Reexamination of the Depth Error in XBT Data

Abstract

By using the accumulated datasets of CTD-XBT comparison experiments since 1985, the depth errors for both T-7 and T-6 probes were reexamined. All the XBT probes used here were manufactured by the Tsurumi-Seiki Company, Limited, Japan. The same method as that of Hanawa and Yoritaka was adopted for the detection of depth error. The empirical depth-time equation for T-7 probes newly obtained from an average of all datasets was very similar to that by Hanawa and Yoritaka: depth difference between the corrected and uncorrected data was about 25 m at 800 m. The new equation for T-6 probes based on a single dataset also showed that the depth diference between the corrected and uncorrected data was greater than 10 m at 500 m. It was confirmed that the free-fall velocity estimated by the XBT manufacturer considerably underestimates the actual velocity for both T-7 and T-6 probes.