Evaluation of the Sparton Tight-Tolerance AXBT

Forty-six near-simultaneous pairs of conductivity-temperature-depth (CTD) and Sparton “tight tolerance” air expendable bathythermograph (AXBT) temperature profiles were obtained in summer 1991 from a location in the Sargasso Sea. The data were analyzed to assess the temperature and depth accuracies of the Sparton AXBTs. The tight-tolerance criterion was not achieved using the manufacturer's equations but may have been achieved using customized equations computed from the CTD data. The temperature data from the customized equations had a one standard deviation error of 0.13°C. A customized elapsed fall time-to-depth conversion equation was found to be z = 1.620t−2.2384 × 10−4 t2 + 1.291 × 10−7 t3, with z the depth in meters and t the elapsed fall time after probe release in seconds. The standard deviation of the depth error was about 5 m; a rule of thumb for estimating maximum bounds on the depth error below 100 m could be expressed as +12% of depth or +10 m, whichever is greater. This equation gave greater depth accuracy than either the manufacturer's supplied equation or the navy standard equation.