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You are here: GES DISC Home Giovanni - Interactive Visualization and Analysis Giovanni-3 Operation Technical Summary: Parameter Weighting

Giovanni-3 Operation Technical Summary: Parameter Weighting

Parameter Weighting

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.

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Last updated: Nov 10, 2011 12:08 PM ET