Victor I. Sapritsky

Absolute measurements of black-body emitted radiance

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 mum) 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.

Investigation of high-temperature black body BB3200

During an international comparison of radiation temperature measurements performed at the AllRussian Institute for Optophysical Measurements (VNIIOFI), Moscow, in June 1997 by participants from the VNIIOFI, the National Physical Laboratory (NPL), Teddington, and the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, detailed measurements of the characteristics of two different types of high-temperature black-body source took place. Both of the black bodies consisted of a pyrolytic-graphite cavity and differed only in the design of the electrodes, which were either axial or coaxial. All investigations were carried out covering a temperature range from 1380 K to 3100 K. The electrical characteristics of the black bodies were investigated at all temperature points; and measurements of the temperature drift were performed to determine the stability of the systems in constant-current mode and in optical-feedback control mode. The uniformity of the black-body radiation field was measured in the radiance mode by using narrowband, interference-filter-based radiometers with imaging optics from the NPL and in the irradiance mode by using broadband-filter detectors from the PTB to scan the irradiated area. The results confirm the suitability of the BB3200 for both radiance and irradiance measurements at national metrological institutes.

Development of metal–carbon high-temperature fixed-point blackbodies for precision photometry and radiometry

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%.

Melting points of gallium and of binary eutectics with gallium realized in small cells

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.

Intercomparison of radiation temperature measurements over the temperature range from 1600?K to 3300?K

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.

Medium-background radiometric facility for calibration of sources or sensors

A new Medium-Background Facility (MBF) for the calibration of infrared sources and sensors has been designed by specialists from the All-Russian Research Institute for Optophysical Measurements (VNIIOFI) under contract to the Xian Institute of Applied Optics (China). The facility consists of several detachable modules, the configuration of which can be changed to suit the requirements of a specific task. The modular design allows flexible and independent use of the main components and simplifies upgrading. The facility was designed to allow absolute radiometric calibration of black-body sources and IR sensors; to compare the radiometric scale with predictions for measured temperatures; to allow measurements over an extended temperature range (up to the indium point); and to serve as the IR spectral radiance standard. Intended for the calibration of IR sensors and sources under vacuum conditions (10−3 Pa) and a medium-background environment (liquid-nitrogen-cooled shroud), the MBF is briefly described with reference to its design, operating principles and measurement results.

International comparison of radiation-temperature measurements with filtered detectors over the temperature range 1380 K to 3100 K

A series of black-body radiation-temperature measurements has been made over the temperature range 1380 K to 3100 K using two different designs of pyrolytic-graphite black bodies with calculated emissivities of 0.999. All measurements were performed at the All-Russian Research Institute for Optophysical Measurements (VNIIOFI) during June 1997. A filter photometer from the VNIIOFI, broadband glass-filter detectors from the Physikalisch-Technische Bundesanstalt (PTB) and narrowband interference-filter-based radiometers from the National Physical Laboratory (NPL) were used to perform the temperature measurements in either radiance or irradiance mode using both black bodies. Across the entire temperature range, the NPL and PTB instruments showed consistent results with both black bodies and differing geometrical arrangements. Results from the VNIIOFI photometer were also broadly consistent for a wide temperature range.

The Global Earth Observation System of Systems (GEOSS) and metrological support for measuring radiometric properties of objects of observations

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.

Light measurements of high-luminance LEDs

The achievements of modern optoelectronics have resulted in the widespread use of light-emitting diodes (LEDs) in products designed to visualize information, especially in light devices for use in road-safety systems. These developments highlight the importance of metrological support for measurements of the photometric characteristics of semiconductor light sources. A standard light-source model based on Corvette Light Corporation high-luminance LEDs has been created and studied. The high-luminance LEDs were manufactured to a unique design using planar technology. The results of the study demonstrate the stability of the metrological characteristics of the LED-based standard source.

Current activity of Russia in measurement assurance of Earth optical observations

The All-Russian Research Institute for Optical and Physical Measurements is currently carrying out a project on developing an integrated system for measurement assurance of Earth observations. The system should provide ground calibration of instruments and their control during space-borne observations. Such tasks require appropriate measurement facilities as well as regulatory documentation. In this paper we discuss the newly created radiometric facility, traceable to SI standard, for precise calibration of instruments for Earth observations, the project on precise monitoring of the stability of the instruments in-flight performance and the development of national regulatory documentation in harmony with the international document Quality Assurance Framework for Earth Observation—QA4EO.