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Uncertainty in Cloud Optical Depth Estimates Made from
Satellite Radiance Measurements
Robert Pincus,
Malgorzata Szczodrak, Jiujing Gu, and Philip H. Austin
Journal of Climate, May 1995,
8, No. 5, pages 1453-1462
Abstract
The uncertainty in optical depths retrieved from satellite measurements of
visible wavelength radiance at the top of the atmosphere is quantified.
Techniques are briefly reviewed for the estimation of optical depth from
measurements of radiance, and it is noted that these estimates are always
more uncertain at greater optical depths and larger solar zenith angles.
The lack of radiometric calibration for visible wavelength imagers on
operational satellites dominates the uncertainty retrievals of optical
depth. This is true for both single pixel retrievals and for statistics
calculated from a population of individual retrievals. For individual
estimates or small samples, sensor discretization (especially for the VAS
instrument) can also be significant, but the sensitivity of the retrieval
to the specification of the model atmosphere is less important. The
relative uncertainty in calibration affects the accuracy with which
optical depth distributions measured by different sensors may be
quantitatively compared, while the absolute calibration uncertainty,
acting through the nonlinear mapping of radiance to optical depth, limits
the degree to which distributions measured by the same sensor may be
distinguished.
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