1. Statistical detection of meteor showers using data from the Swedish infrasound network Ludwik Liszka Swedish Institute of Space Physics SLU 901 83 Umea, Sweden

2. Swedish Infrasound Network Present stations: Kiruna Jamton Lycksele Uppsala

3. Search for small and medium meteor events – objectives: To search for meteor events below the infrasonic background level To establish a set of indicators which can be used to discriminate a single event To develop techniques for extraction of events from combined multi-station data

4. Meteor on 2002-12-30 in Morjärv, Northern Sweden

5. Morjärv Meteor

6. Angle-of-arrival = 208º Vp = 350 m/s

7. Morjärv Meteor

8. How to optimize the indicators? Principal Component Analysis (PCA) of multiple indicator data Indicators are distributions of variables: Angle-of-arrival Phase velocity Crosscorrelation Spectral slope

9. Principal component analysis Purpose: to find a direction where maximum variance may be found in multivariate data

10. PCA Direction of maximum variance

11. Angle-of-arrival Entropy = -1.18 (Emax=0, Emin=-2.42)

12. Phase velocity Vp

13. Cross-correlation

14. Spectral slope

15. Parameters of the analysis 1 window = 128 data points (7.11 sec) The window is moved in 32p steps (overlap) Distributions are created for each sample of 50 positions of the window 16 samples / 30 minutes

16. Discrimination of meteor impacts Selection of data to find proper combination of indicators: Concorde vs. North Sea Meteor Another approach is to apply PCA without pre-selecting transformation coefficients

17. Comparison of indicators

18. Plot of component loadings

19. High cross-correlation counts

20. Meteor discrimination

21. Bavarian Meteor 2002-04-06 5th principal component

22. Discriminant function based on 5 th PC

23. Small meteors – meteor showers Leonids – 2002-11-18

24. Small meteors – meteor showers Leonids – 2001-11-18

25. Combination of information from 2 stations (North Sea Meteor) Lycksele - Jamton

26. Combination of information from 2 stations (North Sea Meteor) Lycksele - Kiruna

27. Combination of information from 2 stations (Leonids 2002-11-18) Lycksele - Jamton

28. Conclusions PCA may be used to discriminate events with a specific signature, like meteor impacts The method may be applied to events below the noise level, for example, meteor showers