JR18007 BODC CTD Data Processing
Data Processing
Processed CTD data from Changing Arctic Ocean cruise JR18007 were submitted to BODC in ascii format. The data were not calibrated against independent samples and so calibrations were applied by BODC. The calibrated data were then transferred to BODC internal format using standard BODC procedures. The variables provided in the files were mapped to BODC parameter codes as follows:
| Originator's Variable | Originator's Units | BODC Parameter Code | BODC Units | Comment |
|---|---|---|---|---|
| Pressure | db | PRESPR01 | db | - |
| Temperature | °C | TEMPST01 | °C | - |
| Temperature, 2 | °C | TEMPST02 | °C | The channel was transferred and then dropped following BODC processing as there was no difference in the quality of the data from the first or second sensor. |
| Salinity1_cal | PSU | PSALCC01 | Dimensionless | - |
| Salinity2_cal | PSU | PSALCC02 | Dimensionless | The channel was transferred and then dropped following BODC processing as there was no difference in the quality of the data from the first or second sensor. |
| Conductivity | S m -1 | CNDCST01 | S m -1 | |
| Conductivity, 2 | S m -1 | CNDCST02 | S m -1 | The channel was transferred and then dropped following BODC processing as there was no difference in the quality of the data from the first or second sensor. |
| Fluorescence | µg L -1 | CPHLPR01 | mg m -3 | Equivalent units |
| Attenutation | m -1 | ATTNMR01 | m -1 | - |
| Transmission | % | POPTDR01 | % | |
| PAR | µE cm -2 s -1 | IRRDSV01 | µE cm -2 s -1 | |
| Altimeter | m | AHSFZZ01 | m | |
| Oxygen_cal (µmol L -1 ) | µmol L -1 | DOXYSC01 | µmol L -1 | |
| Oxygen_raw | V | OXYOCPVL | V | |
| OXYSZZ01 | % | Derived during transfer using DOXYSC01, TEMPST01 and PSALST01 | ||
| POTMCV01 | °C | Derived during transfer using TEMPST01, PSALST01 and PRESPR01 | ||
| POTMCV02 | °C | Derived during transfer using TEMPST02, PSALST02 and PRESPR01. Channel dropped as the data from the derived parameter from the primary sensors was kept in the final files. | ||
| SIGTPR01 | kg m -3 | Derived during transfer using POTMCV01, PSALST01 and PRESPR01 | ||
| SIGTPR02 | kg m -3 | Derived during transfer using POTMCV02, PSALST02 and PRESPR01. Channel dropped as the data from the derived parameter from the primary sensors was kept in the final files. | ||
| TOKGPR01 | kg m -3 | Computed during transfer using TEMPST01 and PSALST01 | ||
| TOKGPR02 | kg m -3 | Computed during transfer using TEMPST02 and PSALST02. Channel dropped as the data from the derived parameter from the primary sensors was kept in the final files. |
Post transfer analysis and crosschecks were applied according to BODC procedures including the screening of data using BODC in house visualisation software.
Calibrations
Temperature
A total of 857 independent temperature readings were used to determine a calibration equation for temperature data. Two hypothesis were tested: a regression and offset. After outliers were identified and removed from the final dataset, a total of 841 readings for the primary sensor and 837 for the secondary remained. The two hypothesis were tested and it was found that none improved the data quality significantly, therefore it was decided that no calibration would be applied to these data.
Salinity
A total of 44 discrete salinity samples were analysed throughout the cruise, covering a wide range of salinity values. To collect samples for salinity analysis, the sample bottles were rinsed three times with water from the Niskin bottle before being filled. Once full, a plastic insert was fitted into the sample bottle, the bottle's neck was wiped, and a lid was put on. Once a crate of 24 bottles was full, it was placed in the Autosal laboratory to acclimatise to temperature for at least one day prior to analysis. At the start and end of each crate a standard seawater (SSW) sample was analysed, in order to monitor the drift of the instrument but no clear drift pattern was visible.
There did not appear to be any temporal drift in the sensors, or a drift relative to pressure and once an outlier was identified and removed from the dataset, a constant offset was used to correct the data for both sensors.
| Number of Samples | Salinity offset | |
|---|---|---|
| Sensor 1 | 43 | 0.009581395 |
| Sensor 2 | 43 | 0.005976744 |
Oxygen
The oxygen calibration equation was determined by Tim Brand from Scottish Association for Marine Science and applied to the data:
O 2 _calibrated = (O 2 _raw - 51.919) / 0.7544
