The Roberts radio current meter was the first moored system to automatically record and transmit ocean current data. It was used by one of NOAA’s predecessor agencies, the U.S. Coast and Geodetic Survey.
The Roberts radio current meter was the first moored system to automatically record and transmit ocean current data. It was used by one of NOAA’s predecessor agencies, the U.S. Coast and Geodetic Survey.
Early current systems required on-site observers to operate and retrieve data. In the simplest method, observers would go out on an anchored ship and deploy a , tracking the amount of time and direction it took to cross a certain distance. Using rudimentary math, the observer could determine the current’s velocity, typically measured in a unit called knots . Other mechanical meters at the time required the instruments to be hauled up, recorded, and reset manually after each measurement. These processes could be costly, time intensive, and even dangerous in severe weather. To address this issue, Captain Elliott B. Roberts of the U.S. Coast and Geodetic Survey invented the Roberts radio current meter system in 1938. This system included the radio current meter itself and a moored buoy, which carried a battery-operated radio transmitter and antenna. It was the first current system to automatically record and transmit current data, and may have been the first moored instrument to automatically measure any variable in the field of physical oceanography. Inventor Elliott B. Roberts kneels next to a streamlined buoy, preparing for deployment of the Roberts radio current meter.Here’s how it works: The meter is lowered into the water at the desired depth and is connected to a specialized buoy on the surface using an electrical cable. The buoy houses a battery-operated radio transmitter and an antenna, which allow it to transmit the data using radio. A radio-receiving station, often located either on a nearby ship or on the shore, picks up these signals and records the data onto a paper record called a chronograph tape.The current meter itself functioned mechanically. It was designed to naturally point in the direction that the water was flowing, similar to a weather vane. A small propeller called an “impeller” would spin as water flowed through it. The faster the current, the faster the impeller would spin. The impeller's rotation triggered an internal switch mechanism regulated by a magnetic compass. This switch generated electrical pulses that encoded both the current velocity and direction, which were then transmitted up the cable. The chassis and impeller detached from the main body, showing the main elements of the meter mechanism. Shown disassembled for adjustment and electrical tests and assembled .in 1942, the Roberts radio current meter was introduced for current surveys. Patented in 1954, the system's use was most extensively documented by the U.S. Coast and Geodetic Survey during 1950s surveys of Tampa Bay and the Aleutian Islands. Its final deployment was in 1970 to observe three stations in the East River within New York Harbor. Modern day current meters operate with many of the same principles as the Roberts radio current meter, but have advanced in sophistication and accuracy over time. Most commonly used today are . This technology has shifted from the radio current meter’s mechanical point measurement to an acoustic technology based on the Doppler effect, which can create full profiles of the current throughout the water column. The Roberts radio current meter took the U.S. Coast and Geodetic Survey from manual to automatic instrumentation data collection, advancing both physical oceanography and marine navigation technologies. This pioneering step laid the foundation for today's advanced current profilers, modernizing the way we measure and understand the ocean's currents. Have an idea for an artifact, photo, or document from NOAA’s history that you think we should feature in “Friday Finds!”? Send an email with a description and, if possible, a photo to
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