The ionosphere weather service SWACI and its capability for estimating propagation effects of transionospheric radio signals

Transcription

1 The ionosphere weather service SWACI and its capability or estimating propagation eects o transionospheric radio signals Norbert Jakowski Institute o Communications und Navigation German Aerospace Center Kalkhorstweg 53, D-1735 Neustrelitz, Germany LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 1

2 OUTLINE Space Weather Application Center Ionosphere (SWACI) Ground based ionospheric monitoring Space based ionospheric monitoring Radio wave propagation through the ionosphere Range errors (regular eects) Space weather impact Storms TIDs Scintillations Impact o solar radio bursts on GPS Summary & Conclusions LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page

3 Ground and space based ionosphere monitoring CHAMP 3 Monitoring o the Ionosphere by: - GNSS Ground stations 1 over a ull solar cycle Europe, since 1995 North pole area, since 001 South pole area, since 00 1 Space Weather Application Center SWACI - LEO Satellites carrying GNSS receivers onboard Radio occultation Topside reconstruction CHAMP since 001 GRACE since Non-GNSS based techniques Vertical sounding + GNSS Beacon measurements 3 LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 3

4 Data basis - ground based measurements GNSS- Networks used in SWACI SAPOS ascos IGS (since 1995) EUREF GNSS data provision via NTRIPtechnology in 1s streaming mode SWACI I (30 GPS stations) SWACI II (300 GPS Stations) New Monitoring concept GPS Data coverage (example) 17/05/00 1:00UT, Elevation > 30 Ground stations Piercing points LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 4

5 Dual requency GNSS measurements Total Electron Content TECV = ne ( h) Receiver R E n e (h) Center o Earth e dh χ hi raypath s d I K = GNSS TEC Ionospheric range error up to about 100 m Estimation o ionospheric perturbation degree is a practical need Statistics and case studies required Δ 1 P = P P1 = K TEC+ ε TEC can be derived rom dual requency GNSS measurements. 1 o GPS based TEC measurements and mapping in DLR Neustrelitz Europe post proc. (1 day) since operational (5 min) since North Pole post proc. (1 day) since 00 LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 5

6 GNSS based TEC Monitoring Sample: 16 Stations TEC monitoring over Europe in DLR Neustrelitz since 1995 based on dual requency GPS measurements o IGS, EUREF, ascos networks Model assisted technique to calibrate instrumental biases and to reconstruct TEC maps rom GPS measurements LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 6

7 Storm on 9 October 003 / Polar TEC Polar TEC on 9 October 003 derived rom IGS ground based measurements Map resolution Τime: 10 min Latitude:.5 deg Longitude: 7.5 deg LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 7

8 Beacon satellite measurements in SWACI Ionospheric traces Neustrelitz (DLR) Wachtberg (FGAN) Two-station calibration method applied Dierential carrier phase measurements (150/400MHz) at two stations allow calibration o TEC by two-station calibration method High sensitivity o beacon measurements (gravity wave and ionisation ront detection) Snapshot character o measurements (advantage or studying spatial structures) Several satellites can be used (e.g. OSCAR, FORMOSAT) LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 8

9 TEC orecast NRT TEC Forecast 1 h ahead Quality o orecast Near real time reconstruction o TEC over Europe (update within 5 min.) Hourly predictions o TEC over Europa Evaluation o the previous prediction by the percentage deviation om the measurements at the corresponding time. LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 9

10 GNSS sounding o the ionosphere onboard a LEO satellite GPS GPS Satellite Radio Signal LEO Orbit CHAMP GRACE LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 10

11 Space based monitoring onboard CHAMP Topside reconstructions 8 / 9 October 003 IRO Proiling night day Automatic retrieval o electron density proiles ( > 70% successully) More than 300,000 proiles on global scale retrieved so ar in DLR D reconstructions/day More than 30,000 reconstructions obtained so ar Data access via LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 11

12 Topside ionosphere / plasmasphere sounding Distance / 10 3 km GPS Galileo Distance / 10 3 km D projection o a typical radio link distribution or a ull CHAMP revolution within 93 minutes. The GPS navigation data measured onboard CHAMP (0.1 Hz sampled) provide up to about 3000 measurements during one revolution usable or the reconstruction o the electron density distribution. Assimilation o the TEC data obtained or one revolution into the PIM model reveals the D electron density distribution close to the CHAMP orbit height. S. Heise, et al., Sounding o the Topside Ionosphere/Plasmasphere Based on GPS Measurements rom CHAMP: Initial Results, Geophysical Research Letters, 9, No. 14, /00GL014738, 00 LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 1

13 SWACI Web Portal LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 13

14 Radio wave propagation through the ionosphere Electron density 1, m,7 m 1,1 m Height / km Night Ionosphere Day ρ LoS s Ray path > Reraction Ionosphere causes Signal delay Fluctuations o signal strength Rotation o Polarisation plane All radio systems operating at requencies < 10 GHz are concerned LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 14

15 Radio wave propagation Opticalpathlength(L) along ray path rom satellite to receiver L = nds n reractive index ds ray path element Geometric path length or true range ρ LoS ρ s Ray path ρ = L + (1 n) R S ds Δs B 1 1 > phase delay excess path length Reraction LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 15

16 Radio wave propagation - Reractive index - 1 Reractive index n o the ionosphere (Appleton-Hartree ormula) n = 1 (1 X ) Y T X (1 ± [ Y 4 T X ) + 4 (1 X ) Y L ] 1 / X Y = = p g = p g Y T = e eb n e = Y sin /( 4π m eε 0 ) /( πm e ) Θ Y L Plasma requency < 30 MHz Gyro requency 1.4 MHz = Y cos Θ m e : electron mass, ε 0 : ree space permittivity, n e : electron density, B: magnetic induction, : signal requency, Θ : angle between ray direction and B ield vector +/- signs are related to ordinary / extra-ordinary waves LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 16

17 Radio wave propagation - Reractive index - Phase reractive index n = 1 p ± p g cos 3 Θ 8 4 p 4 n gr = n + dn d First order term Second order term Third order term Group reractive index n p p g cos Θ gr = 1 + m p 4 The ionosphere is a dispersive and non-isotropic propagation medium. The ionospheric impact becomes smaller with increasing requency. LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 17

18 Phase delay Phase delay: d R (1) ( ) ( 3 ) p q I = (1 n ) ds = d I + d I + d I = S 3 u 4 p R = 40.3 n ds = TEC S q = q e.6 10 Total electron content R S 1 Bcos Θ n ds e BcosΘ TEC u = 437 R S n e ds LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 18

19 Ionospheric Range Error - 1 st order Elevation: m GPS (L1) Range error (m) d (1) I K K = neds = TEC TEC Because the ranging error is directly proportional to TEC, there is a close relationship to the ionospheric behaviour. Three correction options or single requency users IRE may be corrected by a wellqualiied ionospheric model IRE may be corrected by using vertical TEC-maps that enable the extraction o speciic correction inormation needed by a single requency user (EGNOS) Extraction o TEC by combining Code and carrier phase measurements Jakowski, N., TEC Monitoring by Using Satellite Positioning Systems, Modern Ionospheric Science, (Eds. H.Kohl, R. Rüster, K. Schlegel), EGS, Katlenburg-Lindau, ProduServ GmbH Verlagsservice, Berlin, pp ,1996 LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 19

20 Ionospheric Range Error nd order Anisotropy o the ionosphere due to the geomagnetic ield B TEC V : 100 TECU ε: elevation angle ε: 10 ε: 30 ε: 60 B Φ Rx : 51 N, λ Tx : 10 E Ionospheric nd order errors are usually ignored in the measurement praxis (< 0 cm). d ( ) I K F = B cos Θ neds 3 Hoque,M.M., N. Jakowski, Mitigation o higher order ionospheric eects on GNSS users in Europe, GPS Solutions, DOI /s , 007 Hoque, M. M., N. Jakowski, Estimate o higher order ionospheric errors in GNSS positioning, Radio Science, 008 LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 0

21 Solar radiation impact on the ionosphere Solar Flux Index F 10.7cm 300 Solar Radio Flux Index F10.7cm Solar Flux Index F 10.7cm Year Long-term variation 11- years cycle Mid-term variation 7- days rotation period Solar wind and CME s Short-term variation Solar eruptions (Flares) Total Electron Content/ TECU Total Electron Content Total Electron Content 50 N; 15 E 13UT 50 N; 15 E 13:00 UT Ionospheric Range Error/ m DLR Year 0 LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 1

22 Solar lare induced storm on 8 October 003 Strong Solar Flare was observed on 8 October 003 at 11:05 UT Total solar irradiation enhances within a ew minutes by 67 ppm Rapid and strong increase o TEC at all GPS measurements (range error up to 3.5 m) Number o usable GPS measurements dropped down rom 30 to 7 TECr / TECu Time UT/ hrs. Geographic Latitude / N LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page

23 Magnetosphere Das ionospheric weather is strongly coupled with processes in the magnetosphere LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 3

24 Ionospheric perturbations on 9 / 30 October 003 Numerous perturbations in Com/Nav Systems in Europe and in the USA IMF / nt Close correlation o TEC behaviour with the southward component o the IMF UNPERTURBED LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 4

25 Propagation o TIDs during ionospheric storms Latitude / N Universal Time / hrs TIDs pattern on 3 May 00 (v SW 800 m/s) Wavelike propagation o disturbances during the storm on 0 November 00 observed (southward propagation, speed Ionosphärische 800 m/s) Störungsprozesse Knowledge o direction and speed o perturbation ronts enables short term über Europa orecast Storm related TIDs: scale length 000km, period 60min, speed 680m/s LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 5

26 Radio scintillations in L-band Plasma turbulences High Latitudes Low latitudes Jicamarca, Peru Turbulences o Plasma density S = I 4 I I 1/ Fluctuations o Signal strength Loss o P1, P, L1, L GPS phases in a dual requency GPS receiver requires saety concept to solve the positioning and navigation tasks by single requency use only, complete loss also observed LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 6

27 Scintillation characteristics Amplitude spectrum o scintillation event on L1 signal Occurrence probability o S4 > S4 cuto Occurrence Probability /% Solar Radio Flux F10.7 ~ Let hand side: PRN 5 amplitude spectrum during scintillation Right hand side: Occurrence probability o S4 > S4 cuto measured in Bandung in 006 and 007 LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 7

28 Saety o Lie application - Aviation GPS signal amplitude Loss o signal SoL applications require high integrity, continuity and availability o the signals Service must be robust to severe or worst case ionospheric conditions Ground based augmentation systems require Deinition o an ionospheric threat model (worst case) Detection o ionospheric perturbations (GBAS/external services) Ionosphere Threat model LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 8

29 Impact o Solar Radio Bursts on GPS Receivers December 6, 006 Solar Radio Burst Eect on GPS Receivers Source: P. Doherty LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 9

30 GPS receivers impacted by Solar Radio Burst All Receivers Receivers impacted by the solar radio burst The yellow markers indicate GPS receivers in the International Global Navigation Satellite System Service (IGS) and the Continuously Operating Reerence Station (CORS) networks. The red markers receivers that were tracking ewer than 4 GPS satellites during the peak o the solar radio burst. For a navigation solution, the GPS receiver needs to be tracking 4 or more GPS satellites. Source: P. Doherty LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 30

31 Summary SWACI provides regular ionosphere data service (e.g. ground based TEC over Europe 5 min update) Radio systems operating at requencies <10 GHz should take into account ionospheric impact High precision ranging requires the mitigation o higher order reraction eects (bending, Faraday rotation) Small scale ionospheric irregularities may cause loss o lock in GNSS Solar radio bursts may seriously aect GNSS signals in the L- band LOFAR Workshop, 4/5 June 009, Potsdam, Germany Page 31