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 <aaron.sweeney at noaa.gov> 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.
>
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