Vol. 23: SeaWiFS Prelaunch Radiometric Calibration and Spectral Characterization.
Citation:
Barnes, R.A., A.W. Holmes, W.L. Barnes, W.E. Esaias, C.R. McClain, and T. Svitek, 1994: SeaWiFS Prelaunch Radiometric Calibration and Spectral Characterization, NASA Tech. Memo. 104566, Vol. 23, S.B.
Hooker, E.R. Firestone, and J.G. Acker, Eds., NASA Goddard Space Flight Center, Greenbelt, Maryland, 55
pp., (in press).
Based on the operating characteristics of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS),
calibration equations have been developed that allow conversion of the counts from the radiometer into Earth-
exiting radiances. These radiances are the geophysical properties the instrument has been designed to measure.
SeaWiFS uses bilinear gains to allow high sensitivity measurements of ocean-leaving radiances and low
sensitivity measurements of radiances from clouds, which are much brighter than the ocean. The calculation of
these bilinear gains is central to the calibration equations. Several other factors within these equations are also
included. Among these are the spectral responses of the eight SeaWiFS bands. A band's spectral response
includes the ability of the band to isolate a portion of the electromagnetic spectrum and the amount of light that
lies outside of that region. The latter is termed out-of-band response. In the calibration procedure, some of the
counts from the instrument are produced by radiance in the out-of-band region. The number of those counts for
each band is a function of the spectral shape of the source. For the SeaWiFS calibration equations, the out-of-
band responses are converted from those for the laboratory source into those for a source with the spectral shape
of solar flux. The solar flux, unlike the laboratory calibration, approximates the spectral shape of the Earth-
exiting radiance from the oceans. This conversion modifies the results from the laboratory radiometric
calibration by 1-4%, depending on the band. These and other factors in the SeaWiFS calibration equations are
presented here, both for users of the SeaWiFS data set and for researchers making ground-based radiance
measurements in support of SeaWiFS.
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