Showing papers in "Metrologia in 1993"
TL;DR: The agreement between calculation and experiment within an experimental uncertainty of ± 3 × 10-8 was established in this paper. But the agreement was only for the case where the carbon dioxide content of normal laboratory air has increased.
Abstract: The Edlen equation for the refractive index of air, published in 1966, is still widely used. Subsequent to its formulation, however, improved data have become available on the density of air and the refractivity of water vapour. The practical temperature scale has also been revised and the carbon dioxide content of normal laboratory air has increased. These effects result in a discrepancy of typically 1 × 10-7. The consequent revision of the equation brings the agreement between calculation and experiment within an experimental uncertainty of ± 3 × 10-8.
503 citations
TL;DR: In this article, the Hamamatsu S1337 photodiode was found to be the best suited for use as a high accuracy transfer standard for both the visible and UV spectral regions.
Abstract: Different types of photodiode have been characterized with respect to uniformity, linearity, stability of responsivity and temperature coefficient at several wavelengths between 257 nm and 799 nm based on cryogenic radiometry and intensity stabilized lasers. The Hamamatsu S1337 photodiode was found to be the best suited for use as a high accuracy transfer standard for both the visible and UV spectral regions. For low-level radiant power measurement, this kind of photodiode can be calibrated via a cryogenic radiometer with a total uncertainty as low as ±0,02% in the visible and ±0,25% in the UV.
76 citations
TL;DR: In this article, the ratio of the NMR spin precession frequencies of optically pumped low pressure helium-3 and of protons in water, using free induction decay, was measured by direct substitution in a flux density of 0,1 T of samples in an accurately spherical 25 mm diameter sample cell.
Abstract: We have measured the ratio of the NMR spin precession frequencies of optically pumped low pressure helium-3 and of protons in water, using free induction decay. This was done by direct substitution in a flux density of 0,1 T of samples in an accurately spherical 25 mm diameter sample cell, without removing the sample cell from the magnet. The water measurements were corrected to 25°C. The two sets of measurements were each referred to a 10 mm diameter spherical reference water sample which was ratioed out. A new method was devised to measure and correct for the different averaging of the residual inhomogeneities in the magnetic field by the helions and by the protons in the water. Our final result is μh (3He)/μ'p= − 0,761 786 131 3(33). Using the CODATA 1986 recommended value for γp gives γh/2π = 32,434 092 1(97) MHz T-1. Combining the result with a measurement of γh (3He)/γp (H2 gives the shielding factor of H2 as σH2 = 26,350(19) × 10-6, in good agreement with a theoretical value. Combining our result with a measurement of μp/μB yields μh (3He)/μB= − 1,158 671 471(14) × 10-3.
68 citations
TL;DR: In this article, a technique is presented for realizing spectral irradiance using a large-area, high temperature, uniform, black-body source and filter-radiometers that are calibrated using a High Accuracy Cryogenic Radiometer.
Abstract: A technique is presented for realizing spectral irradiance using a large-area, high temperature, uniform, black-body source and filter-radiometers that are calibrated using a High Accuracy Cryogenic Radiometer. The method will be studied by calibrating irradiance lamps with this new technique and comparing the results with those obtained by the method currently employed at the National Institute of Standards and Technology (NIST). Progress to date and preliminary results are presented. The ultimate goal of the programme is to reduce the measurement uncertainties in the spectral irradiance scales that are made available to industry by calibrating deuterium and tungsten-halogen irradiance lamps.
52 citations
TL;DR: In this article, an automated interferometer equipment is described which can be used for calibration of gauge blocks with lengths up to 1, 000 mm, and the measurement method is based on scanning and it utilizes a white-light source and one stabilized 633 nm laser.
Abstract: An automated interferometer equipment is described which can be used for calibration of gauge blocks with lengths up to 1 000 mm. The main advantage of the new type of interferometer is that no prior knowledge on the length of the gauge block is required. The measurement method is based on scanning and it utilizes a white-light source and one stabilized 633 nm laser. White-light interference signals from the reference flat and from the front surface of the gauge block indicate the distance to be measured with the laser. The final length is determined from the average laser-signal phase shift between the gauge and the reference flat. Environmental conditions are measured and the necessary corrections are made automatically. An integrating sphere used for evaluation of the surface roughness correction is described. Results of the various test measurements with both short and long gauge blocks are given. The estimated overall uncertainty (2 σ) is 30 nm for a 100 mm gauge block and 160 nm for a 1 000 mm gauge block. Repeatability of wringing is the main source of uncertainty with short gauge blocks. With long gauge blocks, the accuracy is limited by uncertainty in the temperature of the gauge and in the air refractive index.
49 citations
TL;DR: In this article, the authors discuss spectral linearity measurements using both absolute and relative methods on typical silicon and germanium photodiodes and show the agreement between the two methods.
Abstract: The paper discusses automated spectral linearity measurements using both absolute and relative methods. Results of measurements on typical silicon and germanium photodiodes are presented. These measurements show the agreement between the two methods. They also illustrate some interesting linearity properties: wavelength dependence, detector-to-detector variation, current versus current-density dependence, geometrical effects, and effect of reverse bias. In particular, it is shown that some silicon and germanium detectors must be underfilled with radiation to avoid edge effects. These cause nonlinearities which are generally small (1% level) but, in certain types of thermoelectrically cooled germanium detectors, can be very large (8% to 10%).
45 citations
TL;DR: In this article, the uncertainty contributions of different input parameters for establishing the independent radiometric scales are analyzed in detail, and the results of the comparison between BESSY and the cryogenic radiometer are in agreement with the uncertainty analysis.
Abstract: At the PTB radiometric scales are compared which are based on electrodynamics (electron storage ring BESSY), on thermodynamics (black body of known temperature T90 of the International Temperature Scale) and on a thermal detector in combination with the electrical substitution principle (cryogenic radiometer). The uncertainty contributions of the different input parameters for establishing the independent radiometric scales are analysed in detail. According to this analysis spectral radiant powers in the visible are realized or expected to be realized (black body) with uncertainties (1 σ level) of 0,10% (BESSY), of 0,07% (black body, λ>650 nm) and of 0,007% (cryogenic radiometer). Filter radiometers calibrated at the three independent primary standards are used as transfer instruments for the comparison. The measured values of the responsivities of the filter radiometers are estimated to be uncertain by 0,11% (BESSY), 0,08% (black body, λ>650 nm), and 0,03% (cryogenic radiometer). Preliminary experimental results of the comparison between BESSY and the cryogenic radiometer are in agreement with the uncertainty analysis.
43 citations
TL;DR: Two spectral responsivity scales have been established at the National Physical Laboratory, UK as mentioned in this paper, for the spectral region 400 nm to 920 nm, with an uncertainty of less than 1.6%.
Abstract: Two spectral responsivity scales have been established at the National Physical Laboratory, UK. High quantum efficiency silicon photodiodes have been used to establish a continuous spectral responsivity scale for the spectral region 400 nm to 920 nm. The scale can be disseminated by the NPL with an uncertainty of ?0,1%. Pyroelectric detectors fitted with a reflecting hemispherical cavity have been used to establish a spectral responsivity scale for the spectral region 1 ?m to 20 ?m. This scale has an uncertainty of less than ?1,6%.
40 citations
TL;DR: In this paper, the extent and causes of air refractivity differences in industrial environments have been assessed at the level of less than 1 part in 107 by the PTB and the NPL using a refractometer instrumentation package capable of both direct measurement and calculation of the refractive index of the atmosphere using an interferer and atmospheric sensor measurements.
Abstract: The extent and causes of air refractivity differences in industrial environments have been assessed at the level of less than 1 part in 107 by the PTB and the NPL using a refractometer instrumentation package capable of both direct measurement and calculation of the refractive index of the atmosphere using an interference refractometer and atmospheric sensor measurements. The results of these measured and calculated values are discussed, together with the comparison of a number of industrial air refractivity measurement sensors.
36 citations
TL;DR: In this paper, the progress in development and optimization of a high accuracy measurement facility using a cryogenic radiometer as the primary standard is presented, and the following features are highlighted: method of dynamic power substitution; temperature dependence of the absorptance of the cavity; error reduction by distance-error-free calibration transfer; and concept of window-correction-free transfer.
Abstract: The PTB primary standards for radiant power in Braunschweig are the German national standard for detector calibrations within the spectral range of 200 nm to 2,5 μm. This paper presents the progress in development and optimization of a high accuracy measurement facility using a cryogenic radiometer as the primary standard. The following features are highlighted: method of dynamic power substitution; temperature dependence of the absorptance of the cavity; error reduction by distance-error-free calibration transfer; and concept of window-correction-free transfer.
36 citations
TL;DR: The EOS Multi-angle Imaging SpectroRadiometer (MISR) as mentioned in this paper was used to study the ecology and climate of the Earth through acquisition of global multi-angle imagery.
Abstract: The EOS Multi-angle Imaging SpectroRadiometer (MISR) will study the ecology and climate of the Earth through acquisition of global multi-angle imagery. The MISR employs nine discrete cameras, each a push-broom imager. Of these, four point forward, four point aft and one views the nadir. Absolute radiometric calibration will be obtained pre-flight using high quantum efficiency (HQE) detectors and an integrating sphere source. After launch, instrument calibration will be provided using HQE detectors in conjunction with deployable diffuse calibration panels. The panels will be deployed at time intervals of one month and used to direct sunlight into the cameras, filling their fields-of-view and providing through-the-optics calibration. Additional techniques will be utilized to reduce systematic errors, and provide continuity as the methodology changes with time. For example, radiation-resistant photodiodes will also be used to monitor panel radiant exitance. These data will be acquired throughout the five-year mission, to maintain calibration in the latter years when it is expected that the HQE diodes will have degraded. During the mission, it is planned that the MISR will conduct semi-annual ground calibration campaigns, utilizing field measurements and higher resolution sensors (aboard aircraft or in-orbit platforms) to provide a check of the on-board hardware. These ground calibration campaigns are limited in number, but are believed to be the key to the long-term maintenance of MISR radiometric calibration.
TL;DR: In this article, two independent methods of measurement were used to determine the absolute spectral responsivity and external quantum efficiency of light-trapping silicon photodiode packages, and the two sets of measurements agree to better than 0.1% at 633 nm and 0.25% at 442 nm.
Abstract: Two independent methods of measurement were used to determine the absolute spectral responsivity and external quantum efficiency of light-trapping silicon photodiode packages. These trap packages were calibrated first by the NIST High Accuracy Cryogenic Radiometer at laser wavelengths of 633 nm and 442 nm. They were also measured in the NIST Spectral Comparator Facility with working standards traceable to a 100% quantum efficient radiometer (QED-200). The two sets of measurements agree to better than 0,1% at 633 nm and 0,25% at 442 nm.
TL;DR: In this article, transfer source standards have been developed for the ESA/NASA SOHO (Solar and Heliospheric Observatory) space mission to observe the solar disk and corona in the wavelength range 15 nm to 160 nm.
Abstract: On board the ESA/NASA space mission SOHO (Solar and Heliospheric Observatory) there will be several VUV telescope/spectrometer systems to observe the solar disk and its corona in the wavelength range 15 nm to 160 nm. To determine the absolute spectral sensitivity of these instruments prior to launching, transfer source standards have been developed. These transfer standards consist of a high-current hollow cathode source combined with collimating optics. One standard uses a concave mirror at normal incidence for the wavelength range 50 nm to 160 nm and the other standard uses Wolter type II grazing incidence optics for the range 16 nm to 80 nm. These transfer source standards are calibrated against the electron storage ring BESSY as a primary radiometric source standard.
TL;DR: In this paper, flat-plate diffusers of measured angular scattering properties are illuminated by NIST standards of spectral irradiance to provide a calculated spectral radiance standard in the wavelength region 250 nm to 340 nm for space-borne SBUV-2 instruments used to determine long-term changes in stratospheric ozone.
Abstract: Historically, flat-plate diffusers of measured angular scattering properties are illuminated by NIST standards of spectral irradiance to provide a calculated spectral radiance standard in the wavelength region 250 nm to 340 nm for space-borne SBUV-2 instruments used to determine long-term changes in stratospheric ozone. Correspondingly, space-borne large-aperture scanning radiometers used to measure spectroradiometric properties of Earth scenes in the red and near-infrared regions have used internally illuminated integrating spheres. The spectral radiance of the aperture of an integrating sphere is calculated from its spectral irradiance which is referenced to NIST standards of spectral irradiance. Spectral radiance calibration constants in the region 250 nm to 340 nm derived using the flat-plate diffuser and spherical integrator techniques agree to within 1% in the wavelength region from 250 nm to 340 nm. The results presented are for the radiometric calibration of the SBUV-2 flight model number two which is the next instrument scheduled for flight.
TL;DR: For about one year the time scales UTC (OCA) and TUG (TUG) were compared by means of GPS common-view and two-way satellite time transfer.
Abstract: For about one year the time scales UTC (OCA) and UTC (TUG) were compared by means of GPS common-view and two-way satellite time transfer. At the end of the experiment, both links were independently "calibrated" by measuring the differential delays of the GPS receivers and the satellite Earth stations by transportation of one GPS receiver and one satellite terminal to the other site. The results obtained by the two methods differ by about 3 ns, but reveal a seasonal variation of about 8 ns which, most likely, is mainly the result of temperature-dependent delays in the GPS receiving equipment used.
TL;DR: In this article, surface analysis techniques, including X-ray photoelectron spectroscopy (XPS), were applied to specimens cut from prototype material of Pt-10% Ir alloy.
Abstract: To examine the stability of prototypes of the kilogram after cleaning, surface analysis techniques, including X-ray photoelectron spectroscopy (XPS), were applied to specimens cut from prototype material of Pt-10% Ir alloy. Traditional steam-jet cleaning (SJC) was compared with ultrasonic cleaning with solvents (UCS) in terms of cleaning effects and the progress of contamination. The results show that mass changes due to metallic factors such as oxidation, reduction and dissolution were negligibly small. In terms of carbon decrease and adsorption of water, UCS was superior to SJC. From analyses of peak area ratio by XPS, it was shown that the cleaner the surfaces, the higher the rate of contamination. But the contamination levels converged to a common value after a six-month exposure to air, irrespective of the cleaning method used. This finding is of great importance for the preservation of prototypes. The contaminating substances were found to be hydrocarbons from the ambient air. The mass gain for the surfaces of a prototype due to hydrocarbons after a six-month exposure to ambient air is estimated to be 4,3 μg for SJC and 16 μg for UCS.
TL;DR: The SSBUV has now flown four times, over a thirty-month period beginning in October 1989, and is an update to the results reported after the first SS BUV flight as mentioned in this paper.
Abstract: The SSBUV is part of the National Plan for monitoring the stratosphere. Ozone monitoring from space employs backscatter ultraviolet-type instruments on NOAA operational, NASA research and foreign environmental satellites. The SSBUV provides calibration data for these instruments using nearly coincident observations of the Earth's ultraviolet albedo from a series of Space Shuttle flights. The SSBUV also measures the middle ultraviolet solar irradiance as part of the ozone measurement. A major requirement for the SSBUV is that its calibration be known to about 1% from one flight to the next. To achieve this, the SSBUV conducts a rigorous calibration program involving multiple standard sources and detectors. The SSBUV has now flown four times, over a thirty-month period beginning in October 1989. This paper deals with the calibration and radiometric stability before and after each of four Shuttle flights and is an update to the results reported after the first SSBUV flight. For the more recent flights, laboratory calibration precision continues to be better than 1%. Instrument sensitivity continued to degrade by 1% to 3% after each flight, and is wavelength dependent. Measurements of the solar irradiance in the wavelength region 200 nm to 400 nm have a precision of 1% to 2% from one flight to the next. Comparison of the SSBUV and the NOAA-11 SBUV-2 solar irradiance measurements indicates that the SBUV-2 instrument is degrading less than 1% per year at wavelengths longer than 300 nm and by as much as 6% per year at wavelengths shorter than 250 nm.
TL;DR: A brief history of the development of quantum-efficient detectors and their incorporation into light-trapping configurations is presented in this article, where a new refractive configuration is described which yields the largest field-of-view reported to date.
Abstract: A brief history of the development of quantum-efficient detectors and their incorporation into light-trapping configurations is presented. Various light-trapping schemes are surveyed. A new refractive configuration is described which yields the largest field-of-view reported to date.
TL;DR: In this paper, the results obtained in the calculation of the pressure distortion coefficients of two 100 MPa piston-cylinder units and one 500 MPa unit were compared with the calculated results.
Abstract: Elastic distortions in piston-cylinder units, used in primary standard piston gauges, are responsible for large uncertainties in pressure measurement values typically higher than 50 MPa. The present study considers the results obtained in the calculation of the pressure distortion coefficients of two 100 MPa piston-cylinder units and one 500 MPa unit. The calculation of distortions in the above piston-cylinder units follows the application of an analytical technique taking account iteratively of mechanical distortions and pressure distribution in the piston-cylinder clearance. The distortion values experimentally determined on the outer surface of the cylinders are compared with the calculated results. Pressure distributions in the piston-cylinder clearances, and piston and cylinder radial displacements, are calculated for various conditions of use and the results allow the pressure distortion coefficient of each unit to be obtained. Different effects on piston-cylinder units are evaluated to acquire useful information on piston gauges and to improve their accuracy.
TL;DR: In this paper, a model based on estimates of the convective heat transfer rate and the overall average velocity of convective air current was used to interpret the experimental results, and the observed temperature dependence was analyzed.
Abstract: Apparent mass differences due to free convection were measured for 1 kg mass standards. The observed temperature dependence was analysed, also that of some 20 g artefacts reported earlier. A model based on estimates of the convective heat transfer rate and the overall average velocity of the convective air current was used to interpret the experimental results.
TL;DR: The experiment SOVA (SOlar VAriability) on board EURECA (EUropean Retrievable CArrier) contains two types of radiometers sunphotometers for measuring the total and spectral irradiance at five wavelengths between 335 nm and 862 nm as discussed by the authors.
Abstract: The experiment SOVA (SOlar VAriability) on board EURECA (EUropean REtrievable CArrier) contains two types of radiometers sunphotometers for measuring the total and spectral irradiance at five wavelengths between 335 nm and 862 nm. Besides the direct observation of variations of the solar irradiance, these measurements will also be used for the observation of solar oscillations. Preliminary results are presented from the observations of total and spectral irradiance during the first five months of the mission (August to December 1992).
TL;DR: In this paper, the properties of a new large area InGaAs photodiode with near unity internal quantum efficiency are described and compared with measurements on germanium photodiodes.
Abstract: The paper describes the properties of a new large area InGaAs photodiode with near unity internal quantum efficiency. Measurements of linearity, spatial uniformity and dark current of the photodiodes are presented and compared with measurements on germanium photodiodes. The paper also describes the performance of a detector constructed from an arrangement of three of these photodiodes and shows how it has a calculable responsivity from 980 nm to 1 640 nm. It also describes how such a detector can be used as a sensor for a fibre-optic power meter with an uncertainty of around 0,1%.
TL;DR: In this paper, the system of radiometric and photometric standards at the PTB is presented, emphasizing traceability, cross-linking, and future developments; the future realization of the detector-based spectral irradiance scale resulting in a reduced uncertainty is described.
Abstract: The system of radiometric and photometric standards at the PTB is presented, emphasizing traceability, cross-linking, and future developments. Traceability from the national standards to the respective reference standards of calibration laboratories of the German Calibration Service (DKD) is also included. The future realization of the detector-based spectral irradiance scale resulting in a reduced uncertainty is described.
TL;DR: In this article, the current misuse of the term intensity in physics and optics is deplored, and means of remedying the situation are suggested to correct the misuse of this term.
Abstract: The current misuse of the term intensity in physics and optics is deplored. Means of remedying the situation are suggested.
TL;DR: In this paper, the 3He vapour-pressure scale was calculated using thermal and PVT data for the liquid and vapour phases, and good agreement was obtained between a calculated vapour pressure scale and recent experimental observations based on magnetic thermometry.
Abstract: New thermodynamic calculations have been made of the 3He vapour-pressure scale using recently-published thermal and PVT data for the liquid and vapour phases. It is shown that by making reasonable choices of the data for the second and third virial coefficients of the vapour, and for the heat capacity of the liquid, good agreement can be obtained between a calculated vapour-pressure scale and recent experimental observations based on magnetic thermometry. These have revealed deviations of the ITS-90 from thermodynamic temperature of up to 1 mK at 0,65 K.
TL;DR: In this paper, the stabilities of type 715, T-1, tungsten calibration lamps were evaluated aboard three spacecraft platforms during the period 1984 to 1989, using shortwave thermistor bolometers and active-cavity radiometers.
Abstract: The stabilities of type 715, T-1, tungsten calibration lamps were evaluated aboard three spacecraft platforms during the period 1984 to 1989. In the 0,2 μm to <5,0 μm broadband spectral region, the emitted radiant power from each lamp was measured using shortwave thermistor bolometers and active-cavity radiometers. The radiant power was found to be constant to ±1%. The responses of filter and silicon photodiode monitoring systems used to evaluate the lamps were found to degrade as much as 6% during the first two years in orbit.
TL;DR: In this paper, a multispectral optical imager of high spatial resolution for remote sensing of land surfaces and clouds from orbit, which will be launched in 1998 on NASA's EOS-AM1 spacecraft, is described.
Abstract: Pre-flight and in-flight radiometric calibration plans are described for a multispectral optical imager of high spatial resolution for remote sensing of land surfaces and clouds from orbit, which will be launched in 1998 on NASA's EOS-AM1 spacecraft. The instrument named ASTER consists of three radiometers for three separate spectral regions, the visible and near-infrared radiometer (VNIR), the shortwave infrared radiometer (SWIR), and the thermal infrared radiometer (TIR). Absolute radiometric accuracy to better than 4% is required for the VNIR and SWIR radiance measurements, and from 1 K to 3 K, depending on the temperature region, from 200 K to 370 K for the TIR temperature measurements. The basic approach to in-flight calibration is to introduce a reference beam at the front end of the radiometer to calibrate the whole system in orbit. Thus the ASTER instrument is installed with internal on-board calibration units which include, as reference sources, incandescent lamps for the VNIR and SWIR and a black-body radiator for the TIR. Calibration reliability of the VNIR and SWIR is enhanced by a dual system of on-board calibration units and high stability halogen lamps. A ground calibration system of spectral radiances traceable to fixed-point black bodies is used for the pre-flight VNIR and SWIR calibrations.
TL;DR: In this article, a complete description of a frequency standard based on the 3P1-3P0 24Mg transition at 601 GHz is presented, in particular the metastable atomic source, the Ramsey-type interaction region, the submillimetric frequency synthesizer and the frequency control loop.
Abstract: We report a complete description of a frequency standard based on the 3P1-3P0 24Mg transition at 601 GHz; in particular the metastable atomic source, the Ramsey-type interaction region, the submillimetric frequency synthesizer and the frequency-control loop are described both theoretically and experimentally. The main experimental results concerning the operation of the atomic beam, the Ramsey signal intensity and width versus some important parameters and the signal-to-noise ratio, with and without optical pumping, are reported and compared with theoretical predictions. The clock transition frequency has been measured with respect to UTC (IEN) with an uncertainty of ± 1 × 10-12; at present the frequency instability reaches the value of 2 × 10-13 for counting times of 3 000 s and the repeatability the level of 3 × 10-13. The accuracy budget is also reported and discussed as are possible improvements of the present prototype.
TL;DR: In this paper, the authors carried out high resolution spatial measurements of the surface reflectance and responsivity of single and trap-configured silicon photodiodes at laser wavelengths between 325 nm and 780 nm.
Abstract: We have carried out high resolution spatial measurements of the surface reflectance and responsivity of single and trap-configured silicon photodiodes at laser wavelengths between 325 nm and 780 nm. The results indicate that the spatial nonuniformity of quantum efficiency for a given photodiode varies with laser wavelength and internal structure. For radiometric quality diodes this nonuniformity of response leads to uncertainties in detector measurements which can be reduced to 0,03% or better.
TL;DR: In this paper, a spectroscopic study of the B-X system of 127I2 iodine molecule at 633 nm was performed using a continuous-wave tunable dye laser.
Abstract: A spectroscopic study of the 33P (6-3) line in the B-X system of 127I2 iodine molecule at 633 nm was undertaken using a continuous-wave tunable dye laser. The uncertainty in the frequency interval measurements between the hyperfine components, of a few kilohertz, allows determination of the differences between the constants of the four principal hyperfine interactions.