Dear Jonathan,
Thank you very much for your comment. The parenthetical "...from
different sources /(such as observations and models)/" is missing from
section 3.3 (Standard Name) of the CF Conventions v1.6 (and draft
v1.7). This is important for proper interpretation. On initial reading
of the section 3.3, I interpreted the word "sources" to mean data
providers. I would recommend adding your parenthetical to the
documentation and possibly refer the reader to ACDD v1.3 to address the
question of how to attribute a variable as originating from observation,
model, or other, as suggested by John Graybeal.
Cordially,
Aaron
Date: Mon, 15 Dec 2014 14:03:48 +0000 From: Jonathan Gregory
<[email protected]> To: [email protected] Subject: Re:
[CF-metadata] how to indicate a variable representing a physical
quantity is an observation, a modelled value, a difference or
residual, etc. Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii Dear Aaron
I think there's a reason CF names don't naturally distinguish between measured
or observed values?CF names tend to describe the meaning of the value, and
explicitly avoids saying how it was derived. The derivation is reserved to
other attributes, like the 'source' (which should distinguish between a model
and an observation, though not in a computable way), or 'history'.
I agree with this remark of John's. In fact, the main purpose of the CF
standard names is to indicate which quantities should be regarded as
comparable. Usually, we want to compare quantities derived from different
sources (such as obs and models), so we give the corresponding quantities the
same standard names, in order to indicate they can be meaningfully compared:
that they are apples from different trees, rather than apples and oranges.
Best wishes
Jonathan
On 12/12/2014 12:46 PM, John Graybeal wrote:
Just yesterday (really!) I was looking at the almost-ready ACDD 1.3
convention, and saying "What is the 'coverage_content_type' attribute
good for?" It appears to be good for almost exactly what you want.
This attribute is 'highly recommended' for all NetCDF variables, and
is defined as "An ISO 19115-1 code to indicate the source of the data
(image, thematicClassification, physicalMeasurement,
auxiliaryInformation, qualityInformation, referenceInformation,
modelResult, or coordinate)." However, this covers only 2/3 of what
you want: physicalMeasurement for in-situ observations, and
modelResult for a value from a model. The difference is also a
modelResult in my opinion, but that doesn't help your use case.
If you are looking for a pure CF answer, there's not a complete
answer, but there are standard names that refer to differences --
these usually end with the phrase _anomaly (Definition: "anomaly"
means difference from climatology."); or there's one, umm, anomaly
that starts with difference_
(difference_of_air_pressure_from_model_reference). Because the phrase
_anomaly is already in 5 terms, it shouldn't be an issue to add more
as needed. And that conveniently bridges the above gap in your use case.
I think there's a reason CF names don't naturally distinguish between
measured or observed values—CF names tend to describe the meaning of
the value, and explicitly avoids saying how it was derived. The
derivation is reserved to other attributes, like the 'source' (which
should distinguish between a model and an observation, though not in a
computable way), or 'history'.
Hope that helps, at least a bit.
John
References:
* ACDD 1.3 convention, almost done now:
http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_1-3
* coverage_content_type attribute:
http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_1-3#coverage_content_type
* purpose of a standard name:
http://cfconventions.org/faq.html#stdnames_purpose
---------------
John Graybeal
Marine Metadata Interoperability Project: http://marinemetadata.org
MMI Ontology Registry and Repository: http://mmisw.org/orr
On Dec 12, 2014, at 11:01, Aaron Sweeney <[email protected]
<mailto:[email protected]>> wrote:
Hi,
I've looked through the latest CF Conventions and CF Standard
Names documents, but have been unable to find an answer (or example)
to the following question:
How do I indicate that a variable representing a physical
quantity is an in situ observation, a value that came from a model,
or a difference or residual between an observation and a modelled
value (observed minus modelled)?
My initial thought was to use the same standard name for each
variable, but provide a standard name modifier. But after reading
the appendix on modifiers, they seem to be used for something else.
The standard names themselves only describe the physical quantity,
but not whether or not they are an observed value or modelled value.
Please point me toward the appropriate documentation, if it
exists. Thanks for your kind attention.
Cordially,
Aaron
--
Aaron D. Sweeney
Water Level Data Manager
Cooperative Institute for Research in Environmental Sciences (CIRES)
University of Colorado at Boulder
and
NOAA National Geophysical Data Center
Marine Geology and Geophysics Division
325 Broadway, E/GC3
Boulder, CO 80305-3328
Phone: 303-497-4797, Fax: 303-497-6513
DISCLAIMER: The contents of this message are mine personally and do
not necessarily reflect any position of NOAA.
_______________________________________________
CF-metadata mailing list
[email protected] <mailto:[email protected]>
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--
Aaron D. Sweeney
Water Level Data Manager
Cooperative Institute for Research in Environmental Sciences (CIRES)
University of Colorado at Boulder
and
NOAA National Geophysical Data Center
Marine Geology and Geophysics Division
325 Broadway, E/GC3
Boulder, CO 80305-3328
Phone: 303-497-4797, Fax: 303-497-6513
DISCLAIMER: The contents of this message are mine personally and do not
necessarily reflect any position of NOAA.
_______________________________________________
CF-metadata mailing list
[email protected]
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
