Scattering Attenuation Research Articles

Vegetation Scattering Attenuation Characteristics of Terahertz Wave

A terahertz (THz) wave transmitted through vegetation experiences both absorption and scattering caused by the air molecules and leaves. This paper presents the scattering attenuation characteristics of vegetation in a THz range. The theoretical path loss model near the vegetation yields the average attenuation of THz waves in a mixed channel composed of air and vegetation leaves. Furthermore, a simplified model of the vegetation structure is obtained for generic vegetation types based on a variety of parameters, such as leaf size, distribution, and moisture content. Finally, based on specific vegetation species and different levels of air humidity, the attenuation characteristics under different conditions are calculated, and the influence of different model parameters on the attenuation characteristics is obtained.

Impacts of Aerosol Scattering Attenuation on Free-Space Optical Communication in Owerri, Nigeria

In spite of the several benefits of using free-space optical (FSO) communication systems as complementary platforms for next-generation networks, the existence of atmospheric disturbances such fog and scintillations are key sources of signal impairment that affect system performance. Thus, it is crucial to learn about the specific weather patterns of the areas where FSO lines will be installed. The purpose of this work is to estimate the availability performance of FSO lines broadcasting at both 850 nm and 1550 nm by performing a statistical analysis of meteorological visibility data gathered for Owerri in Nigeria over a 21-year period (2000-2021). The results shows that the visibility during the most common fog events in Owerri is 100 meters. The probabilities of encountering and exceeding the scattering attenuations associated with Owerri’s most common fog event are 0.0002 and 0.0229, respectively. This research could be expanded in the future by exploring the effects of varying localized climatic conditions on the many forms of optical signals, such as plane, spherical, and Gaussian beam waves.

Optical coherence tomography application for assessing variation in bone mineral content: a preclinical study.

Optical Coherence Tomography (OCT) is a non-invasive imaging technique that produces cross-sectional images through biological tissues, allowing three-dimensional reconstruction and analysis. Aim was to evaluate if OCT may discriminate among tissues with different bone density and composition, by measuring the depth of light penetration in porcine and rat bone samples. Two carpal bone samples (2 cm length) were harvested from the porcine forelimb and fixed overnight in 3.7% buffered formal saline. Following fixation, one sample was decalcified in a 1:1 mixture of 8% hydrochloric acid and 8% formic acid solution for three days, with solution changes each day. Samples were imaged using an OCT microscope. Furthermore, the calvaria, ulnar, alveolar and basal bone of the mandible of 6 male and 6 female rats were cleared of overlying soft tissues and scanned under OCT. The light penetration depth in each sample was measured using the software Image J, and Scattering Attenuation Microscopy. In the mineralized bone the average depth (µm) and standard deviation (SD) of light penetration were 790.1±18.05 and 410.4±21.7 for periosteal and endosteal surface, respectively, and 507.3±21.03 for cross-section surfaces, while it was 858.4±32.03 for periosteal surface, 1150±26.9 for endosteal, and 627.3±31.8 for cross-section bone surfaces in demineralized porcine bone. There was a significant difference (p<0.001) in depth of light penetration between normal and de-mineralized bone for all regions evaluated. No systematic significant difference in light penetration depth between-gender was found at any site evaluated, while there were variations between sites (p<0.001). The OCT detected differences in bone mineral and porosity among gender (p<0.0001) CONCLUSIONS: This study suggests that OCT may represent a valuable technique to estimate local variations in bone mineral content.

Scattering attenuation of transient SH-wave by an orthotropic gaussian-shaped sedimentary basin

• Scattering attenuation of transient SH -wave. • Orthotropic Gaussian-shaped sedimentary basin. • Time-domain boundary element method. • Illustrating the responses in time and frequency domains. • Isotropy-factor, wave angle, and geometrical effect of sedimentary basin. The surface motion of an orthotropic Gaussian-shaped sedimentary basin embedded in a linear elastic half-space was successfully obtained under transient SH -wave propagation. In the use of the time-domain boundary element approach, a simple model was developed only by discretizing the interface. To achieve better convergence of the response, an attenuation rule was implemented with the assistance of the reduction exponential function applied in the boundary integral equations. After a brief overview of the method, the heterogonous sub-structured basin model was created and decomposed into two parts to satisfy the modified continuity conditions based on the normal direction at the interface node position. Then, the coupled matrices were temporarily solved at each time-step to obtain the boundary values. The developed computer code was tested by solving a validation example. Finally, to illustrate the valley surface response in the time/frequency-domain, a general sensitivity analysis was performed by considering the parameters of frequency, shape-ratio, isotropy-factor, and wave angle in the form of snapshots, seismograms, and amplification patterns. The results showed that the effect of orthotropic anisotropy was very efficient on the ground response and different seismic patterns on the surface of sedimentary basins were extracted by changes in the quantity of this parameter.

Transport and Localization of Elastic Waves in Two‐Dimensional Fractured Media: Consequences on Scattering Attenuation

AbstractWe present numerical simulations of elastic wave transport in two‐dimensional fractured media. Natural fracture systems, following a power‐law length scaling, are modeled by the discrete fracture network approach for geometrically representing fracture distributions and the displacement discontinuity method for mechanically computing fracture‐wave interactions. The model is validated against analytical solutions for wave reflection, transmission, and scattering by single fractures, and then applied to solve the wavefield evolution in synthetic fracture networks. We find that the dimensionless angular frequency ῶ = ωZ/κ plays a crucial role in governing wave transport, where ω, Z, and κ are the angular frequency, seismic impedance, and fracture stiffness, respectively. When ῶ is smaller than the critical frequency ῶc (≈5), waves are in the extended mode, either propagating (for small ῶ) or diffusing by multiple scattering (for intermediate ῶ); as ῶ exceeds ῶc, waves become trapped, entering either the Anderson localization regime (kl* ≈ 1) in well‐connected fracture systems or the weak localization regime (kl* &gt; 1) in poorly‐connected fracture systems, where k is the incident wavenumber and l* is the mean free path length. Consequently, the inverse quality factor Q−1 scales with ῶ obeying a two‐branch power‐law dependence, showing significant frequency dependence when ῶ &lt; ῶc and almost frequency independence when ῶ &gt; ῶc. Furthermore, when ῶ &lt; ῶc, the wavefield exhibits a weak dependence on fracture network geometry, whereas when ῶ &gt; ῶc, the fracture network connectivity has an important impact on the wavefield such that strong attenuation occurs in well‐connected fracture systems.

Experimental Analysis of Ultrasonic Multiple Scattering Attenuation through the Air with Fine Dust

In this study, we experimentally evaluated the application of multiple scattering theory for measuring ultrasonic attenuation. Based on the independent approximation theory, the method adopted for calculating the attenuation of coherent waves through air with fine dust is discussed. To obtain a scattering wavefield, a unique ultrasonic scattering hardware was developed, and signal processing schemes were suggested. Four cases of standard particle doses (0, 0.004, 0.008, and 0.012 g) were investigated inside a chamber. The results obtained from the experiments demonstrate that the proposed signal processing approach successfully calculates the scattering attenuation, which correlates well with the applied doses of fine dust. In addition, we discuss the irregular shape and composition of fine dust relative to the scattering cross-section.

Mapping Intrinsic and Scattering Attenuation in the Southern Aegean Crust Using S Wave Envelope Inversion and Sensitivity Kernels Derived From Perturbation Theory

AbstractWe applied sensitivity kernels based on perturbation theory to map the crustal intrinsic and scattering attenuation of S wave envelopes in the southern Aegean. The southern Aegean crust is under extension due to the rollback of the Nubian plate, which is subducting beneath the Aegean plate. The waveforms of 104,531 crustal events (&lt;40 km) were used to calculate S wave envelopes in four frequency bands. The S wave envelopes were modeled using the 3‐D isotropic solution of the radiative transfer equation with a factor for energy leakage. A two‐stage grid search with linear least squares was applied to estimate the attenuation parameters from each S wave envelope. Then we calculated the 2‐D scattering and absorption sensitivity kernels for each wave path based on perturbation theory. These kernels and the envelope attenuation parameters were inverted using the Markov chain Monte Carlo algorithm to obtain maps of intrinsic and scattering attenuation (Qi−1 and Qsc−1). High Qi−1 has thermal origin associated with fluids while high Qsc−1 stems from velocity contrasts caused by deformed structure such as faults, folds, or fractures. The Corinth rift, the Santorini‐Amorgos zone, and the Gulf of Gökova show strong extensional deformation, which may produce high Qsc−1. The deformed oceanic material accreted below the continental crust and fractures generated by large thrust earthquakes likely produce high Qsc−1 in Crete. The Corinth rift with its repeated earthquake swarms demonstrates fluid activity, which can explain high Qi−1. Thermal contrasts generated by metamorphic core complexes are a potential source of Qi−1 in Cyclades and Crete.

A Survey on Fractional Derivative Modeling of Power-Law Frequency-Dependent Viscous Dissipative and Scattering Attenuation in Acoustic Wave Propagation

This paper aims at presenting a survey of the fractional derivative acoustic wave equations, which have been developed in recent decades to describe the observed frequency-dependent attenuation and scattering of acoustic wave propagating through complex media. The derivation of these models and their underlying elastoviscous constitutive relationships are reviewed, and the successful applications and numerical simulations are also highlighted. The different fractional derivative acoustic wave equations characterizing viscous dissipation are analyzed and compared with each other, along with the connections and differences between these models. These model equations are mainly classified into two categories: temporal and spatial fractional derivative models. The statistical interpretation for the range of power-law indices is presented with the help of Lévy stable distribution. In addition, the fractional derivative biharmonic wave equations governing scattering attenuation are introduced and can be viewed as a generalization of viscous dissipative attenuation models.

Multiple lapse time window analysis using solely single events in South Korea

Scattering (Qs–1) and intrinsic (Qi–1) attenuation, important parameters for inferring both the materials and the physical condition of the regional lithosphere, are generally separated by the method of multiple lapse time window analysis (MLTWA). Recently, depth variation of crustal Qs–1 and Qi–1 by applying single events to MLTWA was first shown; however, this application inevitably combined several events due to insufficient data caused by a window with limited range. In this study, we demonstrated that a flexible range window can be applied successfully to solely single events in MLTWA. In particular, a more reliable constraint was obtained than in the previous study, with a reduced amount of data. This technique may be particularly useful for seismically stable regions due to the limitation of available combinations of similar depth events.

Stress-Associated Intrinsic and Scattering Attenuation from Laboratory Ultrasonic Measurements on Shales

Seismic attenuation is sensitive to stress-induced subtle changes in the physical state of rocks. In this study, the stress- and frequency-associated attenuation is quantified through ultrasonic measurements on three differently oriented cylindrical shale samples under various axial stresses. As an improvement to the single-scattering model, the elastic Monte Carlo method is employed to investigate multiple-scattering attenuations by incorporating the boundary reflections and wave conversions. Our results show that, as the axial stress increases, the intrinsic attenuation decreases in all directions, while the scattering attenuation decreases slightly in the direction perpendicular to the bedding but increases largely and nonlinearly in other directions. These discrepancies result from different attenuation mechanisms. Both the intrinsic and scattering attenuation are found to be largest in the direction 45° to the bedding, but least in the perpendicular direction. The S-wave attenuation is larger and more sensitive to stress changes than P-wave attenuation due to its shorter wavelength. As expected from sandstone examples, the scattering attenuation in shales is significantly larger and more sensitive to stress changes than the intrinsic attenuation. The frequency dependence of scattering attenuation suggests that the peak frequency with the maximum scattering attenuation is independent of axial stresses, but varies in different directions of an individual rock with different heterogeneity and anisotropy scales. The peak frequency of S-coda is smaller and its peak scattering attenuation is larger than P-coda. In conclusion, the stress and frequency dependence of ultrasonic attenuations in shales differ largely in various directions, indicating significant anisotropy and heterogeneity.

Depth‐Dependent Crustal Scattering Attenuation Revealed Using Single or Few Events in South Korea

Few studies have been conducted on the variance of scattering (![Graphic][1] ) and intrinsic attenuation (![Graphic][2] ) with depth in the crust. Furthermore, these values, routinely estimated using multiple lapse time window analysis (MLTWA), were seriously affected by different earthquake depths. Based on earthquakes recorded by dense seismic networks in South Korea, we used the MLTWA method on single or small clusters of events with similar depths. The depths of 54 earthquakes, relocated using seven velocity models, provide a typical seismogenic layer with the brittle–plastic transition (BPT) depth at 11 km, which correlated well with the seismicity of Korea. The depth was also used for the theoretical model based on the direct‐simulation Monte Carlo method. As the result of MLTWA, events with shallow focal depths exhibit higher ![Graphic][3] correlated with dense scatter, whereas those with deeper focal depths exhibit lower ![Graphic][4] . This depth dependency of the ![Graphic][5] value is indicated by the significant difference between the upper and lower parts of the BPT depth in the seismogenic layer. We also found that ![Graphic][6] values do not show depth dependency, whereas ![Graphic][7] values do. Thus, this study demonstrates for the first time that the crustal depth dependency of total (![Graphic][8] ) attenuation originates from ![Graphic][9] rather than from ![Graphic][10] . The approach using single or few events may be helpful for a regional study of ![Graphic][11] and ![Graphic][12] in seismically inactive regions for which insufficient data exist and may provide insight into the seismogenic layer related to potential seismic hazards. Online Material: Tables of residuals and range of multiple lapse time window analysis (MLTWA) parameters and Q −1 values for studied events. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif [6]: /embed/inline-graphic-6.gif [7]: /embed/inline-graphic-7.gif [8]: /embed/inline-graphic-8.gif [9]: /embed/inline-graphic-9.gif [10]: /embed/inline-graphic-10.gif [11]: /embed/inline-graphic-11.gif [12]: /embed/inline-graphic-12.gif

Separation of Intrinsic and Scattering Attenuation Using Single Event Source in South Korea

Abstract Simultaneous use of numerous events in the multiple lapse time window analysis (MLTWA) method is the most effective way to obtain and values. Such simultaneous use of numerous events normally shows a large observational scatter, which may be caused by different radiation pattern and focal depth of each earthquake, and regional alteration of the local structure. To avoid these scattering factors, the current study attempted to use single event source as the input data in MLTWA for South Korea. The direct simulation Monte Carlo (DSMC) method was used to simulate the observations, which showed realistic results when the number of recorded stations was eight or more. The obtained values of seismic albedo ( B 0 ) were less than 0.5, which were in accordance with the same in the previous results. Three envelopes constructed by combination of three regional values of at 1 Hz produced regional variations, of which the ones at high frequencies of and at low frequencies of were remarkable. This result, showing the local variation indicated an advantage of the study using single source event over the previous studies in South Korea that involved extensively distributed data. Because DSMC was known to be applicable to 3D structure due to its simple algorithm, the current study also tried to correct radiation pattern of the observations by inserting focal mechanism algorithm to the code of the DSMC method. Such insertion, however, generated extremely low values of because the geometrically shrunk receiver could not capture most of the scattered particles. This receiver problem is most likely to be a major obstacle of the 3D study of DSMC. In addition, the significant depth effect of Q −1 was identified for the prior MLTWA studies resulting from different measurement range and focal depth.

Poroelastic finite-difference modeling for ultrasonic waves in digital porous cores

Scattering attenuation in short wavelengths has long been interesting to geophysicists. Ultrasonic coda waves, observed as the tail portion of ultrasonic wavetrains in laboratory ultrasonic measurements, are important for such studies where ultrasonic waves interact with small-scale random heterogeneities on a scale of micrometers, but often ignored as noises because of the contamination of boundary reflections from the side ends of a sample core. Numerical simulations with accurate absorbing boundary can provide insight into the effect of boundary reflections on coda waves in laboratory experiments. The simulation of wave propagation in digital and heterogeneous porous cores really challenges numerical techniques by digital image of poroelastic properties, numerical dispersion at high frequency and strong heterogeneity, and accurate absorbing boundary schemes at grazing incidence. To overcome these difficulties, we present a staggered-grid high-order finite-difference (FD) method of Biot’s poroelastic equations, with an arbitrary even-order (2L) accuracy to simulate ultrasonic wave propagation in digital porous cores with strong heterogeneity. An unsplit convolutional perfectly matched layer (CPML) absorbing boundary, which improves conventional PML methods at grazing incidence with less memory and better computational efficiency, is employed in the simulation to investigate the influence of boundary reflections on ultrasonic coda waves. Numerical experiments with saturated poroelastic media demonstrate that the 2L FD scheme with the CPML for ultrasonic wave propagation significantly improves stability conditions at strong heterogeneity and absorbing performance at grazing incidence. The boundary reflections from the artificial boundary surrounding the digital core decay fast with the increase of CPML thicknesses, almost disappearing at the CPML thickness of 15 grids. Comparisons of the resulting ultrasonic coda Qsc values between the numerical and experimental ultrasonic S waveforms for a cylindrical rock sample demonstrate that the boundary reflection may contribute around one-third of the ultrasonic coda attenuation observed in laboratory experiments.

Monte Carlo Simulation of Stress-Associated Scattering Attenuation from Laboratory Ultrasonic Measurements

Abstract Seismic coda waves scattered by small‐scale heterogeneities contain information on stress changes of the medium, because of changes in the physical state of materials. Based on the ultrasonic measurements under different stresses for a cylindrical sandstone sample, we investigate the influence of stress changes on ultrasonic S ‐coda attenuation and aim to characterize its stress/frequency‐dependent pattern. Considering the complexity of ultrasonic coda waveforms measured from finite‐size rock samples in laboratory experiments, the Monte Carlo simulation is employed to synthesize ultrasonic envelopes, which act by incorporating the effect of multiple scatterings and boundary reflections on coda waves. The optimal simulation parameters, estimated by minimizing the residual between the observed and synthesized envelopes, indicate that the rock sample under study presents moderate heterogeneities. The relationship between attenuation and stress is similar for direct and coda S waves and remains stable in the range of high‐effective stresses around 30–60 MPa, with less stress sensitivity. Enhanced attenuation for both types of waves occurs at lower‐effective stresses, but with coda attenuation much faster and stronger, presenting a quite different nonlinear behavior with respect to stress. Coda attenuation increases drastically at extremely low‐effective stresses below 15 MPa because of the increase in rock compliance, showing much greater sensitivity to high‐pore pressure than intrinsic attenuation. This study improves our understanding of the mechanism of ultrasonic coda attenuation and its scaling dependence on stress and frequency.

Volumetric In Vivo Visualization of Upper Urinary Tract Tumors Using Optical Coherence Tomography: A Pilot Study

Knowledge of tumor stage and grade is paramount for treatment decision making in cases of upper urinary tract urothelial carcinoma but this condition cannot be accurately assessed by current techniques. Optical coherence tomography can hypothetically provide the urologist with real-time intraoperative information on tumor grade and stage. In this pilot study we report what are to our knowledge the first results of optical coherence tomography for grading and staging upper urinary tract urothelial carcinoma. Eight consecutive patients underwent ureterorenoscopy for suspicion or followup of upper urinary tract urothelial carcinoma. Optical coherence tomography data sets were intraoperatively obtained from the ureter and renal pelvis. All patients eventually underwent nephroureterectomy. Optical coherence tomography staging was done by visual inspection of lesions found on optical coherence tomography images. Optical coherence tomography grading was done by quantifying optical coherence tomography signal attenuation in mm(-1) on lesions and comparing results with the histopathological diagnosis. The Wilcoxon rank sum test was used for statistical analysis. For 7 in vivo optical coherence tomography diagnoses staging was in accordance with histology. In patient 8 tumor thickness transcended optical coherence tomography imaging depth range and, therefore, invasiveness findings were inconclusive. For grading the median attenuation coefficient for grade 2 and 3 lesions was 1.97 (IQR 1.57-2.30) and 3.53 mm(-1) (IQR 2.74-3.94), respectively (p<0.001). Healthy urothelium was too thin to reliably determine the attenuation coefficient. Optical coherence tomography is a promising, minimally invasive tool for real-time intraoperative optical diagnosis of tumors in the upper urinary tract. Our results warrant future research in a larger sample size to determine the accuracy of grading and staging by optical coherence tomography, and its possible implementation in the diagnostic algorithm for upper urinary tract urothelial carcinoma.

Time Reversal Optical Tomography

There has been a surge of interest in diffuse optical tomography (DOT) that uses near-infrared light to detect, localize and diagnose maladies such as breast cancer and brain injury. Scattering and light attenuation limit the resolution and accuracy of DOT methods that use small differences in optical properties to distinguish lesions from normal tissue. Researchers need a DOT approach that can, for example, quickly reconstruct images to detect and map tumors at early growth stages and determine if they are malignant or benign.

Erratum to Scattering and Intrinsic Attenuation of Short-Period S Waves in the Gyeongsang Basin, South Korea, Revealed from S-Wave Seismogram Envelopes Based on the Radiative Transfer Theory

Erratum to Scattering and Intrinsic Attenuation of Short-Period S Waves in the Gyeongsang Basin, South Korea, Revealed from S-Wave Seismogram Envelopes Based on the Radiative Transfer Theory

Ambiguity Between the Residual Geometrical Spreading and Scattering Attenuation

By introducing a residual geometrical spreading factor, a new model was proposed in recent papers of Morozov to improve the estimates of seismic Q, and some published seismic Q observations were reinterpreted under the framework of the new model. We found that in these papers the definitions about the residual geometrical spreading and seismic scattering attenuation were conceptually confusing, and physically impossible negative values of seismic Q may arise in the new model. We argue that the estimates of the residual geometrical spreading in the new model are influenced by seismic scattering. Thus, the correlation between the residual geometrical spreading and tectonic activity, and the observation of temporal variations of the residual geometrical spreading and apparent attenuation, as reported by Morozov, are not surprising.

Scattering and Intrinsic Attenuation of Short-Period S Waves in the Gyeongsang Basin, South Korea, Revealed from S-Wave Seismogram Envelopes Based on the Radiative Transfer Theory

Abstract Examining seismic envelopes for local earthquakes that occurred in the Gyeongsang Basin, South Korea, we estimated coda Q values in the crust and measured the total scattering coefficients for frequency bands 1–2, 2–4, 4–8, and 8–16 Hz using the Monte Carlo simulation method based on radiative transfer theory. In the seismic envelope synthesis, we assumed acoustic multiple isotropic scattering and adopted a depth-dependent S -wave velocity model that is slightly modified from a receiver function result in the middle of the study region. The estimated total scattering coefficients range from 3.8×10 -3 to at 1–16 Hz, which agrees well with the average values in the crust. These values are corresponding to less than 0.5 of seismic albedo. This result represents that intrinsic absorption is a dominant contributor to the attenuation process for all frequency bands in the Gyeongsang Basin.

Site Amplification, Scattering, and Intrinsic Attenuation in the Mississippi Embayment from Coda Waves

We estimate site amplification, intrinsic Q ( Q I ) and scattering Q ( Q S ) values from three-component coda of broadband data recorded by Cooperative New Madrid Sesimic Network stations for center frequencies 0.2, 0.5, 1.0, 2.0, and 5.0 Hz. Near 0.5 and 1.0 Hz, site amplification factors for the transverse component recorded by stations in the Mississippi embayment are between 1.7 and 18, compared with stations outside the embayment. The amplification factor becomes smaller at frequencies lower than 0.5 Hz and higher at those greater than 1.0 Hz. The radial component shows a similar amplification; however, the vertical component shows relatively less amplification. Q I and Q S are estimated from coda using an energy flux model for two time windows after the direct S wave and at 0.5 and 1.0 Hz center frequencies. The two time windows include coda up to and after twice the S -wave travel time at each station. Coda parameters change with the time window and are attributed to a mixture of incoherent coda with coherent S-wave reverberations directly after the S wave. Q I and Q S inferred from stations outside of the embayment have higher values than those from stations within the embayment. A plane wave model qualitatively explains the lack of coda amplification at high frequencies compared with a low frequency without recourse to anelastic attenuation arguments. However, the plane wave model cannot explain the very large observed coda amplifications at 1 and 0.5 Hz seen in the data, suggesting that other wave-scattering effects must be occurring in the embayment velocity structure. This is consistent with the relatively low Q S values inferred from the energy flux model for stations within the embayment. In addition to coda amplification, we performed a synoptic noise study that revealed that pre-event ambient background noise behaves in a similar manner to the coda for stations within and outside of the embayment. The presence of large lateral velocity heterogeneities in the embayment may cause Q S values to be low there.