- 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, ...
An instrument for determining the depth of water by measuring the time it takes a sound pulse to travel from the water's surface to the bottom and back, multiplying by the speed of sound, and dividing by 2. One type consists of an oscillator which generates the pulses, a hydrophone for detecting the echo, a clock for measuring the time elapsed between sending out the pulse and receiving the echo, and a recorder which converts the elapsed time to a corresponding depth and plots that depth on a continuous chart. Another type displays the depth digitally, records the value on magnetic tape as a function of location, and plots the depth on a fair sheet or chart. Early models of echo sounders used hammers or similar devices for generating pulses. Present day models use submerged loudspeakers or magnetostrictive or piezoelectric oscillators.
Industry:Earth science
A gradual change in the characteristics of a gravimeter, as determined by calibration.
Industry:Earth science
A positive photographic film showing an array of regularly spaced dots. The grid is used as an overlay in determining areas.
Industry:Earth science
A pendulum similar in structure to working pendulums but equipped with a thermometer and fastened rigidly in its container so that it cannot swing during observations. The dummy pendulum is subject to the same temperatures as the working pendulums, and is used for determining their temperature when in use.
Industry:Earth science
The flat surface, in a rectifier or printer, onto which the image is projected.
Industry:Earth science
Chaining in which the graduated tape is kept horizontal at each step, using a plumb line to correlate the mark on the tape with the mark on the ground. Also written drop-chaining.
Industry:Earth science
(1) Any operation involving moving large amounts of earth. (2) In particular, the operations connected with excavations and embankments of earth, in preparing foundations of buildings, in constructing canals, railroads, highways, etc. (3) An embankment or other construction made of earth.
Industry:Earth science
(1) An equipotential surface of a body which has the same mass as the Earth, whose center of mass coincides with that of the Earth, and which rotates with the Earth. It is axially symmetric and is symmetric with respect to a plane through the center of mass and perpendicular to the axis of rotation. (2) The equipotential surface assumed to be the Earth's outer surface and to have the same volume as the geoid.
Industry:Earth science
The interval of time between two successive conjunctions of the Sun with the same node of the Moon's orbit. It averaged 346d 14h 53m 50. 7s in 1900 and was increasing by 2. 8s per century.
Industry:Earth science
Radar capable of determining not only distance to an object but also the object's radial velocity by measuring the Doppler shift in the frequency of the pulses.
Industry:Earth science
