Robert J. Barton

Characterization of scattered acoustic intensity fields in the resonance region of a motionless rigid sphere

In this study, the properties of the scattered acoustic vector fields generated by simple rigid motionless spheres are investigated. Analytical solutions are derived from general acoustic pressure scattering models, and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented. The ability to extract scattered field features is illustrated with measurements obtained from a recent in-air experiment using an anechoic chamber and acoustic intensity probes to measure the scattered acoustic vector field from motionless rigid spheres.

A characterization of the scattered acoustic intensity field in the resonance region for simple spheres

The properties of the scattered acoustic vector fields generated by simple spheres illuminated by monotonic continuous wave (CW) plane waves are investigated. Analytical solutions are derived from general acoustic pressure scattering models and analyzed for wave numbers in the resonance region. Of particular interest is the understanding of the characteristics of the scattered acoustic vector field in the near-to-far-field transition region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented for the near and transition regions for a rigid sphere. A method of mapping nulls in the scattered intensity field components is described. The analysis is then extended to include a simple fluid-filled boundary and finally the evacuated thin-walled shell. Near field acoustic intensity field structures are compared against mechanical material properties of vacuous shells. The ability to extract scattered field features is illustrated with measurements obtained from a recent in-air experiment using an anechoic chamber and acoustic vector sensor probes to measure the scattered acoustic vector field from rigid spheres.

The application of EZ-Gram sonar display aids to the Marine Mammal Monitoring on Navy Undersea Ranges (M3R) system

In order to understand and address the environmental impact of sonar and acoustic systems testing, the Naval Undersea Warfare Center (NUWC) and its partners are developing new techniques and applications for the passive classification and tracking of marine mammals in designated Navy acoustic sensor testing areas. The combined transient and broadband nature of the whale clicks contains a richly unique structure that can be exploited for completely non-evasive tracking and localization. NUWC has developed unique harmonic classification tools and other advanced visual tactical decision aids for the US Navys latest sonar systems, designed to maximize operator performance and awareness of the undersea environment. In this paper, we explore the use of harmonic frequency and temporal-patterned structures in the detection and tracking of whales on the Atlantic Undersea Test and Evaluation Center (AUTEC) acoustic range. We demonstrate and report the results of the analysis of actual at-sea recorded blue whale vocalizations utilizing advanced sonar visualization and classification tools, and new tracking applications being developed.

Characterization of scattered acoustic intensity fields of finite cylinders in the resonance region

The properties of the scattered acoustic vector fields generated by infinite-length and finite rigid and elastic cylinders are investigated. Analytical solutions are derived from general acoustic pressure scattering models and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented for the near and transition regions. A finite element model is developed for a rigid cylinder and compared to measured results in-air using an anechoic chamber and acoustic vector sensor probes to measure the scattered acoustic vector field. The finite cylinder model and analysis is then extended to include an evacuated thin-walled elastic shell. The vector properties of the time-independent complex intensity components and their relations to field energy density quantities are summarized.

A comprehensive examination of the acoustic vector fields scattered by cylindrical bodies

In this study, the properties of the scattered acoustic vector fields generated by infinite-length and finite-length rigid and elastic cylinders are investigated. Analytical solutions are derived from general acoustic pressure scattering models, and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented for the near field and transition regions. A finite element model is developed for both rigid and elastic cylindrical bodies. The finite cylinder model and analysis is then extended to include interactions with an elastic half space. The vector properties of the time-independent complex intensity components and their relations to field energy density quantities are summarized.

Characterization of the near scattered acoustic vector field.

In this study, we investigate the properties of the scattered acoustic vector fields generated by simple geometric objects, including the infinite rigid plate, disk, and sphere. Analytical solutions are derived from acoustic target strength scattering models in the near field region. Of particular interest is the understanding of the characteristics of energy flow of the scattered acoustic vector field in the near to far‐field transition region. We utilize the time and space separable instantaneous active and reactive acoustic intensity to investigate the relative phase properties of the scattered field. Numerical results are presented for the near region scattered acoustic vector field of simple objects in both two and three dimensions.

Near field scattering measurements using acoustic vector sensors

The objective of this research is to measure and characterize acoustic energy flow surrounding underwater objects in the near field condition. To accomplish this, we employ prototype acoustic vector sensors which simultaneously measure acoustic pressure and three-dimensional acoustic particle acceleration at a singular point, allowing for precise vector field measurements. In March of 2018, a test at the U.S. Navy’s Dodge Pond Test Facility examined the intensity field surrounding hollow spheres at low ka (wavenumber × radius) values. Phase differences between varying acoustic path lengths from reflected, scattered, and creeping waves result in interference patterns around the object. Various intensity processing techniques are used to reconstruct the acoustic field. Instantaneous intensity describes the time-dependent energy flux of the field and can be divided into active (real) and reactive (imaginary) components, which represent physically real elements. Time-averaged intensity shows energy transport and can be visualized in the form of acoustic streamlines.The objective of this research is to measure and characterize acoustic energy flow surrounding underwater objects in the near field condition. To accomplish this, we employ prototype acoustic vector sensors which simultaneously measure acoustic pressure and three-dimensional acoustic particle acceleration at a singular point, allowing for precise vector field measurements. In March of 2018, a test at the U.S. Navy’s Dodge Pond Test Facility examined the intensity field surrounding hollow spheres at low ka (wavenumber × radius) values. Phase differences between varying acoustic path lengths from reflected, scattered, and creeping waves result in interference patterns around the object. Various intensity processing techniques are used to reconstruct the acoustic field. Instantaneous intensity describes the time-dependent energy flux of the field and can be divided into active (real) and reactive (imaginary) components, which represent physically real elements. Time-averaged intensity shows energy transport ...

Underwater techniques to characterize the near scattered acoustic vector field

In this study, we investigate the properties of the scattered acoustic vector fields generated by simple geometric objects, including the infinite rigid plate, disk, and sphere. Analytical solutions are derived from acoustic target strength scattering models in the near‐field region. Of particular interest is the understanding of the characteristics of energy flow of the scattered acoustic vector field in the near- to far- field transition region. We utilize the time and space separable instantaneous active and reactive acoustic intensities to investigate the relative phase properties of the scattered field. Numerical results are presented for the near region scattered acoustic vector field of simple objects in both two and three dimensions. Previous in-air measurements are summarized, and an approach to taking water-borne measurements is offered.

Scattered acoustic intensity field measurements of a rigid motionless sphere and cylinder

In this study, the properties of the scattered acoustic vector fields generated by a simple rigid motionless sphere and cylinder are investigated. Analytical solutions are derived from general acoustic pressure scattering models, and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. The ability to extract scattered field features is illustrated with measurements obtained from in-air experiments using an anechoic chamber and acoustic intensity probes to measure the scattered acoustic vector field resulting from continuous plane wave illumination.

A characterization of scatterred acoustic intesity fields in the resonance region.

In this study, we investigate the properties of the scattered acoustic vector fields generated by simple rigid and fluid‐filled spheroids. Analytical solutions are derived from acoustic target strength scattering models in the near field region. Of particular interest is the understanding of the characteristics of energy flow of the scattered acoustic vector field in the near‐ to far‐field transition region. We utilize the separable active and reactive acoustic intensity fields to investigate the structural features of the scattered field components. Numerical and in‐air measured results are presented for the near and transition region scattered acoustic vector field of simple spheroids. A qualitative method is developed for characterizing submerged scatterer properties based on boundary condition and features of the scattered vector field.