Estimating the Vertical Component of Water Velocity from Measurements Collected with a Free-fall Vehicle

Abstract

Abstract Estimated of the vertical component of water velocity are made with measurements of the pressure-change rate and rotation rate recorded by the free-fall vehicle “Cartesian diver” (CD). Using buoyancy control, this device moves alternately up and down, essentially at its terminal velocity through the surrounding water. Four angled wings fix the lift and rotational characteristics of the instrument. The rate of rotation is directly proportional to the terminal velocity of the instrument and is not sensitive to vertical water accelerations except at scale lengths somewhat less than the instrument height. When the pressure distribution is hydrostatic, the pressure-change rate is proportional to the sum of the instrument's terminal velocity and the vertical water velocity. Because the terminal velocity is a function of the instrument buoyancy, which varies slowly with depth, the fluctuations in vertical water velocity are well resolved by the fluctuations of the pressure-change-rate sensor. The orbita...