||A self-contained CTD with platinized 4-electrode glass conductivity cell, pressure-protected, aged thermistor temperature sensor, a semiconductor strain gauge pressure sensor and an integral data logger. The CTD offers the options of logging data continuously, at user selected depth increments, at user selected time increments, or upon request. Data can be viewed in real time and downloaded on recovery of the CTD. The instrument can be used for profiling to 5000 m or for in-situ long term deployments and has a sampling frequency of 11 Hz. It can support four additional sensors, the options being temperature-compensated pressure, dissolved oxygen, pH, redox, turbidity, radiometer and fluorometer.