Single Bounce Research Articles

Angle of Arrival Distribution in an Underwater Acoustic Communication Channel With Incoherent Scattering

Angle of arrival (AoA) analysis is essential for the statistical characterization of the underwater (UW) channel where the acoustic signal propagation is confined to a restricted geometry. In UW channels, the acoustic signal reaches the receiver either through the line of sight path or through scattering from the sea surface and bottom. Low-frequency acoustic signals (few Hz) undergo reflection from the sea surface and bottom. This is called coherent scattering, where the scattered paths are assumed to be in phase and concentrated around the specular paths. At relatively higher frequencies (above 10 kHz), incoherent scattering occurs, resulting in an omnidirectional scattering pattern at each point of interaction with the sea surface. In this work, we derive a closed-form expression for the AoA distribution for a single bounce (SB) path that undergoes incoherent scattering from the surface/bottom in an UW channel. The analysis is extended to the case of paths involving multiple bounces (MB). The AoA distribution is further used to evaluate the Doppler spread in an UW channel.

A 3D Non-Stationary GBSM for Vehicular Visible Light Communication MISO Channels

The potential of using visible light communication (VLC) technologies for vehicular communication networks has recently attracted much attention. The underlying VLC channels, as a foundation for the proper design and optimization of vehicular VLC communication systems, have not yet been sufficiently investigated. Vehicular VLC link impairments can have a significant impact on the system performance and capacity. Such impairments include the optical wireless channel distortion and background noise. This paper proposes a novel three-dimensional (3D) regular-shaped geometry-based stochastic model (RS-GBSM) for vehicular VLC multiple-input single-output (MISO) channels. The proposed 3D RS-GBSM combines a two-sphere model and an elliptic-cylinder model. Both the line-of-sight (LoS) and single-bounced (SB) components are considered. The proposed model jointly considers the azimuth and elevation angles by using von-Mises-Fisher (VMF) distribution. Based on the proposed model, the relationship between the communication range and the received optical power is analyzed and validated by simulations. The impact of the elevation angle in the 3D model on the received optical power is investigated by comparing with the received optical power of the corresponding two-dimensional (2D) model. Furthermore, the background noise is also modeled to evaluate the system's signal-to-noise ratio (SNR).

Accelerated Computation of the Physical Optics Approximation for Near-Field Single- and Double-Bounces Backscattering

This article deals with the acceleration of the physical optics (PO) approximation for the backscattering computation in the near and far fields, for both single-bounce (SB) and double-bounce (DB) PO contributions. It is based on physical arguments, which allow us to apply either a closed-form expression (rapid calculation) or a numerical double integration to evaluate the scattered field from subsurfaces of a given mesh. The use of the closed-form expression is governed by two criteria, which must be extended to the bistatic case and also to the DB: the conventional Fraunhofer (related to the far-field zone) criterion and the chord error (related to the surface curvature) criterion. The proposed method is tested on a dihedral geometry.

Pixel Tracking to Estimate Rivers Water Flow Elevation Using Cosmo-SkyMed Synthetic Aperture Radar Data

The lack of availability of historical and reliable river water level information is an issue that can be overcome through the exploitation of modern satellite remote sensing systems. This research has the objective of contributing in solving the information-gap problem of river flow monitoring through a synthetic aperture radar (SAR) signal processing technique that has the capability to perform water flow elevation estimation. This paper proposes the application of a new method for the design of a robust procedure to track over the time double-bounce reflections from bridges crossing rivers to measure the gap space existing between the river surface and bridges. Specifically, the difference in position between the single and double bounce is suitably measured over the time. Simulated and satellite temporal series of SAR data from COSMO-SkyMed data are compared to the ground measurements recorded for three gauges sites over the Po and Tiber Rivers, Italy. The obtained performance indices confirm the effectiveness of the method in the estimation of water level also in narrow or ungauged rivers.

A Unified Hollow-Disk Scattering Model: Angle-of-Departure and Time-of-Arrival Statistics

In order to ensure the required wireless communication system performances, it is necessary to have an efficient communication channel model, which is capable of considering all channel degradation factors fairly. In this paper, a unified hollow-disk geometrically based stochastic channel model is derived. This model assumes that the scatterers are distributed in a hollow-disk area around a mobile station. Namely, the scatterer distribution is derived as a projection of $\boldsymbol{d}$ -dimensional uniformly distributed scatterers into two-dimensional space. According to this generalization, derived model is capable of obtaining uniform circular, uniform ring, uniform hollow-disk, and unified disk scattering model as special cases, as well as modeling a whole new group of hollow-disk models. Under an assumption of single bounce scattering and omnidirectional antennas at transmitter and receiver, joint probability density function (PDF) of angle-of-departure and angle-of-arrival, as well as the joint PDF of time-of-arrival and angle-of-arrival are derived. Subsequently, the corresponding marginal PDFs are provided in a closed form. Thus, derived PDFs are suitable for any position of the base station, (base station placed inside or outside of scattering region). The proposed model is validated by several measured channels. The curve fitting results shown the high flexibility of the proposed model and outperforming results compared with several other geometric scattering models.

Satellite Imagery for Classification of Rice Growth Phase Using Freeman Decomposition in Indramayu, West Java, Indonesia

Monitoring at every growth of rice plants is an important information for determining the grain pro-duction estimation of rice. Monitoring must to be have timely work on the rice plant development. However, timely monitoring and the high accuracy of information is a challenge in remote sensing based on rice agriculture monitoring and observation. With increased quality of synthetic aperture radar (SAR) systems utilizing polarimetric information recently, the development and applications of polarimetric SAR (PolSAR) are one of the current major topics in radar remote sensing. The ad-vantages provided by PolSAR data for agricultural monitoring have been extensively studied for applications such as crop type classification and mapping, crop phenology monitoring, productivity assessment based on the sensitivity of polarimetric parameters to indicators of crop conditions. Freeman and Durden successfully decomposed fully PolSAR data into three components: Single bounce, double bounce, and volume scattering. The three-component scattering provide features for distinguishing between different surface cover types. These sensitivities assist in the identification of growing phase. The observed growing phase development in time series, reflected in the consistent temporal trends in scattering, was generally in agreement with crop phenological development stages. Supervised classification was performed on repeat-pass Radarsat-2 images, with an overall classification accuracy of 77.27% achieved using time series Fine beam data. The study demonstrated that Radarsat-2 Fine mode data provide useful information for crop monitoring and classification of rice plants.

A 2-D Non-Stationary GBSM for Vehicular Visible Light Communication Channels

In this paper, a new non-stationary regular-shaped geometry-based stochastic model (RS-GBSM) is proposed for vehicular visible light communications (VVLC) channels. The proposed model utilizes a combined two-ring model and a confocal ellipse model, in which the received optical power is constructed as a sum of single-bounced (SB) and double-bounced (DB) components, in addition to the line-of-sight (LoS) component. Using the proposed RS-GBSM, the channel impulse response is generated and utilized to investigate VVLC channel characteristics, such as channel gain and root-mean-square (RMS) delay spread. The received optical power is computed considering the distance between the optical transmitter (Tx) and the optical receiver (Rx). Moreover, the impact of the Rx height on the received power is considered for the LoS scenario. The results show that the LoS power highly depends on the distance, Rx height, and the optical source pattern. For the SB components, it is confirmed that the channel gain in dB and the RMS delay spread follow Gaussian distributions. Finally, the results indicate that the detected optical power from the DB components is low enough to be overlooked.

The CST bounce universe model — A parametric study

A bounce universe model with a scale-invariant and stable spectrum of primordial density perturbations was constructed using a consistent truncation of the D-brane dynamics from Type IIB string theory. A coupling was introduced between the tachyon field and the adjoint Higgs field on the D3-branes to lock the tachyon at the top of its potential hill and to model the bounce process, which is known as the Coupled Scalar and Tachyon Bounce (CSTB) Universe. The CSTB model has been shown to be ghost free, and it fulfils the null energy condition; in addition, it can also solve the Big Bang cosmic singularity problem. In this paper we conduct an extensive follow-up study of the parameter space of the CSTB model. In particular we are interested in the parameter values that can produce a single bounce to arrive at a radiation-dominated universe. We further establish that the CSTB universe is a viable alternative to inflation, as it can naturally produce a sufficient number of e-foldings in the locked inflation epoch and in the post-bounce expansion to overcome the four fundamental limitations of the Big Bang cosmology, which are flatness, horizon, homogeneity and singularity, resulting in a universe of the current size.

Deterministic and stochastic simulators for non-isotropic V2V-MIMO wideband channels

In this paper, we consider a novel two-dimensional (2D) geometry-based stochastic model (GBSM) for multiple-input multiple-output (MIMO) vehicle-to-vehicle (V2V) wideband fading channels. The proposed model employs the combination of a two-ring model and a multiple confocal ellipses model, where the signal is sum of the line-of-sight (LoS) component, single-bounced (SB) rays, and double-bounced (DB) rays. Based on the reference model, we derive some expressions of channel statistical properties, including space-time correlation function (STCF), Doppler spectral power density (DPSD), envelope level crossing rate (LCR) and average fade duration (AFD). In addition, corresponding deterministic and stochastic simulation models are developed based on the reference model. Moreover, we compare the statistical properties of the reference model and the two simulation models in different scenarios and investigate the impact of different vehicular traffic densities (VTDs) on the channel statistical properties of the proposed model. Finally, the great agreement between simulation models and the reference model demonstrates not only the utility of simulation models, but also the correctness of theoretical derivations and simulations.

Early-Stage Deforestation Detection in the Tropics With L-band SAR

Polarimetric characteristics of early-stage deforestation areas were examined with L -band synthetic aperture radar (SAR) to develop a forest early warning system. Time series of PALSAR-2/ScanSAR data and Landsat data were used to examine the differences in detection timing of deforestation in the most active deforestation sites in Peru and Brazil. The γ0HH value increased by 0.8 dB on average for areas undergoing early-stages of deforestation, in which felled trees were left on the ground. The detection timing was almost the same as that of using the optical sensor. On the other hand, the γ0HV value does not show significant γ0 change at this early-stage of deforestation. The γ0HV value started to decrease 1–1.5 months after the deforestation was detected by Landsat. The γ0 HV value decreased by 1.5–1.6 dB, 4–5 months after the deforestation. To understand the radar backscattering mechanism at the early-stage deforestation sites, field experiments were carried out 2–16 days after the PALSAR-2/fully-polarimetric observations. The early-stage deforestation sites revealed 1.1–2.5 dB and 2.9–4.0 dB increases for σ 0HH and σ 0surface, respectively. This can be explained by the direct (single bounce) scattering from felled trees left on the ground. The sites in which felled trees were removed and the surfaces were flattened showed 5.2–5.3 dB and 5.3–5.5 dB decreases for σ 0HV and σ 0volume, respectively. This can be explained by the lower sensitivity of the HV polarization to both the branches remaining on the ground and the surface roughness, along with its increased sensitivity to the forest biomass. We conclude that an increase in L -band γ0HH is a good indicator for detecting early-stage deforestation sites, where felled trees are left on the ground, while γ0HV may be useful for detecting later-stage deforestation sites.

Consistent scalar and tensor perturbation power spectra in single fluid matter bounce with dark energy era

We investigate cosmological scenarios containing one canonical scalar field with an exponential potential in the context of bouncing models, where the bounce happens due to quantum cosmological effects. The only possible bouncing solutions in this scenario (discarding an infinitely fine tuned exception) must have one and only one dark energy phase, either occurring in the contracting era or in the expanding era. Hence,these bounce solutions are necessarily asymmetric. We calculate the spectral indexes and amplitudes of scalar and tensor perturbations numerically, considering the whole history of the model, including the bounce phase itself, without making any approximation or using any matching condition on the perturbations. As the background model is necessarily dust dominated in the far past, the usual adiabatic vacuum initial conditions can be easily imposed in this era. Hence, this is a cosmological model where the presence of dark energy behavior in the Universe does not turn problematic the usual vacuum initial conditions prescription for cosmological perturbation in bouncing models. Scalar and tensor perturbations end up being almost scale invariant, as expected. The background parameters can be adjusted, without fine tunings, to yield the observed amplitude for scalar perturbations, and also for the ratio between tensor and scalar amplitudes, $r = T/S \lesssim 0.1$. The amplification of scalar perturbations over tensor perturbations takes place only around the bounce, due to quantum effects, and it would not occur if General Relativity has remained valid throughout this phase. Hence, this is a bouncing model where a single field induces not only an expanding background dark energy phase, but also produces all observed features of cosmological perturbations of quantum mechanical origin at linear order.

Chemical Dynamics Simulation of Low Energy N2 Collisions with Graphite

A chemical dynamics simulation was performed to study low energy collisions between N2 and a graphite surface. The simulations were performed as a function of collision energy (6.34 and 14.41 kcal/mol), incident polar angle (20–70°) and random azimuthal angle. The following properties were determined and analyzed for the N2 + graphite collisions: (1) translational and rotational energy distributions of the scattered N2; (2) distribution of the final polar angle for the scattered N2; (3) number of bounces of N2 on the surface before scattering. Direct scattering with only a single bounce is dominant for all incident angles. Scattering with multiple collisions with the surface becomes important for incident angles far from the surface normal. For trajectories that desorb, the parallel component of the N2 incident energy is conserved due to the extremely short residence times of N2 on the surface. For scattering with an incident energy of 6.34 kcal/mol, incident polar angle of 40°, and final polar angle of 5...

Quantified, Interactive Simulation of AMCW ToF Camera Including Multipath Effects.

In the last decade, Time-of-Flight (ToF) range cameras have gained increasing popularity in robotics, automotive industry, and home entertainment. Despite technological developments, ToF cameras still suffer from error sources such as multipath interference or motion artifacts. Thus, simulation of ToF cameras, including these artifacts, is important to improve camera and algorithm development. This paper presents a physically-based, interactive simulation technique for amplitude modulated continuous wave (AMCW) ToF cameras, which, among other error sources, includes single bounce indirect multipath interference based on an enhanced image-space approach. The simulation accounts for physical units down to the charge level accumulated in sensor pixels. Furthermore, we present the first quantified comparison for ToF camera simulators. We present bidirectional reference distribution function (BRDF) measurements for selected, purchasable materials in the near-infrared (NIR) range, craft real and synthetic scenes out of these materials and quantitatively compare the range sensor data.

Probabilistic pharmacokinetic models of decompression sickness in humans: Part 2, coupled perfusion-diffusion models

Decompression sickness (DCS) can be experienced following a reduction in ambient pressure; such as that associated with diving or ascent to high altitudes. DCS is believed to result when supersaturated inert gas dissolved in biological tissues exits solution and forms bubbles. Models to predict the probability of DCS are typically based on nitrogen and/or helium gas uptake and washout in several theoretical tissues, each represented by a single perfusion-limited compartment. It has been previously shown that coupled perfusion-diffusion compartments are better descriptors than solely perfusion-based models of nitrogen and helium uptake and elimination kinetics observed in the brain and skeletal muscle of sheep. In this work, we examine the application of these coupled pharmacokinetic structures with at least one diffusion compartment to the prediction of the incidence of decompression sickness in humans. We compare these models to LEM-NMRI98, a well-described U.S. Navy gas content model, consisting of three uncoupled perfusion-limited compartments incorporating oxygen and linear-exponential kinetics. Pharmacokinetic gas content models with a diffusion component describe the probability of DCS in human bounce dives made with air, single non-air bounce dives, and oxygen decompression dives better than LEM-NMRI98. However, for the full data set, LEM-NMRI98 remains the best descriptor of the data.

Modelling broadband scatter from periodic sea surfaces

Surface waves are the primary source of short time-scale variation of the channel impulse response in underwater transmission scenarios when source and receiver positions are fixed. This study proposes an exact method for modeling the single surface bounce path of the channel impulse response, which contains most of short time-scale effect. This method is designed for one dimensional, periodic wave profiles, and solves the scattering problem as a series of motionless surfaces. To create a time series for each surface, the proposed method solves the Helmholtz equation at many frequencies, performing three steps at each frequency. First, the point source is decomposed into a series of plane waves, each of which scatter from the surface at a finite number of Bragg angles. Second, the amplitudes of these discrete scattered plane waves are found with an exact method. Finally, the surface response for a three-dimensional point source is recovered with a plane wave synthesis of these scattered plane waves. The results of this study are intended as a reference to inform the interpretation of surface scattering results from more common underwater acoustic models.

Scattering property based contextual PolSAR speckle filter

Reliability of the scattering model based polarimetric SAR (PolSAR) speckle filter depends upon the accurate decomposition and classification of the scattering mechanisms. This paper presents an improved scattering property based contextual speckle filter based upon an iterative classification of the scattering mechanisms. It applies a Cloude-Pottier eigenvalue-eigenvector decomposition and a fuzzy H/α classification to determine the scattering mechanisms on a pre-estimate of the coherency matrix. The H/α classification identifies pixels with homogeneous scattering properties. A coarse pixel selection rule groups pixels that are either single bounce, double bounce or volume scatterers. A fine pixel selection rule is applied to pixels within each canonical scattering mechanism. We filter the PolSAR data and depending on the type of image scene (urban or rural) use either the coarse or fine pixel selection rule. Iterative refinement of the Wishart H/α classification reduces the speckle in the PolSAR data. Effectiveness of this new filter is demonstrated by using both simulated and real PolSAR data. It is compared with the refined Lee filter, the scattering model based filter and the non-local means filter. The study concludes that the proposed filter compares favorably with other polarimetric speckle filters in preserving polarimetric information, point scatterers and subtle features in PolSAR data.

Antialiasing complex global illumination effects in path-space

We present the first method to efficiently predict antialiasing footprints to pre-filter color-, normal-, and displacement-mapped appearance in the context of multi-bounce global illumination. We derive Fourier spectra for radiance and importance functions that allow us to compute spatial-angular filtering footprints at path vertices for both uni- and bi-directional path construction. We then use these footprints to antialias reflectance modulated by high-resolution maps (such as color and normal maps) encountered along a path. In doing so, we also unify the traditional path-space formulation of light transport with our frequency-space interpretation of global illumination pre-filtering. Our method is fully compatible with all existing single bounce pre-filtering appearance models, not restricted by path length, and easy to implement atop existing path-space renderers. We illustrate its effectiveness on several radiometrically complex scenarios where previous approaches either completely fail or require orders of magnitude more time to arrive at similarly high-quality results.

Antialiasing Complex Global Illumination Effects in Path-Space

We present the first method to efficiently predict antialiasing footprints to pre-filter color-, normal-, and displacement-mapped appearance in the context of multi-bounce global illumination. We derive Fourier spectra for radiance and importance functions that allow us to compute spatial-angular filtering footprints at path vertices for both uni- and bi-directional path construction. We then use these footprints to antialias reflectance modulated by high-resolution maps (such as color and normal maps) encountered along a path. In doing so, we also unify the traditional path-space formulation of light transport with our frequency-space interpretation of global illumination pre-filtering. Our method is fully compatible with all existing single bounce pre-filtering appearance models, not restricted by path length, and easy to implement atop existing path-space renderers. We illustrate its effectiveness on several radiometrically complex scenarios where previous approaches either completely fail or require orders of magnitude more time to arrive at similarly high-quality results.

A Study for Acoustic Target Strength Characteristics of Submarines Using Kirchhoff Approximation

AbstractAcoustic target strength (TS) is one of the most important factors for a submarine's stealth ability and survivability. As modern submarines are larger than their predecessors, TS must be reduced to improve stealth ability. In this paper, an analysis program based on the Kirchhoff approximation in a high-frequency range and developed for predicting TS of submarines is discussed. This program can analyze TS with respect not only to the single bounce effect in the exterior structure but also to the multibounce effect in the exterior and interior structures through a combination of geometric optics and physical optics methods, anechoic coating effect by using the reflection coefficient, and response time pattern for the detected target. TS calculations of a submarine model with the above effects were simulated by using this developed program, and its results are discussed.

Probabilistic pharmacokinetic models of decompression sickness in humans, part 1: Coupled perfusion-limited compartments

Decompression sickness (DCS) is a disease caused by gas bubbles forming in body tissues following a reduction in ambient pressure, such as occurs in scuba diving. Probabilistic models for quantifying the risk of DCS are typically composed of a collection of independent, perfusion-limited theoretical tissue compartments which describe gas content or bubble volume within these compartments. It has been previously shown that ‘pharmacokinetic’ gas content models, with compartments coupled in series, show promise as predictors of the incidence of DCS. The mechanism of coupling can be through perfusion or diffusion. This work examines the application of five novel pharmacokinetic structures with compartments coupled by perfusion to the prediction of the probability and time of onset of DCS in humans. We optimize these models against a training set of human dive trial data consisting of 4335 exposures with 223 DCS cases. Further, we examine the extrapolation quality of the models on an additional set of human dive trial data consisting of 3140 exposures with 147 DCS cases. We find that pharmacokinetic models describe the incidence of DCS for single air bounce dives better than a single-compartment, perfusion-limited model. We further find the U.S. Navy LEM-NMRI98 is a better predictor of DCS risk for the entire training set than any of our pharmacokinetic models. However, one of the pharmacokinetic models we consider, the CS2T3 model, is a better predictor of DCS risk for single air bounce dives and oxygen decompression dives. Additionally, we find that LEM-NMRI98 outperforms CS2T3 on the extrapolation data.