Computation of Ray Amplitudes in Inhomogeneous Media with Curved |
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| Authors: | Popov MM P&#;en&#;&#;k I |
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| Institution: | (1) Astronomical Institute, Acad. Sci. Czech Rep., Bo ní II/1401, 141 31 Prague 4, Czech Republic;(2) Institute of Physical Geodesy, Darmstadt University of Technology, Darmstadt, Germany;(3) National Imagery and Mapping Agency, St. Louis, MO 63118-3399, USA;(4) Geodetic Survey Division, Natural Resources Canada, 615 Booth Street, Ottawa, K1A0E9, Canada;(5) Geographic Service of the Czech Armed Forces, Military Topographic Institute VTOPÚ, Dobru ka, Czech Republic |
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| Abstract: | The TOPEX/POSEIDON (T/P) satellite altimeter data from January 1, 1993 to January 3, 2001 (cycles 11–305) was used for investigating the long-term variations of the geoidal geopotential W
0 and the geopotential scale factor R
0 = GM÷W
0 (GM is the adopted geocentric gravitational constant). The mean values over the whole period covered are W
0 = (62 636 856.161 ± 0.002) m2s-2, R
0 = (6 363 672.5448 ± 0.0002) m. The actual accuracy is limited by the altimeter calibration error (2–3 cm) and it is conservatively estimated to be about ± 0.5 m2s-2 (± 5 cm). The differences between the yearly mean sea surface (MSS) levels came out as follows: 1993–1994: –(1.2 ± 0.7) mm, 1994–1995: (0.5 ± 0.7) mm, 1995–1996: (0.5 ± 0.7) mm, 1996–1997: (0.1 ± 0.7) mm, 1997–1998: –(0.5 ± 0.7) mm, 1998–1999: (0.0 ± 0.7) mm and 1999–2000: (0.6 ± 0.7) mm. The corresponding rate of change in the MSS level (or R
0) during the whole period of 1993–2000 is (0.02 ± 0.07) mm÷y. The value W
0 was found to be quite stable, it depends only on the adopted GM,  and the volume enclosed by surface W = W
0. W
0 can also uniquely define the reference (geoidal) surface that is required for a number of applications, including World Height System and General Relativity in precise time keeping and time definitions, that is why W
0 is considered to be suitable for adoption as a primary astrogeodetic parameter. Furthermore, W
0 provides a scale parameter for the Earth that is independent of the tidal reference system. After adopting a value for W
0, the semi-major axis a of the Earth's general ellipsoid can easily be derived. However, an a priori condition should be posed first. Two conditions have been examined, namely an ellipsoid with the corresponding geopotential which fits best W
0 in the least squares sense and an ellipsoid which has the global geopotential average equal to W
0. It is demonstrated that both a-values are practically equal to the value obtained by the Pizzetti's theory of the level ellipsoid: a = (6 378 136.7 ± 0.05) m. |
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| Keywords: | geoidal geopotential TOPEX/POSEIDON altimetry Earth's dimension |
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