Dear Jonathan:
Thanks for the reply..
The specific geophysical quantity where this issue came up are the
different cloud phase categories (std name = cloud_phase_category). that
are reported for the entire image on a percentage basis. Note that we have
not yet proposed standard names for the specific cloud phase categories,
and are exploring other data design options.
Moving forward we will propose "percent_" standard_names as required.
very respectfully,
randy
----------------------------------------
From: "Jonathan Gregory" <j.m.gregory at reading.ac.uk>
Sent: Thursday, June 13, 2013 1:28 PM
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] percent coverage by GOES-R geophysical variables
Dear Randy
You added the following to ticket 102. It's a reasonable point, but I
don't
think it belongs in that ticket. I suggest we discuss it on the email
list.
> On GOES-R ground, some of the data we report for a given geographic
region
> (i.e. a cell containing many observations) is the percent that a
> particular geophysical quantity exists.
>
> We were planning on using the cell method "sum" because it generally
> conforms to the definiiton of sum in Appendix E (The data values are
> representative of a sum or accumulation over the cell. This is the
default
> method for a quantity that is extensive with respect to the specified
> dimension.)
>
> The problem with doing this is ...
>
> Percent is not the same units of the geophysical quantity. To solve
this,
> the units column for the "sum" row in appendix E could be modified to
> allow percent.
>
> Another option may be to treat "percent" as a cell method.
I would say that the percent existence of X is a different geophysical
quantity
from X and therefore needs its own standard name, which will be
dimensionless
as you say (not in the units of X). This is like area_fraction quantities
e.g.
cloud_area_fraction or area_fraction_below_surface. Could you give some
examples of X? The appropriate cell_method for the derived variable is
"sum",
as you suggest, since it represents the entire cell, not a point.
Best wishes
Jonathan
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