Echo Simulation Research Articles

Simulation of Laser Beam Scattering from Complex Targets in the near Field

A model of laser fuse echo simulation based on radiometry is developed. Process of target/beam interaction is determined by target surface optical scattering properties, which can be characterized by bidirectional reflectivity distribution function (BRDF). Signal features of the near-zone echo wave scattered from complex target are analyzed. The results may provide reference for algorithm design of laser proximity fuse. The simulator has been successfully applied in semi-physical simulation of the fuse.

A General IF Radar Echo Simulator Based on PC and FPGA

A general radar echo simulator hardware architecture based on PC and FPGA is proposed, which is a kind of PC+FPGA+D/A simulation system,and the simulator architecture has come to be a good choice with the development of PC technique and advanced chip field.The system is mainly based on a kind of PCI board which includes Virtex-4 FPGA and high performance D/A convertor with latest techniques and flexibility.Compared with traditional instruments,it is scalable,programmable and suitable for upgrading.The developed simulator has been tested and results show that the technical performance can meet the requirements of our application.

Pulsed Gradient Spin Echo Nuclear Magnetic Resonance Measurement and Simulation of Two-Fluid Taylor Vortex Flow in a Vertically Oriented Taylor–Couette Device

Magnetic resonance microscopy and Ansys Fluent© computational fluid dynamics simulation have been used to classify Taylor vortex flows (TVF) for several single fluid and axially stratified two-fluid systems in a vertically oriented Taylor–Couette device. A Rheo-NMR (nuclear magnetic resonance) Couette system (Magritek Ltd, New Zealand) with a 1.05-mm gap was used to evaluate the transition from Couette flow to TVF in 1.65 cSt silicone oil, 1 cSt deionized water, and 0.65 cSt silicone oil. The rotation rate at which instability onset occurred agreed between experiment and simulation, as did the critical wavelength. Velocities were mapped for axially stratified two-fluid systems. The vortex containing the two-fluid interface was found to form with a significantly longer wavelength than that observed in the pure fluids. For experiments and simulations in the TVF regime, a region with no secondary flows was found at the interface, indicating interface stabilization by surface tension forces.

基于仿真数据的HJ-1C 卫星SAR 成像处理方法

Synthetic-aperture radar (SAR) is an important method for earth remote sensing. HJ-1C will be launched in the near future as the first civil space-borne SAR satellite. This paper examines the key methods that form the basis of SAR imaging. These include a more accurate range model and related ECS(extended chirp scaling)factors, a fast echoes simulation method in the frequency domain, an accurate Doppler parameters calculation method and an improvement in the ScanSAR mosaic of sub-swath images. Simulations show that ECS and related methods are well suited for space-borne SAR imaging in Stripmap and ScanSAR mode with a larger squint angle.

SAR Echo and Image Simulation of Complex Targets Based on Electromagnetic Scattering

摘要: 复杂目标的SAR图像仿真技术，对于目标识别与解译研究具有重要意义。该文提出的仿真算法，从目标的3维模型出发，运用弹射线原理，通过仿真全方位，全频带的目标散射系数来构建回波并成像。改传统平面波入射为球面波入射，使得算法不仅能够仿真远场成像系统，也适用于近场仿真成像。标准体实验，验证了算法的近远场，全极化，多角度，宽频带的仿真能力；复杂目标的仿真结果，同实测数据相比十分逼真。 关键词: 合成孔径雷达 / 弹射线法 / SAR回波仿真 / 复杂目标

Analysis of radar micro-Doppler signatures from rigid targets in space based on inertial parameters

Micro-Doppler features have intrinsic relations with the physical properties of objects, which provide great potential for use in the target discrimination. A model and theoretical analysis of micro-Doppler based on inertial parameters for aerospace rigid targets are presented. According to the attitude kinematics in space, mathematical formulas of the micro-Doppler model based on inertial parameters are derived without the limitation of micro-motion types. Moments of inertia and initial rotational angular velocities are used to analyse their impact on micro-motions and micro-Doppler of free rigid targets. After the simulation of radar echoes from objects with various micro-motions, the joint time–frequency analysis is then utilised to demonstrate the time-varying micro-Doppler features and confirm the effectiveness of the model and theoretical analysis. The proposed method highlights the relationship between the model and the attributes of objects and gets rid of the restriction on the specified target shapes, which illustrates more explicit physical meaning and flexibility in the application.

Fast Raw-Signal Simulation of Extended Scenes for Missile-Borne SAR With Constant Acceleration

Fast raw-signal simulation is of considerable value for missile-borne synthetic aperture radar (SAR) algorithm development. On the basis of the two-dimensional (2-D) Fourier simulation method for stripmap SAR, we present a fast echo simulation method suitable for missile-borne SAR diving with constant acceleration. The analytical expression for the 2-D signal spectrum is derived and then converted to a stripmap one. Simulation results for a point target and a real scene demonstrate its validity and effectiveness.

An Adaptive Filter to Approximate the Bayesian Strategy for Sonographic Beamforming

A first-principles task-based approach to the design of medical ultrasonic imaging systems for breast lesion discrimination is described. This study explores a new approximation to the ideal Bayesian observer strategy that allows for object heterogeneity. The new method, called iterative Wiener filtering, is implemented using echo data simulations and a phantom study. We studied five lesion features closely associated with visual discrimination for clinical diagnosis. A series of human observer measurements for the same image data allowed us to quantitatively compare alternative beamforming strategies through measurements of visual discrimination efficiency. Employing the Smith-Wagner model observer, we were able to breakdown efficiency estimates and identify the processing stage at which performance losses occur. The methods were implemented using a commercial scanner and a cyst phantom to explore development of spatial filters for systems with shift-variant impulse response functions. Overall we found that significant improvements were realized over standard B-mode images using a delay-and-sum beamformer but at the cost of higher complexity and computational load.

Simulation of radar sounder echo from lunar surface and subsurface structure

Space-borne high frequency (HF) radar sounder is an effective tool for investigation of lunar subsurface structure in lunar exploration. The primary strategy of radar sounder technology for subsurface structure detection is utilization of the nadir echoes time delay and intensity difference from the lunar surface and subsurface. It is important to fully understand electromagnetic wave propagation, scattering, and attenuation through the lunar media in order to retrieve information of lunar layering structure from weak nadir echoes of the subsurface, which is simultaneously interfered by strong off-nadir surface clutters. Based on the Kirchhoff approximation (KA) of rough surface scattering and the ray tracing of geometric optics, a numerical simulation of radar echoes from lunar layering structures is developed. According to the lunar surface feature, the topography of mare and highland surfaces is numerically generated, and the triangulated network is employed to make digital elevations of the whole lunar surface. Scattering from the lunar surface and subsurface is numerically calculated using KA approach. Radar echoes and its range images are numerically simulated, and their dependence on the parameters of lunar layering interfaces is discussed. The approach of this paper can also be utilized to investigate subsurface structures in Mars and other planetary exploration.

Modeling of precise onset spike timing for echolocation in the big brown bat, Eptesicus fuscus.

The neuronal circuits enabling highly accurate sonar performance in bats are not well understood. In this research, a computational neuroscience model was developed based on Meddis’ auditory peripheral model and a biologically plausible network of integrate-and-fire neurons. The stimuli presented to the model include acoustic simulations of target echoes using wideband FM echolocation calls recorded from Eptesicus fuscus. Synaptic connectivity of the neural network was varied to explore its effect on the precision of onset spike timing. Results show that precisely timed spike codes can relay sufficient information of echo time-frequency representations to account for performance observed in laboratory experiments. This research represents a portion of our overarching goal to reverse engineer the bat’s critical auditory functions into a refined sonar signal processing algorithm. A necessary first component of this process is to understand the functionality of relevant circuitry in the auditory midbrain. Such biomimetic processing schemes may be useful in active sonar applications suffering from a high degree of environmental clutter, where man-made systems typically demonstrate poor performance.

Ultrafast relaxation and 2D IR of the aqueous trifluorocarboxylate ion

The asymmetric stretching vibration of the amphiphilic trifluoroacetate ion and its (13)C=(16)O isotopologue in D(2)O were investigated with infrared spectroscopy (FTIR), ultrafast infrared pump probe, and two dimensional vibrational photon echo techniques and simulations. Trifluoroacetate ions have a nonexponential depopulation of the first vibrational excited state, which is well described by a kinetic mechanism involving a temperature dependent solvent assisted relaxation to the symmetric stretch mode. The vibrational spectrum of the asymmetric stretch of the (13)C=(16)O isotopologue presents an unusual spectral shape. The frequency-frequency autocorrelation function shows a static term not present in the (13)C=(16)O form, which is caused by an accidental degeneracy with a combinational mode. A newly developed frequency map for carboxylate is used to characterize the processes and dynamics observed in the frequency fluctuations of the carboxylate asymmetric stretch mode in aqueous solution. An assignment of the molecular processes that govern the frequency fluctuations is suggested from an analysis of the solvation shell configurations obtained from molecular dynamics simulations.

Prediction of flaw response in polycrystalline metals for an ultrasonic pulse echo simulation using Born approximation

The objective of this paper is to predict the flaw response in an isotropic polycrystalline solid medium. Multi-Gaussian Beam (MGB) model is used to represent the incident ultrasonic beam. The effect of ultrasonic attenuation and phase velocity dispersion due to grain scattering is included in the predictions. The variation of received voltage is analysed against the distance of the flaw from the transducer for different dimensions of spherical void. The effect of variation of mean diameter of the grains on the received voltage for different domain of interest is also studied.

Weather Radar Ground Clutter. Part I: Identification, Modeling, and Simulation

Abstract Real-time ground-clutter identification and subsequent filtering of clutter-contaminated data is addressed in this two-part paper. Part I focuses on the identification, modeling, and simulation of S-band ground-clutter echo. A new clutter identification parameter, clutter phase alignment (CPA), is presented. CPA is a measure primarily of the phase variability of the in-phase and quadrature-phase time series samples for a given radar resolution volume. CPA is also a function of amplitude variability of the time series. It is shown that CPA is an excellent discriminator of ground clutter versus precipitation echoes. A typically used weather model, time series simulator is shown to inadequately describe experimentally observed CPA. Thus, a new technique for the simulation of ground-clutter echo is developed that better predicts the experimentally observed CPA. Experimental data from the Denver Next Generation Weather Radar (NEXRAD) at the Denver, Colorado, Front Range Airport (KFTG), and NCAR’s S-band dual-polarization Doppler radar (S-Pol) are used to illustrate CPA. In Part II, CPA is used in a fuzzy logic algorithm for improved clutter identification.

Weather Radar Ground Clutter, Part I: Identification, Modeling and Simulation

Real-time ground-clutter identification and subsequent filtering of clutter-contaminated data is addressed in this two-part paper. Part I focuses on the identification, modeling, and simulation of S-band ground-clutter echo. A new clutter identification parameter, clutter phase alignment (CPA), is presented. CPA is a measure primarily of the phase variability of the in-phase and quadrature-phase time series samples for a given radar resolution volume. CPA is also a function of amplitude variability of the time series. It is shown that CPA is an excellent discriminator of ground clutter versus precipitation echoes. A typically used weather model, time series simulator is shown to inadequately describe experimentally observed CPA. Thus, a new technique for the simulation of ground-clutter echo is developed that better predicts the experimentally observed CPA. Experimental data from the Denver Next Generation Weather Radar (NEXRAD) at the Denver, Colorado, Front Range Airport (KFTG), and NCAR’s S-band dual-polarization Doppler radar (S-Pol) are used to illustrate CPA. In Part II, CPA is used in a fuzzy logic algorithm for improved clutter identification.

Ultrasonic pulse propagation in a bonded three‐layered structure

Bonded layers are used in the assembly of many critical functional parts of industrial equipment. In this work, ultrasonic pulse propagation in a steel‐rubber‐rubber bonded composite structure is investigated by means of computer simulation and pulse echo experimental evaluation. Ultrasonic pulse propagation is modelled using a 2D time domain finite‐difference software. For the experimental measurements, two test samples were fabricated by bonding a thin layer of steel and two thin layers of rubber, including debonded areas at marked regions of each interface. Several ultrasonic traces were acquired by contact pulse‐echo testing, using a 5 MHz wideband transducer, from the external steel surface. The large acoustic impedance mismatch existing between steel and rubber layers makes that only a very small part of the ultrasonic energy is transmitted through the first (steel‐rubber)interface. The high attenuation in rubber materials and the possible overlapping of multiple echoes are additional characteristics of the complex ultrasonic pulse propagation in this flat structure. Some differences in time and frequency domains, between the received signals from normal bonded areas and completely debonded areas are discussed, looking for defect detection at the first (steel‐rubber) and second (rubber‐rubber) interfaces.

The development of standards for ophthalmologic ultrasound diagnosis

The performance data of ultrasonic apparatus and transducer probes are decisive in view of the information content of the echograms. Clinically applicable measurement methods, therefore, were developed already in the early sixties for ophthalmic ultrasonography. The sensitivity of each probe apparatus combination was measured first by means of a variable absorption path, the working frequency by counting the oscillations per microsecond in the rf echo signal of a plane reflector. Depth and lateral resolution were determined using monofil filaments mounted to a micrometer gauge. These measurements resulted in marked improvement of safety of diagnosis. In view of the IEC document 854, we developed a test reflector. It reflects a standard echo which can be measured within the control range of most diagnostic machines without need of additional dB-calibrated attenuators. Now, each echo amplitude can be referred to this standard echo (whose difference to the ideal reflector echo is-17 dB). An electronic device (echo simulator) permits additional checking of distinct equipment parts (especially of the dB control, time scale and amplifier dynamics). The entirely empirical use of ultrasonic diagnostic apparatus without measurement of the diagnostically relevant performance data and without readjustment and documentation of comparable examination conditions is, in our opinion, an outdated approach. Repeated measurements at regular intervals and especially after repairs or change of transducer probes are mandatory.

Interaction between excitons determines the non-linear response of nanocrystals

The non-linear response of semiconductor quantum dots is investigated using three-pulse photon echo peak shift (3PEPS) experiments and simulations. The third-order non-linear response is modeled by a three-level system, utilizing Brownian oscillators to model the line-broadening functions. Our results show that biexciton formation and exciton–exciton scattering significantly influence the non-linear response of quantum dots. The exciton to biexciton excited state absorption pathways are also investigated for quantum dots with different crystal structures. Our calculations suggest that the probability of excited state absorption to the biexcitonic state is higher for zinc-blende structured nanocrystals.

Simulation of ultrasonic phased array technique for imaging and sizing of defects using longitudinal waves

Phased array ultrasonics can be used as a rapid tool for imaging and sizing crack-like defects. This paper reports the simulation of phased array ultrasonic wave interaction with the defects using the finite-difference time domain (FDTD) method. Experiments were conducted to validate modeling results for pulse–echo simulations of the phased array transducer on a mild-steel (MS) pipe sample with circumferential internal surface notches of three different sizes. Experiments were carried out on the MS pipe specimen using a conventional ultrasonic technique with a 5 MHz transducer at 45° refracted angle within the specimen and the defects were imaged and sized using the relative arrival time technique (RATT). The experimental B-scans obtained using the conventional ultrasonic techniques were compared with the experimental B-scans obtained using the phased array instrument. Simulation studies were also carried out by steering the beam to the requisite angles by the phased array transducer to study the effect of various angles of incidence on the defect definition, i.e., with respect to imaging and sizing, using the RATT.

Numerical simulation of polarimetric radar pulse echoes from the lunar regolith layer with scatter inhomogeneity and rough interfaces

To explore the potential utilities of lower‐frequency (L band) radar pulse penetration on Moon exploration, a theoretical model of stratified lunar regolith media and numerical simulation of polarimetric radar pulse echoes are developed. The lunar regolith layer consists of the low lossy regolith layer with randomly rough top and bottom interfaces, and a layer of random stone scatterers (spatially oriented oblate spheroids are assumed) is embedded and overlays the underlying rock media. The time domain Mueller matrix solution derived from vector radiative transfer formulations contains seven scattering mechanisms of the stratified media: surface scattering from the rough top and bottom interfaces, volumetric scattering from random stone scatterers, and their multi‐interactions. Temporal characteristics and structure of the polarimetric echo profile as functional dependence on model parameters such as the layer thickness and the content of FeO + TiO2, are numerically simulated and well display an image of regolith structures. Polarimetric pulse echoes might reveal rich information on the lunar regolith layer depth and other structure properties and might demonstrate a potential new way to explore the Moon surface in the future.

Plasma and electromagnetic wave simulations of meteors

Every day billions of meteoroids impact and disintegrate in the Earth’s atmosphere. Current estimates for this global meteor flux vary from 2000 to 200,000 tons per year, and estimates for the average velocity range between 10 km/s and 70 km/s. The basic properties of this global meteor flux, such as the average mass, velocity, and chemical composition remain poorly constrained. We believe much of the mystery surrounding the basic parameters of the interplanetary meteor flux exists for the following reason, the unknown sampling characteristics of different radar meteor observation techniques, which are used to derive or constrain most models. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. We present our results on meteor plasmas simulations of head echoes using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross section of the simulated meteor plasmas. These simulations have shown that the radar cross section depends in a complex manner on a number of parameters. These include the angle between radar and meteor entry, a large dependence on radar frequency, which shows that for a given meteor plasma size and density, the reflectivity as a function of probing radar frequency varies, but typically peaks below 100 MHz.