Influence of Ionospheric Irregularities on GNSS Remote Sensing

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).

Some Possibilities of Spatial Signal Processing in an Inhomogeneous Medium Based on DWFT

“…Therefore, the elimination of diffraction effects through Fresnel inversion proved to be essential for precision measurements with GNSS (Mortensen & Hoeg, 1998). Figure 7 presents the results (Tinin, 2015b) of calculation of average (a) and standard deviation (b) of corrections of first (dashed line) and third (solid line) orders for GPS frequencies after processing 21 as function of screen distance for elevation angles of 20 ∘ (red lines), 50 ∘ (green lines), and 90 ∘ (blue lines). Figure 7c shows how the scintillation index for the L1 GPS frequency varies in this case.…”

“…By solving this system, we can find and eliminate ionospheric errors of different orders. However, due to ionospheric irregularities with scales smaller than the Fresnel radius, coefficients in these series begin to depend on frequency, thereby leading to diffraction errors in multifrequency GNSS (Tinin, 2015a, 2015b). Therefore, the elimination of diffraction effects through Fresnel inversion proved to be essential for precision measurements with GNSS (Mortensen & Hoeg, 1998).…”

“…Elimination of diffraction effects in the average (a) and standard deviation (b) of corrections of first (dashed line) and third (solid line) orders for GNSS measurements for elevation angles of 20° (red lines), 50° (green lines), 90° (blue lines); scintillation index for L1 GPS frequency (c) (Tinin, 2015b). …”

Variable-step 3D numerical ray-tracing method for simulating oblique ionogram via inversion analysis

“…[1][2][3][4][5] In addition, the irregularities in the ionosphere may control the efficiency and reliability of these navigation and positioning systems. 6,7 Therefore, the forecast of ionospheric plasma density is becoming an important topic recently. Ionogram inversion is a widely used method to obtain the plasma density distribution, and the vertical plasma density profile is the common inversion result.…”

“…For example, the plasma in the ionosphere may cause hundreds of meters of delay to waves emitted by the high-frequency (HF) communication systems, the Sky-wave over-the-horizon radars, and the global navigation satellite system 1 – 5 In addition, the irregularities in the ionosphere may control the efficiency and reliability of these navigation and positioning systems 6 , 7 . Therefore, the forecast of ionospheric plasma density is becoming an important topic recently.…”