Sea level rise is measured primarily using tide gauges and satellite altimeters. These technologies work together to provide a comprehensive picture of how sea levels are changing globally and regionally over different time scales.
Key Measurement Methods
Understanding how sea level is monitored requires looking at both ground-based and space-based techniques. As stated in the reference, "Together, tide gauges and altimeters tell us how sea level is changing both regionally and globally, and over periods from minutes to decades."
Here are the primary methods used:
1. Tide Gauges
- What they are: These are instruments typically located along coastlines, on piers, or in harbors. They measure the height of the sea surface relative to a fixed point on land.
- How they work: Modern tide gauges often use acoustic or radar sensors to measure the distance to the water surface. Older methods included mechanical floats. Continuous measurements capture the rise and fall of tides, storm surges, and longer-term sea level changes.
- What they tell us: Tide gauges provide valuable data on local and regional sea level changes. They offer long-term historical records, in some cases spanning over a century, which are crucial for understanding past trends and validating satellite data. They measure sea level changes relative to the land beneath them, which can sometimes be affected by land sinking or rising.
2. Satellite Altimetry
- What it is: Satellites equipped with radar altimeters orbit the Earth and measure the distance from the satellite to the sea surface.
- How it works: The satellite emits a radar pulse towards the ocean and measures the time it takes for the pulse to return after reflecting off the surface. This time is used to calculate the distance. By knowing the satellite's precise orbit, scientists can determine the absolute height of the sea surface in the Earth-centered frame of reference.
- What it tells us: Satellite altimetry provides global coverage of sea level height. It is particularly effective at monitoring large-scale changes and has revolutionized our understanding of global average sea level rise since the early 1990s. These measurements are not affected by land motion like tide gauges are, providing a measure of the absolute height of the ocean surface.
Combining the Data
Scientists combine data from both tide gauges and satellite altimeters to get the most accurate and complete picture.
- Satellite altimetry provides essential global coverage and measures the absolute sea surface height.
- Tide gauges provide critical long-term records at specific coastal locations and measure sea level relative to the land.
By integrating these datasets, researchers can validate measurements, fill in spatial gaps, and distinguish between regional variations and global trends. The reference confirms that these combined measurements show that "sea level is rising both globally and regionally."
These methods, used in conjunction, allow scientists to track sea level changes from short-term fluctuations (like tides) to long-term trends spanning decades, providing the data necessary to understand and predict the impacts of rising seas.
