John,
So then the surface needs to be defined relative to some known datum, no?
Maybe we need platform_altitude_above_datum and a specification of
the vertical datum (EPSG:5701 (MSL), EPSG:5703 (NAVD88), etc)
On Thu, Sep 18, 2014 at 1:47 PM, John Graybeal
<john.graybeal at marinexplore.com> wrote:
> I assume surface_altitude is an important variable for providing the vertical location of measurements relative to a surface (as opposed to relative to a geoid -- notwithstanding the definition issue).
>
> John
>
> On Sep 18, 2014, at 08:30, Signell, Richard <rsignell at usgs.gov> wrote:
>
>> Maybe a simpler approach would be to just adopt "platform_altitude" as
>> an alias for "surface_altitude" and suggest deprecating the use of
>> "surface_altitude"?
>>
>> On Thu, Sep 18, 2014 at 11:15 AM, John Graybeal
>> <john.graybeal at marinexplore.com> wrote:
>>> Interesting that there is so little discussion of this language in the mail list, only in John Caron's 2011.09.16 mail on standard names for stations (which refers to words already in draft 1.6, I think) -- which came at the tail end of a long thread on platform names/IDs.
>>>
>>> From those words, I infer that the original drafter thought surface_altitude was just as good for describing platform location, as it was for describing observation location. I suspect the assumption was that any corresponding observations were at the same location as the platform.
>>>
>>> Since this is not always true, I'm with you that there should be a term platform altitude, and it should be the one used in this sentence.
>>>
>>> I hereby propose the standard name platform_surface_altitude (m), "Standard names for platform describe the motion and orientation of the vehicle from which observations are made e.g. aeroplane, ship or satellite.
>>> The surface called "surface" means the lower boundary of the atmosphere. Altitude is the (geometric) height above the horizontal reference surface."
>>>
>>> Note I've changed the standard wording of the _altitude definition, which generally says ".. above the geoid, which is the reference geopotential surface. The geoid is similar to mean sea level." This seems clearly in conflict with the definition of surface_altitude and this new term, and I think it should be changed in surface_altitude's definition too.
>>>
>>> I suppose if people agree with you and me, we need to do a Trac ticket for the corresponding change to the standard.
>>>
>>> John
>>>
>>>
>>>
>>> On Sep 18, 2014, at 06:40, Signell, Richard <rsignell at usgs.gov> wrote:
>>>
>>>> In the CF-1.6 and CF-1.7 draft doc, in section H.2, we have:
>>>>
>>>> "It is recommended that there should be station variables with
>>>> standard_name attributes " platform_name ", " surface_altitude " and ?
>>>> platform_id ? when applicable."
>>>>
>>>> Why is this "surface_altitude" instead of "platform_altitude"?
>>>>
>>>> In the ocean, we have lots of upward-looking Acoustic Doppler Current
>>>> Profilers (ADCP), where the instrument with transducer and other
>>>> sensors is located some distance below the ocean surface. While
>>>> velocity and other properties are measured in vertical bins above the
>>>> instrument (timeSeriesProfile), other properties like pressure and
>>>> temperature are measured at the instrument.
>>>>
>>>> Since the instrument is not at the surface, it seems misleading to use
>>>> the standard_name "surface_altitude" instead of "platform_altitude",
>>>> particularly when we already have "platform_name" and "platform_id".
>>>>
>>>> In this example CF_1.6 ADCP dataset:
>>>>
>>>> http://geoport.whoi.edu/thredds/dodsC/usgs/data2/rsignell/data/adcp/7201adc-a_cf16.nc.html
>>>>
>>>> the variable "platform_altitude" has a value of -10.4522 m:
>>>> http://geoport.whoi.edu/thredds/dodsC/usgs/data2/rsignell/data/adcp/7201adc-a_cf16.nc.ascii?platform_altitude
>>>>
>>>> but we are forced to use a standard_name of "surface_altitude".
>>>>
>>>> Why not "platform_altitude"?
>>>>
>>>> Thanks,
>>>> Rich
>>>>
>>>> --
>>>> Dr. Richard P. Signell (508) 457-2229
>>>> USGS, 384 Woods Hole Rd.
>>>> Woods Hole, MA 02543-1598
>>>> _______________________________________________
>>>> CF-metadata mailing list
>>>> CF-metadata at cgd.ucar.edu
>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>
>>
>>
>>
>> --
>> Dr. Richard P. Signell (508) 457-2229
>> USGS, 384 Woods Hole Rd.
>> Woods Hole, MA 02543-1598
>
--
Dr. Richard P. Signell (508) 457-2229
USGS, 384 Woods Hole Rd.
Woods Hole, MA 02543-1598
Received on Thu Sep 18 2014 - 13:42:25 BST
