Fused silica diffusers, made by forming scattering centers inside fused silica glass, can exhibit desirable optical properties,
such as reflectance or transmittance independent of viewing angle, spectrally flat response into the ultraviolet wavelength
range, and good spatial uniformity. The diffusers are of interest for terrestrial and space borne remote sensing instruments,
which use light diffusers in reflective and transmissive applications. In this work, we report exploratory measurements of
two samples of fused silica diffusers. We will present goniometric bidirectional scattering distribution function (BSDF)
measurements under normal illumination provided by the National Institute of Standards and Technology (NIST)’s
Goniometric Optical Scatter Instrument (GOSI), by NIST’s Infrared reference integrating sphere (IRIS) and by the
National Aeronautics and Space Administration (NASA)’s Diffuser Calibration Laboratory. We also present
hemispherical diffuse transmittance and reflectance measurements provided by NIST’s Double integrating sphere Optical
Scattering Instrument (DOSI). The data from the DOSI is analyzed by Prahl’s inverse adding-doubling algorithm to obtain
the absorption and reduced scattering coefficient of the samples. Implications of fused silica diffusers for remote sensing
applications are discussed.
The Advanced Baseline Imager (ABI) is the next-generation imaging sensor for the National Oceanic and Atmospheric Administration’s (NOAA’s) operational meteorological satellites in geostationary orbit. One pathway for traceability to reference standards of the visible and near-infrared radiometric response for ABI is to a 1.65 m diameter integrating sphere source standard of spectral radiance. This source illuminates the full entrance pupil via the ABI Earth-view port, thus determining the absolute spectral radiance responsivity in the visible and shortwave infrared. The spectral radiance values of the large sphere are assigned by Exelis using a double monochromator and a 15.24 cm diameter integrating sphere source standard that is calibrated by NIST. As part of the ABI program, Exelis was required by NASA to have the spectral radiance values assigned by Exelis to the large sphere be validated by NIST. Here we report the results of that activity, which took place in April, 2013. During the week of April 8, Exelis calibrated the 1.65 m diameter sphere at all 24 levels that correspond to the ABI calibration protocol. During the week of April 15, the NIST validation exercise for five selected levels took place. NIST deployed a portable spectral radiance source, a filter radiometer restricted to the visible and near-infrared, and two spectroradiometers that covered from 350 nm to 2500 nm. The NIST sphere source served as the validation standard. The comparison results, which are reported at the ABI bands, agreed to within the combined uncertainties. We describe the methodology, results, and uncertainty estimates related to this effort.
Scales of spectral irradiance are disseminated by NIST using assignment of values to FEL lamp standards for defined
conditions. These lamp standards can be used for absolute calibrations of irradiance radiometers, or more typically, be
used in conjunction with a diffuse reflectance standard to establish a scale of spectral radiance and for subsequent
absolute calibrations of radiance radiometers. The NIST FEL standards are valuable artifacts requiring special care.
Many users optimize resources by in-house transfer of their primary standard to working standards. There are a number
of sources of uncertainty in utilizing FEL lamps, e.g., lamp current, alignment, distance setting, instrument aperture size,
drift, scattered light, and interpolation in the wavelength grid for the specified irradiance values. In this work, we
validated the transfer activity by ITT of their primary, NIST-traceable FEL lamp standards. A portable irradiance bench
that had kinematic mounts for an FEL lamp, on-axis baffle, and three different irradiance radiometers was built, tested,
and deployed to ITT in Rochester, NY. We report the results of this comparison activity. An uncertainty budget was
developed and it was found that the results agreed well within the combined uncertainties of 1.5% to 1.6% (k = 2).
The Landsat Data Continuity Mission (LDCM) project at the National Aeronautics and Space Administration (NASA)
Goddard Space Flight Center (GSFC) is supervising the manufacture and calibration of the Operational Land Imager
(OLI) satellite instrument by Ball Aerospace in Boulder, Colorado. As part of that oversight function, the project is preparing
a set of radiometers to monitor long-term changes (if any) in the radiance from the integrating sphere used for the
radiance calibration of the OLI instrument. That sphere, calibrated at the National Institute of Standards and Technology
(NIST), serves as an artifact for establishing traceability of the OLI radiance calibration to SI units, that is, to the radiance
scale at NIST. This paper addresses the characterization of two Analytic Spectral Devices (ASD) Fieldspec spectrometers
that are part of the NASA/NIST program to validate radiometric reference standards in the LDCM project. In
particular, we report on a series of measurements at NIST to determine the ASD spectrometers' long-term stability.
Along with other radiometers, the ASDs will be used in the monitoring of changes in the OLI reference sphere from its
calibration at NIST to its use in the calibration of the OLI satellite instrument. The ASD stability measurements will
continue through the conclusion of the calibration of OLI.
In June 2007, a spherical integrating source was calibrated in the National Aeronautics and Space Administration
(NASA) Goddard Space Flight Center's (GSFC) Calibration Facility as part of the prelaunch characterization program
for the NPOESS Preparatory Program (NPP) Ozone Mapping and Profiler Suite (OMPS) instrument. Before shipment to
the instrument vendor, the sphere radiance was measured at the Remote Sensing Laboratory at the National Institute of
Standards (NIST) and then returned to the NASA Goddard facility for a second calibration. For the NASA GSFC calibration,
the reference was a set of quartz halogen lamps procured from NIST. For the measurement in the Remote
Sensing Laboratory, the reference was an integrating sphere that was directly calibrated at NIST's Facility for Spectroradiometric
Calibrations (FASCAL). For radiances in the visible and near-infrared (400 nm to 1000 nm), the agreement
between the NASA GSFC calibration and the validation measurements at the Remote Sensing Laboratory was at the 1 %
level. For radiances in the near ultraviolet (250 nm to 400 nm), the agreement was at the 3 % level.
The NIST role in supporting our Nation's climate research is described. The assembly of climate data records over
decadal time scales requires assimilating readings from a large number of optical sensors deployed in space and on the
Earth by various nations. NIST, in partnership with NASA and NOAA, develops and disseminates the calibration tools
and standards to ensure that the measurements from these sensors are accurate, comparable, and tied to international
standards based on the SI system of units. This effort helps to provide confidence that the small decadal changes in
environmental variables attributed to climate change are not an artifact of the measurement system. Additionally, it
ensures that the measurements are physics based and thus comparable to climate models.
For the past decade, the Marine Optical Buoy (MOBY), a radiometric buoy stationed in the waters off Lanai, Hawaii,
has been the primary in-water oceanic observatory for the vicarious calibration of U. S. satellite ocean color sensors,
including the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectrometers
(MODIS) instruments on the National Aeronautics and Space Administration's (NASA's) Terra and Aqua satellites.
The MOBY vicarious calibration of these sensors supports international effort to develop a global, multi-year time series
of consistently calibrated ocean color data products. A critical component of the MOBY program is establishing
radiometric traceability to the International System of Units (SI) through standards provided by the U. S. National
Institute of Standards and Technology (NIST). A detailed uncertainty budget is a core component of traceable
metrology. We present the MOBY uncertainty budget for up-welling radiance and discuss additional considerations
related to the water-leaving radiance uncertainty budget. Finally, we discuss approaches in new instrumentation to
reduce the uncertainties in in situ water-leaving radiance measurements.
A comparison of the area measurements of the limiting apertures used for total solar irradiance measurements in the Active Cavity Radiometer Irradiance Monitor II (ACRIM II) and Active Cavity Radiometer Irradiance Monitor III (ACRIM III) were conducted between the National Institute of Standards and Technology (NIST) and the Jet Propulsion Laboratory (JPL). The ACRIM apertures, due to their unique size and design, necessitated modifications to the NIST aperture measurement system. The changes and the validation procedures undertaken are described in this paper. This is part of an Earth Observing System (EOS)-sponsored international comparison of aperture area measurements of apertures that have institutional heritage with historical solar irradiance measurements.
The water-leaving spectral radiance is a basic ocean color remote sensing parameters required for the vicarious
calibration. Determination of water-leaving spectral radiance using in-water radiometry requires measurements of the
upwelling spectral radiance at several depths. The Marine Optical System (MOS) Remotely Operated Vehicle (ROV) is
a portable, fiber-coupled, high-resolution spectroradiometer system with spectral coverage from 340 nm to 960 nm.
MOS was developed at the same time as the Marine Optical Buoy (MOBY) spectrometer system and is optically
identical except that it is configured as a profiling instrument. Concerns with instrument self-shadowing because of the
large exterior dimensions of the MOS underwater housing led to adapting MOS and ROV technology. This system
provides for measurement of the near-surface upwelled spectral radiance while minimizing the effects of shadowing. A
major advantage of this configuration is that the ROV provides the capability to acquire measurements 5 cm to 10 cm
below the water surface and is capable of very accurate depth control (1 cm) allowing for high vertical resolution
observations within the very near-surface. We describe the integrated system and its characterization and calibration.
Initial measurements and results from observations of coral reefs in Kaneohe Bay, Oahu, extremely turbid waters in the
Chesapeake Bay, Maryland, and in Case 1 waters off Southern Oahu, Hawaii are presented.
Determination of the water-leaving spectral radiance using in-water instrumentation requires measurements of the upwelling
spectral radiance (Lu) at several depths. If these measurements are separated in time, changes in the
measurement conditions result in increased variance in the results. A prototype simultaneous multi-track system was
developed to assess the potential reduction in the Type A uncertainty in single set, normalized water-leaving radiance
achievable if the data were acquired simultaneously. The prototype system employed a spectrograph and multi-track
fiber-coupled CCD-detector; in situ in-water tests were performed with the prototype system fiber-coupled to a small
buoy. The experiments demonstrate the utility of multi-channel simultaneous data acquisition for in-water measurement
applications. An example of the potential impact for tracking abrupt responsivity changes in satellite ocean color
sensors using these types of instruments as well as for the satellite vicarious calibration is given.
Absolute stellar photometry is based on 1970s terrestrial measurements of the star Vega calibrated by using
the Planck radiance from a Cu fixed-point blackbody. Significant advances in absolute radiometry have
been made in the last 30 years that offer the potential to improve both terrestrial and space-based absolute
stellar photometry. These advances include new high-temperature blackbody standards, absolute cryogenic
radiometry, solid-state optical radiation sources, improved atmospheric transmittance modeling, and laser-based
radiometric calibration. We describe the possible use of these new technologies for ground-based
calibration of standard stars and their impact on stellar photometry, including present efforts to achieve
highly accurate measurements from the ultraviolet to the near infrared for cosmological applications.
In this work, we describe radiometric platforms able to produce realistic spectral distributions and spatial scenes for the
development of application-specific metrics to quantify the performance of sensors and systems. Using these platforms,
sensor and system performance may be quantified in terms of the accuracy of measurements of standardized sets of
complex source distributions. The same platforms can also serve as a basis for algorithm testing and instrument
comparison. The platforms consist of spectrally tunable light sources (STS's) coupled with spatially programmable
projection systems. The resultant hyperspectral image projectors (HIP) can generate complex spectral distributions with
high spectral fidelity; that is, scenes with realistic spectral content. Using the same fundamental technology, platforms
can be developed for the ultraviolet, visible, and infrared regions. These radiometric platforms will facilitate advanced
sensor characterization testing, enabling a pre-flight validation of the pre-flight calibration.
As part of an effort to reduce uncertainties in the radiometric calibrations of integrating sphere sources and standard lamp irradiance sources, the Goddard Space Flight Center (GSFC) Radiometric Calibration Facility's (RCF) primary radiometer was characterized at the NIST facility for Spectral Irradiance and Radiance Calibrations with Uniform Sources (SIRCUS). Based on those measurements, a nominal slit scattering function was developed for the radiometer. This allowed calculations of band averaged spectral radiances and irradiances for the radiometer's measurements of sphere and standard lamp sources, respectively. From these calculations the effects of bandwidth and spectral stray light were isolated for measurements in the blue spectral region. These effects, which depend on the spectral distribution of the source being measured, can be as large as 8% for measurements at 400 nm. The characterization results and a correction algorithm for these effects are presented here.
Spectrographs are used in a variety of applications in the field of remote sensing for radiometric measurements due to the benefits of measurement speed, sensitivity, and portability. However, spectrographs are single grating instruments that are susceptible to systematic errors arising from stray radiation within the instrument. In the application of measurements of ocean color, stray light of the spectrographs has led to significant measurement errors. In this work, a simple method to correct stray-light errors in a spectrograph is described. By measuring a set of monochromatic laser sources that cover the instrument's spectral range, the instrument's stray-light property is characterized and a stray-light correction matrix is derived. The matrix is then used to correct the stray-light error in measured raw signals by a simple matrix multiplication, which is fast enough to be implemented in the spectrograph's firmware or software to perform real-time corrections: an important feature for remote sensing applications. The results of corrections on real instruments demonstrated that the stray-light errors were reduced by one to two orders of magnitude, to a level of approximately 10-5 for a broadband source measurement, which is a level less than one count of a 15-bit resolution instrument. As a stray-light correction example, the errors in measurement of solar spectral irradiance using a highquality spectrograph optimized for UV measurements are analyzed; the stray-light correction leads to reduction of errors from a 10 % level to a 1 % level in the UV region. This method is expected to contribute to achieving a 0.1 % level of uncertainty required for future remote-sensing applications.
Exo-atmospheric solar irradiance measurements made by the solar irradiance community over the past 25 years incorporated limiting apertures measured by a number of metrology laboratories using a variety of techniques. Knowledge of the aperture area is a critical component in the conversion of radiant flux measurements to solar irradiance. An Earth Observing System (EOS)-sponsored international comparison of aperture area measurements of limiting apertures provided by solar irradiance researchers is under way, the effort being executed by the National Institute of Standards and Technology (NIST) in coordination with the EOS Project Science Office. Apertures that have institutional heritage with historical solar irradiance measurements are measured using the absolute aperture measurement facility at NIST. The measurement technique employs non-contact video microscopy using a high-precision stage. The aperture area comparison aims to quantify the relative differences between the participating institutions' aperture area measurements. Preliminary results of the comparison will be reported.
Organic materials in the oceans have spectral signatures based on their light-scattering properties. These optical properties are related to bio-physical and bio-chemical data products such as the concentration of phytoplankton chlorophyll-α through bio-optical algorithms. A primary quantity of interest in ocean color research is the water-leaving spectral radiance Lw(λ), often normalized by the incident solar flux. For quantitative studies of the ocean, derivation of the relationship between the optical properties and physically meaningful data products is critical. There have been a number of recent advances in radiometry at the National Institute of Standards and Technology that directly impact the uncertainties achievable in ocean-color research. These advances include a new U.S. national irradiance scale; a new laser-based facility for irradiance and radiance responsivity calibrations; and a novel tunable, solid-state source for calibration and bio-optical algorithm validation. These advances, their relevance to measurements of ocean color, and their effects on radiometrically derived ocean-color data products such as chlorophyll-α are discussed.
We describe the development of a mechanically simple, radiometrically stable transfer radiometer designed for both radiance and irradiance measurements. The filter radiometer consists of a six-element Si trap detector, a temperature stabilized filter wheel with up to 5 filters, and two precision apertures in a Gershun tube arrangement. With the Gershun tube installed, the instrument operates in radiance mode; with the front aperture removed, in irradiance mode. Two trap detector filter radiometers have been designed and built by the National Institute of Standards and Technology (NIST) for use in remote sensing applications. The filter radiometers have been characterized for optical and electrical performance, and have been calibrated for responsivity using both narrow-band, tunable-laser-illuminated and broad-band, lamp-illuminated integrating sphere sources. This paper describes the filter radiometer design, characterization, and deployments for two remote sensing projects.
Sun photometers are used to characterize the radiative properties of the atmosphere. They measure both the incident solar irradiance as well as the sky radiance (from scattered incident flux). Global networks of sun photometers provide data products such as aerosol optical thickness derived from these measurements. Instruments are typically calibrated for irradiance responsivity by cross-calibration against a primary reference sun photometer and for radiance responsivity using a lamp-illuminated integrating sphere source. A laser-based facility for Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) has been developed at the National Institute of Standards and Technology. Sensors can be calibrated in this facility for absolute spectral irradiance and radiance responsivity with combined expanded (k = 2) uncertainties ranging from 0.15% to 0.25%. Two multi-channel filter radiometers used in the Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) program of the National Aeronautics and Space Administration (NASA) at the Goddard Space Flight Center (GSFC) were calibrated for radiance and irradiance responsivity using conventional approaches and using laser-illuminated integrating spheres on SIRCUS. The different calibration methods are compared, the uncertainties are evaluated, and the impact on remote sensing applications is discussed.
The Marine Optical Buoy (MOBY) provides values of water- leaving radiance for the calibration and validation of satellite ocean color instruments. Located in clear, deep ocean waters near the Hawaiian Island of Lanai, MOBY measures the upwelling radiance and downwelling irradiance at three levels below the ocean surface plus the incident solar irradiance just above the surface. The radiance standards for MOBY are two integrating spheres with calibrations based on standards traceable to the National Institute of Standards and Technology (NIST). For irradiance, the MOBY project uses standard lamps that are routinely calibrated at NIST. Wavelength calibrations are conducted with a series of emission lines observed from a set of low pressure lamps. Each MOBY instrument views these standards before and after its deployment to provide system responses (calibration coefficients). During each deployment, the stability of the MOBY spectrographs and internal optics are monitored using three internal reference sources. In addition, the collection optics for the instrument are cleaned and checked on a monthly basis while the buoy is deployed. Divers place lamps over the optics before and after each cleaning to monitor changes at the system level. As a hyperspectral instrument, MOBY uses absorption lines in the solar spectrum to monitor its wavelength stability. When logistically feasible during each deployment, coincident measurements are made with the predecessor buoy before that buoy's recovery. Measurements of the underwater light fields from the deployment vessel are compared with those from the buoy. Based on this set of absolute calibrations and the suite of stability reference measurements, a calibration history is created for each buoy. These calibration histories link the measurement time series from the set of MOBY buoys. In general, the differences between the pre- and post-deployment radiance calibrations of the buoys range from +1% to -6% with a definitive bias to a negative difference for the post- deployment values. This trend is to be expected after a deployment of 3 months. To date, only the pre-deployment calibration measurements have been used to adjust the system responses for the MOBY time series. Based on these results, the estimated radiometric uncertainty for MOBY in-water ocean color measurements is estimated to be about 4% to 8% (kequals1). As part of a collaboration with NIST, annual radiometric comparisons are made at the MOBY calibration facility. NIST personnel use transfer radiometers and integrating spheres to validate (verify) the accuracy of the MOBY calibration sources. Recently, we began a study of the stray light contribution to the radiometric uncertainty in the MOBY systems. A complete reprocessing of the MOBY data set, including the changes within each MOBY deployment, will commence upon the completion of the stray light characterization, which is scheduled for the fall of 2001. It is anticipated that this reprocessing will reduce the overall radiometric uncertainty to less than 5% (kequals1).
As part of the Triana mission, the Scripps Earth Polychromatic Imaging Camera (Scripps-EPIC) will view the full sunlit side of Earth from the Lagrange-1 point. The National Institute of Standards and Technology and the Scripps Institution of Oceanography, in collaboration with the contractor, Lockheed-Martin, planned the radiometric calibration of Scripps-EPIC. The measurements for this radiometric calibration were selected based upon the optical characteristics of Scripps-EPIC, the measurement equation relating signal to spectral radiance, and the available optical sources and calibrated radiometers. The guiding principle for the calibration was to perform separate, controlled measurements for each parameter in the measurement equation, namely dark signal, linearity, exposure time, and spectral radiance responsivity.
KEYWORDS: Calibration, Radiometry, Remote sensing, Sensors, Black bodies, Temperature metrology, Radio optics, Lamps, Reflectivity, Defense and security
We provide an historical overview of NIST research and development in radiometry for space-based remote sensing. The applications in this field can be generally divided into two areas: environmental and defense. In the environmental remote sensing area, NIST has had programs with agencies such as the National Aeronautical and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) to verify and improve traceability of the radiometric calibration of sensors that fly on board Earth-observing satellites. These produce data used in climate models and weather prediction. Over the years, the scope of activities has expanded from existing routine calibration services for artifacts such as lamps, diffusers, and filters, to development and off-site deployment of portable radiometers for radiance- and irradiance-scale intercomparisons. In the defense remote sensing area, NIST has had programs with agencies such as the Department of Defense (DOD) for support of calibration of small, low-level infrared sources in a low infrared background. These are used by the aerospace industry to simulate ballistic missiles in a cold space background. Activities have evolved from calibration of point-source cryogenic blackbodies at NIST to measurement of irradiance in off-site calibration chambers by a portable vacuum/cryogenic radiometer. Both areas of application required measurements on the cutting edge of what was technically feasible, thus compelling NIST to develop a state-of-the-art radiometric measurement infrastructure to meet the needs. This infrastructure has led to improved dissemination of the NIST spectroradiometric quantities.
The Optical Technology Division (OTD) at the National Institute of Standards and Technology (NIST) maintains the thermodynamic temperature scale above the silver freezing point using spectral radiance ratios according to the International Temperature Scale of 1990 (ITS-90). Radiance temperature calibration services are performed in the OTD, and NIST's calibration services support industry, government agencies, national standards laboratories, pyrometer and blackbody manufacturers, universities, and U.S. military service calibration laboratories. In addition, the OTD also offers a four day Short Course on Temperature Measurement by Radiation Thermometry every year that extensively covers many aspects of radiation thermometry. Routine intercomparisons of the thermodynamic temperature scale are done with other national measurement laboratories for international verification of the accuracy of the issued calibrations. We describe research into alternatives to the ITS-90: the use of absolute detector standards to directly measure the temperature of a high temperature blackbody.
EOS satellite instruments operating in the visible through the shortwave infrared wavelength regions (from 0.4 micrometer to 2.5 micrometer) are calibrated prior to flight for radiance response using integrating spheres at a number of instrument builder facilities. The traceability of the radiance produced by these spheres with respect to international standards is the responsibility of the instrument builder, and different calibration techniques are employed by those builders. The National Aeronautics and Space Administration's (NASA's) Earth Observing System (EOS) Project Science Office, realizing the importance of preflight calibration and cross-calibration, has sponsored a number of radiometric measurement comparisons, the main purpose of which is to validate the radiometric scale assigned to the integrating spheres by the instrument builders. This paper describes the radiometric measurement comparisons, the use of stable transfer radiometers to perform the measurements, and the measurement approaches and protocols used to validate integrating sphere radiances. Stable transfer radiometers from the National Institute of Standards and Technology, the University of Arizona Optical Sciences Center Remote Sensing Group, NASA's Goddard Space Flight Center, and the National Research Laboratory of Metrology in Japan, have participated in these comparisons. The approaches used in the comparisons include the measurement of multiple integrating sphere lamp levels, repeat measurements of select lamp levels, the use of the stable radiometers as external sphere monitors, and the rapid reporting of measurement results. Results from several comparisons are presented. The absolute radiometric calibration standard uncertainties required by the EOS satellite instruments are typically in the plus or minus 3% to plus or minus 5% range. Preliminary results reported during eleven radiometric measurement comparisons held between February 1995 and May 1998 have shown the radiance of integrating spheres agreed to within plus or minus 2.5% from the average at blue wavelengths and to within plus or minus 1.7% from the average at red and near infrared wavelengths. This level of agreement lends confidence in the use of the transfer radiometers in validating the radiance scales assigned by EOS instrument calibration facilities to their integrating sphere sources.
A comparison of spectral diffuse reflectance between different national standards laboratories is being planned under the direction of the Comite Consultatif de Photometrie et Radiometrie (CCPR). A similar comparison of bidirectional reflectance distribution factor among laboratories in the United States in support of optical remote sensing measurements is nearing completion. Since this comparison provides valuable lessons for the one organized by the CCPR, pertinent results and their implications are presented.
As a part of the Earth observing system (EOS) cross- calibration activities before the first flight (denoted AM- 1), a radiometric measurement comparison was held in February 1995 at the NEC Corporation in Yokohama, Japan, Researchers from the National Institute of Standards and Technology (NIST), the National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC), the University of Arizona Optical Sciences Center, and the National Research Laboratory of Metrology (NRLM) used their portable radiometers to measure the spectral radiance of the advanced spaceborne thermal emission and reflection radiometer (ASTER) visible/near-infrared (VNIR) integrating sphere at three radiance levels. The levels each correspond to 83% of the maximum radiance that is expected to be measured using the three VNIR bands of the EOS ASTER instrument, which are centered at 0.56 micrometer, 0.66 micrometer, and 0.81 micrometer. These bands are referred to as bands 1, 2, and 3. The average of the measurements of the four radiometers was between 1% and approximately 1.5% higher for all three bands when compared to the NEC calibration of the sphere. A comparison of the measurements from the participating radiometers resulted in good agreement. These results are encouraging and will be followed by extension to other EOS AM-1 instrument calibration sources.
KEYWORDS: Black bodies, Calibration, Power supplies, Radiometry, Optical filters, Pyrometry, Temperature metrology, Standards development, Lamps, Feedback control
Development of a new spectral irradiance scale realization at the National Institute of Standards and Technology (NIST) requires a careful and complete calibration of a high- temperature blackbody between 1200 K and 2800 K. Filter radiometers have been calibrated to measure the spectral radiance (or radiance temperature) of the blackbody. Using a monochromator, the blackbody spectral radiance will then be used to determine the spectral irradiance distributions of primary and secondary spectral irradiance lamp standards at NIST. In this paper, a calibrated pyrometer and V((lambda) ) filter radiometer will be used to evaluate the high-temperature blackbody for determination of the optimum calibration method for the blackbody. The blackbody apparatus will be described in detail. When the power supply is the sole source of current control, the blackbody current is stable to within 0.056%, resulting in 0.72% for the uncertainty in the blackbody spectral radiance. To achieve our goal of 0.1% in the final blackbody radiance, a blackbody current stability of 0.007% is required. Due to the day-to-day variations in the current, calibrations of the blackbody msut be made frequently. Several feedback control options are recommended as possible solutions for improving both the short term and long term current stability.
Victor Sapritsky, B. Carol Johnson, Robert Saunders, Lev Vlasov, Konstantin Sudarev, Boris Klevnoy, Vjcheslav Shapoval, Igor Dmitriev, Leonid Buchnev, Alexsandr Prochorov
This paper reviews the research and design of high temperature blackbody sources for the temperature interval from 2000 K to 3000 K. Sources with large apertures are addressed specifically, as these are well suited to the important problem of spectral irradiance scale realizations.
Ronald Johnson, Robert Ayres, John Broberg, Roy Cutler, Philip Debenham, B. Carol Johnson, Eric Lindstrom, David Mohr, John Rose, Julian Whittaker, Neil Wilkin, Mark Wilson, Samuel Penner, Cha-Mei Tang, Phillip Sprangle
A free-electron laser facility (FEL) is being constructed at the National
Institute of Standards and Technology (NIST) in collaboration with the Naval
Research Laboratory (NRL) . The FEL will be driven by the electron beam from the
NIST racetrack microtron (RTM). The anticipated performance of the FEL is: (1)
wavelength variability from 200 run to 10 tim; (2) continuous train of 3-ps pulses at
66 MHz; and (3) average power of 10 W to 200 W. This excellent performance will be
achieved primarily because of the unique characteristics of the RTM. This
accelerator will provide a continuously pulsed electron beam with high brightness
and low energy spread at energies from 17 MeV to 185 MeV. For FEL operation high
peak current is required and a new injector for this purpose has been designed. The
undulator for the project is 3.64-m long with 130 periods and a peak field of 0.54
T. The construction of the undulator is nearly complete and delivery is expected
shortly. The 9-m optical cavity has been designed and is under construction. An
experimental area is being prepared for FEL users which will have up to six
stations. Initial operation of the FEL is scheduled for 1991. The NIST-NRL FEL
will provide a powerful, tunable light source for research in biomedicine, materials
science , physics , and chemistry.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.