# Elaboration of equipotential surfaces of planets using biorthogonal expansions

2016;
: pp. 39– 43

Authors:
1
Lviv Polytechnic National University
2
Lviv polytechnic National University
3
Department of Cartography and Geospatial Modeling of Lviv Polytechnic National University

Purpose. Using known and fixed Earth potential, presented asthe biorthogonal expansion, to culculate the geoid surface, which describes the actual shape of the planet. The external gravitational field is generally described by the series of spherical functions. Since the geoid is determined with the help of such functions,  a question arises converning the identity to define the shape, moreover its several points does not belong to the region of convergence. Methodology and results. We consider representation of potential by convergent series everywhere, which makes it possible to find the geoid without specifying the location of points on the surface, although the geoid heights calculation is carried out by various relations. According to the known function of the mass distribution of the Earth, represented by the second degree polynomial, internal and external potential of elliptical planet are defined and the equipotential surfaces are found. Calculated values via these formulas and their degree of coincidence was analyzed. Defined in two ways surfaces do not coincide with each other because the difference in the values of the radius-vector amouts up to ten meters. So, when applying biorthogonal expansions of higher orders in constructing equipotential surfaces based on information about the external gravitational field it is necessary to take into account characteristics of expansion. Originality. Method of determining the shape of the Earth using the biorthogonal expansions of mass distribution function is proposed. This representation is characterized by a convergence for considered series and gives the opportunity to build digital models of the geoid (volumetric or as an isolines map). Practical significance. The results of numerical experiments, described in the article, led to the conclusion about the possibility of determining the equipotential surfaces that adequately describe the physical surface of the planet not only of the second but higher orders using biorthogonal expansions only with additional investigations. Calculation of geoid heights with high accuracy opens the way to observe many regional and local geodynamic phenomena, such as the movement of tectonic plates, and high accuracy leveling using GPS technology can solve a number of geodetic problems.

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