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: http://www.atnf.csiro.au/computing/software/askapsoft/sdp/docs/current/BETApipelines/ScienceFieldSpectralLineImaging.html
Дата изменения: Unknown Дата индексирования: Tue Apr 12 13:04:10 2016 Кодировка: IBM-866 Поисковые слова: m 8 |
There are several steps involved in running the spectral-line imaging, with several optional pre-processing steps:
Following this pre-processing, the resulting MS is imaged by the simager task, creating a set of spectral cubes. At this point, no mosaicking of these is done, but this will be added in a future version of the pipeline.
The variables presented below work in the same manner as those for the continuum imaging, albeit with names that clearly refer to the spectral-imaging.
Variable | Default | Parset equivalent | Description |
---|---|---|---|
DO_SPECTRAL_IMAGING | false | none | Whether to do the spectral-line imaging |
Preparation of spectral dataset | |||
DO_COPY_SL | false | none | Whether to copy a channel range of the original full-spectral-resolution measurement set into a new MS. If the original MS is original.ms, this will create original_SL.ms. |
CHAN_RANGE_SL_SCIENCE | “1-NUM_CHAN_SCIENCE“ | channel (mssplit (Measurement Splitting/Averaging Utility)) | The range of channels to copy from the original dataset (1-based). |
TILENCHAN_SL | 1 | stman.tilenchan (mssplit (Measurement Splitting/Averaging Utility)) | The number of channels in the tile size used for the new MS. The tile size defines the minimum amount read at a time. Since the simager will process single channels, making this 1 (the default) means the simager workers only read what they need to . |
DO_APPLY_CAL_SL | false | none | Whether to apply the gains calibration determined from the continuum self-calibration (see GAINS_CAL_TABLE in User Parameters - Continuum Self-calibration). |
DO_CONT_SUB_SL | false | none | Whether to subtract a continuum model from the spectral-line dataset. If true, the clean model from the continuum imaging will be used to represent the continuum, and this will be subtracted from the spectral-line dataset (either the original full-spectral-resolution one, or the reduced-channel-range copy), which gets overwritten. |
Continuum subtraction | |||
CONTSUB_METHOD | Cmodel | none | This defines which method is used to determine the continuum that is to be subtracted. It can take one of three values: Cmodel (the default), which uses a model image constructed by Cmodel (cmodel (Model Image Generator)) from a continuum components catalogue generated by Selavy (Selavy Basics); Components, which uses the Selavy catalogue directly by in the form of components; or CleanModel, in which case the clean model from the continuum imaging will be used. |
CONTSUB_SELAVY_NSUBX | 6 | nsubx (Selavy Basics) | Division of image in x-direction for source-finding |
CONTSUB_SELAVY_NSUBY | 3 | nsuby (Selavy Basics) | Division of image in y-direction for source-finding |
CONTSUB_SELAVY_THRESHOLD | 6 | snrCut (Selavy Basics) | SNR threshold for detection with Selavy in determining components to go into the continuum model. |
CONTSUB_MODEL_FLUX_LIMIT | 0mJy | flux_limit (cmodel (Model Image Generator)) | Flux limit applied to component catalogue - only components brighter than this will be included in the model image. Parameter takes the form of a number+units string. Default (0mJy) implies all compoennts are used. |
Basic variables for imaging | |||
NUM_CPUS_SPECIMG_SCI | 2000 | none | The total number of processors allocated to the spectral-imaging job. One will be the master, while the rest will be devoted to imaging individual channels. |
CPUS_PER_CORE_SPEC_IMAGING | 20 | none | The number of processors per node to use (max 20). |
IMAGE_BASE_SPECTRAL | i.cube | Helps form Images.name (simager) | The base name for image cubes: if IMAGE_BASE_SPECTRAL=i.blah then we’ll get image.i.blah, image.i.blah.restored, psf.i.blah etc |
DIRECTION_SCI | none | Images.direction (simager) | The direction parameter for the image cubes, i.e. the central position. Can be left out, in which case it will be determined from the measurement set by mslist. This is the same input parameter as that used for the continuum imaging. |
NUM_PIXELS_SPECTRAL | 2048 | Images.shape (simager) | The number of spatial pixels along the side for the image cubes. Needs to be specified (unlike the continuum imaging case). |
CELLSIZE_SPECTRAL | 10 | Images.cellsize (simager) | The spatial pixel size for the image cubes. Must be specified. |
REST_FREQUENCY_SPECTRAL | HI | Images.restFrequency (simager) | The rest frequency for the cube. Can be a quantity string (eg. 1234.567MHz), or the special string ‘HI’ (which is 1420.405751786 MHz). If blank, no rest frequency will be written to the cube. |
Gridding | |||
GRIDDER_SPECTRAL_SNAPSHOT_IMAGING | true | snapshotimaging (Gridders) | Whether to use snapshot imaging when gridding. |
GRIDDER_SPECTRAL_SNAPSHOT_WTOL | 2600 | snapshotimaging.wtolerance (Gridders) | The wtolerance parameter controlling how frequently to snapshot. |
GRIDDER_SPECTRAL_WMAX | 2600 | WProject.wmax (Gridders) | The wmax parameter for the gridder. |
GRIDDER_SPECTRAL_NWPLANES | 99 | WProject.nwplanes (Gridders) | The nwplanes parameter for the gridder. |
GRIDDER_SPECTRAL_OVERSAMPLE | 4 | WProject.oversample (Gridders) | The oversampling factor for the gridder. |
GRIDDER_SPECTRAL_MAXSUPPORT | 512 | WProject.maxsupport (Gridders) | The maxsupport parameter for the gridder. |
Cleaning | |||
SOLVER_SPECTRAL | Clean | solver (Solvers) | Which solver to use. You will mostly want to leave this as ‘Clean’, but there is a ‘Dirty’ solver available. |
CLEAN_SPECTRAL_ALGORITHM | Basisfunction | Clean.algorithm (Solvers) | The name of the clean algorithm to use. Note that the default has changed to ‘Basisfunction’, as we don’t need the multi-frequency capabilities of ‘BasisfunctionMFS’. |
CLEAN_SPECTRAL_MINORCYCLE_NITER | 500 | Clean.niter (Solvers) | The number of iterations for the minor cycle clean. |
CLEAN_SPECTRAL_GAIN | 0.5 | Clean.gain (Solvers) | The loop gain (fraction of peak subtracted per minor cycle). |
CLEAN_SPECTRAL_SCALES | “[0,3,10]” | Clean.scales (Solvers) | Set of scales (in pixels) to use with the multi-scale clean. |
CLEAN_SPECTRAL_THRESHOLD_MINORCYCLE | “[30%, 0.9mJy]” | threshold.minorcycle (Solvers) | Threshold for the minor cycle loop. |
CLEAN_SPECTRAL_THRESHOLD_MAJORCYCLE | 1mJy | threshold.majorcycle (Solvers) | The target peak residual. Major cycles stop if this is reached. A negative number ensures all major cycles requested are done. |
CLEAN_SPECTRAL_NUM_MAJORCYCLES | 0 | ncycles (Solvers) | Number of major cycles. |
CLEAN_WRITE_AT_MAJOR_CYCLE | false | Images.writeAtMajorCycle (simager) | If true, the intermediate images will be written (with a .cycle suffix) after the end of each major cycle. |
Preconditioning | |||
PRECONDITIONER_LIST_SPECTRAL | “[Wiener, GaussianTaper]” | preconditioner.Names (Solvers) | List of preconditioners to apply. |
PRECONDITIONER_SPECTRAL_GAUSS_TAPER | “[50arcsec, 50arcsec, 0deg]” | preconditioner.GaussianTaper (Solvers) | Size of the Gaussian taper - either single value (for circular taper) or 3 values giving an elliptical size. |
PRECONDITIONER_SPECTRAL_WIENER_ROBUSTNESS | 0.5 | preconditioner.Wiener.robustness (Solvers) | Robustness value for the Wiener filter. |
PRECONDITIONER_SPECTRAL_WIENER_TAPER | “” | preconditioner.Wiener.taper (Solvers) | Size of gaussian taper applied in image domain to Wiener filter. Ignored if blank (ie. тАЬтАЭ). |
Restoring | |||
RESTORE_SPECTRAL | true | restore (simager) | Whether to restore the image cubes. |
RESTORING_BEAM_SPECTRAL | fit | restore.beam (simager) | Restoring beam to use: ‘fit’ will fit the PSF in each channel separately to determine the appropriate beam for that channel, else give a size (such as 30arcsec, or тАЬ[30arcsec, 30arcsec, 0deg]тАЭ). |
RESTORING_BEAM_REFERENCE | mid | restore.beamReference (simager) | Which channel to use as the reference when writing the restoring beam to the image cube. Can be an integer as the channel number (0-based), or one of ‘mid’ (the middle channel), ‘first’ or ‘last’ |
RESTORING_BEAM_LOG | beamLog.IMAGE.txt (with IMAGE from IMAGE_BASE_SPECTRAL) | restore.beamLog (simager) | The ASCII text file to which will be written the restoring beam for each channel. If blank, no such file will be written. |