In the Parameter Weighting operation, one parameter (Scientific Data Set, or (SDS)) is weighted by another when computing any average (or a similar statistical quantity such as standard deviation). The averaging can be done either spatially or temporally.
The parameter-weighted average of a quantity x is computed as ﴾ ∑ (wi ∙ xi ) ﴿ / ﴾ ∑ wi ﴿ , where the sums in both numerator and denominator are taken over all grid cells i (in the spatial/temporal averaging region) for which the parameter being averaged, xi , and the weighting parameter, wi , both have valid values.
Notes: At present, Parameter Weighting is only applied to the MODIS data product "Aerosol Small Mode Fraction" which is weighted by Aerosol Optical Depth (AOD). In this case, a valid weight is defined to be any AOD ≥ 0. (Note that this definition is equivalent to resetting any negative measurement of AOD to 0 for the purpose of the weighting operation.)
If area-weighting is also being applied, the above formula still holds, but with the weights (wi’s), replaced by their product with the area of their grid cell: (wi ∙ ai ).
This Technical Summary page is under development -- for information on this operation while the documentation is being prepared, please send a message to GES DISC Help.