Volume Scattering Research Articles

Artificial neural network classification of surface reflectors and volume scatterers using sequential echoes acquired with a biomimetic audible sonar.

This paper investigates classifying two target groups, surface reflectors (SR) and volume scatterers (VS), using echo envelope features. SR targets have convex surface patches that exhibit echo persistence over aspect angle, while VS targets are composed of random range-distributed and oriented reflectors producing echoes that become uncorrelated with small changes in aspect angle. The SR target group contains single-post (P1) and multiple-post (PM) types and the VS group contains Ficus benjamina (F) and Schefflera arboricola (S) foliage types with leaf areas that differ by a factor of 4. A biomimetic sonar emitting audible clicks acquired sequences of up to three binaural echoes from target views separated by 18°. Two artificial neural networks performing linear and nonlinear classification first differentiated SR/VS target groups and then P1/PM and F/S types. Classification performance improved with echo number, from a single monaural echo to three pairs of binaural echoes, demonstrating the benefit of sequential echoes. Linear and nonlinear classification of SR/VS targets achieved a minimum generalization error probability PEG = 0.003. Nonlinear P1/PM classification achieved PEG = 0.009 that was four times smaller than linear classification. Nonlinear F/S classification achieved PEG = 0.220, indicating that envelope features by themselves are inadequate to accurately differentiate foliage targets.

Detection efficiency for underwater coaxial photon-counting lidar.

Backscatter has significant influence on detection efficiency for underwater lidar, especially for coaxial photon-counting lidar using a Geiger-mode avalanche photodiode. In this paper, based on our underwater coaxial photon-counting lidar structure and volume scatter function, a detection model with consideration of backscatter and refraction indices is proposed. Using this detection model, analysis of the detection efficiency is conducted. It reveals that in an underwater environment, higher pulse energy or a closer target range is not necessarily helpful for a higher target detection probability, which is vastly different from our traditional concepts. For example, the detection probability for a 5 m target would be 0.76 using a 200 pJ pulse and 0.55 using a 1000 pJ pulse for our coaxial photon-counting lidar. Monte Carlo simulation is conducted to verify our model and analysis, and some practical methods for improving the target detection probability in an underwater environment are proposed.

Neutrophil Volume, conductivity and scatter (VCS) as a screening tool in neonatal sepsis

The initial evaluation of a suspected sepsis in a neonate is always challenging. There are many methods to screen a neonate with suspected sepsis. One of newer method is to assess the changes in neutrophil volume conductivity and scatter. The objective of this study was to establish changes in Neutrophil volume conductivity scatter (VCS) in neonatal sepsis and to determine appropriate cut off levels using receiver operating characteristic (ROC) curves. Neonates with suspected sepsis were evaluated with blood counts, culture and neutrophil VCS parameters. Based on these parameters neonates were classified into sepsis group (Blood culture positive), Probable sepsis group (clinical course consistent with sepsis and positive sepsis screen and negative blood culture), No sepsis group (Clinical course not suggestive of sepsis with negative sepsis screen and blood culture). A total of 304 neonates were included in the study of which 144 were in sepsis group and 160 in no sepsis group respectively. Among the neutrophil VCS parameters there was significant difference between the groups with respect to mean neutrophil volume (MNV) and volume distribution width (VDW) (180 vs 163 vs 150) (p < 0.01). MNV and VDW had good sensitivity (95%, 82%) and specificity (86%, 74%) for diagnosis of sepsis. In conclusion, Neutrophil VCS parameters, especially MNV, can be incorporated with other sepsis screen parameters in diagnosis of neonatal sepsis.

Seven-Component Decomposition Using Refined Volume Scattering Models and New Configurations of Mixed Dipoles

In this article, an extended seven-component decomposition method using refined volume scattering models and new configurations of mixed dipoles (M7SD) is proposed to interpret the scattering mechanisms of various terrain types. In the M7SD, refined volume scattering models are proposed to reasonably characterize the scattering mechanisms of various land covers with different orientation angles, and the redefined configurations of the mixed dipoles, which have better explanations for the scattering mechanisms, are introduced. Although the diameter of the dipole used in the experiment is very small, the superposition of two dipoles in the same plane will cause one of the dipoles to have a distance from the plane. According to the experimental results, since the distance between one of the dipoles and plane cannot be ignored, it will cause an error between the scattering matrix obtained by the experiment and the scattering matrix obtained under ideal conditions. In this case, in the M7SD, two dipoles are placed in two planes, respectively, with a distance of half wavelength. The performance of the proposed method is demonstrated and evaluated with the spaceborne C-band GaoFen-3, Radarsat-2, and airborne L-band ESAR fully polarimetric data over different study sites. The experimental results demonstrate that the use of the M7SD can reasonably interpret the scattering mechanisms of various terrain types (especially the building areas with large orientation angles), overcome the overestimation of the volume scattering and reduce the percentage of negative scattering power pixels.

基于Sahu-Shanmugam和Fournier-Forand体积散射函数的水下激光传输特性分析

基于Sahu-Shanmugam和Fournier-Forand体积散射函数的水下激光传输特性分析

Superdiffusive stochastic Fermi acceleration in space and energy

ABSTRACTWe analyse the transport properties of charged particles (ions and electrons) interacting with randomly formed magnetic scatterers (e.g. large-scale local ‘magnetic fluctuations’ or ‘coherent magnetic irregularities’ usually present in strongly turbulent plasmas), using the energization processes proposed initially by Fermi in 1949. The scatterers are formed by large-scale local fluctuations (δB/B ≈ 1) and are randomly distributed inside the unstable magnetic topology. We construct a 3D grid on which a small fraction of randomly chosen grid points are acting as scatterers. In particular, we study how a large number of test particles are accelerated and transported inside a collection of scatterers in a finite volume. Our main results are: (1) The spatial mean-square displacement &amp;lt;(Δr)2 &amp;gt; inside the stochastic Fermi accelerator is superdiffusive, $\lt (\Delta r)^2\gt \sim t^{a_{r}},$ with ar ∼ 1.2–1.6, for the high-energy electrons with kinetic energy (W) larger than 1 MeV, and it is normal (ar = 1) for the heated low-energy (W &amp;lt; 10 keV) electrons. (2) The transport properties of the high-energy particles are closely related with the mean-free path that the particles travel in-between the scatterers (λsc). The smaller λsc is, the faster the electrons and ions escape from the acceleration volume. (3) The mean displacement in energy $\lt \Delta W\gt \sim t^{a_{W}}$ is strongly enhanced inside the acceleration volume (aW = 1.5–2.5) for the high-energy particles compared to the thermal low-energy particles (aW = 0.4), i.e. high-energy particles undergo an enhanced systematic gain in energy. (4) The mean-square displacement in energy &amp;lt;W2 &amp;gt; is superdiffusive for the high-energy particles and normal for the low-energy, heated particles.

Comparing a compact hematology analyzer based on direct optical measurements using blue LED with the VCS reference technology for neutrophil differential count

Technologies for the automated blood cell count have been evolving over the last decades. Hematology analyzers enable identifying blood elements, including leukocytes differential. In the bloodstream, the most abundant leukocyte, the neutrophil, presents multi-lobed nuclei, requiring, therefore, combined measurement principles for their detection and classification. Due to the lack of white blood cells’ certified reference materials or reference measurement method, it has been customary to evaluate the performance of new hematology analyzers by comparing them with traditionally available and well-consolidated systems. In 2015, a technology based on axial light loss using a blue LED, the Beckman Coulter DxH500, was launched. This hematology analyzer presents reduced cost, fewer chemical reagents, and a compact design. This work compares the performance of the DxH500 with an analyzer frequently employed in large-scale laboratory routine, the Beckman Coulter LH750, based on the well-established combination of volume (impedance), conductivity and light scatter principles. The study examined 310 paired samples taken out randomly from the routine of a general hospital laboratory. The analyses evaluated the correlation coefficient, p-value, and the linear regression equation. The equivalence of results provided by both analyzers for the characterization of neutrophils in the leukocyte population points to the performance adequacy of the new low-cost and portable technology, suitable for small-sized clinical laboratory’s routines.

Signal processing for biological transients emitted by dolphins and snapping shrimp

In temperate and tropical waters, the dominant source of biological noise in shallow bays, harbors and inlets is snapping shrimp, which can adversely affect the performance of high-frequency sonar systems. The modified method for passive ranging by wavefront curvature enables the source position and source level of individual snaps to be measured in situ. The results are presented for a sequence of 1000 snaps. The principal habitat of the local snapping shrimp population coincides with a narrow wharf, which is 120 m in length. Next, this passive ranging method is used to localize free-ranging dolphins in their natural habitat. The peak-to-peak sound pressure levels of the biosonar pulses (clicks) emitted by Indo-Pacific dolphins (Tursiops aduncus) are measured for source ranges from 30 m to 300 m, even when the dolphins are echolocating at the same time. The waveforms and signal properties of the click signals are presented, along with their effectiveness for probing the shallow-water environment. The bistatic scattering impulse responses of the sea floor, sea surface and scatterers in the water volume are shown. Finally, consideration is given to the contexts in which snaps and clicks are made.

Measuring the Three-Dimensional Volume Scattering Functions of Microsphere Suspension: Design and Laboratory Experiments

The measurement of the volume scattering function (VSF) of suspended particles is an ongoing research topic since it has the potential to provide a rapid, nondestructive means of analyzing hydrosols. Despite the success of scattering theory, the measurement of multidirectional scattering intensity distributions over a wide, continuous range of scattering angles and multiple scattering planes, which is described by a three-dimensional VSF (3D VSF), has proven to be difficult. To measure the 3D VSF of submicron particles suspended in water, a measurement approach is proposed, built and tested with several standard submicron particles with diameters ranging from 60 nm to 1 μm. The experimental results indicate that the proposed setup can obtain an accurate 3D VSF for scattering angles from 21° to 160° and azimuthal angles from 1° to 179°. Comparisons between the experiment and theory show a high level of consistency for particles with diameters less than 200 nm. The variation in the VSF in response to the polarization direction of the incident light is also discussed. Both the experiment and theory show the potential of the device to detect the 3D VSF of marine submicron biological particles.

Comparison of Tomographic SAR Reflectivity Reconstruction Algorithms for Forest Applications at L-band

Forest structure is a key parameter for forest applications, but it is difficult to be estimated at the required spatial and temporal scales. In this context, synthetic aperture radar Tomography (TomoSAR) that allows, at lower frequencies, the 3-D imaging of natural volume scatterers with high spatial and temporal resolution may be a game changer. The aim of this article is to evaluate three TomoSAR algorithms, Fourier beamforming (FB), Capon beamforming (CB), and compressive sensing (CS) with respect to their performance in the reconstruction of the 3-D forest reflectivity. The implications of volumetric forest scattering, as well as the temporal decorrelation of scatterers, are analyzed. The algorithms are compared on a set of simulated scenarios and then evaluated on an experimental L-band data set composed by four acquisition dates, each one consisting of five tomographic tracks. The data were acquired in 2014, within a time span of two months, over the Traunstein forest (Germany) using the F-SAR system. Additionally, discrete airborne Lidar has been used for a qualitative evaluation. The results indicate that the CS reconstruction is, for many practical cases, superior when compared to FB or CB reconstructions as they achieve higher vertical resolution, especially in cases with a lower number of acquisitions and complex forest scenarios. By combining acquisitions performed at different days, the effect of temporal decorrelation on each algorithm for two different tomographic implementations (repeat-pass vs. single-pass) has been assessed. The results indicate that simultaneously acquired image pairs allow a better reconstruction of the 3-D forest reflectivity.

Elimination of imaging artifacts in second harmonic generation microscopy using interferometry.

Conventional second harmonic generation (SHG) microscopy might not clearly reveal the structure of complex samples if the interference between all scatterers in the focal volume results in artefactual patterns. We report here the use of interferometric second harmonic generation (I-SHG) microscopy to efficiently remove these artifacts from SHG images. Interfaces between two regions of opposite polarity are considered because they are known to produce imaging artifacts in muscle for instance. As a model system, such interfaces are first studied in periodically-poled lithium niobate (PPLN), where an artefactual incoherent SH signal is obtained because of irregularities at the interfaces, that overshadow the sought-after coherent contribution. Using I-SHG allows to remove the incoherent part completely without any spatial filtering. Second, I-SHG is also proven to resolve the double-band pattern expected in muscle where standard SHG exhibits in some regions artefactual single-band patterns. In addition to removing the artifacts at the interfaces between antiparallel domains in both structures (PPLN and muscle), I-SHG also increases their visibility by up to a factor of 5. This demonstrates that I-SHG is a powerful technique to image biological samples at enhanced contrast while suppressing artifacts.

Coherence-based SAR tomography for spaceborne applications

Future SAR missions will provide three-dimensional images of semi-transparent media, such as vegetation and ice, through SAR tomography. Access to information on the internal structure of these volume scatterers is a key factor for a better understanding of ecosystem dynamics and climate change. Because of this, several concepts are nowadays examined to implement SAR tomography in a spaceborne framework.In order to do that, it is necessary to gather different observations of the area of interest. Unfortunately, a consequence of the time that elapses between acquisitions is that the electromagnetic properties of the medium may vary. This implies that, there may be inconsistencies in the acquired data, leading to errors in the final inversion. A solution to partially cope with this temporal decorrelation, is to acquire data employing two or more sensors operating with a reduced (or even absent) temporal gap and then to collect several acquisitions at different time instants. By means of this imaging concept, the required line-of-sight diversity is granted and the desired resolution in the height direction ensured. In this way, sets of temporal decorrelation-free interferometric coherences can be built and the vertical scattering profile can be retrieved via coherence-based tomography.This contribution analyzes a two-sensor system like TanDEM-X (Krieger et al., 2007), Tandem-L (Moreira et al., 2015), or SAOCOM-CS (Davidson et al., 2014). In particular, the potential of coherence-based tomography are shown with data acquired with the TanDEM-X sensors for boreal and Amazon forest. In addition, a technique to partially cope with temporal decorrelation through covariance matrix filtering is also presented in the paper.

Phenomenological modelling of light transmission through nanowires arrays

A phenomenological model has been developed and discussed. The model is able to describe the experimentally measured light transmission of nanowires arrays. Two representative samples were studied in this report. A well aligned nanowires sample was first modelled by an effective layer model with surface roughness added. Then a slightly tilted nanowires sample with round top was phenomenologically modelled by a two layers model with a first top layer of an effective medium which includes a volume scattering contribution (Mie theory). Roughness and waviness are added to account for the nanowires small and large scale fluctuation in height. This phenomenological description was proven to be feasible by fitting experimental data. As a conclusion, light transmitted through randomly distributed nanowires can be explained by the combination of volume and surface scatterings using respectively Mie theory and rough Fresnel coefficients at the interfaces.

Progress of measurement technology and application of general-angle Volume Scattering Function of water

Progress of measurement technology and application of general-angle Volume Scattering Function of water

Measurements of the Volume Scattering Function and the Degree of Linear Polarization of Light Scattered by Contrasting Natural Assemblages of Marine Particles

The light scattering properties of seawater play important roles in radiative transfer in the ocean and optically-based methods for characterizing marine suspended particles from in situ and remote sensing measurements. The recently commercialized LISST-VSF instrument is capable of providing in situ or laboratory measurements of the volume scattering function, β p ( ψ ) , and the degree of linear polarization, DoLP p ( ψ ) , associated with particle scattering. These optical quantities of natural particle assemblages have not been measured routinely in past studies. To fully realize the potential of LISST-VSF measurements, we evaluated instrument performance, and developed calibration correction functions from laboratory measurements and Mie scattering calculations for standard polystyrene beads suspended in water. The correction functions were validated with independent measurements. The improved LISST-VSF protocol was applied to measurements of β p ( ψ ) and DoLP p ( ψ ) taken on 17 natural seawater samples from coastal and offshore marine environments characterized by contrasting assemblages of suspended particles. Both β p ( ψ ) and DoLP p ( ψ ) exhibited significant variations related to a broad range of composition and size distribution of particulate assemblages. For example, negative relational trends were observed between the particulate backscattering ratio derived from β p ( ψ ) and increasing proportions of organic particles or phytoplankton in the particulate assemblage. Our results also suggest a potential trend between the maximum values of DoLP p ( ψ ) and particle size metrics, such that a decrease in the maximum DoLP p ( ψ ) tends to be associated with particulate assemblages exhibiting a higher proportion of large-sized particles. Such results have the potential to advance optically-based applications that rely on an understanding of relationships between light scattering and particle properties of natural particulate assemblages.

Impact of Ice Surface and Volume Scatterings on the Microwave Sea Ice Apparent Emissivity

AbstractEmissivity retrieval for sea ice from passive microwave measurements has been an important problem in climate/environmental research because of its link to various snow/ice variables. However, so far, it has been a difficult task because of the influences of surface and snow/ice induced volume scatterings. Here we examine the influences of scatterings on the ice emissivity from 10.65, 18.7, 23.8, and 36.5 GHz Advanced Microwave Scanning Radiometer (AMSR)‐E brightness temperatures over the Arctic Ocean. In doing so, we use a two‐dimensional roughness parameterization, modified with surface facet orientations with an assumption that the facet emission follows the Fresnel relationship. Emitting layer temperature and refractive index retrieved from AMSR‐E 6.9 GHz brightness temperature measurements were used in this study and applied to other channels of interest. We demonstrated that the obtained roughness index has a strong linear relationship with the root‐mean‐square height measured by Atmospheric Terrain Mapper on the National Aeronautics and Space Administration (NASA) P‐3 aircraft. The obtained roughness index showed that surface scattering on the emissivity is generally insignificant except for some first‐year ice regions in particular at higher frequencies. This fact implies that Fresnel relations can be applicable for most of sea ice at the low‐frequency microwave spectrum. By contrast, volume scattering is found to be significant in emissivity retrieval in case of multiyear ice. Nonetheless, volume scattering influence over first‐year ice appears to be minor. We suggest that Fresnel‐type emissivity can be estimated once a correction factor is used for removing surface scattering and volume scattering contributions from the apparent emissivity.

Asymptotic analysis of resonances of small volume high contrast linear and nonlinear scatterers

We consider the asymptotic analysis of the resonances of high contrast small volume scatterers for linear and nonlinear scalar waves. The resonance problem is formulated as a nonlinear eigenvalue problem. We derive asymptotic formulae for linear scatterers and nonlinear scatterers of the Kerr type. Our results are illustrated with numerical examples.

Airborne and shipborne polarimetric measurements over open ocean and coastal waters: Intercomparisons and implications for spaceborne observations

Comprehensive polarimetric closure is demonstrated using observations from two in-situ polarimeters and Vector Radiative Transfer (VRT) modeling. During the Ship-Aircraft Bio-Optical Research (SABOR) campaign, the novel CCNY HyperSAS-POL polarimeter was mounted on the bow of the R/V Endeavor and acquired hyperspectral measurements from just above the surface of the ocean, while the NASA GISS Research Scanning Polarimeter was deployed onboard the NASA LaRC's King Air UC-12B aircraft. State-of-the-art, ancillary measurements were used to characterize the atmospheric and marine contributions in the VRT model, including those of the High Spectral Resolution Lidar (HSRL), the AErosol RObotic NETwork for Ocean Color (AERONET-OC), a profiling WETLabs ac-9 spectrometer and the Multi-spectral Volume Scattering Meter (MVSM). An open-ocean and a coastal scene are analyzed, both affected by complex aerosol conditions. In each of the two cases, it is found that the model is able to accurately reproduce the Stokes components measured simultaneously by each polarimeter at different geometries and viewing altitudes. These results are mostly encouraging, considering the different deployment strategies of RSP and HyperSAS-POL, which imply very different sensitivities to the atmospheric and ocean contributions, and open new opportunities in above-water polarimetric measurements. Furthermore, the signal originating from each scene was propagated to the top of the atmosphere to explore the sensitivity of polarimetric spaceborne observations to changes in the water type. As expected, adding polarization as a measurement capability benefits the detection of such changes, reinforcing the merits of the full-Stokes treatment in modeling the impact of atmospheric and oceanic constituents on remote sensing observations.

Noncritical fluctuations of (net) charges and (net) protons from the iebe-vishnu hybrid model

In this paper, we investigate the non-critical fluctuations of (net) charges and (net) protons in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 39 and 200 GeV, using iEBE-VISHNU hybrid model with Poisson fluctuations added in the particle event generator between hydrodynamics and UrQMD. Various effects, such as volume fluctuations hadronic evolution and scatterings, resonance decays, as well as realistic centrality cuts and acceptance cuts have been embedded in our model calculations. With properly tuned parameters, iEBE-VISHNU roughly describe the centrality dependent moments and cumulants of (net) charges and (net) protons measured in experiment. Further comparison simulations show that the volume fluctuation is the dominant factor to influence the multiplicity fluctuations, which makes the higher moments of (net) charges largely deviate from the Poison baselines. We also find that the effects from hadronic evolutions and resonance decays are pretty small or even negligible for the multiplicity fluctuations of both (net) charges and (net) protons.

Applicability of volume conductivity and scatter parameters for early prediction of dengue virus infection

Introduction: Dengue virus infection is an acute febrile illness endemic in several countries including India. Although the management is empirical, early diagnosis is crucial for timely intervention to reduce the morbidity and mortality. The diagnosis of dengue virus infection mainly depends on serological testing and virus isolation which are costly and time-consuming. A simple blood test like complete blood count (CBC) run on five-part differential cell counter with volume conductivity, and scatter (VCS) data can help in predicting dengue infection without additional cost. Methods: In the present study, we analyzed VCS parameters of 337 febrile patients over the period of 1 year (January 2016 to December 2016). Out of these, 255 cases were positive for dengue serology and 82 were febrile controls. Comparative analysis of utility of previously published dengue factor, lymph index, and monocyte factor along with the “New Dengue Factor” introduced in the present study. Results: The “New Dengue Factor” proposed by us gave highest “positive likelihood ratio” for the diagnosis of dengue virus infection. Dengue factor proposed by Sharma et al. was the most “sensitive,” and “lymph index” proposed by Hawaldar et al. was the most specific followed by the “New dengue factor” introduced in the present study. Conclusion: Factors derived from VCS parameters are useful for early prediction of dengue virus infection without incurring additional cost and thus would contribute to better patient care.