Comparison of XBT vs CTD Data

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Comparison of XBT vs CTD Data

• Presented By
• LT. Haris Rana PN

Project For OC 3570
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Summary of Presentation

• Introduction
• Data Collection and Equipment
• Data Selection and Quality Control
• Processing and Analysis
• Results
• Comparison with Previous Studies
• Conclusion
• Recommendations

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Introduction

• In Todays 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

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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.

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Data Collection Equipment
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Collection Points on Map
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Equipment
Sea Bird 911CTD/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
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Data Selection and Quality Control
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Drop Separation
Pair 9,13,15,25 26 were Flagged as being more
than 1.5 Km Apart
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Visual Inspection
Pair 14 15 showed an unusual Temperature
Profile and were Excluded from the comparison
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Visual Inspection
Pair 6 12 were T-7 XBTs , Never reached their
max operational depth
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Points on Map
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Finally 22 Pairs were considered for Subsequent
Comparison
Excluding Pair 6, 12, 14 15
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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

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Sample Figure 1
Plot 1 3 (XBT T-7 DB )
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Sample Figure 2
Plot 4 6 (XBT T-7 DB)
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Sample Figure 1
Plot 1 3 (XBT T-10)
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Sample Figure 2
Plot 4 6 (XBT T-10)
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Results
Results were computed in two different sets For
XBT (T10), (T7 DB)
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Temperature Difference
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Sound Speed Difference
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Isotherm Depth Difference
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Isotherm Depth Difference
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Results at a Glance for Whole Data Set

•  On the Average
• XBT has a warm Bias of 0.0537 0C over CTD.
• XBT gives Sound Speed 3.7489 m/sec slower than
  CTD.
• XBT measures Isotherm Depths 4.7204 m deeper
  than CTD.

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Comparison with the Previous Studies
Temperature Difference
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Comparison with the Previous Studies

• Sound Speed Difference was compared with
• Whelan (2007)
• Whelan Haris
• 5.06 m/s 3.74 m/s
• Isotherm Depth Difference was compared with
• Dixon (2003)
• Dixon Haris
• 13.53 m 8.33 m

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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 Doesnt 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

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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

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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

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Questions ?
Picture by Lt. Montgomery USN