In August 2011, a demonstration of the Battelle TEM-8 system was conducted in support of a project for the U.S. Army Corps of Engineers (USACE) - Memphis District (CE-MVM) to evaluate the levee surrounding the city of Cairo, Illinois that protects Cairo from the Mississippi and Ohio Rivers during flood events. The objective of the project was to conduct trials of airborne geophysical systems for delineating potential areas of concern or structural weakness within the levee system. Ancillary data were also acquired with the Battelle VG-16 airborne magnetic system. Both airborne systems are mounted on booms that extend to the sides and/or front of a Bell 206L helicopter. They were initially designed for mapping and detection of unexploded ordnance and other shallow metallic objects, to be flown at 1-5m above ground level (AGL). The TEM-8 time-domain electromagnetic system was reconfigured for this project by disabling the transmitter on the port side of the helicopter and acquiring near- and far-offset data (relative to the activated starboard transmitter loop) on the starboard and port sides respectively. Time gate settings were also modified from the values used for UXO surveys. The VG-16 system provided indications of power lines, conduits, and other metallic sources of interference, and, in one area, provided indications of subtle variations in the magnetic mineral content of in situ soils VG-16 data has previously been observed to identify clay-rich zones, or segments of stream channels where heavy (and often magnetite-bearing) minerals are concentrated. The airborne data were evaluated by comparison with historic boring logs, records of sand boils and ground-based electromagnetic data acquired at selected sites along the levee with a DualEM 642 system. Early interpi-etation indicates a strong relationship between portions of the levee system that have low electrical conductivity and zones that have historically high rates of seepage and concentrations of sand boils.
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