Hi John,
I agree with Philip. Not only does changing existing definitions go against all my gut instincts, there's another problem with just having a single sea pressure label.
Although the practice to correct to zero at sea level is almost universal when pressure is used as the z co-ordinate, in situations where pressure is measured as a geophysical phenomenon (e.g. sea level time series measured by a seabed-mounted pressure sensor) working practices are more variable. Some subtract actual atmospheric pressure measurements, some subtract a nominal value and others do nothing. This digs a hole that I think is a little too deep for semantics to come to the rescue.
Cheers, Roy.
________________________________
From: Cameron-smith, Philip [cameronsmith1 at llnl.gov]
Sent: 11 January 2013 01:30
To: John Graybeal
Cc: Lowry, Roy K.; cf-metadata at cgd.ucar.edu; sdn2-netcdf at seadatanet.org
Subject: RE: [CF-metadata] sea_water_pressure
Hi John,
I have seen similar situations in atmospheric chemistry. I participated in an intercomparison in which we submitted exactly what the std_name required, only to find out that every other group had submitted what they assumed it meant, which was several orders of magnitude different.
I think the bar for retroactively changing a definition should be very high (without commenting on the merits of your case). One thing we can do to help, without causing any problems, is to add to existing descriptions a list of related std_names so that a user will get a 'heads up' to look at other std_names. I know this is only a partial solution, but better than nothing.
Best wishes,
Philip
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Dr Philip Cameron-Smith, pjc at llnl.gov, Lawrence Livermore National Lab.
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From: John Graybeal [mailto:jgraybeal at ucsd.edu]
Sent: Thursday, January 10, 2013 3:48 PM
To: Cameron-smith, Philip
Cc: Lowry, Roy K.; cf-metadata at cgd.ucar.edu; sdn2-netcdf at seadatanet.org
Subject: Re: [CF-metadata] sea_water_pressure
It looks sensible to me, too, but I have to ask a stupid question. Of all the data with "sea_water_pressure" CF standard names in the world, how many are actually presenting what CF defines that to be? (If the answer is "very few", maybe the answer is that the definition is just mis-stated for what the community expected, and we need a new term to go with the existing definition.)
(Yes, this is a perspective that only an ontologist could offer without embarrassment.)
John
On Jan 10, 2013, at 15:16, Cameron-smith, Philip wrote:
Hi Roy,
This looks sensible to me.
Philip
-----------------------------------------------------------------------
Dr Philip Cameron-Smith, pjc at llnl.gov<mailto:pjc at llnl.gov>, Lawrence Livermore National Lab.
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From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Lowry, Roy K.
Sent: Thursday, January 10, 2013 1:01 AM
To: cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>
Cc: sdn2-netcdf at seadatanet.org<mailto:sdn2-netcdf at seadatanet.org>
Subject: [CF-metadata] sea_water_pressure
Dear All,
It has been pointed out to me that the SeaDataNet NetCDF specification uses 'sea_water_pressure' as the Standard Name in cases where pressure is used as the z co-ordinate in observational data such as CTD profiles. The definition for this Standard Name is:
the pressure that exists in the medium of sea water. It includes the pressure due to overlying sea water, sea ice, air and any other medium that may be present.
Consequently the expected pressure z co-ordinate labelled 'sea_water_pressure' would be approximately 10 decibars at the sea surface. However, it is almost universal practice to either calibrate or correct the pressure z co-ordinate so that it reads zero at the sea surface. Consequently, I think we need a new Standard Name:
sea_water_pressure_due_to_sea_water defined as
the pressure that exists in the medium of sea water due to overlying sea water. Excludes the pressure due to sea ice, air and any other medium that may be present.
Apologies to anybody else who like me had used 'sea_water_pressure' for their Z co-ordinate without looking at the definition.
Cheers, Roy.
Please note that I now work part-time from Tuesday to Thursday. E-mail response on other days is possible but not guaranteed!
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John Graybeal <mailto:jgraybeal at ucsd.edu> phone: 858-534-2162
Product Manager
Ocean Observatories Initiative Cyberinfrastructure Project:
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Marine Metadata Interoperability Project:
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