Dear Jonathan: In the case of the GOES-R derived motion winds product, the error estimate (i.e. more formally referred to as Expected Error) is based on a custom algorithm. This expected error algorithm is specific to atmospheric wind vectors derived from satellte data. The overarching concept of the wind algorithms generated from satellite data is doing pattern matching of phenomena (like clouds) across multiple images of the same region separated by some period of time The GOES-R incarnation of this Expected Error approach makes use of a set of error predictors including (1) NWP model data (wind shear, temperature gradient), (2) wind speed, direction, and consistency quality indicators output from the winds algorithm proper, and (3) a wavelength dependent constants (GOES-R generates sets of wind vectors from a visible and several emissive bands) I also found an article on the web that discusses it: https://www.eumetsat.int/cs/idcplg?IdcService=GET_FILE&dDocName=pdf_conf_p42 _s2_le_marshall&allowInterrupt=1&noSaveAs=1&RevisionSelectionMethod=LatestRe leased very respectfully, randy Dear all OK, I agree that if it's useful to compare them, then they should be described in a standardised way. Why is this *not* a standard error? I suppose that to be described as a standard error it should be a number you could regard as the standard deviation of the true value around the stated value. If it's not that, are there other ways you would use such a number? Best wishes Jonathan
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