A. D. Vinogradov - Dr.Sci. (Eng.), Professor, Senior Research Scientist, Federal State Official Military Educational Institution of Higher Professional Education Military Educational-Research Centre of the Air Force «Air Force Academy named after professor N.E. Zhukovsky and Y.A. Gagarin» (Voronezh). E-mail: mvvad@mail.ru
V. V. Gribanov - Ph.D. (Phys.-Math.), Research Scientist, Federal State Official Military Educational Institution of Higher Professional Education Military Educational-Research Centre of the Air Force «Air Force Academy named after professor N.E. Zhukovsky and Y.A. Gagarin» (Voronezh). E-mail: vgribanov@yandex.ru
P. A. Levachov - C.Sc. (Eng.), Associate Professor, Senior Research Scientist, Federal State Official Military Educational Institution of Higher Professional Education Military Educational-Research Centre of the Air Force «Air Force Academy named after professor N.E. Zhukovsky and Y.A. Gagarin» (Voronezh). E-mail: z_trade@mail.ru

The paper considers estimations of accuracy of bistatic triangulation (goniometric) long range positioning system. The account of the Earth's sphericity and its influence on the accuracy is studied. Radial (circular) mean square error of radio source positioning is used as a quantitative characteristic of positioning accuracy. Equations for circular (radial) mean square error of radio source location are presented for that bistatic system equipped with radio direction finders of equal accuracy, both for plane and spherical models of the Earth. The equations accounts angular MSE of the direction finders, base length of terrestrial positioning system (TPS) and distance of the radio source measured from the center of the base line. It is shown, that the longer the distance from the base line center, the greater the difference between the values of the radial MSE for planar and spherical models of the Earth. Unlike the radial MSE for the planar model the radial MSE for the spherical model takes its maximum value at distances of about 10.000 km. At 18.000 km ranges, which corresponds antipodal sites, the radial MSE for the spherical model of the Earth takes its minimum value. It is suggested to use the equation for radial (circular) MSE, which accounts the Earth's sphericity, in order to estimate the accuracy of radio source positioning with goniometric TPS at over 2000 km ranges,