XBT Data Acquisition System Intercomparison JCOMMSOT4 Scientific and

XBT Data Acquisition System Intercomparison JCOMM/SOT-4 Scientific and Technical Session Derrick Snowden Gustavo Goni Molly Baringer JCOMM SOT-4 April 2007

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 JCOMM SOT-4 April 2007

XBT Data Collection System Controller Software Digitizer/Recorder 1. AOML/DOS 1. MK 12 2. Scripps/DOS 2. MK 21 3. SEAS 2000 3. CSIRO Devil 4. CSIRO Devil JCOMM SOT-4 April 2007 Launchers 1. AOML Autolauncher 2. Scripps Autolauncher 3. Sippican LM 3 A Hand launcher

CTD System • SBE 25 Internally logging CTD • Sample rate 8 Hz raw data, reduced data 1 m • Pressure offset on deck is negligible ( -. 08 to. 06 dbars) JCOMM SOT-4 April 2007

Instruments List System Name Launcher Type Recorder Type Controller Software (PC) aomlauto AOML Autolauncher MK-12 AOML (DOS 386 PC) devilhand Sippican LM-3 A Devil Software (Win XP PC) seasauto AOML Autolauncher MK-21 SEAS 2000 (Win. XP PC) seashand Sippican LM-3 A MK-21 SEAS 2000 (Win XP PC) sioauto SIO Autolauncher MK-21 SEAS 2000 (Win XP PC) siok 98 SIO Autolauncher MK-12 K 98 Software JCOMM SOT-4 April 2007 (DOS 386 PC)

Station Drop Plan 7 CTD Stations 366 XBT profiles JCOMM SOT-4 April 2007

Drop Summary Instrument Total Profiles Trimmed at z< 500 m Trimmed at z<150 m aomlauto 65 2 2 devilhand 52 3 3 seasauto 68 5 2 seashand 54 1 0 sioauto 59 10 1 siok 98 68 6 4 Totals 366 27 12 JCOMM SOT-4 April 2007

Regional Characteristics Mean CTD T(z) SCMI/Port of LA Approx Station Catalina Island JCOMM SOT-4 April 2007 Depth (m) 0 900 5 20

MSE Bias Variance JCOMM SOT-4 April 2007

Partitioning XBT Error A B XBT differs from the CTD due to : A: inaccurate depth measurements B: inaccurate temperature measurements • Probe fall rate error • Thermistor calibration error JCOMM SOT-4 April 2007 • Signal digitization error • Geophysical noise

Magnitude of Expected Errors 0 Depth (m) Temperature accuracy 0. 1 deg C (red curve) Depth accuracy is 2% of the total depth 800 0 JCOMM SOT-4 April 2007 0. 25

XBT/CTD Profiles JCOMM SOT-4 April 2007

Temperature Error: Isostads • Attempt to isolate the temperature error by concentrating on depths where the temperature gradients are minimal JCOMM SOT-4 April 2007 After Heimiller et al 1983

Isostad Analysis (cont’) 1. aomlauto 2. devilhand 3. seasauto 4. seashand 5. sioauto 6. siok 98 JCOMM SOT-4 April 2007

Corrected Profiles: Isostads 1. aomlauto 2. devilhand 3. seasauto 4. seashand 5. sioauto 6. siok 98 JCOMM SOT-4 April 2007

Conclusions • Temperature error is within manufacturer specs for all instruments (In the deepest thermostad the mean offset was less than 0. 055 deg. C 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. JCOMM SOT-4 April 2007

Participants Name Affiliation Equipment/Responsibility Steve Cook NOAA/AOML SEAS 2 K Hand Launcher Derrick Snowden NOAA/AOML Janet Roseli NOAA/AOML Uli Rivero NOAA/AOML Data collection and analysis/Backup CTD SEAS 2 K Software support and Autolauncher operation AOML/DOS Autolancher Carrie Wolfe SCMI AOML/SEAS 2 K Autolauncher Glenn Pezzoli UCSD/Scripps SIO/SEAS 2 K Autolauncher Valerie Cannon UCSD/Scripps Bob Beattie CSIRO SIO/SEAS 2 K Autolauncher/Backup AOML/SEAS 2 K Autolauncher CSIRO Devil Handlauncher Adam Willingham SCMI SBE-25 CTD JCOMM SOT-4 April 2007

MSE Bias Variance JCOMM SOT-4 April 2007