Geodesy

Other Definitions

Numerous other definitions of geodesy are complementary to that distilled above. Examples are the science of measuring the size, shape, and gravity field of the earth; scientific discipline concerned with the size and shape of the earth, its gravitational field, and the location of fixed points; the science related to the determination of the size and shape of the earth (geoid) by direct measurements; science concerned with surveying and mapping the earth's surface to determine, for example, its exact size, shape, and gravitational field; a branch of applied mathematics concerned with the determination of the size and shape of the earth (geoid); applied mathematics dealing with the measurement, curvature, and shape of the earth, rather than treating it as a sphere; the scientific discipline that deals with the measurement and representation of the earth, its gravitational field, and geodynamic phenomena (polar motion, earth tides, and crustal motion) in three-dimensional time-varying space; and the scientific study of the earth's surface by surveying (especially by satellite) and mapping in order to determine its exact shape and size and to measure its gravitational field. Geodesy is primarily concerned with positioning and the gravity field and geometrical aspects of their temporal variations.

In 1889, Helmet defined geodesy as the science of measuring and portraying the earth's surface. Since then, the scope of geodesy has broadened to be the discipline that deals with the measurement and representation of the earth, including its gravity field, in a three-dimensional time-varying space. Since geodesy has now become quite a diverse discipline, it is often broken down into subclasses. Four key pillars of modern geodesy are as follows (not in any order of preference):

• 1.
  Geophysical geodesy: techniques used to study geodynamic processes, such as plate-tectonic motions, postglacial rebound (now called “glacial isostatic adjustment”), or variations of earth rotation and orientation in space.
• 2.
  Physical geodesy: the observation and use of gravity measurements (from ground, air, and space) to determine the figure of the earth, notably the geoid or quasigeoid, which involves the formulation and solution of boundary-value problems.
• 3.
  Geometrical/Mathematical geodesy: computations, usually on the surface of the geodetic reference ellipsoid, to yield accurate positions from geodetic measurements, including map projections, which involves aspects from differential geometry.
• 4.
  Satellite/Space geodesy: determination of the orbits of satellites (hence inferring the earth's external gravity field) or for determining positions on or near the earth's surface from ranging measurements to/from navigation satellites.

On the other hand, the official international scientific organization in geodesy, the International Association of Geodesy (IAG), has four main

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