Response of the free-fall profiler FPS

The free-fall profiler "FPS" measures profiles of horizontal current velocity, temperature and electrical conductivity down to a depth of 500 m. The vertical resolution is about 0.15 m. Motions lead errors in the current measurement. The response of the profiler to varying ocean velocities is studied here. The equations of motion are derived, and corrections for the velocity are obtained. After comments on basic principles and problems the model of Hayes et al. (1984) is applied to the FPS, and transfer functions are given. The response to shear flow is simulated for selected artificial current profiles. The model is compared to a simplified point-mass model.