While controlled-source electromagnetic geophysics has been often hailed as a potential breakthrough technology for subsurface hydrology, the current reality is that hydrogeologists often experience severe difficulties in interpreting electromagnetic data. In simple cases, where the electrical properties of the subsurface are reasonably approximated by a smooth or piecewise-constant distribution, classical geophysical methods of low-frequency electromagnetic induction are useful in constraining our knowledge of the hydrologic system. However, in cases where the setting is more complicated ? for instance, where the subsurface is characterized by length-scale-dependent heterogeneity ? the classical methods of electromagnetic induction must be modified accordingly. A promising analytic approach uses the historical methods of fractional calculus to accommodate scale-dependent lithologic complexity in the governing Maxwell Equations. Through a systematic study of the fractional Maxwell response (FMR) and corresponding classical electromagnetic simulations of appropriate complexity, we aim to illuminate geological settings where the FMR is present and to interpret the FMR in terms of hydrologic parameters such as porosity, clay content, pore water salinity, fracture density, position of a saline wedge or contaminant zone, etc. The technical innovation of our current proposal is based on extending traditional electromagnetic geophysics into new territory with the development of anomalous diffusion of electromagnetic fields into scale-dependent geological media. The broad sweep of electromagnetic geophysics, both traditional and innovative, must however be better communicated to the hydrological community. Accordingly we plan to utilize the newly developed virtual institute ?OpenEM.org? as a platform to better engage the hydrologic community in the application of electromagnetic geophysics.
