Vol. 16: The Second SeaWiFS Intercalibration Round-Robin Experiment, SIRREXB, June 1993.
Citation:
Mueller, J.L., B.C. Johnson, C.L. Cromer, J.W. Cooper, J.T. McLean, S.B. Hooker, and T.L. Westphal, 1994:
The Second SeaWiFS Intercalibration Round-Robin Experiment, SIRREXB, June 1993. NASA Tech. Memo.
104566, Vol. 16, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, Greenbelt,
Maryland, 121 pp.
This report presents the results of the second Sea-viewing Wide Field-of-view Sensor (SeaWiFS)
Intercalibration Round-Robin Experiment (SIRREX-2), which was held at the Center for Hydro-Optics and
Remote Sensing (CHORS) at San Diego State University (SDSU) on 14--25 June 1993. SeaWiFS is an ocean
color radiometer that is scheduled for launch in 1994. The SIRREXs are part of the SeaWiFS Calibration and
Validation Program that includes the National Aeronautics and Space Administration's (NASA) Goddard Space
Flight Center (GSFC), CHORS, the National Institute of Standards and Technology (NIST), and several other
laboratories. GSFC maintains the radiometric scales (spectral radiance and irradiance) for the SeaWiFS
program using spectral irradiance standard lamps, which are calibrated by NIST. The purpose of each SIRREX
is to assure that the radiometric scales which are realized by the laboratories who participate in the SeaWiFS
Calibration and Validation Program are correct; that is, the uncertainties of the radiometric scales are such that
measurements of normalized water-leaving radiance using oceanographic radiometers have uncertainties of 5%.
SIRREX-1 demonstrated, from the internal consistency of the results, that the program goals would not be met
without improvements to the instrumentation. The results of SIRREX-2 demonstrate that spectral irradiance
scales realized using the GSFC standard irradiance lamp (F269) are consistent with the program goals, as the
uncertainty of these measurements is assessed to be about 1%. However, this is not true for the spectral
radiance scales, where again the internal consistency of the results is used to assess the uncertainty. This is
attributed to inadequate performance and characterization of the instrumentation. For example, spatial non-
uniformities, spectral features, and sensitivity to illumination configuration were observed in some of the
integrating sphere sources. The results of SIRREX-2 clearly indicate the direction for future work, with the
main emphasis on instrument characterization and the assessment of the measurement uncertainties so that the
results may be stated in a more definitive manner.
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