1. Importance Of Very Low Frequency Radio Signal Data Registered By VLF-receiver System A. Nina, V. Čadež and V. Srećković Institute of Physics, Belgrade, Serbia Astronomical Observatory, Belgrade, Serbia Astronomical Observatory, Belgrade, Serbia

2. Contents Ionosphere VLF signals – “ionospheric probes”VLF signals – “ionospheric probes” Importance of creating a database for studying the ionosphere and its applications in technical and scientific researchImportance of creating a database for studying the ionosphere and its applications in technical and scientific research such as: - detection of different events by VLF signals - detection of different events by VLF signals -ionospheric diagnostics -ionospheric diagnostics -study of physical and chemical processes -study of physical and chemical processes

3. Introduction Terrestrial ionosphere Methods of investigation Our study: low ionosphere

4. VLF signals – “ionospheric probes” VLF wave propagation Advantages: - continual emission, - large area involved for analyses, - international collaboration: AWESOME AbsPALSAVNET AARDDVARK AWESOME, AbsPAL, SAVNET, AARDDVARK Belgrade VLF station

5. Significance of low 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

6. Importance 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

7. Detection of events Sun: - regular variation - transient variations Outer space Earth: - in the atmosphere - in the lithosphere pure natural man-induced HESSI SGR 1806-20

8. Ionospheric 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 ionosphere Numerical program for simulation VLF signal propagation: LWPC LWPC (Long-Wave Propagation Capability)

9. Physical and chemical processes (preliminary results) G(t) – electron gain rate L(t) – electron loss rate Upper half of D region: P(t) – photo-ionization rate R(t) – recombination rate I(t) – radiation flux by satellite α eff – effective recombination coefficient K s – coefficient (dependent on energy interval of data registered by satellite) I - Quasi equilibrium regime II - Photo-ionization regime III - Recombination regime

10. Conclusions 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