Evaluation of the Topographic Effect using the Various Gravity Reduction Methods for Precise Geoid Model in Korea
The topographic effect is a most important component in the solution of the geodetic boundary value problem (geodetic BVP) and should be considered properly for developing a precise geoid model. It is necessary to select a proper gravity reduction method
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Evaluation of the Topographic Effect using the Various Gravity Reduction Methods for Precise Geoid Model in Korea S.B. Lee and D.H. Lee
Abstract The topographic effect is a most important component in the solution of the geodetic boundary value problem (geodetic BVP) and should be considered properly for developing a precise geoid model. It is necessary to select a proper gravity reduction method in order to calculate the topographic effect precisely, especially in mountainous area. The selection of the gravity reduction method in context of precise geoid determination depends on the magnitude of its indirect effect, the smoothness and magnitude of the reduced gravity anomalies, and their related geophysical interpretation. In this paper, we studied gravimetric geoid solutions using various gravity reduction methods such as Helmert’s second method of condensation, RTM method and Airy topographic-isostatic method and evaluated the usefulness of each method. In Korea, the gravimetric geoid model was determined by restoring the gravity anomalies (included TC) and the indirect effects was computed from various reduction methods on the EIGEN-CG03C reference field and the results were compared to geoid undulations at 503 GPS/levelling points after LSC fitting. According to the results, the RTM method is the most suitable for calculating topographic effect in the precise geoid determination in Korea.
S.B. Lee () Department of Civil Engineering, Jinju National University, Jinju 660-758, Korea e-mail: [email protected]
35.1 Introduction The topographic effect is one of the most important components in the solution of the geodetic boundary value problem. Therefore, the topographic effect should be treated properly for the precise determination of the geoid. The classical solution of the geodetic BVP using Stokes’s formula for gravimetric geoid determination assumes that there are no masses outside the geoid. The gravity anomalies as input data should refer to the geoid, which requires the Earth’s topography to be regularized in some way. Thus, the gravimetric reduction method plays an important role on precise (local or regional) gravimetric geoid determination (Bajracharya, 2003). There are several reduction techniques, which all differ depending on how these topographical masses outside the geoid are dealt with. (Bajracharya, 2003). In theory, gravimetric solution for geoid determination using different mass reduction methods should give the same results, provided that the corresponding indirect effect is taken into account properly and consistently (Heiskanen and Moritz, 1967). However, the results from each reduction methods do differ slightly (Omang and Forsberg, 2000). Variation within each method also exist; e.g. Stokes’ formula may be calculated using either summation over compartments or FFT, producing different results. One the reason for differences in the results is inability of the FFT method to handle data biases properly (Omang and Forsberg, 2000). Therefore, the topographic effect should be considered pro
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