Dear David, John,
thanks for those comments.
Just to re-iterate, the current UDUNITS library does not include "dB", but it does include "dBZ" and some other variations which are decibels with a fixed specified reference value.
The 2014 UDUNITS discussion which John links to is interesting. It appears to have covered the ground we have covered below, and Sean Arms has just re-started the discussion there with a link to this thread (thanks Sean). The latest proposal appears to be that a generic `dB` unit could be introduced with the reference level be specified in an additional attribute (yet to be defined).
The 2nd link from John is a discussion about the R package wrapper for UDUNITS, which does appear to have support for "dB" added, but simply defined in terms of the logarithm of a dimensionless number. This looks like a neat programmers solution which avoids having to worry about what the physical parameter is.
I've looked into this a bit further, and found that "bel" and "decibel" are recognised by ISO and the International Electrotechnical Commission (IEC 60027-3:2002), along with the "neper", which is the natural logarithm of a ratio. A "bel" is either the log10 of the ratio for a "power" quantity or 2 times log10 of the ratio for a "field" quantity. The IEC standard goes onto say that "dB" can be used to define power relative to a reference level, and information about reference levels should be attached to the quantity not to the unit -- which is in line with the current usage in 4 CF standard names.
There might be some value in trying to follow the ISO/IEC approach.
regards,
Martin
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Moroni, David F (398G) <David.F.Moroni at jpl.nasa.gov>
Sent: 12 November 2018 06:24
To: John Graybeal; Jonathan Gregory
Cc: CF Metadata List
Subject: Re: [CF-metadata] Decibel units in CF standard names
John and others interested,
I was part of the initial request that dated back to 2014. Here?s the original GitHub ticket (still open) capturing the correspondence with the UDUNITS team:
https://github.com/Unidata/UDUNITS-2/issues/33
I was corresponding with ?mhidas? and ?semmerson?, so I don?t know if these people are still on this project, as no further correspondence has taken place since July 2015. I made another attempt last year to bring some life to this request, but to no avail.
There was another user inquiring about representing dB as a unit, but that ticket has since closed and it?s not clear to me from the thread whether there was a positive resolution. Here?s that link:
https://github.com/r-quantities/units/issues/176
Others on here are more than welcome to pursue this further.
Cheers,
David
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of John Graybeal <jbgraybeal at mindspring.com>
Date: Sunday, November 11, 2018 at 9:33 PM
To: Jonathan Gregory <j.m.gregory at reading.ac.uk>
Cc: CF Metadata List <cf-metadata at cgd.ucar.edu>
Subject: Re: [CF-metadata] Decibel units in CF standard names
Just as an aside (or maybe not), the udunits support list has been asked before to include dB, and I understood that they had (I think I actually saw it, but can?t find written confirmation). So it wouldn?t surprise me if the library included dB.
In case it?s useful I pasted in a bit of the old thread below.
john
---------------------------------------
John Graybeal
jbgraybeal at mindspring.com<mailto:jbgraybeal at mindspring.com>
On Nov 4, 2018, at 09:03, Jonathan Gregory <j.m.gregory at reading.ac.uk<mailto:j.m.gregory at reading.ac.uk>> wrote:
Dear Martin
Your points are good ones and have been raised before. More than once we have
talked about maintaining a CF version of the udunits definition to include dB
and sverdrup, or ask udunits to add them (if they're not there). dB is a dimen-
sionless unit, equivalent to 1. I suggest that dBZ should be changed to dB,
as I don't think we ought to have several of them. I believe that the default
reference levels are mostly conventional and stated in the definitions of the
standard name, as you say. They can be overridden by supplying a size-one or
scalar coordinate variable. You have previously suggested an xml table to
contain more information about the definition of standard names, haven't you?
It seems to me that an arrangement like that would be the right place to store
the default reference levels and scale factor in a machine-readable way.
Best wishes
Jonathan
----- Forwarded message from Martin Juckes - UKRI STFC <martin.juckes at stfc.ac.uk<mailto:martin.juckes at stfc.ac.uk>> ??
Begin forwarded message:
From: "Moroni, David F (398M)" <David.F.Moroni at jpl.nasa.gov<mailto:David.F.Moroni at jpl.nasa.gov>>
Subject: Re: [CF-metadata] [cf-satellite] normalized_radar_backscatter_coefficient
Date: August 8, 2014 at 3:10:50 PM PDT
To: John Graybeal <john.graybeal at marinexplore.com<mailto:john.graybeal at marinexplore.com>>, "rhorne at excaliburlabs.com<mailto:rhorne at excaliburlabs.com>" <rhorne at excaliburlabs.com<mailto:rhorne at excaliburlabs.com>>
Cc: "Weiss, Barry H (398B)" <barry.h.weiss at jpl.nasa.gov<mailto:barry.h.weiss at jpl.nasa.gov>>, Jonathan Gregory <j.m.gregory at reading.ac.uk<mailto:j.m.gregory at reading.ac.uk>>, "cf-satellite at unidata.ucar.edu<mailto:cf-satellite at unidata.ucar.edu>" <cf-satellite at unidata.ucar.edu<mailto:cf-satellite at unidata.ucar.edu>>, CF Metadata List <cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>>
Hi John,
Thanks for providing the email link. I've already emailed Unidata and they are processing my request to include dB within UDUNITS.
Cheers,
David
From: John Graybeal <john.graybeal at marinexplore.com<mailto:john.graybeal at marinexplore.com>>
Date: Friday, August 8, 2014 10:57 AM
To: "rhorne at excaliburlabs.com<mailto:rhorne at excaliburlabs.com>" <rhorne at excaliburlabs.com<mailto:rhorne at excaliburlabs.com>>
Cc: "Weiss, Barry H (398B)" <barry.h.weiss at jpl.nasa.gov<mailto:barry.h.weiss at jpl.nasa.gov>>, David F Moroni <David.F.Moroni at jpl.nasa.gov<mailto:David.F.Moroni at jpl.nasa.gov>>, Jonathan Gregory <j.m.gregory at reading.ac.uk<mailto:j.m.gregory at reading.ac.uk>>, "cf-satellite at unidata.ucar.edu<mailto:cf-satellite at unidata.ucar.edu>" <cf-satellite at unidata.ucar.edu<mailto:cf-satellite at unidata.ucar.edu>>, CF Metadata List <cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>>
Subject: Re: [CF-metadata] [cf-satellite] normalized_radar_backscatter_coefficient
This request has now been made by me of UDUNITS on general principle, but I think individuals could also express their desire as a way to move the ball forward.
John
On Aug 7, 2014, at 07:57, rhorne at excaliburlabs.com<mailto:rhorne at excaliburlabs.com> wrote:
Dear Barry and David:
For udunits support, send an email to support-udunits at unidata.ucar.edu<mailto:support-udunits at unidata.ucar.edu>.
very respectfully,
randy
________________________________
From: "Weiss, Barry H (398B)" <barry.h.weiss at jpl.nasa.gov<mailto:barry.h.weiss at jpl.nasa.gov>>
Sent: Thursday, August 07, 2014 10:06 AM
To: "Moroni, David F (398M)" <David.F.Moroni at jpl.nasa.gov<mailto:David.F.Moroni at jpl.nasa.gov>>, "Jonathan Gregory" <j.m.gregory at reading.ac.uk<mailto:j.m.gregory at reading.ac.uk>>
Cc: "Niedfeldt, John C (398M-Affiliate)" <John.C.Niedfeldt at jpl.nasa.gov<mailto:John.C.Niedfeldt at jpl.nasa.gov>>, "CF Metadata List" <cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>>, "John Graybeal" <john.graybeal at marinexplore.com<mailto:john.graybeal at marinexplore.com>>, "cf-satellite at unidata.ucar.edu<mailto:cf-satellite at unidata.ucar.edu>" <cf-satellite at unidata.ucar.edu<mailto:cf-satellite at unidata.ucar.edu>>
Subject: Re: [cf-satellite] [CF-metadata] normalized_radar_backscatter_coefficient
Jonathan,
As the data product engineer for the SMAP project, I second David's
request.
We are attempting to employ CF metadata in our products. This is not a
challenge at level 2 and above where our products provide geophysical
measure, but is a challenge at level 1, where our products provide
instrument measurements.
Please consider inclusion of dB units. That should include dB based on
unit less measure, as well as dB relative to watts and volts.
Thanks and Regards,
Barry
On 8/6/14 7:49 PM, "Moroni, David F (398M)" <David.F.Moroni at jpl.nasa.gov<mailto:David.F.Moroni at jpl.nasa.gov>>
wrote:
>Hi Jonathan,
>
>Just as follow up from my last email, I noticed an online email exchange
>where you had responded to a request to use units of dB (decibels) even
>though it is not currently in the udunits database:
>http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2013/056572.html
>
>We also agree it would be wise to include dB in the udunits database, and
>we will be applying these units for our scatterometer datasets.
>
>We hope to see this incorporated in the near future.
>
>Thanks again for your considerations.
>
>Cheers,
>David
>
Received on Tue Nov 13 2018 - 07:03:40 GMT
