Review of the Classical Methods for the Determination of Geodetic Datums

International Astronomical Union Colloquium ◽

10.1017/s0252921100051149 ◽

1975 ◽

Vol 26 ◽

pp. 321-339 ◽

Cited By ~ 2

Author(s):

I.I. Mueller

Keyword(s):

Sea Level ◽

Natural Coordinates ◽

Mean Sea Level ◽

Arbitrary Size ◽

The Earth ◽

Geometric Length ◽

Level Height

In conventional geodetic systems, locations of points on the surface of the Earth may be defined either by means of natural (astronomic) or geometric gepdetic cooprdinates. The natural coordinates, the astronomic latitude (Φ), longitude (λ), and the orthometric (mean sea level) height (H), being gravity dependent, are conventionally referenced, to the geoid and are determined from “natural” observations (astronomic, gravimetric observations and spirit leveling). The geometric coordinates, the geodetic latitude (φ), longitude (λ) and height (h) are referenced to a (generally) rotational ellipsoid of arbitrary size, shape and orientation, and are determined from geometric (length and/or direction) observations.

Download Full-text

Note on Selection of Coordinate Systems for Geodynamics

International Astronomical Union Colloquium ◽

10.1017/s0252921100051174 ◽

1975 ◽

Vol 26 ◽

pp. 395-407

Author(s):

S. Henriksen

Keyword(s):

Sea Level ◽

The Other ◽

Coordinate Systems ◽

Mean Sea Level ◽

The Earth ◽

The One ◽

Static Systems ◽

Selection Of

The first question to be answered, in seeking coordinate systems for geodynamics, is: what is geodynamics? The answer is, of course, that geodynamics is that part of geophysics which is concerned with movements of the Earth, as opposed to geostatics which is the physics of the stationary Earth. But as far as we know, there is no stationary Earth – epur sic monere. So geodynamics is actually coextensive with geophysics, and coordinate systems suitable for the one should be suitable for the other. At the present time, there are not many coordinate systems, if any, that can be identified with a static Earth. Certainly the only coordinate of aeronomic (atmospheric) interest is the height, and this is usually either as geodynamic height or as pressure. In oceanology, the most important coordinate is depth, and this, like heights in the atmosphere, is expressed as metric depth from mean sea level, as geodynamic depth, or as pressure. Only for the earth do we find “static” systems in use, ana even here there is real question as to whether the systems are dynamic or static. So it would seem that our answer to the question, of what kind, of coordinate systems are we seeking, must be that we are looking for the same systems as are used in geophysics, and these systems are dynamic in nature already – that is, their definition involvestime.

Download Full-text