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Concept
Geodetic astronomy
Résumé
Geodetic astronomy or astronomical geodesy (astro-geodesy) is the application of astronomical methods into geodetic networks and other technical projects of geodesy.
The most important applications are:
Establishment of geodetic datum systems (e.g. ED50) or at expeditions
apparent places of stars, and their proper motions
precise astronomical navigation
astro-geodetic geoid determination
modelling the rock densities of the topography and of geological layers in the subsurface
Monitoring of the Earth rotation and polar wandering
Contribution to the time system of physics and geosciences
Important measuring techniques are:
Latitude determination and longitude determination, by theodolites, tacheometers, astrolabes or zenith cameras
time and star positions by observation of star transits, e.g. by meridian circles (visual, photographic or CCD)
Azimuth determination
for the exact orientation of geodetic networks
for mutual transformations between terrestrial and space methods
for improved accuracy by means of "Laplace points" at special fixed points
Vertical deflection determination and their use
in geoid determination
in mathematical reduction of very precise networks
for geophysical and geological purposes (see above)
Modern spatial methods
VLBI with radio sources (quasars)
Astrometry of stars by scanning satellites like Hipparcos or the future Gaia.
The accuracy of these methods depends on the instrument and its spectral wavelength, the measuring or scanning method, the time amount (versus economy), the atmospheric situation, the stability of the surface resp. the satellite, on mechanical and temperature effects to the instrument, on the experience and skill of the observer, and on the accuracy of the physical-mathematical models.
Therefore, the accuracy reaches from 60" (navigation, ~1 mile) to 0,001" and better (a few cm; satellites, VLBI), e.g.:
angles (vertical deflections and azimuths) ±1" up to 0,1"
geoid determination & height systems ca.
Source officielle
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