A long-term temperature and depth logger for ocean mooring system

Temperature, depth and conductivity (CTD) are the most essential physical properties of sea water. CTD instrument is one of the most efficient approaches for collecting the accurate ocean information. However, traditional CTD instruments are not best suited for applications that require high resolution data by a large number of sensors because of their large size and high cost. This paper describes the design of a compact, high-accuracy, and low-cost temperature and depth (TD) logger for ocean mooring system. The noise floor of the TD logger was evaluated in lab for determining the logger measurement resolution. A specific calibration method was implemented for pressure transducer calibration to eliminate the thermal affect. The initial temperature accuracy of TD logger is ±0.002°C and the pressure accuracy is ±0.05% of full scale. The effective resolution is 0.0001°C and 0.001% full scale for temperature and pressure measurement, respectively. A 150-day off-shore experiment yielded 0.41 million temperature and pressure measurements that confirmed the stability of TD logger measurement. The correlation analysis revealed a maximum deviation of 0.2°C and 0.8m compared to independent measurements.