[daip] CNTR (levels)

[Ian Pattison]

I wish to set CLEV to be equal to the rms locally in an image (since I
have ran PBCOR and so the noise varies alot over my wide-field image).
What is the most accurate way to measure the noise? I have tried 2 methods
so far:

1) using TVWIN and IMSTAT to find the rms in a number of boxes close to
the source of interest.

2) using IMEAN to find the "true" rms over a larger box covering the
source (source at centre).

These two methods provide similar, but not equal, results. How "good" is
IMEAN at calculating the true noise rms (since the rms of the source must
somehow be subtracted).



Thankyou.

Ian Pattison

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::               Ian Pattison                 ::
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::Department of Physics & Astronomy           ::
::University of Leeds                         ::
::LS2 9JT                                     ::
::United Kingdom                              ::
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::Tel: +44 (0)113 2333872                     ::
::email: ip at ast.leeds.ac.uk                   ::
::WWW: http://ast.leeds.ac.uk/~ip             ::
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