Backscattering Data Research Articles

Comparison of Seafloor Roughness and Scattered Acoustic Temporal Decorrelation

Connecting changes in acoustic scattering from the seafloor with changes in seafloor topography is essential for modeling the time dependence of the scattering and the development of acoustics as a tool for the remote sensing of benthic activity. An equation is derived that links the decorrelation of scattered acoustic power with the decorrelation of seafloor roughness spectral estimates. The result is assessed through a comparison of decorrelation values generated by processing topographical data recorded by a digital photogrammetry system and backscattering data acquired with a translating source/receiver assembly. Both data sets were collected off the western coast of Florida as part of the U.S. Office of Naval Research (ONR)-sponsored sediment acoustics experiment (SAX04), during which the primary mechanism of topographical change at the frequencies of interest appeared to be fish feeding. Although decorrelation curves proved to be both space and time dependent, and the collection of data sets was neither collocated nor synchronized, the agreement between averaged topographical and acoustic decorrelation values was reasonable. Both types exhibited a strong frequency dependence, which should prove beneficial in classifying and quantifying sources of seabed transformation if it is mechanism specific.

An Assessment of QuikSCAT Ku-Band Scatterometer Data for Soil Moisture Sensitivity

The QuikSCAT enhanced (2.225-km) backscattering product is investigated for sensitivity to changes in soil moisture and its potential for spatial disaggregation of Advanced Microwave Scanning Radiometer (AMSR-E) soil moisture. Specifically, an active-passive methodology based on temporal change detection is tested using data from the 2006 National Airborne Field Experiment data set. This campaign was carried out from October 29 to November 20, 2006 in a 60 km times 40 km area of the Murrumbidgee catchment, southeast Australia. Temporal change detection analysis and accuracy in terms of spatial pattern distribution throughout the domain were assessed using a passive microwave airborne product derived from the Polarimetric L-band Multibeam Radiometer at 1-km spatial resolution. QuikSCAT-AMSR-E intercomparisons indicated higher correlations when using C-band observations. The greatest sensitivity to soil moisture was observed when using V-polarized backscatter measurement. While backscattering data showed adequate temporal sensitivity to changes in soil moisture due to precipitation events, the spatial agreement was complicated by the presence of irrigation and standing water (rice fields). This resulted in low Cramer's Phi values (less than 0.06), which were used as a measure of spatial correspondence in terms of change in soil moisture and backscatter. In addition, the high QuikSCAT sensor frequency and existence of noise in the observed data contributed to the observed discrepancies.

Reconstruction of singularities from full scattering data by new estimates of bilinear Fourier multipliers

We prove that the singularities of a complex valued potential q in the Schrodinger hamiltonian Δ+q can be reconstructed from the linear Born approximation for full scattering data by averaging in the extra variables. We prove that, with this procedure, the accuracy in the reconstruction improves the previously known accuracy obtained from fixed angle or backscattering data. In particular, for \({q \in W^{\alpha,2}}\) for α ≥ 0, in 2D we recover the main singularity of q with an accuracy of one derivative; in 3D the accuracy is \({\epsilon > 1/2}\), increasing with α. This gives a mathematical basis for diffraction tomography. The proof is based on some new estimates for multidimensional bilinear Fourier multipliers of independent interest.

Permittivity range profile reconstruction of multilayered structures from microwave backscattering data by using particle swarm optimization

AbstractA method for the investigation of multilayered structures by using microwave probes is proposed. An iterative optimization procedure reconstructs the permittivity range profiles of such structures from backscattering data by optimizing a functional consisting of a term depending on the data and a regularization term. A linear process is also accounted for the global smoothness enforced by classical regularization. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2390–2394, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24642

Ultrasonic device for real-time sewage velocity and suspended particles concentration measurements

In the frame of a technological research and innovation network in water and environment technologies (RITEAU, Réseau de Recherche et d'Innovation Technologique Eau et Environnement), our research group, in collaboration with industrial partners and other research institutions, has been in charge of the development of a suitable flowmeter: an ultrasonic device measuring simultaneously the water flow and the concentration of size classes of suspended particles. Working on the pulsed ultrasound principle, our multi-frequency device (1 to 14 MHz) allows flow velocity and water height measurement and estimation of suspended solids concentration. Velocity measurements rely on the coherent Doppler principle. A self developed frequency estimator, so called Spectral Identification method, was used and compared to the classical Pulse-Pair method. Several measurements campaigns on one wastewater collector of the French city of Strasbourg gave very satisfactory results and showed smaller standard deviation values for the Doppler frequency extracted by the Spectral Identification method. A specific algorithm was also developed for the water height measurements. It relies on the water surface acoustic impedance rupture and its peak localisation and behaviour in the collected backscattering data. This algorithm was positively tested on long time measurements on the same wastewater collector. A large part of the article is devoted to the measurements of the suspended solids concentrations. Our data analysis consists in the adaptation of the well described acoustic behaviour of sand to the behaviour of wastewater particles. Both acoustic attenuation and acoustic backscattering data over multiple frequencies are analyzed for the extrapolation of size classes and respective concentrations. Under dry weather conditions, the massic backscattering coefficient and the overall size distribution showed similar evolution whatever the measurement site was and were suggesting a global wastewater particles behaviour. By comparison to sampling data, our data analysis lead to the characterization of two particle groups: the ones occurring during rain events and the ones typical of wastewater under dry weather conditions. Even with already encouraging results on the several weeks of data recorded on several wastewater collectors, the validation of our data inversion method is still under progress.

Inverse scattering with non-overdetermined data

Let A ( β , α , k ) be the scattering amplitude corresponding to a real-valued potential which vanishes outside of a bounded domain D ⊂ R 3 . The unit vector α is the direction of the incident plane wave, the unit vector β is the direction of the scattered wave, k > 0 is the wave number. The governing equation for the waves is [ ∇ 2 + k 2 − q ( x ) ] u = 0 in R 3 . For a suitable class M of potentials it is proved that if A q 1 ( − β , β , k ) = A q 2 ( − β , β , k ) , ∀ β ∈ S 2 , ∀ k ∈ ( k 0 , k 1 ) , and q 1 , q 2 ∈ M , then q 1 = q 2 . This is a uniqueness theorem for the solution to the inverse scattering problem with backscattering data. It is also proved for this class of potentials that if A q 1 ( β , α 0 , k ) = A q 2 ( β , α 0 , k ) , ∀ β ∈ S 1 2 , ∀ k ∈ ( k 0 , k 1 ) , and q 1 , q 2 ∈ M , then q 1 = q 2 . Here S 1 2 is an arbitrarily small open subset of S 2 , and | k 0 − k 1 | > 0 is arbitrarily small.

Comparison of Aerosol Optical Depth (AOD) Derived from Ground-Based LIDAR and MODIS

The performance and application of AOD products from the Moderate Resolution Imaging Spectroradiometer (MODIS) are studied by comparing with the AOD derived from the ground-based Doppler LIDAR inside the Hong Kong International Airport (HKIA). The backscattered power data of the LIDAR are used to determine the extinction coefficient profile, from which the AOD is calculated. The AOD determined from the LIDAR is found to have good quality by comparing with the AOD measurements from a hand-held sun photometer at HKIA over a period of three months, and as such it is used to study the quality of AOD estimated from MODIS. The 1-km resolution AOD product from MODIS is found to have better correlation with the LIDAR AOD in comparison to the 10-km resolution product. Moreover, since AOD is a column-integrated quantity, its application to the monitoring of the surface visibility changes should be made with caution during the presence of elevated layers of higher aerosol concentrations. Examples of the effects of such elevated aerosol layers are studied.

Detection of Karenia brevis blooms on the west Florida shelf using in situ backscattering and fluorescence data

Using shipboard data collected from the central west Florida shelf (WFS) between 2000 and 2001, an optical classification algorithm was developed to differentiate toxic Karenia brevis blooms (>10 4 cells l −1) from other waters (including non-blooms and blooms of other phytoplankton species). The identification of K. brevis blooms is based on two criteria: (1) chlorophyll a concentration ≥1.5 mg m −3 and (2) chlorophyll-specific particulate backscattering at 550 nm ≤ 0.0045 m 2 mg −1. The classification criteria yielded an overall accuracy of 99% in identifying both K. brevis blooms and other waters from 194 cruise stations. The algorithm was validated using an independent dataset collected from both the central and south WFS between 2005 and 2006. After excluding data from estuarine and post-hurricane turbid waters, an overall accuracy of 94% was achieved with 86% of all K. brevis bloom data points identified successfully. Satisfactory algorithm performance (88% overall accuracy) was also achieved when using underway chlorophyll fluorescence and backscattering data collected during a repeated alongshore transect between Tampa Bay and Florida Bay in 2005 and 2006. These results suggest that it may be possible to use presently available, commercial optical backscattering instrumentation on autonomous platforms (e.g. moorings, gliders, and AUVs) for rapid and timely detection and monitoring of K. brevis blooms on the WFS.

Local Smoothing for the Backscattering Transform

An analysis of the backscattering data for the Schrödinger operator in odd dimensions n ≥ 3 motivates the introduction of the backscattering transform . This is an entire analytic mapping and we write where B N v is the Nth order term in the power series expansion at v = 0. In this paper we study estimates for B N v in H (s) spaces, and prove that Bv is entire analytic in v ∈ H (s) ∩ ℰ′ when s ≥ (n − 3)/2.

Roles of fucoidan, an anionic sulfated polysaccharide on BSA-stabilized oil-in-water emulsion

Fucoidan, a sulfated polysaccharide derived from brown seaweed, is an important material valued for its various biological functions, including anti-coagulation, anti-aging, and immune system support. In this study, we examined the potential of fucoidan as a novel emulsifying agent in BSA (bovine serum albumin)-stabilized emulsion at a neutral pH. We measured the dispersed oil-droplet size, surface zeta-potential and creaming formation of 0.5 wt% BSA emulsion (20 wt% oil fraction) in the absence and presence of fucoidan. The average particle size and zeta-potential value were 625.4 nm and -30.91 mV in only BSA-stabilized emulsion and 745.2 nm and -44.2 mV in 1.0 wt% fucoidan-added BSA emulsion, respectively. This result suggested that some positive charges of the BSA molecules interacted with the negative charges of fucoidan to inhibit the flocculation among the oil droplets. The creaming rate calculated from the backscattering data measured by Turbiscan dramatically decreased in 1.0 wt% fucoidan-added BSA emulsion during storage. Accordingly, the repulsion forces induced among the oil particles coated with 1.0 wt% fucoidan in emulsion solution resulted in significantly increased emulsion stability. The turbid- ity of the BSA-stabilized emulsion at 500 nm decreased during five days of storage. However, the fucoidan-added BSA emulsion exhibited a higher value of turbidity than the BSA-stabilized emulsion did. In conclusion, an anionic sulfated fucoidan lowered the surface zeta-potential of BSA-coated oil droplets via the electrostatic interaction, and subsequently inhibited the flocculation among the oil droplets, thereby clearly minimizing the creaming and phase separation of the emulsion.

Use of the distorted wave Born approximation to predict scattering by inhomogeneous objects: Application to squid

A new method has been developed to predict acoustic scattering by weakly scattering objects with three-dimensional variability in sound speed and density. This variability can take the form of inhomogeneities within the body of the scatterer and/or geometries where the acoustic wave passes through part of the scattering body, into the surrounding medium, and back into the body. This method applies the distorted wave Born approximation (DWBA) using a numerical approach that rigorously accounts for the phase changes within a scattering volume. Ranges of validity with respect to material properties and numerical considerations are first explored through comparisons with modal-series-based predictions of scattering by fluid-filled spherical and cylindrical fluid shells. The method is then applied to squid and incorporates high resolution spiral computerized tomography (SCT) scans of the complex morphology of the organism. Target strength predictions based on the SCT scans are compared with published backscattering data from live, freely swimming and tethered squid. The new method shows significant improvement for both single-orientation and orientation-averaged scattering predictions over the DWBA-homogeneous-prolate-spheroid model.

Stability of high internal phase emulsions with sole cationic surfactant and its tailoring morphology of porous polymers based on the emulsions

Stable w/o high internal phase emulsion (HIPE) using cetyltrimethylammonium bromide (CTAB) as the sole surfactant was prepared with long time further mixing of the emulsion after the addition of aqueous phase was completed, although it was generally considered the emulsion would be unstable according to Bancroft rule. The delta backscattering data of these emulsions showed that the further mixing enhanced the stability of the HIPE significantly, because a dram partial of monomers was initiated in the period of preparing the emulsion, which reduced the diffusion of CTAB from the oil phase to aqueous phase and increased the viscosity of the continuous phase. In addition, the morphology of polyHIPEs based on this type HIPEs was tailored. Increasing aqueous phase fraction resulted in the increase of pore volume which could be up to 24.0ml/g. Increasing the polymerization temperature led to an increase in average void and interconnect diameter in the resulting porous materials. Additionally, the presence of additives, PEG and ethanol, in the aqueous phase was found to increase the average void diameter remarkably. The interconnect diameter of the materials could be controlled at constant pore volume by tuning PEG and ethanol concentration in the aqueous phase. It was suggested that coalescence was the dominant effect in determining the morphology of the polyHIPEs prepared in the presence of PEG, and Ostwald ripening was the major role in tailoring the morphology of the porous materials with ethanol.

Ion beam induced mixing of co-sputtered Au–Ni films analyzed by Rutherford backscattering spectrometry

Co-sputtered Au–Ni thin films having thickness of 30 nm were deposited on Si(1 0 0) substrates and irradiated with 160 keV Ar 40 + under ambient condition at a number of fluences and analyzed using Rutherford backscattering spectrometry (RBS). The variation of Au signal counts in the RBS spectra with ion fluence has been investigated. The distribution of Au, Ni and Si atoms over various depths within the as deposited and irradiated samples have been computed using the backscattering data by means of a direct analytical method. Au and Si profiles have been fitted with error function and the relative changes in variance for various ion fluences compared to that of as deposited profiles have been studied. The spreading rates of different constituents across the interface due to Ar ion impact have also been discussed.

Simulated and measured X‐band radar reflectivity of land in mountainous terrain using a fan‐beam antenna

A computer program for meteorological radar siting, previously developed for pencil‐beam antenna, long‐range, C‐band radars, has been adapted for fan‐beam antenna, short‐range, X‐band radars. The simulator uses topographic information in the form of a raster digital elevation model and a surface backscattering cross‐section per unit area at grazing angles derived from the literature. It is independent of specific radar sites and radar systems. Its use will enhance optimized scanning strategies, antenna design tailored to mountainous terrain and knowledge of land‐clutter measurements at low grazing angles. The raster‐based approach used in implementing the program makes it compatible with any desired spatial resolution. Simplicity and short simulation times have been pursued as primary goals during the planning and implementation phases of the routines. A preliminary validation of the simulator using backscattering data acquired in the Alps is presented in this letter.

Atmospheric aerosols measurements and the reliability problem

The role and place of the problem on global ecological security in a general problem on global security and risk have been analysed within the experiments programmes initiated by academician K. Ya. Kondratyev. The data obtained within these programmes have necessitated particularly more detailed investigations of atmospheric aerosols characteristics. This paper discusses the problem of the reliability with which the characteristics of atmospheric aerosols are determined from the results of lidar, photoelectric, and filter measurements including mono‐ and multiposition measurements of backscattering signals, measurements of weak backscattering signals and data comparisons. Rigorous differential and approximate solutions of the lidar equation are analysed. The results of determining the transparency of atmospheric air contaminated with industrial discharges, and automotive exhausts are presented. Substantial variations are found in the relationship between the backscattering coefficient and the extinction coefficient in an inhomogeneous atmosphere. It is concluded that the efficiency of lidar methods for probing the atmosphere based on a rigorous solution of the problem is determined by the definiteness of the region in which they are applicable. The accuracy of lidar measurements can be improved using the dependence of the results on the measurement range. The comparison shows that the asymmetric data‐processing scheme is much more effective then the symmetric scheme.

레이다 표적 인식에서 3D MEMP 기법을 이용한 표적의 3차원 산란점 예측

본 논문은 레이다 표적 인식에서 레이다 산란신호에 대한 3차원 산란점 추출을 위한 고해상도 기법에 대해 기술하고 있다. 또한, 3차원 산란점 추출에서 신호의 극점을 획득하기 위해 3차원 짝 맞춤 절차를 소개하고 있다. 짝 맞춤 절차는 기존의 일반적인 방법보다 더 정확하고 견고한 특징을 가지고 있다. 3차원 산란점을 추출하기 위해서는 우선 주어진 3차원 레이다 산란 데이터로부터 상호 분산 행렬을 생성해야 한다. 그리고 matrix pencil 기법을 이용하여 3차원 산란점을 추출한다. 본 논문에서 MSSP를 이용하여 상호 분산 행렬을 생성하였으며, 관측 행렬은 sparse scanning order conception 방법을 이용하여 만들었다. 제시한 기법의 성능을 보여주기 위해서 본 논문에서는 이상적인 점 산란체를 생성하여 이에 대한 결과를 보여주고 있다. This paper presents high resolution techniques of three-dimensional(3D) scattering center extraction for a radar backscattered signal in radar target recognition. We propose a 3D pairing procedure, a new approach to estimate 3D scattering centers. This pairing procedure is more accurate and robust than the general criterion. 3D MEMP(Matrix Enhancement and Matrix Pencil) with the 3D pairing procedure first creates an autocorrelation matrix from radar backscattered field data samples. A matrix pencil method is then used to extract 3D scattering centers from the principal eigenvectors of the autocorrelation matrix. An autocorrelation matrix is constructed by the MSSP(modified spatial smoothing preprocessing) method. The observation matrix required for estimation of 3D scattering center locations is built using the sparse scanning order conception. In order to demonstrate the performance of the proposed technique, we use backscattered field data generated by ideal point scatterers.

GaN doped with neodymium by plasma-assisted molecular beam epitaxy

We report in situ doping of GaN with the rare earth element Nd by plasma-assisted molecular beam epitaxy. For the highest Nd effusion cell temperatures, Rutherford backscattering and secondary ion mass spectroscopy data indicate ∼5at.% Nd in epilayers grown on c-plane sapphire. X-ray diffraction found no evidence of phase segregation under nitrogen-rich conditions with up to ∼1at.% Nd, with the highest luminescence intensities corresponding to doping of ∼0.5at.%. Spectral correlation of the Nd emission multiplets for above (325nm) and below (836nm) GaN bandgap excitations implies enhanced substitutional doping at the Ga site.

Analysis of radar sea return for breaking wave investigation

Low‐grazing angle backscattering data collected by a coherent dual‐polarized radar installed on a fixed tower in the ocean are analyzed to investigate the properties of sea spikes attributable to wave breaking. The distribution of breaking wave speed is narrow‐banded with an average speed between 2.0 and 2.6 m/s in mixed seas with wind speeds between 7 and 14.5 m/s. The corresponding breaking wavelength is between 2.5 and 4.3 m. The length or velocity scale of wave breaking is not proportional to the length or velocity scale of the dominant wave. This observation reflects the localized nature of the breaking process and may have significant implications on quantifying various breaking properties such as the energy dissipation or area of turnover by breaking waves. The fraction of sea spike coverage generally increases with wind speed but the trend of increase is modified by the intensity and relative direction of background swell. Parameterizations of sea spike coverage needs to take into consideration both wind and wave factors. Similarities and differences between sea spikes and whitecaps are discussed. In particular, while both quantities show a similar power law dependence on wind speed, the fraction of sea spike coverage is considerably higher than that of whitecap coverage. This result reflects the prevalence of steep features that produce quasi‐specular facets and short‐scale waves bounded to intermediate waves during breaking. These quasi‐specular facets and bound waves contribute significantly to enhancing the radar sea return but may not entrain air to produce whitecap signature.

Quantitative Evaluation of Elastic Properties of Nano-Crystalline Nickel Using Atomic Force Acoustic Microscopy

Atomic force acoustic microscopy (AFAM) is a near-field technique, where the vibration behavior of a micro-fabricated elastic cantilever beam in contact with a sample surface is sensitive to its local elastic properties. The resolution of this technique is given by the contact radius a c of the atomic force microscope sensor-tip on the sample surface. Taking into account only the Hertzian forces, a c depends on the static load applied by the cantilever, on the elastic constants of the tip and the sample and on the geometry of the contacting bodies. The shape of the sensor tip used in atomic force acoustic microscopy is between a sphere and a flat punch. Hence a c extends from just below 10nm to a few tens of nanometers. In this review, we give an overview of the AFAM technique, present data on the indentation moduli of nanocrystalline nickel, and discuss some of the error sources in quantitative AFAM. The AFAM indentation moduli measured are comparable to the values obtained by nanoindentation and lower than the indentation moduli calculated from ultrasonic velocity measurements. There seems to be a decrease of the indentation modulus with decreasing grain size for grain sizes below 30nm. The data are discussed taking into account X-ray diffraction and electron back-scattering data revealing some texture and macro-strain due to internal stresses in the samples investigated.

Incoherent quasielastic neutron scattering study of molecular dynamics of 4-n-octyl-4′-cyanobiphenyl

We report incoherent quasielastic neutron scattering experiments on the thermotropic liquid crystal 4-n-octyl-4'-cyanobiphenyl. The combination of time-of-flight and backscattering data allows analysis of the intermediate scattering function over about three decades of relaxation times. Translational diffusion and uniaxial molecular rotations are clearly identified as the major relaxation processes in, respectively, the nanosecond and picosecond time scales.