Velocity Calibration of Doppler Current Profiler Transducers

Abstract

Doppler current profilers are used in oceanography to measure oceanic circulation but also in hydrology to calculate the flow of rivers. They allow the retrieval of water mass profiles in terms of velocity and direction. Direction is obtained via an electronic compass and tilt sensors, while velocity is obtained by measuring Doppler pulse shifts back-scattered by particles located in water cells allocated along the instrument’s measurement range. Current meters are usually tested in towing basins or hydrodynamic channels, but these facilities present limits in terms of the measurement range, particles concentration and time costs. This paper presents a novel method developed to test the trueness of these velocity measurements in the laboratory, along with the uncertainty of this test and the results obtained with current meters and stand-alone profilers. The method is based on the measurement of the frequency of pulses emitted by each transducer of the instrument independently, and on the simulation of received echoes by a variable frequency sinusoidal signal.