[CF-metadata] Units for dimensionless quantities

From: Dave Allured - NOAA Affiliate <dave.allured>
Date: Tue, 20 Aug 2013 17:30:40 -0600

Michael,

Use a unit of "count" for anything that is a dimensionless count. You
will need either Udunits-1, or Udunits-2 version 2.1.18 or greater.

--Dave

On Tue, Aug 20, 2013 at 1:41 PM, Carlomusto, Michael
<mcarlomu at harris.com> wrote:
> Good day.
>
> As a data producer I am seeking a resolution on the use of units="1" for dimensionless quantities.
>
> Page 10 of CF Metadata Conventions version 1.6 states:
>
> "Units are not required for dimensionless quantities. A variable with no units attribute is assumed to be dimensionless. However, a units attribute specifying a dimensionless unit may optionally be included. The Udunits package defines a few dimensionless units, such as percent, but is lacking commonly used units such as ppm (parts per million). This convention does not support the addition of new dimensionless units that are not udunits compatible. The conforming unit for quantities that represent fractions, or parts of a whole, is "1"."
>
> This clearly states that units="1" should be used for fractions or parts of a whole.
>
> However, in the standard name table, units="1" is used for dimensionless quantities that are not fractions.
> See for example, land_binary_mask or sea_ice_classification. Is units="1" valid for dimensionless quantities that are not fractions? Or is units="1" simply used as the default for all standard names that are dimensionless?
>
> What units if any should be used for a variable named "number_of_cloud_pixels" in a dataset containing a satellite image of the earth?
>
> Thank you.
>
>
> Michael Carlomusto
> mcarlomu at harris.com
> Harris Corp.
> GOES-R Ground System
> Melbourne, FL, USA
> +1-321-309-7905
>
Received on Tue Aug 20 2013 - 17:30:40 BST