Dear Jonathan,
For years - even the odd decade - I believed 'direction' and 'direction_to' to be 100% synonymous for currents. However, I can recall current meter data delivered to BODC in the late 90s with channels labelled 'speed' and 'direction' where QC showed that the direction was in fact 'direction_from'. Enquiries revealed that the current meter data had been 'prepared' for assimilation into a metocean model based on meteorological conventions.
Not a very common use case, especially as these days Cartesian rather than polar co-ordinates are more common, but I think its worth covering.
Cheers, Roy.
Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to enquiries at bodc.ac.uk. Please also use this e-mail if your requirement is urgent.
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Jonathan Gregory <j.m.gregory at reading.ac.uk>
Sent: 02 June 2017 13:44
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] sea water speed and direction?
Dear John and Roy
direction_of_X is a construction in the standard name table, and I believe it's
assumed it's a to_direction. For wind, which is the oldest vector in the table,
we have to_direction and from_direction because of the potential confusion of
e.g. westerly and westward wind. Is there a confusion in practice for sea water
and sea ice? I mean, does anyone use "from" directions for these velocities?
If there is a use-case, I agree we ought to distinguish.
Best wishes
Jonathan
----- Forwarded message from "Lowry, Roy K." <rkl at bodc.ac.uk> -----
> Date: Fri, 2 Jun 2017 09:20:26 +0000
> From: "Lowry, Roy K." <rkl at bodc.ac.uk>
> To: John Maurer <jmaurer at hawaii.edu>, "cf-metadata at cgd.ucar.edu"
> <cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] sea water speed and direction?
>
> Dear John,
>
>
> That's a good point about the ambiguity of 'direction_of_sea_water_velocity'. As an observational oceanographer its built into my core program that 'direction' means 'direction_to' for currents. I'm not alone here, which is probably how the ambiguity got overlooked when the Standard Name was set up. My suggestion for corrective action would be to alias 'direction_of_sea_water_velocity' to 'sea_water_to_direction' whilst adding a new Standard Name 'sea_water_from_direction'. I prefer your suggestions here to the more verbose alternatives such as 'to_direction_of_sea_water_velocity'.
>
>
> You could then use 'sea_water_speed' and 'sea_water_to_direction' for your data as polar co-ordinates. You could also consider transforming to cartesian co-ordinates and using 'eastward_sea_water_velocity' and 'northward_sea_water_velocity' for the Standard Names.
>
>
> I am opposed to the creation of separate 'surface' Standard Names unless there is a case that the measured phenomenon is different. If you read the definition of 'surface_eastward_sea_water_velocity' you will see that it represents a different phenomenon to 'eastward_sea_water_velocity' because it allows for the boundary between water body and atmosphere being either water or ice. Consequently, unless there was a specific need to specify a water-or-ice surface motion in terms of polar co-ordinates I would recommen against adding the new 'surface' names that you suggest.
>
>
> Cheers, Roy.
>
>
> Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to enquiries at bodc.ac.uk. Please also use this e-mail if your requirement is urgent.
>
>
> ________________________________
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of John Maurer <jmaurer at hawaii.edu>
> Sent: 01 June 2017 20:37
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] sea water speed and direction?
>
> Please provide guidance on which CF Standard Names to use for sea water surface velocity. We will soon have a new buoy with an acoustic current meter (ACM) that records speed (m/s) and direction (degrees) of the surface currents. Are these the recommended CF Standard Names to attribute for these measurement parameters?:
>
> * sea_water_speed
> * direction_of_sea_water_velocity
>
> The latter does not indicate the "from" or "to" direction of the variable, which concerns me. I am used to applying "wind_from_direction" or "wind_to_direction" for wind measurements to solve this ambiguity. Thoughts on replacing this with "sea_water_from_direction" and "sea_water_to_direction"?
>
> Also, I note there are CF Standard Names that exist for "surface_eastward_sea_water_velocity" and "surface_northward_sea_water_velocity". I would expect and recommend the addition of the following surface names:
>
> * surface_sea_water_speed
> * surface_sea_water_from_direction
> * surface_sea_water_to_direction
>
> Please advise.
> Thanks!,
> John Maurer
> Data System Engineer
> Pacific Islands Ocean Observing System (PacIOOS)
> University of Hawaii at Manoa
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