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| − | == Help on feather task: ==
| + | {{feather}} |
| − | <pre>
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| − | Combine two images using their Fourier transforms
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| − | This algorithm, called feathering, is a simple method for combining two
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| − | images with different spatial resolution. The processing steps are:
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| − | 0. regrid the low resolution image to a temporary copy matching the
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| − | high resolution image,
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| − | 1. transform each image to the gridded visibility plane,
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| − | 2. sum the gridded visibilities
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| − | 3. transform back to the image plane.
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| − | The task name comes from the smooth switching from
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| − | one data set to the other using weights assigned according to the
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| − | sensitivity of each at any given spatial frequency. Gaps, if any,
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| − | between the spatial frequency ranges are not filled.
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| − | Each image must have a well-defined beam shape (clean beam) for
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| − | feathering to work well. The two images must have the same flux
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| − | density normalization scale.
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| − | This task is somewhat experimental and will improve as more experience
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| − | with single-dish and interferometric data is obtained over the next few years.
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| − | Keyword arguments:
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| − | imagename -- Name of output feathered image
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| − | default: none; example: imagename='orion_combined.im'
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| − | highres -- Name of high resolution (interferometer) image
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| − | default: none; example: highres='orion_vla.im'
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| − | This image is often a clean image obtained from synthesis
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| − | observations.
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| − | lowres -- Name of low resolution (single dish) image
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| − | default: none; example: lowres='orion_gbt.im'
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| − | This image is often a image from a single-dish observations
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| − | or a clean image obtained from lower resolution synthesis
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| − | observations.
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| − | Comments:
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| − | The advantage of feathering is that one does not have to go back to
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| − | the visibility data and then image and deconvolve. It starts with
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| − | the high-quality image (with the accurate clean beam). This is
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| − | particularly useful for combining a high-resolution interferometric
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| − | image with a lower-resolution single-dish image, although
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| − | D-configuration and A-configuration EVLA data can also be combined.
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| − | There are often uncertainties in the relative flux density scales
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| − | between the two images, and the current implementation of feathers
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| − | does not adjustment.
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| − | The clean task also has a method of combining two sets of data with
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| − | different resolution. The high resolution visibility data begins
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| − | deconvolution, starting with a modelimage of the lower-resolution
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| − | image. The lower-resolution image must be clean components (or a
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| − | sky model), not the low resolution image with its intrinsic
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| − | resolution.
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| − | </pre>
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