a comparison of six expendable bathythermograph data acquisition systems derrick snowden molly...

A Comparison of Six Expendable Bathythermograph Data Acquisition

Systems

Derrick SnowdenMolly BaringerGustavo Goni

Instruments ListSystem Name

Launcher Type

Recorder Type

Controller Software (PC)

aomlauto AOML Autolauncher

MK-12 AOML (DOS 386 PC)

devilhand Sippican LM-3A

Devil Devil Software(Win XP PC)

seasauto AOML Autolauncher

MK-21 SEAS2000 (WinXP PC)

seashand Sippican LM-3A

MK-21 SEAS2000(Win XP PC)

sioauto SIOAutolauncher

MK-21 SEAS2000(Win XP PC)

siok98 SIO Autolauncher

MK-12

366 total profiles

XBT Errors

XBT differs from the CTD due to :

A: inaccurate depth measurements

B: inaccurate temperature measurements

A B0

800

Depth

(m

)

0.25

0

MSE

Bias

Variance

0

800

Depth

(m

)

0.25

0

Fall Rate Error: Initial Conditions

Hallock and Teague 1992

Fall Rate Equation

a: Change of mass of the probe due to spooling wire.

b: Probe geometry and initial terminal velocity

c: Describes startup transients i.e. initial conditions

Currently used FRE (WMO 1770:52) for Deep Blue probes contains no constant term ( c ).

e.g. Hallock and Teague (1992)

Determining Depth Offset

Focus on the temperature gradient: derivative of temperature with respect to depth

Minimize temperature error effect

Hanawa et al (1995)

Depth Offset Prior to Correction

Depth Correction Algorithm

• Assemble the depth offsets (dZ)

• Recalculate XBT depths Znew = Zxbt+dZ

• Back calculate time (t)

• Fit new fall rate equation to (t)

z = at^2 + bt + c

Depth Offset: Post-Correction

Summary of Fall Rate Coefficients

A B C

Wmocode 52 -0.00225 6.691 0

this study -0.00191 6.487 0

this study -0.00299 6.639 -4.5117

other studies (1)

-0.00131 –

-0.00329

6.440 –

6.798

0 - 0

1: Taken from Hanawa et al 1995

1. aomlauto

2. devilhand

3. seasauto

4. seashand

5. sioauto

6. siok98