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XBT Bias Depth and Temperature Corrections

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Gouretski and Koltermann (2007) shows statistics from Expendable Bathythermograph (XBT) vs. Conductivity-Temperature-Depth (CTD)/reversing thermometer instrument comparisons which reveal a warm bias in XBT temperatures. This bias varies over time and over depth. The bias may be due to both errors in the calculation of depth and in measurement of the temperature. An important deviation from the majority of existing correction schemes is that depth correction varies with depth.

A NOAA sponsored XBT Fall Rate Workshop was held in Miami, FL, March 10-12, 2008 to discuss this problem. Results of that meeting came to no conclusion as to the best way to correct the bias.

A second XBT Fall Rate Workshop was held August 25-27, 2010 in Hamburg, Germany. Final report (pdf, 0.2 MB).

The First XBT Science Workshop (XSW-1) was held in Melbourne, Australia, July 7-8, 2011. Information on the meeting and presentations from the meeting*.

A number of papers with estimates of corrections have been published or submitted to scientific journals. The corrections proposed in some of these works are provided here to facilitate intercomparison by the scientific community. The corrections proposed by Gouretski and Koltermann (2007) are not included here, as they have been superceded by the corrections proposed by Gouretski and Reseghetti (2010).

Gouretski, V. V., and K. P. Koltermann, 2007, How much is the ocean really warming? Geophysical Research Letters, L01610, doi:10.1029/2006GL027834

Wijffels, Susan E., Josh Willis, Catia M. Domingues, Paul Barker, Neil J. White, Ann Gronell, Ken Ridgway, John A. Church, 2008: Changing Expendable Bathythermograph Fall Rates and Their Impact on Estimates of Thermosteric Sea Level Rise. J. Climate, 21, 56575672. doi: http://dx.doi.org/10.1175/2008JCLI2290.1 Wijffels et al. depth corrections: Table 1 (in situ comparison), Table 2 (in situ-altimeter comparison).

Ishii, M. and M. Kimoto, 2009: Reevaluation of Historical Ocean Heat Content Variations With An XBT depth bias Correction. J. Oceanogr. 65, 287299, doi:10.1007/s10872-009-0027-7. Ishii and Kimoto depth corrections. New corrections in conjunction with version 6.12* analysis of ocean temperature and salinity.

Levitus, S, J. Antonov, T. Boyer, Global ocean heat content 1955-2007 in light of recently revealed instrumentation problems (Geophys. Res. Lett. , 36, L07608, doi:10.1029/2008GL037155). Levitus et al. temperature corrections; updated temperature corrections: September, 2010; April, 2011.

Gouretski, V. and F. Reseghetti, 2010, On depth and temperature biases in bathythermograph data: Development of a new correction scheme based on analysis of a global ocean database. Deep-Sea Research I, Vol. 57(6), pp. 812-834, doi:10.1016/j.dsr.2010.03.011, Gouretski, Reseghetti depth and temperature corrections, updated corrections.

Good, S.A, 2011,Depth biases in XBT data diagnosed using Bathymetry data ,Journal of Atmospheric and Oceanic Technology, 28, 287-300, doi: 10.1175/2010JTECHO773.1 Good depth corrections.

Hamon, M., G. Reverdin, P-Y Le Traon, 2012, Empirical correction of XBT data. Journal of Atmospheric and Oceanic Technology, doi:10.1175/JTECH-D-11-00129.1, in press. Hamon et al. depth and temperature corrections.

Gouretski, V., 2012, Using GEBCO digital bathymetry to infer depth biases in the XBT data, Deep Sea Research-I, 62,40-52. Gouretski depth and temperature corrections.

Cowley, R., S. Wijffels, L. Cheng, T. Boyer, S. Kizu: Biases in Expendable BathyThermograph data: a new view based on historical side-by-side comparisons, Journal of Atmospheric and Oceanic Technology, 30, 11951225, doi:10.1175/JTECH-D-12-00127.1. XBT pairs database used in study. Thermal gradient correction (TG), Cheng correction (CH).



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