Handling near surface effects in imaging by using common focal point technology

Abstract

Summary With the common focal point (CFP) technology the ef- fects of weathering layers can be integrated in prestack migration. CFP operators can be determined directly from the data through an updating procedure, independent from a velocity model. The updating of operators, which is not trivial in the presence of weathering layers, can be carried out by a semi-automatic procedure. With the aid of the CFP operators a clearly defined migrated section can be constructed. In this paper we consider the near surface as part of the imaging problem. The CFP imaging technology (Berkhout 1997) gives us a tool to describe the subsurface, including the weathered layer, in terms of a lateral distribution of operators. These op- erators can in principle be derived without knowing the correct macro model. This is an advantage over conventional methods since models of the near surface are often very complex. The synthetic results show that clearly defined time migrated images can be derived. Near surface imaging Common focal point migration Through reciprocity theorems a forward model can be derived which describes the measured seismic reflection data, backscat- tered from a depth level . Neglecting angle dependent reflectivity, the oneway integral representation for the primary upgoing scattered data at a receiver position ,a s result of a contrasting interface , and a point source at with source characteristic is given by,