How are ocean currents measured with current meters?

Direct measurement of ocean currents using a current meter is known as the Eulerian method, which involves measuring the velocity of water flow past a fixed point, such as an anchored line, a moored ship, or a structure.12

To perform these measurements, a system is typically deployed using a surface or near-surface float connected to a line of wire and nylon that holds the meters in place. A release mechanism, triggered acoustically, allows researchers to drop an anchor and retrieve the system after data collection, which can last for more than a year.1

A standard current meter typically employs a rotor paired with a small direction vane that aligns with the flow. Modern instruments, such as the Vector Averaging Current Meter (VACM), utilize solid-state microelectronics to sample speed and direction multiple times per rotor revolution. These devices compute the north and east components of velocity and store the data, allowing for accurate measurements even in wave fields. Additionally, specialized meters can be designed to move along a fixed line to provide vertical profiles of velocity.1