Abstract
Intercomparison of 306 casts in the tropical Pacific of Sippican T-4 (∼450-m depth) and 139 casts in the Sargasso Sea of Sippican T-7 (∼750 m depth) expendable bathythermographs (XBT's) and calibrated Neil Brown conductivity-temperature-depth (CTD) profiles has been performed to detect errors in XBT temperature and depth. Also included are results from previous XBT-CTD intercomparisons.
Systematic temperature errors were determined in depth ranges where the vertical temperature gradient was small and the contribution from depth errors would be small. In all cases the XBT temperatures were systematically higher than CTD temperatures.
Isotherm depths from XBT's were systematically less than CTD depth below an intermediate depth. The depth error dependence is a characteristic of the instrument, and for the T-7 XBT it is repeatable in at least two regions of differing thermal structure. The standard deviation of the depth error is approximately 10 m for both T-4 and T-7 instruments.
The accuracy of XBT data can be significantly improved by periodic XBT-CTD intercomparison. An algorithm is given to correct the T-7 XBT systematic depth error.
