Abstract
Absolute gravity meters are by definition calibrated instruments that measure gravity in natural units m s − 2 traceable to metrological standards. The first absolute gravity meters were pendulums, but these were eventually replaced by measurements of freely falling test masses in a vacuum. The most accurate instruments currently track a falling mirror with a laser interferometer. In the future, these instruments may become smaller by replacing the falling mirrors with atoms. Relative gravity meters are typically characterized by a mass on some type of spring support. Relative gravity meters must be calibrated to determine the scale factor that converts spring stretch into equivalent force and finally into gravity. Both types of gravity meters are useful for measuring gravity at a point near the surface of the Earth or at many points over a survey region. These measurements are useful for commercial resource exploration and management. They can also be used to determine the shape of the Earth's gravity field, which in turn defines the shape of the Earth. Gravity measurements repeated over time can be useful to look for changes in subsurface density or even to help understand problems of global sea-level rise or the melting of the ice sheets.
Published Version
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