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UV Table handling

Besides the magentaREAD UV and magentaWRITE UV commands to read or write uv tables, [rgb]1,0,0IMAGER has a number of commands to manipulate the current uv table buffer. These commands have names starting by magentaUV_. Most of them are in the blueCLEAN\ language, some in the blueADVANCED\ one.

[rgb]1,0,0IMAGER works using UV buffers. Most commands only work on the current UV buffer, but some of them keep track of the previous buffer to allow the user to revert the operation.

Data inspection and editing:
  • magentaSHOW COVERAGE display the uv coverage
  • magentaSHOW UV display the uv data
  • magentaUV_FLAG allow flagging visibilities
  • magentaUV_PREVIEW provides a quick view of the visibilities as a function of frequencies, and attempts to automatically find the continuum level and parts of the bandwidth with spectral line emissions.

Data size reduction routines:
  • magentaUV_COMPRESS is a simple spectral smoothing, providing only channel averaging by integer number of channels.
  • magentaUV_RESAMPLE provides a more flexible spectral smoothing and resampling facility.
  • magentaUV_TIME can be used to time-average the UV data set, leading to faster processing. However, using magentaUV_TIME too early may limit your ability to perform accurate phase self-calibration.

Continuum processing commands:
  • magentaUV_BASELINE allows to remove the continuum baseline, by 0th or 1st order baseline fitting of each visibility.
  • Conversely, magentaUV_FILTER will filter the spectral line range to leave only the channels with continuum emission. Both magentaUV_BASELINE and magentaUV_FILTER can use the results provided by magentaUV_PREVIEW to specify where spectral lines may be found.
  • magentaUV_CONTINUUM converts a spectral line uv table into a bandwidth synthesis continuum uv table. magentaUV_CONTINUUM is only useful for UV plane analysis: see Section [*] for details.
  • magentaUV_MERGE /FILE can merge several UV continuum tables with a specified spectral index to optimize the sensitivity.

Image preparation:
  • magentaUV_CHECK inspects the uv data to figure out how many different synthesized beams are needed.
  • magentaUV_SHORT adds the short (or zero) spacing information provided by an additional single dish data, read by magentaREAD SINGLE.
  • magentaUV_STAT evaluates the impact of robust weighting and tapering on the synthesized beam. It provides recommendations for the image and pixel sizes.
  • magentaUV_TRUNCATE restricts the uv baseline length range.

UV Plane analysis:
  • magentaUV_FIT fit simple source models to the visbilities.
  • magentaSHOW UV_FIT display the fit results, usually as a function of frequency, but also in other ways.

Miscellaneous:
  • magentaUV_DEPROJECT de-projects the $(u,v)$ coordinates given a specified phase center, orientation and inclination. This can be useful for inclined, flattened, nearly axi-symmetric structures such as proto-planetary disks or galaxies.
  • magentaUV_CIRCLE and magentaUV_RADIAL compute the azimutal average of the visibilities. They are useful for rotationally symmetric structures such as proto-planetary disks or circumstellar envelopes, for example.
  • magentaUV_REWEIGHT changes the visibility weights.
  • magentaUV_SHIFT changes the phase center. This can be useful for UV plane analysis.
  • magentaUV_MERGE /FILE can merge several UV tables, Line or Continuum. It also allows stacking different spectral lines, by aligning them in velocity, as well as stacking emission from different sources.

The remaining magentaUV_... commands are related to imaging and deconvolution: magentaUV_MAP computes the dirty image, magentaUV_RESTORE computes the Clean image from a Clean component list by removal of the Clean components in the uv plane, and imaging of the residuals. magentaUV_RESIDUAL just computes the residuals by subtraction of the Clean components.

Finally, magentaUV_SELF, in the blueCALIBRATE\ language, is a specific variant of magentaUV_MAP used to compute the intermediate images required for self-calibration. It is not intended for direct use by normal users.


next up previous contents index
Next: Single-field imaging and deconvolution Up: The input data: UV Previous: Reading UV tables   Contents   Index
Gildas manager 2023-06-01