Start-up transient of XBT measurement

The start-up transient of XBT measurements is statistically investigated for five types of recorder system: Z-60-16 II and III by Murayama Electric Co., Ltd., and MK-130 by Tsurumi Seiki Co., Ltd., which are commonly used in Japan, and Sippican MK-9 and MK-12, which are popular in the United States and other countries. The UNESCO recommendation to exclude XBT-measured temperatures in the top 3.7 m layer from the bathythermograph report is justified within a nominal precision of 0.2°C for Tsurumi Seiki T-7 probes. However, it is shown that the depth where the transient ceases differs for different types of recorder. If we require a more strict accuracy constraint of 0.02°C, the estimated depth of the transient is 2 m for MK-130, MK-9 and MK-12, 3 m for Z-60-16 III and 10 m for Z-60-16 II.