Earthshine blog

Earthshine blog

"Earthshine blog"

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

Need to flatten?

Bias and Flat fieldsPosted by Daddy-o Jun 10, 2013 01:01PM
These are calibrated B-V images from JD2455945.17, as explained at this link.

The one on the left is generated WITH flatfielding of the B and V images used, while the one on the right is generated WITHOUT flatfielding. They are almost identical, but not quite. Here is the difference between the two:

The pattern is the expected pattern from the CCD chip. The histogram of the values is here:

So there is a difference which is distributed around 0 with S.D. 5 millimagnitudes. The effect of flattening would appear to be small - but recall that these are difference images.

Apart from various problems related to aligning images it is rather nice to work with difference images - problems tend to cancel out! However, note in the above how some of the structure on the DS in the B-V image looks like the features of the falt field - as if perhaps the flatfield we used did nothave enoughj 'amplitude' in the stripes.

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