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The geoid undulation (also known as geoid height or geoid anomaly), N, is the height of the geoid relative to a given ellipsoid of reference. N = h − H {\displaystyle N=h-H} The undulation is not standardized, as different countries use different mean sea levels as reference, but most commonly refers to the EGM96 geoid.
The Indian Ocean Geoid Low (IOGL) is a gravity anomaly in the Indian Ocean. A circular region in the Earth's geoid, situated just south of the Indian peninsula, it is the Earth's largest gravity anomaly. [1] [2] It forms a depression in the sea level covering an area of about 3 million km 2 (1.2 million sq mi), almost the size of India itself.
GeographicLib provides a utility GeoidEval (with source code) to evaluate the geoid height for the EGM84, EGM96, and EGM2008 Earth gravity models. Here is an online version of GeoidEval . The Tracker Component Library from the United States Naval Research Laboratory is a free Matlab library with a number of gravitational synthesis routines.
Earth Gravity Field Anomalies, geoid format, NASA Earth Observatory Earth Geoid Field Anomaly globe, NASA Earth Observatory Mars free-air gravity map Venus gravity anomaly map. A gravity map is a map that depicts gravity measurements across an area of space, which are typically obtained via gravimetry.
The separation between the geoid and the reference ellipsoid is called the undulation of the geoid, symbol . The geoid, or mathematical mean sea surface, is defined not only on the seas, but also under land; it is the equilibrium water surface that would result, would sea water be allowed to move freely (e.g., through tunnels) under the land.
The geoid is a gently undulating surface due to the irregular mass distribution inside the Earth; it may be approximated however by an ellipsoid of revolution called the reference ellipsoid. The currently most widely used reference ellipsoid, that of the Geodetic Reference System 1980 , approximates the geoid to within a little over ±100 m.
The U.S. space agency's robotic OSIRIS-REx spacecraft in 2020 collected the samples from the near-Earth asteroid, a rocky remnant of a larger celestial body that had formed near the dawn of the ...
The deflections reflect the undulation of the geoid and gravity anomalies, for they depend on the gravity field and its inhomogeneities. Vertical deflections are usually determined astronomically. The true zenith is observed astronomically with respect to the stars , and the ellipsoidal zenith (theoretical vertical) by geodetic network ...