- 行业: Earth science
- Number of terms: 93452
- Number of blossaries: 0
- Company Profile:
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 constant (1) which cannot be eliminated from a function without changing the set of values taken by the function, regardless of what changes are made in the other constants in the function. In the equation.
Industry:Earth science
The theoretical replacement of matter between geoid and Earth's surface by an equivalent layer of mass on the geoid. If the average density of matter between geoid and Earth's surface is D and the elevation is H, then the average amount m of mass per unit area on the geoid is m = DH.
Industry:Earth science
A magnetic compass similar to a surveyor's compass but constructed so that the line of sight can be rotated to conform with the direction of the needle or be directed to any desired setting on the horizontal circle. It is used in determining the magnetic declination. Some models are self registering or recording.
Industry:Earth science
A point of horizontal control that has been established by photogrammetric triangulation.
Industry:Earth science
Bonds that promise payments of interest and principal but pledge no specific assets. Holders have first claim on the issuer's income and unpledged assets. Also known as <i>unsecured bonds</i>.
Industry:Earth science
The constant of proportionality G or k appearing in formula for the force of attraction between two bodies. If the bodies can be considered points with masses M<sub>1</sub> and M<sub>2</sub>, the formula is f = G M<sub>1</sub> M<sub>2</sub>(r<sub>2</sub> - r<sub>1</sub>)/r<sub>3</sub> , in which r<sub>1</sub> and r<sub>2</sub> are the vectors from the origin to masses M<sub>1</sub> and M<sub>2</sub>, respectively, and r is the distance between the two masses. The value of the numerical constant depends upon the units in which the force f, the vectors r<sub>1</sub> and r<sub>2</sub> and the distance r, and the masses M<sub>1</sub>and M<sub>2</sub> are expressed. The value adopted for G by the International Astronomical Union in 1976 is 6. 672 x 10<sup>-11</sup> m3/(kg s²). Recent measurements of the variation of gravity with depth in the Earth, and data from nuclear experiments, suggest that a fifth force, similar to gravitation, may exist or that the inverse square law for the variation of gravitation with distance is not quite correct. The uncertainties in the data, however, are such that no definite conclusions are possible at present. The symbol k² is reserved for the gravitational constant when the masses are expressed in units of the mass M<sub>s</sub> of the Sun, distances are expressed in terms of the astronomical unit (A. U. ), and time is expressed in ephemeris days (E. D. ; 86 400 ephemeris seconds). The quantity k, also called the Gaussian constant or Gaussian gravitational constant, has the defined value 0. 017 202 098 950 (A. U. )3/(M<sub>s</sub> (E. D. )²). This value then specifies the astronomical unit through Kepler's third law k² M<sub>s</sub> (1 + M1/Ms) = (2ð/To)² a<sub>3</sub>, in which To is the period of an orbiting point mass of mass M<sub>1</sub> and a is the radius of the circular orbit. Note that the astronomical unit is not the same as the average semi major axis of the Earth's orbit. The difference arose because Gauss, in calculating k, used a value for the mass of the Earth about 7% too small. If k is calculated instead of being defined, it can be determined to many more significant figures than can G because, with the units adopted, k is equal to the average angular speed of the Earth in its orbit, divided by (1 + mass of Earth in units of solar mass). The mass of the Earth in these units is a very small quantity and is known to better than 6 significant figures; the average angular speed is immediately calculable from the period of revolution of the Earth, which is known to better than 10 significant figures.
Industry:Earth science
The tidal constituent which represents the effect of the rotation of the Earth (with respect to the Moon) on the tides. Its period is 12. 42 hours and its angular speed is 28. 9841 degrees per hour. Its symbol is M2; the Doodson number is 255. 555.
Industry:Earth science
A method of drawing contour lines spacing them at intervals proportional to the differences of elevation between points at which the slope changes. The method is based on the fact that contours are equally spaced along a uniform slope. It permits contour lines of adequate accuracy to be drawn from carefully located elevations and makes it unnecessary to run a level line for every contour.
Industry:Earth science
(1) The intersection of a solid with a developable surface (usually a plane). For example, a vertical section of the ground or of underlying strata. A cross section, in this sense, should not be confused with a profile, which is the intersection of a surface with a developable surfaced. (2) The trace, in a vertical plane perpendicular to a given, horizontal line or route, of the terrain through which the plane passes. (3) A horizontal grid laid out on the ground for determining contours, quantities of earthwork, etc. , using the elevations of the intersections of the grid. (4) A section taken perpendicularly to the center line of a proposed construction such as a road, canal or dam.
Industry:Earth science
