Geodetic astronomy
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Geodetic astronomy or astronomical geodesy (astro-geodesy) is the application of
geodetic networks and other technical projects of geodesy
.
Applications
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 subsurface
- Monitoring of the Earth rotationand polar wandering
- Contribution to the geosciences
Measuring techniques
Important measuring techniques are:
- 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 transformationsbetween terrestrial and space methods
- for improved accuracy by means of "Laplace points" at special fixed points
- for the exact orientation of
- Vertical deflection determinationand their use
- in geoid determination
- in mathematical reduction of very precise networks
- for geophysical and geologicalpurposes (see above)
- in
- Modern spatial methods
- VLBI with radio sources (quasars)
- Gaia.
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.:
- 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"
- HIPPARCOSstar positions ±0,001"
- VLBI quasar positions and Earth's rotationpoles 0,001 to 0,0001" (cm...mm)
Astrogeodetic geoid undulations for an area becomes a matter for simple integration of vertical deflection, as it represents the horizontal spatial gradient of the geoid undulation.
See also
- Arc measurement
- Astronomy, stellar triangulation, spherical trigonometry
- Satellite, electro-optics, CCD
- Satellite geodesy
- Space geodesy
- tacheometer
- Astronavigation, Karl Ramsayer
- Astrometry
- Spherical astronomy
- Surveying
- Zenith camera
References
External links
- Thomson, D. B. "Introduction to Geodetic Astronomy" (PDF). Department of Geodesy and Geomatics Engineering University of New Brunswick.
- "Geodetic Astronomy at NGS: Past and Present". geodesy.noaa.gov. NOAA.
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