3.5 Imaging/deconvolution: a brief sequence of commands

For the user, IMAGER reduces the number of actions to the strict minimum. The imaging sequence is always the same:

    1- Reading data
       READ UV MyData.uvt /RANGE Min Max Type
       ! here, optionally use UV_TIME, UV_COMPRESS to average data,
       ! and UV_BASELINE or UV_FILTER to remove continuum or filter lines.
    2- Imaging
       UV_MAP
    3- Deconvolving
       CLEAN
       ! here, optionally use UV_RESTORE
    4- Looking at the result
       VIEW CLEAN      ! or SHOW CLEAN
    5- Writing the result
       WRITE * MyData

• Step 1: Reading the specified internal buffer (here UV) from the input file ( .uvt file type), loading only the channels falling in the range defined by the variables Min and Max, of Type CHANNEL, VELOCITY or FREQUENCY. IMAGER recognizes whether the UV table is for a single field or a mosaic. The only difference between the single field and mosaic cases is that IMAGER yields a Sky brightness image for Mosaics, while the computed sky brightness of a single field is not automatically corrected for the primary beam attenuation. Imaging for multiple fields will be presented in Section 6. Single Dish data can also be loaded in the following way : READ SINGLE  File.
• Step 2: Computing a dirty map and beam from a UV data. UV_MAP processes single fields as well as Mosaics.
• Step 3: Deconvolving the DIRTY image map (a Single-field or Mosaic) using the dirty BEAM with the current METHOD. The default for the SIC variable METHOD is HOGBOM, the other supported methods being CLARK, MRC, MULTI and SDI. See CLEAN ? for the other SIC variables controlling the deconvolution process. The outputs are the CLEAN and RESIDUAL images, and the Clean Component Table CCT, all being stored in dedicated SIC variables.
• Step 4: Plotting the result in the specified internal buffer ( CLEAN). Optionaly, the user can restrict the plot to a subset of channels through the optional arguments First and Last. SHOW CLEAN can also be used instead, and produces a different type of plot.
• Step 5: Writing all modified image-like buffers (not the UV tables) under the common file name ” MyData”. In the case of the present example, the following files are produced: MyData.lmv, MyData.lmv-clean, MyData.cct, MyData.beam, which correspond to the buffers: DIRTY, CLEAN, CCT, and BEAM, respectively. WRITE UV  MyData would only write the internal buffer ( UV) in the file MyData.uvt (the default extension corresponds to the specified buffer data type).