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XBT Data System Comparison for Enhanced Ocean Data Collection

This scientific session compares six distinct XBT data systems to assess the impact of changing collection elements, focusing on accuracy improvements through standard system adjustments. The study includes comparisons with a Conductivity-Temperature-Depth (CTD) system to enhance data integrity.

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XBT Data System Comparison for Enhanced Ocean Data Collection

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  1. XBT Data Acquisition System Intercomparison JCOMM/SOT-4 Scientific and Technical Session Derrick Snowden Gustavo Goni Molly Baringer

  2. Cruise Purpose/Participants • Assess the impact of changing two elements of the standard xbt data collection system by comparing the results from six distinct systems with each other and with a higher accuracy Conductivity Temperature Depth (CTD) system. • NOAA/AOML, SIO, CSIRO

  3. XBT Data Collection System Controller Software Digitizer/Recorder Launchers • AOML/DOS • Scripps/DOS • SEAS2000 • CSIRO Devil • AOML Autolauncher • Scripps Autolauncher • Sippican LM3A Hand launcher • MK12 • MK21 • CSIRO Devil

  4. CTD System • SBE 25 Internally logging CTD • Sample rate 8 Hz raw data, reduced data 1m • Pressure offset on deck is negligible (-.08 to .06 dbars)

  5. System Name Launcher Type Recorder Type Controller Software (PC) aomlauto AOML Autolauncher MK-12 AOML (DOS 386 PC) devilhand Sippican LM-3A Devil Devil Software (Win XP PC) seasauto AOML Autolauncher MK-21 SEAS2000 (WinXP PC) seashand Sippican LM-3A MK-21 SEAS2000 (Win XP PC) sioauto SIO Autolauncher MK-21 SEAS2000 (Win XP PC) siok98 SIO Autolauncher MK-12 Instruments List K98 Software (DOS 386 PC)

  6. Station Drop Plan 7 CTD Stations 366 XBT profiles

  7. Drop Summary

  8. Regional Characteristics Mean CTD T(z) 0 SCMI/Port of LA Approx Station Depth(m) Catalina Island 900 5 20

  9. MSE Bias Variance

  10. B A Partitioning XBT Error XBT differs from the CTD due to : A: inaccurate depth measurements B: inaccurate temperature measurements • Probe fall rate error • Thermistor calibration error • Signal digitization error • Geophysical noise

  11. Magnitude of Expected Errors 0 Temperature accuracy 0.1 deg C (red curve) Depth (m) Depth accuracy is 2% of the total depth 800 0 0.25

  12. XBT/CTD Profiles

  13. Temperature Error: Isostads • Attempt to isolate the temperature error by concentrating on depths where the temperature gradients are minimal After Heimiller et al 1983

  14. Isostad Analysis (cont’) • aomlauto • devilhand • seasauto • seashand • sioauto • siok98

  15. Corrected Profiles: Isostads • aomlauto • devilhand • seasauto • seashand • sioauto • siok98

  16. Conclusions • Temperature error is within manufacturer specs for all instruments (In the deepest thermostad the mean offset was less than 0.055 degC for all instruments). • There is a detectable bias that is in part due to fall rate error. • Correcting the fall rate equation reduces the mean differences well below manufacturer specs and published results in all cases. • Two instruments (aomlauto, and devilhand) had mean offsets that were appreciably lower than the other four instruments.

  17. Name Affiliation Equipment/Responsibility Steve Cook NOAA/AOML SEAS2K Hand Launcher Derrick Snowden NOAA/AOML Data collection and analysis/Backup CTD Janet Roseli NOAA/AOML SEAS2K Software support and Autolauncher operation Uli Rivero NOAA/AOML AOML/DOS Autolancher Carrie Wolfe SCMI AOML/SEAS2K Autolauncher Glenn Pezzoli UCSD/Scripps SIO/SEAS2K Autolauncher Valerie Cannon UCSD/Scripps SIO/SEAS2K Autolauncher/Backup AOML/SEAS2K Autolauncher Bob Beattie CSIRO CSIRO Devil Handlauncher Adam Willingham SCMI SBE-25 CTD Participants

  18. MSE Bias Variance

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