JCOMM SOT-4 April 2007 XBT Data Acquisition System Intercomparison JCOMM/SOT-4 Scientific and...

JCOMM SOT-4 April 2007

XBT Data Acquisition System Intercomparison

JCOMM/SOT-4Scientific and Technical

SessionDerrick Snowden

Gustavo GoniMolly Baringer


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


XBT Data Collection System

1. AOML/DOS

2. Scripps/DOS

3. SEAS2000

4. CSIRO Devil

1. AOML Autolauncher

2. Scripps Autolauncher

3. Sippican LM3A Hand launcher

1. MK12

2. MK21

3. CSIRO Devil

Controller Software

Digitizer/Recorder

Launchers


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)


Instruments ListSystem Name Launcher

TypeRecorder 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 SIOAutolauncher

MK-21 SEAS2000(Win XP PC)

siok98 SIO Autolauncher

MK-12 K98 Software

(DOS 386 PC)


Station Drop Plan

7 CTD Stations

366 XBT profiles


Drop SummaryInstrument Total Profiles Trimmed at

z< 500mTrimmed at z<150m

aomlauto 65 2 2

devilhand 52 3 3

seasauto 68 5 2

seashand 54 1 0

sioauto 59 10 1

siok98 68 6 4

Totals 366 27 12


Regional Characteristics

0

900

Dep

th (

m)

Mean CTD T(z)

5 20

Approx Station

Catalina Island

SCMI/Port of LA


MSE

Bias

Variance


Partitioning XBT Error

XBT differs from the CTD due to :A: inaccurate depth measurementsB: inaccurate temperature measurements

A B

•Probe fall rate error•Thermistor calibration error

•Signal digitization error •Geophysical noise


Magnitude of Expected Errors

Temperature accuracy 0.1 deg C (red curve)

0

800

Dep

th (

m)

0.25

0

Depth accuracy is 2% of the total depth


XBT/CTD Profiles


Temperature Error: Isostads

• Attempt to isolate the temperature error by concentrating on depths where the temperature gradients are minimal

After Heimiller et al 1983


Isostad Analysis (cont’)

1. aomlauto

2. devilhand

3. seasauto

4. seashand

5. sioauto

6. siok98


Corrected Profiles: Isostads

1. aomlauto

2. devilhand

3. seasauto

4. seashand

5. sioauto

6. siok98


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.


ParticipantsName 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


MSE

Bias

Variance

JCOMM SOT-4 April 2007 XBT Data Acquisition System Intercomparison JCOMM/SOT-4 Scientific and...

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