Re: [TASS] photometric vs. non-photometric

[Herbert R Johnson <hjohnson@PLUTO.NJCC.COM>]

On         Thu, 2 Sep 1999 12:31:08 -0700, Chris Albertson <calbertson@LOGICON.COM> wrote:
*>Stupendous Man wrote:
*>
*>>   A better idea is to have a VERY simple program scan each new image
*>> and look for "cloudiness" -- Peter McCullough finds that Stardial
*>> images during cloudy weather are easy to distinguish from those taken
*>> during clear conditions, by several metrics.  If any image shows
*>> hints of "cloudiness", then declare the night "not photometric".
*>>
*>>   One might consider classifying two halves of the night (early and late)
*>> separately, or even each hour .... but that's overkill, to my mind.
*>
*>Sometime when you have a computer "overkill" is easyer than then doing
*>what would seem easy.  If Peter McCullough has a method that can look at
*>one image and determine if the conditions are "photometric" or not why not
*>feed _every_ image into his precedure?  Yes it may be overkill but the
*>other option is to write yet another procedure that decides which images
*>to evalutate.  Easyer to simply evaluate them all.

>From my review of Mark III sites and software, my impression is that each
site sets their own standards for what is acceptable conditions for data
collection. It should be kept in mind that the TASS project intends to work
under less-than-"photometric" conditions. My impression as a reader of
sites' reports is that some sites simply reject some images, at some point
during or before processing. Their casual reports aren't specific - you
might ask them! Certainly each Mark III site has set their own parameters of
their software's operation to suit conditions or the desired results (see
my recent Tech Note).

I have two points to make: first, I doubt there is "a method" that everyone
would accept to determine photometric conditions. People will write or find
methods that suit their interests and conditions. Second, there is
apparently the option of deciding not to process an image, or to
stop processing an image when the results suggest the image will not
be "productive". Some sites apparently find that "easier" for Mark III,
so I would guess they would not be interested in "overkill" methods for
Mark IV even if the datasets are much bigger and faster.

*>If you evaluate all images then you can switch programs after say,
*>three images in a row tell you than condidtions have changed.
*>This shouln't be too out of line.  I think everyone want's to move
*>toward real-time data reduction.  Maybe in a year or so.  Until then
*>maybe we can use some kind of manual switch
*>
*>  Chris Albertson

If you keep the "data reduction" software seperate from the "real time"
software, then sites can choose whether to run real-time or not. Certainly
they may want (or need!) to re-run old data if the methods are revised. It's
happened before in TASS. And, any third-party use of raw data may request
to use our reduction software; or conversely any third-party user of our
software on THEIR data.

The Mark III scheme seems to be effective: a series of programs that
can be run together or seperately, allowing sites to add or remove programs
from the "chain"; and independent of data collection but capable of being
called in "real time". And, programs with "parameters" than can be tweaked
to suit each site's observing needs and experiences.

Herb Johnson

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