Articles | Volume 7, issue 6
Ocean Sci., 7, 733–743, 2011
https://doi.org/10.5194/os-7-733-2011
Ocean Sci., 7, 733–743, 2011
https://doi.org/10.5194/os-7-733-2011

Research article 08 Nov 2011

Research article | 08 Nov 2011

A computational method for determining XBT depths

J. Stark1, J. Gorman1, M. Hennessey1, F. Reseghetti2, J. Willis3, J. Lyman4, J. Abraham1, and M. Borghini5 J. Stark et al.
  • 1University of St. Thomas, School of Engineering, St. Paul, MN 55105-1079, USA
  • 2ENEA, UTMAR-OSS, Forte S. Teresa, 19032 Pozzuolo di Lerici, Italy
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
  • 4Pacific Marine Environmental Laboratory/NOAA, Seattle, WA, 98115-6349, USA
  • 5CNR-ISMAR, Forte S. Teresa, 19032 Pozzuolo di Lerici, Italy

Abstract. A new technique for determining the depth of expendable bathythermographs (XBTs) is developed. This new method uses a forward-stepping calculation which incorporates all of the forces on the XBT devices during their descent. Of particular note are drag forces which are calculated using a new drag coefficient expression. That expression, obtained entirely from computational fluid dynamic modeling, accounts for local variations in the ocean environment. Consequently, the method allows for accurate determination of depths for any local temperature environment. The results, which are entirely based on numerical simulation, are compared with the experiments of LM Sippican T-5 XBT probes. It is found that the calculated depths differ by less than 3% from depth estimates using the standard fall-rate equation (FRE). Furthermore, the differences decrease with depth. The computational model allows an investigation of the fluid flow patterns along the outer surface of the probe as well as in the interior channel. The simulations take account of complex flow phenomena such as laminar-turbulent transition and flow separation.