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 <rsignell at 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.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
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
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