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

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

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

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.”

Data Collection & Equipment

Collection Points on Map

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

Data Selection and Quality Control

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

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

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

Points on Map

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

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

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

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

Sample Figure 1 Plot 1 – 3 (XBT T-10)

Sample Figure 2 Plot 4 – 6 (XBT T-10)

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

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

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

Isotherm Depth Difference

Isotherm Depth Difference XBT (T7 & DB) XBT (T10) Mean Depth Diff (m) 8.3315 1.1094 Max 16.8433 6.0692 Min -2.7709 -6.7639 Mean Depth Diff Std (m) 16.3902 5.1478 32.3478 15.1997

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.

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

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

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

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

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

Questions ? Picture by: Lt. Montgomery USN