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

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

Our goal Our data: G-band images and LOS velocity maps (obtained from the FeI line at 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

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

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

Sunspots (Turman et al, 2002)

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

Granulation (Hirzberger et al, 1997)

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

Granulation (Bovelet & Wiehr, 2001)

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

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

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

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

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 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

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

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

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

Thank you for your attention !

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

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

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

G-band bright points sizes: 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)