1. ?adek, O. and Martinec, Z.: 1991, ?Spherical Harmonic Expansion of the Earth's Crustal Thickness up to Degree and Order 30?,Studia Geoph. et Geod. 35, 151?165.
2. Dziewonski, A. M. and Anderson, D. L.: 1981, ?Preliminary Reference Earth Model?,Phys. Earth Planet Inter. 25, 297?356.
3. Heiskanen, W. A. and Moritz, H.: 1967,Physical Geodesy, Freeman and Co., San Francisco.
4. Kopal, Z.: 1960,Figures of Equilibrium of Celestial Bodies, Univ. of Wisconsin, WI, pp. 135.
5. Marsh, J. G., Lerch, F. J., Putney, B. H., Christodoulidis, D. C., Felsentreger, T. L., Sanchez, B. V., Smith, D. E., Klosko, S. M., Martin, T. V., Pavlis, E. C., Robbins, J. W., Williamson, R. G. Colombo, O. L., Chandler, N. L., Rachlin, K. E., Patel, G. B., Bhati, S. and Chinn, D. S.: 1988, ?An Improved Model of the Earth's Gravitational Field: *GEM-T1*?, NASA Techn. Memorandum4019, pp. 354.