Subsurface acoustic imaging system

In this study, we demonstrate an acoustic system for high-resolution imaging of objects buried in soil. Our goal is to image cultural artifacts in order to assess, in a rapid, highly sampled manner, the historical significance of a potential construction site. In a preliminary study conducted at the Biacoustics Research Laboratory, the acoustic propagation properties of six types of soil were evaluated. The current study will describe the imaging system and present preliminary images produced from data collected from a soil phantom. We have built the imaging system, which incorporates a single element source transducer and a receiver array, both obtained from the Applied Research Laboratory at Pennsylvania State University. The source and receiver array are moved together along a linear path to collect data to form a B-mode image. The source is well approximated as a point source. The transmitted signal is a cosine weighted pulse of 6 cycles at a center frequency of 6 kHz. A 52-element sonar array (8×8, 3.56 cm² close-packed elements with 3 elements missing from each corner) acts as the receiver and allows for beamforming on receive, which is accomplished off-line using delay-and-sum beamforming. This system is in operation at the U.S. Army Construction Engineering Research Laboratory (CERL) in Champaign, IL, where the data are collected in a controlled volume (120×120×60 cm) of dry sand. Using this system, we have obtained B-mode images of several targets buried up to 13 cm deep.