- 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, ...
Conversion of the measured length of a base line to the length of the vertical projection of the base line onto a specified surface defined by reference to mean sea level. Theoretically, the specified surface should be an equipotential surface. Because the shape of the surface must be known for the definition to be practical and because the shape of an equipotential surface is known only approximately, if at all, a sphere or rotational ellipsoid is usually specified instead. This works because a base line is so short that a sphere or rotational ellipsoid is a very good fit to an equipotential surface over the length of the base line. Base lines are reduced to sea level when the location of the geoid and the location of the reference ellipsoid are not known.
Industry:Earth science
(1) A conformal map projection of the whole sphere into an area bounded by an ellipse. The map projection was devised by O. Adams but contained some singularities. These were removed by a method devised by I. Lee in 1965. (2) A conformal map projection of the sphere into a square, with the poles on a diagonal of the square and symmetrical about the center. (3) An equal area map projection of the pseudo cylindrical type, projecting the sphere onto a cylinder in such a fashion that the parallels of latitude go into straight lines parallel to the x axis and spaced at the distance 2kR <sub>a</sub> sin1/2<font face = symbol>B</font> from the origin. k is a scale factor, R <sub>a</sub> is the radius of the authalic sphere, <font face = symbol>B</font> is the authalic latitude and x = (R <sub>a</sub> (<font face = symbol>l</font> - <font face = symbol>l</font> <sub>o</sub> ) cos<font face = symbol>B</font>)/cos1/2<font face = symbol>B</font>, in which <font face = symbol>l</font> is the longitude and <font face = symbol>l</font><sub>o</sub> is the longitude of the reference meridian. (4) A conformal projection of the sphere into a regular hexagon.
Industry:Earth science
Determining elevations, or differences of elevation, by measuring the boiling point of water. The temperature at which water boils at any point on the Earth depends on the atmospheric pressure at that point, and the atmospheric pressure depends on the elevation of the point. Factors other than elevation also affect atmospheric pressure, and factors other than atmospheric pressure affect the boiling point. Hence, thermometric altimetry is less precise than barometric altimetry.
Industry:Earth science
The solid angle bounded by a set of planes that intersect at a common point in such a way that each plane is bounded by the lines of intersection and intersects exactly to other planes. The solid angles at the apices of a pyramid are polyhedral angles.
Industry:Earth science
An apparatus consisting of a bar or disk, with associated machinery for lowering and hoisting, which is lowered from the side of a ship to an accurately known depth. The depth is then measured independently by the ship's depth sounder.
Industry:Earth science
The angular elevation of a celestial object near the celestial meridian and observed to determine latitude.
Industry:Earth science
A fictitious star assumed to move along the celestial equator at a uniform rate corresponding to the frequency of one of the several harmonic constituents of the tide producing force. Each astre fictif crosses the meridian at a time corresponding to the maximum of the constituents it represents.
Industry:Earth science
Adjustment of the coordinates of points in a geodetic network by formulating each observation as a function of the adjusted coordinates and the errors (residuals). The condition equations, which are usually few, are the exact relationships between the adjusted values of the coordinates.
Industry:Earth science
