Here's how it's typically done:

* Wave Buoys: These are floating devices anchored to the seabed. They contain sensors that measure the vertical movement of the water surface. The difference between the highest and lowest points recorded over a specific time interval gives the wave height.

* Radar Systems: Some radar systems use Doppler technology to measure the movement of the water surface and calculate wave height.

* Satellite Imagery: Satellites equipped with altimeters can measure the height of the sea surface and identify wave patterns. This data can be used to estimate average wave height over large areas.

* Visual Observation: While not as precise as other methods, experienced observers can estimate wave height by visually comparing the wave to a known reference point, like a boat or a lighthouse.

It's important to note that:

* Wave height can vary significantly over time and location.

* The method used to measure wave height will influence the accuracy of the measurement.

* Wave height can be expressed in various units, such as meters, feet, or even the Beaufort scale.

Let me know if you'd like to explore any of these methods in more detail!