- 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 map positioned within the borders of a larger map but otherwise separate from and usually on a different scale than the larger map.
Industry:Earth science
An inequality caused by the Moon's moving from the celestial equator into the northern and southern hemispheres, and having a period of one-half a tropical month - 13.66 days. Besides the lunar declinational inequality, there is also a solar declinational inequality, which depends on the Sun's declination.
Industry:Earth science
A photographic process by which material for large-scale maps is selectively reproduced so as to retain only indexed contours. The indexed contours are then used to indicate relief on medium scaled maps. The method is no longer much used.
Industry:Earth science
The images, on two or more photographs, of the same point in image space.
Industry:Earth science
Of equal or constant entropy with respect to either space or time.
Industry:Earth science
A method of measuring distances by using surveyor's measuring tape or wire freely suspended between two marks or supports about 25 meters apart and kept under a constant tension. The method does not involve a support midway between the two marks as do other methods that use much longer tape or wire. It was introduced by E. Jäderin about 1880 and was used in most European countries.
Industry:Earth science
One half the average difference between the two high (low) waters of each day observed over an extended period. It is obtained by subtracting the average of all high (the lower low) waters from the average of the higher high (all low) waters. The definitions given here for mean diurnal high- water or low - water inequalities are applicable only to either semi diurnal or mixed tides.
Industry:Earth science
A small, transparent container holding a transparent medium of large dielectric constant (such as nitrobenzene) and a pair of metallic plates to which is applied a large voltage producing a strong electric field across the medium. The cell is usually placed between a pair of prisms transmitting only plane polarized light. The assemblage is used in one of two ways. (a) The prisms are so oriented that their planes of polarization are parallel. Light transmitted by the one is then normally transmitted by the other. With no difference of voltage between the plates, the electric field is zero and light can pass through the system. When voltage is applied to the plates, the resulting electric field rotates the plane of polarization of light passing through the Kerr cell and no light passes through. (b) The prisms are so oriented that their planes of polarization are not parallel. No light normally passes through, and applying voltage to the plates then rotates the plane of polarization of the light passing the first prism until it does pass through the second prism. The Kerr cell is used as a shutter, e.g., to generate pulses of light or to time the intervals between pulses. Some distance measuring instruments use Kerr cells for timing pulses or determining phase difference.
Industry:Earth science
