Inter-manufacturer difference and temperature dependency of the fall-fate of T-5 expendable bathythermograph

Shoichi Kizu, Shin Ichi Ito, Tomowo Watanabe

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21 Citations (Scopus)


The fall-rate of the T-5 expendable bathythermograph (XBT) produced by Tsurumi Seiki (TSK) Co., Ltd and that by Sippican Inc., are intercompared by a series of contemporaneous and colocated measurements with conductivity-temperature-depth (CTD) profilers. It is confirmed that the fall-rates of the two manufacturers' T-5 differ by about 5 percent, despite the fact that they had been believed to be identical for many years. The cause of the difference is discussed on the basis of a detailed cross-examination of the two T-5 models. It is found for the first time that the two models are different in several respects. The manufacturer's fall-rate equation is only applicable to the Sippican T-5, for which Boyd and Linzell's (1993) equation seems to be slightly more accurate. Kizu et al.'s (2005) equation gives a clearly less biased depth than the manufacturers' equation for the TSK T-5. It is also found that the fall-rates of both T-5 models are dependent on water temperature, perhaps because of viscosity. The temperature-dependency of the fall-rate of the TSK T-5 is larger than that of the Sippican T-5.

Original languageEnglish
Pages (from-to)905-912
Number of pages8
JournalJournal of Oceanography
Issue number5
Publication statusPublished - 2005 Oct


  • Expendable bathythermograph
  • Fall-rate equation
  • T-5
  • Temperature measurement
  • Time-depth conversion equation
  • VOS monitoring
  • Water viscosity
  • XBT

ASJC Scopus subject areas

  • Oceanography


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