Radio wave scintillation: Aspects of interest for ionospheric physics and radio astronomy - PDF Document

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  1. Radio wave scintillation: Aspects of interest for ionospheric physics and radio astronomy B. Forte (1), R. Fallows (2), M. Bisi (3), and C. Coleman (4) (1) University of Bath (UK) (b.forte@bath.ac.uk) (2) ASTRON (The Netherlands) (3) RAL STFC (UK) (4) University of Adelaide (Australia) Warsaw, 02-03 June 2016 LOFAR Workshop

  2. Radio Waves Scintillation – the problem Warsaw, 02-03 June 2016 LOFAR Workshop

  3. Methods for handling the problem 1 – Weak scattering (usually occurring with low scintillation) Thin phase screen. Weakly scattering medium. Single scattering. Leading to high scintillation if strong single scattering is assumed. Diffractive scattering. Caused by irregularities smaller than the Fresnel scale. 2 – Multiple scattering (usually occurring with high scintillation) Thick phase screen. Weakly scattering medium. Multiple scattering. Refractive scattering. Caused by irregularities larger than the Fresnel scale. Focal scale starts to matter. Warsaw, 02-03 June 2016 LOFAR Workshop

  4. What is known from satellite data Warsaw, 02-03 June 2016 LOFAR Workshop

  5. Global morphology of ionospheric scintillations Basu S., MacKenzie E. and Basu Su., Ionospheric constraints on VHF/UHF communications links during solar maximum and minimum periods, Radio Sci., Vol. 23, N. 3, pp. 363-378, 1998 Warsaw, 02-03 June 2016 LOFAR Workshop

  6. High Latitudes Forte et al, 2002 Warsaw, 02-03 June 2016 LOFAR Workshop

  7. Middle Latitudes Forte et al, 2002 Warsaw, 02-03 June 2016 LOFAR Workshop

  8. Low Latitudes Forte et al, 2002 Warsaw, 02-03 June 2016 LOFAR Workshop

  9. TEC Estimates from different instruments: EISCAT vs GPS Warsaw, 02-03 June 2016 LOFAR Workshop

  10. Previous studies Field Lines Vertical TEC Radar Beam Radar Antenna GPS Link GPS Antenna Lilensten and Cander, 2003 Warsaw, 02-03 June 2016 LOFAR Workshop

  11. Previous studies Lilensten and Cander, 2003 Warsaw, 02-03 June 2016 LOFAR Workshop

  12. Previous studies Field Lines Vertical TEC Radar Scan Radar Antenna GPS Link GPS Antenna Jakowski et al, 1996 Warsaw, 02-03 June 2016 LOFAR Workshop

  13. Previous studies Jakowski et al, 1996 Warsaw, 02-03 June 2016 LOFAR Workshop

  14. EISCAT measurement geometry – new experiment Field Lines Radar Beam GPS Link Radar Antenna GPS Antenna Forte et al, 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  15. EISCAT measurement geometry – new experiment T0 Field Lines Radar Beam GPS Link Radar Antenna T0 + 5 min GPS Antenna Forte et al, 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  16. Electron density profiles – 150 sec average Forte et al, 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  17. Time alignment Forte et al, 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  18. TEC: EISCAT vs GPS Tromso, 12 December 2011 Forte et al, 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  19. TEC Fluctuations: EISCAT vs GPS Tromso, 12 December 2011 Forte et al, 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  20. TEC Fluctuations: EISCAT vs GPS Tromso, 12 December 2011 Forte et al, 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  21. Origin of L-band scintillation: EISCAT and GPS Warsaw, 02-03 June 2016 LOFAR Workshop

  22. Forte et al, 2016 under final review 17 October 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  23. Forte et al, 2016 under final review 16 October 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  24. Forte et al, 2016 under final review Structure function 17 October 2013 16 October 2013 Warsaw, 02-03 June 2016 LOFAR Workshop

  25. Examples of the effects of the ionosphere on LOFAR Warsaw, 02-03 June 2016 LOFAR Workshop

  26. Coleman, Forte et al, 2016 under preparation The Effect of the Ionsphere on LOFAR §  Ionosphere can severely affect radio signals at low frequencies. §  Below are signal paths that would land at origin without ionosphere. •  In particular, if frequency too low, signals cannot penetrate ionsophere. •  Below are low angle paths from 5MHz to 50Mhz (no penetration below 20MHz ). Warsaw, 02-03 June 2016 LOFAR Workshop

  27. Coleman, Forte et al, 2016 under preparation The Effect of the Ionosphere on Phase •  Figures show the phase corrections for angles of 0˚, 30˚ and 60˚ from vertical. •  Major LOFAR sites marked as crosses. Considerable variation across array. Warsaw, 02-03 June 2016 LOFAR Workshop

  28. Coleman, Forte et al, 2016 under preparation Effect of Disturbances on Propagation •  Gravity waves in the neutral atmosphere cause TIDs, fluctuations in ionospheric plasma (Hooke, 1968) •  Fluctuations in plasma cause fluctuations in signal path geometry •  In addition, they cause significant fluctuations in phase corrections •  Fluctuations depend on inclination of incoming paths Warsaw, 02-03 June 2016 LOFAR Workshop

  29. Coleman, Forte et al, 2016 under preparation Variation in Phase Correction Over a Cycle •  •  • ◄ ▼▲ •  • ► Warsaw, 02-03 June 2016 LOFAR Workshop

  30. Mitigation of space weather threats to GNSS services THEME [SPA.2013.2.3-01] Recent developments on the estension of EGNOS into Africa The research leading to these results has received funding from the European Community's Seventh Framework Programme ([FP7/2007-2013]) under grant agreement n° 607081. http://misw.info/ Warsaw, 02-03 June 2016 LOFAR Workshop

  31. Beneficiaries 1.  2.  3.  4.  5.  6.  7.  8.  9.  10.  CENTRUM BADAN KOSMICZNYCH POLSKIEJ AKADEMII NAUK (Poland) 11.  SVEUCILISTE U ZAGREBU FAKULTET ELEKTROTEHNIKE RACUNARSTVA UNIZG-FER (Croatia) 12.  MET OFFICE (UK) UNIVERSITY OF BATH (UK) THALES ALENIA SPACE ITALIA SPA THALES ALENIA SPACE FRANCE THE UNIVERSITY OF NOTTINGHAM (UK) POLITECNICO DI TORINO POLITO (Italy) ISTITUTO NAZIONALE DI GEOFISICA E VULCANOLOGIA (Italy) EISCAT SCIENTIFIC ASSOCIATION (Sweden) JRC JOINT RESEARCH CENTRE - EUROPEAN COMMISSION (Belgium) DANISH TECHNOLOGICAL UNIVERISTY (Denmark) Warsaw, 02-03 June 2016 LOFAR Workshop

  32. The concept of SBAS Warsaw, 02-03 June 2016 LOFAR Workshop

  33. WAAS CONUS Credit: FAA Warsaw, 02-03 June 2016 LOFAR Workshop

  34. SBAS coverage Credit: ESA Warsaw, 02-03 June 2016 LOFAR Workshop

  35. The limitations to the extension of SBAS into low latitudes 1.  Mapping techniques do not accommodate strong gradients 2.  The ground network of reference receivers are not robust in tracking through scintillation events, 3.  Accurate fore-warning of significant space weather events is not available Warsaw, 02-03 June 2016 LOFAR Workshop

  36. Objectives 1.  scintillation at low, high and middle latitudes 1.  To quantify the impact of ionospheric gradients and scintillation on satellite navigation signals, receivers, and overall satellite navigation systems. 2.  To develop innovative algorithms to mitigate against space weather vulnerabilities (i.e. scintillation) at receiver level (including Galileo signals). 3.  To develop innovative algorithms to mitigate against space weather vulnerabilities (i.e. ionisation gradients and scintillation) at service level, e.g. SBAS. 4.  To devise recommendations on best practices for GNSS future services with reference to space weather. To monitor and characterise ionospheric gradients and Warsaw, 02-03 June 2016 LOFAR Workshop

  37. The problem of ionisation gradients Warsaw, 02-03 June 2016 LOFAR Workshop

  38. EUROCONTROL PEG-TN-SBAS Doc. No.: Project: PEGASUS Issue: Date: I 17/06/2003 How to calculate corrections to ionopheric delays Technical Notes on SBAS 49 of 96 Sheet Direction To SV Pierce Point Φ pp pp , λ local tangent plane User Φ u , λ u E hI Earth Ellipsoid Ψpp Re Earth Centre Credit: RTCA Ionosphere Warsaw, 02-03 June 2016 Figure 7: Central Earth Angle for Pierce Point Computations LOFAR Workshop 7.5 The Selection of Interpolation Grid Points Although the data base broadcast to the user is in the form of vertical IGP delays, these points do not generally correspond to the computed IPP location (see section before). Thus, it is necessary for the equipment to interpolate from the broadcast IGP delays to that at the computed IPP location. It should be noted that the user only has to collect and save the vertical delays for IGPs located within about ±20° of his location, which would all be located in one or two bands. After determining the location of the user ionospheric pierce point, the user must select the IGP to be used to interpolate the ionospheric correction value and its corresponding error bound. This selection is done based only on the information provided in the mask, and must be done without regard to whether or not the selected IGP are monitored, not monitored or a “do not use” event is issued. ÿ if the latitude of an ionospheric pierce point is between N55° and S55°: IGP tored IGP ÿ if four IGP that define a 5° x 5° rectangular cell around the IPP are set in the IGP mask, they are selected, else ÿ if three IGP that define a 5° x 5° triangular cell around the IPP are set in the IGP mask, they are selected, else IPP not used IGP ÿ if four IGP that define a 10° x 10° rectangular cell around the IPP are set in the IGP mask, they are selected. There are four potential 10° x 10° cells that must be checked, any one of which may be used. There is no hierarchy fpr selecting among multiple cells if they are defined. Else Figure 8: 10° x 10° rectangular and triangular cell ÿ if three IGP that define a 10° x 10° triangular cell around the IPP are set in the IGP mask, they are selected, else ÿ an ionospheric correction is not available

  39. EUROCONTROL PEG-TN-SBAS Doc. No.: Project: PEGASUS Issue: Date: I 17/06/2003 EUROCONTROL Technical Notes on SBAS Doc. No.: PEG-TN-SBAS 51 of 96 Sheet Project: PEGASUS Issue: Date: I 17/06/2003 7.6 The Interpolation Scheme Technical Notes on SBAS 51 of 96 Sheet Once the nodes of an interpolation cell of the IGP grid that surround the IPP to a satellite have been determined (see chapter before), the equipment must interpolate from those nodes to the pierce point using the following algorithm. This situation is illustrated in figures 13 for the square cell and figure 15 for the triangular cell. 7.6 The Interpolation Scheme For the four-point interpolation, the mathematical formulation for the interpolated vertical IPP delay as a function of the IPP latitude and longitude is given by: Once the nodes of an interpolation cell of the IGP grid that surround the IPP to a satellite have been determined (see chapter before), the equipment must interpolate from those nodes to the pierce point using the following algorithm. This situation is illustrated in figures 13 for the square cell and figure 15 for the triangular cell. 4 ∑ = i (25) Φ ( , ) W ( x , y ) τ λ = τ For the four-point interpolation, the mathematical formulation for the interpolated vertical IPP delay as a function of the IPP latitude and longitude is given by: How to calculate corrections to ionopheric delays vpp pp pp i pp pp vi 1 with vertical ionospheric delay at pierce point τ vpp vertical ionospheric delay at grid points τ W vi 4 weighting function ∑ = i (25) Φ ( , ) W ( x , y ) τ λ = τ i vpp pp pp i pp pp vi Credit: RTCA 1 y Φ with vertical ionospheric delay at pierce point τ vpp grid point 2 grid point 3 vertical ionospheric delay at grid points τ W vi 1 Φ2 weighting function i ypp grid point 2 grid point 3 user’s IPP Φpp xpp grid point 1 grid point 4 0 1 x Φ1 λ1 λpp λ2 λ Warsaw, 02-03 June 2016 LOFAR Workshop grid point 1 grid point 4

  40. EUROCONTROL PEG-TN-SBAS Doc. No.: Project: PEGASUS Issue: Date: I 17/06/2003 Technical Notes on SBAS 47 of 96 Sheet σ2 σ2 GIVEI GIVEI i,GIVE i,GIVE 0.0084 m2 0.0333 m2 0.0749 m2 0.1331 m2 0.6735 m2 0.8315 m2 1.1974 m2 1.8709 m2 0 8 1 9 2 10 3 11 0.2079 m2 0.2994 m2 0.4075 m2 0.5322 m2 3.3260 m2 20.7870 m2 187.0826 m2 4 12 5 13 6 14 7 15 Not monitored Table 26: Conversion from GIVEI to σ2 i,GIVE The Grid Ionospheric Vertical Error Indicator GIVEI is used to transmit an upper bound on the residual error after the application of the ionospheric corrections in the form of a standard deviation. Identical to the procedure with the fast corrections, not the actual error bound is broadcast, but an indicator value for this error bound. The table 26 contains the relationship between the Grid Ionospheric Vertical Error Indicator GIVEI and the actual Grid Ionospheric Vertical Error σ2 Example of ionispheric grid points i,GIVE. W40 W20 0 E20 E40 Credit: RTCA MT 26 block id and delay number together with IGP grid number, N80 N80 Band 3 Band 4 Band 5 IGP supported by ESTB 128 0-09 178 1-10 27 0-09 77 1-10 127 2-11 178 3-12 27 0-11 77 2-01 128 3-06 N60 151 1-01 201 2-02 50 1-01 100 2-02 151 3-03 201 4-06 50 1-05 100 2-10 149 3-13 174 4-05 N40 ted ted by ESTB IGP not suppor- 119 0-01 145 0-10 1-02 170 195 1-11 19 0-01 44 0-10 69 1-02 1-11 94 119 2-03 145 2-12 3-04 170 N20 193 3-13 17 0-01 0-12 42 67 1-06 92 2-02 118 2-11 3-07 143 168 3-14 Warsaw, 02-03 June 2016 LOFAR Workshop

  41. EGNOS monitoring stations – courtesy ESSP Credit: ESSP Warsaw, 02-03 June 2016 LOFAR Workshop

  42. Examples of ionisation structures Scenarios in the Euro-African sector Warsaw, 02-03 June 2016 LOFAR Workshop

  43. Rate of Change of TEC and Scintillation 23 June 2015 23 June 2015 Trondheim (63.42 N, 10.41 E) Ny Alesund (78.93 N, 11.06 E) Warsaw, 02-03 June 2016 LOFAR Workshop

  44. Warsaw, 02-03 June 2016 LOFAR Workshop

  45. Examples of ionisation structures over African low latitudes Warsaw, 02-03 June 2016 LOFAR Workshop

  46. Examples of ionisation structures over Africa Example TEC maps over Africa Credit: MIDAS Warsaw, 02-03 June 2016 LOFAR Workshop

  47. An additional problem at low latitudes: scintillation Warsaw, 02-03 June 2016 LOFAR Workshop

  48. An additional problem: scintillation L1 L2 10 March 2012 PRN31 Warsaw, 02-03 June 2016 LOFAR Workshop

  49. An additional problem: scintillation Warsaw, 02-03 June 2016 LOFAR Workshop

  50. An additional problem: scintillation L2 L1 Warsaw, 02-03 June 2016 LOFAR Workshop