Subtle Differences from Regular ISCCP DX Data Product

ISCCP-ScaRaB DX dataset is constructed to be as close as possible to the regular ISCCP DX dataset. However, due to the nature of ScaRaB instrument, ISCCP-ScaRaB DX dataset slightly differs from the regular ISCCP DX dataset in the following three aspects:

• Although the regular ISCCP DX native (NAT) dataset has a nominal resolution of 30 km 30 km sampled image pixels), the retrieved cloud (and surface) properties are actually radiatively weighted averages over the small-scale (~5 km) variations present in each pixel. The cloud and surface retrievals in the special ISCCP-ScaRaB DX dataset, however, represent radiatively weighted averages over a larger spatial area (~60 km at nadir) as a result of the coarse resolution of ScaRaB scanner.
• In the polar regions of regular ISCCP DX dataset, near-infrared (NIR: ~3.7 um) radiances are used to augment detection and radiative analysis of clouds over snow and ice surfaces. Because the NIR channel is not available on the ScaRaB scanner, cloud detection and retrieval are perfomed using VIS and IR channels only (over the entire globe). As a result, the three NIR-related variables are not meaningful in this dataset.
• In the regular ISCCP DX dataset, three bytes are used to store radiances for up to three extra wavelengths, if available. In the special ISCCP-ScaRaB DX dataset, the TOA broadband SW and LW fluxes (estimated by the ERBE methodology from broadband radiances, measured by the ScaRaB instrument and co-located with the narrowband radiances used for the ISCCP analysis) are packed into these three bytes. These two flux values can be extracted using the sample read program.

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