How to Read a Sea Surface Height Map

Altimeters on the satellites measure the distance from the satellite to the surface of the earth. The earth's 'level' surface based on the force of gravity is referred to at the geoid. On the waters, the geoid is the level surface that water would have if it were not acted on by outside forces ( wind, tides, etc.).

In reality, sea height is not the same all over the world. The satellites measure sea surface height relative to the geoid surface with calibration and adjustment based on local ground data (mean sea level measurements). The anomaly sea surface height satellite maps show the difference measured sea height from the calculated mean sea level. These images are color-coded and the scale is often in centimeters.