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cf-convention / vocabularies

Issues and source files for CF controlled vocabularies
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issues with Doppler current profiler descriptions #189

Closed jklymak closed 3 years ago

jklymak commented 3 years ago

In cf-convention/vocabularies#72 you very kindly added CF names for acoustic Doppler current profilers, which is super helpful. This data needs to appear in ADCP files to affect meaningful quality control.

There are some misleading statements in the descriptions that could perhaps be modified. Reference to https://www.comm-tec.com/Docs/Manuali/RDI/BBPRIME.pdf

beam_consistency_indicator_from_multibeam_acoustic_doppler_velocity_profiler_in_sea_water

The "beam_consistency_indicator" is the degree to which the magnitudes of a collection (ensemble) of acoustic signals from multiple underwater acoustic transceivers relate to each other.

To me this makes it sound like the pings are compared to each other, but in fact they are being individually correlated with the transmitted pulse. The strength of the correlation is a signal-to-noise quality, and the phase of the correlation is what is used to measure the Doppler shift:

The "beam_consistency_indicator" is the degree to which the received acoustic pulse is correlated with 
the transmitted pulse.

I guess I think this was unfortunately named, but I don't know what your scope is to change this now...

indicative_error_from_multibeam_acoustic_doppler_velocity_profiler_in_sea_water

 It is determined by differencing duplicate error velocity measurements made using different pairs of beams.

This isn't correct either. You can form a solution for u,v, w, with three beams, and the ADCPs usually have 4, so the error velocity is the absolute difference in w between two 3-beam solutions. Perhaps:

It is determined by the difference between the vertical velocity calculated from two 3-beam solutions.

Thanks a lot!

roy-lowry commented 3 years ago

Many thanks for the clarifications. I support their replacing the existing text in the descriptions.

feggleton commented 3 years ago

I have added these changes in the cfeditor (http://cfeditor.ceda.ac.uk/proposals/1). Please comment if there is any further discussion. If there are no further comments in the next 7 days I think these small changes can be accepted in order to clarify the definitions.

feggleton commented 3 years ago

These two terms have now been accepted.

japamment commented 3 years ago

Changes applied in version 78 of the standard name table.