A Tree Algorithm for Helmholtz Potential Wavelets on Non-Smooth Surfaces: Theoretical Background und Application to Seismic Data Postprocessing
- The interest of the exploration of new hydrocarbon fields as well as deep geothermal reservoirs is permanently growing. The analysis of seismic data specific for such exploration projects is very complex and requires the deep knowledge in geology, geophysics, petrology, etc from interpreters, as well as the ability of advanced tools that are able to recover some particular properties. There again the existing wavelet techniques have a huge success in signal processing, data compression, noise reduction, etc. They enable to break complicate functions into many simple pieces at different scales and positions that makes detection and interpretation of local events significantly easier. In this thesis mathematical methods and tools are presented which are applicable to the seismic data postprocessing in regions with non-smooth boundaries. We provide wavelet techniques that relate to the solutions of the Helmholtz equation. As application we are interested in seismic data analysis. A similar idea to construct wavelet functions from the limit and jump relations of the layer potentials was first suggested by Freeden and his Geomathematics Group. The particular difficulty in such approaches is the formulation of limit and jump relations for surfaces used in seismic data processing, i.e., non-smooth surfaces in various topologies (for example, uniform and quadratic). The essential idea is to replace the concept of parallel surfaces known for a smooth regular surface by certain appropriate substitutes for non-smooth surfaces. By using the jump and limit relations formulated for regular surfaces, Helmholtz wavelets can be introduced that recursively approximate functions on surfaces with edges and corners. The exceptional point is that the construction of wavelets allows the efficient implementation in form of a tree algorithm for the fast numerical computation of functions on the boundary. In order to demonstrate the applicability of the Helmholtz FWT, we study a seismic image obtained by the reverse time migration which is based on a finite-difference implementation. In fact, regarding the requirements of such migration algorithms in filtering and denoising the wavelet decomposition is successfully applied to this image for the attenuation of low-frequency artifacts and noise. Essential feature is the space localization property of Helmholtz wavelets which numerically enables to discuss the velocity field in pointwise dependence. Moreover, the multiscale analysis leads us to reveal additional geological information from optical features.