Reliability of Underwater Acoustic Imaging and Underwater Ultrasonic Testing

One of the most difficult locations to inspect infrastructure is under the water’s surface. The two most frequently used underwater nondestructive evaluation (NDE) technologies include underwater acoustic imaging and underwater ultrasonic testing. The ability to observe the submerged surroundings and underwater infrastructure (e.g., bridge foundations, bulkheads, earth retaining walls, embankments, marine facilities, etc.) with acoustic surface imaging provides tremendous value. Additionally, ultrasonic testing of concrete, steel, and timber members can provide tangible data on the remaining thickness/internal integrity of these materials. But the reliability of these technologies could be questioned if proper practices are not followed since there is limited reliability research and few standards. Underwater acoustic imaging reduces risks in many situations by providing geomatic metrology insight about the submerged elements. Underwater acoustic imaging can enhance underwater observations and provide high resolution 2-D and 3-D imagery documentation at any time; but its greatest value is most often demonstrated during extreme flood events when divers are unable to collect any information due to the hazardous conditions. Recent research data from the University of Wisconsin – Milwaukee is discussed in this paper, as well as the reasonableness of expectations when using underwater technologies. This paper provides lessons learned for using acoustic imaging and ultrasonic testing in the subsurface marine environment. Information is provided on obtaining high quality 2-D and 3-D acoustic images as well as meaningful ultrasonic testing thickness data. Knowledgeable equipment selection and appropriate qualifications are recommended for both underwater acoustic imaging and ultrasonic testing.

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