Acoustic Imaging of Shallow Water Sediments
Final rept. 1 Jan 1997-31 Dec 1998
WASHINGTON UNIV SEATTLE APPLIED PHYSICS LAB
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Sediment volume inhomogeneity on the centimeter scale has a major impact on the design and application of high-frequency sonars, especially when operated in shallow water. An acoustic imaging system was developed to measure, image and model such inhomogeneities using acoustic tomography. The in-situ sediment acoustic imaging system consists of an array of needle-like probes that may be pressed into the sediment. Each probe is a line array of transducers. The current system consists of three identical probes attached to a sturdy frame. Each probe. contains 20 transducers, spaced 5 cm apart. Two probes are oriented vertically and pressed into the sediment about one meter apart. The third probe is oriented horizontally, just above the sea floor between the vertical probes. The transducers have a resonant frequency of 100 kHz and a bandwidth of approximately 40 kHz. The objective is to estimate travel time and transmit-to-receive amplitude on all possible raypaths. Two data sets were processed. Spreading of sound speed due to diffraction was observed, and attenuation coefficients in mud varied from 10 dBm to 65 dBm. The effects of gas bubbles and multiple scattering will require modeling. The advantages of the probe system are apparent It can measure sound speed and attenuation coefficients and provide information to the marine geology and biology communities.
- Physical and Dynamic Oceanography
- Acoustic Detection and Detectors