A tide gauge is a crucial instrument used to measure the changing sea level over time. While the methods have evolved, the goal remains the same: to provide accurate data on tides and water levels.
Modern Acoustic Tide Gauges
Today, the most common type of tide gauge relies on advanced acoustics and electronics. These modern systems use a technique similar to sonar to determine the distance to the water's surface.
How the Acoustic Measurement Works:
- Sending the Signal: The tide gauge recorder sends an audio signal downwards.
- Sounding Tube: This signal travels down a narrow pipe, often called a "sounding tube", which is typically about a half-inch wide. The tube helps focus the sound wave and dampens interference from surface waves.
- Reflection: The audio signal hits the water's surface at the bottom of the tube and is reflected back upwards.
- Measuring Time: The recorder precisely measures the time it takes for the reflected signal to return.
- Calculating Distance: Since the speed of sound in air is known (and adjusted for factors like temperature and humidity), the gauge can calculate the distance from the sensor to the water's surface based on the travel time.
- Determining Water Level: By subtracting this distance from the known height of the sensor (relative to a fixed point), the gauge determines the water level.
In essence, 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. This measurement is taken repeatedly over time to track the rise and fall of the tides.
Historical Methods
Historically, tide-measuring stations used more mechanical approaches. These often involved mechanical floats inside a stilling well (a structure that calms the water surface) connected to a recorder that would trace the water level onto a paper roll.
Modern acoustic gauges offer advantages like fewer moving parts, easier maintenance, and digital data recording, making them standard in monitoring networks today.
