Effect of a high-resolution global crustal model on gravimetric geoid determination: a case study in a mountainous regio
- PDF / 587,696 Bytes
- 16 Pages / 475.945 x 680.426 pts Page_size
- 57 Downloads / 202 Views
ABSTRACT A precise gravimetric geoid model is determined by using Stokes formula assuming that there is no topography above the geoid. Then, the geoid model is simply corrected by considering the constant crustal density of 2670 kg m3 for topographical mass. In fact, the actual density of topographical mass differs about 20% from the constant value. Recently a global crustal density model within 30 resolution has been released by the University of New Brunswick in Canada. The paper is devoted to the study of the effect of using this model on the accuracy of gravimetric geoid in a mountainous region in Turkey. Numerical results prove that the differences in the geoid height due to this model may reach up to several decimetres, which should not be ignored in a precise geoid modelling with 1-cm geoid. Thus, it is concluded that the effect of topographical density variations, contained in this model, is significant and should be taken into account in precise geoid determination, particularly in mountainous regions. K e y w o r d s : Earth crustal model, gravimetric geoid, LSMS method, LSMSSOFT, mountainous region
1. INTRODUCTION Geoid, one of the equipotential surfaces of the Earth’s gravity field, partially coincides with the mean sea level, and extends inside the topographical masses. Since the geoid is the reference surface for the physical heights and depths, it has an essential importance in Earth sciences such as geodesy, geophysics, oceanography, etc. Thereby, precise geoid modelling is one of the main goals of scientists for technical and geoscientific purposes. For the precise geoid determination, Stokes approximation is used by terrestrial gravimetric data. During the process, Stokes method neglects the existence of topographic and atmospheric masses above the mean sea level. Then, the computed approximate geoid height is generally corrected by regarding the constant value of 2670 kg m3 (Harkness, 2012) for the topographical mass as well as gravity reductions. Thus, the geoid height obtained from Stokes theory depends upon the selected density distribution for the topographical mass. It is well known that the actual density of topographical mass changes
Stud. Geophys. Geod., 64 (2020), DOI: 10.1007/s11200-020-1023-z, in print © 2020 Inst. Geophys. CAS, Prague
i
R.A. Abbak
about 1020% of the constant density. For illustration, sedimentary rocks have a density of less than 2300 kg m3 whereas basic and ultrabasic igneous rocks such as basalt, gabbro, dunite, and peridotite have a density of greater than 2900 kg m3. Therefore, using a constant density causes systematic errors in the free-air gravity anomalies (g) and geoid height (N). Since three decades, few investigations have been performed to study the effect of more realistic crustal density of the topographical mass. Martinec (1993) is one of the pioneers of studies of the effect of density variations on the geoid height. That the density is regarded as constant, is too crude approximation especially in mountainous regions. He also estimated
Data Loading...
