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Experience of Quality Control of Profiling Floats in the North Atlantic

Experience of Quality Control of Profiling Floats in the North Atlantic. Lars Böhme Brest, France 9 March 2004. Experience of Quality Control of Profiling Floats in the North Atlantic. Introduction Float's Raw Data Quality Control System Objective Mapping of a Reference

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Experience of Quality Control of Profiling Floats in the North Atlantic

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  1. Experience of Quality Control of Profiling Floats in the North Atlantic Lars Böhme Brest, France 9 March 2004

  2. Experience of Quality Control of Profiling Floats in the North Atlantic • Introduction • Float's Raw Data • Quality Control System • Objective Mapping of a Reference • Time-Varying Correction • Results of GyroScope Project • Questions need to be resolved • Summary

  3. Boundary Currents • Deep Convection • Eddies of warm, salty Mediterranean water (meddies) Introduction GyroScope was an european project and deployed 84 floats as part of Argo from July 2001 to September 2002. About 4477 profiles were executed. Profile locations of all GyroScope floats

  4. FSI - Sensor Float’s Raw Data Provor floats with FSI sensors are corrected due to the influence of the damping disc. • external fields: • could be influenced from outside Same part for each float due to damping disc. experiments at Ifremer and FSI showed an offset in conductivity for Provor floats equipped with FSI sensors Individual part due to the pre-shipping calibration?

  5. Quality Control System- Objective Mapping of a Reference - based on Wong et al. (2003) No data from historical profiles are rejected due to temperature inversion. Based on spatial distance D and fractional distance in potential vorticity F.

  6. Individual correction for most float profiles linear-fit for time-dependent correction to smooth out outlierers. linear fit is used to correct for a slope and offset Quality Control System- Time-Varying Correction -

  7. Results of GyroScope About 80% of the floats (64/81) work within an accuracy of ± 0.01

  8. Disc correction ≈ +0.020 QC : +0.077 Ifremer lab : +0.096 Results of GyroScope • Tests on FSI-sensors attached to Provor floats at Ifremer and FSI have shown that conductivity measurements are modified by the presence of the damping disk. Such data are corrected due to the disc. • But there are still individual offsets seen in FSI data during the tank tests. The QC shows also such individual offsets for each FSI sensor. With the tank tests and the QC such an offset is easily detectable and the data could be corrected. => 90% good data!

  9. Could be corrected (linear, cubic….?) Correctable or bad data? Results of GyroScope- Is there a need for correction? - • Still some floats with an offset and/or drift. • Shift in conductivity measurements.

  10. Questions to be solved • Pre-deployement tests for FSI sensors? • Yes, because all FSI sensors seem to have an offset. • 2. What should be done with measurements taken after a shift? • Divide the timeseries in two parts, compute corrections and put them together.

  11. Questions to be solved • Only one linear fit, several linear fits or a non-linear fit? All together? linear parts or non-linear linear!

  12. Questions to be solved • In which case should a proposed correction be applied or not? • Should the correction be applied everytime? • Should the correction be applied if float measurements • are outside of one standard deviation? • are outside of two times the standard deviation? • Should we include the estimated accuracy of the sensor?

  13. Questions to be solved • If there is a linear correction, should we wait half a year? • Each new profile could easily be corrected. known offset

  14. Questions to be solved • What is done in areas with only a few historical profiles? (i.e. Southern Ocean) • Float data should be included to the historical database. (80% of the data is good!) • This corrected float data should be again added to the database for the next calibration run.

  15. Summary • Most sensors are stable and work within the desired accuracy of 0.01 in salinity (80 – 90%). • Provor floats with FSI sensors are corrected for an offset due to the damping plate. • Floats with FSI sensors need a better pre-shipping calibration or an additional pre-deployement test. • Floats which need a correction are obvious. • Still questions to solve to make the salinity adjustment as uniform and consistent as possible.

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