Oral

IAPSO

P07 - Thermophysical and chemical properties of Seawater

Examination and Calibration of CTD under Simulated Full-Ocean Depth Pressure and Temperature Environment: Using SBE CTDs as an Example

Accurate measurement of deep-ocean salinity, temperature, and pressure is crucial for studying global warming, oceanic carbon sinks, physical oceanography, weather forecasting, and geobiochemistry. To ensure high accuracy, oceanic sensors need to be regularly calibrated, especially before and after each oceanic deployment. However, all previous examinations and calibrations of conductivity, temperature, and pressure (CTD) sensors have been conducted under one-atmospheric pressure and in the room-teperature, following the standards of ISO 22804:2023 and JJG 763-2019 (China), which neglect the impact of the high-pressure, low-temperature environment of the deep ocean. This oversight can result in significant errors that should not be overlooked. In this study, we present a method for examining and calibrating CTD instruments under combined pressure and temperature conditions that simulate the oceanic profile. By placing the instruments in a precisely controlled pressure and temperature chamber, and using the well-known SBE3 (10500 meters temperature sensor), SBE4 (10500 meters conductivity sensor), and SBE37 (7000 meters CTD) as examples, we demonstrate that the drift in these CTDs could be as large as 10 mK, 0.05 PSU, and 8 dbar, respectively, as pressure and temperature vary along the profiling curve of the full-ocean depth and temperature range. Additionally, we report that these errors can be corrected to below the manufacturer��s original specifications using our combined pressure-temperature calibration data and algorithm.