Examples

Feathering is a simple method for combining two images with different spatial resolution.  The processing steps are:

  1. Regrid the low-resolution image to a temporary copy matching the resolution of the high-resolution image,
  2. Transform each image to the spatial-frequency plane (gridded).\
  3. Scale the low-resolution image (uv-grid) by the ratio of the volumes of the two 'clean beams' (high-res/low-res).
  4. Add to this, the uv-grid of the high-resolution image, scaled by (1-wt) where 'wt' is the Fourier transform of the 'clean beam' defined in the low-resolution image.
  5. Transform back to the image plane.

Both input images must have a well-defined beam shape for this task to work.  This could be a 'clean beam' for interferometric images, and a 'primary-beam' for a single-dish image.

The two images must also have the same flux density normalization scale.

    Keyword arguments:
        imagename -- Name of output feathered image
                default: none; example: imagename='orion_combined.im'
        highres -- Name of high resolution (interferometer) image
                default: none; example: highres='orion_vla.im'
         This image is often a clean image obtained from synthesis
        observations.
        lowres -- Name of low resolution (single dish) image
                default: none; example: lowres='orion_gbt.im'
         This image is often a image from a single-dish observations
            or a clean image obtained from lower resolution synthesis
        observations.
         sdfactor -- value by which to scale the Single Dish image. Default is 1.0
                         Basically modifying the flux scale of the SD image
     effdishdiam -- New effective SingleDish diameter to use in m. Obviously one can only reduce the dish effective dish diameter in feathering. Default -1.0 means leave as is.
     lowpassfiltersd -- If True the high spatial frequency in the SD image is rejected.
                                   Any data outside the maximum uv distance that the SD
                                   has illuminated  is filtered out.

Comments:

This task can be used as one method of combining single-dish and interferometric images after they have been separately made.
       

The clean task allows another method of combining single-dish and interferometric data. The single-dish image can be used as a starting model for the interferometric image-reconstruction. If there is some overlap between the spatial-frequencies contained in the single-dish image and the interferometer sampling function, then, such a starting model will help constrain the solutions on the short-baselines of the interferometric data.