A new fall-rate equation for T-5 expendable bathythermograph (XBT) by TSK

Shoichi Kizu, Hiroyuki Yoritaka, Kimio Hanawa

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26 Citations (Scopus)


The accuracy of the manufacturer's fall-rate equation for the T-5 Model of expendable bathythermograph (XBT) has been investigated based on about 300 collocated pairs of XBT-CTD (Conductivity-Temperature-Depth profiler) measurements in various climatological regions. We found that the equation systematically overestimates depth by about 5% for the T-5 produced by Tsurumi Seiki, Co. Ltd. (TSK), but almost no bias is associated with the T-5 produced by Sippican, Inc., in USA. The cause of this difference is not clear, because the two manufacturers' T-5 probes are reported to have identical shape and weight in water. We propose a new fall-rate equation for the TSK T-5: z(t) = 6.54071 t - 0.0018691 t2, where z(t) is depth in meters at time, t, in seconds.

Original languageEnglish
Pages (from-to)115-121
Number of pages7
JournalJournal of Oceanography
Issue number1
Publication statusPublished - 2005 Feb


  • Expendable bathythermograph
  • Fall-rate equation
  • T-5
  • Temperature measurement
  • VOS monitoring
  • XBT


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