- Industry: 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 nautical chart intended for anchorage and navigation in harbors and smaller waterways.
Industry:Earth science
A ring-shaped region centered at a point P on a level ellipsoid of rotation, having inner and outer radii specified according to a scheme devised by Hayford for calculating the effects of topographic masses on gravity. The first 15 zones from the center outward are labeled A through O, consecutively. The next 18 zones are labeled 18 through 1, consecutively. Zone A consists of the entire region within a circle 2 m in radius; zone O has an inner radius of 99 km and an outer radius of 166.7 km (1<sup>o</sup> 29' 58"). Zone 1 extends from 150<sup>o</sup> 56' to 180<sup>o</sup>. Zones C through O are frequently subdivided each into two zones differentiated by subscripts 1 and 2: e.g., zone C<sub>1</sub> and zone C<sub>2</sub>
Industry:Earth science
The coordinates of a point on a map, expressed in terms of the letters and numbers of the grid or in terms of numerical coordinates only. Conventionally, easting is given before northing.
Industry:Earth science
(1) A condition, in measuring distances by transmission of radio waves between the points of interest, in which some of the radiation is reflected from the ground or water's surface between the points and interferes with that radiation which travels directly between the points, causing the measuring instrument to give an erroneous value for the distance. (2) The variation of a distance, measured with an electromagnetic distance measuring instrument at radio frequencies, from the average value of the distance as the wavelength of the measuring frequency is varied. The condition exists because some of the radiation is reflected from the ground or other objects along the way from the instrument to the target and back. This condition is called multipath radiation. Radiation arriving at the instrument by other than the direct path from instrument to target and back interferes with the direct traveling radiation and causes the instrument to give erroneous or unreadable measurements. By varying the wavelength of the modulating waves, the error can be made to vary cyclically and be averaged out to a great extent. (2) The erroneous measurements themselves.
Industry:Earth science
The plane perpendicular to the normal at a point on the reference ellipsoid.
Industry:Earth science
(1) A rotational ellipsoid, derived by Hayford in 1909, having the dimensions<br>
Industry:Earth science
An instrument carried on a spacecraft and capable of measuring the gradient (spatial rate of change) of gravitational force or acceleration. Note that a spaceborne gravity gradiometer measures gravitational gradient, not gravity gradient. However, the basic design may be the same in both kinds of instruments.
Industry:Earth science
The statement that every point on the instantaneous position of a wave front (equal phase) may itself be regarded as a source of spherical waves. The position of the wavefront a moment later is then determined as the envelope of all the waves emitted from points on the preceding wavefront, and this procedure of constructing successive wavefronts can be continued as long as desired. The principle is extremely useful in explaining effects due to refraction, diffraction, and scattering, for acoustic radiation as well as for electromagnetic radiation. The principle can be justified theoretically but its extensive use is based on its practically applications.
Industry:Earth science
