Ionospheric data collection and analysis over Indian region

- Recent resultsBy

C.L.Indi, Jt. GM (GAGAN)

Surendra Sunda, Manager (GAGAN)

Airports Authority of India

First Meeting of ionospheric Studies Task Force (ISTF/1)27th -29th Feb 2012

Overview

Current status of GAGAN Receiver and Data formats Data Processing TEC variability Recent results

Scintillation GSAT-8 Loss of lock Depletions

GAGAN works as per ICAO SARPS

EGNOSWAAS MSAS

2004 2007 2008

2013

GAGAN

SDCM

2011

GAGAN supports for interoperability of SBAS & seamless air navigation in the World

GAGAN Segments

GAGAN Space Segment

GAGAN User Segment

INMCC(2)

INLUS (3)

INRE(15)

DCN(4)

128KBps/2MBps

GAGAN Ground Segment

Civilian Aircraft

GPS (24) GEO (3)

GAGAN SIS

15 INRES: (GAH,GBG,GBS,GCC,GDP,GGO,GGT,GGY,GJU,

GJR,GMN,GNP.GPB,GPR,GTV)

2 INMCC (Bangalore- GBM & GBC)

3 INLUS (Bangalore – GBL & GLL & Delhi - GDL. )

4 DCN

24 GPS core Constellation

3 GEO – GSAT-8, GSAT-10, GSAT-15

(@ 55° , 82° , 83° longitude)

GAGAN for safety of life application. Provides GEO PRN127 & 128 with certified RNP0.1 (for Enroute) & APV1 (for Approach) level of service

GAGAN – Ground Segment

Jammu

Delhi

Ahmedabad

Guwahati

Calcutta

Port Blair

Bangalore

Trivandrum

Dibrugarh

Nagpur

Patna

Porbandar

GOA

Jaisalmer

Bhubaneswar

GayaGaya

GLLGBL

GBM GBC

GDL

*

GAGAN Reference Station (15)

GAGAN Master Control Centre (2)

GAGAN Land Up Link Station (3)

Bangalore INRES Facility 43

12

GAGAN Ground Segment Sites

VSAT Antenna (6.3m Dia)

INMCC CTF Building INLUS 11m Antenna

GAGAN ConfigurationGSAT-10

INLUS #3PRN 127 (DD)

GSAT- 15

GSAT-15 In-orbit Spare

INLUS #1PRN 127(BG)

GSAT-8

INLUS #2PRN128 (BG)

DATA COMMUNICATION NETWORK @ 2 Mbps / 128 Kbps (OFC Link)

DATA COMMUNICATION NETWORK @ 2 Mbps / 128 Kbps (OFC Link)

INMCC #1(BG)

DATA COMMUNICATION NETWORK @ 128 Kbps /2Mbps(OFC & V Sat - 4 Link)

INMCC #2(BG)

GPS 1 to 32

INRES-2INRES-1 INRES-15● ● ● ●

SIS with PRN 127

SIS with PRN 128

DATA COMMUNICATION NETWORK @ 128 Kbps /2Mbps(OFC & V Sat - 4 Link)

# Sub System No of Sites

Location Status

1 Master Control Centre (INMCC) 2 Bengaluru Operational2 Land Uplink Station (INLUS) 2

1Bengaluru Delhi

OperationalInstallation in Progress

3 Reference Station (INRES) 15 1. Ahmedabad2. Bengaluru3. Bhubaneswar4. Kolkata5. Delhi6. Dibrugarh7. Gaya8. Goa9. Guwahati10. Jaisalmer11. Jammu12. Nagpur13. Porbandar14. Portblair15. Trivandrum

Operational

4 Data communication Network(DCN)

4 2 OFC Networks 2 VSAT Networks

1 OFC & 1 VSAT Circuits Operational

5 GEO Satellites 3 GSAT8, GSAT10 & GSAT15 GSAT 8 Integrated & Test SIS available

GAGAN Configuration

GAGAN Space Segment Coverage

GS

AT

- 8 at 55°

GS

AT

-15 at 83°

GS

AT

-10 at 82°

PRN127 PRN128

GAGAN Milestone

TDS Phase(2003-07) FOP Phase(2009-13)TDS RFP(2002) TDS RFP(2009)1 Yrs 4 Yrs1 Yrs4 Yrs

Grid Based Ionosphere Model For GAGAN

IGM-MLDF (Indian GIVE Model- Multi Layer Data Fusion):

New Multi layer Grid Based Model

Uses Data Fusion Technique

Provides GIVD, GIVE at 350 km (as per MOPS)

This model does not call for any change to the existing SBAS

message structure

No change for the legacy users

Algorithm evaluated using :

GAGAN TEC receiver data

High quality live data (supertruth) collected over 15 INRES locations

Achievable APV1 performance during nominal days:

76% over Indian land mass

GPS- TEC data Stations

Total 26 receiver stations

Latitude range – 8.5o N to 31o N

Longitude range- 72.2 o E to 92.7o E

Minimum separation- 400 Km

12

Receiver and Data Format

Data format- continued

RINEX (Level 1) Raw binary data is converted into RINEX V.2.10 using the

Novatel’s ‘Convert4’ tool. Sampling interval is 10 seconds. Format is different from that of IGS stations.

ISMR (Level 2) Standard output format in GSV receivers. Provides slant TEC, Scintillation index, C/No, satellite

position, Lock time etc. at one minute interval. Kalman filter is used for receiver bias still there is an issue

in bias estimation.

RINEX V.2.10 sample

2.10 OBSERVATION DATA G (GPS) RINEX VERSION / TYPEConvert 27-Aug-2009 09:58 PGM / RUN BY / DATE Signal Strength values S1,S2 are in dBHz COMMENT MARKER NAME MARKER NUMBER OBSERVER / AGENCY NovAtel GPSCard REC # / TYPE / VERS ANT # / TYPE 1668621.9862 5475083.1776 2805416.9267 APPROX POSITION XYZ 0.0000 0.0000 0.0000 ANTENNA: DELTA H/E/N 1 1 WAVELENGTH FACT L1/2 1 1 7 G02 G03 G04 G06 G07 G08 G09WAVELENGTH FACT L1/2 1 1 7 G10 G11 G12 G13 G14 G15 G16WAVELENGTH FACT L1/2 1 1 7 G17 G18 G19 G20 G21 G22 G23WAVELENGTH FACT L1/2 1 1 7 G24 G25 G26 G27 G28 G29 G30WAVELENGTH FACT L1/2 1 1 2 G31 G32 WAVELENGTH FACT L1/2 COMMENT COMMENT 8 C1 L1 D1 S1 P2 L2 D2 S2 # / TYPES OF OBSERV 10.000 INTERVAL 2008 09 11 06 24 40.0000000 GPS TIME OF FIRST OBS 2008 09 12 06 24 30.0000000 GPS TIME OF LAST OBS Leap Seconds Unknown COMMENT END OF HEADER 08 09 11 06 24 40.0000000 0 9G23G13G08G27G25G07G28G03G19 -33768328.06149-177453830.89549 -2902.06249 49.619 -33768324.54448-138275715.81748 -2261.50048 46.266 -35328933.82449-185654810.44349 -1173.87549 51.669 -35328931.46449-144666068.99349 -914.87549 51.600 -33034931.25049-173599714.79949 2254.62549 48.078 -33034927.88447-135272481.22747 1756.68847 44.583 -33946541.40549-178390264.37449 1471.25049 50.869 -33946538.78749-139005377.87249 1146.25049 50.019 -34300753.31149-180251685.45049 227.31249 51.596 -34300750.36449-140455847.24249 176.93849 51.127

DATA PROCESSING

Raw binary data

ISMR

APPLY SATELLITE BIAS

APPLY RECEIVER BIAS

ISMR OUTPUT ( EXCEL)

KALMAN FILTER

Rx Bias

CODE Website

P1C1 BiasMonthly

Monthly

TEC Variability

TEC shows a good correlation with solar activity.

Annual, semi-annual, seasonal and diurnal variations of TEC have been studied using the continuous data measurement from 2004 onwards.

Large day-to-day variations are prominent feature of anomaly region.

0 5 10 15 20 25 30 35 40 455

10

15

20

25

30

35

Sunspot Number

TE

CR=0.75

Loss of lock

Loss of lock

Poor GDOP

Outage of GNSS

Service

Reduced Accuracy

GIVE

Under Sampling

Signal Fading

Reduced Availability

Scintillation Effects on GNSS

GPSSBAS

Grid based model

user position

Recent results on scintillation

A sharp rise in the number of scintillation events with their strength and duration has been observed with increasing solar activity in 2011.

Total scintillation epochs (S4>0.4) from all the receivers in 2004 were around 6000 whereas in 2011 they shoot up to 60,000 i.e. 900% increase in the scintillation occurrence.

The maximum duration of scintillation event/patch (continuous S4>0.4) observed in 2004 was of 25 minute whereas it is of 80 min in 2011.

October 2011 witnessed the maximum scintillation of moderate to severe intensity. It was almost a daily phenomena during this month.

-continued

The characteristics have been defined very well using the continuous data of 2004-2011 over the Indian equatorial and low latitude region.

Maximum probability of scintillation occurrence is between 2000 hrs to 2230 hrs local time.

The strength of scintillation increases in accordance with EIA. It is severe at the crest of EIA due to high background electron density and moderate to low at magnetic equator from where it originates.

Day-wise Scintillation occurrence in October 2011

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 310

200

400

600

800

1000

1200

1400

1600

1800

Days of October 2011

No.

of

Sci

ntill

atio

n E

ven

ts

Scintillation examples in 2011

PRN-18

12/10/2011 Hyd

MUM12/10/2011

PRN-15

PRN-15

13/10/2011 Hyd

12/10/2011 VIZ

PRN-22

Scintillation observations from GSAT-8

Observations from GAGAN satellite GSAT-8 (PRN-127) may give new insight into the spatial and temporal variations of scintillation due to its fixed position (IPP) contrary to GPS satellites.

It can be helpful in determining the plasma bubble drift velocity.

Very strong scintillation of the duration of about 2 hours have been observed.

Scintillation impact on SBAS satellite is more severe as it directs affects the GNSS Service and its availability.

Two to Three SBAS satellites at different positions may help in avoiding the scintillation impact.

Examples of GSAT-8 Scintillation measurements

12 14 16 18 20 22 2440

45

50

55

60

L1 C

/No

(dB

-Hz)

915 281011 PRN=127

12 14 16 18 20 22 240

0.2

0.4

0.6

0.8

S4

12 14 16 18 20 22 240

2

4

6x 10

4

L1 L

ock

Tim

e (S

ec)

UT (Hr)

12 14 16 18 20 22 2440

45

50

55

60

L1 C

/No

(dB

-Hz)

925 281011 PRN=127

12 14 16 18 20 22 240

0.2

0.4

0.6

0.8

S4

12 14 16 18 20 22 240

2

4

6x 10

4

L1 L

ock

Tim

e (S

ec)

UT (Hr)

IPP- 21.50 N, 71.20 E IPP- 23.20 N, 780 E

28/10/2011

Comparison of GPS and GSAT-8

15.5 16 16.5 17 17.5 18 18.5 190

0.20.40.60.8

214 091111 PRN=31

S4

15.5 16 16.5 17 17.5 18 18.5 190

50

100

ST

EC

15.5 16 16.5 17 17.5 18 18.5 1910

20

30

Lat

. N

15.5 16 16.5 17 17.5 18 18.5 1972

74

76

Lon

. E

UT (Hr)

15 15.5 16 16.5 17 17.5 18 18.5 190

0.20.40.60.8

214 101111 PRN=31

S4

15 15.5 16 16.5 17 17.5 18 18.5 190

100

200S

TE

C

15 15.5 16 16.5 17 17.5 18 18.5 1910

20

30

Lat

. N

15 15.5 16 16.5 17 17.5 18 18.5 1972

74

76

Lon

. E

UT (Hr)

15 15.5 16 16.5 17 17.5 18 18.5 1940

45

50

55

60

L1

C/N

o (

dB-H

z)

214 101111 PRN=127

15 15.5 16 16.5 17 17.5 18 18.5 190

0.20.40.60.8

S4

15 15.5 16 16.5 17 17.5 18 18.5 190

2

4

6x 10

4

L1

Lo

ck T

ime

(S

ec)

UT (Hr)

15.5 16 16.5 17 17.5 18 18.5 1940

45

50

55

60

L1

C/N

o (

dB-H

z)

214 091111 PRN=127

15.5 16 16.5 17 17.5 18 18.5 190

0.20.40.60.8

S4

15.5 16 16.5 17 17.5 18 18.5 190

2

4

6x 10

4

L1

Lo

ck T

ime

(S

ec)

UT (Hr)

Nov 9 Nov 10

GSAT-8

GPSPRN-31

26

Impact of Scintillation- Loss of lock

Loss of lock is one of the major effects of scintillation.

Severe scintillation over a large coverage area may impact more than 2 satellites leading to loss of lock.

This may lead to poor GDOP thereby reducing the accuracy of position.

A case study on quantitative analysis of loss of lock is carried out on a severe scintillation day.

Though L2 gets unlock more often than L1 due to weaker strength, the analysis was done on L1 signal unlock which is also used as downlink frequency for SBAS satellites.

The analysis is based on RINEX data (10 sec interval),.

27

Loss of lock- effect on satellite availability

0 1 2 3 4 5 6 7 8 9

x 104

4

5

6

7

8

9

10

313 April 6, 2011

No.

of

To

tal

Sat

elli

tes

Time(Sec) of day

0 1 2 3 4 5 6 7 8 9

x 104

4

5

6

7

8

9

10

313 April 9, 2011

No.

of

To

tal

Sat

elli

tes

Time(Sec) of day

0 1 2 3 4 5 6 7 8 9

x 104

4

5

6

7

8

9

10

357 April 6, 2011

No.

of

To

tal

Sat

elli

tes

Time(Sec) of day

Scintillation Free day

April 6April 6

Kolkata Gaya

No. of Visible satellites going downdue to scintillation

SevereScintillation Day

April 9 April 9

Impact of Scintillation – Loss of lock

Total number of IPPs drop down drastically during scintillation period starting from ~14 UT to ~19 UT.

There is ~15% reduction in the number of IPPs during severe scintillation period (14UT to 16 UT).

28

6 April, 2011- Severe Scintillation Day

9 April,2011- Scintillation Free day

Depletion

Deep depletions (plasma bubbles) have been observed at various stations during 2011.

Depletions are mostly associated with scintillation.

Depth of depletion in the order of 30-80 Slant TEC units ( 5 m - 13m slant delay) are observed.

MUM 13/10/11 PRN-3

Bubble

Loss of Lock

90 TEC

Depletion

A very large depletion / plasma bubble, with the depth of 46 TEC units ~ 7.5 meters is observed at Ahmedabad for PRN-13 on March 29, 2011 between 16-17 UT.

The width of bubble is ~ 200 Km through which satellite signal traverses for close to 30 min.

The onset IPP is 19.430 N, 73.300 E and end IPP is 17.620 N, 73.630 E, thus satellite was traveling in opposite direction of bubble.

11 12 13 14 15 16 17 180

20

40

60

80

TEC

214 290311 PRN=13

11 12 13 14 15 16 17 180

20

40

60

80

Elev

atio

n

11 12 13 14 15 16 17 18-0.2

0

0.2

0.4

0.6

Time (UT)

S4

Ahmedabad bubble

Slant differential range delay

Slant Differential range delay is calculated using 3 GPS receivers at Ahmedabad for PRN -13.

RX ID – 925 and 214 are collocated at SAC and RX ID 527 is installed at Ahmedabad Airport having a radial distance of ~15 km

Sharp rise in differential delay for SAC and Ahmedabad airport receivers is observed at the boundaries of bubble.

Differential Delay

March 29, 2011 PRN 13

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

Sow

Slan

t Dif

fren

tial

Del

ay (M

eter

)

527-214

527-925

925-214