Data processing steps

Underway data processing for projects

Underway data processing ©

Underway instruments continuously take measurements of sea surface data (e.g. salinity, temperature, attenuance, chlorophyll and nutrients), meteorology, navigation and bathymetry. They usually measure a continuously pumped surface sea water supply available on most research vessels.

The continuous underway data set includes the following

• Navigation from the ship
• Data from the meteorological package
• Data from the thermosalinograph
• Data from other instruments attached to the pumped water supply (e.g. fluorometer, pCO₂ system, nutrient analysers)

The current procedure for processing underway data is

1. Archive original data. When the data are first received they go through our Accession procedure. The data are securely archived in their original form along with any associated documentation.

2. Merge data into a single binary file of standard format using time as the common variable. The sampling interval is usually set to 30 seconds for short cruises, or 60 seconds for longer cruises.

3.  Check navigation record for gaps and improbable ship speeds (>15-19 knots depending on vessel). Gaps are filled with log sheet information where they are longer than 15 minutes, or by interpolation for shorter periods.

4.  Screen data on a graphics workstation. Suspect values are flagged as suspect, null values as null. Where there are particular problems (e.g. poor quality of bathymetry data or wind speed data) a warning is made in accompanying documentation.

5.  Calibrate data. Manufacturer's calibrations are applied to convert the data to scientific units. Some channels are calibrated against sample data or other calibrated instruments such as the CTD. Relative wind speed and direction are corrected to absolute speed and direction. This is achieved by using the data for the ship's velocity in the North-South and East-West direction and the ship's heading.

6. Document data. Documentation is written containing information about instruments, calibration, sampling techniques, parameters and sea areas.

7. Distribution and delivery. Data are distributed to project participants on request. Data may be listed from the binary file using BODC in-house software.

Related BODC pages