We describe what is believed to be a new approach developed for the National Polar-Orbiting Operational Environmental Satellite System (NPOESS) to retrieve pixel-level, cirrus cloud top temperatures (CTTs) from radiances observed in the 8.55 and bandpasses. The methodology solves numerically a set of nonlinear algebraic equations derived from the theory of radiative transfer based upon the correlation between emissivities in these two bandpasses. This new approach has been demonstrated using NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) as a proxy to Visible Infrared Imager Radiometer Suite (VIIRS) data. Many scenes have been analyzed covering a wide range of geophysical conditions, including single-layered and multilayered cirrus cloud situations along with diverse backgrounds and seasons. For single-layer clouds, the new approach compares very favorably with the MODIS resolution cloud products; the mean CTT for both methods are very close, while the standard deviation for the new approach is smaller. However, in multilayered cloud situations, the mean CTTs for the new approach appear to be colder than the CTTs from MODIS cloud products, which are acknowledged to be too warm. Finally, partly because the new approach is applied at the pixel level, CTTs do not increase toward cloud edges as is seen in the MODIS products. Based upon these initial results, the new approach to retrieve improved VIIRS cloud top properties has been incorporated into the ground-based data processing segment of the NPOESS system where prelaunch testing of all VIIRS algorithms continues.
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