AN ESTIMATION OF ACCURACY OF THE ATMOSPHE RIC REFRACTIVE-INDEX RECOVERY FROM MEASUREMENTS OF DOPPLER SHIFTS AT FREQUENCIES USED IN THE NAVSTAR SYSTEM

Doppler shifts at radio frequencies 1227.6 and 1575.42 MHz used in the NAVSTAR navigation system are considerably influenced by ionosphere. As it is shown in the paper the use of dispersion method at NAVSTAR fr equencies allows to eliminate the influence of ionosphere on the recov ery of the atmospheric refractive index distribution (at least up to a ltitude of 45 km above the Earth surface). It provides almost the same accuracy of recovery as in the absence of ionosphere. It is also show n that absence of spherical symmetry of ionosphere doesn't influence o n the accuracy of atmospheric refraction index recovery using formulae based on spherical layered medium approach.