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A blog about a system to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.

Brighter-Fatter effect

From flux to AlbedoPosted by Peter Thejll Feb 09, 2014 01:33PM
In an interesting paper by Antilogus, et al subtle effects of electron interactions inside the CCD material itself are discussed, which could be a tool for understanding and perhaps quantifying CCD nonlinearity.

We have tested our own Andor BU987 CCD camera for these effects and see them.

Plots of row- or column-neighbour means vs correlations. Top row: first panel: full set of values of means vs column-correlations - we note the strong non-linearities that set in at about 50.000, and some outliers.
Top row: second panel: for just the range of mean values below the onset of non-linearity a robust regression is performed (red line).
Bottom row: same as top row but now for row-correlations.
We note the general correspondence to results in the 'brighter-fatter' paper: rows are more strongly correlated with their neighbours than are columns - the ratio of slopes is about 2.0.

Can this be used quantitatively to correct for non-linearity in our CCD? The camera linearity was already tested for linearity while in Lund. See Figure 8 in the report.

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Posted by Augustin May 09, 2014 10:37AM

Hello,
I found you with a 'brighter-fatter' search on Google.

Cheers,

Augustin

Posted by Peter Thejll May 07, 2014 05:51PM

Hi! Thanks for your comment! We will discuss it and get back to you. How did you find our blog entry?

Cheers,

Peter

Posted by augustin May 07, 2014 05:42PM

"Can this be used quantitatively to correct for non-linearity in our CCD?"

I see figure 8 of your Report that you talk about PTC non linearity and not non-linearity of CCD sensitivity.

Yes indeed, pixels spatial correlation is the reason why you see PTC non linearity.
Be careful about what you assume to be a gain measurement. Your method is highly biased.