Thanks, Alison. After further consideration as well as discussion with some
of our water quality colleagues, I think the dimensionless units of NTU may
be better expressed in UDUNITS as "1" instead of "1e-3" (parts per
thousand) since the values normally range in the 0-10+ range (rather than
0.001-0.01+). So, I would modify the units to "1" and slightly modify your
proposed definition to the following:
'Turbidity is a dimensionless quantity which is expressed in NTU
(Nephelometric Turbidity Units). Turbidity expressed in NTU is the
proportion of white light scattered back to a transceiver by the
particulate load in a body of water, represented on an arbitrary scale
referenced against measurements made in the laboratory on aqueous
suspensions of formazine beads. Sea water turbidity may also be measured by
the quantity with standard name secchi_depth_of_sea_water.'
Cheers,
John
Message: 2
Date: Wed, 6 Mar 2013 12:08:09 +0000
From: <alison.pamment at stfc.ac.uk>
To: <cf-metadata at cgd.ucar.edu>
Subject: Re: [CF-metadata] sea_water_turbidity
Message-ID:
<014539AC4976BE4490A360410A8C2017569ECD91 at EXCHMBX01.fed.cclrc.ac.uk>
Content-Type: text/plain; charset="iso-8859-1"
Dear John and Roy,
Thanks for your comments. Based on the explanations you have provided I
suggest that the wording of the definition should be 'Turbidity is a
dimensionless quantity which is expressed in NTU (Nephelometric Turbidity
Units), which are normally given as 1e-3 or 0.001 i.e. parts per thousand.
Turbidity expressed in NTU is the proportion of white light scattered back
to a transceiver by the particulate load in a body of water, represented on
an arbitrary scale referenced against measurements made in the laboratory
on aqueous suspensions of formazine beads. Sea water turbidity may also be
measured by the quantity with standard name secchi_depth_of_sea_water.'
I suggest also that we could improve the definition of the secchi_depth
name to make it clearer that the quantity relates to turbidity and add a
cross-reference to the new name:
secchi_depth_of_sea_water - ' Depth is the vertical distance below the
surface. A Secchi disk is a patterned disk that is used to measure water
transparency, also called turbidity, in oceans and lakes. The disk is
lowered into the water and the depth at which the pattern is no longer
visible is the called the secchi depth. Sea water turbidity may also be
measured by the quantity with standard name sea_water_turbidity.'
Do you agree?
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of
John Maurer
Sent: 05 March 2013 00:23
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] sea_water_turbidity
Yes, I agree with Roy's assessment. Thank you.
Cheers,
John
Date: Wed, 27 Feb 2013 21:19:01 +0000
From: "Lowry, Roy K." <rkl at bodc.ac.uk>
To: "alison.pamment at stfc.ac.uk" <alison.pamment at stfc.ac.uk>,
? ? ? ? "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
Subject: Re: [CF-metadata] sea_water_turbidity?
Message-ID:
? ? ? ? <40829B0E077C1145A6DE44D39B3830A922989BD586 at nerckwmb1.ad.nerc.ac.uk>
Content-Type: text/plain; charset="Windows-1252"
Hello Alison,
I had been hanging back waiting for John to respond to Jonathan's comment,
because nephelometric turbidity is a phenomenon that I've seen described -
but not necessarily defined - in a couple of different ways. ?However,
whilst both turbidity and secchi disk depth (and attenuance to the matter)
have values related to the SPM load in the water body, they differ markedly
for a given SPM load and so I think a new standard name is justified.
As a prompt, I'll give one of my understandings of turbidity in NTU, which
is 'The proportion of white light scattered back to the transceiver by the
particulate load in a body of water, represented on an arbitrary scale
referenced against measurements made in the laboratory on aqueous
suspensions of formazine beads.' ?Before going any further we need John to
either confirm that this is what he means or come up with an alternative.
?Others might also have their own ideas....
Cheers, Roy.
______________________________
__________
From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] On Behalf Of
alison.pamment at stfc.ac.uk [alison.pamment at stfc.ac.uk]
Sent: 27 February 2013 14:04
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] sea_water_turbidity?
Dear John,
Thank you for your proposal.
We currently have one existing standard name relating to turbidity of sea
water, secchi_depth_of_sea_water, which has units of metres and is defined
as ?Depth is the vertical distance below the surface. A Secchi disk is a
patterned disk that is used to measure water transparency in oceans and
lakes. The disk is lowered into the water and the depth at which the
pattern is no longer visible is the called the secchi depth.?
I agree with Jonathan that it would be helpful if you could provide a
(fairly brief) definition for the new name or perhaps a suitable reference.
Best wishes,
Alison
------
Alison Pamment ? ? ? ? ? ? ? ? ? ? ? ? ?Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre ? ?Email: alison.pamment at stfc.ac.uk<
mailto:J.A.Pamment at rl.ac.uk>
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of
John Maurer
Sent: 21 February 2013 00:52
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] sea_water_turbidity?
Dear CF-Metadata,
I would propose the addition of "sea_water_turbidity" to the CF Standard
Names. This has units of NTU (Nephelometric Turbidity Units), which would
be represented in UDUNITS as "1e-3" (similar to how sea_water_salinity is
in PSS (or PSU) and commonly represented as 1e-3).
Thanks,
John Maurer
Data System Administrator
Pacific Islands Ocean Observing System (PacIOOS)
University of Hawaii at Manoa
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