Gravity anomalies

prefLabel
  • Gravity Anomalies
definition
  • The Earth's gravity field is determined by how the material that makes up the Earth is distributed throughout the Earth. Because gravity changes over the surface of the Earth, the weight of an object changes along with it. One can define standard gravity as the value of gravity for a perfectly smooth 'idealized' Earth, and the gravity 'anomaly' is a measure of how actual gravity deviates from this standard. A map of gravity anomalies (usually expressed in units of milliGals) tends to highlight short wavelength features better than a map of the geoid.
inScheme
broader
Abstract from DBPedia
    The gravity anomaly at a location on the Earth's surface is the difference between the observed value of gravity and the value predicted by a theoretical model. If the Earth were an ideal oblate spheroid of uniform density, then the gravity measured at every point on its surface would be given precisely by a simple algebraic expression. However, the Earth has a rugged surface and non-uniform composition, which distorts its gravitational field. The theoretical value of gravity can be corrected for altitude and the effects of nearby terrain, but it usually still differs slightly from the measured value. This gravity anomaly can reveal the presence of subsurface structures of unusual density. For example, a mass of dense ore below the surface will give a positive anomaly due to the increased gravitational attraction of the ore. Different theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. The Bouguer, free-air, and isostatic gravity anomalies are each based on different theoretical corrections to the value of gravity. A gravity survey is conducted by measuring the gravity anomaly at many locations in a region of interest, using a portable instrument called a gravimeter. Careful analysis of the gravity data allows geologists to make inferences about the subsurface geology.

    重力異常(じゅうりょくいじょう、gravity anomaly)とは、重力の実測値(あるいは観測値)と、理論モデルから予測される値との差のことである。測地学・地球物理学の分野と、天文学・宇宙物理学の分野の双方で、上記の意味で同じ用語が使われているが、対象が異なるため概念も異なる。

    (Source: http://dbpedia.org/resource/Gravity_anomaly)

data publication(s) found by GCMD Science Keywords)