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Dr Ralf Schaa completed his MSc at the University of Cologne in Germany with a focus on Abel-transformation of radio-occultation data from the ESA Mars Express mission. After completion of his MSc he came to Tasmania on a scholarship to complete his PhD study in applied geophysics, concentrating on rapid 3D inversion of transient electromagnetic data. Since 2010 Ralf has continued his research on this topic in his current capacity as a research fellow.
Three-dimensional geophysical inversion of EM data aims to give an idealised estimate of the 3D geoelectrical structure of the subsurface which can meaningfully describe a set of observations.
Rigorous 3D inversion of time-domain electromagnetic data is an onerous computational challenge, often taking several hours or even days. Motivated by the demand for a rapid and reliable 3D inversion method for TEM data, a fast, approximate 3D inversion scheme of transient electromagnetic data has been developed.
The new scheme combines the TEM moments concept and geologically constrained 3D inversion methodology. The TEM moment inversion scheme builds on the pre-existing VPmg potential field modelling and inversion framework which has been extended and modified so as to accommodate approximate 3D TEM inversion.
The method has potential for fast, constrained 3D inversion of large airborne TEM data sets. The moment transform of TEM data is a time-weighted integral of the impulse response which accentuates late-time features. Due to the time integration, a TEM decay is effectively reduced to a single value, which, in effect, converts the nonlinear 3D TEM inversion problem into a linear 3D magnetic inversion problem. Typically, for ground-TEM, the fast approximate 3D inversion completes in minutes, thus facilitating exploration of non-uniqueness. The inversion scheme was successfully tested on synthetic fixed-loop TEM examples and on fixed-loop TEM field data from South Africa.
Authorised by the Head of School, Earth Sciences
12 November, 2012