- 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, ...
The ratio of the density of a substance at a given temperature and pressure to the density of some other substance used as standard, at the same temperature and pressure. Sometimes called density by oceanographers. For liquids and solids, the usual standard is the density of distilled water at 4<sup>o</sup>C and at standard atmospheric pressure (760 mm of mercury)
Industry:Earth science
A zone devoted to the landing and taking off or helicopters. The heliport may also provide fuel, a place to eat, etc.
Industry:Earth science
Any reference system developed for use where no grid is available or practicable, or where military security is desired for the reference.
Industry:Earth science
The tidal datum used as chart datum for the coastal waters of the Gulf Coast of the United States of America and defined as mean lower low water when the tide is of the mixed type and as mean low water when the tides are diurnal. The datum was abandoned by the National Ocean Survey in 1980 and replaced by mean lower low water for the region involved.
Industry:Earth science
A stereographic map projection the center of projection at some parallel of latitude other than the Equator.
Industry:Earth science
A modification of the Hayford-Bowie method of gravity reduction. The topographic effect of an infinite slab of density 2.67 g/cm3 and a thickness equal to the elevation of the point at which gravity was measured is first computed; this is then cor-rected for curvature of the geoid, the effect of topography, and finally for variation of the actual topography from the slab. The first step in the computation gives the ordinary Bouguer gravity correction for topography; the second step takes account of the departure of the actual topography from a plate (or smooth cap, if this is used instead of a slab) whose thickness is equal to the elevation of the point. Applying the correction for curvature in the lettered zones (of the Hayford template) reduces the effect of the flat slab to that of a plateau or cap extending to the outer limits of those zones and curved to fit the reference surface. Topography is taken into account by applying a correction for deviations of the topography from the surface of the plateau or cap. This method was devised by E.C. Bullard as a substitute for the Hayford-Bowie method of gravity reduction in the lettered zones of the Hayford template.
Industry:Earth science
The quantity hNnd calculated from the formula hNnd = (U(L(N), Φ(N), hN) - U(L(N), Φ(N), hmsl))/τ <sub>45</sub> , in which U(L(N), Φ(N), hN) is a specified spheropotential function, τ <sub>45</sub> is the value of gravity acceleration calculated from (δU/δh) at 45<sup>o</sup> latitude for h = 0, and hmsl is that value of h in U which causes the corresponding equipotential surface to go through the mean-sea-level mark at a specified tide-gage. Note: Since, in general, mean sea level and the geoid do not coincide, the values of the spheropotential function on the geoid and at mean sea level will be different.
Industry:Earth science
The difference between the geodetic height of a point on the Earth's surface above the reference ellipsoid, and the normal height of that point.
Industry:Earth science
The surface defined by a term representing centrifugal potential, and by the zero-th, second-, and fourth-degree terms in a representation of the Earth's gravity potential by a series of Legendre functions.
Industry:Earth science
An instrument which, while in motion (as on a ship or aircraft), can measure the rate at which gravity changes with change of location. The torsion balance, another gravity gradiometer, must remain in place while making a measurement. At present there are two types of moving base gravity gradiometer. One uses rotating masses whose dynamic weights are determined by stress gages. The other uses pairs of accelerometers contained in superconducting circuits.
Industry:Earth science
