What are Ocean Waves?
Ocean waves are disturbances in the surface of the ocean. Ocean waves come in many shapes and sizes, ranging in length from a fraction of a centimeter for the smallest ripples to half the circumference of Earth for the tides. They are formed by wind, gravity, earthquakes, and submarine landslides disturbing the water surface. Once formed, and regardless of origin, ocean waves can travel great distances before reaching the coast. The ocean waves arriving at the shore today may have had their beginnings many hours or even days earlier a hemisphere away.
How are Ocean Waves Measured?
Ocean altimeter satellite missions, such as TOPEX/Poseidon and the Jason-series, measure significant wave height, which is the average wave height (from trough to crest) of the highest third of waves in a given sample period. The spacecrafts' radar altimeters measure the precise distance between the satellite and sea surface. The round-trip travel time of microwave pulses bounced from the spacecraft to the sea surface and back to the spacecraft provides data indicating sea surface height and the topography of the ocean surface. The precise altitude of the satellite is determined by a sophisticated estimation procedure based on instrument systems onboard the satellite and a network of ground receivers across the globe. The details of the shape of the returned radar pulses also give information on wind speed and the wave height.