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Revisiting the XBT Fall Rate Equation (Sippican Deep Blue):Implications and Recommendations

Revisiting the XBT Fall Rate Equation (Sippican Deep Blue):Implications and Recommendations

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## Revisiting the XBT Fall Rate Equation (Sippican Deep Blue):Implications and Recommendations

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**Revisiting the XBT Fall Rate Equation (Sippican Deep**Blue):Implications and Recommendations JCOMM/SOT-4 Derrick Snowden Gustavo Goni Molly Baringer**Outline**• Introduction to the data • XBT Error Partioning • Estimating a New Fall Rate Equation • Implications for Climate Studies • Conclusions and Recommendations**System 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 SIO Autolauncher MK-21 SEAS2000 (Win XP PC) siok98 SIO Autolauncher MK-12 Instruments List 366 total profiles**Outline**• Introduction to the data • XBT Error Partioning • Estimating a New Fall Rate Equation • Implications for Climate Studies • Conclusions and Recommendations**Partitioning XBT Error**XBT differs from the CTD due to : A: inaccurate depth measurements B: inaccurate temperature measurements A B**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 ).**Fall Rate Error: Initial Conditions**Hallock and Teague 1992**Outline**• Introduction to the data • XBT Error Partioning • Estimating a New Fall Rate Equation • Implications for Climate Studies • Conclusions and Recommendations**Determining Depth Offset**Focus on the temperature gradient: derivative of temperature with respect to depth Minimize temperature error effect**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**Summary of Fall Rate Coefficients**1: Taken from Hanawa et al 1995**Outline**• Introduction to the data • XBT Error Partioning • Estimating a New Fall Rate Equation • Implications for Climate Studies (Wijffels and Thresher 2007) • Conclusions and Recommendations**Recommendations**• Future Work: Tropical Atlantic Cruise (May 2007) will conduct additional side by side XBT-CTD comparisons • Reinvorgorate research toward understanding fall rate issues • Metadata to include coefficients and the form of the equations (it isn’t sufficient to list A,B need to know z=at^2 + bt + c + … (including exchange files and metadata servers) • Quality flags should be listed level by level not just for the entire profile • Communication with the manufacturers to better understand the timing and nature of changes in XBT manufacturing procedures.