Multiple altitude axes in one NetCDF file

• To: netcdfgroup@xxxxxxxxxxxxxxxx
• Subject: Multiple altitude axes in one NetCDF file
• From: "Stephens, A (Ag) " <A.Stephens@xxxxxxxx>
• Date: Thu, 5 Jun 2003 09:11:50 +0100

Dear all,

I have been trying to convert a colleague to using NetCDF and conforming to
the Climate and Forecasts Metadata Convention. However, she has some sodar
data that has an interesting quirk to it.

The instrument sits on the ground and looks vertically up, measuring the
profile of wind speed and direction. It therefore has two coordinate
variables: time and altitude.

There are two modes in which the instrument can measure which vary the
altitude coordinates so during the course of a day the sodar may be run in
each mode for different periods. This produces output with two altitude
dimensions. 

The easiest option for NetCDF would be to output to a new file each time the
mode changes. However, it is useful to be able to plot the entire day onto
one graph. Does NetCDF have a suitable solution to this problem?

My hunch would be to create two altitude dimensions, say 'altitude1' and
'altitude2' and two lots of wind parameters that vary with each altitude.
Alternatively, you can define the altitudes for each time step throughout
the measurement period (but this is inefficient).

I would hope there was a more elegant solution which would allow plotting
packages to view the entire dataset as continuous rather than separate
variables defined on separate dimensions.

Any ideas?

Thanks,

Ag
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Ag Stephens                           Ph : +44 (0)1235 446220
Data Scientist,                       Fax: +44 (0)1235 446314
British Atmospheric Data Centre,     
Rutherford Appleton Laboratory,               
Chilton, Didcot, OX11 0QX, U.K. 
Email:   A.Stephens@xxxxxxxx      Web: http://badc.nerc.ac.uk
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• Follow-Ups:
  • Re: Multiple altitude axes in one NetCDF file
    • From: Steve Hankin