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Expendable Acoustic Source for AUV Based Geoacoustic and Geotechnical Survey Operations


OBJECTIVE: Provide future Naval Oceanographic Office survey teams with expendable calibrated sources for use in determining the bottom sediment acoustic properties necessary for planning and operation of low and mid frequency ASW sonars in shallow water. Further, the inversion of the acoustic information for geotechnical properties will support classification for mine burial prediction. DESCRIPTION: Acoustic sources on the bottom are advantageous for bottom acoustics surveying, as: 1) there is less spreading loss to reach the medium and 2) within a few meters of the bottom, a pressure source can excite Scholte waves, which can provide information about bottom shear properties. When coupled with a near bottom receiver (like a terrain hugging AUV), such a source/ receiver configuration sees the Scholte wave. Absent such a source, AUV based surveys must rely on sources of opportunity like passing ships, which are band limited, surface wave noise, which is inherently high angle, or an AUV based source on a separate vehicle which has the same endurance as the receiver vehicle. One time use sources (sonabuoys) are frequently used in Maritime Patrol Aircraft ASW efforts. They can also be found in the form of acoustic countermeasures employed by submarines for evasion and escape, but the application to bottom survey would be novel. PHASE I: Design and demonstrate through simulation or limited testing the potential to develop a 0.1 - 4 kHz coherent source that is low cost and has the potential to operate at depths down to 100 meters for up to two hours prior to scuttling. PHASE II: Demonstrate a prototype source in a realistic environment. This phase will include development of hardware. A completely functional prototype is not required; however, the feasibility and the expected performance of a final design should be clearly evident within the demonstration. PHASE III: A low cost prototype 0.2 - 4 kHz coherent source system that has the potential to transition into the LBS-UUV POR. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: A dual use application could be basic and applied research related to Geoacoustic and Geotechnical Inversion and Survey technique development.
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