3 Estimation of Near Surface effects ; an alternative approach to statics

In DELPHI Volume IV, Chapter 3 (1993) it was argued that by making assumptions about the propagation behavior of a synthesized (plane) wave through a weathered layer it is possible to consider the weathered layer effects at the source and receiver side separately. The fast weathered layer distortion to the (plane) wave front at the source side is largely restored during propagation through the medium (far field). For the upgoing wave field this restoration does not occur because the receivers measure the distorted wave field in the near field of the weathered layer. Starting with these assumptions an estimate of the weathered layer interface can be made. In this Chapter this estimate is obtained in an iterative way and used to make a correction to the weathered layer influence at the receiver side. The procedure can be repeated at the source side (reciprocity). At the end of this Chapter a proposal is made to include the weathered layer problem in macro model estimation.