Dear Randy > The GOES-R ground system generates level 2+ products such as aerosol optical > depth, for the hemispheric, continental US, and mesocale (100 km x 1000 km) > regions. > > The NetCDF product files need to contain statistics (min, max, mean, and > standard deviation) associated with ALL the gridded data associated with a > region. > > It would seem the use of cell methods to express these statistics in the > product file makes sense even though there is only one cell (i.e. the one > cell that captures the statistic for the entire region).
Yes, I agree. > It is stated in the first sentence of CF standard para. 7.3.3 that the > statistical method is evaluated over the entire horizontal area of the cell. > In the case of our level 2+ products, this is not always the case, so we have > a need to somehow express that the statistic is associated with a subset of > the cell. > > For example, in the case of the Aerosol Optical Depth (AOD) product, the > algorithm that generates the gridded data is has solar zenith angle and > platform zenith angle constraints. > > Essentially, these statistics apply to a portion of the single cell. > Unfortunately, the "where <area_type>" features discussed in CF standard > para. 7.3.3 do not work for us because the AOD product constraints are > associated with the solar zenith angle and platform zenith angle at the time > of observation, not one of the area_types. > > Given the currently available cell method constructs, which allow for > capturing the original spacing of the gridded data elements and the ability > to include non-standardized information, we have applied the existing CF > cell_method constructs as follow: > > float minimum_AOD_for_region ; > > coordinates = "solar_zenith_angle platform_zenith_angle time y x" ; > > cell_methods = "time: sum area: sum (interval: 2 km > comment:solar_zenith_angle and platform_zenith_angle conforming pixels only)" > ; > > Is the way we are applying cell methods consistent with the CF standard ? Yes, I think that is fine, if it's OK for you to use non-standardised information. This sort of application was the intention of the standard. Is "sum" really the right cell_method? I would have expected "mean". Best wishes Jonathan _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
