Digitization in Kodaikanal Observatory

References and useful links : http://solar.physics.montana.edu/ypop/Spotlight/Magnetic/index.html http://solarscience.msfc.nasa.gov/index.html http://www.windows2universe.org/sun/sun.html http://sdo.gsfc.nasa.gov

What is Digitization of an Image?

•Recording Image intensity through

optics and rectangular array of sensing

element (Figure 1)

•Dividing the image into a set of blocks i.e. pixels [sampling] (Figure 1)

•Each block being assigned an integer value representing image intensity [quantization]

Kodaikanal Solar Image Archive

•Full disc images of Sun from the year 1904 in white light and different wavelengths [CaK (393.37 nm), Hα (656.28 nm)] are recorded in photographic plates and films.

•Different structures on Sun are visible from these images.

Digitization Process

•Digital images are recorded through light source, imaging optics and sensing device (Figure 1)

•Using automated detection techniques we identify different solar structures (Figures 3,4,5)

•Automated detection are more accurate and less subjective.

•One can study the different solar phenomena.

Digitization Process

Charge Coupled Device

•Invented in 1969 at  AT & T

Bell labs

•Used as image sensor

•Based on semiconductor

material

•Light intensity is converted

to bulk of charge

Collection of lenses

Pixel size:15μmCCD size:4096х4096

Full

Solar

Disc

Digital image of Sun in Hα (656.28nm)

Figure 4: Center-to-boundary Figure 5: Automated Detection darkening corrected Image of filaments

Figure 2: Digital Image of Full Solar Disc captured in Film

Figure 1: Schematic of the digitization

Solar Filament/ ProminenceFilaments, on-disc dark elongated structures, are representative of magnetic activity on Sun. They can erupt (Figure 6) and have some impact on space weather. Kodaikanal data archive on filaments can act as a missing link for study of solar activity variation over large time span. Different parameters related to temporal periodicity can be extracted based on this historical data and can also be correlated with other dynamic phenomena of Sun such as sunspot cycle.

Figure 6:Closer look at filaments/ Prominence(Image source: Solar Dynamics Observatory, NASA)

Figure 3: Shift and rotation corrected image

Keywords:

•Film: Used for photography. It is a sheet of transparent plastic base coated on one side with gelatine emulsion containing infinitesimally small light-sensitive silver halide crystals called grains. Size and other parameters of these grains determine resolution, contrast, light sensitivity.

•Imaging Optics: Lenses of different power arranged one after another with systematic interspacing for imaging the object on CCD plane with proper quality and magnification.

•Full Solar Disc: 2 dimensional view of the spherical shell at a radial distance of 6.955 × 105km from center of sun.

•Solar structures/features: Sunspots, filaments, active regions, flares, coronal mass ejections.

•Solar Cycle: Periodicity in time for different structures/features on sun with respect to their number/position . They help to understand dynamic phenomena happening in sun having impact on space climate.

http://www.iiap.res.in/http://www.iiap.res.in/iiaoutreach/ Poster Credit: Subhamoy Chatterjee