1. Comparison of XBT vs CTD Data
Presented By:
LT. Haris Rana PN
Project For OC 3570

2. Summary of Presentation
Introduction
Data Collection and Equipment
Data Selection and Quality Control
Processing and Analysis
Results
Comparison with Previous Studies
Conclusion
Recommendations

3. Introduction
In Today’s Modern Times when the world is shrinking and becoming a global village, gives us the blessings of being close to each other but at the same time it has exponentially increased the security concerns all over the world
Naval assets are becoming more and more important in terms of providing sustainable security to a nation
Talking of Naval Warfare, Underwater warfare is its most vital part
The most effective underwater search and detection source of energy is Sound, ray path of which is greatly dependant on underwater Temperature profile
In terms of Underwater warfare most important Environmental Parameter to be known is the temperature profile of that certain area

4. Goal behind the study
The two most common methods in use today of determining ocean temperature profiles are via a Conductivity, Temperature, and Depth (CTD) profiler or via an Expendable Bathythermograph (XBT) probe
CTD is a more sophisticated instrument and provide accurate measurements of Temperature and other environmental Factors, whereas XBT is considered not as accurate as CTD
XBT is widely used in Navy to calculate the Sound Speed Profiles
The Goal of this project is to determine “Is there a Significant Difference between XBT and CTD temperature measurements.”

5. Data Collection & Equipment

6. Collection Points on Map

7. Equipment Sippican Mark 12 XBT System LM-3A Hand Held Launcher
Sea Bird 911+CTD/Rosette (12 position)
with standard sensor suite
Max cast this study: 2182 m
Total of 26 Pairs were Identified for the Study
Sippican Mark 12 XBT System
LM-3A Hand Held Launcher
XBT: T-7 & DB Max Depth: 760 m
XBT: T-10 Max Depth: 200 m

8. Data Selection and Quality Control

9. Pair 9,13,15,25 & 26 were Flagged as being more than 1.5 Km Apart
Drop Separation
Pair 9,13,15,25 & 26 were Flagged as being more than 1.5 Km Apart

10. Visual Inspection
Pair 14 & 15 showed an unusual Temperature Profile and were Excluded from the comparison

11. Visual Inspection
Pair 6 & 12 were T-7 XBTs , Never reached their max operational depth

12. Points on Map

13. Finally “22” Pairs were considered for Subsequent Comparison
Excluding Pair 6, 12, 14 & 15

14. Processing and Analysis
CTD Measurements were considered as Reference
CTD depths were converted from dbars to Meters
Sampling rate of XBT was interpolated with CTD
sampling rate
CTD casts were limited to max sampling depth of XBT
Total of 6 Plots were made for each Pair
Comparison in three Different Properties
Temperature Difference
Sound Speed Difference
Isotherm Depth Difference

15. Sample Figure 1
Plot 1 – 3 (XBT T-7 & DB )

16. Sample Figure 2
Plot 4 – 6 (XBT T-7 & DB)

17. Sample Figure 1
Plot 1 – 3 (XBT T-10)

18. Sample Figure 2
Plot 4 – 6 (XBT T-10)

19. Results were computed in two different sets
For XBT (T10), (T7 & DB)

20. Temperature Difference
XBT (T7 & DB)
XBT (T10)
Mean Temp Diff (0C)
0.0712
0.0362
Max(Warm)
0.1514
0.2083
Min
0.0183
Mean Temp Diff Std (0C)
0.1242
0.1160
0.2949
0.2383
0.0462
0.0514

21. Sound Speed Difference
SSP Diff
XBT (T7 & DB)
XBT (T10)
Mean SSP Diff (m)
3.7887
3.7092
Max
4.2472
4.3545
Min
2.7023
2.6144
Mean SSP Diff Std (m)
2.0230
1.6894
2.2895
1.9671
1.4234
1.2897

22. Isotherm Depth Difference

23. Isotherm Depth Difference
XBT (T7 & DB)
XBT (T10)
Mean Depth Diff (m)
8.3315
1.1094
Max
6.0692
Min
Mean Depth Diff Std (m)
5.1478

24. Results at a Glance for Whole Data Set
 On the Average
XBT has a warm Bias of C over CTD.
XBT gives Sound Speed m/sec slower than CTD.
XBT measures Isotherm Depths m deeper than CTD.

25. Comparison with the Previous Studies
Temperature Difference
Author, Yr (sample size)
Mean T diff(0C)
Std Dev (0C)
Schmeiser, 2000 (18)
0.1549
0.2151
Roth, 2001 (9)
0.0783
0.1047
Boedeker, 2001 (27)
0.0882
0.2147
Fang, 2002 (28)
0.1074
0.1546
Dixon, 2003 (24)
0.1275
0.0598
Laird, 2006 (13)
0.0407
0.0936
Whelan, 2007 (21)
0.0344
0.1012
Haris, 2008 (22)
0.0537
0.1790
Average
0.0856
0.1403

26. Comparison with the Previous Studies
Sound Speed Difference was compared with
Whelan (2007)
Whelan Haris
5.06 m/s m/s
Isotherm Depth Difference was compared with
Dixon (2003)
Dixon Haris
13.53 m m

27. Conclusion
XBT Precede CTD for Operational and Tactical use in the following ways
XBTs are considerably cheaper than CTD
Can be launched in any Sea State
Launching Doesn’t jeopardize the maneuverability of a warship
A single XBT launch Takes very Less time as compared to a CTD cast(depending on the sampling depth)
CTD Launching Require Multiple Persons, whereas for XBT can be operated by a single person or from a fixed Launcher
No need to have a dedicated superstructure for its Launcher
XBT can be deployed by both Ships and Submarines
Smaller in size and can be stored easily onboard smaller vessels like Mine Hunters or Submarines.
Warm bias in XBT on the average is consistent throughout the depth, therefore can be refined to get an accurate measurement

28. Conclusion
A CTD may be Preferred for Scientific Research and Precedes its importance over XBT in the following ways
It gives Accurate measurements of different ocean parameters at the same time
Generally for Scientific Research Accuracy of the measurements is more important than getting it more quickly
In Developing Strategic Environmental Data Bases for future use

29. Recommendations
XBT may be dropped during the CTD cast in order to get Min Drop Separation
Placement of a fixed XBT Launcher may be considered at a suitable place on the ship, which could reduce occasional dropping errors
In future a Project may be considered to analyze the Results from all the Previous studies

30. Questions ?
Picture by: Lt. Montgomery USN