Standard names: *ocean measurements: dissolved organic matter*

[ykern]

Proposer's name Yannick Kern & Colin Stedmon

Date 17.03.2023

spectral_slope_of_volume_absorption_coefficient_of_radiative_flux_in_sea_water_due_to_dissolved_organic_matter

(adopted from: volume_absorption_coefficient_of_radiative_flux_in_sea_water_due_to_dissolved_organic_matter)

A measure of the dependency of the volume_absorption_coefficient_of_radiative_flux_in_sea_water_due_to_dissolved_organic_matter on wavelength. The wavelength range it has been calculated over is stated as an radiation_wavelength attribute (e.g. “275-295 nm”).

- Units: μm-1

concentration_of_colored_dissolved_organic_matter_in_sea_water_expressed_as_fluorescence_in_raman_units

(adopted from: concentration_of_colored_dissolved_organic_matter_in_sea_water_expressed_as_equivalent_mass_fraction_of_quinine_sulfate_dihydrate)

Also commonly known as Chromophoric Dissolved Organic Matter (CDOM). CDOM plays an important role in the carbon cycling and biogeochemistry of coastal waters. It occurs naturally in aquatic environments primarily as a result of matter released from decaying plant and animal matter, which can enter coastal areas in river run-off containing organic materials leached from soils. Fluorescence intensity is normalised to the integrated Raman scattering peak of pure water from excitation at 350 nm, and therefore reported in Raman Units. The wavelengths that fluorescence is measured at will depend on the sensor used and is stated as an radiation_wavelength attribute (eg. “Ex350nm Em460nm”).

- Units: nm-1 (Raman unit)

[JonathanGregory]

Dear Yannick @ykern

Thanks for your proposals.

• By "spectral slope" do you mean the derivative of the volume absorption coefficient with respect to wavelength? We have a pattern for derivatives in the guidelines. Following that pattern, we could call this derivative_wrt_wavelength_of_volume_absorption_coefficient_of_radiative_flux_in_sea_water_due_to_dissolved_organic_matter. Another possibility is to follow the example of the many existing standard names for spectral radiative fluxes, and call it volume_absorption_coefficient_per_unit_wavelength_of_radiative_flux_in_sea_water_due_to_dissolved_organic_matter. Does either of those seem OK to you?

• For the second one, expressed_as_fluorescence is fine (as far as I know, not being an expert), but we never state units within the standard name. I don't really understand what physical quantity you mean. Please could you (or someone else) explain in some more detail, so we can understand why the units are reciprocal length?

Thanks

Jonathan

[DocOtak]

Hi @ykern My group has some spectral slope data so I'm excited to see this proposal!

I'd first like to point out that the usual usage of radiation_wavelength is as a variable not an attribute and is tied to the parent variables using the ancillary_variables attribute. However, your proposals have both ranges and separate ex/em wavelengths. @JonathanGregory This feels like a shortcoming of the current conventions, how do we express a range? And how do we separate the ex and em wavelengths? My group became aware of some fluorescence data from discrete sea water samples where the ex and em wavelengths were both scanned though with about 1000 steps each.

@ykern I've seen spectral slope reported for some nonlinear fit and linear fit of the log transformed data often reported together. It is likely worth specifying this in the definition/name.

I think Raman Units describe a peak shift using wavenumbers, not an expert in this one either. We do have a few standard names with wavenumber in them.

[ykern]

Thanks for your comments. I have forwarded this in our group and either I or a colleague will get back to you on this.

[Mats-polar]

I must admit, we are quite amateurs when it comes to the conventions (except for @ykern ) .. But we did not find anything that existed that fitted our data (to our surprise).

"spectral slope" - unfortunately there are different methods to calculate the slope (as @DocOtak notes), and not a derivative as such. And from what I understood "radiation_wavelength" is in many cases supposed to be used as attribute when we talk about spectral data and one needs to specify the exact wavelength. But that is just me reading the variable descriptions as a novice. And indeed one needs to specify the range of (from to) wavelengths that is used, and also here there is no standard in the research community what to use rather this varies from study to study (although a few widely used ranges have emerged). And the research community calls this "spectral slope", but I guess that is no argument to stick to that naming. Thus if we separate the way the "slope" is calculated (linear, exponential fit, etc.) not sure how to best include that..

"concentration_of_colored_dissolved_organic_matter_in_sea_water_expressed_as_fluorescence_in_raman_units" this we mirrored from something that already existed: http://vocab.nerc.ac.uk/collection/P07/current/6OP5LKSX/ that does have units in the name IMHO. "concentration_of_colored_dissolved_organic_matter_in_sea_water_expressed_as_equivalent_mass_fraction_of_quinine_sulfate_dihydrate"

[JonathanGregory]

Dear @Mats-polar

There isn't a unit as such in concentration_of_colored_dissolved_organic_matter_in_sea_water_expressed_as_equivalent_mass_fraction_of_quinine_sulfate_dihydrate. The expressed_as part means it's got to be in units which are permissible for a mass fraction. A mass fraction is a dimensionless quantity, and the canonical unit is 1. It could be given as any equivalent unit, such as percent. Which physical quantity do you mean by "fluorescence"? That's the name of a physical phenomenon, of course, but I suppose there may be several ways to quantify it.

You mention using a fit (linear, exponential, etc.) to calculate the spectral slope. Using the fit, do you calculate the slope of the tangent at the wavelength in question, perhaps? I think it would be correct to call that a derivative.

Best wishes

Jonathan

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This issue has had no activity in the last 30 days. This is a reminder to please comment on standard name requests to assist with agreement and acceptance. Standard name moderators are also reminded to review @feggleton @japamment

[efisher008]

Hello @ykern and @Mats-polar ,

Would either of you like to respond to @JonathanGregory's most recent comment on units and slope fit?

I noticed in the CF editor (https://cfeditor.ceda.ac.uk/proposal/4779/edit) the unit which has been associated with the first proposed term spectral_slope_of_volume_absorption_coefficient_of_radiative_flux_in_sea_water_due_to_dissolved_organic_matter is actually m-1, not μm-1 as originally written. Is this an error or has it been altered on the basis of a new comment?

Best regards, Ellie

[ykern]

Thanks for following up on this @efisher008 @Mats-polar can hopefully answer the scientific part of the questions. As for the change of unit from μm-1 to m-1 this must either be an error or it means that maybe units shall be given without prefixes?

Best regards, Yannick

[efisher008]

Hi @ykern and @Mats-polar,

As this issue has not seen any activity in the past 7 months, as there any way we could revive the discussion? As for the units, I would imagine that m-1 is the canonical unit for the quantity, I think @japamment had something to add on how this might have been entered in the editor if I remember correctly.

Best wishes, Ellie

[efisher008]

Hello @ykern @Mats-polar,

I am revisiting this issue after the migration of standard name proposals from the cf-conventions/discuss repo to the newly created cf-conventions/vocabularies repo, as it is a fairly long-standing open issue which has not reached a conclusion.

Just to update you, these names are currently in the editor as:

1. derivative_wrt_wavelength_of_volume_absorption_coefficient_of_radiative_flux_in_sea_water_due_to_dissolved_organic_matter (your first suggestion in this comment). https://cfeditor.ceda.ac.uk/proposal/4779/edit

2. concentration_of_colored_dissolved_organic_matter_in_sea_water_expressed_as_fluorescence_in_raman_units https://cfeditor.ceda.ac.uk/proposal/4780/edit

If there are any comments you'd like to make to revive/continue this discussion, that would be appreciated!

Thank you and best wishes, Ellie

[colinstedmon]

Hi @efisher008 A big thank you for following up on this. Much appreciated. I have been working with both @ykern and @Mats-polar on this and offered to try to finish this up. It is a little unclear to me where we are and what is needed to finish. I would appreciate some guidance.

After reviewing the thread here I can conclude... Regarding 1. Our suggestion to use "spectral_slope" is not accepted and you would prefer "derivative_wrt_wavelength". We can accept this but would like to propose we then modify the description to mention words " spectral slope". e.g. "A measure of the dependency of the volume_absorption_coefficient_of_radiative_flux_in_sea_water_due_to_dissolved_organic_matter on wavelength, also know as spectral slope. The wavelength range it has been calculated over is stated as an radiation_wavelength attribute (e.g. “275-295 nm”)."

Regarding 2. As I understand Jonathan is suggesting we remove the units and "fluorescence" from the name. This is ok as the description includes all the necessary information (that it is a fluorescence signal and it is calibrated to waters Raman signal). So it becomes just "concentration_of_colored_dissolved_organic_matter_in_sea_water"

Regards Colin