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0.1.24 feather

Requires:

Synopsis
Combine two images using their Fourier transforms

Description

The algorithm converts each image to the gridded visibility plane, combines them, and reconverts them into an combined image. Each image must include a well-defined beam shape (clean beam) in order for feathering to work well. The two images must have the same flux density normalization scale.



Arguments





Inputs

imagename

Name of output feathered image

allowed:

string

Default:

highres

Name of high resolution (interferometer) image

allowed:

string

Default:

lowres

Name of low resolution (single dish) image

allowed:

string

Default:

sdfactor

Scale factor to apply to Single Dish image

allowed:

double

Default:

1.0

effdishdiam

New effective SingleDish diameter to use in m

allowed:

double

Default:

-1.0

lowpassfiltersd

Filter out the high spatial frequencies of the SD image

allowed:

bool

Default:

False

Example

 
 
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.  
 
 


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