Provided by: wsclean_2.6-1build2_amd64 bug

NAME

       WSClean - Fast generic widefield interferometric imager

SYNOPSIS

       wsclean [options] <input-ms> [<2nd-ms> [..]]

DESCRIPTION

       WSClean  (w-stacking  clean)  is  a  fast generic widefield imager. It uses the w-stacking
       algorithm and can make use of the w-snapshot algorithm. As of Feb 2014, it is  2-12  times
       faster  than  CASA's w-projection, depending on the array configuration. It supports full-
       sky imaging and proper beam correction for homogeneous dipole arrays such as the MWA.

       WSClean allows Hogbom and Cotton-Schwab cleaning, and can  clean  polarizations  joinedly.
       All operations are performed on the CPU (it is not specialized for GPUs).

OPTIONS

   GENERAL OPTIONS
       -version
              Print WSClean's version and exit.

       -j <threads>
              Specify  number of computing threads to use, i.e., number of cpu cores that will be
              used. Default: use all cpu cores.

       -mem <percentage>
              Limit memory usage to the given fraction of the total system  memory.  This  is  an
              approximate value. Default: 100.

       -absmem <memory limit>
              Like -mem, but this specifies a fixed amount of memory in gigabytes.

       -reorder, -no-reorder
              Force  or  disable  reordering  of  Measurement  Set.  This  can be faster when the
              measurement set needs to be  iterated  several  times,  such  as  with  many  major
              iterations  or  in  channel  imaging  mode.  Default:  only reorder when in channel
              imaging mode.

       -tempdir <directory>
              Set the temporary directory used when reordering files. Default: same directory  as
              input measurement set.

       -no-dirty
              Do not save the dirty image.

       -saveweights
              Save the gridded weights in the a fits file named <image-prefix>-weights.fits.

       -saveuv
              Save  the  gridded  uv  plane, i.e., the FFT of the residual image. The UV plane is
              complex, hence two images will be output:  <prefix>-uv-real.fits  and  <prefix>-uv-
              imag.fits.

       -apply-primary-beam
              Calculate and apply the primary beam and save images for the Jones components, with
              weighting identical to the weighting as used by  the  imager.  Only  available  for
              LOFAR.

       -reuse-primary-beam
              If a primary beam image exists on disk, reuse those images (not implemented yet).

       -use-differential-lofar-beam
              Assume  the  visibilities  have  already  been  beam-corrected  for  the  reference
              direction.

       -update-model-required (default), -no-update-model-required
              These two options specify whether the model data  column  is  required  to  contain
              valid  model  data  after  imaging.  It  can save time to not update the model data
              column.

       -verbose (or -v)
              Increase verbosity of output.

       -log-time
              Add date and time to each line in the output.

       -quiet Do not output anything but errors.

   WEIGHTING OPTIONS
       -weight <weightmode>
              Weightmode can be: natural, uniform, briggs. Default: uniform. When  using  Briggs'
              weighting, add the robustness parameter, like: "-weight briggs 0.5".

       -superweight <factor>
              Increase  the  weight  gridding  box size, similar to Casa's superuniform weighting
              scheme. Default: 1.0 The factor can be rational  and  can  be  less  than  one  for
              subpixel weighting.

       -mfsweighting
              In  spectral  mode,  calculate the weights as if the image was made using MFS. This
              makes sure that the sum of channel images equals the MFS  weights.  Otherwise,  the
              channel image will become a bit more naturally weighted.  This is only relevant for
              weighting modes that require gridding  (i.e.,  Uniform,  Briggs').   Default:  off,
              unless -joinchannels is specified.

       -nomfsweighting
              Opposite  of  -mfsweighting; can be used to turn off MFS weighting in -joinchannels
              mode.

       -weighting-rank-filter <level>
              Filter the weights and set high weights to the  local  mean.  The  level  parameter
              specifies  the  filter  level; any value larger than level*localmean will be set to
              level*localmean.

       -weighting-rank-filter-size <size>
              Set size of weighting rank filter. Default: 16.

       -taper-gaussian <beamsize>
              Taper the weights with a Gaussian function. This will reduce  the  contribution  of
              long  baselines.   The  beamsize is by default in asec, but a unit can be specified
              ("2amin").

       -taper-tukey <lambda>
              Taper the outer weights with a Tukey transition. Lambda specifies the size  of  the
              transition; use in combination with -maxuv-l.

       -taper-inner-tukey <lambda>
              Taper  the  weights  with  a  Tukey  transition.  Lambda  specifies the size of the
              transition; use in combination with -minuv-l.

       -taper-edge <lambda>
              Taper the weights with a rectangle, to keep a space of lambda between the edge  and
              gridded visibilities.

       -taper-edge-tukey <lambda>
              Taper  the  edge  weights  with  a  Tukey  window.  Lambda is the size of the Tukey
              transition. When -taper-edge is also specified, the Tukey transition starts  inside
              the inner rectangle.

   INVERSION OPTIONS
       -name <image-prefix>
              Use image-prefix as prefix for output files. Default is 'wsclean'.

       -size <width> <height>
              Default: 2048 x 2048

       -trim <width> <height>
              After inversion, trim the image to the given size.

       -scale <pixel-scale>
              Scale  of  a  pixel.  Default  unit is degrees, but can be specificied, e.g. -scale
              20asec. Default: 0.01deg.

       -nwlayers <nwlayers>
              Number of w-layers to use. Default: minimum suggested #w-layers for first MS.

       -nwlayers-for-size <width> <height>
              Use the minimum suggested w-layers for an image of the given size. Can e.g. be used
              to increase accuracy when predicting small part of full image.

       -channelsout <count>
              Splits the bandwidth and makes count nr. of images. Default: 1.

       -predict
              Only  perform  a single prediction for an existing image. Doesn't do any imaging or
              cleaning.  The input images should have the same name as the  model  output  images
              would have in normal imaging mode.

       -predict-channels <nchannels>
              Interpolate  from  a  given  number  of  images  to the number of channels that are
              predicted as specified by -channelsout. Will interpolate using the  frequencies  of
              the  images.   Use  one  the -fit-spectral-... options to specify the interpolation
              method / freedom.  Only used when -predict is specified.

       -subtract-model
              Subtract the model from the data column in the first iteration. This can be used to
              reimage an already cleaned image, e.g. at a different resolution.

       -nosmallinversion, -smallinversion
              Perform  inversion at the Nyquist resolution and upscale the image to the requested
              image size afterwards.  This speeds up inversion considerably, but  makes  aliasing
              slightly worse. This effect is in most cases <1%. Default: on.

       -gridmode <"nn", "kb" or "rect">
              Kernel and mode used for gridding: kb = Kaiser-Bessel (default with 7 pixels), nn =
              nearest neighbour (no kernel), rect = rectangular window. Default: kb.

       -gkernelsize <size>
              Gridding antialiasing kernel size. Default: 7.

       -oversampling <factor>
              Oversampling factor used during gridding. Default: 63.

       -make-psf
              Always make the psf, even when no cleaning is performed.

       -make-psf-only
              Only make the psf, no images are made.

       -savegridding
              Save the gridding correction image. This  shows  the  effect  of  the  antialiasing
              filter. Default: not saved.

       -dft-prediction
              Predict  via  a  direct  Fourier  transform.  This  is  slow,  but  can account for
              direction-dependent effects. This has only effect when -mgain is set or -predict is
              given.

       -dft-with-beam
              Apply the beam during DFT. Currently only works for LOFAR.

       -visibility-weighting-mode [normal/squared/unit]
              Specify  visibility  weighting  modi.  Affects how the weights (normally) stored in
              WEIGHT_SPECTRUM column are applied. Useful for estimating e.g.  EoR  power  spectra
              errors.   Normally  one  would  use  this  in  combination  with -no-normalize-for-
              weighting.

       -no-normalize-for-weighting
              Disable the normalization for the weights, which makes  the  PSF's  peak  one.  See
              -visibility-weighting-mode. Only useful with natural weighting.

   DATA SELECTION OPTIONS
       -pol <list>
              Default:  'I'.  Possible values: XX, XY, YX, YY, I, Q, U, V, RR, RL, LR or LL (case
              insensitive).  Multiple values can be separated with commas,  e.g.:  'xx,xy,yx,yy'.
              Two  or  four polarizations can be joinedly cleaned (see '-joinpolarizations'), but
              this is not the default. I, Q, U and V polarizations will  be  directly  calculated
              from  the visibilities, which is not appropriate for telescopes with non-orthogonal
              feeds, such as MWA and LOFAR. The 'xy' polarization will output both a real and  an
              imaginary  image,  which  allows  calculating  true  Stokes polarizations for those
              telescopes.

       -interval <start-index> <end-index>
              Only image the given time interval. Indices specify the  timesteps,  end  index  is
              exclusive.  Default: image all time steps.

       -intervalsout <count>
              Number of intervals to image inside the selected global interval. Default: 1

       -channelrange <start-channel> <end-channel>
              Only  image  the given channel range. Indices specify channel indices, end index is
              exclusive.  Default: image all channels.

       -field <fieldid>
              Image the given field id. Default: first field (id 0).

       -datacolumn <columnname>
              Default: CORRECTED_DATA if it exists, otherwise DATA will be used.

       -maxuvw-m <meters>, -minuvw-m <meters>
              Set the min/max baseline distance in meters.

       -maxuv-l <lambda>, -minuv-l <lambda>
              Set the min/max uv distance in lambda.

       -maxw <percentage>
              Do not grid visibilities with a w-value higher than the given percentage of the max
              w, to save speed.  Default: grid everything

   DECONVOLUTION OPTIONS
       -niter <niter>
              Maximum number of clean iterations to perform. Default: 0

       -threshold <threshold>
              Stopping clean thresholding in Jy. Default: 0.0

       -gain <gain>
              Cleaning  gain:  Ratio  of peak that will be subtracted in each iteration. Default:
              0.1

       -mgain <gain>
              Cleaning gain for major iterations: Ratio of peak that will be subtracted  in  each
              major iteration. To use major iterations, 0.85 is a good value. Default: 1.0

       -joinpolarizations
              Perform cleaning by searching for peaks in the sum of squares of the polarizations,
              but subtract components from the individual images. Only possible when imaging  two
              or four Stokes or linear parameters. Default: off.

       -joinchannels
              Perform  cleaning  by searching for peaks in the MFS image, but subtract components
              from individual channels.  This will turn on mfsweighting by default. Default: off.

       -multiscale
              Clean on different scales. This is a new algorithm. Default: off.   This  parameter
              invokes  the  v1.9 multiscale algorithm, which is slower but more accurate compared
              to the older algorithm, and therefore  the  recommended  one  to  use.   The  older
              algorithm is now invoked with -fast-multiscale.

       -fast-multiscale
              Clean on different scales. This is a new fast experimental algorithm. Default: off.
              This method used to  be  invoked  with  -multiscale  before  v1.9,  but  the  newer
              multiscale algorithm is somewhat more accurate and therefore recommended.

       -multiscale-threshold-bias
              Parameter  to lower the threshold for larger scales. The used threshold for a scale
              is threshold(scale)=pointsource_threshold x tbias^scale. A lower  bias  will  clean
              larger scales deeper. Default: 0.7

       -multiscale-scale-bias
              Parameter  to prevent cleaning small scales in the large-scale iterations. A higher
              bias will give more focus to larger scales. Default: 0.6

       -multiscale-scales <comma-separated list of sizes in pixels>
              Sets a list of scales to use in multi-scale cleaning. If unset, WSClean will select
              the  delta  (zero)  scale,  scales  starting at four times the synthesized PSF, and
              increase by  a  factor  of  two  until  the  maximum  scale  is  reached.  Example:
              -multiscale-scales 0,5,12.5

       -iuwt  Use the IUWT deconvolution algorithm.

       -moresane-ext <location>
              Use the MoreSane deconvolution algorithm, installed at the specified location.

       -moresane-arg <arguments>
              Pass  the specified arguments to moresane. Note that multiple parameters have to be
              enclosed in quotes.

       -moresane-sl <sl1,sl2,...>
              MoreSane --sigmalevel setting for each major loop iteration.  Useful  to  start  at
              high levels and go down with subsequent loops, e.g. 20,10,5

       -cleanborder <percentage>
              Set  the  border  size  in  which  no  cleaning  is performed, in percentage of the
              width/height of the image.  With an image size of 1000 and clean border of 1%, each
              border is 10 pixels. Default: 5 (%).

       -fitsmask <mask>
              Use the specified fits-file as mask during cleaning.

       -casamask <mask>
              Use the specified CASA mask as mask during cleaning.

       -smallpsf
              Resize the psf to speed up minor clean iterations. Not the default.

       -nonegative
              Do not allow negative components during cleaning. Not the default.

       -negative
              Default on: opposite of -nonegative.

       -stopnegative
              Stop on negative components. Not the default.

       -fit-spectral-pol <nterms>
              Fit  a polynomial over frequency to each clean component. This has only effect when
              the channels are joined with -joinchannels.

       -fit-spectral-log-pol <nterms>
              Like fit-spectral-pol, but fits a logarithmic polynomial over frequency instead.

       -deconvolution-channels <nchannels>
              Decrease the number of channels as specified by -channelsout to  the  given  number
              for  deconvolution.  Only  possible  in  combination  with one of the -fit-spectral
              options.  Proper residuals/restored images will only be returned when mgain < 1.

       -squared-channel-joining
              Use with -joinchannels to perform peak finding in the sum of  squared  values  over
              channels,  instead  of  the normal sum. This is useful for imaging QU polarizations
              with non-zero rotation measures, for which the normal sum is insensitive.

       -force-dynamic-join
              Use alternative joined clean algorithm (feature for testing).

   RESTORATION OPTIONS
       -beamsize <arcsec>
              Set the FWHM beam size in arcsec  for  restoring  the  clean  components.  Default:
              longest projected baseline defines restoring beam.

       -beamshape <maj in arcsec> <min in arcsec> <position angle in deg>
              Set  the FWHM beam shape for restoring the clean components. Defaults units for maj
              and min are arcsec, and degrees for PA. Can be overridden, e.g.  '-beamshape  1amin
              1amin 3deg'.

       -fitbeam
              Determine beam shape by fitting the PSF (default if PSF is made).

       -nofitbeam
              Do not determine beam shape from the PSF.

       -theoreticbeam
              Write  the  beam  in  output  fits  files  as calculated from the longest projected
              baseline.  This method results in slightly less accurate integrated fluxes, but  in
              simple imaging provide a beam size even without making the PSF. Default: off.

       -circularbeam
              Force the beam to be circular: bmin will be set to bmaj.

       -ellipticalbeam
              Allow the beam to be elliptical. Default.

AUTHOR

       André Offringa <offringa@gmail.com>