BENEFIT OF TIDAL OBSERVATIONS TO GRAVITY AND GPS NETWORKS | ||||
| Journal of Egyptian Geophysical Society | ||||
| Volume 3, Issue 1, 2005, Page 89-98 PDF (2.45 MB) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/jegs.2005.375636 | ||||
 View on SCiNiTO | ||||
| Author | ||||
| K.H. Zahran | ||||
| National Research institute of Astronomy and Geophysics, Helwan, Cairo, Egypt | ||||
| Abstract | ||||
| Earth tides affect almost all geodetic observations. Gravity tides can reach a magnitude up to 0.3mgal in equatorial regions and the displacements due to Earth tides can reach up to 40cm for the vertical component and about third of this value for the horizontal components. An accurate correction of tidal effects is thus required, not only for absolute gravity measurements, but also for the reduction of relative instruments. Global tidal prediction based on the position of Moon and Sun will never reach a sufficient precision, as they cannot take into account the systematic differences between the tidal factors of the different tidal waves. These differences can reach up to 10% with respect to the normal response of the Earth to the tidal forces. To take these effects into account theoretically, it is necessary to use a tidal potential development. The precision of the tidal prediction will of course depends from the number of terms in the potential, from 505 in Cartwright-Tayler-Edden (CTE505) development to 12,935 in Hartmann-Wenzel one. To achieve a higher accuracy, observed tidal factors obtained with a well-calibrated gravimeter have to be applied to represent the real response of the crust in the studied region. On the other hand, the present quality of modeling of space techniques such as GPS is in principle sensitive to the tidal effect. Accurate determination of the local site displacements due to Earth tides has to be taken into account. An improved tidal correction demands, in addition to the theoretical calculations of the tidal displacements, the real response to the tidal wave deduced from the tidal observations. Aswan regional geodetic network has been used as a case study for the current work. The obtained tidal parameters, due to the tidal observation representing the real response of the Earth have been used to study the benefit of tidal observations on the accuracy of gravity and GPS geodetic networks. The study shows that, even when using an accurate theoretical prediction of the gravity and displacements tide, observed tidal parameters are needed if a higher accuracy is to be achieved. | ||||
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