Australian XBT Quality Control Cookbook Version 2.1.

Abstract

Expendable Bathythermographs (XBTs) have been used for many years by oceanographers to measure the temperature of the upper ocean. These instruments are simple devices which are designed to be deployed from moving vessels, enabling the use of ships of opportunity to collect data in repeated transects. The XBT has accordingly played an important role in several large international research programs, and the global data archives reflect this. Quality Control (QC) procedures are described for data recorded by XBTs. Examples are shown and described for commonly observed oceanographic features and instrument malfunctions. A QC system is described, which aids in the process of future validation and documentation of real features, and in the elimination of erroneous temperature profiles. There are some modes of malfunction of the XBT which appear very similar to real oceanographic features. This manual enables the user to better distinguish between the two. A knowledge of the different types of real and erroneous features, when combined with a local knowledge of water mass structure, statistics of data anomalies, the depth and gradient of the thermocline, and cross validation with climatological data in a statistical sense, ensures a data set of the best possible quality. This document is an update to the original ‘Quality Control Cookbook for XBT Data’ Version 1.1 (Bailey et al, 1994). Over time, the QC routines used by the Australian team have developed and many codes have become redundant due to improvements in the recording systems and our understanding of failure modes. The older, redundant codes are now summarised in the Section 4.8 and the Appendices A to C. We urge the reader to refer to Bailey et al (1994) for more detail on these historical codes.