I think I'd have to defer to Roy and John about whether these are
really different geophysical quantities or just different scales, since
I have no experience with pH measurements (yet).
On the other hand, Roy, it's no less daunting to provide definitions
for attributes that characterize the 5 (to date) different scales than to
define new standard names for them, if we went that route. It's just
the down side of using a standard - definitions will be required,
either way.
One question for Jonathan, and I apologize if this has already been
determined - I appreciate the time you're putting into this.
If we went with the approach that these are different ways to measure
the same quantity, and used a single standard name, how would you
implement this to allow different units? Would we need to use
dimensionless
units (1) and provide the actual units in the new attribute? That might
make
the data fairly difficult to use and share effectively.
I don't know of any other measured parameters that are treated this way;
you mentioned cloud area fraction, but I'm not clear on how that was
implemented to allow different scales, and since "fraction" is part of the
standard name, it does seem that "1" is a more appropriate unit there than
here. Having the actual units specified (or worse, implied) in another
attribute it wouldn't be anything we'd deal with in existing code. Not
that this couldn't be written, but as a programmer, I think limiting the
number of special cases we have to deal with is generally a good thing.
Thanks - Nan
> Hello Jonathan,
>
> I don't see the different pH scales as the same geophysical quantity measured in different ways. I see them more as subtley different geophysical quantities (activities or concentrations of different groups of species) expressed through a common syntax (negative log transform).
>
> My initial reaction to an additional attribute is one of caution. I can see the need but have concerns as to how it would be populated. Plaintext doesn't scale and standardised sensor descriptions have kept a group of us in MMI pretty busy over the past year, which makes doing the same for analytical methods look very daunting.
>
> Cheers, Roy.
>
> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jonathan Gregory
> Sent: 08 May 2009 10:29
> To: cf-metadata at cgd.ucar.edu; Lowry, Roy K
> Subject: [CF-metadata] new standard name request for pH
>
> Dear John
>
> Thanks for the helpful information and all your time, and your colleagues',
> spent on this.
>
> If the conclusion is "There are several ways of measuring pH and this is the
> best one for the circumstances", as you say, it sounds to me that pH is the
> geophysical quantity, and "total scale" is a measurement technique. That
> means I tend to the solution of not including it in the standard name, and
> deciding on another attribute to record it in. We do not define distinct
> standard names for different ways of measuring the same quantity. That's a
> point that came up, for instance, regarding cloud area fraction from different
> satellites. But it is still important to record the information, since the
> results may be systematically different. Maybe we need a new CF attribute
> for this kind of purpose. What do you think, Roy, Nan and others?
>
> Best wishes
>
> Jonathan
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> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
>
--
*******************************************************
* Nan Galbraith (508) 289-2444 *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 *
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Received on Mon May 11 2009 - 09:27:49 BST
