LOCODOX :a matlab toolbox to correct Argo-O2 data

Emilie Brion, Altran OuestVirginie Thierry, LOPS/IfremerCathy Lagadec, LOPS/IFREMER

Argo Oxygen• Measurements done by

Aanderaa or Seabirdoptodes or other sensor(Rinko)

• 3 useful parameters: Dissolved oxygen

concentration: DOXY (µmol/kg)

Percentage of saturation PSAT (%)

Partial pressure of oxygenPPOX_DOXY (mBar)

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Optode aanderaa

What is Locodox ?LOCODOX is a matlab toolbox designed to correct oxygen data following 3 methods :

WOA : based on climatological atlas(WOA09 in mL/L)

REF : based on in situ reference profiles collected at float deployment for instance

INAIR : based on in air oxygenmeasurements done by the float

LOCODOX produced delayed mode NetCDF files complying with argo 3.1 format and following the BGC/DOXY QC manuals

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Takeshita et al, 2013Bittig et Kortzinger, 2015

Exemple of diagnostics

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QC Maps

Interpolation

Drift Correction

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Data

• DOXY, PTS (sensor pressure and temperatureif they exist, …)

• Pumped and unpumped profiles (near surface): « vertical sampling scheme »

« monoprofile » files

• PPOX, PT (sensor temperature if it exists).• To colocalise with NCEP data:

• Ascent End Time : timing associated withPPOX measurements if we have no othertiming data

• Argos localisation

« trajectory » files

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Methodology• Profiles, Traj• Climatology, InSitu Reference, atmospheric dataREAD

• Hook removal• Select QC 1 et 2QC

• Drift corrected if needed• Reference data interpolated on argo levels and

trackPREPARE

• Correction with WOA, REF or In Air• Compute correction on ascendant profilesCOMPUTE CORRECTION

• Apply to both ascendant and descendant profiles• Apply to both pumped and unpumped profilesAPPLY

• scientific calibration fields and history fieldsupdated (Argo Quality Control Manual for BioGeoChemical Data).

Write NetCDF

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Contrôle Qualité : Hook

Data used and considered for the correction are those witha QC = [1,2]

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Hook removal : Many profiles have a hook on about the first 50m of the ascending profile

LOCODOX proposes to the user to remove this hook by systematicallyapply a flag 4 to the base of the profiles:

If Pmax> 840 => [ QC = 4, data = NaN ] on the deepest 50m of the profile

Interpolation

WOA Correctioninterpolation of WOA alongthe float path+ interpolation

on argo level

REF Correctioninterpolation of referencedata on levels of the Argo profile to be compared to

the reference profile

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Drift estimates and correctionLOCODOX estimate a temporal drift in comparing the Argo time serie with a reference time serie :

• WOA : WOA2009 interpolated on 5 float levelsbelow 1500db (every 100db)

• INAIR : NCEP data compared to float in air measurements (not coded yet)

LOCODOX suggests to not apply the drift correction if :• The timeserie < 1 year• Less than 10 profiles have a pressure max >

1500m• Drift is very small (less than 1,5 mumol/kg)

=> Operator decides

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Drift estimates and correction

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• Argo vs WOA• About 5 years of

data• Drift : -3,1841

umol/kg

⇒ But no correction is necessary

end

start

WOA09 or REF correction

• Data from the Primary sampling profile (Vertical SamplingScheme)

• Ascending profilesArgo data

• Interpolation on Argo levelsReference data (WOA or in situ)

• Gradient : dDOXY/dz < 0,2 on argo and reference data• Remove outliers ( « argo – référence > +/- 2,8 std)

Data selection to be used for the regression

• DOXY_ADJUSTED=C1*DOXY + C0• if R2 < 0.8, a constant correction is applied and

DOXY_ADJUSTED=DOXY+C0

Linear regression between entre ARGO profile(s) and reference

profile(s) (WOA09 ou REF)

• Ascending and descending profiles• Primary and all other available profiles Application

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Based on Takeshita et al., 2013

WOA09 or REF correction

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IN AIR correction

• PO2 NCEP (atmospheric reanalyses)• PO2 Optode acquired when the sensor is in the air:

available in « trajectory » file (PPOX)• PO2 Optode acquired in the water (subsurface) : in

current case, data are taken from the near-surface profile (DOXY converted as PPOX), also available in trajectoryfile

Data

• Takes into account bias due to the occasionalsubmersion of the sensor during the in air data acquisition (c : submersion factor, m : correction)

• PO2(air,obs)=c*pO2(water,obs)+(1-c)/m*pO2(air, ncep)Regression

• 𝒑𝒑𝑶𝑶𝟐𝟐(𝒐𝒐𝒐𝒐𝒐𝒐)𝒄𝒄𝒐𝒐𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄 = 𝒎𝒎 × 𝒑𝒑𝑶𝑶𝟐𝟐(𝒐𝒐𝒐𝒐𝒐𝒐)• Application aux données pompées et non pompées• Application aux profils ascendants et descendants

Correction : apply

correction factor m to

the rawdata

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Based on Bittig and Kortzinger, 2015

IN AIR correction

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PSAT float raw PSAT float corrected PSAT WOA

PO2 float water PO2 float in-air PO2 ncep

PO2 float water corrected PO2 float in-air corrected

m = 1,0026 mBar

R2 = 95%

Comparison

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Raw data

REF corr data

INAIR corr data

WOA corr data

Profils moyens

Hook

Output

Monocycle NetCDF files complying with argo format 3.1• Update the « DOXY_adjusted » fields:

DOXY_adjusted, DOXY_adjusted_qc,, DOXY_adjusted_error

• Update metadata according to QC manuals: date_update, data_moded, data_state_indicator, parameter_data_mode, history fields, scientific calibfields

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ConclusionLOCODOX take it easy !• Input : NetCDF argo 3.1 files• 3 methods to correct the data depending on availability

of reference data• Output NetCDF argo 3.1 files, follow last Argo/Bio-Argo

recommendations, files went successfully through the format checker

• Easy to use and available to the community, but …

Warnings !• Still debugging the tool, some minor adjustements and

improvements are necessary• Some files are still in format version < 3.1• IN AIR correction method needs to be finalized; needs

to define storage of PPOX_DOXY and near-surface DOXY data

• REF correction: No tool to update the database with in situ reference profiles

• MATLAB + statistic Toolbox• Development stopped until next year (subcontract)

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Conclusion

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• We used LOCODOX with the floats we deployed in the North-Atlantic

• Note those floats were redecoded according to the last cookbook specifications

• 12 floats are now available on the GDAC with DM corrections. More soon

• We already corrected few bugs in LOCODOX• Still some adjustments to do

• PSAL of 1st profile flagged to 4, PSAL is used in LOCODOX DOXY_ADJUSTED=NaN and DOXY_AJUSTED_QC=1

• Need to manage multiple adjustment• Need to take into account that part of the files might be in

Dmode and the other part in Rmode

Remarks on the storage of in air measurements / in water data used for the in air adjustment

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LOCODOX needs to know where to get in air and in water measurements for the in air adjustment

For some PROVOR/ARVOR floats, in air data are acquired at the end of the ascending profile (end of the unpumped profile):– The entire profile (PO2 and T) (with in water and in air data) are

stored in PPOX_DOXY in the traj file– In the future the in air measurements + last in water

measurement will be easily identifiable in a dedicated phase and stored in the PPOX data in the traj file

What is done for the other floats ? We need to agree on how to store those data.

REFERENCES

Takeshita et al, 2013: A climatology-based quality control procedurefor profiling float oxygen data: Qc Procedure for Profiling FloatOxygen, J. Geophys. Res. Oceans, 118, 5640–5650, doi:10.1002/jgrc.20399

Bittig and Kortzinger, 2015: Tackling Oxygen Optode Drift: Near-Surface and In-Air Oxygen Optode Measurements on a Float Provide an Accurate in Situ Reference, JAOT, 32, 1536-1543, doi: 10.1002/jgrc.20399

Argo Quality Control Manual For BioGeoChemical data, sur le site web de l’Argo Data Management (http://www.argodatamgt.org/Documentation)

Argo User’s Manual, sur le site web de l’Argo Data Management (http://www.argodatamgt.org/Documentation)

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