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.
For over three decades, the Radiometric Calibration Facility (RCF) at NASA's Goddard Space Flight Center (GSFC) has maintained calibrated uniform radiance sources for use by the global remote sensing community. As part of a continuing effort to reduce measurement uncertainties while improving efficiency, the calibration transfer hardware and operational protocols are systematically examined, with improved equipment and techniques being incorporated. This paper describes the optical characterization and presents radiance measurements of a new spectroradiometer, the GSFC 750/Integrating Sphere Irradiance Collector (ISIC), using a new input optical system. The performance of the new input optical system is compared with the two previous input systems.
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 (RCF) primary radiometer was characterized at the NIST facility for Spectral Irradiance and Radiance Calibrations with Uniform Sources (SIRCUS). Specifically, the radiometer's slit spectral function was measured and the magnitude of out-of-band stray light was determined. The characterization also revealed significant contributions of spectral stray light due to fluorescence of the radiometer's input sphere. The RCF examined the effects of stray light and sphere fluorescence in the radiometer on source radiance calibrations along with approaches to reduce those sources of measurement error.
Two critical requirements of any calibration source are short and long-term operational stability and repeatability. Source monitoring is necessary in quantifying overall source performance including stability and repeatability. The NASA GSFC Code 920.1 Radiance Calibration Facility (RCF) developed a Filter Radiometer Monitoring System (FRMS) to continuously monitor the performance of its integrating sphere calibration sources. FRMS bands are in the 0.4 -2.4 μm region, with several bands selected to coincide with common remote sensing bands. The FRMS was designed and fabricated in the year 2000. Early in 2001, the FRMS was reconfigured prior to being deployed on the RCF 180cm integrating sphere. This paper describes the instrument modifications resulting from the FRMS reconfiguration and presents FRMS monitor data for three RCF integrating sphere sources.
Two critical requirements of a calibration source are short- and long-term operational stability and repeatability. Monitoring the source is an asset in determining the origin of temporal changes, thus increasing confidence in source performance and quantifying repeatability. Monitor data which fall outside established parameters indicate that the source requires maintenance or re-calibration against the standard. The NASA GSFC Code 920. 1 Radiance Calibration Facility (RCF) has developed a Filter Radiometer Monitoring System (FRMS) to continuously monitor the performance of its integrating sphere calibration sources in the 400-2400nm region. Sphere output change mechanisms include lamp aging, coating (BaSO4) deterioration, and water vapor level. FRMS wavelength bands are selected to be sensitive to changes caused by these mechanisms. Several FRMS bands coincide with common remote sensing instrument bands.
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