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Assessment of the Accuracy of the MOBY Spectral Radiance Calibration Sources Using the SXR and the VXR



Bettye C. Johnson, Howard W. Yoon, M Feinholz, D K. Clark


The Marine Optical Buoy (MOBY) and its related optical system the Marine Optical Sensor (MOS) consist of dual CCD-based spectrographs. MOBY, MOS, and other instruments operated by the MOBY team are used to provide in situ measurements of water-leaving spectral radiance, which is a key data product for ocean color satellite sensors. The goal is to determine the water-leaving spectral radiance with a relative standard uncertainty between 1% and 5%. MOBY and MOS are calibrated before and after the deployments at the field locations using NIST-traceable standards of spectral irradiance and radiance. The spectral radiance standards used are commercial lamp-illuminated integrating sphere sources that are calibrated from 300 nm to 900 nm by the manufacturer at regular intervals of lamp burning hours.The Sea-viewing, Wide Field-of-view Sensor (SeaWiFS) and the Earth Observing System (EOS) projects at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center have sponsored the development of two six channel filter radiometers at NIST. Termed the SeaWiFS transfer Radiometer (SXR) and the Visible Transfer Radiometer (VXR), these radiometers have been used at the MOBY calibration site in Honolulu, Hawaii to provide an independent assessment of the accuracy of the MOBY spectral radiance standards. Because the source and radiometer standards are all NIST-traceable, the comparisons should agree within the combined uncertainties. This paper presents the results of the SXR comparison in 1996 and the VXR comparisons in 1999 and 2000. For the latter two comparisons, a NIST-developed portable sphere source was also used. For all three comparisons, two other portable radiometers were used. These radiometers were developed by NIST for the National Atmospheric and Oceanic Administration (NOAA) so the MOBY team could assess the accuracy and stability of the spectral radiance (or irradiance) standards at two wavelengths at any time. Because they are also calibrated at NIST, measurements during the MOBY/NIST comparisons should be consistent with results derived from the SXR or the VXR for all of the integrating sphere sources in the comparisons. The level of agreement is used to estimate the accuracy of the radiometric calibration of MOBY and MOS.
Conference Dates
October 9-13, 2000
Conference Location
Venice, IT
Conference Title
NASA Web Site


MOBY, ocean color, spectroradiometry, SXRY, transfer radiometers, VXR


Johnson, B. , Yoon, H. , Feinholz, M. and Clark, D. (2000), Assessment of the Accuracy of the MOBY Spectral Radiance Calibration Sources Using the SXR and the VXR, NASA Web Site, Venice, IT (Accessed April 20, 2024)
Created October 1, 2000, Updated February 17, 2017