Temperature measurement in the sea

Abstract

The importance of measuring sea temperature is explained and the various methods employed for this purpose are reviewed. Instruments used for spot measurement of water temperature at the sea surface and at discrete depths (bucket thermometer, reversing thermometers, T.S. Bridge), recording of temperature variation with depth or temperature-depth profile (bathy-thermographs), recording of temperature variation near the sea surface and at different (fixed) depths (thermographs, recording current meters with temperature sensors, moored data buoys and drifting buoys) are described in brief. Specialised equipment used for studying oceanic features like internal waves, thermal fronts and temperature microstructure (thermistor chain, isotherm follower, C/STD systems and Batfish) are also described. Upper ocean temperature measurements carried out recently in the Indian Ocean, using a thermistor chain from an Indian research ship for the first time, are described and the relevant data processing and analysis are presented. Sea surface temperature measurement by infrared and microwave remote sensing techniques (shipborne/airborne precision radiation thermometers, spaceborne very high resolution infrared radiometers, microwave radiometers), their advantages and limitations are also touched upon. Calibration of various instruments used for temperature measurement in the sea and the special setup/facilities needed for this purpose are also discussed