Inversion of multi-source time domain electromagnetic data

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Electrical conductivity is a key physical property associated with mineral deposits, oil and gas, water, and environmental contaminants. Electromagnetic surveys have been devised to acquire data that are sensitive to the unknown conductivity. Typically, the electric and/or magnetic fields caused by a grounded dipole or a current loop source are recorded, and the practical difficulty is then to recover the 3D conductivity structure that caused these measured data. Previous research at the UBC Geophysical Inversion Facility has resulted in methodologies and software programs for inverting both frequency (FEM) and time domain (TEM) data when only a few transmitter sources are employed. The outcomes are in use at sponsoring companies. However, 3D inversion of TEM data is a computationally challenging task that increases with the number of transmitter locations, and current techniques are not viable for surveys using many transmitter locations. In this research we propose to develop robust and efficient 3D inversion methods for multi-source TEM data sets associated with airborne or ground surveys. An important  component of the research is to develop workflows and efficient strategies for handling these large data sets. We propose to develop practical software and work closely with industry sponsors to achieve this goal. Final codes will be distributed to the sponsors. First, Maxwell's equations will be reformulated in terms of electric and magnetic fields and the subsequent forward modeling matrix will be decomposed. The quasi-Newton methodology we developed earlier will be implemented. The beta-version of the code will be tested on synthetic and field data sets provided by sponsors, including ground and airborne surveys with multiple sources. Workflow and utility programs will be developed as testing progresses. A final inversion code (converted from MatLab into Fortran) will be delivered to sponsors, including GUI interfaces to run the codes, documentation, and workflow elements.