Experimental study on integrated and autonomous conductivity-temperature-depth (CTD) sensor applied for underwater glider

Abstract

This paper studies a novel CTD sensor (SZQ1-1) which is developed for underwater glider to meet the requirement of autonomous acquisition of high-quality profile hydrodynamic oceanography data. An independently developed electromagnetic induction type conductivity sensor, a quick response thermistor and a high-precision pressure sensor is used to integrate the CTD sensor. Several designs of compact mechanical structure and low-power control acquisition circuit are developed in the CTD sensor. The SZQ1-1 CTD is calibrated with measuring instrument in the laboratory and fourth-degree polynomial fitting equations are developed to fit the curves. After software-based calibration, the SZQ1-1 is compared with SBE 19plus by sea trial. The SZQ1-1 and SBE 19plus were carried by an underwater glider which dived in Northern South China Sea with a maximum depth of 500.36 m. Because the thermal lag error exists in the original data measured with the CTD sensor in the underwater glider, the measured conductivity and salinity data are revised again in the software. According to sea trial results, the real-time temperature, salinity and depth profile data obtained by SZQ1-1 sensor is consistent with the data measured with SBE 19plus.