The motivation to use image recognition techinques in investigations of solar photosphere

1. The motivation to use image recognition techinques in investigations of solar photosphere Kasia Mikurda, Friedrich Wöger Kiepenheuer Institut Für Sonnenphysik Freiburg, Germany

2. Photospheric structures • sunspots, active regions (ARs) • granulation • faculae • photospheric bright points (G-band bright points, filigree...)

3. Our goal • Our data: G-band images and LOS velocity maps (obtained from the FeI line at 557.6 nm with TESOS – triple Fabry-Perot interferometer at VTT) • Our aims: - to detect the BPs in the G-band images- to find the corresponding structures on the velocity maps- to trace BPs in order to find their horizontal motions- to combine the results in order to get the 3D velocity vector of BPs

4. Examples of papers • sunspots • Turmon et al, 2002 • granulation • Bovelet & Wiehr, 2001 • Roudier & Muller, 1986 • Hirzberger et al, 1997 • faculae • Bovelet & Wiehr, 2001 • photospheric bright points • Berger et al, 1998 • Ballegooijen et al, 1998 • Nisenson et al, 2003

5. Sunspots(Turman et al, 2002) • investigation of solar cycle (magnetic flux, intensity) • identification and labelling of sunspots and ARs on SOHO/MDI images • good for searching in large image databases

6. Sunspots(Turman et al, 2002)

7. Granulation(Roudier and Muller, 1986; Hirzberger et al, 1997) • FBR (Fourier Based Recognition) • Investigations of distribution of sizes, and brightness of granules • 2-D passband Fourier filter is applied to the data and preserve only those frequencies that are expected to be characteristic for granular structures

8. Granulation(Hirzberger et al, 1997)

9. Granulation(Bovelet & Wiehr, 2001) • MLT (multilevel tracking) • application: mostly the same as previously mentioned method • uses iterative tresholding with multiple clip levels • recognizes and tags structures • unfortunately not yet well documented

10. Granulation(Bovelet & Wiehr, 2001)

11. Granulation(Bovelet & Wiehr, 2001)

12. Granulation(Bovelet & Wiehr, 2001)

13. Granulation(Bovelet & Wiehr, 2001)

14. G-band bright points(Berger et al., 1998) • G-band bright points are detected on the differential images (G-band image – wideband image @ 468.6 nm) by thresholding • measures the location of the centroid of GBPs • tracks the centroid location from one frame to consecutive one

15. G-band bright points (Berger et al, 1998)

16. G-band bright points(Nisenson et al, 2003) • G-band bright points are recognized visually • positions of G-band bright points are traced in a reference frame tied to the solar granulation • the GBs are then followed using correlation tracking (only clearly separated BPs are used) • only good for smaller amount of investigated structure

17. G-band bright points(Nisenson et al, 2003)

18. G-band bright points(Ballegooijen et al., 1998) • uses small circular discs (´corks`) to represent the brightenings on G-band images • uses ´magnetic images´ (difference images made by substracting the 468.6 nm images from the corresponding G-band images) • in the first step corks are randomly distributed • an artificial flow field proportional to the intensity gradient in the magnetic image is introduced • corks are driven to the brightest regions in the image • the velocities of the corks represent the velocities of GBPs • good for statistical investigation of velocities

19. G-band bright points(Ballegooijen et al., 1998)

20. References • Ballegoijen et al, 1998, ApJ 509, 435 • Berger et al, 1998, ApJ 495, 973 • Bovelet & Wiehr, 2001, SPh 201, 13 • Hirzberger et al, 1997, ApJ 480, 406 • Nisenson et al, 2003, ApJ 587, 458 • Roudier & Muller, 1986, SPh 107, 11 • Turmon et al., 2002, ApJ 568, 396

21. Discussion What kind of method of recognizing and tracing is the best for us ?

22. Thank you for your attention !

23. Sunspots • sizes: about few tousands of km in diameter (up to 30.000 km) • lifetime: from hours to weeks

24. Granulation • size: 1-2” • characteristic time scale: ~8 min (up to 15 min) • contrast between granules and intergranular lanes: ~10-30%

25. Faculae • often associated with sunspots, but can also exist apart from them • longer living than spots, lifetimes even up to 90 days • important in investigation of solar irradiance variation

26. G-band bright points • sizes: 150-250 km (up to 600 km) • lifetimes: ~8-9 min • splitting and merging time scale: ~3-4 min • horizontal motion: ~0.8 km/s (up to several km/s)