Hi Roy and all -
This is really the same physical parameter, so I think we should
use the normal standard name and provide the additional information
about how its position in the water column is defined - keeping
the specific deployment information separate from the id of the
parameter being output by an instrument.
I can appreciate that BODC puts more information into a standard
name than NetCDF would do, so I'd take Roy's example (Thanks,
Roy!) and see what parts need to be replicated. The "corrected to
read zero at sea level" would be an attribute of the measurement,
but it seems more logical to provide the "fixed/tethered" info as a
modifier to the measurement's depth coordinate.
Reading through the CF documentation, I thought I was close to
an answer, but didn't find anything that used reference levels other
than sea surface. IMHO, that's the key to making the distinction
in the meaning of the data. There are a lot of levels defined, but I
wasn't able to find anything about the sea floor. (Then again, it
was late ...)
If at all possible, I'd like to do it in a way that will be clear outside
the oceansites users, so even though the CF community isn't
especially focused on sea floor measurements, this seems like
the group to ask.
This sort of info is also important for ADCPs and possibly some
other instruments that are sometimes set on the bottom and sometimes
on a mooring line - facing down or up. Having a standard way to
describe this deployment information within CF would be really useful
to us.
Thanks -
Nan
> Hi Nan,
>
> All I can do is tell you what we do. In P011 parameter vocabulary there are the following terms:
>
> tethered mooring pressure sensor - Pressure (measured variable) exerted by the water column by semi-fixed in-situ pressure sensor
>
> seafloor of oilrig leg mounted pressure sensor - Pressure (measured variable) exerted by the water column by fixed in-situ pressure sensor and corrected to read zero at sea level
>
> Initially this was just 'Pressure (measured variable) exerted by the water column by fixed in-situ pressure sensor' but our data scientists had trouble seeing the difference between that and 'Pressure (measured variable) exerted by the water column plus atmosphere by fixed in-situ pressure sensor' - what I use for total pressure: approx 10 db at sea level). So, I said the same thing twice at different leveles of subtlety to make sure the message got across.
>
> I also have:
>
> CTD pressure sensor - Pressure (spatial co-ordinate) exerted by the water column by profiling pressure sensor and corrected to read zero at sea level
>
> I admit that this is inelegant and verbose, but it seems to work in BODC.
>
> Cheers, Roy.
>
>
>
>>>> Nan Galbraith <ngalbraith at whoi.edu> 8/19/2008 2:13 am >>>
>>>>
>
> I'm pasing along this question from a discussion going
> on among OceanSITES participants.
>
> Can (or should) the CF standard differentiate between these
> two very different measurements of sea water pressure:
>
> 1. A mooring with pressure sensors at various depths along
> the wire, where the pressure values give information about
> how the mooring was tilted by ambient currents.
>
> 2. Bottom pressure sensors, e.g. mounted rigidly at a fixed
> location at or above the seafloor, where the pressure values
> are a dynamically important quantity that integrates water
> column weight (cf. air pressure on weather charts).
>
>
>
--
*******************************************************
* Nan Galbraith (508) 289-2444 *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 *
*******************************************************
Received on Tue Aug 19 2008 - 06:42:34 BST
