LASCO MONTHLY MINIMUM (BACKGROUND) IMAGES

(updated 2002/09/26 by N. Rich)

created by mk_monthly_min.pro


PROCEDURE:

	A sequence of daily median images is read. For each pixel, the 
minimum non-zero value is selected. The amount of images used varies, 
but it is no more than 27 days for single-year minimums. The date in the 
filename is the MID-POINT in the sequence, and corresponds to the date of 
the file for which you want a background. The number of days used appears 
in the header, as does the first and last days used. The characters 'xx' 
in the place of the year in a filename indicates that images from more 
than one year were used. (As of now, the date for the xx files is still 
the last day in the sequence.) For C3, images used are from 1996/05/01 - 
1998/06/24. For C2, images used are from 1996/02/27 - 1999/12/31. The same 
interval is chosen for each year. (For example, March 3-30 for 1997 and 1998, 
in the case of C3.)

	In the case of yearly images, all daily medians for a given year 
are used to compute the minimum image.


FILE NAMING schemes:

 	tm_fwpw_yymmdd.fts

	where 	t  = telescope [1,2,3]
		m  = m (monthly image)
		fw = filter abbreviation from abbrv_filpol.pro
		pw = polarizer abbreviation from abbrv_filpol.pro
		yymmdd = date of the MIDPOINT of the range of days used -or-
			 in the case of xx, date of the LAST day used

- or -

	ty_fwpw_yyyy.fts

	where 	y  = y (yearly image)
		yyyy = year


See FITS header for additional information about a given image.


OTHER FILES:

changes.txt: Lists symbolic links providing "bookends" to periods adjacent to 
large gaps or stray light changes.

rolled.txt: Lists daily median images in $MONTHLY_IMAGES/rolled/. Corresponds 
to days when SOHO was rolled GT 2 degrees, and the regular backgrounds can not 
be used.

Written 2001/12/10 by N. Rich, NRL <nathan@calliope.nrl.navy.mil>.