Abstract:
Understanding of the spatial variability of sediment properties is crucial to many applications of underwater acoustics. Although core samples can provide satisfactory resolution of the vertical variability of sediments, horizontal samplings are too sparse to provide a centimeter-scale horizontal resolution. A two-dimensional acoustic tomographic system is under development at the Woods Hole Oceanographic Institution capable of providing in situ 2-D acoustic images of shallow water sediments. The system can provide a spatial resolution up to a few centimeters and differentiate 2% variations in sound speed within the tomographic region. It consists of three identical probes, each includes twenty 5-cm-spaced transducers. Two of the probes are oriented vertically and separated by about 1 m, and the third is positioned horizontally right above the two vertical probes. Improving upon the conventional cross-hole tomographic technique, the horizontal probe greatly helps provide a higher horizontal resolution. The acoustic tomography is performed in a 2-D vertical slice of about 1 m[sup 2] (1 mx1 m). To test the robustness and precision of the inversion technique used, numerical simulations are performed in terms of influences from a variety of potential error sources such as transducer position errors. Preliminary experimental results are also presented. [Work sponsored by ONR.]