1. Operational Oceanography Cruise February 2003
Comparison of
Expendable Bathythermograph
and
Conductivity, Temperature and Depth Profilers
LT Jeffrey S. Dixon
OC 3570

2. Sampling Equipment
Sippican
T7 XBT
Sea-Bird SBE911 CTD

3. Study Process Field Sampling Data Processing Analysis Conclusions
Quality Control
Analysis
Temperature vs. Depth Comparison
Comparison to Previous Studies
Conclusions
Impact on Sound Velocity Profiles
The CTD is the Accepted Standard!

4. Field Sampling 26 XBT/CTD Pairs (2 later thrown out)
February 2003 Cruise XBT/CTD Stations 26
XBT/CTD
Pairs
(2 later
thrown out)

5. 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

6. Quality Control – Visual Inspection
Natural Variability
or Bad Data??

7. Quality Control – Visual Inspection
XBT / CTD
Pair 18
Thrown Out

8. Quality Control – Visual Inspection
Less Obvious
Problem?

9. Quality Control – Compare to Ambient Temperature
Quantitative
Quality Control
Measure
Temperature of each
> or = 0.2 deg C
than temperature
of the average of
two adjacent levels?

10. Quality Control - Compare to Ambient TemperatureZn
Tn+1 Tn
Tn-1
Possible
Bad Points
Zn-1
Pn-1 Zn Pn
File generated:
Zn+1
Pn+1
Text25.txt
XBT flagged flagged bottom CTD flagged flagged bottom
If |Tn - ( Tn+1 + Tn-1 ) /2| > 2 Std. (~0.2°C)
Then Pn Flagged as Possible bad data point
37 total points were found–but retained
(Fang 2002)

11. Data Analysis – 3 Steps

12. Average Temperature Difference
Greatest
Variability
Consistent
Warm
Bias
-.1275oC

13. Temperature Stats - Compare to Previous Studies

14. Isotherm Depth Difference
Temperature deg C 5 6 7
CTD 10
Isotherm
Depth
Difference ~ 5m
XBT 20 30 40

15. Average Isotherm Depth Difference

16. Sound Velocity Profile Differences – Impact of XBT Warm Bias

17. SVP for all XBTs and CTDs
Slight Warm
Bias
Disagreement
At Surface
XBT
CTD
Some Qualitative Disagreement

18. 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

19. 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…

20. …He Can’t Launch Weather Balloons
Damn Juan who put that
antenna there?
Que?
Someday I’ll get to go
on a research cruise without students.