MOBILE GEOPHYSICAL METHODS: IMPROVING HYDROGEOLOGIC CHARACTERIZATION AT LOCAL TO REGIONAL SCALES (Invited Presentation)

Conventional geophysical methods have proven utility in support of hydrologic and hydrogeologic investigations at the site scale. However, conventional, stationary, or hand-carried surface geophysical methods are slow and relatively labor intensive, limiting the number of soundings or distance that can be profiled per day, which challenges productivity over large areas at the local- and regional-scale.

Recent innovations in mobile geophysical methods using towed platforms and increased use of airborne methods are improving geophysical investigation efficacies. Airborne electromagnetic (AEM) surveys allow the collection of hundreds of line-kilometers (ln km) of data per day, have depths of investigation (DOI) that typically exceed 100 m, and provide lateral resolution along the flight line ranging from 10 to 50 m. However, financial, and logistical metrics limit the application of AEM in many investigations. Recently, a towed time-domain electromagnetic (TEM) system, called tTEM has been developed that provides a mobile solution for continuous geophysical imaging capable of ‘bridging the gap’ between site-scale conventional geophysical surveys and regional-scale AEM surveys. The tTEM method allows the collection of up to 100 ln km of continuous TEM data per day, with a DOI ranging from 50-100 m and lateral resolution of 5-10 m in areas accessible by an all-terrain vehicle (ATV) or small boat. Results of tTEM surveys demonstrate the utility of the method for local- and regional-scale hydrologic and hydrogeologic mapping applications.