Temperature error in digital bathythermograph data

摘要

Simultaneous Digital Bathythermograph (DBT) and Nansen Cast data collected during two cruises of R. V. Gaveshani (GV-117 and GV-118) and archived in Indian Oceanographic Data Centre (IODC) are used to determine existing temperature errors in DBT. The resulting mean error for DBT data from the GV-117 cruise varies from -0.5 to - 1 ℃, while it varied between -0.3 and -0.6 ℃ for data from cruise GV-118. For both the data sets, the error shows consistently negative bias from surface to 800 m depth, however there is no apparent or measurable systematic dependence of the error on depth. Considering the given temperature accuracy of 0.05 ℃, the observed DBT error, varying from -0.3 to -1 ℃, is significant and such offsets should be removed from DBT archives. It is found that a corrective measure of +0.5 ℃, equivalent to the mean surface offset obtained from two cruises, can considerably reduce the temperature error at all DBT depths.