SATELLITE ALTIMETRY

THE OCEAN SURFACE IS AN "EQUIPOTENTIAL" OF THE EARTH'S GRAVITY FIELD. (LETS IGNORE WAVES, WINDS, TIDES AND CURRENTS FOR THE MOMENT.) THIS MEANS THAT IF ONE COULD PLACE BALLS EVERYWHERE ON THE SURFACE OF THE OCEAN, NONE OF THE BALLS WOULD ROLL DOWNHILL BECAUSE THEY ARE ON THE SAME "LEVEL".

THE ACTUAL OCEAN SURFACE DEVIATES FROM THIS IDEAL, WITH BUMPS AND DIPS CAUSED BY MINUTE VARIATIONS IN THE EARTH'S GRAVITATIONAL FIELD. FOR EXAMPLE THE EXTRA GRAVITATIONAL ATTRACTION DUE TO A MOUNTAIN ON THE OCEAN FLOOR ATTRACTS WATER, CAUSING A BUMP.

THESE BUMPS AND DIPS ARE MEASURED USING A RADAR ON A SATELLITE THAT MEASURES OCEAN SURFACE

TO THE NEAREST INCH.

THESE DATA ARE USED TO MAP THE SEA BOTTOM AND ARE VALUABLE BECAUSE MUCH OF THE WORLD'S OCEANS HAVE NOT BEEN MAPPED. THEY SHOW MANY GEOLOGICAL STRUCTURES NOT PREVIOUSLY RECOGNIZED.

(University of California)