Operational Oceanography Cruise February 2003

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Operational Oceanography Cruise February 2003
Comparison of Expendable Bathythermograph and
Conductivity, Temperature and Depth Profilers
LT Jeffrey S. Dixon OC 3570
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Sampling Equipment
Sippican T7 XBT
Sea-Bird SBE911 CTD
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Study Process

• Field Sampling
• Data Processing
• Quality Control
• Analysis
• Temperature vs. Depth Comparison
• Comparison to Previous Studies
• Conclusions
• Impact on Sound Velocity Profiles

The CTD is the Accepted Standard!
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Field Sampling
February 2003 Cruise XBT/CTD Stations
26 XBT/CTD Pairs (2 later thrown out)
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Data Processing

• Used Matlab 53
• Code Adaptation / Modification
• (4 Previous Studies)
• Interpolation Steps for
• Common Comparison
• 2 Step Quality Control Process
• Visual Inspection of
• Temperature vs. Depth
• Comparison to Ambient
• Temperatures

CTD Divides into 383 Equal Depth Levels
XBT T7 Max Depth 760 meters
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Quality Control Visual Inspection
Natural Variability or Bad Data??
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Quality Control Visual Inspection
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Quality Control Visual Inspection
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Quality Control Compare to Ambient

Temperature
Quantitative Quality Control Measure

• Temperature of each
• gt or 0.2 deg C
• than temperature
• of the average of
• two adjacent levels?

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Quality Control - Compare to Ambient

Temperature
Zn
Tn
Tn1
Tn-1
Possible Bad Points
Zn-1
Pn-1
Zn
Pn
File generated
Zn1
Pn1
Text25.txt XBT 35.7290 flagged 87.3400
flagged759.0460 bottomCTD 51.6080
flagged 53.6050 flagged759.0460 bottom
If Tn - ( Tn1 Tn-1 ) /2 gt 2 Std.
(0.2C) Then Pn Flagged as Possible bad data
point 37 total points were foundbut retained
(Fang 2002)
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Data Analysis 3 Steps
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Average Temperature Difference
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Temperature Stats - Compare to Previous Studies
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Isotherm Depth Difference
Temperature deg C
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6
7
CTD
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Isotherm Depth Difference 5m
XBT
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30
40
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Average Isotherm Depth Difference
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Sound Velocity Profile Differences Impact of
XBT Warm Bias
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SVP for all XBTs and CTDs
Slight Warm Bias
Disagreement At Surface
XBT
CTD
Some Qualitative Disagreement
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Sound Velocity Profile Differences
XBT bias due to warm temperature bias and a
constant salinity of 33.5psu as well
0.1275oC temperature increase will increase sound
speed 0.51m/s
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Conclusions

• XBT Exhibits Distinct Bias Compared to CTD
• SVP bias due to both temperature bias and
  salinity constant
• Affect on Sound Velocity Profiles is Measurable
• However Impact Considered Small!
• XBT Should Not be Used as a Research Tool
• XBT Valid Tool to Determine SVP for Navy
• And Jeff should continue to focus on oceanography
  because

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He Cant Launch Weather Balloons