Multiple Bounce Research Articles

Building 3D reconstruction of TomoSAR using multiple bounce scattering model

Tomographic synthetic aperture radar (TomoSAR) plays a critical role in the 3D reconstruction of complex urban targets with the capability of 3D imaging. Nevertheless, multipath scattering interference is common in 3D point clouds, seriously affecting the structure of the 3D model. In this letter, the multipath scattering phenomenon of buildings is analysed and the building 3D reconstruction of TomoSAR using multiple bounce scattering model is proposed. The superiority of the proposed method is demonstrated for experiments on array TomoSAR data. It is found that the proposed method not only achieves interference suppression but also improves integrity and accuracy taking advantage of multiple scattering information.

Efficient GPU implementation of the time-domain shooting and bouncing rays method on electrically large complex target

In order to rapidly obtain the scattered echo from large complex target, we have developed a high-frequency simulation tool through the combination of time-domain shooting and bouncing rays (TDSBR) method and time-domain physical optics (TDPO). For ray tracing is time consuming, compute unified device architecture (CUDA) and OptiX from Nvidia are used to reduce computational time. The closed-form expression of TDPO integral is adopted to predict the far field of the illuminated area. A new TDPO integral expression is derived based on the original expression for ray tube integral area in multiple bounce scattering. The simulation results are compared with full-wave method to demonstrate the accuracy of our method. Finally, this improved TDSBR-TDPO method is used to simulate the scattering echo from complex realistic targets and the results are also discussed. The simulation time and hardware configuration are given to show the efficiency of our work.

Spectral Element Modeling of Acoustic to Seismic Coupling Over Topography

AbstractAcoustic waves in the atmosphere are commonly recorded on seismometers as they couple into the ground. These signals, here called ground coupled airwaves, are not commonly considered in numerical modeling of infrasound propagation, which often assumes a rigid unmeshed boundary. Starting from an analytically‐tractable spherical wave model, we analyze how the coupling of an acoustic wave into a planar elastic halfspace changes over a wide range of scenarios. We use energy admittance to quantify acoustic to seismic coupling over both a planar elastic halfspace and meshed topography. Our spectral element and analytic calculations have different maxima as a function of incidence angle, with very high admittance values for near‐vertical incidence (maximum ≈78%). Energy admittance calculations at shallow incidence angles are much smaller (less than 1%). In simulations over the complex topography of Sakurajima Volcano, we attribute the variable spatial pattern of energy admittance to changes in earth parameters between each model. The observed pressure difference over the simulated 15 km region appears to be . While this value is relatively small, the cumulative addition over 100s of km and multiple acoustic bounce points may be significant. Acoustic to seismic coupling along the propagation path may bias long distance yield estimates, particularly when infrasound propagates over regions with steep topography or particularly slow seismic velocities, such as alluvial planes.

Monitoring river water level using multiple bounces of bridges in SAR images

Monitoring river water level is of great importance to understand hydrological and hydraulic processes and evaluate flood and landslide risk. This paper proposes a method for estimating river water levels under bridges using multi-temporal high-resolution synthetic aperture radar (SAR) intensity images. Due to the side-looking characteristics of SAR data acquisitions, bridges crossing over rivers usually exhibit multiple bounce echoes in SAR images caused by the multipath scattering. The range difference of the multiple returns is proportional to the clearance between the water surface and the bridge. In this study, the water level oscillation of Yangtze River under Badong Yangzte River Bridge (China) was calculated by estimating the range pixel distances of the multiple bounces in ALOS-2 PALSAR-2 images using cross correlation algorithm. Besides, a linear correlation between the range pixel distance of the multiple bounces and in situ water level measurements was found, with a coefficient of determination equal to 0.9985. This relationship allowed estimating the river water level in each SAR acquisition, with an average error equal to −0.39 m and root mean square error of 0.51 m, and the elevation of the bridge, with an error of about 0.5 m, which is smaller than the theoretical uncertainty of the method (1.24 m). The obtained results show the efficiency of the method in estimating river water levels.

Finite gyroradius multidimensional electron hole equilibria

Finite electron gyroradius influences on the trapping and charge density distribution of electron holes of limited transverse extent are calculated analytically and explored by numerical orbit integration in low to moderate magnetic fields. Parallel trapping is shown to depend upon the gyroaveraged potential energy and to give rise to gyroaveraged charge deficit. Both types of average are expressible as convolutions with perpendicular Gaussians of width equal to the thermal gyroradius. Orbit-following confirms these phenomena but also confirms for the first time in self-consistent potential profiles the importance of gyrobounce resonance detrapping and consequent velocity diffusion on stochastic orbits. The averaging strongly reduces the trapped electron deficit that can be sustained by any potential profile whose transverse width is comparable to the gyroradius rg. It effectively prevents equilibrium widths smaller than ∼rg for times longer than a quarter parallel-bounce-period. Avoiding gyrobounce resonance detrapping is even more restrictive, except for very small potential amplitudes, but it takes multiple bounce periods to act. Quantitative criteria are given for both types of orbit loss.

109 Social Emergency Medicine: Pakistan Perspective

WHO defines Social Determinants of Health (SDH) as “conditions in which people are born, grow, live, work and age, shaped by the distribution of money, power and resources at global, national and local levels.” The term “Social Emergency Medicine (SEM)” caters to the concept that emergency departments (EDs) provide resource intensive, critical care to high risk patients but also address social health determinants. In USA, ACEP has an established SEM section .with Social Medicine and Population Health Interest Group at SAEM. Fellowships in SEM also focus on incorporation of the patient’s social context into Emergency management. The Indus Hospital (TIH) is a 212 bed, tertiary care center, providing quality treatment, free of cost in Pakistan where social determinants of health result in multiple ED visits, bounce back and loss of income for both the patient and care giver. TIH is in the unique position to address SDH and affect masse, resulting in improved patient outcome. The specialty of emergency medicine (EM) in Pakistan is in its early years and lack of well established primary care has traditionally placed a huge burden on EDs. Preventive role of ED is not taught at undergraduate or postgraduate level. Bedside application of social determinants of health and using it to reach out into the community with well formulated plans will reduce the burden of disease and cost of managing it. The introduction of SEM at national level will develop emergency physicians cognizant of social determinants of health and better trained to address them. a) Collection of data on social determinants of health through ED centered studies with interventions to show improvement in SDH over one year. This data shall be shared with other hospitals in Pakistan running EM programs and presented to local and international donors to secure grants. b) US based fellowship programs in SEM will be approached for collaborative partnerships with the ED at TIH. With our history of collaborative programs, rotating international EM faculty can be engaged to provide training to our residents. c) The College of Physicians and Surgeons (CPSP), the national residency accrediting body has a well-defined EM curriculum. We have designed a three-month module based on SEM which will be used to teach and train our residents as a pilot. It will be presented to CPSP as a proposal to incorporate into the EM curriculum. This will ensure that all Emergency physicians being trained across Pakistan receive a formal education in SEM. d) Similar ED based programs that have met with success can be used as reference and models to develop our own programs. Examples of Chicago based “Better Health through Housing” and “Project HEAL (HIV & HCV Screening, Education, Awareness, Linkage to Care) can be used to develop local programs focused on our social determinants of health. The concept of SEM is the need of the day in LMIC like Pakistan where recognizing and preventing progression of disease and the factors that influence it can be cost-effective. Resources in health care, especially in the public sector are scarce and their wise utilization has to be practiced. By focusing on the vulnerable population presenting to EDs, it is hoped that social determinants of heath can be improved and this can result in shifting the paradigm from cure to prevention

Standard model vacuum decay in a de Sitter background

We present a calculation of thick-wall Coleman-de-Luccia (CdL) bounces in the Standard Model effective potential in a de Sitter background. The calculation is performed including the effect of the bounce back-reaction on the metric, which we compare with the case of a fixed de-Sitter background, and with similar full-backreaction calculation in a model polynomial potential. The results show that the Standard Model potential exhibits non-trivial behavior: rather than a single CdL solution, there are multiple (non-oscillating) bounce solutions which may contribute to the decay rate. All the extra solutions found have higher actions than the largest amplitude solution, and thus would not contribute significantly to the decay rate, but their existence demonstrates that CdL solutions in the Standard Model potential are not unique, and the existence of additional, lower action, solutions cannot be ruled out. This suggests that a better understanding of the appearance and disappearance of CdL solutions in de Sitter space is needed to fully understand the vacuum instability issue in the Standard Model.

Anisotropic multiple bounce models

We analyze the Galileon ghost condensate implementation of a bouncing cosmological model in the presence of a non negligible anisotropic stress. We exhibit its structure, which we find to be far richer than previously thought. In particular, even restricting attention to a single set of underlying microscopic parameters, we obtain, numerically, many qualitatively different regimes: depending on the initial conditions on the scalar field leading the dynamics of the universe, the contraction phase can evolve directly towards a singularity, avoid it by bouncing once, or even bounce many times before settling into an ever-expanding phase. We clarify the behavior of the anisotropies in these various situations.

Extraction of Weak Scatterer Features Based on Multipath Exploitation in Radar Imagery

We proposed an improved solution to two problems. The first problem is caused by the sidelobe of the dominant scatterer masking a weak scatterer. The proposed solution is to suppress the dominant scatterer by modeling its electromagnetic effects as a secondary source or “extra dependent transmitter” in the measurement domain. The suppression of the domain scatterer reveals the presence of the weak scatterer based on exploitation of multipath effects. The second problem is linearizing the mathematical forward model in the measurement domain. Improving the quantity of the prediction, including multipath scattering effects (neglected under the Born approximation), allows us to solve the inverse problem. The multiple bounce (multipath) scattering effect is the interaction of more than one target in the scene. Modeling reflections from one target towards another as a transmitting dipole will add the multiple scattering effects to the scattering field and permit us to solve a linear inverse problem without sophisticated solutions of a nonlinear matrix in the forward model. Simulation results are presented to validate the concept.

A generative physical model approach for enhancing the stroke palette for robotic drummers

Achieving human-like musical expressivity in musical robots has been a long standing goal for roboticists and musicians who work in the emerging field of robotic musicianship. In robotic drumming, a major subfield of robotic musicianship, research toward achieving this goal has focused on the development of musical analysis and improvisational algorithms, design of robots that respond in a contextually appropriate way to music and methods to utilize gestures in collaborative music making. This research addresses the “what” in robotic drumming, that is, what are the notes, dynamics, inter-onset times and the rhythmic parameters that a robot should play in response to the musical analysis. Much less research has gone into “how” each of these notes are played and how to enrich the acoustical and timbral expressions of robotic drummers.The main technical contribution of this work is a generative model for stroke generation in robotic drummers based on the physics of the interaction between human hand and a drumstick. A wide palette of strokes such as multiple bounce, double and triple strokes can be generated using the same model by varying one single parameter, the time-varying torque applied by the thumb on the stick. We have also developed a number of post-processing tools have been developed to further modify the strokes produced by the physical model in an effort to simulate and capture the acoustic variety and richness of natural human drumming. We present results from a pilot study in which 22 subjects participated in a listening test in which they listened to 10 pairs of audio files, each consisting of a human and a robotic drummer playing multiple bounce strokes. Inferential confidence interval approach was used to determine the maximum probable difference between the data obtained from the listening test and a simulated experiment in which the robotic drummer was perceptually indistinguishable from a human drummer. The results indicate that this generative physics model marks an important step toward achieving human-like musical expressivity in robotic drummers.

Statistical Modeling of Ultrawideband MIMO Propagation Channel in a Warehouse Environment

This paper describes an extensive propagation channel measurement campaign in a warehouse environment for line-of-sight (LOS) and nonline-of-sight (NLOS) scenarios. The measurement setup employs a vector network analyzer operating in the 2–8-GHz frequency band combined with an $8 \times 8$ virtual multiple-input multiple-output (MIMO) antenna array. We develop a comprehensive statistical propagation channel model based on high-resolution extraction of multipath components and subsequent spatiotemporal clustering analysis. The intracluster direction of departure (DoD), direction of arrival (DoA), and the time of arrival (ToA) are independent, both for the LOS and NLOS scenarios. The intracluster DoD and DoA can be approximated by the Laplace distribution, and the intracluster ToA can be approximated by an exponential mixture distribution. The intercluster analysis, however, shows a dependency between the cluster DoD, DoA, and ToA. To capture this dependency, we separately model the clusters caused by single and multiple bounce scattering along the aisles in the warehouse. The intercluster DoD distribution follows a Laplace distribution, while the cluster DoA conditioned on the DoD is approximated by a Gaussian mixture distribution. The model was validated using the capacity and delay-spread values.

ANALYSIS OF MULTIPATH PIXELS IN SAR IMAGES

As the received radar signal is the sum of signal contributions overlaid in one single pixel regardless of the travel path, the multipath effect should be seriously tackled as the multiple bounce returns are added to direct scatter echoes which leads to ghost scatters. Most of the existing solution towards the multipath is to recover the signal propagation path. To facilitate the signal propagation simulation process, plenty of aspects such as sensor parameters, the geometry of the objects (shape, location, orientation, mutual position between adjacent buildings) and the physical parameters of the surface (roughness, correlation length, permittivity)which determine the strength of radar signal backscattered to the SAR sensor should be given in previous. However, it's not practical to obtain the highly detailed object model in unfamiliar area by field survey as it's a laborious work and time-consuming. In this paper, SAR imaging simulation based on RaySAR is conducted at first aiming at basic understanding of multipath effects and for further comparison. Besides of the pre-imaging simulation, the product of the after-imaging, which refers to radar images is also taken into consideration. Both Cosmo-SkyMed ascending and descending SAR images of Lupu Bridge in Shanghai are used for the experiment. As a result, the reflectivity map and signal distribution map of different bounce level are simulated and validated by 3D real model. The statistic indexes such as the phase stability, mean amplitude, amplitude dispersion, coherence and mean-sigma ratio in case of layover are analyzed with combination of the RaySAR output.

ANALYSIS OF MULTIPATH PIXELS IN SAR IMAGES

Abstract. As the received radar signal is the sum of signal contributions overlaid in one single pixel regardless of the travel path, the multipath effect should be seriously tackled as the multiple bounce returns are added to direct scatter echoes which leads to ghost scatters. Most of the existing solution towards the multipath is to recover the signal propagation path. To facilitate the signal propagation simulation process, plenty of aspects such as sensor parameters, the geometry of the objects (shape, location, orientation, mutual position between adjacent buildings) and the physical parameters of the surface (roughness, correlation length, permittivity)which determine the strength of radar signal backscattered to the SAR sensor should be given in previous. However, it's not practical to obtain the highly detailed object model in unfamiliar area by field survey as it's a laborious work and time-consuming. In this paper, SAR imaging simulation based on RaySAR is conducted at first aiming at basic understanding of multipath effects and for further comparison. Besides of the pre-imaging simulation, the product of the after-imaging, which refers to radar images is also taken into consideration. Both Cosmo-SkyMed ascending and descending SAR images of Lupu Bridge in Shanghai are used for the experiment. As a result, the reflectivity map and signal distribution map of different bounce level are simulated and validated by 3D real model. The statistic indexes such as the phase stability, mean amplitude, amplitude dispersion, coherence and mean-sigma ratio in case of layover are analyzed with combination of the RaySAR output.

Scattering Dynamics, Survival, and Dispersal of Dimethyl Methylphosphonate Interacting with the Surface of Multilayer Graphene.

We explored the interaction of a molecular beam of dimethyl methylphosphonate with a multilayer graphene surface to better understand the fate of chemical warfare agents in the environment. The experiments were done at surface temperatures between 120 and 900 K and translational energies between 200 and 1500 meV. At the lowest temperatures, the dimethyl methylphosphonate is adsorbed, with the molecules next to the carbon surface held slightly more strongly than the bulk molecular film that grows with continued dosing. We measured the desorption energy for submonolayer coverage using modulated beam techniques and found a value of 290 meV (28 kJ/mol). At higher surface temperatures, where the residence times are very short, we measured the scattering of the dimethyl methylphosphonate as a function of angle and translational kinetic energy. For a surface temperature of 250 K, with translational kinetic energies between 200 and 1500 meV, much of the incident flux has nearly been accommodated by the surface temperature and has no memory of the incident momentum. The internal energy also seems to be at least partially accommodated. As the surface temperature increases, the scattering transitions to direct-inelastic reflection, where much of the incident translational energy is retained, and the intensity of the scattering peaks superspecularly toward glancing final angles. These results demonstrate the efficacy of using kinetic energy controlled molecular beams to probe the interactions of complex organic molecules with well-defined surfaces, extending our fundamental understanding of how the dynamics for such systems crossover from trapping-desorption to direct inelastic scattering. Moreover, these results indicate that simulations that model the dispersal of chemical warfare agents using common interfaces in the environment need to account for multiple bounce trajectories and survival of the impinging molecules.

The importance of accurate adiabatic interaction potentials for the correct description of electronically nonadiabatic vibrational energy transfer: a combined experimental and theoretical study of NO(v = 3) collisions with a Au(111) surface.

We present a combined experimental and theoretical study of NO(v = 3 → 3, 2, 1) scattering from a Au(111) surface at incidence translational energies ranging from 0.1 to 1.2 eV. Experimentally, molecular beam-surface scattering is combined with vibrational overtone pumping and quantum-state selective detection of the recoiling molecules. Theoretically, we employ a recently developed first-principles approach, which employs an Independent Electron Surface Hopping (IESH) algorithm to model the nonadiabatic dynamics on a Newns-Anderson Hamiltonian derived from density functional theory. This approach has been successful when compared to previously reported NO/Au scattering data. The experiments presented here show that vibrational relaxation probabilities increase with incidence energy of translation. The theoretical simulations incorrectly predict high relaxation probabilities at low incidence translational energy. We show that this behavior originates from trajectories exhibiting multiple bounces at the surface, associated with deeper penetration and favored (N-down) molecular orientation, resulting in a higher average number of electronic hops and thus stronger vibrational relaxation. The experimentally observed narrow angular distributions suggest that mainly single-bounce collisions are important. Restricting the simulations by selecting only single-bounce trajectories improves agreement with experiment. The multiple bounce artifacts discovered in this work are also present in simulations employing electronic friction and even for electronically adiabatic simulations, meaning they are not a direct result of the IESH algorithm. This work demonstrates how even subtle errors in the adiabatic interaction potential, especially those that influence the interaction time of the molecule with the surface, can lead to an incorrect description of electronically nonadiabatic vibrational energy transfer in molecule-surface collisions.

TerraSAR-X画像の機械学習による津波被災地の自動検出

A method for rapid detection of tsunami devastated areas using multi-temporal TerraSAR-X data is proposed. To develop the method, machine learning algorithm, a branch of artificial intelligence (AI), is applied. We focus on the multiple bounce reflection which is a specific feature on Synthetic Aperture Radar (SAR) data to estimate building devastated areas. Finally, classifiers which enable automated classifications of damage patterns into predicted damage classes were built. The evaluation of the model was conducted through cross-validation and the best accuracy was obtained as 89.2 %.

RCS of Complex Targets: Original Representation Validated by Measurements—Application to ISAR Imagery

In this paper, we propose and investigate a model based on asymptotic methods, designed to compute the radar cross section (RCS) of complex targets. A combined method of physical optics, geometrical optics, and the equivalent current method is applied to establish an effective backscattering analysis procedure. The scattering model includes shadowing effects, multiple bounce, and diffraction by edges. This model is used for RCS estimation and to generate inverse synthetic aperture radar (ISAR) raw data for imaging applications. We review the theoretical aspects and describe the proposed model and experimental setup in detail. Numerical results are provided and compared with the experimental results obtained in the anechoic chamber of ENSTA Bretagne to validate the approach through the computation of the RCS for canonical objects and a generic boat. Finally, a parallelepiped representation of the RCS is presented to be used for ISAR imagery, and the first results concerning the ISAR imaging of a generic boat are provided.

The Pacific lithosphere‐asthenosphere boundary: Seismic imaging and anisotropic constraints from SS waveforms

The lithosphere‐asthenosphere boundary (LAB) separating the rigid lid from the underlying weaker, convecting asthenosphere is a fundamental interface in mantle dynamics and plate tectonics. However, the exact depth and defining mechanism of the LAB interface remain poorly understood. The ocean plates are ideal for testing hypotheses regarding the nature of a plate since they make up 70% of Earth's surface area and have a relatively simple geological history. Seismically imaging the oceanic LAB at high resolution has proved challenging. Yet, several studies have recently increased resolution with provocative results. We summarize recent imaging of discontinuity structure beneath much of the Pacific using receiver functions from ocean floor borehole seismometers and land stations located at ocean‐continent margins, SS precursors, and waveform modeling of multiple phases including multiple bounce S waves, ScS reverberations, and surface waves. Overall, there is much agreement among these different approaches about the reported depth of a negative discontinuity that occurs near the expected depth of the LAB. Some of the apparent discrepancies in depth are explained by the variation in sensitivity of seismic waves that sample structure at different wavelengths. Yet, when the results are considered together, no single age‐depth relationship is illuminated. There are also puzzling discrepancies in where the discontinuity is detected, which again suggests greater complexity. Here we test the possibility that discrepant detection of a strong sharp discontinuity is caused by anisotropic structure. We stack SS waveforms with bounce points in the central Pacific into azimuthal bins. We use two methods, one that inverts for discontinuity structure based on subtle variations in the character of the SS waveform, and another that considers SS at higher frequency. We find azimuthal variation in the amplitude of the waveform, including a polarity reversal. We suggest that anisotropy is an important factor in imaging and constraining discontinuity structure of the oceanic plate, and must be carefully considered to constrain the age‐depth dependence and defining mechanism of the oceanic lithosphere.

Electron energy diffusion and advection due to non-linear electron-chorus wave interactions

Non-linear plasma waves effects such as phase bunching and phase trapping can cause drastic changes (tens keVs) in the energies of electrons in the magnetosphere at the timescale of a few seconds. Previous studies of non-linear wave effects mainly focused on the energy changes of an electron passing through a plasma wave region, thus covering only a fraction of the electron's single-trip trajectory between its two mirror points. In this study, we use a test-particle method to study the cumulative non-linear wave effects over multiple electron bounce periods. From our simulation results and analyses, we find that non-linear wave-particle interactions are rather common with the presence of chorus waves. The non-linear wave effects take the form of energy advection, which can accelerate electrons rather efficiently. However, energy advection is often accompanied by electron pitch angle advection, causing electron pitch angles to decrease and constraining electron energy advection. The test particle approach we present here can be used to estimate nonlinear transport coefficients, which need to be incorporated into global radiation belt models.

근접장 구면파 소스의 다중 반사 효과를 고려한 수중함의 음향표적강도 해석

For the analysis of Acoustic Target Strength(TS) that indicates the scattered acoustic intensity from the underwater vehicles, an analysis program that is applicable to scatterers insonified by spherical wave source in near field is developed. In this program, the Physical Optics(PO) method is embedded as a base component. To increase the accuracy of the program, multiple bounce effects based on Geometrical Optics(GO) method are applied. To implement multiple bounce effects, GO method is used together with PO method. In detail, GO method has a concern in the evaluation of the effective area, and PO method is involved in the calculation of Acoustic Target Strength for the final effective area that is evaluated by GO method. For the embodiment of near field spherical wave source originated multiple bounce effects, image source concept is implemented additively to the existing multiple bounce algorithm which assumes plane wave insonification. Various types of models are tested to evaluate the reliability of the developed program and finally, a submarine is analyzed as an arbitrary scatterer.