Field experiments on a towed vehicle 'flying fish' for physical and chemical measurement in the upper mixed layer of the ocean

A pitch, roll and depth controllable towed vehicle called 'Flying Fish' houses an acoustic Doppler current profiler (ADCP), CO₂ analyzer and sensors for measuring temperature, salinity, dissolved oxygen, pH, turbidity and chlorophyll. Flying Fish enables us to obtain the space continuous data of physical and chemical properties efficiently in the upper mixed layer of the ocean from the surface to a depth of 200m. Length of the vehicle is 3.84m, breadth 2.26m, height 1.4m, weight in air 1400kg and weight in the water is about 0kg. From 1994 to 1995 ocean observations were carried out in the Japan Sea with Flying Fish on a line from the west coast of Japan's Hokkaido island and the Russian coast near Vladivostok. Interesting results on velocity profiles, water temperature, conductivity and dissolved oxygen are discussed relevant to Tushima warm current and the cold water mass from the north. Engineering tests confirmed the performance of Flying Fish and showed the very high accuracy of the motion control system, depth control within an error of ±0.1m and, roll and pitch of under ±1 degree when being towed at a steady speed. Even during a depth change the maximum pitch and roll angle were less than 3 degrees. Performance of the vehicle in these experiments was compared with that estimated from numerical simulations based on the six degree freedom motion equations for an underwater vehicle and lumped mass method for the towing cable.