high latitude scintillation analysis for marine and aviation...

High Latitude Scintillation Analysis for

Marine and Aviation Applications

F. Ghafoori and S. Skone

University of Calgary

2

Outline

• Auroral/polar scintillation mechanisms

• Scintillation data set

• Simulation tools

• Results

• Summary

Ionospheric Scintillation

Irregularities in

electron density

Wave propagation

Wavefront

Emerging

wavefront

0 10 20 30 40 50 60-1

-0.5

0

0.5

1

Time (Second)

Am

pli

tud

e (

dB

)

Realization of Amplitude @ f =1575 MHz

σχ=0.0359

0 10 20 30 40 50 60-1

-0.5

0

0.5

1

Time (Second)

Ph

ase

(R

ad

ian

)

Realization of Phase for Signal @ f =1575 MHz

σφ=0.31

3

4

High Latitude Scintillations

Polar Cap

Auroral Oval

Auroral Irregularities

E-region:

October 1, 2006

Polar Irregularities

E- & F-region:

January 7, 2005

7

The CANGIM receivers measure

• 50 Hz raw GPS observations

• Phase scintillation index (σ)

• Amplitude scintillation index (S4)

Calg

Athb

Yell

Sub-auroral

Station Geographic Geomagnetic

Lat. Long. Lat. Long.

Yell 62.48º -114.48º 68.80º 298.37º

Athb 54.72º -113.31º 61.52º 305.67º

Calg 51.08º -114.13º 57.86º 306.43º

Note: - The coverage areas for IPP above 20º

are indicated as circles.

CANGIM Database

To develop flexible tools to study high latitude

scintillation impact on receiver performance for

various user groups (marine, aviation)

Objective

Method

• Determine scintillation characteristics for auroral and polar regions (CANGIM)

• Develop simulation based on observed high latitude characteristics

• Develop flexible tracking loops to assess impact – determine thresholds for loss of lock

• Quantify duration and frequency of receiver impact, number of satellites affected, etc.

8

Auroral Substorm Current Wedge

Magnetometer signature

9

10

00

12

06 18

Auroral Oval 08 : 00 UT

ESKIFCHUGILLISLL

PINA

RANK

TALO

135 ° W

120 ° W

105° W 90° W

75° W

60° W

45 ° N

60 ° N

75 ° N

Churchill Line --(CARISMA)

-500

-250

0

250

500TALO

H-Component

04:00 08:00 12:00 16:00 20:00 24:00-500

-250

0

250

500PINA

UT (Hours)

-500

-250

0

250

500ISLL

-500

-250

0

250

500GILL

-500

-250

0

250

500FCHU

20070928;

Polar Scintillation

Auroral Scintillation

Auroral Boundary Estimation

Event Selection

2002 2003 2004 2005 2006 20070

100

200

SS

N

Daily SSN variation

2003 2004 2005 2006 20070

200

400

Year

Number of Phase and Amplitude Scintillation >= 0.2 (Elevation Cutoff = 20o)

No

. o

f O

bs.

Aurora Phase Obs.

Polar Phase Obs.

11

• Phase scintillation is dominant

• Low amplitude scintillation (S4<0.1) for all events

Auroral Scintillation Characteristics

Weak Scintillation Moderate Scintillation Strong Scintillation

[Yell], PRN29, 10-Jan-2003

0 0.5 1 1.50.04

0.045

0.05

0.055

0.06

0.065

0.07S

4

σφ60

[Yell], PRN25, 29-Oct-2003

0 0.5 1 1.50.02

0.03

0.04

0.05

0.06

0.07

S4

σφ60

0 0.5 1 1.5

0.03

0.04

0.05

0.06

0.07

S4

σφ60

[Yell], PRN23, 12-Feb-2003

12

Polar Scintillation Characteristics

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

Phi 1Sec

Co

rr S

4

S4 and Phase Scintillation Correlation on 26 August 2005

• Amplitude scintillation is significant

• S4 in range 0.4 to 0.8 for severe events

• Pairs (σ, S4) determined for scintillation simulations

13

0 200 400 600 800 1000 1200 1400 1600 1800 2000

-5

0

5

Representation of 2000 samples of the simulated GPS signal for PRN # 1, 3, 7 and 11 (without scintillation)

samples

2000 samples (PRN 1,3,7,11)

Discrete-time

VCO

Look-up table

C/A-code

System

dynamics

Cosine wave

1.023 MHz Counter C/A-code

Look-up

navigation data

Discrete-time

VCO

Counter navigation

period

Counter navigation

message

10.23 MHz

-3 dB

Q

I

Thermal

noise

GPS

signal

Navigation

message

Scintillation

Scintillation

System

dynamics

Sine wave

Multipath

Scintillation

Thermal noise

Multipath

System dynamics

Conventional

parameters for low-

cost receivers

GPS Signal Simulator

14

Ionospheric phase scintillation follows zero-mean Gaussian distribution with

standard deviation σφ.

( ) βα

δ

αβ

βδδ /

1

/1

)()()( xIm

m

mm

ex

em

ImxIf

−

−

Ω−−

Γ=

ΩΓ==

1

,1

,1 2

42

4

=Ω

==== SmS

m βα

Nakagami-m Bivariate Gamma

22 2/

2

1)( φσφ

φσπφ

−= ef

Ionospheric intensity scintillation follows Nakagami-m distribution with normalized

standard deviation S4. The intensity scintillation signal can be generated using

bivariate gamma function G(α,β) with marginal density function given as follows:

Scintillation Simulator

15

Digital IF

Carrier

wipe off

Code

wipe off

90°

Prompt replica

code

Phase

discriminator

F(s)

VCO

I

Q

Ip

Qp

Replica carrier

Integrate

and dump

1/T ∫dτ

1/T ∫dτ

Generic Costas Carrier Tracking Loop

Tracking loop bandwidth

Pre-detection integration time

Tracking Loops

16

0 1 2 3 4 5 6 7 8 9 10-1

-0.5

0

0.5

1

Time (sec)

σ (

rad

ian

s)

Total Error Std = 0.24461 (rad)

Ϭϕ60 = 0.1 radS4 = 0.05

Ϭϕ60 = 0.5 radS4 = 0.05

Ϭϕ60 = 0.7 radS4 = 0.05

Near the tracking threshold

0 1 2 3 4 5 6 7 8 9 10-1

-0.5

0

0.5

1

σ (

rad

ian

s)


0 1 2 3 4 5 6 7 8 9 10-1

-0.5

0

0.5

1φ60

σ (

rad

ian

s)


Weak Scintillation

Moderate Scintillation

Strong Scintillation

(Bn = 15 Hz, C/N0 = 46 dB-Hz)

Carrier Tracking Error Auroral Region

0 1 2 3 4 5 6 7 8 9 10-1

-0.5

0

0.5

1

σ (

radia

ns)


0 1 2 3 4 5 6 7 8 9 10-1

-0.5

0

0.5

1

σ (

radia

ns)


0 1 2 3 4 5 6 7 8 9 10-1

-0.5

0

0.5

1

Time (sec)

σ (

radia

ns)


σφ = 0.2 rad

S4 = 0.6

σφ = 0.4 rad

S4 = 0.6

σφ = 0.6 rad

S4 = 0.6

Near the tracking threshold

(Bn = 15 Hz, C/N0 = 46 dB-Hz)

Carrier Tracking Error Polar Region

Weak Scintillation

Moderate Scintillation

Strong Scintillation

Example: Loss of Lock

0 5 10 15 200

0.2

0.4

0.6

0.8

1

[Yellowknife 20-Oct-2003] σφ60

for all visible satellites

Time (hour)

60-s

econd p

hase s

igm

a

[Yellowknife 29-Oct-2003]

Threshold = 0.7

0 5 10 15 20

0

2

4

6

Number of satellites for which σφ60

threshold is exceeded simultaneously

Time (hour)

No.

of

sate

llite

s

Yellowknife 29-Oct-2003

v

Yellowknife

Auroral Polar

19

Simultaneous Loss of Lock

0 1 2 3 4 50

200

400

600

800

1000

1200Yellowknife (29-Oct-2003) - Number of simultaneous loss of satellites

No. of Satellites

Num

ber

of

loss (

1-m

in m

easure

ment

epochs)

20

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

0.16

0.18

0.2

0.22

0.24

0.26

0.28Tracking Error (C/N0 = 46 dB-Hz, S4 = 0.06)

phase scintillation index (σφ)

trackin

g e

rror

(radia

ns)

Bn = 09 Hz

Bn = 11 Hz

Bn = 15 Hz

Bn = 25 Hz

Optimum loop

bandwidth is

around10-15 Hz.

(C/N0 = 46 dB-Hz, S4 = 0.06)

Optimal Tracking Loop Bandwidth

21

Summary

• High latitude scintillations are due to different

physical drivers (auroral versus polar regions)

• Simulations developed for auroral and polar

regions

• Carrier tracking loop performance evaluated for

generic low-cost receiver

• Receiver tracking loops may be challenged during

severe scintillation

22

high latitude scintillation analysis for marine and aviation...

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