REFINING GEOIDAL HEIGHTS COMPUTED BY FULLY-NORMALISED SPHERICAL HARMONICS COEFFICIENTS OF THE EARTH GRAVITATIONAL MODEL EGM2008 BY ADJUSTMENT OF COMBINED GPS/LEVELLING/GEOID NETWORK

Abstract

The paper presents the combined adjustment of GPS/Levelling bservations on benchmarks with gravimetric geoid heights of the Earth Gravitational Model EGM2008 on both terms of theoretical and practical point of view. For the parametric models to be used, various choice have been tested, namely well-known four- and five-parameter similarity transformation models and 1st, 2nd, 3rd order polynomial ones.The geoid heights of GPS/Levelling points in Vietnam territory were computed by the use of fully-normalised spherical harmonic coefficients of the Earth Gravitational Model (EGM) 2008 up to degree 2190.All five models have been tested employing GPS/Levelling observations, geoid heights from EGM2008 with a uniform accuracy for all height types. The mean deviation can be attributed to some datum bias and other systematic errors which was eliminated by the mathematical models after the fit. From the results which are summarized in the paper, it becomes evident that the best fit is achieved when the 3rd order polynomial model is employed to model the residuals. After the fit by 3rd polynomial model, a reduction by 54 cm and 1cm correspoding to RMS and standard deviation is achieved while the range reduces from 1.783m to 1.714m.

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