4/30/2023 0 Comments Anomaly 2 localHowever, he found that the clock ran too slowly in Cayenne, compared with the apparent motion of the stars. Richter was equipped with a highly precise pendulum clock which had been carefully calibrated at Paris before his departure. ![]() Gravity anomalies were first discovered in 1672, when the French astronomer, Jean Richter, established an observatory on the island of Cayenne. For Earth, the reference ellipsoid is the International Reference Ellipsoid, and the value of gravity predicted for points on the ellipsoid is the normal gravity, g n. Gravity on the surface of this reference ellipsoid is then given by a simple formula which only contains the latitude. Typically the model is based on simplifying assumptions, such as that, under its self-gravitation and rotational motion, the planet assumes the figure of an ellipsoid of revolution. The gravity anomaly is the difference between the observed acceleration of an object in free fall ( gravity) on a planet's surface, and the corresponding value predicted from a model of the planet's gravitational field. Careful analysis of the gravity data allows geologists to make inferences about the subsurface geology. The Bouguer, free-air, and isostatic gravity anomalies are each based on different theoretical corrections to the value of gravity.Ī gravity survey is conducted by measuring the gravity anomaly at many locations in a region of interest, using a portable instrument called a gravimeter. For example, a mass of dense ore below the surface will give a positive anomaly due to the increased gravitational attraction of the ore.ĭifferent theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. This gravity anomaly can reveal the presence of subsurface structures of unusual density. 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. However, the Earth has a rugged surface and nonuniform composition, which distorts its gravitational field. 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 formula. ![]() 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. For the formulas, see Gravity of Earth § Mathematical models.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |