“ Virtual source ” methods for diffusive fields

The phrase virtual source refers to two different techniques in this dissertation. In the first half of the dissertation, it refers to interferometry and in the second half it uses the concept of the synthetic aperture technique. In interferometry, a receiver is converted to a “virtual source”. In the synthetic aperture technique, a large “virtual source” is constructed by adding small sources. Interferometry has been popularly used in the seismology community since the beginning of this century. The wave propagation between two receivers can be reconstructed by cross correlating the wave fields excited by uncorrelated sources on a closed surface surrounding two receivers, providing the medium is enclosed by sources. Cross-correlation interferometry is also proven to be applicable to diffusive fields. In this thesis, I pursue the application of interferometry to low frequency diffusive electromagnetic fields used in Controlled Source Electromagnetics (CSEM). For such diffusive fields, interferometry requires a volume distribution of sources to reconstruct the diffusion response between receivers. In practice, finding the optimal distribution of sources for interferometry is critical because there are only a finite number of sources. I study the required source distribution in crosscorrelation interferometry for both wave propagation and diffusion. Although it is possible to apply interferometry to diffusive fields using a finite number of sources, sources close to the receivers have the largest contribution in the reconstruction. Therefore, there is no obvious advantage to apply interferometry to diffusive fields. I also investigate the feasibility of applying multi-dimensional-deconvolution interferometry to low frequency diffusive electromagnetic fields. I show that the imprint of reservoirs significantly increases after applying multi-dimensional-deconvolution interferometry