How NOAA Monitors the Tides, Every Six Minutes

Around the coasts of the United States and the Great Lakes, 210 permanent stations measure the level of the water continuously, and report it every six minutes. They are run by NOAA's Center for Operational Oceanographic Products and Services, and they rely on sound, electronics and satellites.

The Chesapeake City tide station in Chesapeake City, Maryland, an active water level gauge in NOAA's National Water Level Observation Network. Credit: NOAA.

Measuring with sound

Each station has a recorder that sends an audio signal down a half-inch-wide sounding tube and times how long the signal takes to bounce back from the water's surface. That time gives the height of the water.

More than the tide

Besides tidal heights, the stations record up to 11 other ocean and weather measurements, including:

• wind speed and direction
• current speed and direction
• air and water temperature
• barometric pressure

Timed and sent by satellite

Stations collect data every six minutes, with their timing controlled by a Geostationary Operational Environmental Satellite (GOES), and they use the same satellites to send their data to NOAA headquarters every six minutes. Field teams can check and maintain the systems quickly with laptop computers, and all the raw and processed data is available online.

Sources

Based on "How do we monitor tides?" from NOAA's National Ocean Service, a work of the United States government in the public domain.