Propeller Current Sensors

Abstract

The primary problem in measurement of upper ocean currents is separation of the weak low frequency ‘signal’ from the energetic high frequency ‘noise’ of surface waves and the mooring motion they produce. Overcoming this problem requires either perfectly responsive, although possibly nonlinear, sensors or completely linear sensors, possibly with limited frequency response. If neither requirement is met, a rectification error must result. A well known example of such rectification errors is the result of computing mean velocity from a speed sensor and a vane sensor which respond slowly; the mean velocity cannot be computed from the mean speed and mean direction because the relation between speed and direction and the desired velocity components is nonlinear. A slow response velocity component sensor, on the other hand, yields the mean velocity.