Development of a diver-deployed instrument for the measurement of sediment density gradients by X-ray attenuation measurements
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Acoustical interactions with ocean sediments effect a wide range of sonar applications in littoral environments. An important factor in understanding the acoustical behavior of the ocean bottom is how the sediment density changes with depth. Although there are existing techniques for obtaining information about sediment gradients, these methods are unable to provide direct measurements of the sediment density gradient without significantly disrupting the test site and requiring significant diver support for installation and implementation. The proposed X-Ray Attenuation Measurement (XRAM) device aims to improve upon these existing techniques with the goal of being a portable diver operated device that can perform direct in situ measurements of sediment density gradients without significant disruption of the ocean bottom. To accomplish this, the XRAM utilizes the attenuation of x-rays passing through the sediment to measure the density as a function of depth, and is arranged in a compact, portable design that can be deployed and operated by a single diver. The layout and basic design of the XRAM device is discussed, and a physical model of its operation is developed. Results of experimental testing on homogeneous liquid samples and liquid/solid mixtures to evaluate the effectiveness of the XRAM device in measuring density gradients are presented. Based on the analysis of these results, recommendations of improved performance for future development are given.