Hi Jim,
The practice of storing one CTD profile per file (be it netCDF or anything else) is widespread in the oceanographic community and is largely driven by the heterogeneous nature of the Z co-ordinate (pressure or depth) which increases steadily most of the time (but not always) and can increase by either regular or irregular amounts. Whilst this can be cleaned up by binning, we have been condemned for doing this by some users because it destroys the fine structure signal they want to use.
Cheers, Roy.
________________________________
From: cf-metadata-bounces at cgd.ucar.edu [cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jim Biard [jim.biard at noaa.gov]
Sent: 02 April 2012 13:06
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] Ocean CTD data following CF Conventions v1.6
Hi.
Here's my best understanding (which could be flawed, so I look forward to finding out if I have missed something). Assuming that your time, latitude, and longitude are all proper coordinate variables (no fill values), either choice for the shape of your salinity variable works. If you use the more complex shape, then you don't need to have the coordinates attribute, as the relationships are declared through the shape. Speaking of that, the coordinates attribute doesn't need to have PRESSURE in it. Doesn't hurt anything, but it isn't necessary.
Having said all that, I find myself wondering why you are storing each salinity profile in a separate file. Would you mind sharing what went into deciding to take this approach?
Grace and peace,
Jim
On Mon, Apr 2, 2012 at 2:51 AM, andrew walsh <awalsh at metoc.gov.au<mailto:awalsh at metoc.gov.au>> wrote:
Hi CF list,
We are working on coding up some 1000's netCDF files off CTD
instruments and want to make usre we are following the
latest netCDF conventions (v1.6) OK. As background the CTD records
a profile pressure, temperature and salinity.
Here is a summarised CDL version (not all attributes+variables+qc flags there, just majors for now)
of what we propose:
dimensions:
TIME=1
PRESSURE=729
LATITUDE=1
LONGITUDE=1
variables:
double TIME(TIME) ;
TIME:standard_name = "time" ;
TIME:units = "days since 1950-01-01 00:00:00Z" ;
TIME:axis = "T" ;
TIME:valid_min = 0. ;
TIME:valid_max = 999999. ;
double LATITUDE(LATITUDE) ;
LATITUDE:standard_name = "latitude" ;
LATITUDE:units = "degrees_north" ;
LATITUDE:axis = "Y" ;
LATITUDE:valid_min = -90. ;
LATITUDE:valid_max = 90. ;
double LONGITUDE(LONGITUDE) ;
LONGITUDE:standard_name = "longitude" ;
LONGITUDE:units = "degrees_east" ;
LONGITUDE:axis = "X" ;
LONGITUDE:valid_min = -180. ;
LONGITUDE:valid_max = 180. ;
double PRESSURE(PRESSURE) ;
PRESSURE:standard_name = "sea_water_pressure" ;
PRESSURE:units = "decibars" ;
PRESSURE:axis = "Z" ;
PRESSURE:valid_min = 0. ;
PRESSURE:valid_max = 12000. ;
PRESSURE:positive = "down" ;
double TEMPERATURE(PRESSURE) ;
TEMPERATURE:standard_name = "sea_water_temperature" ;
TEMPERATURE:units = "degrees_C" ;
TEMPERATURE:_FillValue = -99.99 ;
TEMPERATURE:valid_min = -2. ;
TEMPERATURE:valid_max = 40. ;
TEMPERATURE:coordinates="TIME LATITUDE LONGITUDE PRESSURE"
double SALINITY(PRESSURE) ;
SALINITY:standard_name = "sea_water_salinity" ;
SALINITY:units = "psu" ;
SALINITY:_FillValue = -99.99 ;
SALINITY:valid_min = 0. ;
SALINITY:valid_max = 40. ;
SALINITY:coordinates="TIME LATITUDE LONGITUDE PRESSURE"
// global attributes:
:conventions = "CF-1.6" ;
:featureType = "profile"
:cdm_data_type = "profile"
+ several other attributes later for ISO19115 metadata generation
I am not sure if I should have TEMPERATURE and SALINITY arrays with 4 dimensions
like TEMPERATURE(TIME,LATITUDE,LONGITUDE,PRESSURE) or just 1 dimension
like I have above i.e. TEMPERATURE(PRESSURE). ?
Any feedback on the above is greatly appreciated.
Andrew Walsh
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--
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<mailto:jim.biard at noaa.gov>
828-271-4900
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