part ii mapping the ionosphere with gps

Civil and Environmental Engineering and Geodetic Science

Part II

MAPPING THE IONOSPHERE WITH GPS

GS894G


References

Wielgosz, P. The impact of ionospheric effects on GPS data reduction, PhD dissertation, UWM, Poland, 2002 (in Polish)Bosy, J, M. Figurski, P. Wielgosz. The strategy of GPS data processing in precise local networks during high solar activity, GPS Solutions, 2003 (in

print)Schaer, S. Mapping and Predicting the Earth's Ionosphere Using the Global Positioning System, PhD thesis, University of Bern, 1999.

Ron Muellerschoen, R. and Powers, E. Errors in GPS due to Satellite C1-P1 Code Biases

Hajj, G. A. et al. (2000): COSMIC GPS Ionospheric Sensing and Space Weather, TAO, Vol. 11, No. 1, pp. 235-272.

http://www.spaceweather.com/

http://www.ips.gov.au/Main.php?CatID=8http://nssdc.gsfc.nasa.gov/space/model/models_home.htmlhttp://www.cx.unibe.ch/aiub/ionosphere.htmlhttp://www.sunspotcycle.com/


• The ionosphere is the part of the upper atmosphere where free electrons occur in sufficient density to have a substantial influence on the propagation of radio frequency electromagnetic waves (such as GPS)

• The ionization depends primarily on the solar activity

• Ionospheric structures and peak densities in the ionosphere vary greatly with time and location, and thus, must be monitored

Introduction to the ionosphere


• The spatial and temporal distributions of ionospheric disturbances, such as storms and Traveling Ionospheric Disturbances (TIDs), are of primary interest in their own scientific context, but they are also of special interest to communication, surveillance and radio-navigation, since they affect the skywave signal channel characteristics.

• Thus, the communication and navigation systems (GPS) relying on trans-ionospheric propagation must be able to account for the effects of the abrupt changes in total electron content (TEC), associated with the storm time disturbance effects, including the occurrence of the ionospheric trough at mid-latitudes.

• Conversely: if the GPS receiver’s location is known, GPS observable may allow to track ionospheric properties

Why do we need to study ionosphere?


• As our dependence on technology in space grows, continuous and global sensing of the Earth’s atmosphere is becoming a technological necessity.

• The awareness of the potentially hazardous effects of space weather on technological systems motivated the creation of the National Space Weather Program (NSWP)

• NSWP places particular emphasis on the need to provide timely, accurate, and reliable space environment observations, specifications, and forecasts

• These requirements are similar to what is already accomplished with a great measure of success in the Numerical Weather Prediction (NWP) – currently exclusively relying on remote sensing techniques.



Accurate specification and forecasting of space weather phenomena is very difficult because it requires:

• accurate modeling of the coupling between the sun, the magnetosphere, the thermosphere, the ionosphere, and the mesosphere,

• continuous, reliable and accurate observations of all of these regions

• the ability to assimilate the data into the models in an optimal and self-consistent manner.

Current challenges

GPS can contribute greatly by providing near real-time, high resolution, global TEC estimates


• Ionization is caused by:

X-ray radiation

ultraviolet radiation

corpuscular radiation from the Sun

Ionospheric structures and peak densities vary with:

time (sunspot cycle, season, local time, i.e., day vs. night)

geographic location (polar, auroral zones, mid-latitudes (lowest ionospheric variability), and equatorial regions (the largest electron content))

certain solar-related ionospheric disturbances

The motion and distribution of the electrons is affected by Earth magnetic field

Electrons move along magnetic lines of force

Thus, electron distribution is described in terms of geomagnetic coordinates

north geomagnetic pole: 79.41 and –71.64 (epoch 1998.5) slowly moving (0.03 and 0.07 per year)


Solar – Earth connection

Influence of the solar wind on earth’s magnetosphere



• Peak values of electron density are encountered in the equatorial region, normally in the early afternoon

• Region with very high electron concentration at geomagnetic latitudes of about +/- 20 deg during early evening (maxima are referred to as equatorial anomaly)

• The mid-latitude ionosphere shows the least variations. It is also best observed as most of the ionosphere sensing instruments are located in this region.

• In the high latitudes and auroral zones the peak electron densities are smaller than in lower latitudes. However, this sector is extremely rich in plasma instabilities, which implies that short-term variations in the electron density are more pronounced there than at lower latitudes

• At polar caps, where the solar zenith angle is essentially constant, a diurnal variation is still detectable, indicating that apart from solar illumination there are other factors that affect the state of the ionosphere


Global TEC map at 14:30 UT September 11, 1994.Clearly visible equatorial anomaly (National Space Science

Data Center)


Why do we need to study ionosphere: ionospheric irregularities

• significant variations in electron density are caused by traveling ionospheric disturbances (TIDs)

• large-scale TIDs, periods of 30 min to 3 hours, and horizontal wavelengths exceeding 1000 km

• medium-scale TIDs, periods from 10 min to 1 hour, and horizontal wavelength of several hundreds of km

• small-scale TIDs, periods of several minutes, and horizontal wavelength of tens of km

• smallest-scale structures in the electron density distribution cause scintillation1 effects, rapid variations in the line-of-sight electron content (equatorial, high-latitude and polar regions)

• ionospheric storms: vast and massive ionospheric events, often coupled with severe disturbances in the magnetic field and intense solar eruptions (flares)

• usually results in a tremendous increase of electron content


Vertical electron distribution

• Vertical regions

• Peak density in F region

• Different distribution during day and night

Ne

-


Vertical electron distribution

• Region F starts at ~150 km

• Consists of F1 and F2• formed primarily due to ultraviolet radiation

• Regions E and D are due to X-ray radiation

• Effect of D on GPS signal propagation are negligible

• F1 combined with E effects accounts for 10% of GPS ionospheric delay

• F2 has the highest electron concentration (250-450 km) and largest variability, and accounts for up to 80% of GPS ionospheric delay

• Upper boundary of ionosphere is not clearly defined, however, above 1000 km the electron density is very low

• The ionospheric delay caused by the layer above 1000 km amounts to about 10% of the total effect during the day and ~50% during the nigh


Sunspots (February 2000)

The Sun - The dark areas are the sunspots


050

100150200250300350400

1952

1955

1959

1962

1965

1969

1972

1976

1979

1982

1986

1989

1992

1996

1999

Year

SS

N

SSN=10g+s,

where:g – number of groups of sunspots,s – number of individual spots.

SSN - Sunspot Number


Current cycle of solar activity

SSN

year


Solar flareCME

(Coronal Mass Ejection)

Solar events


Solar wind speed during disturbances


Kp 0o 0+ 1- 1o 1+ 2- 2o 2+ 3- 3o 3+ 4- 4o 4+ap 0 2 3 4 5 6 7 9 12 15 18 22 27 32 Kp 5- 5o 5+ 6- 6o 6+ 7- 7o 7+ 8- 8o 8+ 9- 9oap 39 48 56 67 80 94 111 132 154 179 207 236 300 400

Indices of geomagnetic activity

Kp 4 - quiet magnetosphereKp = 4 - active magnetosphereKp = 5 - minor stormKp 6 - major storm

Kp and ap are derived every 3 hours from magnetometric observations


Geomagnetic activity during November 2001


0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

1 31 61 91 121 151 181 211 241 271 301 331 361

DOY 1999

TE

CU

, 0

.1 S

SN

GPS TEC at 1:00 UT

SSN

Correlation between SSN and TEC: global average


Wave propagation in the ionosphere

The refractive index - n describes the wave propagation in given medium.

v

cn

Where:c – the speed of the light in the vacuumv - the speed of the light in the medium

nion > 1 for code GPS observable (code delay) nion < 1 for phase GPS observable (phase advance)


The refractive index nion can be expanded in the reciprocal frequency f of the electromagnetic wave as:

422

30

2

8cos

221 fN

CfHN

CCfN

Cn e

xe

yxe

xion

With the constants:

,4 0

2

2

e

xm

eC

ey m

eC

20

Where:

Ne – electron density, H0 – magnetic field strength, – angle between the propagation direction of the electromagnetic wave and the vector of the geomagnetic field, e – charge of one electron, 0 – electric permittivity1 in the vacuum, me – mass of electron, 0 – magnetic permeability2 in the vacuum.

dnion distance measured


Approximated values of the terms in equation below:

2nd = 210-4 - delay/advance (we account for this part only)3rd = 210-7 - bending (neglected in the ion computation)4th = 210-8 - different ray paths (neglected in the ion computation)

422

30

2

8cos

221 fN

CfHN

CCfN

Cn e

xe

yxe

xion


• the signal delay depends on the total electron content (TEC) along the signal’s path and on the frequency of the signal itself as well as on the geographic location and time and solar activity, as explained earlier

• integration of the refractive index renders the measured range, and the ionospheric terms for range and phase are as follows:

• TEC is the line-of-sight TEC in electrons per square meter. Usually expressed in TECU (TEC Units), where one TECU corresponds to 1016 electrons contained in a cylinder aligned along the line of sight with a cross-section of one square meter, so 1 TECU = 1016 el/m2

range geometric theis where]mper electrons [10 )(TEC

TECcontent electron total where3.40

distance measured

0216

0

2

0

dN

TECf

dn

e

ion

ionion


Wave propagation in the ionosphere

2

2x

ion

CTECf

ion – path delay due to the ionosphere

Cx/2 40.3 m3s-2 (40.3 1016 ms-2 TECU-1) – constant corresponding to the square of the plasma frequency divided by the electron density ( = e2/(420m ) = 40.3

Ne is the electron density (number of electrons per cubic meter) along the signal’s path

Naturally, if ion is known, TEC value can be estimated

( )eTEC N d


Integrated electron density

• For the propagation of microwaves through the ionosphere the electron density integrated along the ray path, generally called TEC (Total Electron Content), is the important ionospheric quantity

• Ne is the electron density (number of electrons per cubic meter) along the signal’s path

• The term TEC is often used to designate the VTEC (Vertical TEC) – slant TEC reduced to the vertical using mapping function F(z), which is a ratio of slant TEC to VTEC

3.40

)(3.40

22VTEC

fzFTEC

fion


SLM – Single Layer Model

SLM assumes that all free electrons are contained in a shell of infinitesimal thickness at altitude H

VTEC

TECzF )(

'sin1

1)(

2 zzF

z’ is elevation angle at ionosphere piercing point

zHR

Rz sin'sin


Ionospheric path delay caused by 1TECU of free electrons

Linearcombination

path delay / 1 TECU

m cycles

L1

L2

L3 (iono. Free)L4 (geo. free)

L5 (wide-lane)

0.1620.267

0-0.105-0.208

0.8531.095

0-1.948-0.248

Define a constant

that gives the ionospheric path delay per TECU referred to the first GPS frequency f1 (also denoted as 1)

MHzfTECUmfCx

E 42.1575/162.02 1

21

The path delays expressed in meters per TECU are equal to

Where , 4 and 5 equal to

EEEE 54 ,,,

283.12

15

f

f647.014 647.12

2

21

f

f


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1 1 .0 8 .1 9 9 9 g .1 3 :0 0

1 1 .0 8 .1 9 9 9 g .1 5 :0 0

1 1 .0 8 .1 9 9 9 g .1 7 :0 0

Sze

roko

ść

D łu g o ść

TECU

13 UT

15 UT

17 UT

Global TEC maps

Lati

tude

longitude


-1,0-0,8-0,6-0,4-0,20,00,20,40,60,81,0

0 4 8 12 16 20 24

UT hours

Cyc

les

L5

-1,0

-0,8-0,6

-0,4-0,2

0,0

0,20,4

0,60,8

1,0

0 4 8 12 16 20 24

Godziny UT

Cyk

le L

5

DD residual ionospheric delay on wide-line

combination for 300 kmbaseline

Processing without ionospheric information from the maps

Processing with ionospheric information from the maps

Cycl

es

L5

Cycl

es

L5

UT hours

UT hours


2max

1

cos2 fzR

VTECCxl

lion

Where lion is the iono-induced distance bias to be expected, and l is the baseline vector

R is the length of the geocentric receiver vector (approximately the Earth radius)

zmax is the maximum satellite zenith distance imposed in the processing

Negative sign implies an apparent reduction in baseline length


Influence of the Antarctic ionosphere on static GPS positioning: example

Data processing:

• IGS observations

• 24-hour sessions with 1 hour overlap

• 7 deg. elevation mask

• Elevation-dependent observation weighting

• QIF (Quasi Ionosphere Free) ambiguity resolution


272 276 280 284 288 292 296 300 304 308 312 316 320 324 328 332 336

D O Y 2001

1.5

2

2.5

3

3.5

4rm

s er

rors

of

am

big

uiti

es

[mm

]

5

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45

Ave

rag

ed T

EC

(C

AS

1,D

AV

1) [T

EC

U]The rm s errors o f the am bigu ities

m 0 24h m ov.aver. (TE CC AS 1

+TE CD A V 1

)/2

C A S 1-D A V 1

1 2 1 6 2 0 2 4 2 8 3 2 3 6 4 0 4 4

A v e r a g e d T E C ( C A S 1 , D A V 1 ) [ T E C U ]

1 .5

2

2.5

3

3.5

4

rms

erro

rs o

f a

mbi

gu

itie

s [m

m]

C oef of determ ination, R -squared = 0 .34

Correlation between averaged TEC over a baseline and rms of obtained ambiguities


280 290 300 310 320 330

DO Y2001

6

8

10

12

14

16

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20

Dis

tanc

e-1

,39

7,6

36,0

00 [

mm

]

9 0

8 0

7 0

6 0

5 0

4 0

3 0

2 0

% r

ozw

iaza

nych

nie

ozna

czon

osc

i

DAV1-C AS1

2 0 4 0 6 0 8 0

% r o z w i a z a n y c h n i e o z n a c z o n o s c i

8

1 2

1 6

2 0D

ista

nce-

1,3

97,

636

,000

[m

m] 273-334 D O Y2001 D AV1-C AS1

R =0.28

% of resolved ambiguities

% o

f re

solv

ed a

mbig

uit

ies

Correlation between% of resolved ambiguitiesand obtained length of the vector


TEC estimation with GPS


• Ionospheric delay observed by the ground-based permanently tracking stations

• almost impossible to derive height-dependent ionospheric profile

• Observed GPS delay by the Low Earth Orbiter (LEO) at the instant of GPS satellite occultation by Earth limb

• GPS signal bent and delay are associated with the vertical profiles of atmospheric parameters

• With full GPS constellation several hundreds of daily occultations can be observed by a single LEO

• A constellation of LEOs is needed for global coverage

• Ionosphere tomography

• Only ground-based solution is considered here


• Only ground-based solution is considered here

• For ground-based absolute TEC mapping, the TEC along the vertical is of main interest

• GPS provides in principle slant TEC, so mapping function is needed to convert it to VTEC

• to refer the resulting VTEC to specific solar-geomagnetic coordinates, the single-layer (thin shell) model is usually adopted for the ionosphere

• Assume that free electrons are all contained in a shell of infinitesimal thickness at altitude H (350, 400 or 450 km)



• Difference in ionospheric delay between the observables on L1 and L2 is used

• Each 1 meter of differential delay between L1 and L2 corresponds roughly to 10 TECU1

• Geometry-free combination is most commonly used

• Relative TEC – from carrier phase

• Absolute TEC – from pseudorange



SLM – Single Layer Model

'sin1

1)(

2 zzF

VTEC

zTEC

E

zEzF

v

)()()(

SLM assumes that all free electrons are contained in a shell of infinitesimal thickness at altitude H


zHR

Rz sin'sin

z and z’ are zenith distance at GPS receiver and ionosphere piercing point (IPP); R is geocentric distance to the receiver and H is the assumed height of the ionospheric layer (here assumed at 450 km)

'sin1

1)()(

2 zVTEC

zTECzF

Assuming the homogeneous satellite distribution over the entire sky, the semi diameter of the ionospheric cap probed by a single receiver is defined by the maximum central angle zmax.


The number of stations sufficient to sound out the entire Earth ionosphere equals to:

maxcos1

24

zAnA

So, for zmax=80 deg, nA = ~ 80 stations

The steradian (symbolized sr) is the Standard International (SI) unit of solid angular measure. There are 4 pi, or approximately 12.5664, steradians in a complete sphere.

A steradian is defined as conical in shape, as shown in the illustration. Point P represents the center of the sphere. The solid (conical) angle q, representing one steradian, is such that the area A of the subtended portion of the sphere is equal to r2, where r is the radius of the sphere.


Ionospheric delay in GPS equations

ik bb ,

-satellite and receiver hardware delays in units of time; normally ignored as they cannot be separated from the clock errors. Clock errors compensate for hardware delays

)( ki ttc - satellite and receiver clock errors wrt GPS time

kiB 1,

-constant bias expressed in cycles; in principal, it contains the initial carrier phase ambiguity; it is a real-valued number containing the integer ambiguity, effect of phase windup1and satellite and receiver hardware delays


Introducing the ionosphere variable Iik ( ), which represents the ionospheric

delay related to first frequency, 1 (notice that 1 corresponds to our earlier notation f1)

kioni ,


Pseudorange smoothing

Smoothed, dual frequency pseudorange at epoch t

and

The noise on smoothed pseudorange is reduced by sqrt(n), where n is the number of epochs used in the smoothing process; it is used in ionosphere estimation


Double difference equations

Ambiguities, N, are integers, as clock errors and hardware biases were eliminated (greatly reduced) by differencing.


Geometry free linear combination (LC): of vital interest to ionosphere estimation

In un-differenced mode

4 1 2L L L cancels frequency independent errors


What are DCBs and what is the reason for non-zero DCBs?

• P1-P2 and P1-C1 biases

• must be estimated for satellites and receivers


ICD-GPS-200, Revision C, Initial Release, 10 October 1993

3.3.1.8 Signal Coherence. All transmitted signals for a particular SV shall be coherently derived from the same on-board frequency standard; all digital signals shall be clocked in coincidence with the PRN transitions for the P-signal and occur at the P-signal transition speed. On the L1 channel the data transitions of the two modulating signals (i.e., that containing the P(Y)-code and that containing the C/A-code) shall be such that the average time difference between the transitions does not exceed 10 nanoseconds (two sigma).


User Error Problem

• GPS control segment uses GPS P-code measurements to compute the broadcast GPS orbits and clocks corrections.

• For a CA only user, using the P-code based broadcast parameters results in range error

• CA-code user would subtract from his P-code based broadcast/differential clock a P1-C1 bias.

– but this effects phase residuals too

• This bias can be estimated via a network solution

• P-C1 code bias +/- 50 cm max; known with accuracy of ~ 5cm


-0.4

-0.2

0

0.2

0.4

0 100 200 300 400 500

Hourly Solutions of CA-P for the First 6 PRNs

prn1prn2prn3prn4prn5prn6

CA

-P C

ode

Bia

s (

met

ers

)

time ( hours )


Potential Effect on User Error

• If the user had perfect knowledge of the clocks/orbits/ionosphere/troposphere, what would be effect of ignoring the P1-CA bias ?

– use IGS orbits and IGS CA clocks.

– use pre-computed zenith troposphere delay for model.

– use phase only to smooth the multipath in the range data.

– kinematically position a dual-freq. P code receiver

• case 1.) account for P1-C1 code bias

• case 2.) don’t account for P1-C1 code bias


-4

-3

-2

-1

0

1

2

3

4

0 4 8 12 16 20 24

Potential Vertical User Error from CA/P Bias

not accounting for CA/P bias: 0.75 m rms.

accounting for the CA/P bias: 0.65 m rms.ve

rtic

al

erro

r (

met

ers

)

time ( hours )


Differential code bias

• Both P1-P2 and P1-C1 biases are estimated for satellites and receivers

• Daily P1-P2 repeatability is about 0.2 ns RMS

• Contain the information about long term stability of instrumental biases

• Experience little variation and are usually assumed constant (usually known to within 1-2TECU)

• http://www.cx.unibe.ch/aiub/ionosphere.html


CODE'S 30-DAY P1-P2 DCB SOLUTION ENDING DAY 095, 2003 09-APR-03 14:26

--------------------------------------------------------------------------------

DIFFERENTIAL (P1-P2) CODE BIASES FOR SATELLITES AND RECEIVERS:

PRN / STATION NAME VALUE (NS) RMS (NS)

*** **************** *****.*** *****.***

G01 -1.568 0.009

G02 -2.731 0.009

G03 -0.952 0.007

G04 0.191 0.011

G05 -1.161 0.008

CODE'S 30-DAY P1-C1 DCB SOLUTION ENDING DAY 095, 2003 09-APR-03 14:26

--------------------------------------------------------------------------------

DIFFERENTIAL (P1-C1) CODE BIASES FOR SATELLITES AND RECEIVERS:


*** **************** *****.*** *****.***

G01 -0.132 0.007

G02 -1.013 0.010

G03 0.168 0.007

G04 1.491 0.008


CODE'S 30-DAY P1-P2 DCB SOLUTION ENDING DAY 095, 2003 09-APR-03 14:26

--------------------------------------------------------------------------------

DIFFERENTIAL (P1-P2) CODE BIASES FOR SATELLITES AND RECEIVERS:


*** **************** *****.*** *****.***

G01 -1.568 0.009

G02 -2.731 0.009

………………………………………………….

………………………………………………….

G ALBH 40129M003 21.892 0.065

G ALGO 40104M002 6.129 0.144

G ALIC 50137M001 24.355 0.111

G ALRT 40162M001 -2.289 0.053


Geometry free linear combination (LC): of vital interest to ionosphere estimation

Ambiguities, N, are integers, as clock errors and hardware biases were eliminated (greatly reduced) by differencing. If ambiguities N can be fixed to integers (for example using wide-lane LC), the term is known.kl

ijB 4,

This takes care of differential ionosphere estimation, however, absolute ionosphere estimation is not that straightforward


Absolute TEC estimation with geometry free LC

To rewrite the geometry free LC for absolute TEC estimation, let’s denote:

MHzfTECUmfCx

E 42.1575/162.02 1

21


Absolute TEC estimation

And the observation equations can be written as:

kiL 4,

105.04 EkiB 4,

m/TECU - constant

- zero difference L4 observable

- bias parameter

kiP 4, - zero difference phase-smoothed P code observable

)( ik bbc - satellite and receiver DCBs (Differential Code Bias)


Corresponding double-differenced equation

The unknowns in the above equations (smoothed code and un-differenced and double difference carrier phase, geometry free LCs) are

• absolute TEC (Ev(,s))

• the satellite and receiver differential code biases (DCBs)

• the ambiguity (bias) terms and

• Consequently, one cannot directly derive absolute TEC information from single-epoch GPS data. To separate TEC from DCBs or ambiguity parameters, it is necessary to process data accumulated over certain time span.

ik bb

kiB 4,

klijB 4,


Alternative observation equations used for TEC estimation: single differences

d corresponds to Cx/2 in our earlier notation


Alternative observation equations used for TEC estimation: single differences


Most commonly used LC for TEC estimation: summary

Relative (r) precise (p) TEC

B is a constant bias, v is a noise

Absolute (a) noisy (n) TEC

C is a sum of transmitter and receiver DCBs, is a noise

Relative (r) noisy (n) TEC from single frequency data

B’ is a constant bias, is a noise


TEC parameterization

• L4 – geometry-free linear combination to determine TEC at ionosphere pierce points of SLM

o Network of points allows for global (local) model derivation

o Spherical harmonic expansion 1515

o Spatial resolution 100 – 200 km

o Temporal resolution at least 5 minutes


n

mmnmnmn

n

nv msSmsCPsE

0,,,

0

))sin(~

)cos(~

)((sin~

),(max

– geomagnetic (or geographic) latitude of IPP

s=-0 – sun-fixed longitude of IPP

– longitude of IPP

0 – longitude of the Sun

nmax – maximum degree of SH expansion

– normalized associated Legendre function

Nnm – normalization function

Pnm – classical, unnormalized Legendre function

– unknown SH coefficients

Global TEC representation: spherical harmonics (SH)

nmnmmn PNP ,

~

mnC ,

~mnS ,

~

Model resolution:

Where:

maxn

max

2

ms

Vertical TEC is represented in terms of spherical harmonic coefficients of specific degree/order


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1 1 .0 8 .1 9 9 9 g .1 7 :0 0

Sze

roko

ść

D łu g o ść

TECU

13 UT

15 UT

17 UT

Global TEC maps: SH representation

Lati

tude

longitude


Alternative models of Global TEC representation

• Uniform grid

• Gauss-type exponential functions

• Cells of constant TEC

• Spherical wavelets (recent)

• Broadcast ionosphere model


Alternative models of Global TEC representation

• Broadcast ionosphere model:

Eight ionospheric coefficients are broadcast by the GPS satellites; they represent the amplitude and the the period of the cosine function by cubic polynomials


• International GPS Service (IGS) provides

- precise GPS ephemeris

- Earth Rotation Parameters (ERPs)

• x, y polar motion and length of day (LOD)

- IGS tracking station coordinates in SINEX format (Solution IN-dependent EXchange format)

- satellite and station clock information

- since 1997 also station-specific tropospheric zenith delay estimates

Relevant international activities


• IGS Ionosphere working group to coordinate GPS-based work on ionosphere (1998)

• Result distribution:

- IONEX files (grid)

• IONosphere Map EXchange Format

- ionospheric maps

- SH coefficients

- CODE provides regularly 12 2-hourly global TEC solutions and satellite-specific differential code biases (DCBs)

• http://www.cx.unibe.ch/aiub/ionosphere.html

Relevant international activities


The response of the ionosphere over Europe to the geomagnetic storm on March 31, 2001

27.03

0

2

4

6

8

10

Kp

28.03 29.03 30.03 31.03 1.04 2.04 3.04 4.04

27.03 28.03 29.03 30.03 31.03 1.04 2.04 3.04 4.04

-400

-300

-200

-100

0

100

Dst

[nT

]

Day/month

The Dst or disturbance storm time index is a measure of geomagnetic activity used to assess the severity of magnetic storms. It is expressed in nanoteslas and is based on the average value of the horizontal component of the Earth's magnetic field measured hourly at four near-equatorial geomagnetic observatories.


The Dst or disturbance storm time index is a measure of geomagnetic activity used to assess the severity of magnetic storms. It is expressed in nanoteslas and is based on the average value of the horizontal component of the Earth's magnetic field measured hourly at four near-equatorial geomagnetic observatories.


- 2 0 - 1 0 0 1 0 2 0 3 0 4 0

4 0

5 0

6 0

7 0

Data source: ~60 permanent european GPS stations


0

2 0

40

60

TE

CU

0

30

60

TE

CU

0

30

60

TE

CU

0

30

60

TE

CU

0

30

60

TE

CU

0

3 0

60

90

TE

CU

0

3 0

60

90

TE

CU

N YAL (79 o N , 12 o E)

T RO1(70 o N , 19 o E )

VIL 0 (65 o N , 16 o E)

ON S A (57 o N , 12 o E )

L AM A (54 o N , 20 o E)

OR ID (41 o N , 21 o E)

L AM P (35 o N , 17 o E )

2 7 2 8 2 9 3 0 31 1 2 3 4

Diurnal variations of TECat different stations


6 7 7 8 8 90

20

40

60

TE

CU

2 0 2 2 2 4 2 6 2 8long itude

62

64

66

68

70

6 7 8 9 100

20

40

6018 20 22 24 26

long itude

5 8

6 0

6 2

6 4

6 6

6 8

7 0

latit

ude

5 6 7 8 90

20

40

60T

EC

U3 0 3 2 3 4 3 6 3 8

5 8

6 0

6 2

6 4

6 6

6 8

7 0

6 7 8 9 1 00

2 0

4 0

6 02 8 3 0 3 2 3 4 3 6

5 6

5 8

6 0

6 2

6 4

6 6

6 8

latit

ude

5 6 7 8 90

20

40

60

TE

CU

4 0 4 4 4 8 5 2

6 4

6 6

6 8

7 0

7 2

7 4

7 6

6 7 8 9 1 0 1 10

2 0

4 0

6 03 8 4 2 4 6 5 0 5 4

6 2

6 4

6 6

6 8

7 0

7 2

7 4

latit

ude

5 6 7 8 9U T

0

20

40

60

TE

CU

3 0 3 2 3 4 3 6 3 8

6 6

6 8

7 0

7 2

7 4

7 6

6 7 8 9 1 0 1 1U T

0

20

40

6024 28 32 36 40

64

66

68

70

72

74

latit

ude

TROM

VARS

TRDS

VAAS

Variations of TEC along single satellite passes observed at different stations on:• March 30 (blue line)• March 31 (red line) - storm day

Locations of the satellites’ traces on the ionospheric layer are also presented (black line with crosses every 5 min.)

PRN 4 PRN 24


Lati

tude

Longitude

TECU

Quiet-time TEC maps over Europe (March 16, 2001)


Lati

tude

Longitude

TECU

Storm-time TEC maps over Europe (March 31, 2001)


- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 3 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 4 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 5 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 6 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 7 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 8 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 9 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 3 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 4 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 5 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 6 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 7 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 8 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 9 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 3 U T

0 4 8 1 2 1 6 2 0 2 4 2 8 3 2 3 6 4 0 4 4 4 8 5 2 5 6

Average quiet-time TEC maps over Europe (March 15-17, 2001)

TECU


- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 3 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 4 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 5 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 6 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 7 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 8 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 9 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 3 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 4 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 5 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 6 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 7 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 8 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 9 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 3 U T

0 4 8 1 2 1 6 2 0 2 4 2 8 3 2 3 6 4 0 4 4 4 8 5 2 5 6 TECU

Storm–time TEC maps over Europe on March 31, 2001


- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 3 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 4 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 5 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 6 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 7 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 8 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

0 9 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 3 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 4 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 5 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 6 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 7 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 8 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

1 9 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 0 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 1 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 2 U T

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

2 3 U T

- 1 5 0- 1 0 0 - 7 5 - 5 0 - 2 5 - 1 0 0 1 0 2 5 5 0 7 5 1 0 0 1 5 0 %

Differential TEC maps for the first day of the storm (March 31, 2001)

relative to quiet time


- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

7 : 0 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

7 : 1 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

7 : 2 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

7 : 3 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

7 : 4 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

7 : 5 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

8 : 0 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

8 : 1 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

8 : 2 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

8 : 3 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

8 : 4 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

8 : 5 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

9 : 0 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

9 : 1 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

9 : 2 0

- 1 0 0 1 0 2 0 3 0 4 04 0

5 0

6 0

7 0

9 : 3 0

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56TECU

TEC maps with 10 min interval on 07:00 – 09:30 UT, March 31, 2001. The maps demonstrate the presence of large scale structures at high latitude ionosphere during the storm


40 50 60 700

10

20

TE

CU

40 50 60 70 40 50 60 70

40 50 60 70 40 50 60 70 40 50 60 70

40 50 60 70 40 50 60 70 40 50 60 70

40 50 60 70 40 50 60 70 40 50 60 70

40 50 60 70 40 50 60 70 40 50 60 70

40 50 60 70 40 50 60 70 40 50 60 70

40 50 60 70 40 50 60 70 40 50 60 70

0

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010203040506070

0

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01020304050

0102030405060

0

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0102030405060

0102030405060

0

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01020304050

01020304050

0

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CU

01020304050

0

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0

10

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30T

EC

U

01020304050

0

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0

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CU

01020304050

0

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0

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01020304050

0

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40 50 60 70Latitude

40 50 60 70Latitude

40 50 60 70Latitude

00 U T

01 U T

02 U T

03 U T

04 U T

05 U T

06 U T

07 U T

08 U T

09 U T

10 U T

11 U T

12 U T

13 U T

14 U T

15 U T

16 U T

17 U T

18 U T

19 U T

20 U T

21 U T

22 U T

23 U T

Storm-time dynamics of latitudinal TEC profiles:

• quiet day March 17, 2001- black line

• disturbed day March 31, 2001 – red line

• disturbed day April 1,2001 - blue line


Map of high latitude GPS stations used in this study

Phase fluctuations of GPS signals at high latitude ionosphere during the storm


Location of TEC fluctuations derived from GPS measurements at northern hemisphere during two disturbed days: September 12 and 15, in Geomagnetic local time and Corrected Geomagnetic Latitude.

Red and blue lines are the boundaries of the auroral oval

part ii mapping the ionosphere with gps

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