What do tide gauges measure, and why is it significant in geodesy?

Tide gauges play a critical role in measuring the rise and fall of sea levels, which is essential for understanding geoid variations. By monitoring the fluctuations in sea level over time, tidal gauges provide valuable data that can be used to study the dynamic nature of Earth's surface, including the influence of oceanographic processes, climate change, and gravitational forces on the geoid.

In the field of geodesy, the geoid is a reference surface that represents mean sea level across the globe, taking into account the irregularities caused by the Earth's gravitational field. Accurate measurements from tide gauges help geodesists determine how sea levels change relative to this geoid surface, thereby enhancing our understanding of geophysical processes that affect both ocean levels and land movements. Data from tide gauges are crucial for applications like predicting coastal flooding, assessing climate change impacts, and managing resources in coastal regions. This significance lies in the valuable insights gained from understanding how sea levels interact with the Earth's geoid over time.