Measure noise of a FITS file

Beginner’s tutorial showing how to measure the noise of a MadcubaMap object. For a detailed overview go to the documentation page.

First we read the FITS file as a MadcubaMap object.

from madcubapy.io import MadcubaMap

# Read fits file
madcuba_map = MadcubaMap.read(
    "../examples/data/IRAS16293_SO_2-1_moment0_madcuba.fits")

To measure the noise level of the map we have two options:

• We can use the measure_noise() function on the MadcubaMap object to obtain the sigma value in a variable (this also works for CCDData objects):

  sigma = measure_noise(madcuba_map)
  

• Or we can use the MadcubaMap.update_sigma() method to automatically store the measured sigma value in the FITS header, on the SIGMA card, and have it available for future analysis:

  madcuba_map.update_sigma()
  

  Note

  Remember that changes applied to a MadcubaMap object during a python run are not stored into the FITS file until the file is explicitly saved:

  madcuba_map.write("output_file.fits", overwrite=True)
  

How it works

Both options behave in the same way. A window will appear where the user can select polygons using the mouse:

• Left clicks create polygon vertices.

• Right click closes the current polygon, and a subsequent left click starts a new polygon.

This window also offers buttons to change the statistic used to calculate the noise.

Once we have the desired polygons, we can press the Finish button to close the window and return the noise value in a variable (the case of measure_noise()) or stored in the FITS header (the case of MadcubaMap.update_sigma()).