[vsnet-chat 1282] Image Archive

[aah@nofs.navy.mil]

Steve forwarded a message from Jim Waller about archiving SNe images.  We've run into that
problem with TASS, and also several other projects that I'm associated with.  Of course,
the ideal answer is to archive everything, but that is not often practical.  At 175MB per
run, you could archive the data to CD-R media and get ~4 nights per disk.  Since the media
cost is ~US$2 these days, such archiving is not terribly expensive, and then you have
random access to the older images.  I prefer CD-R since it is a very standardized media,
and everyone has a CD reader.  Other choices might be DAT, Travan, etc. tape or even
the new DVD writers that are starting to appear.
  We also considered or used two other methods.  You can compress the images using
hcompress or its equivalent by 5-10X without much loss of information (run in this mode,
it is a lossy compression algorithm).  Or, you can process the image by extracting all
stars and galaxies (position, image shape parameters, photometry) and save the resultant
starlist, and then throw your CCD frame away.  This also nets you about 10x storage
reduction (depending on the density of objects in your frame).  A third technique, especially
for SNe searches, is to just save the 'postage stamp' around the galaxy and throw away
the rest of the frame.
  So my answer is:  if you think your images have some scientific merit, either for
historical images of SNe fields or for variable star studies or ..., then you should
consider saving them for long periods of time.  Otherwise, throw them away and don't
feel guilty.
Arne

--------------------------------------------------------------------
Arne Henden                               Instruments/software/CCDs
US Naval Observatory Flagstaff Station    Cepheids/photometry/IR
P.O. Box 1149                             http://ftp.nofs.navy.mil  
Flagstaff, AZ 86002-1149                  Voice: (520)779-5132
aah@nofs.navy.mil                         FAX:   (520)774-3626

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