Abstract
We have used numerical simulation to study the effects of ionospheric irregularities on accuracy of global navigation satellite system (GNSS) measurements, using ionosphere-free (in atmospheric research) and geometry-free (in ionospheric research) dual-frequency phase combinations. It is known that elimination of these effects from multifrequency GNSS measurements is handi-capped by diffraction effects during signal propagation through turbulent ionospheric plasma with the inner scale being smaller than the Fresnel radius. We demonstrated the possibility of reducing the residual ionospheric error in dual-frequency GNSS remote sensing in ionosphere-free combination by Fresnel inversion. The inversion parameter, the distance to the virtual screen, may be selected from the minimum of amplitude fluctuations. This suggests the possibility of improving the accuracy of GNSS remote sensing in meteorology. In the study of ionospheric disturbances with the aid of geometry-free combination, the Fresnel inversion eliminates only the third-order error. To eliminate the random TEC component which, like the measured average TEC, is the first-order correction, we should use temporal filtering (averaging).
Highlights
At present, remote sensing methods relying on groundbased and low-orbit observations of signals from global navigation satellite systems (GNSS) such as GLONASS and GPS are finding ever-widening application in environmental research [1,2,3,4,5,6,7,8]
Like dualfrequency measurements, triple-frequency measurements yield a system of three observation equations from which we can find D, first-order correction (TEC), and thirdorder correction
Unlike first approximation formula (1), besides the first-order correction proportional to the total electron content I1g = ∫zz0t N(z)dz, the third-order correction (the final term on the right-hand side in (17)) associated with the path deviation from the straight line in the inhomogeneous ionosphere is taken into consideration
Summary
Remote sensing methods relying on groundbased and low-orbit observations of signals from global navigation satellite systems (GNSS) such as GLONASS and GPS are finding ever-widening application in environmental research [1,2,3,4,5,6,7,8]. It has been revealed that in the thin layer approximation whose error is 1-2 mm this correction is expressed through the first-order one [13, 15, 22] It can be taken into account by calculating with the familiar geomagnetic field model [1, 13,14,15] or by considering directly in dual-frequency measurements through modification of the ionosphere-free combination [22, 23]. Like dualfrequency measurements, triple-frequency measurements yield a system of three observation equations from which we can find D, first-order correction (TEC), and thirdorder correction (ray bending) This can only be done, when scales of ionospheric irregularities exceed the Fresnel radius, and the geometrical optics approximation is applicable. We will present results of investigations into residual ionospheric errors of dual-frequency GNSS measurements for both combinations (4) and (5)
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