Important Notes:Using this module does not mean that MOPEX will automatically use the results for outlier detection. In order to use the results from this module, you must set Use Outlier For Rmask in the Mosaic RMask module and set the RMask Fatal Mask Bit Pattern in the Initial Setup module to use bit 1. Note that this is not the same as setting it to a value of 1. See §8.11: Fatal Mask Bit Patterns for more information.
PURPOSE
This module uses the Multiframe Temporal Outlier rejection method (see §8.2.2). For a stack of input images with good coverage, the mean and sigma at each pixel on the sky are computed. Pixels outside an asymmetric sigma envelope are flagged as outliers. If the data have good coverage (>10), this is the best option for finding outliers. For very shallow coverage, this method will not work well.
INPUT
Bottom Threshold: (float) Specifies the upper envelope in sigma to identify outliers from the pixel stack. Default value is 3.0.
Top Threshold: (float) Specifies the lower envelope in sigma for selecting outliers.
Min Pix Number: (int) Minimum number of pixels in the stack needed to estimate sigma.
Tile X(Y) Size: (int) Set these to a smaller size to avoid memory allocation problem if users have a very large mosaic. See the discussion of Tiling (§8.1) for details.
Outlier output subdirectory: The subdirectory of <output_dir> that you wish to use for the output files. Default is Outlier-mosaic.
COMMAND LINE INPUT
&MOSAICOUTLIERIN
BOTTOM_THRESHOLD = 3,
TOP_THRESHOLD = 3,
THRESH_OPTION = 1,
MIN_PIX_NUM = 3,
TILE_XSIZ = 500,
TILE_YSIZ = 500,
&END
In Global Parameters:
OUTLIER_DIR = Outlier-mosaic
THRESH_OPTION: (int; command line only) There are two options for this parameter: 1: "less aggressive" or 2: "more aggressive". The difference lies in the specific algorithm used to estimate sigma (see §8.2.2 for more details). We strongly recommend that all users use THRESH_OPTION = 1. For this reason, this parameter does not exist in the GUI, which uses option 1 by default.
OUTPUT
Outlier Output FITS files (interp_*_outlier.fits): The product of this step is an outlier map. The pixel value is the deviation of that pixel in the input image from the mean in the stack in terms of the number of standard deviations.
DISCUSSION
This module does Multiframe Temporal Outlier detection (§8.2.2) on the interpolated input images. The interpolated input frames are stacked, and for each pixel position in the interpolated grid, the trimmed mean and standard deviation of the pixel values in the stack is calculated. The pixel values outside of the user-specified asymmetrical multi-sigma thresholds are classified as outliers. This method detects both moving objects and radhits. It is not meant to be used in the cases of shallow coverage.
The thresholds - Bottom Threshold and Top Threshold - can be set to 0, which is the default. In this case, the decision of declaring a particular pixel an outlier is put off until running the Mosaic RMask module. The advantage of doing it this way is that the user can experiment with different thresholds for outliers in the Mosaic RMask module, without having to rerun the Mosaic Outlier module.
