Current meter

By precisely measuring the time to travel from the emitter to the receiver, in both directions, the average water speed can be determined between the two points.

This novel approach is for instance employed in the Florida Strait where electromagnetic induction in submerged telephone cable is used to estimate the through-flow through the gateway[2] and the complete setup can be seen as one huge current meter.

The physics behind: Charged particles (the ions in seawater) are moving with the ocean currents in the magnetic field of the Earth which is perpendicular to the movement.

Using Faraday's law of induction (the third of Maxwell's equations), it is possible to evaluate the variability of the averaged horizontal flow by measuring the induced electric currents.

A floating tilt current meter typically consists of a sub-surface buoyant housing that is anchored to the sea floor with a flexible line or tether.

[4] The housing contains a data logger that records the orientation (angle from vertical and compass bearing) of the Tilt Current Meter.

Under the influence of water currents (and wind if the top buoy is above the sea surface) the shape of the mooring line can be determined and by this the actual depth of the instruments.