- Branche: 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, ...
A comparatively thin but continuous covering of ice, conforming generally to the irregularities of the land upon which it rests.
Industry:Earth science
The set of all points lying on one side only of a given (straight) line. Alternatively, the set of all points such that if any two points are connected by a line, that line either lies entirely on a given straight line, called the edge of the half-plane, or has no point in common with the given line.
Industry:Earth science
A hook on a long, graduated shank, having a needle sharp point, and movable vertically with respect to a base. The hook is lowered to just below the surface of the water and then slowly raised until the point just touches the surface. The zero of the scale can be determined by leveling.
Industry:Earth science
A method devised by Hayford and Bowie for calculating the complete topographic and isostatic gravity corrections in the Pratt-Hayford gravity reduction. The complete topographic gravity correction δg <sub>tc</sub> accounts for all matter outside the level surface of reference having an effect at the point of measurement. It is calculated by laying a polar grid (the Hayford template) on a topographic map, with the origin at the point in question, reading off the average elevation within each quadrangle of the grid, and calculating the corre-sponding complete topographic gravity reduction from a formula or table. To this term is added the Pratt-Hayford gravity correction δg <sub>PH</sub>
Industry:Earth science
(1) The process of applying the free air gravity correction to a measured or calculated value of gravity. (2) The free air gravity correction. (3) The process of adding, to a measured or calculated value of gravity, the sum of the free air gravity correction δg <sub>f</sub> and the topographic gravity correction δg <sub>t</sub>. (4) The sum mentioned in the previous definition.
Industry:Earth science
(1) The difference between a gravity anomaly and the average value of the gravity anomalies calculated over a specified region. (2) The quantity g <sub>f</sub> + 2πG Σ (h <sub>i</sub> (ρ <sub>m</sub> - ρ <sub>i</sub>), in which g <sub>f</sub> is the free air gravity anomaly, G is the gravitational constant, h <sub>i</sub> is the thickness of the i-th layer whose density is ρ <sub>i</sub> and ρ <sub>m</sub> is the density of the mantle. This is a sort of Bouguer gravity anomaly removing the effects of compensated crustal topography and uncompensated bulges in the mantle.
Industry:Earth science
A highway that can be entered or left only at a few, widely separated places (usually many tens of kilometers)
Industry:Earth science
That direction, along the south north lines of a grid, which is designated as north i.e., which is approximately the direction of north on the map to which the grid is applied. Grid north coincides with astronomic north only along that line which corresponds to the meridian of origin.
Industry:Earth science
The arc of the celestial equator, or the angle at the celestial pole, between the upper branch of the Greenwich celestial meridian and the hour circle of the vernal equinox, measured westward from the upper branch of the Greenwich celestial meridian through 24 hours. It is equivalent to local sidereal time at the Greenwich meridian, and to the Greenwich hour angle of the vernal equinox expressed in units of time.
Industry:Earth science
The angle, measured westwards, from the plane of the local celestial meridian to the plane of the hour circle passing through the celestial body being observed. It may also be defined as the arc of the celestial equator, or the angle at the celestial pole, measured westwards from the upper branch of the local celestial meridian to the hour circle of a point on the celestial sphere.
Industry:Earth science
