- 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 substance or device that transmits only that part of a periodic input which has frequencies or wavelengths lying between certain limits. The limits are called cut-off points, but no filter can completely include or exclude wavelengths or frequencies outside these limits. Filters operating on electromagnetic radiation at optical and near-optical frequencies are usually simple elements, while filters operating at radio frequencies are usually complex circuits. In a small region in the sub-millimeter part of the electromagnetic spectrum, gratings are often used as filtering elements.
Industry:Earth science
(1) The number of times a design is repeated over a given distance. (2) The number of times a design is repeated per unit distance in a specified direction. In both definitions, the design is assumed to be fixed and not vary with time while the spatial frequency is being determined.
Industry:Earth science
The magnetic field of the Earth. Sometimes referred to, ambiguously, as the magnetic field. The intensity of the geomagnetic field varies from about 0.25 weber/m² in a small region around northern Argentina to over 0.70 weber/cm² near the south magnetic pole. The magnetic force is vertical at the northern and southern magnetic poles; elsewhere, its direction varies considerably. The field is representable, to a first approximation, as a magnetic dipole with a moment of about 1.01 x 1017 weber meters and an angle of about 11<sup>o</sup> with the Earth's axis of rotation. It can be represented well as one large magnetic dipole and 8 to 10 small magnetic dipoles placed about 1640 km from the Earth's center at various longitudes and latitudes. The geomagnetic field has a slow, secular variation, fairly periodic variations which depend on the locations of the Sun and Moon, and large, random variations which are related to disturbances in the Sun's atmosphere. The field does not extend out to infinity, as was once thought, but is inclosed in a cavity in the ionized gases continuously ejected from the Sun. The field lines deflect the gases from the Earth, forming the cavity; at the same time, the lines of magnetic force are bent backward, away from the Sun, by the stream of ionized solar gases. The cavity and its boundaries are called the magnetosphere. The surface separating the geomagnetic field from the interplanetary magnetic field is called the magnetospheric sheath. These is no sharp separation between the two fields; the region of transition is called the magnetopause.
Industry:Earth science
An apparatus auxiliary to the use of a pendulum for determining gravity, which produces a flash of light every time the pendulum passes through a position used as reference; the flash may be recorded on moving photographic paper whose rate of motion is measured, or may be detected by a photoelectric cell and timed electronically.
Industry:Earth science
A photographic film embodying a halftone screen which automatically produces a halftone negative from continuous tone copy.
Industry:Earth science
A gas or a liquid. A state of matter in which only a uniform isotropic pressure can be maintained without infinite distortion.
Industry:Earth science
The separation, along the edges of its base, of a photographic emulsion from its base.
Industry:Earth science
The natural flow or movement of water from an upper estate to a lower estate. This is a servitude which the owner of the lower estate must bear even tho the flowage be not in a natural water course with well-defined banks.
Industry:Earth science
The ratio of the difference between values of gravity, as given by a standard gravity formula, at the pole and at the equator, to the value at the equator. Also, and more properly, called gravity flattening.
Industry:Earth science
