The ionosphere weather service SWACI and its capability for estimating propagation effects of transionospheric radio signals Norbert Jakowski Institute of Communications und Navigation German Aerospace Center Kalkhorstweg 53, D-17235 Neustrelitz, Germany
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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OUTLINE Space Weather Application Center Ionosphere (SWACI) Ground based ionospheric monitoring Space based ionospheric monitoring
Radio wave propagation through the ionosphere Range errors (regular effects)
Space weather impact Storms TIDs Scintillations Impact of solar radio bursts on GPS
Summary & Conclusions LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Ground and space based ionosphere monitoring Monitoring of the Ionosphere by: - GNSS Ground stations 1 CHAMP
2
over a full solar cycle Europe, since 1995 North pole area, since 2001 South pole area, since 2002
3
- LEO Satellites carrying GNSS receivers onboard
1
Radio occultation Topside reconstruction
2 3
CHAMP since 2001 GRACE since 2008
- Non-GNSS based techniques Vertical sounding + GNSS Beacon measurements Space Weather Application Center
SWACI LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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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) 17/05/2002 12:00UT, Elevation > 30° Ground stations Piercing points
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Dual frequency GNSS measurements Total Electron Content
TECV = ∫ ne (h) dh ne(h) e
χ
Receiver
hI RE
Center of Earth
f12 − f 22 ΔP = P2 − P1 = K 2 2 TEC + ε off f1 f 2 ath rayp
s
GNSS
TEC can be derived from dual frequency GNSS measurements.
K d I = 2 ⋅ TEC f Ionospheric range error up to about 100 m Estimation of ionospheric perturbation degree is a practical need Statistics and case studies required
GPS based TEC measurements and mapping in DLR Neustrelitz Europe post proc. (1 day) since 1995 http://www.kn.nz.dlr.de/daily/tec-eu operational (5 min) since 2005 http://swaciweb.dlr.de North Pole post proc. (1 day) since 2002 http://www.kn.nz.dlr.de/daily/tec-np LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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GNSS based TEC – Monitoring
Sample: 16 Stations
TEC monitoring over Europe in DLR Neustrelitz since 1995 based on dual frequency GPS measurements of IGS, EUREF, ascos networks Model assisted technique to calibrate instrumental biases and to reconstruct TEC maps from GPS measurements
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Storm on 29 October 2003 / Polar TEC Polar TEC on 29 October 2003 derived from IGS ground based measurements Map resolution Τime: 10 min Latitude: 2.5 deg Longitude: 7.5 deg
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Beacon satellite measurements in SWACI
Ionospheric traces
Two-station calibration method applied Neustrelitz (DLR)
Wachtberg (FGAN)
Differential carrier phase measurements (150/400MHz) at two stations allow calibration of TEC by two-station calibration method High sensitivity of beacon measurements (gravity wave and ionisation front detection) Snapshot character of measurements (advantage for studying spatial structures) Several satellites can be used (e.g. OSCAR, FORMOSAT) LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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TEC forecast NRT TEC
Forecast 1 h ahead
Quality of forecast
Near real time reconstruction of TEC over Europe (update within 5 min.) Hourly predictions of TEC over Europa Evaluation of the previous prediction by the percentage deviation fom the measurements at the corresponding time. LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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GNSS sounding of the ionosphere onboard a LEO satellite
GPS
GPS Satellite Radio Signal LEO Orbit
CHAMP GRACE LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Space based monitoring onboard CHAMP Topside reconstructions 28 / 29 October 2003
IRO Profiling
night
Automatic retrieval of electron density profiles ( > 70% successfully) More than 300,000 profiles on global
day
15-16 3D reconstructions/day More than 30,000 reconstructions obtained so far
scale retrieved so far in DLR
Data access via http://swaciweb.dlr.de LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Topside ionosphere / plasmasphere sounding Galileo
10 0 -10 -20
Distance / 103 km
20
GPS
-20
-10
0
10
Distance / 103 km
20
2D projection of a typical radio link distribution for a full 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 for the reconstruction of the electron density distribution. Assimilation of the TEC data obtained for one revolution into the PIM model reveals the 2 D electron density distribution close to the CHAMP orbit height. S. Heise, et al., Sounding of the Topside Ionosphere/Plasmasphere Based on GPS Measurements from CHAMP: Initial Results, Geophysical Research Letters, 29, No. 14, 10.1029/2002GL014738, 2002 LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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SWACI Web Portal
http://swaciweb.dlr.de
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Radio wave propagation through the ionosphere Electron density 1,2 m 2,7 m
100 200 300
Height / km
1,1 m
Ionosphere LoS
ρ
Night
Ray path
s
Day
f2 f1
f1 > f2
Refraction
Ionosphere causes • • •
Signal delay Fluctuations of signal strength Rotation of Polarisation plane
All radio systems operating at frequencies < 10 GHz are concerned LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Radio wave propagation Optical path length (L) along ray path from satellite to receiver
L = ∫ nds
LoS
n refractive index ds ray path element
ρ Ray path
s
Geometric path length or true range ρ
ρ = L +
R
∫ (1 − n) ds
− ΔsB
S
phase delay
excess path length
f1> f2 f2
f1 Refraction
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Radio wave propagation - Refractive index - 1 Refractive index n of the ionosphere (Appleton-Hartree formula)
n2 = 1 −
X=
Y =
fp f
2
fg f
2 X (1 − X ) 2 (1 − X ) − Y T2 ± [ Y T4 + 4 (1 − X ) 2 Y L2 ]1 / 2 f p = e 2 n e /( 4 π 2 m e ε 0 )
Plasma frequency < 30 MHz
f g = eB /( 2 π m e )
Gyro frequency ≈ 1.4 MHz
Y T = Y sin Θ
Y L = Y cos Θ
me: electron mass, ε0: free space permittivity, ne: electron density, B: magnetic induction, f : signal frequency, Θ : angle between ray direction and B field vector +/- signs are related to ordinary / extra-ordinary waves LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Radio wave propagation - Refractive index - 2 n = 1 −
Phase refractive index
n
gr
= n + f ⋅
dn df
Group refractive index
f
2 p
2 f
2
±
f
n
gr
= 1 +
2 f
2
3
Second order term
2 p
f g cos Θ 2 f
First order term
f
2 p
m
f
2 p
f g cos Θ f
3
−
f
4 p
8 f
4
Third order term
+
3 f 8 f
4 p 4
The ionosphere is a dispersive and non-isotropic propagation medium. The ionospheric impact becomes smaller with increasing frequency.
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Phase delay Phase delay: R
dI =
(1 ) (2) (3) n ds d d d − = + + = ( 1 ) I I I ∫ S
p q + f 2 2f
3
+
u 3f
4
R
p = 40.3 ∫ ne ds = 40.3 ⋅ TEC S
Total electron content R
q = 2.26 ⋅1012 ∫ B cos Θ ⋅ ne ds S
q ≈ 2.26 ⋅1012 ⋅ B cos Θ ⋅ TEC R
u = 2437 ∫ n e2 ds S
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Ionospheric Range Error - 1st order TEC
Because the ranging error is directly proportional to TEC, there is a close relationship to the ionospheric behaviour. Three correction options for single frequency users
Elevation: 10 °
0
d
(1) I
=
K f2
10 20 30 GPS (L1) Range error (m)
∫ ne ds =
K ⋅ TEC 2 f
40 m
IRE may be corrected by a wellqualified ionospheric model IRE may be corrected by using vertical TEC-maps that enable the extraction of specific correction information needed by a single frequency user (EGNOS) Extraction of 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 371-390,1996
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Ionospheric Range Error – 2nd order Anisotropy of the ionosphere due to the geomagnetic field B
ε: 10° ε: 30° ε: 60°
TECV: 100 TECU ε: elevation angle
B ΦRx: 51° N, λTx: 10° E
Ionospheric 2nd order errors are usually ignored in the measurement praxis (< 20 cm).
d
(2) I
KF = 3 f
∫ B cos Θ ⋅ n ds e
Hoque,M.M., N. Jakowski, Mitigation of higher order ionospheric effects on GNSS users in Europe, GPS Solutions, DOI 10.1007/s10291-007-0069-5, 2007 Hoque, M. M., N. Jakowski, Estimate of higher order ionospheric errors in GNSS positioning, Radio Science, 2008 LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Solar Flux Index F10.7cm
Solar radiation impact on the ionosphere 300
Solar FluxRadio Index F10.7cm Solar Flux
Index F10.7cm
Long-term variation 11- years cycle
Mid-term variation 200
27- days rotation period Solar wind and CME‘s
Short-term variation
100
Solar eruptions (Flares)
Electron ContentContent Total Electron 80 Total 50°N; 15°E 13UT
60
50°N; 15°E 13:00 UT
12
8 40
20
0
4
Ionospheric Range Error/ m
Total Electron Content/ TECU
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Year
DLR 0 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Year
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Solar flare induced storm on 28 October 2003 Strong Solar Flare was observed on 28 October 2003 at 11:05 UT Total solar irradiation enhances within a few minutes by 267 ppm Rapid and strong increase of TEC at all GPS measurements (range error up to 3.5 m)
TECr / TECu
Number of usable GPS measurements dropped down from 30 to 7
Time UT/ hrs.
Geographic Latitude / °N LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Magnetosphere
Das ionospheric weather is strongly coupled with processes in the magnetosphere LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Ionospheric perturbations on 29 / 30 October 2003
IMF / nT
Numerous perturbations in Com/Nav Systems in Europe and in the USA Close correlation of TEC behaviour with the southward component of the IMF
UNPERTURBED
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Latitude / °N
Propagation of TIDs during ionospheric storms
Universal Time / hrs
TIDs pattern on 23 May 2002 (v SW≈ 800 m/s)
Wavelike propagation of disturbances during the storm on 20 November 2002 Ionosphärische ≈ 800 m/s) observed (southward propagation, speed Störungsprozesse Knowledge of direction and speed of perturbation fronts enables short term über Europa forecast Storm related TIDs: scale length ≈ 2000km, period ≈60min, speed ≈ 680m/s LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Radio scintillations in L-band Plasma turbulences • •
High Latitudes Low latitudes
Turbulences of Plasma density Jicamarca, Peru
⎛ I2 − I S4 = ⎜ 2 ⎜ I ⎝
2
1/ 2
Fluctuations of
⎞ ⎟ Signal strength ⎟ ⎠
Loss of P1, P2, L1, L2 GPS phases in a dual frequency GPS receiver requires safety concept to solve the positioning and navigation tasks by single frequency use only, complete loss also observed LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Scintillation characteristics Amplitude spectrum of scintillation event on L1 signal
Occurrence Probability /%
~ f -3
Occurrence probability of S4 > S4 cutoff
Solar Radio Flux F10.7 80.0
73.1
Left hand side: PRN 25 amplitude spectrum during scintillation Right hand side: Occurrence probability of S4 > S4cutoff measured in Bandung in 2006 and 2007 LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Safety of Life application - Aviation GPS signal amplitude
05.04.2006
Loss of signal
SoL applications require high integrity, continuity and availability of the signals Service must be robust to severe or worst case ionospheric conditions Ground based augmentation systems require ¾ ¾
Definition of an ionospheric ‘threat model’ (worst case) Detection of ionospheric perturbations (GBAS/external services)
Ionosphere ‚Threat model‘
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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Impact of Solar Radio Bursts on GPS Receivers December 6, 2006
Solar Radio Burst
Effect on GPS Receivers Source: P. Doherty
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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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 Reference Station (CORS) networks. The red markers receivers that were tracking fewer than 4 GPS satellites during the peak of 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, 24/25 June 2009, Potsdam, Germany
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Summary SWACI provides regular ionosphere data service (e.g. ground based TEC over Europe 5 min update)
Radio systems operating at frequencies <10 GHz should take into account ionospheric impact High precision ranging requires the mitigation of higher order refraction effects (bending, Faraday rotation) Small scale ionospheric irregularities may cause loss of lock in GNSS Solar radio bursts may seriously affect GNSS signals in the L- band
LOFAR Workshop, 24/25 June 2009, Potsdam, Germany
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