A Study of Expendable Bathythermograph (XBT) Temperature and Depth Biases From XBTs Manufactured in the Early 2000s and Six XBT Data Acquisition Systems

Several systems are currently in place to obtain expendable bathythermograph (XBT) data that are comprised of different types of launchers, analog to digital (A to D) converters and software controllers. This manuscript presents the results from a one-day cruise designed to compare XBT data acquisition systems in six distinct configurations. The primary goal of the experiment was to verify that temperature data collected with each system was consistent with each other and with data collected using an independent, high accuracy Conductivity-Temperature-Depth (CTD) system. Particular attention was directed to a new analog to digital recorder introduced by the manufacturer of XBTs. There were no significant differences between the six configurations tested. In the process of testing the different system configurations, temperature and depth biases introduced by the probes were found. Temperature biases were estimated comparing XBT and CTD values during those portions of the casts with minimum temperature gradients. Average differences were considerably less than the manufacturer’s specification. Biases relative to the internationally accepted Fall Rate Equation used to compute depth were found and a new Fall Rate Equation for the early 2000 probes used was determined.