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Controlled illumination by double focussing in the source domain

The CFP-method computes a virtual source in the subsurface by simulating a focal source array at the surface. The response of such a virtual source represents the CFP-gather. It is proposed to construct a distribution of virtual sources along a vertically oriented trajectory. By simulating a second focal array along this trajectory of virtual sources, a ’pencil beam’ is created that illuminates the subsurface in a user-controlled way. The subsurface response of this double focal source array (DFS-array) equals a weighted sum of CFP-gathers.