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Ionospheric Scintillations Propagation Model

Ionospheric Scintillations Propagation Model. Y. Béniguel, J-P Adam IEEA, Courbevoie, France. Outline. Overview. Transmitted field calculation. Scattering function calculation (SAR observations). Practical use. Disturbed Ionospheric Regions Affected by Scintillation.

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Ionospheric Scintillations Propagation Model

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  1. Ionospheric Scintillations Propagation Model Y. Béniguel, J-P Adam IEEA, Courbevoie, France

  2. Outline • Overview • Transmitted field calculation • Scattering function calculation (SAR observations) • Practical use

  3. Disturbed Ionospheric Regions Affected by Scintillation POLAR CAP PATCHES AURORAL IRREGULARITIES SATCOM GPS PLASMA BUBBLES EQUATORIAL F LAYER ANOMALIES DAY NIGHT MAGNETIC EQUATOR SBR GPS SATCOM

  4. GPS / Galileo signal Receiver level Physical Mechanism Drift velocity

  5. Medium Radar Observations Observations at Kwajalen Islands Courtesy K. Groves, AFRL Observations in Brazil Courtesy E. de Paula, INPE The vertical extent may reach hundreds of kilometers

  6. Development of Inhomogeneities (Modelling) t = 20 s. t = 200 s. Solving momentum and continuity equation small scale model Allows estimating dimensions and temporal behaviour

  7. Signal at receiver level (Measurements) Intensity Phase

  8. Scintillations Parameters S4 and sF S4 and  are statistical variables computed over a “reasonable” time period that satisfies both good statistics and stationarity, as follows “Reasonable Time” depends primarily on the effective velocity of the satellite raypath; varies from 10 to 100 seconds; the phase is derived from detrended time series These quantities depend on the density fluctuations in the medium

  9. Seasonal Dependency Seasonal : peak at equinoxes : march & october

  10. Local Time Dependency Local time : post sunset hours

  11. Field received at ground level Solution of the parabolic equation

  12. Field Propagation Equation Solution of the parabolic equation Using the phase index autocorrelation function

  13. Algorithm Phase Screen Technique Propagation : 1st and 3rd terms (Space domain) Diffraction : 1st and 2nd terms (Transform domain)

  14. Phase Screen Technique Transmitter Propagation Scattering Propagation Scattering Propagation Receiver

  15. Medium’s Characterisation 5 days RINEX files in Cayenne considered in the analysis S4 > 0.2 & sigma phi < 2 (filter convergence) 3 parameters :

  16. 2D Analysis : Isotropic transverse medium LOS

  17. Anisotropic vs Isotropic LOS B field Additional geometric factor with respect to the 2D case a, b ellipses axes A, B, C trigonometric terms resulting from rotations related to variable changes

  18. How many screens When it converges matched to the electron density profile As many screens as discretisation points along the LOS Current option : one point every 15 km On average : 7 screens

  19. Signal at receiver level Modelling Intensity Phase

  20. Spectrum

  21. Convergence of Results

  22. Global Maps TEC Map Modelling Scintillation Map Modelling

  23. Comparison with Measurements Upper decile slant S4 index at Marak Parak during September 2000. The dashed line indicates the magnetic equator. GISM Result

  24. Radar Observations Medium Scattering Function

  25. Two Points - Two Frequencies Coherence Function Using the parabolic equation The structure function is quadratic with respect to the distance Same process than previously : propagation 1st & 3rd terms ; diffraction : 1st & 2nd

  26. Propagation 1st & 3rd terms

  27. Medium Scattering Function One screen ; distance = 500 km ; drift velocity = 100 m / s. ; sf = 0.8 F = 400 MHz F = 1.5 GHz The Doppler spreading is related to the drift velocity which can vary with the screen altitude

  28. Including a particular waveform Field intensity Medium’s scattering function

  29. Practical use of the model (GISM)

  30. Medium Characterisation Mean Effects (Sub Models) NeQuick, Terrestrial Magnetic Field (NOAA) Geophysical Parameters SSN, Drift Velocity Scintillations (Fluctuating medium) Spectrum slope (p), BubblesRMS, OuterScale (L0) Anisotropy ratio

  31. Numerical Implementation The model includes an orbit generator (GPS, Glonass, Galileo, …) Inputs Medium Characterisation Geophysical Parameters Scenario Intermediate calculation : LOS,Ionisation along the LOS Outputs Scintillation indices Correlation Distances (Time & Space) Scattering function

  32. Conclusion • The geometry (LOS) with respect to the bubbles orientation is arbitrary • A 1D algorithm applies to all cases • The model allows calculating • the transmitted field at receiver level • the scattering function for radar observations

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