MOPEX User's Guide - IRSA

MOPEX User’s Guide
Apply Overlap Correction: Apply the calculated offsets to the BCD images to create the
new background-corrected images.
COMMAND LINE INPUT
&COMPUTEOVRLAPCORRIN
TOP_THRESHOLD = 3,
BOTTOM_THRESHOLD = 3,
MIN_IMG_NUM = 4,
WEIGHT = 0.0,
&END
WEIGHT: (float; command line only) Determines the overall level that the frames should be
corrected to. In the first method (WEIGHT = 0.0, the default), it determines the overall level
after finding the offsets, by forcing the sum of the offsets of all the images to add up to 0. In
the second method (nominally WEIGHT = 1.0), it minimizes the squared offsets as part of the
origina l minimization. See §4.1 Background Matching Overview for more information.
OUTPUT
Overlap Correction Table (offsets.tbl): A table of calculated offsets for each input DCE is
the primary output of the Overlap flow.
Corrected Images (overlapCorrection_*.fits): If Apply Overlap Correction is turned on, a
new FITS stack is output, with the background-matching offsets applied. These outputs are
written to the Overlap_corr subdirectory.
DISCUSSION
The background matching algorithm (see §8.5) calculates an offset to apply to each image in
order to set their backgrounds to a constant value. After the initial calculation, the offsets are
examined, and outliers are rejected, as long as the minimum number of images are present.
The other inputs to this module control how much of an outlier an offset has to be in order to
be rejected. A rejected outlier will not be used in determining the overall offset level for all
frames, but will still be applied to the corresponding data frame to bring the background to
the same offset as the other input frames.
The offsets and their uncertainties are written in the header of the corresponding output FITS
files. The keywords are OVRLPDC and OVRLPDCD. They keyword OVRLPOUT is set to 1
if the offset was determined to be an outlier. A table, offset.tbl, is also created, containing the
Overlap (overlap.pl) 42
Overlap Modules