The procedure used to derive cloud fraction and cloud top pressure in version-6 is similar to that used in version-5,1,3 but version-6 has a number of significant improvements. The radiatively effective cloud fraction at frequency , is given by the product of , the geometric fractional cloud cover of an AIRS FOV as seen from above, and , the cloud spectral emissivity. The AIRS science team cloud parameter retrieval methodology determines only the product of these two terms, , along with a corresponding cloud top pressure , for each of up to two layers of clouds in a given scene.1,3 A basic simplifying assumption of the cloud retrieval methodology used in both version-5 and version-6 is that the clouds are gray, that is, is independent of frequency. Version-5 simultaneously derived 20 parameters for each AIRS FOR, nine effective cloud fractions and , one pair for each AIRS FOV contained within the AMSU FOR, along with two cloud top pressures , and considered to be representative of the pressures of each of the two layers of clouds covering the entire AIRS FOR. In version-6, the cloud parameter retrieval step is performed separately for each AIRS FOV to determine the four parameters, , , , and , in each FOV. A total radiatively effective cloud fraction for the entire FOR, , is computed as the average cloud fraction according to Display Formula
(4)and an effective cloud top pressure for the entire FOR is computed as the weighted average of all nine values of and in the FOR Display Formula
(5)as was also done in version-5. The version-6 level-2 product contains individual values of , , , for each AIRS FOV, as well as the single FOR heritage values and defined according to Eqs. (4) and (5).