IImportance Of mportance Of Very Low Frequency Very Low Frequency

Radio Signal DataRadio Signal Data Registered By Registered By

VVLFLF-receiver-receiver SystemSystem

A. Nina, V. Čadež and V. SrećkovićInstitute of Physics, Belgrade, SerbiaInstitute of Physics, Belgrade, Serbia

Astronomical ObservatoryAstronomical Observatory, Belgrade, Serbia, Belgrade, Serbia

ContentsContents• Ionosphere

• VLF signals – “ionospheric probes”VLF signals – “ionospheric probes”

• Importance of creating a database for Importance of creating a database for studying the ionosphere and its applications studying the ionosphere and its applications in technical and scientific researchin technical and scientific research such as:

--detection of different events by VLF signalsdetection of different events by VLF signals

-ionospheric diagnostics-ionospheric diagnostics

-study of physical and chemical processes -study of physical and chemical processes

IntroductionIntroduction

• Terrestrial ionosphere

• Methods of investigation

• Our study: low ionosphere

VLF signals – VLF signals – “ionospheric probes”“ionospheric probes”

• VLF wave propagation

• Advantages: - continual emission, - large area involved

for analyses, - international

collaboration: AWESOMEAWESOME,

AbsPALAbsPAL, SAVNETSAVNET, AARDDVARKAARDDVARK

• Belgrade VLF station

Significance of low Significance of low ionospheric study ionospheric study

• ScienceScience - detection of different pure natural and man-induced events - ionospheric diagnostics - study of physical and chemical processes

• TelecommunicationsTelecommunications - radio communications, - planned networks of mobile communication satellites, - high precision applications of global navigation satellite

systems, etc.• Explanation of application our database in scientific

research and, consequently, in prediction of possible problems in the telecommunications

Importance of databaseImportance of database• Processes in the ionosphere are: -very complex - time- and space variable

• Experiment: practically impossible to exactly simulate conditions in

particular cases

• Theory: no real time data available for all necessary parameters

needed for theoretical analyses

• Statistics: requires the existence of a database that can be used to

analyze the ionosphere

Detection of eventsDetection of events• Sun:

- regular variation

- transient variations

• Outer space

• Earth:

- in the atmosphere

- in the lithosphere

pure natural

man-induced

21:30:00 21:30:20 21:30:40 21:31:00

58.0

58.5

59.0

59.5

-130

-125

-120

-11521:30:00 21:30:20 21:30:40 21:31:00

NAA

Am

plit

ud

e (d

B)

NAA

GRB December 27th, 2004

Ph

ase

(o)

Time (UT)

00:00 04:00 08:00 12:00 16:00 20:00 24:0010

20

30

40

10

20

30

40

10

20

30

40

10

20

30

4000:00 04:00 08:00 12:00 16:00 20:00 24:00

Time (UT)

Mart 21, 2011 Mart 22, 2011 Mart 23, 2011

Am

plitu

de

(d

B)

December 21, 2010 December 22, 2010 December 23, 2010

September 22, 2010 September 23, 2010 September 24, 2010

Jun 13, 2010 Jun 19, 2010 Jun 20, 2010

DHO

HESSI

06:00 08:00 10:00 12:00 14:00 16:000

5

10

15

20

10

20

30

0

5

10

15

2006:00 08:00 10:00 12:00 14:00 16:00

Am

plit

ude (

dB

)

G1

NAA

DHO

16_February_2011

1-8A GOES-15

Inte

nsi

ty (

10-6

W/m

2 )SGR 1806-20

00:42 00:44 00:46 00:48

-170

-165

-160

-155

18

19

20

21

Ph

as

e (

o)

Time (UT)

GQD

Am

plitu

de

(d

B)

GQD

Ionospheric diagnosticsIonospheric diagnostics

• The case considered: Solar flare February 18th, 2011

• Recorded data: - GOES-15 satellite - Belgrade AWESOME receiver - DHO (Germany) transmitter (23.4 kHz)

• Theoretical model: Wait’s model of ionosphereWait’s model of ionosphere • Numerical program for simulation

VLF signal propagation: LWPCLWPC (Long-Wave Propagation Capability)

14:05 14:10 14:15 14:20 14:25

52

54

56

58

60

24

26

28

30

10-6

10-5

14:05 14:10 14:15 14:20 14:25

Time (UT)

rec (

o)

Are

c (d

B)

I(W

/m2 )

GOES-15 fit

14:05 14:10 14:15 14:20 14:25

109

1010

1011

N (

m-3)

Time (UT)

Physical and chemical processes Physical and chemical processes

(preliminary results)(preliminary results)

G(t) – electron gain rate

L(t) – electron loss rate

Upper half of D region:

tLtGdt

dN

)()()( 00 tItIKPtPtG sss

tNttRtL eff2

P(t) – photo-ionization rateR(t) – recombination rateI(t) – radiation flux by satelliteαeff – effective recombination coefficientKs – coefficient (dependent on energy interval of data registered by satellite)

14:05 14:10 14:15 14:20 14:25

0

1x1010

2x1010

3x1010

4x1010

5x1010

6x1010

dN

/dt

(m-3s-1

)

Time (UT)

total P R

I II III

I - Quasi equilibrium regime

II - Photo-ionization regime

III - Recombination regime

ConclusionsConclusions• Applications of low ionospheric

investigations in science and information technologies

• Research of low ionosphere by VLF waves

• Importance of VLF radio signal data registered by receiver systems