ISCCP-like Data Processing with ScaRaB Narrowband Radiances

The ScaRaB visible (VIS) and infrared window (IRW) channels are comparable to those used in the ISCCP analysis; thus it is a natural idea to apply the ISCCP algorithm to the ScaRaB VIS and IRW radiances.

Similar to many cloud algorithms, the ISCCP algorithm consists of two basic phases: the cloud detection phase and the cloud properties derivation phase. Based on a series of statistical analyses of the radiance space-time variations, the cloud detection algorithm first infers the clear-sky VIS and IRW radiances for each individual pixel. An individual pixel is then classified as cloudy, if either the VIS or IRW radiance differs from its corresponding clear-sky value by more than the detection thresholds, or clear if otherwise (Rossow and Garder 1993).

If the pixel is cloudy, then comparison of the observed radiances to those predicted by a radiative transfer model determines a cloud top temperature (Tc) from the IRW radiance and a visible optical thickness (Tau; daytime only) from the VIS radiance.

If the pixel is clear, then surface temperature (Ts) and surface visible reflectance (Rs, daytime only) are retrieved. The effects of the atmosphere on the radiances are accounted for and cloud top pressure (Pc) is determined from Tc using the atmospheric temperature and humidity profile from TOVS product.

From the ScaRaB VIS and IRW radiances, cloud and surface properties are retrieved in the same form as the ISCCP DX (pixel level) dataset, and are called ISCCP-ScaRaB DX.

References:

Rossow, W. B., and L. C. Garder, 1993: Cloud detection using satellite measurements of infrared and visible radiances for ISCCP. J. Climate, 6, 2341-2369.

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