- 行业: 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 lengthening of the period of a pendulum, caused by the action, on the pendulum, of the Earth's magnetic field or of a permanent magnetic field in the instrument. The period of an invar pendulum may be increased by as much as 0. 1 microsecond if the magnetic field increases by 0. 02 Oersted. This corresponds to 0. 05 mgal. In regions of large magnetic anomaly, the error may amount to tens of mgals. If the instrument itself is generating the magnetic field, it should be demagnetized by being placed in a Helmholz coil. The best solution is to make the pendulum of a non magnetic material such as quartz. Quartz, however, accumulates an electrostatic charge which affects the period.
Industry:Earth science
A scribing tool that has contact with the scribed material at three points, to compensate for the normal imbalance of the pressure exerted by the operator.
Industry:Earth science
(1) The difference δg <sub>E</sub> between the value of gravity acceleration actually measured by a horizontally moving gravimeter and the value that would be measured if the gravimeter were stationary. The correction is the sum of the vertical components of the accelerations produced by the Coriolis effect and the centrifugal acceleration caused by the gravimeter's motion. It is given by δg <sub>E</sub> = (R<sub>φ</sub> + h)(v<sub>φ</sub> v<sub>e</sub> sinφ sinA<sub>z</sub> + v²) / Rφ , in which v is the speed of the gravimeter, v<sub>e</sub> its eastward component, v<sub>φ</sub> the eastward speed of the Earth at geodetic latitude φ, A<sub>z</sub> the azimuth of the direction in which the gravimeter is moving, R<sub>φ</sub> the radius of the reference ellipsoid at the location of the gravimeter and h the geodetic height of the gravimeter. (2) The quantity 4. 0 v sinα cosφ.
Industry:Earth science
A tabulation of the locations and related data for a celestial body for given epochs (dates) at uniform intervals of time. In particular, a publication containing such data for a number of celestial bodies. The Astronomical Ephemeris (formerly the American Ephemeris and Nautical Almanac) is such a publication. It contains, for specified instants, the coordinates of the principal celestial bodies; the constants specifying the position of the coordinate system used; numbers used in calculating the effects of changes in the location of the observer; and, in general, data on all those phenomena relating to celestial bodies which may be regarded as functions of time and which are of interest to navigation and related arts. The plural of ephemeris is ephemerides. While custom has approved the use of the singular form to designate the publication as a whole, the plural form is used when tabulations for specific bodies are discussed e.g., the ephemerides of Mercury and Venus. When tabulation for one specific body is discussed, the singular form is used e.g., the ephemeris of Mercury.
Industry:Earth science
An adjusted elevation based on the sea level datum of 1929 (now known as the National Geodetic Vertical Datum of 1929).
Industry:Earth science
The celestial reference system determined by the instantaneous positions of the celestial equator and ecliptic. The motion of this system is caused by the progressive effect of precession and the short term, periodic variations of nutation.
Industry:Earth science
One of a set of equations in which the independent variables are each expressed in terms of one or more other independent variables called parameters. For example, instead of studying the equation F(x,y) = 0 directly, one may find it easier to express both x and y in terms of a parameter u: x = g(u); y = h(u). The parameter may or may not have a useful geometric or physical interpretation.
Industry:Earth science
A theory which assumes that the waters covering the face of the Earth respond instantly to the tide producing attractions of the Moon and Sun, and form a surface which is in equilibrium under the action of those attractions. Friction and inertia are ignored, as is the irregular distribution of the land.
Industry:Earth science
The straight line (a degenerate ellipse) formed by letting the eccentricity of an ellipse approach zero while keeping the major axis fixed.
Industry:Earth science
(1) A colloid in which globules of a liquid are dispersed in another liquid with which it is immiscible.
Industry:Earth science
