MOPEX Online Manual
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Mosaic
The Mosaic pipeline performs interpolation and co-addition of FITS images. In Spitzer terms, the software takes the individual Basic Calibrated Data (BCD) frames and combines them to create a mosaic of the observed region. The user has a choice of interpolation and co-addition schemes, and the package also carries out the user's choice of outlier rejection to remove cosmic rays and bad pixels. Three main files are output by the package: a mosaic of the input BCDs, a coverage map showing how many of the input frames were rejected, and an uncertainty mosaic showing the relative uncertanites in each output pixel.
Basic Input Requirements
In order to carry out a basic mosaicking, MOPEX will expect some or all of the following files as input. See the sections on Input for more information on the format of these files.- A text file containing a list of input data images (e.g. Spitzer BCD frames; required)
- A text file containing a list of input uncertainty images (optional)
- A text file containing a list of input status mask images (optional)
- A mask image flagging permanently damaged pixels in the detector (pmask; optional)
- A "namelist" file specifying the parameters to be used for mosaicking (Command-Line MOPEX only; required)
Running Mosaic
Mosaicking is done on the command line using the perl wrapper script mosaic.pl. The syntax is as follows:prompt> mosaic.pl <option flag> <specification>
where <option flag> may be: -n, -I, -S, -d, -M, -R, -F, -O, any one of which, if specified, must be followed by a blank space and a corresponding specification, as given in the following table. More than one option flag (with corresponding specification) can be included, and they can be given in any order. The only option that must be called from the command line is the namelist; the other input files can be defined as parameters within the namelist. The default locations for all of the files except for the namelist file can be overridden by providing the full path name, for example:
prompt> mosaic.pl -n mosaic_I1.nl -I /home/joe/data/IRAC/ch1/bcd/ImageList.txt
See the page on Input for more information on the input and namelist files.
| Option Flag | Specification File (example) | Default Location | Required/Optional |
|---|---|---|---|
| -n | namelist of input parameters (mosaic.nl) | ./cdf/ | required |
| -I | list of input images (ImageList.txt) | ./ | required |
| -S | list of input uncertainty images (SigmaList.txt) | ./ | optional |
| -d | list of DCE status mask images (IMaskList.txt) | ./ | optional |
| -M | permanently damaged pixel mask image (pmask.fits) | ./cal/ | optional |
| -R | list of outlier mask images (RMaskList.txt) | ./ | optional |
| -F | Fiducial Image Frame file (FIF.tbl) | ./<output directory>/ | optional |
| -O | Output directory | ./ | optional |
Mosaicking a Portion of the Total FIF
If you have a list of images covering a large area of the sky, but only wish to make a mosaic covering a small portion of the total area, you can create new input lists for MOPEX using the module Mosaic Geometry. This module takes a user-modified FIF describing only a small portion of the whole coverage area, along with the full lists of all of the input images, and returns only those images that fall within the modified FIF area.
- Create the fiducial image frame based on the full input list. To do this, you should run mosaic.pl with only the following module activated in the namelist (see MOPEX Input Namelist or instructions on setting up your namelist):
run_fiducial_image_frame = 1
This will create the FIF.tbl file that specifies the spatial boundaries of all of your input frames. - Re-run mosaic.pl, but this time with the following settings in the namelist: set run_fiducial_image_frame = 0, specify the name of the new FIF file as input, set run_mosaic_geom = 1, and (usually) set MARGIN to a negative number (see Mosaic Namelist Options for more information on MARGIN).
This will generate new lists of your input data files, mask files and uncertainty files that cross the modified FIF.tbl. These new lists can then be input into MOPEX and run as any other reduction.
Creating a Mosaic of a Moving Object
This functionality is limited to Spitzer data. Some Spitzer observations are designed for moving targets, such as comets or asteroids. Moving target coordinates are written in the input image header with the keywords RA_REF and DEC_REF. The keywords are written in the headers of all input images, regardless of whether the moving object is present in the frame. MOPEX can create a mosaic in the rest frame of the moving object by setting the trigger MOVING_OBJECT_MOSAIC = x in the namelist, where x = the frame number that you wish to select as the stationary sky position. All other frames are then shifted relative to this initial stationary frame. i.e., if MOVING_OBJECT_MOSAIC = 5 then MOPEX will use the pointing and target position in the 5th frame as the stationary reference frame, CRVAL1stat, CRVAL2stat, RA_REFstat and DEC_REFstat. The pointing and target information for the ith image, CRVAL1i, CRVAL2i, RA_REFi and DEC_REFi is therefore redefined as follows:CRVAL1i --> CRVAL1i + ( RA_REFstat - RA_REFi)
CRVAL2i --> CRVAL2i + ( RA_REFstat - RA_REFi)
If the value of MOVING_OBJECT_MOSAIC is greater than the number of images in the set, the script exits with an error message. Setting it to 0 is the same as omitting the trigger word entirely. Specifying this keyword is the only action that the user needs to take to create the moving object mosaic. Be aware that outlier detection in this mode will reject not only cosmic ray hits and bad pixels, but real sources as well. This is because the real sources become transient in the rest frame of the moving object.
| Contents | ~ | Previous: Overlap Modules: Quicklook Mosaic | ~ | Next: Mosaic Pipeline Stages |
