Date: Thu, 15 Oct 2009 12:51:37 -0600
From: Dan Long
Subject: Re: 2.5m obslog 20091014 (MJD 55119)
Thanks Dave.  This makes sense as the PT probably never observed
secondary patches where the imager is looking now for BOSS.  It was
true of the original survey though wasn't it?  I am pretty sure I
remember Steve Kent saying that the reason for the minimum scan
length was to be sure one crossed secondary patches in a scan, but it
has been a while...
-Dan
>Dan,
>
>It has nothing to do with calibration, which makes no use of the PT.
>It's a matter of having a run long enough to characterize the PSF.
>The PDF fitting code is not as robust as we'd like for short scans.
>
>D
>
>
>Sent from my iPhone
>
>On Oct 15, 2009, at 10:14, Dan Long  wrote:
>
>>>                       APACHE POINT OBSERVATORY SDSS 2.5M
>>>
>>>                                 OBSERVING LOG
>>>                           Wednesday October 14, 2009
>>>
>>>                                  (MJD 55119)
>>>
>>>---=== OBSERVING TEAM ===---
>>>
>>>Audrey Simmons
>>>Dan Oravetz
>>>
>>
>>
>>
>>>chose the latter. BTW, can someone please remind us as to the
>>>origin/reasoning
>>>for the 1 hour minimum scan length?
>>>
>>
>>   I understand it has to do with the spacing of calibration patches
>>that were observed by the PT.  They are roughly 15 degrees apart
>>along the stripes, and to get the best calibration of a run, it
>>needs to cross a patch.  The scan rate is sidereal so in an hour at
>>least one patch will have been crossed.  There are other issues of
>>efficiency for preferring longer scans, but I'm pretty sure the
>>reason for the one hour minimum is calibration of the data.
>>
>>                Cheers,
>>
>>                  Dan
>>
>>DSS DSS DSS DSS DSS  Digital Sky Survey DSS DSS DSS DSS DSS DSS
>>DSS *** The information posted to SDSS mailing lists is proprietary ***
>>DSS  This is message 4796 in the sdss-25mlog archive, URL
>>DSS         http://www.astro.princeton.edu:81/sdss-25mlog/msg.4796.html
>>DSS  The index is at http://www.astro.princeton.edu:81/sdss-25mlog/INDEX.html
>>DSS  To join/leave the list, go to
>>DSS
>>http://www.astro.princeton.edu:81/cgi-bin/mailinglists.pl/show_subscription?list=sdss-25mlog
>>DSS  To post a message, mail it to sdss-25mlog@astro.princeton.edu
>>DSS
>>DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS