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Re: Need help reconstructing flat-field. Minimization problem. [message #56528 is a reply to message #56393]

Wed, 24 October 2007 14:06

jdshaw
Messages: 7
Registered: October 2007

Junior Member

Jonathan,

I had a similar problem with a sky survey I did last year. The flats
the telescope operators provided were well below the linear response
area of the chip. So, I don't know if this will help, but this is
what I did:

> From each night's data, I took about forty different images used the
SKY routine from the asto libraries (http://idlastro.gsfc.nasa.gov/
contents.html) to find the sky background and then normalized each
image to its average sky value. I placed these in a 2048x2048x40
array (2048x2048 is the size of the chip). Then took the median value
for each pixel (alternatively, you can sigma-clip out high values and
average the rest).

This is simple but worked surprisingly well at preserving the flux
values.

If you are taking terrestrial - sorry aereal - images this probably is
to crude for your needs but may be a place to start. I suspect you
may need to write your own 'SKY' routine to find suitable
normalization values.

I'd be interested to hear your solution.

- John Shaw
Department of Physics and Astronomy
University of Delaware

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[Message index]

		Re: Need help reconstructing flat-field. Minimization problem. By: b_gom on Wed, 24 October 2007 11:26
		Re: Need help reconstructing flat-field. Minimization problem. By: JJ on Wed, 24 October 2007 07:51
		Re: Need help reconstructing flat-field. Minimization problem. By: Tal on Wed, 24 October 2007 01:46
		Re: Need help reconstructing flat-field. Minimization problem. By: pgrigis on Thu, 25 October 2007 01:13
		Re: Need help reconstructing flat-field. Minimization problem. By: jdshaw on Wed, 24 October 2007 14:06
		Re: Need help reconstructing flat-field. Minimization problem. By: JJ on Wed, 24 October 2007 13:45
		Re: Need help reconstructing flat-field. Minimization problem. By: JJ on Wed, 24 October 2007 13:44

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