Sound scattering by rough elongated elastic objects. I: Means of scattered field

Author Posting. © Acoustical Society of America, 1992. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 92 (1992): 1641-1664, doi:10.1121/1.403905.By use of the recently published deformed cylinder formulation [T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989)], the scattered field due to rough elongated dense elastic objects is derived. The (one-dimensional) roughness is characterized by axial variations of radius. Explicit expressions are derived describing both the mean and mean square of the stochastic scattered field for the rough straight finite length cylinder (broadside incidence) for both ka≪1 and ka≫1 (k is the acoustic wave number and a is the radius) while only the mean is calculated for the prolate spheroid, uniformly bent finite cylinder, and infinitely long cylinder for ka≫1 (again, all broadside incidence). The modal-series-based solution is used in the ka≪1 case as the modal solution simplifies to the sum of two terms (monopole and dipole-like terms). For ka≫1, a more convenient approximate ``ray'' solution is used in place of the modal series solution. The results show that (1) when ka≪1 the roughness-induced variations of the mean and mean-square scattered fields due to the rough straight finite cylinder depend on the roughness, but are independent of frequency—an effect that has no counterpart in the area of scattering by rough planar interfaces. (2) When ka≫1 the mean specular (geometrically reflected) and Rayleigh surface elastic waves of the scattered field of each object are attenuated due to the roughness and their variations are dependent upon the frequency. In addition, the (roughness-induced) attenuation of the Rayleigh wave depends on the number of times the wave has circumnavigated the object. The mean-square values for the straight finite cylinder are attenuated in a similar manner with the additional dependence upon the correlation distance of the surface.This work was supported by the U.S. Office of Naval Research (Grant No. N00014-89-J-1729)

Sound scattering by spherical and elongated shelled bodies

Author Posting. © Acoustical Society of America, 1990. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 88 (1990): 1619-1633, doi:10.1121/1.400321.Describing the scattering of sound by elongated objects with high aspect ratios (ratio of length to diameter) usually involves great numerical difficulties. The recently developed deformed cylinder solution was shown to be increasingly accurate in the limit of very high aspect ratios (≥5:1) while requiring relatively low computation times and was applied to objects of constant composition [T. K. Stanton, ``Sound scattering by cylinders of finite length. III. Deformed cylinders,'' J. Acoust. Soc. Am. 86, 691–705 (1989)]. In this article, the approximate formulation is used to describe scattering by prolate spheroids, straight finite cylinders, and uniformly bent cylinders where the objects are composed of an elastic shell surrounded by fluid and filled with either a fluid or gas. The calculations are compared with those involving spherical shells based on the formulation derived in Goodman and Stern [J. Acoust. Soc. Am. 34, 338–344 (1962)]. The calculations are made over a wide range of frequencies and shell thicknesses (ranging from solid elastic objects to thin-shelled objects). Since the deformed cylinder formulation is most accurate for angles of incidence normal or near normal to the lengthwise axis, the calculations are limited to broadside incidence. The simulations show significant variations in the modal interference structure as the shell thickness and shape are varied. Comparisons are also made between predictions and laboratory data involving straight and bent finite-length cylindrical shells (stainless steel) with 3:1 aspect ratios and 52% shell thicknesses. The study not only shows reasonable agreement between the predictions and data, but also illustrates the dramatic change in scattering cross section due to the bend of the object (12 dB in this case).This work was supported in part by the U.S. Office of Naval Researc

Sound scattering by rough elongated elastic objects. II: Fluctuations of scattered field

Author Posting. © Acoustical Society of America, 1992. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 92 (1992): 1665-1678, doi:10.1121/1.403906.Sonar echoes from unresolved features of rough objects tend to interfere with each other. Because of these interferences, properties of the echoes, such as its envelope level, will vary from realization to realization of stochastically rough objects. In this article, the nature of the fluctuations of the backscattered echo envelope of rough solid elastic elongated objects is investigated. A general formulation is initially presented after which specific formulas are derived and numerically evaluated for straight finite-length cylinders. The study uses both the approximate modal-series- and Sommerfeld–Watson-transformation-based deformed cylinder solutions presented in the first part of this series [T. K. Stanton, J. Acoust. Soc. Am. 92, XXX (1992)]. The fluctuations of the backscattered echo envelope are related to the Rice probability density function (PDF) and shown to depend upon δ/a and [script L]/L in the Rayleigh scattering region (ka≪1) and kδ and [script L]/L in the geometric region (ka≫1), where δ is the rms roughness, a is the radius of the cylinder, [script L] is the correlation length of the roughness, L is the length of the cylinder, and k is the acoustic wave number in the surrounding fluid. There are similarities shown between these fluctuations in the geometric region and those from rough planar interfaces. In addition, analytical expressions and numerical examples show that the fluctuation or ``incoherent'' component of the scattered field is random only in amplitude—its phase approaches a constant value, in phase with the mean scattered field, which needed to be taken into account in the formulation. Finally, applications of the theory developed in this article to backscatter data involving live marine shrimp-like organisms are discussed.This work was supported by the U.S. Office of Naval Research Grant Nos. N00014-89-J-1729 and N00014-90-J-1804

Joining Campus and Community Through Service Learning

Involving students in community-service learning requires campus pro­ gram coordinators and community-agency staff to collaborate in program development. Often, because service-learning programs and community organizations have different goals and priorities, separate constituencies, and even varied organizational cultures, they design their programs independently and at cross-purposes. When this occurs, neither organization achieves its goals for students or for the community. Successful service-learning programs bridge this gap between town and gown by cultivating a spirit of reciprocity, interdependence, and collaboration. When carefully considered, expressed, negotiated, and agreed upon, the needs and resources of each organization become complementary and mutually enhancing. This is not easy, however. Campus and community organizations may have competing goals, timetables, and agendas. Nevertheless, from the authors\u27 experiences both on campuses and in communities following a program-design model and asking certain essential questions are the keys to establishing programs that effectively serve campus, community, and students

Application of pulse compression techniques to broadband acoustic scattering by live individual zooplankton

Author Posting. © Acoustical Society of America, 1998. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 104 (1998): 39-55, doi:10.1121/1.424056.Distinct frequency dependencies of the acoustic backscattering by zooplankton of different anatomical groups have been observed in our previous studies [Chu et al., ICES J. Mar. Sci. 49, 97–106 (1992); Stanton et al., ICES J. Mar. Sci. 51, 505–512 (1994)]. Based mainly on the spectral information, scattering models have been proposed to describe the backscattering mechanisms of different zooplankton groups [Stanton et al., J. Acoust. Soc. Am. 103, 236–253 (1998b)]. In this paper, an in-depth study of pulse compression (PC) techniques is presented to characterize the temporal, spectral, and statistical signatures of the acoustic backscattering by zooplankton of different gross anatomical classes. Data collected from various sources are analyzed and the results are consistent with our acoustic models. From compressed pulse (CP) outputs for all three different zooplankton groups, two major arrivals from different parts of the animal body can be identified: a primary and a secondary arrival. (1) Shrimplike animals (Euphausiids and decapod shrimp; near broadside incidence only): the primary one is from the front interface (interface closest to the transducer) of the animal and the secondary arrival is from the back interface; (2) gas-bearing animals (Siphonophores): the primary arrival is from the gas inclusion and the secondary arrival is from the body tissue ("local acoustic center of mass"); and (3) elastic shelled animals (Gastropods): the primary one is from the front interface and the secondary arrival corresponds to the subsonic Lamb wave that circumnavigates the surface of the shell. Statistical analysis of these arrivals is used to successfully infer the size of the individual animals. In conjunction with different aspects of PC techniques explored in this paper, a concept of partial wave target strength (PWTS) is introduced to describe scattering by the different CP highlights. Furthermore, temporal gating of the CP output allows rejection of unwanted signals, improves the output signal-to-noise ratio (SNR) of the spectra of selected partial waves of interest, and provides a better understanding of the scattering mechanism of the animals. In addition, it is found that the averaged PWTS can be used to obtain a more quantitative scattering characterization for certain animals such as siphonophores.This work was supported by the National Science Foundation under Grant No. OCE-9201264 and the U.S. Office of Naval Research under Grant Nos. N00014-89-J-1729, N00014-94-1-0452, and N00014-95-1-0287

Responding to communities’ information needs : community-based research as service-learning

Most practitioners conceive of service-learning as combining student involvement in service-oriented tasks with and for communities with structured educational activities designed to develop their knowledge, character, and/or social skills and capacities. Whatever the goals for students these tasks tend to be of a direct service kind – e.g., tutoring, teaching classes, assisting the elderly, environmental clean-up, etc. Occasionally these tasks will also include administrative or public policy-related work. Rarely, however, does service-learning venture into the realm of research. This interactive workshop will explore the goals, background, characteristics, and current practices of research as a form of service-learning, including its benefits for community and student development. The facilitators will provide a brief introduction to community-based partnership research (CBPR) - a collaborative form of inquiry that seeks to involve all partners (academically- and community-based) in the research process equitably and in ways that draw on their unique strengths and resources. They will invite participants to contribute and explore CBPR’s theoretical foundations, recent expressions in undergraduate education, and major practice issues. Emphasis will be placed on CBPR as a means of establishing long-term campus-community partnerships, which can enable and sustain impact and social value. Using case examples of CBPR practice in South Africa and Thailand our goal will be both to expose participants to this new, developing form of service-learning and cull their knowledge, resources and experience with it. We hope to discuss, compare and ultimately map current practice as it is rePaper presented by participants in the workshop and known by them throughout the world. We will conclude with a discussion of the potential for developing undergraduate CBPR in Hong Kong and throughout the wider Asia-Pacific region. Existing print and online resources on CBPR in higher education will be shared

Calibration of broadband active acoustic systems using a single standard spherical target

Author Posting. © Acoustical Society of America, 2008. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 124 (2008): 128-136, doi:10.1121/1.2917387.When calibrating a broadband active acoustic system with a single standard target such as a sphere, the inherent resonances associated with the scattering by the sphere pose a significant challenge. In this paper, a method is developed which completely eliminates the source of resonances through isolating and exploiting the echo from the front interface of a sphere. This echo is relatively insensitive to frequency over a wide range of frequencies, lacking resonances, and is relatively insensitive to small changes in material properties and, in the case of spherical shells, shell thickness. The research builds upon the concept of using this echo for calibration in the work of Dragonette et al. [J. Acoust. Soc. Am. 69, 1186–1189 (1981)]. This current work generalizes that of Dragonette by (1) incorporating a pulse compression technique to significantly improve the ability to resolve the echo, and (2) rigorously accounting for the scattering physics of the echo so that the technique is applicable over a wide range of frequencies and material properties of the sphere. The utility of the new approach is illustrated through application to data collected at sea with an air-filled aluminum spherical shell and long broadband chirp signals (30–105 kHz).This work was supported by the U.S. Office of Naval Research Grant Nos. N00014-04-1-0475 and N00014- 04-1-0440 and the J. Seward Johnson Chair at WHOI

Service-learning in the USA and South Africa : the influence of student development

This presentation focuses on the history, theoretical foundations, and broad practice of Service-Learning in two different contexts; the United States and South Africa. It examines Service-Learning pedagogy’s design and practice - curricular, co-curricular, or non-formal – utilized in both countries noting the influence of evolving theories of student development - intellectual, moral, civic - in order to engage conference participants in reflecting on appropriate application and possible futures in Hong Kong and elsewhere

Echo statistics associated with discrete scatterers: A tutorial on physics-based methods

Author Posting. © Acoustical Society of America, 2018. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America, 144(6), (2018): 3124-3171. doi: 10.1121/1.5052255.When a beam emitted from an active monostatic sensor system sweeps across a volume, the echoes from scatterers present will fluctuate from ping to ping due to various interference phenomena and statistical processes. Observations of these fluctuations can be used, in combination with models, to infer properties of the scatterers such as numerical density. Modeling the fluctuations can also help predict system performance and associated uncertainties in expected echoes. This tutorial focuses on “physics-based statistics,” which is a predictive form of modeling the fluctuations. The modeling is based principally on the physics of the scattering by individual scatterers, addition of echoes from randomized multiple scatterers, system effects involving the beampattern and signal type, and signal theory including matched filter processing. Some consideration is also given to environment-specific effects such as the presence of boundaries and heterogeneities in the medium. Although the modeling was inspired by applications of sonar in the field of underwater acoustics, the material is presented in a general form, and involving only scalar fields. Therefore, it is broadly applicable to other areas such as medical ultrasound, non-destructive acoustic testing, in-air acoustics, as well as radar and lasers.The content of this work is based on research conducted in the past from years of support from the U.S. Office of Naval Research and the Woods Hole Oceanographic Institution, Woods Hole, MA. Writing of the manuscript by W.-J.L. was also supported by the Science and Engineering Enrichment and Development Postdoctoral Fellowship from the Applied Physics Laboratory, University of Washington, WA. The authors are grateful to Dr. Benjamin A. Jones of the Naval Postgraduate School, Monterey, CA for his thoughtful suggestions on an early draft of the manuscript. The authors are also grateful to the reviewer for the in-depth and constructive recommendations. W.-J.L. and K.B. contributed equally to this work.2019-06-0

Differences between sound scattering by weakly scattering spheres and finite-length cylinders with applications to sound scattering by zooplankton

Author Posting. © Acoustical Society of America, 1998. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 103 (1998): 254-264, doi:10.1121/1.421135.A modeling study was conducted to determine the conditions under which fluidlike zooplankton of the same volume but different shapes (spherical/cylindrical) have similar or dramatically different scattering properties. Models of sound scattering by weakly scattering spheres and cylinders of finite length used in this analysis were either taken from other papers or derived and herein adapted for direct comparison over a range of conditions. The models were examined in the very low- (ka ≪ 1, kL ≪ 1), moderately low- (ka ≪ 1, kL ≳ 1), and high-frequency regions (ka ≫ 1, kL ≫ 1), where k is the acoustic wave number, a is the radius (spherical or cylindrical) of the body, and L is the length of the cylinders (for an elongated body with L/a = 10, "moderately low" corresponds to the range 0.1 ≲ ka ≲ 0.5). Straight and bent cylinder models were evaluated for broadside incidence, end-on incidence, and averages over various distributions of angle of orientation. The results show that for very low frequencies and for certain distributions of orientation angles at high frequencies, the averaged scattering by cylinders will be similar, if not identical, to the scattering by spheres of the same volume. Other orientation distributions of the cylinders at high frequencies produce markedly different results. Furthermore, over a wide range of orientation distributions the scattering by spheres is dramatically different from that of the cylinders in the moderately low-frequency region and in the Rayleigh/geometric transition region: (1) the Rayleigh to geometric scattering turning point occurs at different points for the two cases when the bodies are constrained to have the same volume and (2) the functional dependence of the scattering levels upon the volume of the bodies in the moderately low-frequency region is quite often different between the spheres and cylinders because of the fact that the scattering by the cylinders is still directional in this region. The study demonstrates that there are indeed conditions under which different shaped zooplankton of the same volume will yield similar (ensemble average) scattering levels, but generally the shape and orientation distribution of the elongated bodies must be taken into account for accurate predictions.This work was supported by the U.S. Office of Naval Research Grant No. N00014-95-1-0287 and the National Science Foundation Grant No. OCE-9201264