As I recall, the original proposal was for station_altitude. We decided to change "station" to "platform". At the same time it was thought that the existing standard name of "surface altitude" would be synonymous. I at least was thinking of ground stations. So I think we make a mistake there and "platform_altitude" would be the right correction.
An altitude of course needs a datum, and I think we have not been clear enough on that. I think we should review our use or non-use of vertical datum. A quick look seems to imply that "WGS 84" is assumed (?) On Thu, Sep 18, 2014 at 1:42 PM, Signell, Richard <rsign...@usgs.gov> wrote: > 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.grayb...@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 <rsign...@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.grayb...@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 <rsign...@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@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 > _______________________________________________ > CF-metadata mailing list > CF-metadata@cgd.ucar.edu > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata >
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