VICKSBURG, Miss. – An 800-pound dart-shaped instrument is the latest tool to map beneath the surface of levees in a partnership between the U.S. Army Corps of Engineers Vicksburg District and the U.S. Geological Survey. For the first time, a regional geophysical survey will provide a full overview of 800 miles of the Mississippi River mainline levees. Sometimes called a bird, the frequency domain system suspended from a helicopter will use frequency technology similar to LiDAR to differentiate between various soil layers and penetrate about 150 feet under the surface.