Data management of Argo oxygen data

V. Thierry, D. Gilbert, T. Kobayashi

Profiling floats equipped with O2 sensor

DO concentration data from 426 profiling floats (~ 117 active floats) are distributed through the Argo data stream

DO concentration measurements

DO concentration measurements

Data processing

Data processing at DAC level

Unit conversion

Internal processing

Transmission of sensor output

SBE43

*****Unit: Count, Hz or V

DOUnit: ml/L

SBE DOXYUnit: u-mol/kg

Optode

Phase shiftUnit: degree

DOUnit: u-mol/L

DOUnit: u-mol/L

Optode DOXY (1)Unit: u-mol/kg

DOUnit: u-mol/L

DOUnit: u-mol/L

Optode DOXY (2)Unit: u-mol/kg

MeasurementPhase shift Unit: degree

Optode

DOUnit: u-mol/L

*****Unit: Count, Hz or V

Phase shiftUnit: degree

AdjustmentSalinity and pressure

Present parameters and recommendations for the management of DO data

• Unit: mol/kg

• DOXY: DO concentration in mol/kg either deduced from the sensor output or transmitted by the Aanderaa optode at Pres=0 and Psal=S0 (and converted from mol/l to mol/kg ).

• DOXY_ADJUSTED: P, S compensation applied for the Aaanderaa optode when DO is transmitted

• BPHASE_DOXY: BPHASE measured by the Aanderaa optode, when it is transmitted

• TEMP_DOXY: Temperature measured by the Aanderaa otpode, when it is transmitted

Management of the O2 data at the DAC level

• Present parameters do not allow us to manage in a consistent way the O2-related variables (with different units) transmitted to the DAC

• The data processing varies from one PI to the other and the data and metadata are reported in different ways

• Unit conversion not systematically applied

• Salinity and pressure compensation applied in the “ADJUSTED” field

• The available DOXY from the different floats are not comparable and a user cannot use with confidence O2 data from other groups

Need to standardize procedures and to provide clear recommendations

Action item 14 from AST10 : D. Gilbert to work with T. Kobayashi and V. Thierry to ensure DACs are processing oxygen data according to recommendations.

We do not address QC issue

• DOXY = DO concentration estimated from the telemetered variables, calibrations coefficients and CTD values: PRES, TEMP (or TEMP_DOXY) and PSAL

• Pressure and salinity compensations (optode) are taken into account

• Converted in the official Argo unit: mol/kg

• DOXY_ADJUSTED is the DO concentration corrected for any sensor drift and offset. DOXY_ADJUSTED is calculated from the other “ADJUSTED” fields.

• Calibration coefficients, equations and references used to convert the telemetered variables in DOXY must be carefully documented in the metadata

Proposition for what could be DOXY

What variables to store ? 1st solution

• Store each telemetered variables in new parameters with meaningful names:– VOLTAGE_DOXY (Unit = V) for SBE43

– FREQUENCY_DOXY (Unit = Hz) for SBE43

– COUNTS_DOXY (no Unit ?) for SBE43

– BPHASE_DOXY (Unit = degree) for Aanderaa optode

– DPHASE_DOXY (Unit = degree) for Aanderaa optode

– CONCENT_DOXY (Unit = mol/l) for Aanderaa optode

– TEMP_DOXY (Unit = degree Celsius) for Aanderaa optode

– XXX_DOXY for any new variables

• Calculate and store DOXY data from the telemetered variables and converted in in M/kg– DOXY (mol/kg)

• Store only DOXY data converted in a DO concentration value consistent with all other from whatever is transmitted by the floats and converted in M/kg :– DOXY (mol/kg)

• Do not store anymore– BPHASE_DOXY (Unit = degree) for Aanderaa optode

– TEMP_DOXY (Unit = degree Celsius) for Aanderaa optode

• “DOXY_ADJUSTED” fields are corrected for any sensor drift or offset of the DO sensor

What variables to store ? 2nd solution

Any other proposition ?

• Do we cover all cases ?• Is 256 character enough to document the processing of O2

data in the “PREDEPLOYMENT_XXX” fields of the metadata file ?

• Need help to review the different cases and to provide advise on how to fill the metadata

• A proposal has been written to provide all necessary information to the DAC. This proposal will be updated according to the agreed solution and provided to anyone interested.

Questions/remarks

Metadata

• Carefully document the telemetered variables in the metadata

• Example for the aanderaa optode transmitting DO concentration in mol/L

SENSOR_UNITS = “micromole/L”

PARAMETER= “CONCENT_DOXY”

PREDEPLOYMENT_CALIB_EQUATION = “O2=C0+C1.P+C2.P^2+C3.P^3+C4.P^4 with Ci=Ci0+Ci1.t+Ci2.t^2+Ci3.t^3 ; CONCENT_DOXY=O2 exp[ S (B0+B1.Ts+B2.Ts^2+B3.Ts^3)+C0S^2]; Ts=ln[(298.15-t)/(298.15+t)]; with P=DPHASE, t=TEMP_DOXY, S=S0”

PREDEPLOYMENT_CALIB_COEFFICIENT = “S0=35” or “S0=0”

PREDEPLOYMENT_CALIB_COMMENT = “CONCENT_DOXY is calculated by the optode from DPHASE, TEMP_DOXY, PRES=0 and S0; see TD218 operating manual oxygen optode 3830, 3835, 3930, 3975, 4130, 4175”

Exemple: transmission of CONCENT_DOXY = DO concentration from optode at PRES=0 and PSAL=S0

• PARAMETER=”DOXY”

• PREDEPLOYMENT_CALIB_EQUATION = “O2c= O2 exp[ (S-S0) (B0+B1Ts+B2Ts^2+B3Ts^3)+C0(S^2-S0^2)]; DO=O2c [1+ 0.032 * PRES/1000]; O2=CONCENT_DOXY; S=PSAL; Ts=ln[(298.15-t)/(298.15+t)]; t=TEMP (or TEMP_DOXY); DOXY[micromole/kg]=DO [micromole/L] / ρ ; ρ= potential density [kg/L] at zero pressure and potential temperature”

• PREDEPLOYMENT_CALIB_COEFFICIENT = “S0=35 (or any other value); B0= -6.24097e-3; B1=-6.93498e-3; B2=-6.90358e-3; B3=-4.29155e-3 ”

• PREDEPLOYMENT_CALIB_COMMENT = “Pressure and salinity compensation are estimated to convert CONCENT_DOXY in DOXY. DOXY is converted from micromole/L to micromole/kg; see TD218 operating manual oxygen optode 3830, 3835, 3930, 3975, 4130, 4175”