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XBT Data Acquisition System Intercomparison

XBT Data Acquisition System Intercomparison

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XBT Data Acquisition System Intercomparison

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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