Depends On: Mosaic Interpolate (or Mosaic Reinterpolate)
Relevant Pipelines: APEX Multiframe; APEX User List Multiframe
Important Notes: There are only two coaddition schemes available in the APEX version of this module. If the APEX pipeline is appended to a Mosaic pipeline, and you intend to use the mosaic.fits file from Mosaic as input into APEX, this module should be omitted from the flow. Note that you must have checked the Keep coadded Tiles box in the Mosaic CoAdder module in the Mosaic pipeline.
PURPOSE
The interpolated images are co-added to create one mosaic image. The pixel values of the mosaic image are equal to the averaged interpolated pixel values. The interpolated uncertainty images are also co-added into one uncertainty mosaic image following the standard assumption of additive variances. The coverage maps are co-added into a single mosaic coverage map.
INPUT
Tile Max X, Y: (int) The X (Y)-size of the tile for performing the co-addition. This should be reduced if computer memory is an issue (see §8.1).
Integration Time Weighted Coadd: Check this box to weight the coaddition by exposure time. MOPEX searches for the header keyword specified, the default is EXPTIME.
Mosaic Co-Adder output subdirectory: The subdirectory of <output_dir> that you wish to use for the output files. Default is Coadd-apex.
COMMAND LINE INPUT
&MOSAICCOADDIN
TILEMAX_X = 1000,
TILEMAX_Y = 1000,
INTEG_TIME_KWD = ‘EXPTIME’,
&END
In Global Parameters:
COADDER_DIR = Coadd-apex
INTEG_TIME_KWD: This is the equivalent of checking the Integration Time Weighted Coadd box in the GUI. If INTEG_TIME_KWD = ‘EXPTIME’ is set in the parameter block, intergration time weighted coadd will be used.
OUTPUT
Tile BCD file (coadd_tile_bcd.txt): This text file lists the input images which contribute to each output tile. The format of the file is the tile ID, the number of contributing images, and the image index within the stack.
Tile table (coadd_tiles.tbl): A table listing the tiles, their sizes, and their offsets in the x- and y-directions with respect to the FIF.
Tile uncertainty list (coadd_Tile_*_Unc.fits): The stack of tiled uncertainty images.
Mosaic uncertainty file (coadd_Tile_*_Std_Unc.fits): The stack of tiled standard deviation images.
DISCUSSION
If the APEX pipeline is appended to a Mosaic pipeline, and you intend to use the mosaic.fits file from Mosaic as input into APEX, this module should be omitted from the flow. Note that you must have checked the Keep coadded Tiles box in the Mosaic CoAdder module in the Mosaic pipeline.
The co-addition can be performed on Tiles (see §8.1), to address computer memory considerations. The Mosaic CoAdder module performs the co-addition on the individual tiles, and the Mosaic Combine module then combines the tiles into a single mosaic. Even if only a single tile is used, Mosaic Combine still needs to be run, in order to produce the expected products.
There are only two weighting schemes available in the APEX version of this module. The interpolated images can be combined using the straight averaging or they can be weighted by exposure time. The co-added uncertainty image is computed, as long as the uncertainty images are given as an input to the program.
Straight Average: (default) If none of the weighting alternatives are selected, then the co-added pixel value O is given by the following expression:
Equation 6.3
Here Ij is the value of the interpolated pixel in image j, and cj is the pixel value of the corresponding coverage map. Co-added uncertainty U = W-1 is given by the following expression:
Equation 6.4
where σj is the pixel value of the corresponding uncertainty image, and co-added coverage C is simply the sum of the individual input coverages:
Equation 6.5
Exposure Time Weighted Average: If Integration Time Weighted Coadd is selected then MOPEX weights the co-added pixels by the exposure time given in the fits header keyword specified. For Spitzer data, the integration time is given by the keyword EXPTIME.
