SOURCE SIGNATURE ESTIMATION BASED ON THE REMOVAL OF FIRST-ORDER MULTIPLES

The estimation of the source signature is often one of the necessary f irst steps in the processing of seismic reflection data. especially if the processing chain includes prestack multiple removal. However, mos t methods for source estimation are based on poststack data or assume that the earth is 1-D. In this work, a new source estimation method fo r prestack data is presented. It consists of finding the source signat ure that permits the removal of events attributable to the first-order free-surface reflections (i.e., first-order multiples). The method ex ploits the formulation of the relationship between the free-surface re flections and the source signature as a scattering Born series. In thi s formulation, the order of the scattering series coincides with that of the free-surface reflections, and the series is constructed exclusi vely with seismic data and the source signature without any knowledge of the subsurface other than the velocity of sea water. By restricting the problem to first-order free-surface reflections, we have rendered the relationship between free-surface reflections and the source sign ature linear, which also corresponds to a truncation of the scattering Born series to its first two terms. Thus, the source signature estima tion can be formulated as a linear inverse problem. Assuming that the removal of first-order free-surface events produces a significant redu ction in the energy of the data, we posed the inverse problem as findi ng the source signature that minimizes this energy. The optimization l eads to an iterative solution. The iterations are needed to correct fo r the truncation effects. Synthetic and real data examples show the ap plicability and stability of the source estimation method as well as i ts use for attenuating free-surface multiples.