CF-metadata,
I would like to propose an expansion of the use and reserved values for the ?positive? attribute (section 4.3), specifically to include values in addition to the two reserved values of ?up? and ?down? to include ?towards? and ?away?.
Most variables define direction in the standard_name, but with instrumentation a standard name is often not available or the correct definition of the name exists with the wrong positive direction. Also, needing to understand or extract direction from the standard_name can be difficult for a simple tool not wanting to review the standard_name definition just to see if a transformation is needed. Expanding the use of the ?positive? attribute would reduce the number of standard names by not needing to include positive direction in the definition. This would also follow the recommendation of being consistent with the definition between the standard_name and positive attribute. The ?positive? attribute is currently reserved for use with coordinate dimensions only, but the same logic can be used with data variables to indicate direction. For example rate of speed for vertical velocities could be described by indicating positive = ?up? when vertical velocities are positive when moving away from the surface.
Instruments are also often not installed perpendicular to the surface, and the coordinate system is better described as towards or away from the instrument. Specifically for radial instruments. Errors in misunderstanding direction with radial velocities or accelerations are comment when not specifically defined. There is no vendor standard.
I?ll leave my suggestion at towards and away, but this could also be expanded to include cardinal direction for East-West/North-South directions.
Thanks,
Ken
Kenneth E. Kehoe
Research Associate - University of Oklahoma
Cooperative Institute for Mesoscale Meteorological Studies
ARM Climate Research Facility - Data Quality Office
e-mail: kkehoe at ou.edu<mailto:kkehoe at ou.edu> | Office: 303-497-4754 | Cell: 405-826-0299
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