Nan,
It seems to me, though, that depending on the long_name attribute to describe the operation used to obtain the quality measure is overly "squishy". So, if it is a standard deviation, I can use a standard name modifier to indicate it. But if it is a standard error, I have no modifier. Shouldn't there be a set of modifiers for the various quality measures? Or, should we perhaps have a single standard name modifier that indicates that the contents are some sort of derived measure, which would then direct the user to read the cell_methods attribute to determine what sort of operation was performed?
It sure feels like this whole area hasn't been well mapped out.
Grace and peace,
Jim
Jim Biard
Research Scholar
Cooperative Institute for Climate and Satellites
Remote Sensing and Applications Division
National Climatic Data Center
151 Patton Ave, Asheville, NC 28801-5001
jim.biard at noaa.gov
828-271-4900
On Mar 26, 2013, at 10:37 AM, Nan Galbraith <ngalbraith at whoi.edu> wrote:
> 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> 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>
>>>> Date: Tue, 26 Mar 2013 09:14:11 -0400
>>>> To: "cf-metadata at cgd.ucar.edu" <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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