[netCDF #PCM-734975]: NetCDF CF Conventions Issue

Hi Adriana,

> Hello Support,
> I'm wondering if you can help me with two questions related to creating
> NetCDFs. The first has to do with unit names. I'm creating a file of water
> isotopic data, the standard unit for which is "permil" or parts per
> thousand. Neither "permil" or "parts per thousand" are acceptable according
> to the CF Conventions checker, which uses the Unidata udunits library.
> However, from a scientific perspective, reporting the isotope ratios in
> "percent" or another such unit does not make sense. Do you have any
> recommendations?

In the “Units” section of the CF Conventions document, the 3rd paragraph 
discusses percent, ppm, etc. I believe it indicates you should use “1e-3” for 
units and further details can be included in the “long_name” attribute (or 
“standard_name” attribute, if appropriate).

> The other question is about flag_values. Would you be able to help me
> understand how to write flag_values so that I do not encounter the
> following error: "ERROR: Attribute flag_values of incorrect type (expecting
> 'Data Variable' type...)" I receive this error message whether I write the
> flag_values as a string, an integer, or a double. My flag values are 0 and
> 1.

The CF “Flags” Section  says that the flag_value has to match the data type of 
the data variable. The flag_meaning is a blank separated string that provides 
the meaning of the flag/data values. Flag variables are most commonly stored as 
bytes. The first example in the “Flags” section provides a CDL snippet of a 
flag variable provides a nice example:

  byte current_speed_qc(time, depth, lat, lon) ;
    current_speed_qc:long_name = "Current Speed Quality" ;
    current_speed_qc:standard_name = "status_flag" ;
    current_speed_qc:_FillValue = -128b ;
    current_speed_qc:valid_range = 0b, 2b ;
    current_speed_qc:flag_values = 0b, 1b, 2b ;
    current_speed_qc:flag_meanings = "quality_good sensor_nonfunctional
                                      outside_valid_range" ;

> Thank you in advance for your help,
> Adriana

Hope that helps.

Also, for CF focused questions like these, the best place to ask for help is 
the CF Discussion forum (also see the CF Discussion page). There are more CF 
experts there than we have here in the netCDF group.

Cheers,

Ethan

Ticket Details
===================
Ticket ID: PCM-734975
Department: Support netCDF
Priority: Normal
Status: Open
===================
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