ERBE-like Data Processing with ScaRaB Broadband Radiances

As a follow-on to ERBE, the first version of the ScaRaB data processing was developed by the Laboratoire de Météorologie Dynamique du C.N.R.S. (LMD) as an "ERBE-like version" to ensure consistency between ERBE and ScaRaB products .

Like all scanning radiometers, ScaRaB measures radiances at specific angles. The filtered SW and LW radiances, after radiometric calibration, are first corrected for spectral filtering effects. The ERBE angular dependence models (ADMs), which account for the anisotropy of the radiation field, are then applied to the unfiltered SW and LW radiances to obtain the SW and LW fluxes at TOA.

Because ADMs depend on the type of surface and the amount of cloud present in the observed scene, the maximum likelihood estimation algorithm is used to identify the scene type (Wielicki and Green 1989). The 12 scene classifications are the same as used by ERBE, based on a combination of five geotypes (ocean, land, snow, desert, coast) and four cloud categories: clear [0%-5% cloud cover], partly cloudy [5%-50% cloud cover], mostly cloudy [50%-95% cloud cover], overcast [95%-100% cloud cover].

Since the objective of the ScaRaB project is to determine the TOA ERB components on a scale appropriate to the study of cloud radiation interactions, an additional procedure is performed to obtain proper averages of the fluxes from temporally and spatially sparse samples (Brooks et al. 1986).

Similar to ERBE, three levels of ScaRaB data are produced by the data processing procedures. In particular, the second level (A2) is directly comparable to the ERBE S-8 product containing instantaneous unfiltered SW and LW radiances, estimated TOA fluxes, as well as scene identifications at the pixel level.

References:

Wielicki, B. A. and R. N. Green, 1989: Cloud identification for ERBE radiative flux retrieval. J. Appl. Meteor., 28, 1133-1146.

Brooks, D. R., E. H. Harrison, P. Minnis, J. T. Suttles, and R. Kandel, 1986: Development of algorithms for understanding the temporal and spatial variability of the Earth's Radiation Balance. Rev. Geophys., 24, 422-438.

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