Swarm, Irregularities and Scintillations, RIM - PDF Document

Presentation Transcript

  1. Swarm, Irregularities and Scintillations, RIM Stephan Buchert, Sharon Aol and Thomas Nilsson IRF Seminar 2018-10-03

  2. Irregularities and Scintillations I density irregularities disturb the on-board GPS (Buchert et al., 2015; Xiong et al., 2016, 2018), I in severe cases (a few) data get lost; I the by far most affected region is ±20◦mag. lat. ∼18–20 MLT; I also high latitudes are affected, southern hemisphere more than northern (?).

  3. How about at the ground? Practically and commercially the more important region: https://www.trimble.com/Positioning-Services/Ionosphere-Scintillation-map.aspx

  4. IPS and radio occultations I interplanetary scintillations are used to study solar wind properties; I occultations in planetary missions give density/temperature/humidity profiles; I Swarm↔ground receiver has the opportunity to measure both, irregularities and scintillations I to better understand their relation; I previous studies at VHF frequencies (strong scintillation effects), I this is the first attempt (?) at GNSS L1 band.

  5. GNSS frequencies, SCINDA I GPS (> 23 satellites) and Galileo (30 sat’s) transmit all on the same band (1575 GHz) I different PRN (pseudo random noise) codes; I similar techniques (MIMO) in mobile phone networks (>4g); I in (advanced) LAN routers; I in phased array radars like MAARSY (Andoya) and future EISCAT_3D.

  6. SCINDA S4 index I (SCINtillation Decision Aid) network established by the US AFRL; I ? stations worldwide measure TEC (and ROTI) using L1 and L2 I and the S4 index characterizing amplitude scintillations at L1: p hI2i − hIi2 hIi S4 = I I signal intensity; I relative standard deviation S4 = 1: noise intensity same as signal; I standard resolution is 1 min. I S4 does not capture phase scintillations; I on-board: S4 ? 1, mainly phase scints; I ground: amplitude near the equator, phase at high latitudes.

  7. GPS SCINDA in Mbarara, Uganda geod. latitude −0.6◦, magnetic latitude ≈ −10◦, height above sea 1473 m;

  8. How relevant are Swarm irregularity data for ground scintillations at L1? Fresnel (physicist in optics, 1788-1827) zone √2λz; I Fresnel scale f = I wavelength λ = 20 cm at L1 frequency; I distance z =460–700 km for Swarm altitude and elevation > 30◦; I ⇒ f ∼430–560 m; I Swarm sampling of Ne at 2 Hz (probes) and 16 Hz (faceplate); I orbital speed ≈ 7.6 kms−1gives a spatial resolution of ≈ 4 km (probes) and ≈ 500 m (faceplate); I Swarm samples not quite fast enough.

  9. Irregularities by Swarm relevant for ground scintillations at L1? I also irregularities larger than the Fresnel scale cause significant amplitude fluctuations; I irregularities are caused by turbulence with non-linear decay to smaller scales; I we argue also that the anisotropy of irregularities is significant: I at 10s of m scales irregularities are “almost perfectly aligned with the geomagnetic field” (Hysell and Farley, 1996), I Swarm samples at small angles with respect to~B I owing to polar orbit; I GNSS signal paths are typically more ⊥ to~B; I → Swarm effectively samples smaller scales than vorb· tsample

  10. Passes over East Africa 2015-03-10, Asc 2015-06-17, Desc SwarmA SwarmC SwarmA SwarmC (a) (a) 12 12 log10(Ne/m³) log10(Ne/m³) 11 11 10 10 9 9 1.0 1.0 (b) (b) dNe[× 10¹²m ³] dNe[× 10¹²m ³] 0.5 0.5 0.0 0.0 -0.5 -0.5 -1.0 6.0 -1.0 6.0 std(dNe)[×10¹¹m ³] std(dNe)[×10¹¹m ³] (c) (c) 4.0 4.0 2.0 2.0 0.0 0.0 20 10 0 10 33.8 35.2 18.04 20 33.9 35.3 18.07 30 34.0 35.4 18.09 20 10 0 10 27.2 28.6 21.32 20 27.3 28.7 21.35 30 27.4 28.8 21.38 QLat (°) Lon-A (°) Lon-C (°) UT (hrs) QLat (°) Lon-A (°) Lon-C (°) UT (hrs) 33.5 34.9 17.54 33.6 35.0 17.57 33.7 35.1 18.00 26.9 28.3 21.23 27.0 28.4 21.26 27.1 28.5 21.29 2015-07-03, Desc 2016-04-18, Desc SwarmA SwarmC SwarmA SwarmC (a) (a) 12 12 log10(Ne/m³) log10(Ne/m³) 11 11 10 10 9 9 1.0 1.0 (b) (b) dNe[× 10¹²m ³] dNe[× 10¹²m ³] 0.5 0.5 0.0 0.0 -0.5 -0.5 -1.0 6.0 -1.0 6.0 std(dNe)[×10¹¹m ³] std(dNe)[×10¹¹m ³] (c) (c) 4.0 4.0 2.0 2.0 0.0 0.0 20 10 0 10 28.2 29.6 20.02 20 28.3 29.7 20.05 30 28.4 29.8 20.06 20 10 0 10 27.1 28.5 18.03 20 27.2 28.6 18.06 30 27.3 28.7 18.09 QLat (°) Lon-A (°) Lon-C (°) UT (hrs) QLat (°) Lon-A (°) Lon-C (°) UT (hrs) 27.9 29.3 19.53 28.0 29.4 19.56 28.1 29.5 19.59 26.8 28.2 17.54 26.9 28.3 17.57 27.0 28.4 18.00 I varying large scale structure, I which is often different between Swarm A and C ≈ 140 km apart; I irregularity criterium: I moving window of 15 s or 31 samples to get residuals dNe, I absolute stdev(dNe) > 1010m−3

  11. Airglow of typical large scale structure: inverted “C”

  12. Looking horizontally 2015-07-03 0.8 12.0 SwarmA SwarmC 14 16 19 27 31 32 0.6 11.5 (a) (a) (a) (a) (a) (a) log10(Ne/m³) 0.4 11.0 S4 0.2 10.5 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 0.0 10.0 20 15 10 5 0 5 10 15 20 25 30 Geographic Latitude (Degrees) 0.8 12.0 SwarmA SwarmC 14 16 19 27 31 32 0.6 11.5 (b) (b) (b) (b) (b) (b) log10(Ne/m³) 0.4 11.0 S4 0.2 10.5 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 19:54 UT-20:04 UT(21:52 LT) 0.0 10.0 26 27 28 29 30 31 32 33 34 35 Geographic Longitude (Degrees) I latitude and longitude must, within limits, match

  13. Looking from above 30 0.6 30 0.6 2015-07-25 20:05 UT-20:16 UT(22:05 LT) SwarmA SwarmC std(dNe)> 1×10¹ m ³ SwarmB std(dNe)> 1×10¹ m ³ 2015-07-03 19:54UT -20:04 UT(21:52LT) 0.5 0.5 20 20 Geographic latitude (Degrees) Geographic latitude (Degrees) 0.4 0.4 10 10 22.05 LT 21.52 LT 21.52 LT 0.3 0.3 21.52 LT S4 S4 21.52 LT MBAR PRN27 MBAR PRN11 0 0 0.2 0.2 PRN32 PRN16 PRN19 10 10 0.1 0.1 20 0.0 20 0.0 26 27 28 29 30 31 32 26 27 28 29 30 31 32 Geographic longitude (Degrees) Geographic longitude (Degrees)

  14. Statistics 60 Swarm A Swarm C Swarm B 50 Percentage Occurrence 40 30 20 10 0 Irregularities and scintillation No irregularities and no scintillation Irregularities but no scintillation No irregularities but scintillation occurs

  15. Can we estimate S4 from the Swarm Nedata? Yes, using the phase screen model (Rhino, 1979): ? ? Γ[(2.5 − ν)/2] S42= (reλ)2LsecθCsZν−0.5 F 2π0.5Γ[(ν + 0.5)/2](ν − 0.5) eiq2ν−2 Cs = 8π3/2h∆N2 Z = λZRsecθ/4π Fresnel zone parameter, ZR= zzs/z + zs, z distance to phase screen, zs distance to the GPS satellite, re classical electron radius, θ zenith angle of signal path, L irregular layer thickness (200 km), qo = 2π/Lo outer-scale cut-off number, Lo irregularity outer scale, p = 2ν − 1 spectral slope. Γ(ν + 0.5)/Γ(ν − 1) turbulence strength, o

  16. 16 Hz data and spectral slopes Swarm A, 2015-07-03 Swarm C, 2015-07-03 Swarm B, 2015-07-25 log10(Ne/m³) log10(Ne/m³) log10(Ne/m³) 11.7 11.4 11.65 11.6 11.3 11.60 11.5 11.2 11.55 1e11 1e10 1e11 1.0 5.0 0.5 0.5 dNe/m³ dNe/m³ dNe/m³ 2.5 0.0 0.0 0.0 2.5 0.5 0.5 5.0 19:55:19 19:55:21 19:55:23 19:55:25 19:55:27 19:55:32 19:55:34 19:55:36 19:55:38 20:06:08 20:06:10 20:06:12 20:06:14 UT (HH:MM:SS) UT (HH:MM:SS) UT (HH:MM:SS) 1023 1021 1021 1022 1020 PSD (km/rad) PSD (km/rad) PSD (km/rad) 1020 1021 1019 p=2.56(0.15) 1020 1019 1018 1019 1017 p=1.83(0.15) 1018 p=2.34(0.16) 1018 1016 1 1 1 100 100 100 10 10 10 k (rad/km) k (rad/km) k (rad/km)

  17. Statistics of spectral slopes p

  18. Modeled S4 SwarmA, 2015-07-03 SwarmC, 2015-07-03 11.5 11.5 log10(Ne/m³) log10(Ne/m³) 11.0 11.0 10.5 std(dNe)[×10¹¹m ³] std(dNe)[×10¹¹m ³] 1.0 1.0 0.5 0.5 0.0 17.5 0.0 18 log10(Cs) log10(Cs) 15.0 16 1.0 1 S4 S4 0.5 0 0.0 UT (HH:MM) Qlat(°) Lon (°) UT (HH:MM) Qlat(°) Lon (°) 19.57 -15 28.10 19.58 -10 28.15 19.59 -5 28.20 20.00 0 28.25 20.01 5 28.30 20.02 10 28.35 19.57 -15 29.55 19.58 -10 29.60 19.59 -5 29.65 20.00 0 29.70 20.01 5 29.75 20.02 10 29.80 SwarmB, 2015-07-25 11.5 log10(Ne/m³) 11.0 std(dNe)[×10¹¹m ³] 1.0 0.5 0.0 18 log10(Cs) 16 14 0.4 0.2 S4 0.0 UT (HH:MM) Qlat(°) Lon (°) 20.06 -15 28.7 20.07 -10 28.8 20.08 -5 28.9 20.09 0 29.0 20.10 5 29.1 20.11 10 29.2

  19. Observed S4 2015-07-03 2015-07-03 1.0 1.0 16 19 0.8 0.8 0.6 0.6 S4 S4 0.4 0.4 0.2 0.2 0.0 0.0 17.0 17.5 18.0 18.5 19.0 19.5 20.0 19.0 19.5 20.0 20.5 21.0 UT (Hours) 2015-07-03 21.5 22.0 22.5 23.0 UT (Hours) 2015-07-03 1.0 1.0 27 32 0.8 0.8 0.6 0.6 S4 S4 0.4 0.4 0.2 0.2 0.0 0.0 18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 18.0 18.5 19.0 UT (Hours) 19.5 20.0 20.5 UT (Hours)

  20. Conclusions I majority of passes: either neither scintillations nor irregularities or both scintillations and irregularities are observed; I counter examples are probably because of intermittent and spatially limited presence of irregularities. I Swarm A and C, at lower altitude (460 km vs 510 km) seem to be slightly more relevant than Swarm B; I using the phase screen model the ground S4 can be estimated from the Swarm Ne variations, with reasonable results.

  21. Future Plani: Swarm RIM I there are IRI (International Reference Ionosphere) and other empirical models for Ne (and Te ...); I quite a number of empirical models for scintillations/S4 (not really global, spatially limited ground data); I no empirical model yet for δNe, the density variations; I we have the Swarm LP/FP data for now 4.5 years; I so we suggested a Swarm RIM (Reference Irregularity Model, a la IRI, but 2d); I → ESA EO ITT (hopefully); I joint application with the DLR Institut für Kommunikation und Navigation in Neustrelitz (space weather institute of the German Space Agency).

  22. Observed S4 2015-07-03 2015-07-03 1.0 1.0 16 19 0.8 0.8 0.6 0.6 S4 S4 0.4 0.4 0.2 0.2 0.0 0.0 17.0 17.5 18.0 18.5 19.0 19.5 20.0 19.0 19.5 20.0 20.5 21.0 UT (Hours) 2015-07-03 21.5 22.0 22.5 23.0 UT (Hours) 2015-07-03 1.0 1.0 27 32 0.8 0.8 0.6 0.6 S4 S4 0.4 0.4 0.2 0.2 0.0 0.0 18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 18.0 18.5 19.0 UT (Hours) 19.5 20.0 20.5 UT (Hours)