Well, this gets into subtleties of meaning and 'stuff', but here's my take:
If I have two values labeled sea_water_temperature, I can assume they are the same fundamental quality, and even if provided on different scales, those values can be converted to the same scale, using the information in the units attribute. So they are interoperable.
On the other hand, if I have two values labeled sea_water_pH, there is a conundrum. I may not know if these values need to be converted (because units will not necessarily give me a clue), and even if they are convertible in some sense, I don't have the auxiliary parameters that would be needed to do the conversion (just knowing the way it was measured is not enough). So we can not know these values are interoperable.
john
On Dec 9, 2011, at 07:58, Upendra Dadi wrote:
> Thank you Jonathan and John for your emails.
>
> I went through your earlier emails. One of the things that occurred to me is that these discussions that you had are as much a part of the standard as the names themselves. I think it would be great if there is better "connection" between your email conversation and the standard name tables. Often the short summary given in the standard name table, while useful, is not sufficient to understand what the name stands for.
>
> Coming to the problem of coming up with a standard name for pH accurately, I can see the issue here. Though I am still not sure why not all five standard names were included. If there is an analogy between sea water pH and sea water temperature, as mentioned in one of the emails, why not have sea_water_pH just as we have sea_water_temperature?
>
> Upendra
>
> On 12/8/2011 1:39 PM, John Graybeal wrote:
>>
>> Hi Upendra,
>>
>> The reason the "reporting scale" is attached to this name is that the fundamental measurement, or property, to which it refers produces numbers that are not comparable to pH derived using other techniques. (They are actually measuring different quantities, not just a different offset/scale value.)
>>
>> From what I (not a scientist!) understand, it is often the case that pH that doesn't mention its scale has been measured in a way that is not an effective indicator of pH in sea water. So it is very important to understand the way the pH was measured, in order that the values be reported compatibly with others.
>>
>> I am not knowledgeable enough to know the right answer to your two questions, but the above may be useful input.
>>
>> John
>>
>> On Dec 8, 2011, at 08:35, Upendra Dadi wrote:
>>
>>> Hi All,
>>> The standard name table has an entry called "sea_water_ph_reported_on_total_scale". I have some data which does not mention the scale used for the measurement of ph. Should there be an another entry which does not mention the scale? Most of the standard names I have seen doesn't mention the scale used. Is it common to attach within standard name, the scale used for the measurement?
>>>
>>> Upendra
>>> _______________________________________________
>>> CF-metadata mailing list
>>> CF-metadata at cgd.ucar.edu
>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>
>>
>
> _______________________________________________
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John Graybeal <mailto:jgraybeal at ucsd.edu>
phone: 858-534-2162
Product Manager
Ocean Observatories Initiative Cyberinfrastructure Project:
http://ci.oceanobservatories.org
Marine Metadata Interoperability Project:
http://marinemetadata.org
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