Direction-dependent Point Spread Functions (PSFs)

With large fields of view, the approximation of considering the dirty image as a convolution of the sky and the PSF yields a higher error. To mitigate this error, WSClean can calculate multiple PSFs in different directions on a grid, using the parameter -dd-psf-grid: the user can specify the number of psfs which should be fit horizontally and vertically in the image. The -dd-psf-grid argument only works together with the -make-psf-only or -parallel-deconvolution arguments:

• If -parallel-deconvolution is used, and the number of cells in the PSF grid exceeds the number of parallel sub-images in one or more dimensions, WSClean prints a warning and reduces the PSF grid size.

• If -make-psf-only is used without -parallel-deconvolution, WSClean uses the PSF grid as supplied by -dd-psf-grid.

• If both -make-psf-only and -parallel-deconvolution are not used, WSClean resets the PSF grid to 1x1 and thus disables using multiple PSFs, too.