USE OF A TOWED ELECTROMAGNETIC INDUCTION(tTEM)SYSTEM FOR SHALLOW AQUIFER CHARACTERIZATION-AN EXAMPLE FROM THE MISSISSIPPI ALLUVIAL PLAIN

摘要

The Mississippi Alluvial Plain(MAP)aquifer system is a vital resource that supports agriculture in one of the most productive regions of the country.The U.S.Geological Survey Water Availability and Use Science Program(WAUSP)is conducting a multi-discipline investigation of the MAP aquifer system.The investigation is utilizing borehole,surface,and airborne geophysical methods to improve the characterization and understanding of the aquifer.The combination of geophysical data collected over a range of spatial scales with varying depths of investigation and resolution is key to determining the distribution of sand and clay within the aquifer.Mobile geophysical methods that enable continuous measurements over large areas improve aquifer characterization with their increased spatial coverage.In support of the MAP investigation,a new towed Time-Domain Electromagnetic(tTEM)imaging system developed by Aarhus University was used near Shellmound,Mississippi(MS),to delineate the distribution of coarse-and fine-grained sediments underlying the site.The tTEM results compare favorably with the results of airborne EM(AEM)surveys flown in the study and improve the resolution of sand and gravel distribution within the tTEM depth of investigation.