GPS TEC error correction

8/11/2019 GPS TEC error correction

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GPS based total electron content (TEC) anomaliesand their association with large magnitudeearthquakes occurred around Indian region

Vishal Chauhan 1O.P. Singh 1, Birbal Singh 2,

1. Department of Physics, Faculty of Engineering & Technology,R.B.S. College, Bichpuri, Agra-283105, India

2. Department of Electronics & Communication Engineering,Faculty of Engineering & Technology,

R.B.S. College, Bichpuri, Agra-283105, India


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Brief description of experimental setup used for TEC measurement.

Data and method of analysis

Statistical methods for detection of anomalous values of TEC.

Results

(i) Study of seismic effects on TEC for the duration of thirty monthsbetween 01 January, 2009 and 30 June, 2011.

(ii) Comparative study of GIM TEC and observed GPS TEC.

(iii) Results of anomalies in observed GPS TEC and GIM TECcorresponding to Wenchuan Earthquake.

Conclusion

Overview of presentation


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Experimental set up used at Agra for

the measurement of TEC

Receiver:Novatels Euro-PAK 3M

GPS receiver system: GSV4004B

Antenna:Novatels GPS-702

The continuous observations are in progress since 24 June, 2006.


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Data and analysis procedure to obtained daily

diurnal curves of TEC data The TEC measurements are being carried out through combined frequencies (L1/L2)

pseudorange and carrier phase measurements. The GSV4004B measures TECusing pseudorange measurements on the L1 and L2 frequencies.

The receiver internal biases are also taken care of prior to final TEC calculations. Thiscan be seen in the formula given below;

TEC = [9.483*(PR L2-PR L1 - C/A-P, PRN ) + TEC RX + TEC CAL] TECU

where PR L2 is the L2 pseudo-range in meters, PR L1 is the L1 pseudo-range inmeters, C/A-P, PRN is the input bias between SV C/A- and P-code chiptransition in meters. TEC RX is the TEC result due to internal receiver L1/L2delay and TEC CAL is the user defined TEC offset.

Continued.


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Obtained vaules of TEC are slant TEC which are converted into vertical TEC (VTEC) usingexpression given by Mannucci et al. 1993.

where R E is the mean radius of the earth in km, h S , the ionosphere (effective)height above the earths surface, z, the zenith angle and E, the elevation anglein degrees. The effective ionospheric height of 350 km is used fordetermination of IPP locations.

Continued.

To avoid the effect of multipath, troposcatterand water vapor at low elevation angles valuesof TEC are taken at higher elevation angles (>50 0).

Local Time (LT)=UT+0530 hrs


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To detect anomalous variations in TEC data we applied the similar statisticalprocedures as adopted by earlier workers from Taiwan, Japan, etc. (Prof. Liu,Prof. Hayakawa, Prof. Hattori..)

15 days backward running mean (m) and running standard deviation

around mean (m2 )* The variation of VTEC is plotted between the curves of m 2 .

The values of VTEC crossing m 2 curves are said to be abnormal.

Statistical procedures to detect anomalousvariations in daily diurnal curves of TEC data


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0

2

4

6

8

10

12

Data m+s m-s

Anomaly

m+2 m-2

V T E C

Days


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differential TEC (dTEC)* dTEC = VTEC 15 days backward running median of TEC at each epoch.* The variation of dTEC is plotted between its fix mean and standard deviation around.

mean (m 2 ).The values of dTEC crossing m+2 or m-2 lines are said to be abnormal.

-5

-4

-3

-2

-1

0

1

2

3

4

5

d T E C m+2

m-2

m

Days

Enhanced anomaly

Depletions


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Quarti le-based statistical method

* At first a median (M) of every successive 15 days of TEC is computed to find the deviation on16 th day.

* Two quartiles , first (or lower) and third (or upper) are calculated which are denoted by LQ and UQrespectively. It has been shown by earlier workers (Klotz and Johnson, 1983; Liu et al., 2009) thatunder the assumption of a normal distribution with mean (m) and standard deviation ( ) for GPSTEC, the expected values of M and LQ or UQ are m and 1.34 respectively.

Finally , the lower bound (LB) and upper bound (UB) are calculated as;

LB=M - 1.5 (M - LQ),

UB= M + 1.5 (UQ-M).

The values of TEC cross ing these LB and UB are detected as abnormal variationin TEC data .


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Results


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Locations of the epicenters of earthquakes

occurred around Indian region(01 January, 2009 30 June, 2011)

AF G AN IS T AN

B A N G LE DE S H

BH U T A N

BUR M A

C H I N A

IN D I A

K Y R G Y Z

N E P A L

O M A N

P A K IS T A N

T AJ IK IS T A N

T H

T U R K M E N I S T A N

6 0

E 7 0 E 80 E 90 E

1 0 0

E 1 0

N

2 0

N

3 0

N

4 0

N

Agra


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Date: 07 November, 2009

Magnitude = 5.5

Lat.=29.49 0NLong.=86.01 0E

Distance from Agra=831 km

Depth=5 km

A F G A N I S T A N

B A N G L E D E S H

B H U T A N

B U R M A

C H I N A

IN D I A

K Y R G

NEPALP AK IS T AN

T A J IK IS T A N

T H

6 0

E 7 0

E 80 E 9 0 E 1 0 0

E 1 0

N

2 0

N

3 0

N

4 0

N

Agra


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Day of the earthquake:07 November, 2009

23 Oct - 22 Nov, 2009

0

10

20

30

40

50

60

GPS-TEC

M=5.6

23 24 25 26 27 28 29 30 31 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22

Days

T E

C U


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Day of the earthquake:07 November, 2009

*To investigate the seismic effect on TEC we omitted the disturb days from all the data

23 Oct - 22 Nov, 2009

0

10

20

30

40

50

60

GPS-TECM=5.6

23 24 25 26 27 28 29 30 31 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22

Days

T E

C U

m+2 m+2


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Date: 08 December, 2010

Magnitude = 5.5

Lat.=39.36 0NLong.=72.86 0E


Depth=10 km

A F G A N I S T A N

B AN G LE DE S H

BH U T AN

BU RM A

C H I N A

IN D I A

K Y R G

NEPALP AK IS T AN

T A J IK IS T A N

T H

6 0

E 7 0

E 80 E 90 E 1 0 0

E 1 0

N

2 0

N

3 0

N

4 0

N

Agra


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Day of the earthquake: 08 December, 2010

Days of December, 2010

T E

C U

0

5

10

15

20

25

30

35

Data

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

M=5.5VTEC

01 December 15 December, 2010


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0

5

10

15

20

25

30

35Data M+2Sig M-2Sigm+2 m-2VTEC

Days of December, 2010

T E

C U

M=5.5

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

Day of the earthquake: 08 December, 2010



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0

2

4

6

01.12.11 04.12.11 07.12.11 10.12.11 13.12.11


M=5.5

Days of January, 2011

T E C U

Variation of VTEC at 0600 hrs local time


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Date: 27 January, 2011

Magnitude = 6.2

Lat.=28.19 0N

Long.=59.01 0E


Depth=12 km

AF G AN IS T AN

B A N G LE DE S H

BH U T A N

BUR M A

C H I N A

IN D I A

K Y R G Y Z

N E P A L

O M A N

P A K IS T A N

T A J IK IS T A N

T H

T U R K M E N I S T A N

6 0

E 7 0 E 80 E 90 E

1 0 0

E 10

N

2 0

N

3 0

N

4 0

N

Agra


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0

5

10

15

20

25

Day of the earthquake: 27 January, 2011

Days of January, 2011

T E C U

20 21 22 23 24 25 26 27 28 29 30 31

M=6.2

20 January 31 January, 2011


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Study of GIM-TEC data and itscomparison with GPS-TEC data

at Agra


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May, 2009

05

1015

20253035

4045

GIM-TECGPS-TEC

An example of the diurnal variation ofGIM-TEC and GPS-TEC data


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12 May, 2009- Q1

0

5

10

15

20

25

30

35

0 10 20 30

Corr. Co.=0.992892

08 May, 2009-D1

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40

Corr. Co.=0.991487

An example of the correlation betweenGIM-TEC and GPS-TEC data

Quiet Day Disturb Day


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Mar, 2009

0

0.1

0.2

0.3

0.4

0.5

0.60.7

0.8

0.9

1

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10

May, 2009

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

D1 D2 D3 D4 D5

An example of the correlation betweenGIM-TEC and GPS-TEC data

Quiet Days

Disturb Days


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C l i


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1. The GPS based TEC measurements are analyzed for the period of 30 months from 01

January, 2009 to 30 June, 2011 in the light of magnetic storms and earthquakes. Thelarge magnitude earthquakes ( M 5.5) which occurred within an epicentral distance of2000 km from the observing station Agra are considered for this study.

2. Anomalous variations in TEC, in the form of enhancements and depletions, areobserved in almost all the cases of earthquakes examined with precursory period lyingbetween 0 and 10 days.

3. The GPS-TEC data obtained at Agra station are also compared with global ionosphericmaps (GIMs) of TEC and a very good correlation is found between the two. .

4. The GPS-TEC data and GIM TEC data at five different locations are analysedcorresponding to the Wenchuan earthquake (M=7.9) occurred on 12 May, 2008 inChina region. The anomalies in TEC data are investigated by using quartile basedstatistical method. It has been found that TEC data obtained at Agra and other locationsshow anomalous depletions 02 to 13 days before and anomalous enhancements 03 to10 days prior to the occurrence of earthquake. It has also been found that the level ofanomalies are more distinct near the epicenter than at the Agra station and theyappeared earlier at the location near the epicenter than other locations.

3. Since to investigate the seismic effects on TEC data the data on disturebed days areomitted hence the observed anomalies in TEC data may be due to the considered

seismic events .

Conclusion


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GPS TEC error correction

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