Astro-geodetic | Wikipedia audio article
Channel: wikipedia tts
Date: 2018-12-31

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Geodetic_astronomy


00:02:51 See also



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SUMMARY
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Geodetic astronomy or astro-geodesy is the application of astronomical methods into networks and technical projects of geodesy.
The most important topics 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
Satellite geodesy using the background of stars
Monitoring of the Earth rotation and polar wandering
Contribution to the time system of physics and geosciencesImportant measuring techniques are:

Latitude 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 measurements
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 measurements 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. 5 cm up to 0,2 cm
astronomical lat/long and star positions ±1" up to 0,01"
HIPPARCOS star positions ±0,001"
VLBI quasar positions and Earth's rotation poles 0,001 to 0,0001" (cm...mm)