RE: Automatic Processing of Data

["Creager, Robert S" <CreagRS@LOUISVILLE.STORTEK.COM>]

Hmmmm,

I was following Tech Note 62 (since I don't yet know what's correct or
incorrect data preparation).
http://www.tass-survey.org/tass/technotes/tn0062.html  Is the section
"Master dark frames" incorrect, or am I not understanding the text
correctly?  The section is as follows:

"I combined dark frames to make a "master" dark frame, which I will use for
further reductions. I used all the dark images from Feb 11, 2000. First, for
all V-band (or I-band) images, I calculated the mean value in a box near the
center of the frame: box center at (1000, 1000) and 500 pixels in size.
Then, I scaled the darks so that they all had the same mean value inside
that box (it required very little scaling in most cases). Finally, I created
a "master dark" frame by taking the median of all the pixel values at each
(row, col) position; I used 31 frames as input to this median procedure."

That's an easy fix to make either way.

Any thoughts on minimum number of frames for a good dark/flats?  Or trying
to quantatize how you reject images for flat creation?

Thanks,
Rob


> -----Original Message-----
> From: aah@nofs.navy.mil [mailto:aah@nofs.navy.mil]
> Sent: Wednesday, December 20, 2000 10:15 AM
> To: Creager, Robert S
> Cc: tass@listserv.wwa.com
> Subject: RE: Automatic Processing of Data
> 
> 
> Rob,
>   Darks are *not* mean scaled before the median is found; only
> flats are scaled.  Darks represent the thermal contribution at
> a constant temperature, and as such should not be scaled but just
> median or average combined. It is only when the flux changes,
> such as in the case of sky flats, that you scale.
> In addition, dark current is not linear and so is difficult
> to scale in any event.
> Arne
>