Jim, I think you use an 'ancillary_variables' attribute to tie quality
or other
variables together.
It's alarming to think people can use an unmodified standard name like
sea_water_temperature for a variable that is in fact a standard deviation
or an error. I'm very curious to know if this is a widespread use of cell
methods, because it seems so ... wrong.
Even if it's legal in CF, I wouldn't do it; I'd give this variable a
long name only,
and attach it to the actual sea_water_temperature (if there is such a
variable in
the file) via an ancillary_variable attribute.
The possible misuse of data provided with a misleading standard name like
this seems much worse than the possibility that the field could be
overlooked
by data discovery systems.
- Nan
On 3/26/13 10:06 AM, Jim Biard wrote:
> Then why is standard deviation a cell method and standard error a
> standard name modifier? To my mind, they both represent "analytical
> methods that have been applied to derive the data values stored in the
> array".
>
> While I'm at it, what is the correct way to provide linkage between
> the primary data variable and the quality measure variables? Would
> this be via an ancillary_coordinates attribute on the primary
> variable? Or do you put an ancillary_coordinates attribute on each
> quality measure variable that names the primary? I'm guessing the
> first answer (if either) is right, but that method is well less
> intuitive when browsing the file contents.
>
> Grace and peace,
>
> Jim
>
>
>
> On Mar 26, 2013, at 9:56 AM, David Hassell <d.c.hassell at reading.ac.uk
> <mailto:d.c.hassell at reading.ac.uk>> wrote:
>
>> Hello,
>>
>> I see it a bit differently. The 'area: mean time: standard_deviation'
>> cell methods, for example, describe analytical methods that have been
>> applied to derive the data values stored in the array. This is not the
>> case, it seems to me, for the standard name modifiers. The presence of
>> a standard name modifier points to, or defines, some metadata which
>> further describes a data variable's array (either its own array, or
>> another's via ancillary variables).
>>
>> All the best,
>>
>> David
>>
>> ---- Original message from Jim Biard (09AM 26 Mar 13)
>>
>>> From: Jim Biard <jim.biard at noaa.gov <mailto:jim.biard at noaa.gov>>
>>> Date: Tue, 26 Mar 2013 09:14:11 -0400
>>> To: "cf-metadata at cgd.ucar.edu <mailto:cf-metadata at cgd.ucar.edu>"
>>> <cf-metadata at cgd.ucar.edu <mailto:cf-metadata at cgd.ucar.edu>>
>>> X-Mailer: Apple Mail (2.1503)
>>> Subject: Re: [CF-metadata] Question from NODC about interplay of
>>> standard
>>> name modifiers, cell_methods, etc.
>>>
>>> This has confused and bothered me as well. There doesn't seem to be
>>> any consistency on whether to use cell methods or standard name
>>> modifiers for the various quality measures. Is it just that no one
>>> has requested a modifier?
>>>
>>> fd
>>>
>>> On Mar 26, 2013, at 8:32 AM, "Kenneth S. Casey - NOAA Federal"
>>> <kenneth.casey at noaa.gov> wrote:
>>>
>>>> Jonathon,
>>>>
>>>> Thanks. The picture is clearer now, but I think I still have a
>>>> question or two. Let me try to summarize first, then ask the
>>>> questions:
>>>>
>>>> Ok, so for example, we have the simple case of the variable
>>>> containing the physical variable of sea water temperature:
>>>>
>>>> float t_an(time, depth, lat, lon) ;
>>>> t_an:standard_name = "sea_water_temperature" ;
>>>> t_an:long_name = "Objectively Analyzed Mean of Sea
>>>> Water Temperature" ; // Expanded long_name following Steve's comment
>>>> t_an:comment = "Objectively analyzed climatologies
>>>> are the objectively interpolated mean fields for an oceanographic
>>>> variable at standard depth levels for the World Ocean." ;
>>>> t_an:cell_methods = "area: mean depth: mean time:
>>>> mean" ; // added space between dimension and method, following
>>>> Jonathan's comment
>>>> t_an:grid_mapping = "crs" ;
>>>> t_an:units = "degrees_celsius" ;
>>>> t_an:FillValue = 9.96921e+36f ;
>>>>
>>>> And, I would point out there there are cell bounds variables as
>>>> well for lat, lon, depth, and a climatology_bounds for
>>>> climatological time (time axis is a climatological time axis). So,
>>>> we have a standard name, plus cell_methods.
>>>>
>>>> The next case for these data is where we have a statistical value
>>>> that is contained in the variable, but where no standard_name
>>>> modifier exists? here is an example then for standard deviation of
>>>> that sea water temperature:
>>>>
>>>> float t_sd(time, depth, lat, lon) ;
>>>> t_an:standard_name = "sea_water_temperature" ; //
>>>> Use the physical parameter's standard_name, following Jonathan's
>>>> comment
>>>> t_an:long_name = "Temporal Standard Deviation about
>>>> the Statistical Mean Sea Water Temperature" ; // Expanded
>>>> long_name following Steve's comment
>>>> t_an:comment = "The temporal standard deviation about
>>>> the statistical mean Sea Water Temperature in each grid-square at
>>>> each standard depth level" ; // just highlighting changes compared
>>>> to our existing draft
>>>> t_an:cell_methods = "area: mean depth: mean time:
>>>> standard_deviation" ; // sequence is correct I think, take
>>>> area-depth mean first, then compute standard deviation over time
>>>> t_an:grid_mapping = "crs" ;
>>>> t_an:units = "degrees_celsius" ;
>>>> t_an:FillValue = 9.96921e+36f ;
>>>>
>>>> Seems simple enough, though I do need to confirm with Tim that the
>>>> variable is in fact a temporal standard deviation. Now the third
>>>> case is where there exists a relevant standard_name modifier, for
>>>> example, for the standard error of the mean:
>>>>
>>>> float t_se(time, depth, lat, lon) ;
>>>> t_an:standard_name = "sea_water_temperature
>>>> standard_error" ; // Use the physical parameter's standard_name
>>>> plus modifier, following Jonathan's comment
>>>> t_an:long_name = "Standard Error about the
>>>> Statistical Mean Sea Water Temperature" ; // Expanded long_name
>>>> following Steve's comment
>>>> t_an:comment = "The standard error about the
>>>> statistical mean Sea Water Temperature in each grid-square at each
>>>> standard depth level" ; // just highlighting changes compared to
>>>> our existing draft
>>>> t_an:cell_methods = "area: mean depth: mean" ; // Is
>>>> this correct?? Since we have a standard name modifier, and no
>>>> cell_methods string for standard error?
>>>> t_an:grid_mapping = "crs" ;
>>>> t_an:units = "degrees_celsius" ;
>>>> t_an:FillValue = 9.96921e+36f
>>>>
>>>> So, my question arises in this last example, where a standard name
>>>> modifier exists. I guess this is the part I don't understand?. is
>>>> there no reference to cell_methods for the time dimension in the
>>>> standard error variable t_se? If so, why is there a standard_error
>>>> standard_name modifier but not one for standard_deviation?
>>>>
>>>> Thanks, Ken
>>>>
>>>>
>>>>
>>>> On Mar 25, 2013, at 1:40 PM, Jonathan Gregory
>>>> <j.m.gregory at reading.ac.uk> wrote:
>>>>
>>>>> Dear Ken
>>>>>
>>>>>> Thanks for your response too (copied here? is it bad form in a
>>>>>> listserv to consolidate responses like this?)
>>>>>
>>>>> I think it's convenient, myself!
>>>>>
>>>>>> That answer seems so easy and obvious that I wonder if I asked
>>>>>> the question properly! I'll have to ask Tim to be sure, but I
>>>>>> think the standard deviation is the standard deviation over time,
>>>>>> of means generated in each time-area-depth cell.
>>>>>
>>>>>> But I think the question still remains about being able to use a
>>>>>> standard name, which we would like to do of course? I am pretty
>>>>>> sure in this example for this standard deviation variable we
>>>>>> should NOT use sea_water_temperature for standard_name, and that
>>>>>> it would be good if there were more standard name modifiers to
>>>>>> choose from. If there were, perhaps we could set standard name
>>>>>> to something like "sea_water_temperature standard_deviation".
>>>>>
>>>>> You *should* use sea_water_temperature as the standard_name. The
>>>>> standard_name
>>>>> alone is not to be regarded as the description of the metadata. It
>>>>> has to be
>>>>> taken in combination with cell_methods and modifiers. Maybe it
>>>>> seems more
>>>>> surprising that a temporal standard deviation of
>>>>> sea_water_temperature has
>>>>> sea_water_temperature for its standard name, but it's really the
>>>>> same kind of
>>>>> idea - i.e. a statistic - as a temporal mean or a temporal
>>>>> maximum, isn't it.
>>>>> Even if it was variance its standard_name would be
>>>>> sea_water_temperature, and
>>>>> in that case the units would be different too.
>>>>>
>>>>> Cheers
>>>>>
>>>>> Jonathan
--
*******************************************************
* Nan Galbraith Information Systems Specialist *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 (508) 289-2444 *
*******************************************************
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