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Description | ||
=========== | ||
================= | ||
Outlier Detection | ||
================= | ||
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:Classes: `jwst.outlier_detection.OutlierDetectionStep` | ||
:Aliases: outlier_detection | ||
Outlier detection uses different algorithms based on the input data type, and so is handled | ||
in separate steps, as follows: | ||
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Processing multiple datasets together allows for the identification of bad pixels | ||
or cosmic-rays that remain in each of the input images, many times at levels which | ||
were not detectable by the :ref:`jump <jump_step>` step. The ``outlier_detection`` step | ||
implements the following algorithm to identify and flag any remaining cosmic-rays or | ||
other artifacts left over from previous calibrations: | ||
#. **Image modes**: 'FGS_IMAGE', 'MIR_IMAGE', 'NRC_IMAGE', 'NIS_IMAGE' | ||
#. **Spectroscopic modes**: 'MIR_LRS-FIXEDSLIT', 'NRS_FIXEDSLIT', 'NRS_MSASPEC' | ||
#. **Time-Series-Observation(TSO) Spectroscopic modes**: 'MIR_LRS-SLITLESS', 'NRC_TSGRISM', 'NIS_SOSS', 'NRS_BRIGHTOBJ' | ||
#. **IFU Spectroscopic modes**: 'MIR_MRS', 'NRS_IFU' | ||
#. **TSO Image modes**: 'NRC_TSIMAGE' | ||
#. **Coronagraphic Image modes**: 'MIR_LYOT', 'MIR_4QPM', 'NRC_CORON' | ||
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#. build a stack of input data | ||
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- all inputs will need to have the same WCS since outlier detection assumes | ||
the same flux for each point on the sky, and variations from one image to | ||
the next would indicate a problem with the detector during readout of that pixel | ||
- if needed, each input will be resampled to a common output WCS | ||
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#. create a median image from the stack of input data | ||
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- this median operation will ignore any input pixels which have a weight | ||
which is too low (<70% max weight) | ||
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#. create "blotted" data from the median image to exactly match each original | ||
input dataset | ||
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#. perform a statistical comparison (pixel-by-pixel) between the median blotted | ||
data with the original input data to look for pixels with values that are | ||
different from the mean value by more than some specified sigma | ||
based on the noise model | ||
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- the noise model used relies on the error array computed by previous | ||
calibration steps based on the readnoise and calibration errors | ||
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#. flag the DQ array for the input data for any pixel (or affected neighboring | ||
pixels) identified as a statistical outlier | ||
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The outlier detection step serves as a single interface to apply this general | ||
process to any JWST data, with specific variations of this algorithm for each | ||
type of data. Sub-classes of the outlier detection algorithm have been developed | ||
specifically for: | ||
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#. Imaging data | ||
#. IFU spectroscopic data | ||
#. TSO data | ||
#. coronagraphic data | ||
#. spectroscopic data | ||
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This allows the outlier_detection step to be tuned to the variations in each type | ||
of JWST data. | ||
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Reference Files | ||
=============== | ||
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The ``outlier_detection`` step uses the PARS-OUTLIERDETECTIONSTEP parameter reference file. | ||
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.. include:: ../references_general/pars-outlierdetectionstep_reffile.inc | ||
FIXME: add links to the docs for each of these |
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