Using an Airgun System for Long Range Low-Frequency Acoustics Propagation
Abstract
For the past three decades there has been renewed focus among researchers in underwater acoustics on sound propagation in shallow wa,ter. The traditional wisdom about shallow water acoustics holds that the interaction of sound with the ocean bottom has considerabl,e impact on the acoustic field in the water. Since sound sources in shallow water are relatively close to the sea floor interface,,sound reflected from the sea floor and sub-bottom interfaces or refracted within the bottom and returned to the water is expected to, make a significant contribution. As a consequence, knowledge of the structure and properties of ocean bottom sediment materials is, considered essential for making predictions of the sound field in the water, and thus to properly assess sonar performance.A centra,l issue in research has been development of experimental and theoretical approaches for characterizing the ocean bottom. This is com,monly done using a method called geoacoustic inversion. This is a remote-sensing approach, based on the observation that sound signa,ls measured at receivers in the water contain information about the ocean medium, including the ocean bottom-through which they have, traveled. The published literature contains a large number of papers reporting successful applications with many different inversio,n methods using various input data, processing and inverse algorithms. Among the diversity, a common point of all the inversion meth,ods is that the result quality cannot be better than the quality of the input data.Under this project, we propose to procure and tes,t an airgun system (mini GI 60 cu.in Sercel). Although airguns are traditionally used in the oil and gas industry, they can also be,used as an acoustic source for geoacoustic inversion experiments. Their interest is two-fold. On the first hand, airguns are industr,y-made, off-the-shelf and widely used systems. Using them thus drastically simplifies acoustic inversion experiments, which usually,rely on custom and complex source systems. On the other hand, airguns are probably the only impulsive source systems producing sourc,e signals that are barely contaminated by bubble pulses. This is a major advantage when compared to traditional ocean acoustic sourc,es (e.g. combustive sound sources or explosives), who all suffered from the bubble pulse drawback. The procured system would be used, to contribute to several major ONR-funded experiments, including the upcoming Seabed Characterization Experiment (2022, New England, Mud Patch) and the Task Force Ocean Department Research Initiative (2022-2023, New England Seamounts).Approved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 16, 2022
- Source ID
- N000142212430
Entities
People
- Julien Bonnel
Organizations
- Office of Naval Research
- United States Navy
- Woods Hole Oceanographic Institution