Coronal Hole Detection

Coronal Hole Detection is carried out using a two-threshold region growing algorithm.

Algorithm

"""
python wrapper function for fortran algorithm
@param image_data: EUV Image data for detection
@param use_chd: matrix of size (nx,ny) which contains 1's where there is valid image data, 
                and non-zero values for areas with invalid/no IMG data.
@param nx, ny: image dimensions
@param t1, t2: threshold values
@param nc: pixel connectivity parameter - number of consecutive pixels needed for connectivity
@param iters: maximum number of iterations allowed
@return ezseg_output: segmentation map where 0 marks a detection
@return iters_used: number of iterations preformed
"""
ezseg_output, iters_used = ezsegwrapper.ezseg(np.log10(image_data), use_chd, nx, ny, t1, t2, nc, iters)

• 1.) viable pixels are checked to see if the intensity level is below threshold 1
  • if so, pixel is marked
• 2.) in each iteration, pixels are checked if their intensity is between threshold 1 and 2, and if they have the required number of connected pixels
  • if so, pixel is marked
• 3.) continues until no more pixels are marked

Example Maps

Example minimum intensity merge maps with and without Coronal Hole Detection overlaid. You can click on image titles to enlarge images. Maps with both methods of minimum intensity merge are shown.

Minimum Intensity Merge with Two Threshold Mu Cutoff Values

April 11, 2011

EUV Map	Combined EUV/CHD Map

May 15, 2011

EUV Map	Combined EUV/CHD Map

July 21, 2011

EUV Map	Combined EUV/CHD Map

August 18, 2011

EUV Map	Combined EUV/CHD Map

October 1, 2011

EUV Map	Combined EUV/CHD Map

Minimum Intensity Merge based on Maximum Mu Value

April 11, 2011

EUV Map	Combined EUV/CHD Map

May 15, 2011

EUV Map	Combined EUV/CHD Map

July 21, 2011

EUV Map	Combined EUV/CHD Map

August 18, 2011

EUV Map	Combined EUV/CHD Map

October 1, 2011

EUV Map	Combined EUV/CHD Map