FOCUS/SWOT-ACC CTD Harmonised Dataset (IN2023_V07)
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Version: 1.0

1. Overview
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This dataset contains harmonised ship-based CTD observations collected during RV Investigator voyage IN2023_V07 as part of the FOCUS/SWOT-ACC observing program in the Southern Ocean.

The harmonised product preserves the original CTD NetCDF files and their existing variables, metadata, dimensions and quality-control information. Additional dissolved oxygen variables expressed as mass concentration (micromoles/kg) have been appended to support cross-platform comparison with the other observing systems used in the FOCUS/SWOT-ACC dataset.

CTD Stations 1, 3 and 4 are not included because they were test stations located outside the target FOCUS/SWOT-ACC study region. All remaining science stations are retained.

2. Source data
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Source product:
IN2023_V07_CTD_CtdAvg_nc

The source CTD data had already undergone platform-specific processing and quality control before the harmonisation described here.

Each harmonised file corresponds to one original CTD station and retains the original filename.

3. Harmonisation performed
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The original NetCDF files were copied in full before any additional processing. No original variables were overwritten or removed.

The following additional variables were appended where the corresponding original oxygen variable was present:

    dissolved_oxygen
    dissolved_oxygenFlag
    dissolved_oxygen_2
    dissolved_oxygen_2Flag

The original variables, including oxygen, oxygenFlag, oxygen_2 and oxygen_2Flag, are retained unchanged.

No additional temperature or salinity offset correction was applied to the CTD data. No time-dependent dissolved oxygen gain correction was applied to the CTD data.

4. Dissolved oxygen unit conversion
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The original CTD dissolved oxygen data are expressed as volumetric concentration (micromoles/L). For consistency with the other observing platforms, dissolved oxygen was additionally expressed as mass concentration (micromoles/kg).

The conversion is:

    O2_mass = O2_volume / (rho / 1000)

where:
    O2_volume = original dissolved oxygen concentration in micromoles/L
    O2_mass   = dissolved oxygen concentration in micromoles/kg
    rho       = in-situ seawater density in kg/m^3

In-situ density was calculated using TEOS-10:

    SA  = gsw_SA_from_SP(SP, P, lon, lat)
    CT  = gsw_CT_from_t(SA, t, P)
    rho = gsw_rho(SA, CT, P)

where SP is Practical Salinity, t is in-situ temperature, P is pressure, and lon/lat are station longitude and latitude.

Consistent with the FOCUS/SWOT-ACC inter-calibration workflow, density was calculated using the primary temperature and salinity measurements and was used for conversion of both the primary and secondary oxygen measurements.

5. Quality-control information
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No additional QC filtering was applied when creating this harmonised release.

The existing CTD quality-control information is preserved in the original NetCDF variables. For the newly derived oxygen variables, the corresponding original oxygen QC flags were copied directly:

    oxygenFlag   -> dissolved_oxygenFlag
    oxygen_2Flag -> dissolved_oxygen_2Flag

The inherited QC flags were not reinterpreted or modified.

6. File organisation
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The release contains one NetCDF file per retained CTD station.

The exact number of files in this release is 108, after exclusion of test Stations 1, 3 and 4 from the original 110 CTD deployments.

7. Provenance
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The harmonised product is derived from the original IN2023_V07 CTD NetCDF files. The original source files remain the authoritative source for the unmodified platform-specific observations.

Users requiring the original volumetric dissolved oxygen measurements should use oxygen and oxygen_2. Users requiring the harmonised mass-based dissolved oxygen measurements should use dissolved_oxygen and dissolved_oxygen_2.

8. Contact
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Senming Sheng
Institute for Marine and Antarctic Studies (IMAS)
University of Tasmania

Lasted update: 06-Oct-2026
