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cta-observatory / ctapipe

Low-level data processing pipeline software for CTAO or similar arrays of Imaging Atmospheric Cherenkov Telescopes
https://ctapipe.readthedocs.org
BSD 3-Clause "New" or "Revised" License
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Hillas uncertainties are systematically under-estimated when cleaning is applied or noise is present. #1847

Open maxnoe opened 2 years ago

maxnoe commented 2 years ago

Describe the bug

When using cleaning or noise is present (aka always), it seems the uncertainties for the hillas parameters are dramatically under-estimated.

The formulas seem only to be valid for the case where all signal is used for the estimation and no noise is present.

To Reproduce

Notebook with toy simulations: https://github.com/maxnoe/notebooks/blob/main/ctapipe/hillas_uncertainties.ipynb

hillas_uncertainties

Expected behavior

The mean uncertainty of the hillas parameters should match the std over random samples from the same population.

andres-baquero commented 2 years ago

@maxnoe Thank you very much for this analysis.

We had not realized that the behavior of the Hillas parameters (length and width) changes so much because we had used a much simpler toy model where the effect of cleaning and noise was not appreciated.

We will continue to analyze this to try to adjust the calculation of the uncertainties and avoid such a large underestimation.