The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Kenneth G. Foote - One of the best experts on this subject based on the ideXlab platform.
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Acoustic Sampling Volume revisited
OCEANS 2019 MTS IEEE SEATTLE, 2019Co-Authors: Kenneth G. FooteAbstract:At the OCEANS 2010 Conference in Seattle, J. E. Ehrenberg co-authored a paper [Steig et al; doi: 10.1109/OCEANS.2010.5664422] that addressed a fundamental problem in fisheries acoustics: that of quantitative Sampling. A definition was formulated for the “effective Sampling Volume of the hydroacoustic system.” As noted in the paper, the effective beam width of the acoustic system is a function of the backscattering cross section, or its logarithmic measure, the target strength, of the fish being observed. However, the effective beam width is also fundamentally stochastic. Given the impetus of the cited paper, an earlier work on the acoustic Sampling Volume [K. G. Foote, J. Acoust. Soc. Am. 90, 959 (1991); doi: 10.1121/1.401963] is reexamined, with further reference to a recent bistatic generalization of the acoustic Sampling Volume [K. G. Foote; IEEE J. Oceanic Eng., 43, 749 (2018); doi: 10.1109/JOE.2017.2713538].
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Organizing error sources in a standard on active-sonar calibration by standard target
OCEANS 2018 MTS IEEE Charleston, 2018Co-Authors: Kenneth G. FooteAbstract:For standards written under the auspices of metrological institutions, formal treatment of uncertainty is a sine qua non. In the case of standards concerning instruments that measure sound underwater, the historical record shows that the treatment often consists of listing error sources without apparent structure or order. Such entries appear to be ad hoc. This may be satisfactory, but lack of an explicit structure leaves open questions about the completeness of such a list, or where to look when there is suspicion of missing significant error sources. This matter is addressed apropos of formulating a standard on the standard-target method of calibrating active sonars for imaging and measuring scattering, ultimately for publication by an international metrological institution. The following categories of error sources are identified: transducer acoustic field structure, free-field conditions, alignment of transducer and target, transmit signal, environmental state, electromagnetic noise, wetting of acoustic surfaces, target scattering properties, acoustic Sampling Volume, overall system response function, and range compensation. These generic sources are organized according to the Joint Committee for Guides in Metrology (JCGM) guidance document on the expression of uncertainty in measurement.
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Standard-Target Calibration of Active Sonars Used to Measure Scattering: Principles and Illustrative Protocols
IEEE Journal of Oceanic Engineering, 2018Co-Authors: Kenneth G. FooteAbstract:The standard-target sonar-calibration method was used as early as the 1940s. Its development since then is reviewed, as is the prerequisite for the method, the standard target. The theoretical basis for the method is established, with the aim of enabling sonar output signals to be expressed in absolute physical units of scattering. This is done with reference to the Volume scattering coefficient sV and physical effects intrinsic to operational sonars. A constituent of sV, the generally bistatic acoustic Sampling Volume, is elaborated. Formulas are developed for the calibration constant in the energy domain and the combined transmit-receive frequency response function in the spectral domain. Practical elements of a calibration are elaborated in terms of the sonar specification, candidate calibration venue, environmental state, and calibration exercise design, including reference-beam approach. These elements are illustrated through the example of a standard-target calibration of a sonar with multiple beams at a land-based facility. The venue is specified in terms of its measurement Volume, and equipment and instrumentation. Preparations for the exercise are enumerated, and reference-beam and nonreference-beam protocols are described. The intended audience for this paper is those who require a basic understanding of principles to be able to organize or undertake the standard-target calibration of new sonars on arbitrary platforms or known sonars on new platforms.
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Ensuring fidelity of underwater acoustic measurements at low frequencies
OCEANS 2017 - Anchorage, 2017Co-Authors: Kenneth G. FooteAbstract:The water column is being investigated increasingly with low-frequency sound, of order 1-10 kilohertz or less, with both conventional sonars and the difference-frequency band of parametric sonars. While high-frequency applications abound, scaling to lower frequencies is not always straightforward. A number of challenges, framed here as considerations, are reviewed to support the overall aim of ensuring measurement fidelity at low frequencies. The particular considerations, or concerns, are those of the nearfield, acoustic Sampling Volume, range compensation, beam patterns, and calibration.
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Maintaining quality of acoustic data: Calibration methods for active and passive devices, with extended Sampling Volume
2014 IEEE Sensor Systems for a Changing Ocean (SSCO)., 2014Co-Authors: Kenneth G. FooteAbstract:A key technology that continues to evolve to meet special requirements of underwater Sampling and observation is that of acoustics. This technology is used both actively to ensonify fish, zooplankton, other marine organisms, and the environment, and passively to listen to and record sounds produced by marine organisms and other sources, e.g., shipping and environmental noise. When calibrated, acoustic devices offer the potential for quantification. The essential case for calibration is made, and principal methods for the calibration of active and passive devices are reviewed. These include the standard-target method for the calibration of active devices, e.g., sonars, and the three-transducer spherical-wave reciprocity method for the calibration of passive devices, e.g., electroacoustic transducers and hydrophones. Recent advances in understanding the spatial structure of the transducer nearfield may safely extend the range at which such calibrations can be performed, as well as extending the range of measurements themselves. This extension can be quantified through the acoustic Sampling Volume. Reference is also made to the IEEE Oceanic Engineering Society (OES) Standards Initiative, with website at http://www.oceanicengineering.org/page.cfm/cat/105/OES-Standards-Initiative/, which is providing a forum for dissemination of information on standards, protocols, quality assurance procedures, and best practices that are important in ocean engineering. This includes information on current calibration methods for acoustic instruments.
Ye Zhou - One of the best experts on this subject based on the ideXlab platform.
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A New Method for Determining the Sampling Volume and the Number of Particles Within It for Particle Concentration Identification in Defocused Interferometric Particle Imaging
IEEE Photonics Journal, 2017Co-Authors: Hongxia Zhang, Ye ZhouAbstract:Interferometric particle imaging (IPI) is a robust technique for measuring particle size and velocity. In defocused IPI that is uniquely valuable to quality control of a spray field, a reliable method for identifying the particle concentration in the Volume sampled by the sheet beam remains outstanding. This paper proposes a new approach to the determination of the Sampling Volume of defocused IPI and the number of particles within the Sampling Volume for informing the particle concentration. The methods for determining the Sampling Volume and the number of particles within the Sampling Volume are documented with a new set of formula derived using conventional ray-tracing and interferometry principles. For any defined measurement geometry, the Sampling Volume is quantitated when the lateral and elevational dimensions of the sheet beam and the defocusing distance are known. The number of particles in the Sampling Volume is counted by determining whether or not a particle is within the Sampling Volume, upon the analysis of the size range [Φpix2, Φpix1] of the interference circle. The method for identifying particle concentration in defocused IPI is tested on synthetic interferogram (1% noise) corresponding to first, particles of the same size of 45 μm at different concentrations ranging from 0.0040 to 0.239 mm-3 and, second, particles of 0.0119 and 0.119 mm-3 concentrations with the sizes ranging from 10 to 90 μm. This new method for quantitating particle concentration in defocused IPI is then examined against experimental concentrations of particles of 10, 21.3, and 45 μm in size, respectively. The largest experimental error for 45 μm particles with the concentration of 0.006 mm-3 is 10.4% and decreases with the increase of the particle concentration. This method for identifying particle concentration is expected to be applicable to various areas wherein particle analysis is to be rendered by defocused IPI.
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Theoretical Analysis and Experimental Validation of Sampling Volume in Tilted Imaging System
IEEE Photonics Journal, 2015Co-Authors: Hongxia Zhang, Mengran Zhai, Ye ZhouAbstract:A method for accurately calculating the Sampling Volume in a tilted imaging system is proposed. Two types of tilted imaging systems are investigated, i.e., Type I (only the object plane is inclined to the optical axis) and Type II (both the object plane and the image plane are inclined to the optical axis). Based on geometrical optics, the Sampling Volumes of these two types of tilted imaging systems have been simulated. Compared with the central magnification of an imaging system and the focal length and F-number of the imaging lens, the effect of the tilted angle of the object plane on the Sampling Volume is determined to be more important. A tilted imaging experimental setup has been established, calibration plate images at various tilted angles and positions have been acquired, and the Sampling Volume has been obtained by image processing. The experimental results are in very good agreement with the theoretical predictions. As the tilted angle increases, for the Type-I system, the Sampling Volume increases, whereas for the Type-II system, the Sampling Volume decreases. In addition, the Sampling Volume of the Type-II system is larger than that of the Type-I system. Knowledge of the Sampling Volume is necessary in many quantitative applications of tilted imaging systems.
Hongxia Zhang - One of the best experts on this subject based on the ideXlab platform.
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A New Method for Determining the Sampling Volume and the Number of Particles Within It for Particle Concentration Identification in Defocused Interferometric Particle Imaging
IEEE Photonics Journal, 2017Co-Authors: Hongxia Zhang, Ye ZhouAbstract:Interferometric particle imaging (IPI) is a robust technique for measuring particle size and velocity. In defocused IPI that is uniquely valuable to quality control of a spray field, a reliable method for identifying the particle concentration in the Volume sampled by the sheet beam remains outstanding. This paper proposes a new approach to the determination of the Sampling Volume of defocused IPI and the number of particles within the Sampling Volume for informing the particle concentration. The methods for determining the Sampling Volume and the number of particles within the Sampling Volume are documented with a new set of formula derived using conventional ray-tracing and interferometry principles. For any defined measurement geometry, the Sampling Volume is quantitated when the lateral and elevational dimensions of the sheet beam and the defocusing distance are known. The number of particles in the Sampling Volume is counted by determining whether or not a particle is within the Sampling Volume, upon the analysis of the size range [Φpix2, Φpix1] of the interference circle. The method for identifying particle concentration in defocused IPI is tested on synthetic interferogram (1% noise) corresponding to first, particles of the same size of 45 μm at different concentrations ranging from 0.0040 to 0.239 mm-3 and, second, particles of 0.0119 and 0.119 mm-3 concentrations with the sizes ranging from 10 to 90 μm. This new method for quantitating particle concentration in defocused IPI is then examined against experimental concentrations of particles of 10, 21.3, and 45 μm in size, respectively. The largest experimental error for 45 μm particles with the concentration of 0.006 mm-3 is 10.4% and decreases with the increase of the particle concentration. This method for identifying particle concentration is expected to be applicable to various areas wherein particle analysis is to be rendered by defocused IPI.
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Theoretical Analysis and Experimental Validation of Sampling Volume in Tilted Imaging System
IEEE Photonics Journal, 2015Co-Authors: Hongxia Zhang, Mengran Zhai, Ye ZhouAbstract:A method for accurately calculating the Sampling Volume in a tilted imaging system is proposed. Two types of tilted imaging systems are investigated, i.e., Type I (only the object plane is inclined to the optical axis) and Type II (both the object plane and the image plane are inclined to the optical axis). Based on geometrical optics, the Sampling Volumes of these two types of tilted imaging systems have been simulated. Compared with the central magnification of an imaging system and the focal length and F-number of the imaging lens, the effect of the tilted angle of the object plane on the Sampling Volume is determined to be more important. A tilted imaging experimental setup has been established, calibration plate images at various tilted angles and positions have been acquired, and the Sampling Volume has been obtained by image processing. The experimental results are in very good agreement with the theoretical predictions. As the tilted angle increases, for the Type-I system, the Sampling Volume increases, whereas for the Type-II system, the Sampling Volume decreases. In addition, the Sampling Volume of the Type-II system is larger than that of the Type-I system. Knowledge of the Sampling Volume is necessary in many quantitative applications of tilted imaging systems.
X L Wang - One of the best experts on this subject based on the ideXlab platform.
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theory of the peak shift anomaly due to partial burial of the Sampling Volume in neutron diffraction residual stress measurements
Journal of Applied Crystallography, 1998Co-Authors: X L Wang, S Spooner, C R HubbardAbstract:A theory is presented to describe the anomalous peak shift encountered in neutron diffraction residual stress measurements as the specimen is translated into and out of the Sampling Volume, which is defined by a pair of masking slits inserted before and after the specimen. Analytical formulae for the anomalous peak shift were obtained for both position-sensitive-detector-based diffractometers and conventional scanning diffractometers. The results indicate that the observed peak shift is a complex function of many variables, including the in-pile collimation, slit widths, slit-to-axis distances, mosaic spread of the monochromating crystal, and mismatch in lattice spacing between the sample and the monochromator. Calculations based on the derived analytical formulae are in good agreement with experimental observations. It is shown that by the choice of appropriate experimental conditions, this peak shift anomaly can be suppressed or, in some cases, eliminated altogether.
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diffraction peak displacement in residual stress samples due to partial burial of the Sampling Volume
Journal of Applied Crystallography, 1997Co-Authors: S Spooner, X L WangAbstract:Near-surface measurement of residual strain and stress with neutron scattering complements and extends the surface residual stress measurements by X-ray diffraction. However, neutron diffraction measurements near surfaces are sensitive to scattering Volume alignment, neutron beam wavelength spread and beam collimation and, unless properly understood, can give large fictitious strains. An analytic calculation and a numerical computation of neutron diffraction peak shifts due to partial burial of the Sampling Volume have been made and are compared with experimental measurement. Peak shifts in a strain-free nickel sample were determined for conditions where the sample surface is displaced so that the scattering gage Volume is partially buried in the sample. The analytic and numerically computed peak shifts take into account the beam collimation, neutron source size, monochromator crystal mosaic spread and the collection of diffracted intensity with a linear position-sensitive counter.
Insa Neuweiler - One of the best experts on this subject based on the ideXlab platform.
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impact of Sampling Volume on the probability density function of steady state concentration
Water Resources Research, 2008Co-Authors: Ronnie L Schwede, Olaf A Cirpka, Wolfgang Nowak, Insa NeuweilerAbstract:[1] In recent years, statistical theory has been used to compute the ensemble mean and variance of solute concentration in aquifer formations with second-order stationary velocity fields. The merit of accurately estimating the mean and variance of concentration, however, remains unclear without knowing the shape of the probability density function (pdf). In a setup where a conservative solute is continuously injected into a domain, the concentration is bounded between zero and the concentration value in the injected solution. At small travel distances close to the fringe of the plume, an observation point may fall into the plume or outside, so that the statistical concentration distribution clusters at the two limiting values. Obviously, this results in non-Gaussian pdf's of concentration. With increasing travel distance, the lateral plume boundaries are smoothed, resulting in increased probability of intermediate concentrations. Likewise, averaging the concentration in a larger Sampling Volume, as typically done in field measurements, leads to higher probabilities of intermediate concentrations. We present semianalytical results of concentration pdf's for measurements with point-like or larger support Volumes based on stochastic theory applied to stationary media. To this end, we employ a reversed auxiliary transport problem, in which we use analytical expressions for first and second central spatial lateral moments with an assumed Gaussian pdf for the uncertainty of the first lateral moment and Gauss-like shapes in individual cross sections. The resulting concentration pdf can be reasonably fitted by beta distributions. The results are compared to Monte Carlo simulations of flow and steady state transport in 3-D heterogeneous domains. In both methods the shape of the concentration pdf changes with distance to the contaminant source: Near the source, the distribution is multimodal, whereas it becomes a unimodal beta distribution far away from the contaminant source. The semianalytical and empirical pdf's differ slightly, which we contribute to the numerical artifacts in the Monte Carlo simulations but also to hard assumptions made in the semianalytical approach. Our results imply that geostatistical techniques for interpolation and other statistical inferences based on Gaussian distributions, such as kriging and cokriging, may be feasible only far away from the contaminant source. For calculations near the source, the beta-like distribution of concentration should be accounted for.
