Abstract :
Electrical and electromagnetic methods are powerful tools in environmentaland geotechnical investigations. Techniques developed for deeper applications, such as mining,geothermal and crustal studies, are scaled for shallow targets by moving to higher frequencies,earlier decay times and/or smaller array configurations. Another extremely important factor is dense stationspacing, to reduce spatial aliasing, and high quality data to resolve small features. Hence, new instrumentsare concerned with making continuous or dense measurements with high precision, and interpretationalmethods fast enough to handle large datasets quickly. Continuously measuring electrical and time-domainelectromagnetic systems have been developed for geological mapping in hydrological investigations withone-dimensional inversion routines that are rapid and robust. At a smaller scale an electrical systemis used for archaeology studies with excellent results. Working to and above the upper limits ofthe quasi-static approximation, a very early time electromagnetic system is proving successful at mapping subsurfaceinfrastructure in areas of conductive, clay cover, where ground penetrating radar is ineffective.Induced polarization (IP) and resistivity systems that employ multiplexing techniques, while not continuouslymeasuring, allow for relatively rapid production rates and dense sampling for applications ranging fromlandfill and contaminant characterization studies, to verifying the integrity of engineeredsubsurface structures and monitoring infiltration in the vadose zone.
