Applications: Geodesy

Geodesy is concerned with the measurement of the Earth's figure and the mapping of parameters related to it. Its products are used extensively in all branches of the Earth sciences. In addition, they are applied to many areas of civil engineering, exploration, mapping and cadastral work and are the basis of all geo-information systems.

The three main quantities of geodesy science are: geoid height, gravity anomaly and vertical deflections.

The geoid is that equipotential surface which would coincide exactly with the mean ocean surface of the Earth, if the oceans were in equilibrium, at rest, and extended through the continents.

The geoid height is the orthornormal height of geoid above the reference ellipsoid. The gravity anomaly in modern definition is the difference between the magnitude of the gravity vector at a point P (on the surface of the Earth), and the magnitude of the reference gravity (normal gravity) at the point Q which has the same gravity potential as at the point P and lies on the normal to the reference ellipsoid passing through P.

The deflection vertical in modern definition is the angular separation of the gravity vector at the point P and the normal gravity vector at point Q which has the same gravity potential as at the point P and lies on the normal to the reference ellipsoid passing through P.

For geodesy branches, GUT allows user for:

1. Computation of global, gridded geoid heights or gravity anomalies at a given, user-specified, degree and order of the spherical harmonic expansion (i.e. at a given spatial resolution).
2. Computation of geoid heights and gravity anomalies at a given spatial resolution and a given point or list of points (e.g. unstructured grid, transect).
3. Computation of vertical deflections at a given, user-specified, degree and order of the spherical harmonic expansion (i.e., at a given spatial resolution) over global grid, or transect.
4. Computation of height anomalies at a given, user-specified, degree and order of the spherical harmonic expansion (i.e. at a given spatial resolution) over global grid, or transect.

The gravity anomaly and vertical deflections are calculated in full (i.e. no spherical approximations used).

The tool gives users the possibility to change reference, ellipsoid, tide system, or to express the degree/order of expansion in term of scale angle or scale length.

Finally, the passage from spatial domain to spectral domain is allowed by implementation of the spherical harmonic synthesis algorithm.