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# Tides and Water Levels

## How are Tides Measured? - The New System

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Advances in technology have helped solve many of the problems  associated with the old tidal recording systems. Microprocessor-based  technologies allow for customized data collection and have improved  measurement accuracy. While older tidal measuring stations used  mechanical floats and recorders, a new generation of monitoring  stations uses advanced acoustics and electronics. Today's recorders  send an audio signal down a half-inch-wide sounding tube and measure  the time it takes for the reflected signal to travel back from the  water's surface. The sounding tube is mounted inside a 6-inch diameter  protective well, which is similar to the old stilling well.

In addition to measuring tidal heights more accurately, the new system  also records 11 different oceanographic and meteorological parameters.  These include wind speed and direction, water current speed and  direction, air and water temperature, and barometric pressure.

Like the old recorders, the new measuring stations collect data every  six minutes. However, whereas the old recording stations used  mechanical timers to tell them when to take a reading, timing is  controlled on the new stations by a Geostationary Operational  Environmental Satellite (GOES). The stations also use these satellites  to transmit their data hourly to NOAA headquarters. In the event of a  storm, the stations can be programmed to transmit their data every six  minutes. Field teams can quickly check and maintain the systems using  laptop computers. In addition, all of the raw and processed data are  available over the Internet.

*While similar in design to older tide houses, these newer enclosures are designed to protect sensitive electronics, transmitting equipment, and backup power and data storage devices. The older stilling well has been replaced with an acoustic sounding tube and the tidal staff with a pressure sensor. The new field equipment is designed to operate with the highest level of accuracy with a minimum of maintenance, transmitting data directly back to NOAA headquarters for analysis and distribution.*

*The earliest tidal monitoring stations were small and self-contained, but they required frequent visits for maintenance and adjustment. Today, stations are still self contained but are very accurate, require little maintenance, and are part of a larger nationwide network. Today, data are transmitted to NOAA headquarters via satellite shortly after they are collected. After rapid computer analysis, the data are immediately posted to one of several Web sites where they can be universally accessed. With these systems in place, scientists can run diagnostic checks on the equipment without needing to travel into the field. This saves both time and money.*

### Tides and Water Levels

              - Welcome
              - What are Tides?
              - What Causes Tides?
              - Gravity, Inertia, and Bulges
              - Changing Angles and Tides
              - The Frequency of Tides
              - Tidal Variations
              - Types and Causes of Tidal Cycles
              - What Else Affects Tides?
              - Monitoring the Tides
              - Old System
              - New System
              - References
              - Roadmap to Resources 
              - Subject Review

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