Current Meters

Current Meters are devices that measure water velocity and direction. Measuring currents is a fundamental practice of physical oceanographers. By determining how ocean waters move, scientists can determine how organisms, nutrients and other biological and chemical constituents are transported throughout the ocean. There are several common types of current meters:

• Mechanical current meters are like underwater pin wheels. The rate at which the wheel spins is used to calculate the current flow. A drawback to mechanical meters is that they do not work well in weak currents.

• Electromechanical current meters are based on the principle that a voltage is produced when a conductor (the water) moves through a magnetic field. The magnetic field is produced by a coil and the voltage is picked up by electrodes on the surface of the instrument. By having two orthogonal pairs of electrodes, two axis flow velocities are obtained from a single probe. The sensor has no moving parts and the system is capable of measuring fast changing flows over a wide dynamic range.

• Acoustic current meters , sometimes called sing arounds, measure how long it takes for sound pulses to travel around a prescribed area. By comparing the phase shift of the signals, very precise measurements can be taken.

• Acoustic Doppler Current Meters measure the Doppler shift of sound bouncing off reflectors suspended in the water. They can be used to take a point measurement at a specific distance from the instrument, or to take a series of measurements known as a profile. Doppler current meters can be mounted in the hulls of ships, installed on buoys or mid-water mooring lines, or mounted on the seafloor looking up towards the surface.

• High-Frequency Radar is used to measure surface currents. HF Radar can map areas of tens to hundreds of square kilometers from shore-based antennae.

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