[CF-metadata] percent coverage by GOES-R geophysical variables

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 13 Jun 2013 18:28:20 +0100

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
Received on Thu Jun 13 2013 - 11:28:20 BST