Space weather and impact on GNSS

1

Presentation to ESESA workshop. 2 – 3 March 2011. Somerset-west.

Dr Ben Opperman. Hermanus Magnetic ObservatoryBen.Opperman@hmo.ac.za

www.spaceweather.co.zawww.hmo.ac.za

Hermanus Magnetic Observatory (Est. 1932)

Buildings on UCT campus which housed the fist magnetic observatory instruments.

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First permanent magnetic observatory in South Africa established on UCT campus – moved to Hermanus in 1941.

The HMO’s first buildings on the outskirts of Hermanus in 1941

Hermanus Magnetic Observatory

The Hermanus Magnetic Observatory (HMO) is a research facility of the National Research Foundation of South Africa and is situated in the Western Cape. It forms part of the worldwide network of magnetic observatories, which monitor and model variations of the Earth’s magnetic field. The HMO’s primary research focus is Space Physics and is to be incorporated in the South African National Space Agency

The mission of the ISES is to encourage and facilitate near-real-time international monitoring and prediction of the space environment by the rapid exchange of space environment information to assist users to reduce the impact of space weather on activities of human interest.

International Space Environment Service

http://spaceweather.hmo.ac.za

10 Oct 20084

http://spaceweather.hmo.ac.za

HERMANUS

Solar-terrestrial environment

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Near –Earth space environment

Ionosphere:

100 - 2000km

6

Plasmasphere:

2 000 - 35 000 km

Plasma causes group delay, phase

advance

Space weather hazards

7

ESKOM Transformer damage

10 Oct 2008 8

Photos: CT Gaunt

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Solar cycle based on number of sunspotsSunspots are concentrations of magnetic flux associated with flares on the sun. They appear dark because they are cooler than the surrounding. The number of sunspots increase and decrease over an 11 year cycle. The peak of the next solar cycle, cycle

24, is currently predicted to be at about 2013.

Solar Cycle & selected data periods

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11-year sun spot cycle

11

Maunder Minimum 1645-1715

14-15 Feb 2011 geomagnetic storm

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GOES observing EM shock from solar X-ray flare

13

ACE Solar wind measurements

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Magnetograms illustrating disturbed magnetosphere

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Complex sunspot activity

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Solar magnetograms

17

SDO HD solar images

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SDO X-ray images

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Aurora: Earliest awareness of space weather

20

Colours produced by ionized oxygen and nitrogen in the upper atmosphere 80-112 km

Satellite computer memory upset over SAMA

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Space science using GNSS

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Global TEC variation (IGS)

23Global Ionosphere Map (GIM)

GPS relevance to Space Physics:Ionospheric structure & dynamics

Ionospheric imaging using GPS data provides the means to create large-scale, time-varying two-dimensional maps of electron concentration in the ionosphere with a time resolution of seconds. This permits studies of:

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permits studies of:

• Temporal and spatial distribution of ionization in the ionosphere• Effects of geomagnetic storms on ionosphere-plasmasphere plasma exchange dynamics• Mechanisms causing ionospheric scintillation

Relevance of local GPS derived TEC mapping

� Applications:- Space Physics Research (Ionospheric dynamics)- Radio Astronomy (SKA, KAT)

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- Radio Astronomy (SKA, KAT)- Precision GPS applications (Surveying, SBAS, GIS

(DGPS) )

Conventional Ionospheric Measurements

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Ionosonde

Ionosonde measurements

1

0

20 sec.rad

21

−

=

m

enp ε

ω

27

Grahamstown ionosonde

28

GPS and Ionosonde Network

-26

-24

-22Madimbo

Mafikeng Nelspruit

Pretoria

Thohoyandu

Ionosondes and CDSM GPS receivers in South Africa

NAMIBIA

BOTSWANA

Tsumeb

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15 20 25 30 35-36

-34

-32

-30

-28

Longitude (Deg)

Latit

ude

(Deg

)

Grahamstown

LouisvaleBloemfontein

Durban

PortElizabeth

Springbok

Cape Town

Upington

Hermanus

Ionosonde limitations

� Cost: R2.3 m per station + running cost� Spacing: 1000 km between stations� None elsewhere in Southern Africa

Data frequently not available or delayed

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� Data frequently not available or delayed� Only measures bottom-side ionosphere

New Approach: GNSS (GPS)

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Global Positioning System (GPS)

GPS satellite constellation

� 24 satellites� Six orbital planes� Four satellites per

orbital plane� Orbital period 12h

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� Orbital period 12h� Circular orbit height

20185 km� Orbit plane inclination

55o inclination

GPS satellite signals

Two carrier frequencies

L1 = 1.57542 GHz, L2 = 1.2276 GHz

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Dual frequency GPS

Pseudorange

Ionosphere

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Pseudorange

Troposphere

ερρρ +∆+∆+∆+= tcP tropion

GPS Ranging Errors

� Ephemeris data –(1 m) Errors in the transmitted location of the satellite

� Satellite clock —(1 m) Errors in the transmitted clock, including SA

� Ionosphere —( 20 m) Errors in the corrections of pseudorange caused by ionospheric effects

� Troposphere —(1 m) Errors in the corrections of

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� Troposphere —(1 m) Errors in the corrections of pseudorange caused by tropospheric effects

� Multipath —(0.5) Errors caused by reflected signals entering the receiver antenna

� Receiver —( 1 m) Errors in the receiver's measurement of range caused by thermal noise, software accuracy, and inter-channel biases

Code-based pseudorange

( ) ( )S R S RP c t c t t c b bc ctropionρ ρ ρ ε= ∆ = + ∆ + ∆ + ∆ − ∆ + + +

t∆ = measured propagation time using PRN code

c = free - space velocity of light

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ρ = true range

,S Rt tc c∆ ∆ = offsets of satellite and receiver clocks

,S Rb b = satellite and receiver hardware time delays

ε = residual error (multi path interference, random errors etc.)

, tropionρ ρ∆ ∆ = range errors due to ionosphere and troposphere delay

Carrier-phase based pseudorange

( )R SL N c t t Bc ctropionλ ρ ρ ρ λ ε= = − ∆ + ∆ + ∆ − ∆ + +

λ λ λ= carrier wavelength ( = 197 mm, = 207 mm)L1 L2

N = measured number of cycles since phase lock

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ρ = true range

,S Rt tc c∆ ∆ = offsets of satellite and receiver clocks

ε = residual error

, tropionρ ρ∆ ∆ = range errors due to ionosphere and troposphere delay

B = initial phase ambiguity (integer number of cycles)

Total Electron Content (TEC)

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TEC definition

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Total Electron Content (TEC)

Along a given signal path between a Satellite (S) and Receiver (R), the total electron content (TEC) is defined as the line integral of the free electron density:

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( , , , ) .S

N h t dse

Rλ φ= ∫TEC

density:

TEC delay vs frequency

TECc t

αρ ⋅∆ = ∆ =

The Ionosphere is a dispersive medium, i.e. ionospheric refraction (subsequently delay) is frequency-dependent, hence different for L1 and L2 frequencies.

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2TEC

c tion ion f

αρ ⋅∆ = ∆ =

1640.3 10α = ⋅

-2 -1ms TECUionρ∆ = ionospheric range error [m]

TEC = Total electron content [TECU]

f = carrier frequency [Hz]

IPP Coverage of multiple GPS receivers

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HMO Regional TEC Model

� Slant TEC derived from L1, L2 phase observables� Vertical TEC estimated using SHM (10-18 degree, order)

{ }0 0

( , ) [sin( )] sin( ) cos( )N n

nm nm nmn m

TEC P a m b mλ φ φ λ λ= =

= +∑∑

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IRI2005

0 0

Sun-fixed longitude

= geographic latitude

Normalized associated Legendre functions

, desired SHM coefficients

n m

nm

nm nm

P

a b

λφ

= =

=

==

0

5

10

15

20

25

30

35

40T

EC

[TE

C u

nits

]

TEC variation at (21.4E, 30.7S). SKA-Hub South Africa. November 2004

TEC variation at (21.4E, 30.7S). SKA-Hub South Africa. 20 November 2004

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5 10 15 20 25 300

Time [Day of Month]

0 5 10 15 200

5

10

15

20

25

30

35

40

Time [Hour of Day UT]

TE

C [

TE

C u

nits

]

TEC variation at (21.4E, 30.7S). SKA-Hub South Africa. 20 November 2004

Geomagnetic storm 7-8 Nov 2004

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5 10 15 20 25 300

5

10

15

20

25

30

35

40

TE

C [T

EC

uni

ts]

[Day of Month]

7

8

Coverage of Antarctic and South Atlantic Islands GPS and Scintillation Receivers near the South Atlantic Anomaly

HERM

10 Oct 200846

10º elevation IPP coverage, hmF2=350 km

VESLSYOG

DAV1MAW1

CAS1PALMOHI2

KERGEULEN

MARIONGOUG

LPGS

INGV

BOUVET

GPS GPS & ISM

HERM

10 Oct 200847

South Atlantic Ionospheric measurement campaign

10 Oct 200848

http://www.hmo.ac.za

Ionospheric Pierce Points (IPPs) at hourly intervals for all satellite ray paths observed along the route of the SA Agulhas on its first trip to Antarctica during which measurements were made of the ionosphere over the South Atlantic Ocean using a GPS dual frequency receiver. The colours indicate bias-corrected VTEC at the IPPs.

Electron density distribution (x1011 /m3) along longitude =0º at 10:00 UT. Derived by ionospheric tomography using MIDAS from measurements made during the trip of the SA Agulhas to Antarctica on day 7 of the trip. The location of the ship at the time is shown by the red dot on the trajectory. Note the interesting high latitude structure resolved by the inversion.

TECUx1011/m3

Interferometer Array:

HF Radar� Part of SuperDARN network� Measures azimuth, elevation

& doppler of ionospheric reflections

10 Oct 200849

HF Radar Main Antenna Array:

16 beamLog-periodicAimed South

Interferometer Array:dipoles with reflector

� Ionospheric Scintillation Monitor (ISM)

� Antenna: Novatel GPS-533 L1/L2 with choke-ring & radome

� Receiver: Novatel GSV4004B� Owned by HMO� Logging 1 minute data since 25 Dec

2006� Data uploaded daily to HMO via ftp

� 2.5 MB/day

GPS

ISM

10 Oct 200850

10 Oct 200851SANAE ISM 15 August 2007 00:00 to 23:59 UT

Application to

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Study Objectives

� TEC variability� foF2-TEC correlation� Spread-F occurence

-20

-10

0

10

20

Latit

ude

(Deg

)

Magnetic Equator

Crest of equatorial anomaly

Malindi, KenyaFranceville,GabonLibreville,Gabon

Zambia

ReunionThohoyondouSt Helena

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-20 -10 0 10 20 30 40 50 60-60

-50

-40

-30

Longitude (Deg)La

titud

e (D

eg)

90th-precentileauroral oval

Reunion

SKA hub (Northern Cape), Namibia, Botswana, Mozambique, Madagascar, Mauritius, Kenya, Gabon, St Helena

Faraday rotation

� A plane-polarized wave propagating parallel to a magnetic field in a plasma experiences a circular rotation of its plane polarization

3 1 de

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3

2 2 2

1

2 0e

den B dsem cπ ν

Ψ=− ∫ �

Ψ : angle of rotation of Electric vector in radians

Annual TEC variation at SKA Hub: South Africa 2000

Mon

th o

f yea

r

Jun

Jul

Aug

Sep

Oct

Nov

Dec

30

40

50

60

SKA Ionospheric stability study

Annual TEC variation at SKA Hub: South Africa 2004

Mon

th o

f yea

r

Jun

Jul

Aug

Sep

Oct

Nov

Dec

30

40

50

60

55

Hour of day [UT]

Mon

th o

f yea

r

0 2 4 6 8 10 12 14 16 18 20 22 24

Jan

Feb

Mar

Apr

May

Jun

0

10

20

30

SKA-Hub (21.4E, 30.7S).

Diurnal, seasonal and solar cycle TEC variationHour of day [UT]

Mon

th o

f yea

r

0 2 4 6 8 10 12 14 16 18 20 22 24

Jan

Feb

Mar

Apr

May

Jun

0

10

20

30

Gough ROTI during Oct 2003 storm

0

5

10

15

20

25

30

RO

TI

ROTI Observed from Gough Island 28 Oct -3 Nov 2003

-40

-39

-38

-37

-36

Latit

ude

Gough Island ROTI scintillation on 28 Oct 2003

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301 302 303 304 305 306 307 3080

Time [Day of year]

0 3 6 9 12 15 18 21 240

5

10

15

20

25

30

Time [UT hours]

RO

TI

Gough Island ROTI scintillation occurence on 28 Oct 2003

344 346 348 350 352 354 356-45

-44

-43

-42

-41

-40

Longitude [Degrees]

Latit

ude

80o

60o

40o

Gough Island ROTI-PP correlation: 2000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.5

1

1.5

2

2.5

3

3.5x 10

6 Gough Island Ne flux - ROTI correlation. 2000

med

ian

Ne

flux

y = -1285343.7308x + 944214.6793

Corr. Coeff = -0.16849

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

1

2

3

4

5x 10

7 Gough Island Ne Energy - ROTI correlation. 2000

med

ian

Ne

Ene

rgy

y = -20180069.6793x + 14539326.249

Corr. Coeff = -0.18046

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7median ROTI

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7median ROTI

0 0.1 0.2 0.3 0.4 0.5 0.6 0.72

4

6

8

10

12

14

16x 10

5 Gough Island Ni flux - ROTI correlation. 2000

median ROTI

med

ian

Ni f

lux

y = -831297.7918x + 716533.6689

Corr. Coeff = -0.21731

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.5

1

1.5

2x 10

7 Gough Island Ni Energy - ROTI correlation. 2000

median ROTI

med

ian

Ni E

nerg

y

y = -7778107.7668x + 6834202.2617

Corr. Coeff = -0.2132

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Computerised Ionospheric Tomography (CIT)

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MIDAS – high latitude

10 Oct 200859

Computerised Ionosheric Tomography using signals from extended GPS coverage. Polar space weather studies.

Model Ionosphere Inversion

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Images Courtesy of Paul Spencer, Invert, University of Bath

GPS occultation

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Occultation double differencing

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� Hundreds of occultations observed per day

� Occultation event lasts 1-2 minutes

Occultation frequency

63Number of occultation events occurred during 24h for a LEO satellite with i=98 deg and H=600km (http://geodaf.mt.asi.it/html/GPSAtmo/space.html)

LEO augmentation of numerical weather forecasts, climate systems studies

� Global coverage

� High vertical resolution

� Long-term stability

All-weather capability

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� All-weather capability

Acknowledgements

The authors would like to thank

� The Chief Directorate Surveys & Mapping (CDSM) of South Africa for making available the GPS data.

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Thank you