A necessary condition for accumulating fundamental climate data records is the use of observation instruments whose stability and accuracy are sufficiently high for climate monitoring purposes; the number of instruments and their distribution in space should be sufficient for measurements with no spatial or temporal gaps. The continuous acquirement of data over time intervals of several decades can only be possible under the condition of simultaneous application of instruments produced by different manufacturers and installed on different platforms belonging to one or several countries. The design of standard sources for pre-flight calibrations and in-flight monitoring of instruments has to meet the most stringent requirements for the accuracy of absolute radiometric measurements and stability of all instruments. This means that the radiometric scales should be stable, accurate, and uniform. Current technologies cannot ensure the high requirements for stability and compatibility of radiometric scales: 0.1% per decade within the 0.3 - 3 µm band and 0.01 K per decade within the 3 - 25 µm band. It is suggested that these tasks can be aided through the use of the pure metals or eutectic alloy phase transition phenomenon that always occur under the same temperature. Such devices can be used for pre-flight calibrations and for on-board monitoring of the stability of radiometric instruments. Results of previous studies of blackbody models based upon the phase transition phenomenon are quite promising. A study of the phase transition of some materials in small cells was conducted for future application in onboard monitoring devices and its results are positive and allow us to begin preparations for similar experiments in space.
The demands of modern radiation thermometry and radiometry are being satisfied by a large variety of high-precision unique BB sources (both fixed-point and variable temperature) designed for a wide range of temperature from 100 K to 3500 K. The paper contains a detailed review of low-, medium- and high-temperature precision blackbodies developed at VNIIOFI as the basis of the spectral radiance and irradiance calibration devices in the rank of National standards. The blackbodies include: 1) variable-temperature (100K..1000K) research-grade extended-area (up to 100 mm) models intended to perform radiometric calibrations by comparison with a primary standard source, as well as can be used as the sources for high-accuracy IR calibration of space-borne and other systems not requiring a vacuum environment; 2) low-temperature fixed-point blackbodies on the basis of phase transitions of pure metals such as In and Ga sources, and the metal-metal eutectics operating within the medium-temperature range (300K to 400K); these are used for pyrometric measurements, IR-radiometry, preflight and (future aspects) in-flight calibration of space borne IR instruments; 3) high-temperature wide aperture variable-temperature blackbodies (1800K to 3500K) such as BB3500MP, BB3500YY designed and fabricated, along with fixed-point cells working above the ITS-90 temperatures on the basis of phase transitions of metal-carbon eutectic alloys (Re-C, TiC-C, ZrC-C, HfC-C), which possess unique reproducibility of 0.1% or less.
The large variety of high-precision unique blackbody sources: those operating at fixed temperatures provided by phase transitions of metals and metal-carbon eutectics, and variable-temperature ones had been designed in VNIIOFI for high-precision radiometry, radiation thermometry and spaceborne remote sensing within a 100 to 3500K temperature range. Paper reviews the blackbodies (BBs) ranged to low, middle and high temperatures, and describes spectral radiance and irradiance calibration facilities on the base of these BBs in IR and V-UV spectral ranges.
The latest investigations of high-temperature fix-points based on metal-carbon eutectics Re-C (2748K) demonstrated an excellent reproducibility of freezing plateau (up to 0.01% in terms of radiation temperature) between series of measurements/crucibles, and about 0.003% within a sample measurement session, i.e. better than 100mK. Further Re-C (spectral irradiance measurements) and TiC-C (3057° C) eutectics are being investigated for use as high-stable radiance/irradiance sources above the conventionally assigned values of temperatures of ITS-90.
It was originally analytically solved the problem of field distribution of a narrow-directed MM-wave beam behind obstacle. Experiments proved anticipated field levels that are 40 dB higher than the levels of omni-directed decimeter (DM) radiation. It was proposed and verified in series of measurements the model of forming of interference structure of MMW beam field in a shadow of vegetation, versus vertical receiver movement. Taking into account MMW beam peculiarities, it was demonstrated the advantages of frequency re-use increasing efficiency in digital cellular network in comparison with existing DM systems, in application to mobile telecommunications and fixed wireless access.
In the paper there are presented the mathematical description and the results of the numerical analysis of frequency response function (FRF) of a turbulent atmospheric radiochannel over the terrestrial surface in Millimeter-wave (MMW) band. Here it is given the analysis of effect on the FRF of the MMW parameters fluctuations due to atmospheric turbulence and rough irregularities of underlying surface. The conditions of validity and demolition of MMW-field interference structure are presented. There are also presented the measurements date ((lambda) equals 2.2 X 10-3 m) under natural conditions of amplitude FRF of atmospheric radiochannel, according to the original technique, and results of the atmospheric transmission bandwidths measurement versus the receiver and transmitter antennas position.
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