- Industry: Earth science
- Number of terms: 93452
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Founded in 1941, the American Congress on Surveying and Mapping (ACSM) is an international association representing the interests of professionals in surveying, mapping and communicating spatial data relating to the Earth's surface. Today, ACSM's members include more than 7,000 surveyors, ...
(1) The science concerned with determining the size and shape of the Earth. This is essentially Helmert's definition of 1880. In practice, it involves determining, in some convenient coordinate system, the coordinates of points on the Earth's surface. Each country originally set up its own coordinate system and developed its own surveying system. Most of these coordinate systems can now be referred to a common coordinate system for geodetic purposes, but many countries still adhere to their own systems for internal use. (2) The investigation of any scientific question connected with the shape and dimensions of the Earth. (3) That science which deals with the size and shape of the Earth, the Earth's external gravitational field, the locations of points above, on, or under the Earth's surface, and, to a limited extent, the internal structure of the Earth. (4) That branch of surveying in which the curvature of the Earth must be taken into account when determining angles and distances. (5) That branch of surveying which is concerned with providing an accurate framework (i.e., set of coordinates, or distances and directions between points) in a country, to which surveys covering smaller regions made at different times and in scattered places can be connected without any fear of discontinuities at the junctions. (6) The art which locates points and determines the Earth's gravity field. Geodesy may be classified as lower geodesy (also called surveying) and higher geodesy (also called geodesy). Lower geodesy contains the techniques and instrumentation of geodesy; higher geodesy contains the theory. Alternatively, lower geodesy may contain that part of geodesy which does not require knowledge of the Earth's curvature, while higher geodesy does require such knowledge. Disciplines part of geodesy by the above definitions are often considered by their practitioners to be separate from geodesy e.g., cartography, photogrammetric mapping, and nautical charting. (7) The determination of the gravitational field of the Earth and the study of temporal variations such as Earth tides, polar motion, and rotation of the Earth.
Industry:Earth science
Formerly, an office of the United States government, a division of the Department of the Interior and originally constituted by Act of Congress in 1812, and having charge of all executive action relating to the public lands, including their surveying, sale, or other disposition and patenting. The General Land Office and the U.S. Grazing Service were consolidated into the Bureau of Land Management, under the Department of the Interior, by the 1946 Reorganization Plan No. 3,403
Industry:Earth science
(1) A mathematical surface derived from the spheroid of reference by applying values of the deflection of the vertical adjusted for the effects of topography and isostatic compensation. The adjusted values of the deflection used in obtaining the isostatic geoid are similar to those used for obtaining the compensated geoid, but are of opposite sign. If the theory and assumptions about the nature of isostasy were correct and exact, and if there were no gravity anomalies, the isostatic geoid would agree with the geoid. (2) A surface lying above (or below) a theoretical, equipotential surface represented by a formula for the geopotential, by the same distance as the geoid lies above the co geoid.
Industry:Earth science
An approximation to the geoid, as determined from gravimetric data.
Industry:Earth science
Referred to the center of the Earth. The Earth has many different centers; which is meant must usually be inferred from the context. The following kinds of center are in common use: (a) the center of an ellipsoid representing the Earth's shape; (b) the center of an ellipsoid representing the geoid; (c) the Earth's center of mass; (d) the point at which the Earth's axis of rotation intersects the plane of the celestial equator.
Industry:Earth science
(1) One of a pair of coordinates x and y of a point on a rotational ellipsoid: y is measured along the central meridian to the intersection with the parallel of latitude through the point; x is measured from the central meridian, along the parallel of latitude, to the point. Some authors interchange x and y in the definition. (2) One of a pair of coordinates in the coordinate system of the transverse Mercator map projection. (3) A Gaussian coordinate with the magnification factor 1, using Bessel's ellipsoid and a system of meridional sectors 3<sup>o</sup> wide.
Industry:Earth science
A magnetic flux density of one field line per square cm of area perpendicular to the direction of the field lines. The gauss is properly defined only for B, the magnetic flux density of a magnetic field. However, it has also been used as a unit of measure for H, the magnetic field intensity. As a unit of magnetic flux density, it is equal to 10<sup>-4</sup> webers per square meter (tesla). As a unit of magnetic field intensity, it is equal to one oersted, or approximately 79.577 472 amperes per meter. The Earth's magnetic field varies in flux density from about 0.25 x 10<sup>-4</sup> webers per square meter to 0.70 webers per square meter and is almost equal, numerically, to the magnetic field intensity. Geophysicists have therefore commonly treated flux density and field intensity as if they were equivalent and used the gamma (10<sup>-5</sup> gauss) as a unit of magnetic field intensity. Under the rules of the Système International d'Unités, this equivalence does not exist. For this reason and because the term is ambiguous, gauss should be used only in quoting or referring to old measurements made in this unit.
Industry:Earth science
The surveyed line beginning at the point where the boundary of Pennsylvania intersected the Ohio River, and intended to run due west (at an azimuth of 270<sup>o</sup> from astronomic north). It was surveyed by Thomas Hutchins, a geographer of the USA and was done ac-cording to the plan provided for in the Ordinance of 1785
Industry:Earth science
A spherical harmonic multiplied by the quantity 3GM <sub>m</sub> R <sub>o</sub>² / (4 d <sub>m</sub><sup>3</sup>), in which G is the gravitational constant, M <sub>m</sub> is the mass of the Moon, d <sub>m</sub> is the average distance of the Moon from the Earth and R <sub>o</sub> is the average radius of the Earth. The term is applied also to the quantity obtained by substituting M <sub>s</sub>, the mass of the Sun, for M <sub>m</sub> and d <sub>s</sub>, the Sun's distance, for d <sub>m</sub>
Industry:Earth science
(1) A blackened diaphragm placed at an image of the aperture stop, in an optical system, to block out stray radiation (i.e., prevent unwanted light from outside, or scattered light from inside, the containing structure from reaching the receptor). (2) In general, any blackened diaphragm placed in an optical system to block unwanted light from the receptor.
Industry:Earth science
