed-point blackbodies based on Re-C and TiC-C metal-carbon eutectic alloys are being investigated for use as radiance and irradiance sources for precise measurements in radiometry, photometry and radiation thermometry above the conventionally assigned values of temperatures on the ITS-90 scale. Graphite crucibles having inner diameters varying between 4 mm and 10 mm were used to prepare the metal-carbon and metal carbide-carbon eutectics; the cells were designed and manufactured at VNIIOFI, Russia using high-purity materials.The melting and solidification temperatures of the cells were measured. Their reproducibility was investigated. The radiance reproducibility of the Re-C and TiC-C fixed points was found to be from 0.01% to 0.03% at 650 nm wavelength depending on the cell. Preliminary investigations of ZrC-C fixed-point reproducibility have been carried out. The radiance of all measured cells agreed at the solidification point within 0.02%.
The international Global Earth Observation System of Systems is at its initial stage. We present some general information about the program and formulate the task of ensuring the uniformity of radiometric measurements to be conducted by all the participating national systems. Methods of solving the task are suggested on the basis of the wide application of standard sources that use phase transition of eutectic alloys and pure metals as well as with the help of improved ground calibration facilities.
An intercomparison of radiation temperature measurements was performed at VNIIOFI during October 2000 using a pyrolytic graphite blackbody operating over the temperature range from 1600 K to 3300 K. A pyrometer and two photometers from VNIIOFI, a pyrometer and four broadband glass filter detectors from PTB, and two narrow-band interference filter based radiometers and a broadband glass filter radiometer from NPL were used to perform the temperature measurements in either radiance or irradiance mode. Across almost the entire temperature range the VNIIOFI, NPL and PTB instruments showed results within the combined standard measurement uncertainties.
Utilization of Earth remote-sensing data to solve scientific and engineering problems within such fields as meteorology and climatology requires precise radiometric calibration of space-borne instruments. High-accuracy calibration equipment in the thermal-IR wavelength range ought to be combined during calibration procedures with the simulation of environmental conditions for space orbit (high vacuum, medium background). For more than 35 years, VNIIOFI has developed and manufactured standard radiation sources in the form of precision blackbodies (BB) functioning within wide ranges of wavelengths and working temperatures. These BBs are the spectral radiance and irradiance calibration devices in the world's leading space research institutions, such as SDL (USA), DLR (Germany), Keldysh Space Center (Russia), RNIIKP/RISDE (Russia), NEC Toshiba Space Systems (Japan), etc. The paper contains a detailed description of low-temperature precision BBs developed at VNIIOFI. The characteristics of variable-temperature (100 K to 400 K) research-grade extended-area (up to 350 mm) BB models BB100-V1 and BB-80/350 are described (they are intended for radiometric calibrations by comparison with a primary standard source), as well as those that can be used as sources for high-accuracy IR calibration of space-borne and other systems not requiring a vacuum environment. The temperature nonuniformity and stability of these BBs are (0.05 to 0.1) K (cavity-type BB100-V1), and 0.1 % for the (1.5 to 15) µm wavelength region under cryo-vacuum conditions of a medium-background environment.
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