[theDentist]

When first detected the waves are about 18 - 24 inches? How in the world can they tell the difference between that wave and normal waves of the same basic height?

[Ready4Freddy]

When the wave is several hundred miles long it's visible to a satellite.

[jimfree]

There are 2.54 cm in an inch. They two waves were only 16" and 8" over deep water. Even more amazing they could be detected from a satellite.

[Strategerist]

When first detected the waves are about 18 - 24 inches? How in the world can they tell the difference between that wave and normal waves of the same basic height?

Because they're incredibly wide. It still takes a lot of processing power and analysis to separate out the noise. The tsunami waves are 18-24 inches high and miles wide.

When water gets warm it also bulges up; when there's a powerful El Nino it causes the sea surface to rise in the Eastern Pacific; these satellites were designed to monitor things like that; when you see an El Nino shot of the Pacific on TV it's usually from these satellites.