A fast and accurate thermistor string

A "fast thermistor string" has been built to accommodate the scientific nee d to accurately monitor internal wave activity in shelf seas and above slop ing bottoms in the ocean. The performance of the thermistors and their cust om-designed electronics allow temperature variations to be registered at an estimated relative accuracy better than 0.5 mK with a response time faster than 0.25 s. Quantization noise is less than about 40 muK and dominates in strumental noise. Currently, the string holds 32 sensors, which are sampled within 4 s. When sampling every 30 s, the batteries and the memory capacit y of the recorder allow deployments up to 3 months. In all respects, this p erformance is about an order of magnitude superior to thermistor strings cu rrently available commercially. Moored in combination with an acoustic Dopp ler current profiler the thermistor string provides data to estimate direct ly quasi-turbulent (high-frequency internal wave band) vertical temperature fluxes and flux gradients. Examples of field observations are given, which show enhanced levels of temperature variance extending above the canonical internal wave spectral levels near the buoyancy frequency, and detailed va riations of high-frequency internal wave variability.