Processing of SDO white-light images 

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The Solar Dynamics Observatory (SDO) was launched in 2010 and is still operational in 2025. 

Numerous images are available, notably from the Helioviewer.org website. Our work involved:

• Acquiring images of the Sun in the continuum using the HMI instrument.

• Detecting and measuring sunspots.

• Tracking the evolution of these events.

• Assessing the distribution of events across the photosphere.

To achieve this, ImageSol, a Python-based program, was developed to:

• Import and analyze images.

• Using the obtained data, a curve similar to the Wolf curve and a butterfly diagram (also known as the Maunder diagram) were created.

The steps of the ImageSol program:

• Image importation is done via an API request (Application Programming Interface) to the URL https://api.helioviewer.org/v2/getJP2Image/ followed by several parameters.

• The images are retrieved on a local PC, which then examines them with ImageSol to detect the solar disk and determine its center and diameter in pixels.

• Sunspots are also detected; the program determines their rectangular coordinates and then calculates their size or, in some cases, the size of a complex sunspot.

• The program determines heliographic elements based on the observation date from SDO. These elements include:

a) P, the angle between the solar north direction and geographic north. 

b) Bo, the heliographic latitude of the solar disk center. 

c) Lo, the longitude of the solar disk center relative to the Carrington meridian.

• Only Bo and Lo values are considered, as SDO does not account for the difference between the solar north direction and geographic north. Knowing the rectangular positions of sunspots makes it easy to calculate their heliographic coordinates.

Below is an example of data from an analysis of a solar image:

Solar disk center: (499, 499),
Diameter: 789
B0: -7.22, L0: 163.91, Rot syn: 2281
-20.07;-191.43;13;12;-36.23;-3.33;160.58
71.93;-42.93;9;9;-13.34;10.57;174.48
91.43;-40.93;12;9;-12.97;13.47;177.38
etc.

The filename (here 2024_02_29_12_00_00.dat) contains the date and time of the observation in the format YYYY_MM_DD_hh_mm_ss.
The first line contains the x, y position of the solar disk center in pixels, here x = 499 and y = 499.
The second line contains the heliographic elements Bo and Lo, as well as the synodic rotation number. Here, Bo = -7.22°, Lo = 163.91°, and Rotation Number = 2281.
The following lines correspond to each sunspot (simple or complex) detected. For example, the line 

-20.07;-191.43;13;12;-36.23;-3.33;160.58

indicates that the sunspot is at x = -20.07 px, y = 191.43 px, measuring 13 and 12 px, with a heliographic latitude of -36.23°, a longitude relative to the solar disk center of -3.33°, and a longitude relative to the Carrington meridian of 160.58°.

These data, compiled with ImageSol, provide insight into the evolution of solar activity.

Firstly, the counting of the sunspot surface area recalls the calculation of the Wolf number. This Wolf number, which has been used to determine the cycle of solar activity, is calculated based on the number of sunspot groups and individual spots. Similarly, ImageSol provides insight into this evolution, not based on the number of spots but on their surface area.

Secondly, the program determines the distribution of sunspots according to their heliographic position to generate the Maunder diagram, which is also correlated with the activity of our star.