Echo Amplitude Research Articles

CONDITIONAL RANDOM FIELDS FOR THE CLASSIFICATION OF LIDAR POINT CLOUDS

Abstract. In this paper we propose a probabilistic supervised classification algorithm for LiDAR (Light Detection And Ranging) point clouds. Several object classes (i.e. ground, building and vegetation) can be separated reliably by considering each point's neighbourhood. Based on Conditional Random Fields (CRF) this contextual information can be incorporated into classification process in order to improve results. Since we want to perform a point-wise classification, no primarily segmentation is needed. Therefore, each 3D point is regarded as a graph's node, whereas edges represent links to the nearest neighbours. Both nodes and edges are associated with features and have effect on the classification. We use some features available from full waveform technology such as amplitude, echo width and number of echoes as well as some extracted geometrical features. The aim of the paper is to describe the CRF model set-up for irregular point clouds, present the features used for classification, and to discuss some results. The resulting overall accuracy is about 94 %.

Preliminary Test and Evaluation of Nondestructive Examination for ITER First Wall Development in Korea

ITER first wall (FW) includes a beryllium armour joined to a Cu heat sink with a stainless steel back plate. These FW panels are one of the critical components in the ITER tokamak with a maximum surface heat flux of 5 MW/m2. Therefore, a qualification test needs to be performed with the goal to qualify the joining technologies required for the ITER FW. Various mock-ups were fabricated to develop the manufacturing procedure of FW components. For the nondestructive examination of the fabricated mock-ups, an ultrasonic test (UT) was performed with optimized probes. The UT was performed by using a three-axis digital ultrasonic C-scan system and software. The system comprised an ultrasonic pulser and receiver, model Panametrics 5800PR; a personal computer having an internal analog/digital converter board and four-axis motion control board; and a three-axis scanning tank. Two types of transducers were used for this experiment. One was Panametrics V312-SU, having a center frequency of 10 MHz (nominal) and a piezoelectric element diameter of 0.25 in with a flat protective layer for the Be/Cu. The other was Panametrics V309-SU with a center frequency of 5 MHz and an element diameter of 0.5 in for the Cu/SS interface. Winspect software controlled all aspects of data acquisition, motion control, data archiving, and image display. Based on the acceptance criteria, the average amplitude of the interface signals, which have about 50% of the reference echo amplitude, was recorded and analyzed on each beryllium tile. An image-analysis software analyzed the statistics of amplitude distribution and calculated the unacceptable area. Each mock-up that passed these UTs was concluded to qualify the joining technologies required for an ITER FW by using a high-heat flux test facility. As a result of these qualification tests based on the acceptance criteria of an ITER FW, the fabrication technologies will be utilized to develop the FW of plasma-facing components.

Digital signal processing and numerical analysis for radar in geophysical applications

Numerical solutions for signal processing are described in this work as a contribution to study of echo detection methods for ionospheric sounder design. The ionospheric sounder is a high frequency radar for geophysical applications. The main detection approach has been done by implementing the spread-spectrum techniques using coding methods to improve the radar’s range resolution by transmitting low power. Digital signal processing has been performed and the numerical methods were checked. An algorithm was proposed and its computational complexity was calculated.The proposed detection process combines two channels correlations with the local code and calculates threshold (Vt) by statistical evaluation of the background noise to design a detection algorithm. The noisy signals treatment was performed depending on the threshold and echo amplitude. In each case, the detection was improved by using coherent integration. Synthetic signals, close loop and actual echoes, obtained from the Advanced Ionospheric Sounder (AIS-INGV) at Rome Ionospheric Observatory, were used to verify the process.The results showed that, even in highly noisy environments, the echo detection is possible.Given that these are preliminary results, further studies considering data sets corresponding to other geophysical conditions are needed.

Echo Amplitude Normalization of Full-Waveform Airborne Laser Scanning Data Based on Robust Incidence Angle Estimation

Full-waveform airborne laser scanning has shown increasing utility for earth feature extraction through enhanced physical object recognition. Such data provides users with additional physical observables of the earth's surface. This information has the potential to be exploited alongside geometric information to overcome signal inconsistencies between overlapping flightlines and to improve existing segmentation methodologies. However, because the laser signal is influenced by many variables during travel between the sensor and the target, direct use of this information is not recommended without performing echo amplitude normalization as a function of the incidence angle effect. While existing normalization approaches have proven to be valid over planar features, they tend to perform poorly over nonplanar surfaces. This is primarily due to the lack of robust local surface normal estimation. Realizing these shortcomings, this paper proposes a new echo amplitude normalization approach, where each echo's incidence angle is estimated based on illumination direction and local surface orientation. The local surface orientation estimation method computes the normal to an individual point using the minimum number of points. 3-D moment invariants are used to deliver the normal vector using a weighting function. Thereafter, a vector dot product in 3-D space is adopted to check planarity, ensuring robustness. This method is shown to overcome the weaknesses of existing approaches, performing strongly in challenging areas of rough natural terrain, as well as for planar features. Consequently, this method could be adopted in order to compensate incidence angle effects in any laser scanning physical signals for a range of downstream radiometric calibration and point cloud segmentation applications.

Experimental Evaluation of Quantitative Diagnosis Technique for Hepatic Fibrosis Using Ultrasonic Phantom

Since clinical diagnosis using ultrasonic B-mode images depends on the skill of the doctor, the realization of a quantitative diagnosis method using an ultrasound echo signal is highly required. We have been investigating a quantitative diagnosis technique, mainly for hepatic disease. In this paper, we present the basic experimental evaluation results on the accuracy of the proposed quantitative diagnosis technique for hepatic fibrosis by using a simple ultrasonic phantom. As a region of interest crossed on the boundary between two scatterer areas with different densities in a phantom, we can simulate the change of the echo amplitude distribution from normal tissue to fibrotic tissue in liver disease. The probability density function is well approximated by our fibrosis distribution model that is a mixture of normal and fibrotic tissue. The fibrosis parameters of the amplitude distribution model can be estimated relatively well at a mixture rate from 0.2 to 0.6. In the inversion processing, the standard deviation of the estimated fibrosis results at mixture ratios of less than 0.2 and larger than 0.6 are relatively large. Although the probability density is not large at high amplitude, the estimated variance ratio and mixture rate of the model are strongly affected by higher amplitude data.

The Research of Active Cancellation Stealth System Design

An active cancellation stealth system was designed based on the phased array techni- que, digital radio frequency memory (DRFM) and field programmable gate array (FPGA). Using the off-line calculation method, which establish goals of omnidirectional radar cross- section (RCS) database, clutter and noise database in advance. Signal processing and control module analyzes the measured radar signal parameter , then find the corresponding target echo data in the RCS database, and real-time adjustment of coherent echo amplitude and phase. Make target scattering field and artificial introduced into radiation field coherent cancellation in radar direction, so that the radar receiver is always in nulls synthesis pattern. Through the combination of software and hardware of the method in engineering realization of active cancellation stealth.

Experimental Evaluation of Quantitative Diagnosis Technique for Hepatic Fibrosis Using Ultrasonic Phantom

Since clinical diagnosis using ultrasonic B-mode images depends on the skill of the doctor, the realization of a quantitative diagnosis method using an ultrasound echo signal is highly required. We have been investigating a quantitative diagnosis technique, mainly for hepatic disease. In this paper, we present the basic experimental evaluation results on the accuracy of the proposed quantitative diagnosis technique for hepatic fibrosis by using a simple ultrasonic phantom. As a region of interest crossed on the boundary between two scatterer areas with different densities in a phantom, we can simulate the change of the echo amplitude distribution from normal tissue to fibrotic tissue in liver disease. The probability density function is well approximated by our fibrosis distribution model that is a mixture of normal and fibrotic tissue. The fibrosis parameters of the amplitude distribution model can be estimated relatively well at a mixture rate from 0.2 to 0.6. In the inversion processing, the standard deviation of the estimated fibrosis results at mixture ratios of less than 0.2 and larger than 0.6 are relatively large. Although the probability density is not large at high amplitude, the estimated variance ratio and mixture rate of the model are strongly affected by higher amplitude data.

Coordination of bat sonar activity and flight for the exploration of three-dimensional objects

The unique combination of flight and echolocation has opened the nocturnal air space as a rich ecological niche for bats. By analysing echoes of their sonar emissions, bats discriminate and recognize three-dimensional (3-D) objects. However, in contrast to vision, the 3-D information that can be gained by ensonifying an object from only one observation angle is sparse. To date, it is unclear how bats synchronize echolocation and flight activity to explore the 3-D shape of ensonified objects. We have devised an experimental design that allows creating 3-D virtual echo-acoustic objects by generating in real-time echoes from the bat's emissions that depend on the bat's position relative to the virtual object. Bats were trained to evaluate these 3-D virtual objects differing in their azimuthal variation of either echo amplitude or spectral composition. The data show that through a very effective coordination of sonar and flight activity, bats analyse an azimuthal variation of echo amplitude with a resolution of approximately 16 dB and a variation of echo centre frequency of approximately 19%. Control experiments show that the bats can detect not only these variations but also perturbations in the spatial arrangement of these variations. The current experimental paradigm shows that echolocating bats assemble echo-acoustic object information - acquired sequentially in flight - to reconstruct the 3-D shape of the ensonified object. Unlike previous approaches, the recruitment of virtual objects allows for a direct quantification of this reconstruction success in a highly controlled experimental approach.

High-frequency bottom-pressure and acoustic variations in a sea strait: internal wave turbulence

During a period of 3 days, an accurate bottom-pressure sensor and a four-beam acoustic Doppler current profiler (ADCP) were mounted in a bottom frame at 23 m in a narrow sea strait with dominant near-rectilinear tidal currents exceeding 1 m s−1 in magnitude. The pressure record distinguishes small and short surface waves, wind- and ferry-induced near-surface turbulence and waves, large turbulent overturns and high-frequency internal waves. Typical low-frequency turbulent motions have amplitudes of 50 N m−2 and periods of about 50 s. Such amplitudes are also found in independent estimates of non-hydrostatic pressure using ADCP data, but phase relationships between these data sets are ambiguous probably due to the averaging over the spread of the slanted acoustic beams. ADCP's echo amplitudes that are observed in individual beams show much better phase correspondence with near-bottom pressure, whether they are generated near the surface (mainly air bubbles) or near the bottom (mainly suspended sediment). These 50-s motions are a mix of turbulence and internal waves, but they are not due to surface wave interactions, and they are not directly related to the main tidal flow. Internal waves are supported by stratification varying between extremely strong thin layer and very weak near-homogeneous stratification. They are driven by the main flow over 2-m amplitude sand-wave topography, with typical wavelengths of 150 m.

Dependence of the subharmonic signal from ultrasound contrast microbubbles on ambient pressure

Ultrasound contrast agents (UCA) micro-bubbles have been well recognized as a potential noninvasive tool for blood pressure estimation. However, previous UCA indices, e.g., the shift of the resonance frequency, echo amplitude and the disappearance time, suffered from problems of low resolution, nonlinearity in the relationship with blood pressure, and only variations of the local pressure but the absolute values etc. In this paper, the effect of ambient pressure on UCA sub-harmonic optimal driving frequency (SODF) was investigated, at which the sub-harmonic scattering signals were the maximum. By applying transmit frequencies between 3MHz and 8MHz and the acoustic pressure of 300kPa, the acoustic attenuation and scattering of micro-bubbles were measured at overpressures of 4mmHg, 50mmHg and 100mmHg, comparable with the healthy human blood pressure. For groups of micro-bubbles with 80% in the diameter range of 1-2 micrometers, the shift of the SODF (SSODF) was 0.6MHz between over-pressures of 4mmHg and 100mmHg, which was approximately twice of the corresponding shift of the resonance frequency, thus had an improved sensitivity of pressure estimation. The SSODF of UCA micro-bubbles may be as a novel and sensitive index of the local blood pressure estimation.

Simulation of noninvasive blood pressure estimation using ultrasound contrast agent microbubbles

The microbubble ultrasound contrast agent (UCA) has been widely recognized as a potential noninvasive tool for blood pressure measurement. However, UCA indices such as the shift in the resonance frequency and echo amplitude have problems of low resolution, nonlinear relationship with blood pressure, etc. In this paper, a novel UCA index, the shift in the subharmonic optimal driving frequency (SSODF) of microbubbles, is proposed. The effectiveness of the index for estimating blood pressure was evaluated by performing a microbubble acoustic response simulation. The behavior of commercial UCA microbubbles was investigated as a function of the driving acoustic pressure (in kilopascals) and ambient overpressure (in millimeters of mercury). Simulation results showed that for a 1.6-μm-diameter microbubble, SSODF increased linearly with the overpressure in a range of 0 to 200 mmHg and was maximum (2.07 MHz) at 380 kPa. Changes of the overpressure as small as 5 mmHg can be detected using SSODF. For a population of microbubbles with a Gaussian size distribution (mean diameter: 1.6 μm, standard deviation: 0.2 μm), SSODF was 1.7 MHz at 280 kPa. With further experimental validation, the proposed method may be developed as a novel noninvasive technique for accurate blood pressure measurement.

On-board telemetry of biosonar sounds from free-flying bats

Analysis of the bat's reactions to relevant target echoes enables us to directly assess biosonar performance. Here, we recorded the sonar broadcast and its echoes the bat received during flight by using an on-board telemetry microphone (Telemike) mounted on the bat's back. Telemike recordings confirmed that flying bats adjust the amplitude and frequency of their sonar broadcasts to compensate for increases in echo amplitude and for Doppler-shifts. For insect capturing, the bat exhibited Doppler-shift compensation for echoes from the static target ahead, but not for echoes from the target moth even though the flying bat attended to the moth for capture. Positive and negative Doppler shifts (acoustic glints) caused by insect fluttering were observed in the constant-frequency component of observed echoes, which synchronized with wingbeat cycle of the moth. Combined frequency and amplitude compensation for the static target may be advantageous for detection of acoustic glints of target prey. We also constructed multiple-microphone arrays for tagging wild aerial-feeding insectivorous bats. Not only the location of the bat, but also direction and directivity of the bat's broadcast can be measured. This will allow us to investigate 3-D search algorithm of multiple targets by the bat. [supported by JSPS and ONR]

Findings on bat sonar through Telemike system

In order to understand how bats conduct echolocation recording what they listen to is essential. Then, we developed an onboard wireless telemetry microphone system (Telemike) for flying bats in our flight chamber. We also developed a sensitive microphone array system for field recordings and for the flight chamber. Some data through microphone array with Telemike will also be introduced. Both CF-FM (Hipposideros turpis, Hipposideros terasensis and Rhinolophus ferrumequinum nippon) and FM bats (Pipistrellus abramus, Miniopterus fuliginosus, and Eptesicus fuscus) were used in the flight chamber experiments, while only FM bats (Pipistrellus abramus and Eptesicus fuscus) were used for the field experiments. In the flight chamber experiment, through Telemike Doppler-shift compensation was confirmed from flying CF-FM bats. Echo amplitude compensation was found in both FM and CF-FM bats. The bats can fly without any collision against walls or their conspecifics in a narrow space. Telemike has recorded overlapped echoes originated from adjacent bats. How they extract weak echo signals in the situation where own echoes are masked by echoes of other bats may be revealed by Telemike experiments. Further, how bats get information from extremely weak echoes coming from a flying small insect will also be clarified in our experiments with Telemike. [Research supported by ONR grant]

Spatially resolved extended phase graphs: Modeling and design of multipulse sequences with parallel transmission

A spatially resolved extended phase graph (SR-EPG) framework is proposed for prediction of echo amplitudes in the presence of spatially variable radio frequency (RF) fields. The method may be used to examine any regularly repeating pulse sequence and provides a design framework for parallel transmission (PTx) systems; in this work signal homogeneity in static pseudo-steady state (SPSS) turbo spin echo (TSE) imaging was investigated. Building on SR-EPG calculations with PTx, a dynamic RF-shimming approach is proposed in which, RF pulse amplitudes and phases are optimized on a per channel and per pulse basis to yield the desired signal response for all echoes. Results show significant improvements over "static" RF shimming (in which the relative amplitude/phase of the PTx channels are fixed for all pulses). SPSS-TSE imaging using dynamic RF shimming resulted in excellent image quality, both in phantoms and in vivo, and confirmed SR-EPG predictions.

Optimization of echo amplitudes resulting from a series of 90° pulses in an inhomogeneous static field

In an inhomogeneous static field, the pulse sequence 90°x−(τ−90°y−τ)n results in a train of echoes, the amplitudes of which settle to be proportional to M0/2 after a transient period. Analysis of the spin dynamics of the general τ−β°−τ refocusing cycle reveals that for ideal RF pulses, adding a preparation pulse followed by a delay to the above sequence can either eliminate the transient behavior, or increase the asymptotic echo intensity. This is achieved by controlling the alignment between the magnetization m→ and the rotation axis of the refocusing cycle. The effect of preparations pulses is demonstrated experimentally in the fringe field of a single sided magnet array. It is shown that for this instrument, transient effects in the echo train can be reduced, and asymptotic signal increased. Spin dynamics calculations indicate that the sequences are robust to finite RF pulse widths, but some discrepancy between theory and experiment is observed due to B1 inhomogeneity. Refocusing sequences of the type studied here are useful in cases where experimental considerations, such as RF power limits, preclude the use of a 180° pulse in the refocusing cycle.

Design of Gain Fuzzy Controller for Underwater Trash Detection System Based on FPGA

In order to improve the performance of the underwater trash detection system effectively, the gain fuzzy controller is employed to make programmable gain amplifier work in the optimum status, and its gain will be adjusted according to target distance and echo amplitude in time. The target distance and the echo amplitude are input fuzzy variables, and the amplifier gain is output fuzzy variable. After designing membership functions and fuzzy control rules, defuzzification of the output variable is achieved according to the largest membership degree algorithm. FPGA is used to realize gain fuzzy controller with the inference lookup table, and the system experiments are completed. The results show: the functions of the gain fuzzy controller based on FPGA are implemented correctly, and the design is effectively simplified, and the real-time performance is improved by using the fuzzy inference lookup table.

Non-invasive determination of hepatic steatosis by acoustic structure quantification from ultrasound echo amplitude

To use leptin-deficient (ob/ob) mice with demonstrated differences in steatosis levels to test a new diagnostic method using the acoustical structure quantification (ASQ) mode and the associated analytical parameter, "focal disturbance ratio" (FD-ratio). Nine ob/ob mice, at 5, 8, and 12 wk of age (n = 3 in each age group), were used as models for hepatic steatosis. Echo signals obtained from ultrasonography in the mice were analyzed by ASQ, which uses a statistical analysis of echo amplitude to estimate inhomogeneity in the diagnostic region. FD-ratio, as calculated from this analysis, was the focus of the present study. FD-ratio and fat droplet areas and sizes were compared between age groups. No fibrosis or inflammation was observed in any of the groups. The fat droplet area significantly (P < 0.01) increased with age from 1.25% ± 0.28% at 5 wk to 31.07% ± 0.48% at 8 wk to 51.69% ± 3.19% at 12 wk. The median fat droplet size also significantly (P < 0.01) increased with age, from 1.33 (0.55-10.52) μm at 5 wk, 2.82 (0.61-44.13) μm at 8 wk and 6.34 (0.66-81.83) μm at 12 wk. The mean FD-ratio was 0.42 ± 0.11 at 5 wk, 0.11 ± 0.05 at 8 wk, and 0.03 ± 0.02 at 12 wk. The FD-ratio was significantly lower at 12 wk than at 5 wk and 8 wk (P < 0.01). A significant negative correlation was observed between the FD-ratio and either the fat droplet area (r = -0.7211, P = 0.0017) or fat droplet size (r = -0.9811, P = 0.0052). This tool for statistical analysis of signals from ultrasonography using the FD-ratio can be used to accurately quantify fat in vivo in an animal model of hepatic steatosis, and may serve as a quantitative biomarker of hepatic steatosis.

Reconstruction of Flaws in Heterogeneous Media Using Image-Based FIT and Time Reversal Approach

Most commercial ultrasonic phased array systems implement B– and C–scan methods which use flight time and amplitude of flaw echoes. However, these methods are based on the fundamental ray–tracing theory in homogeneous media, and they are not directly applicable to heterogeneous media because of the complicated phenomenon of wave propagation. Time reversal techniques are adaptive methods that can be used in nondestructive evaluation to improve flaw detection in heterogeneous media. In this study, we propose a simulation–aided flaw imaging method based on the time reversal approach. Scattered waves from a flaw are recorded using an array transducer, and the time–reversed waves are re–emitted in the image–based FIT simulation. The reemitted waves propagate through the heterogeneous media and focus on the flaw. The shape of the flaw can be visually estimated from the focal point of the ultrasonic wave in the simulation.

J042035 超音波探傷試験における材料組織信号を利用したき裂検査法

Ultrasonic inspection has widely used for internal defect detection of material and is more desired for crack detection of structures with importance of safety. However, the inspection capability is insufficient on crack defection due to low amplitude of crack tip echoes. In order to improve detectivity for crack inspection, we evaluate a difference of bscan grass echo images between before and after crack advance using computer simulation. The technique is found useful for crack detection, and is needed an improvement of difference evaluation technique.

Spin-alignment echo NMR: probing Li+ hopping motion in the solid electrolyte Li7La3Zr2O12 with garnet-type tetragonal structure **Dedicated to Professor Dr Paul Heitjans on the occasion of his 65th birthday.

7Li spin-alignment echo (SAE) nuclear magnetic resonance (NMR) spectroscopy has been used to measure single-spin hopping correlation functions of polycrystalline Li7La3Zr2O12. Damping of the echo amplitude S2(tm,tp), recorded at variable mixing time tm but fixed preparation time tp, turns out to be solely controlled by slow Li jump processes taking place in the garnet-like structure. The decay rates directly obtained by parametrizing the curves S2(tm,tp) with stretched exponential functions show Arrhenius behaviour pointing to an activation energy of approximately 0.5 eV. This value, probed by employing an atomic-scale NMR method, is in very good agreement with that deduced from impedance spectroscopy used to measure macroscopic Li transport parameters. Most likely, the two methods are sensitive to the same hopping correlation function although Li dynamics are probed in a quite different manner.