EXPLORING EARTHS GRAVITY SPECTRUM

What can placing a number of gravity meters on Earth's solid surface t o record the vertical component of gravity tell us about the internal structure of Earth and Earth's motion in space? As one might expect, t his is a far from trivial exercise, one that is not made easier by the extraordinary precision with which these measurements can now be made . The activity involves combining two different types of measurements, static and dynamic. In the familiar mapping mode, measurements of a g ravity field are acquired at as many different locations as possible, both on the solid surface and globally by satellite. Traditional surve y instruments can measure 0.1 mugal (about one part in 10(7) of surfac e gravity). Field instruments with an accuracy of one mugal (one part in 10(9)) are becoming available. This sensitivity is similar to the p erformance of tidal spring gravimeters and the latest generation of ab solute gravity meters.