Much of the computation in `CLEAN' consists of shifting and scaling the dirty beam. As this is essentially a convolution it may, in some circumstances, be done more efficiently with 2-d FFTs. Clark's (1980) `CLEAN' algorithm does this, finding approximate positions and strengths of the point components using only a small patch of the dirty beam.
In detail, the Clark algorithm has two cycles, known as ``minor'' and ``major'' cycles. The minor cycle proceeds as follows:
The algorithm then does a major cycle wherein the point source model found by the minor cycle is transformed via an FFT, multiplied by the weighted sampling function (inverse transform of the beam), transformed back, and subtracted from the dirty image. Errors introduced in a minor cycle by the beam patch approximation are, to some extent, corrected in subsequent minor cycles.
1996 November 4