Echo Waveform Research Articles

Research on Chromatography Feature Extraction from Echo Waveforms of Coherent Radar Targets

Research on Chromatography Feature Extraction from Echo Waveforms of Coherent Radar Targets

A new sense-through-foliage target recognition method based on hybrid particle swarm optimization-based wavelet twin support vector machine

In order to improve the accuracy of sense-through-foliage target recognition, a new recognition method based on sparse representation-based adaptive feature extraction and hybrid particle swarm optimization (HPSO)-optimized wavelet twin support vector machine (WTSVM) is proposed in this paper. First, an adaptive feature extraction approach based on sparse representation is applied to extract the target features from the measured radar echo waveforms, the target feature set is constructed by sparse coefficients that contain most target information. Then, a new recognition method based optimized WTSVM is developed to perform target recognition. Twin SVM (TSVM) is a powerful tool in the field of machine learning, but the kernel and parameters selection problem still affects the performance of TSVM directly. A novel HPSO is developed in this study to determine the optimal parameters for WTSVM with the highest accuracy and generalization ability. As a hybridization strategy, local search is integrated in the PSO algorithm to further refine the performance of individuals and accelerate their convergence toward the global optimality. Finally, the performance of the proposed method is verified by experiments taken in the forest, and the results conform the improved accuracy of target recognition.

Validation of AltiKa Matching Pursuit Rain Flag

The major drawback of Ka band, operating frequency of the AltiKa altimeter on board SARAL, is its sensitivity to atmospheric liquid water. Even light rain or heavy clouds can strongly attenuate the signal and distort the signal leading to erroneous geophysical parameters estimates. A good detection of the samples affected by atmospheric liquid water is crucial. As AltiKa operates at a single frequency, a new technique based on the detection by a Matching Pursuit algorithm of short scale variations of the slope of the echo waveform plateau has been developed and implemented prelaunch in the ground segment. As the parameterization of the detection algorithm was defined using Jason-1 data, the parameters were re-estimated during the cal-val phase, during which the algorithm was also updated. The measured sensor signal-to-noise ratio is significantly better than planned, the data loss due to attenuation by rain is significantly smaller than expected (<0.1%). For cycles 2 to 9, the flag detects about 9% of 1Hz data, 5.5% as rainy and 3.5 % as backscatter bloom (or sigma0 bloom). The results of the flagging process are compared to independent rain data from microwave radiometers to evaluate its performances in term of detection and false alarms.

An approximate model for foliage echoes to study biosonar function in natural environments

Natural environments are difficult for current engineered sonars but apparently easy for at least some species of echolocating bats. To better understand the information that foliage echoes provide for biosonar-based sensing, an approximate model of foliage echoes has been developed. The model simplifies the scattering problem through two key assumptions: (i) multi-path scattering was neglected and (ii) all leaves were assumed to be circular disks. Due to the latter, the parameters of the model were reduced to the number of the disks, their positions, sizes, and orientations. The exact far-field scatter from a disk (i.e., simplified leaf) in response to planar incident waves can be obtained by summation over an infinite series of spheroidal wave functions. To reduce the calculation time, the scattered field has been approximated by exponential, polynomial, and cosine fitting functions that also depend on the disk parameters. This allows the simulation of echoes from 100 leaves in 20 s on a standard PC. The model was able to reproduce the echo waveforms from dense and sparse foliages qualitatively. The model should thus be well suited for generation of large echo datasets to explore the existence and utilization of statistical invariants in the echoes from natural environments.

High-range-resolution imaging using frequency domain interferometry with stabilization techniques for real-time vascular ultrasound

In the present study, we employed two techniques to acquire high-range-resolution images of human carotid arteries in vivo using frequency domain interferometry and the Capon method. One technique ensures the robust depiction of artery interfaces; the other suppresses the deterioration of the imaging performance due to variation of the echo waveform. We applied the proposed method to raw data obtained using a commercial ultrasonographic device with a 7.5 MHz linear array probe. Our method succeeded to depict a horizontal 0.15-mm-thick agar membrane stably, and the standard deviation of the estimated depth was suppressed to 26.7% of that obtained using the conventional method. Our method also succeeded in acquiring high-range-resolution images of six human carotid arteries in vivo. Requiring 0.06 s on a desktop PC with a single CPU for a 1 × 2 cm region of interest, our method is suitable for real-time imaging.

Definition of Shifts of Optical Transitions Frequencies due to Pulse Perturbation Action by the Photon Echo Signal Form

A relative phase shift between the different groups of excited dipoles, which appears as result of its frequency splitting due to action of a pulse of electric or magnetic fields, depends on a time, if the pulse overlaps in time with echo-pulse. As а consequence, the echo waveform is changed. The echo time form is modulated. The inverse modulation period well enough approximates Zeeman and pseudo-Stark splitting in the cases of magnetic and, therefore, electrical fields. Thus the g-factors of ground 4 I15/2 and excited 4 F9/2 optical states of Er3+ ion in LuLiF4 and YLiF4 have been measured and pseudo-Stark shift of R1 line in ruby has been determined.

Anthropogenic pressure on the open ocean: The growth of ship traffic revealed by altimeter data analysis

AbstractMarine ecosystems are under increasing anthropogenic pressures from marine and terrestrial activities. Ship traffic, the major cause of change in the open ocean, and its temporal evolution are still largely unknown because of lack of data. Altimeter data provide a new powerful tool to detect and monitor the ship traffic through a method of analysis of echo waveform. The archive of seven altimeter missions has been processed to create a two decade database of ship locations. The estimated annual density maps compare well with the ones obtained from Automatic Identification System. The ship traffic analysis shows a global fourfold growth between 1992 and 2012, the largest increase being observed in the Indian Ocean and the Chinese seas reflecting the world trade change. Although mainly concentrated along lanes, the traffic has a direct impact on the atmosphere, e.g., on the growth of tropospheric nitrogen dioxide in the Indian Ocean.

A new sense-through-foliage target recognition method based on hybrid differential evolution and self-adaptive particle swarm optimization-based support vector machine

Sense-through-foliage target detection and recognition is of interest to both military and civilian research. In this paper, a new recognition method based on hybrid differential evolution and self-adaptive particle swarm optimization-based support vector machine (SVM) is proposed to recognize targets obscured by foliage. To seek the optimal parameters of SVM, a new hybrid differential evolution and self-adaptive particle swarm optimization (DEPSO) algorithm is developed to determine the optimal parameters for SVM with the highest accuracy and generalization ability. In this work, sparse representation is applied to extract the target features from real target echo waveforms measured by a bistatic ultra-wideband (UWB) radar system. Then, the extracted features are input into the proposed method to automatically recognize the types of targets. This method is validated by experiments taken in the forest environment. Compared with the commonly used particle swarm optimization-optimized SVM (PSO-SVM), SVM, k-nearest neighbor (KNN) and BP neural network (BPNN), the proposed DEPSO-SVM can achieve a higher accuracy. Experimental results demonstrate the effectiveness and robustness of the proposed method for sense-through-foliage target recognition.

Computer Simulation of Broadband Single-target Echo Waveforms and its Application

Computer Simulation of Broadband Single-target Echo Waveforms and its Application

Experimental Ultrasonic Assessment of Steel Induction Hardening by Measuring Two Distinct Times-of-Flight

Ultrasonic NDE of case hardening of steel parts presents an attractive alternative to destructive assessment still used in industry. This experimental study showed that the ultrasonic assessment could be conducted by measuring two average times of flight across different dimensions of a hardened test sample. The consistently observed difference in the corresponding average ultrasound velocities was above the estimated accuracy of the measurements, and the scattered individual calculated values formed distinct clusters. The results were obtained by using a high resolution data acquisition instrument with the equivalent sampling frequency of 1.5 GHz and 512 averages, and differential measurements of the time of flight by determining zero crossings of the echo waveforms.

Design of a Signal Processing System for Digital Laser Altimeter

Laser altimeters are used to measure the elevation and detect the topography of terrain, which have been widely applied in military and civilian field. In the course of measurement, errors will inevitably generate as a result of ground settlement, surface relief and tilt, etc. In order to reduce measurement errors, the technology of laser waveform digitalization was researched. Firstly, the principle of error generation was introduced. Secondly, the basic scheme of signal processing system for digital laser altimeter was present. System components and signal processing procedure were researched. Next, the technology of extracting echo waveform parameters was discussed. Finally the method of using digital waveform parameters to correct measurement errors was provided. The principle of target classification and identification based on echo waveform parameters was introduced also.

Dolphin strategies for long-range object detection and change detection

Dolphin strategies for detecting objects and changes in objects were investigated by having three trained bottlenose dolphins perform long-range echolocation tasks. The tasks featured the use of “phantom” echoes produced by capturing the dolphin’s outgoing echolocation clicks, convolving the clicks with the impulse response of a physical target to create an echo waveform, then broadcasting the delayed, scaled echo waveform back to the dolphin. Dolphins were trained to report the presence of phantom echoes or a change in phantom echoes. Target simulated ranges varied from 25 to 800 m. At ranges below 75 m, all dolphins followed a single click-echo paradigm, where inter-click intervals exceeded the two-transit time (i.e., the dolphins waited to receive the echo from a click before emitting the next click). As the range increased beyond 75 m, two of the three dolphins increasingly produced bursts, or “packets,” of several clicks, then waited for the packet of echoes to return before emitting another packet of clicks. The third dolphin instead utilized very high click repetition rates. The use of click packets may be a response to a limitation in the dolphin’s ability to employ multi-echo processing with large inter-echo delays.

Dolphin “packet” use during long-range echolocation tasks

When echolocating, dolphins typically emit a single broadband "click," then wait to receive the echo before emitting another click. However, previous studies have shown that during long-range echolocation tasks, they may instead emit a burst, or "packet," of several clicks, then wait for the packet of echoes to return before emitting another packet of clicks. The reasons for the use of packets are unknown. In this study, packet use was examined by having trained bottlenose dolphins perform long-range echolocation tasks. The tasks featured "phantom" echoes produced by capturing the dolphin's outgoing echolocation clicks, convolving the clicks with an impulse response to create an echo waveform, and then broadcasting the delayed, scaled echo to the dolphin. Dolphins were trained to report the presence of phantom echoes or a change in phantom echoes. Target range varied from 25 to 800 m. At ranges below 75 m, the dolphins rarely used packets. As the range increased beyond 75 m, two of the three dolphins increasingly produced packets, while the third dolphin instead utilized very high click repetition rates. The use of click packets appeared to be governed more by echo delay (target range) than echo amplitude.

Modeling of Ultrasonic Echo Waveform of Arterial Wall for Accurate Boundary Detection

Modeling of Ultrasonic Echo Waveform of Arterial Wall for Accurate Boundary Detection

Earth Rotation Effect on Satellite Synthetic Aperture Altimeter

Compared with the conventional radar altimeter,the synthetic aperture altimeter that uses the synthetic aperture technology in along track is a new-concept altimeter.As the delay compensation is corrected in the Doppler domain in the data processing,it is important to know the Doppler properties of the return waves.The formula about Doppler frequency is deduced from the relative velocity of the radar and the scatting point.As a result,the Doppler frequency from the earth rotation has an important effect on the echo waveform,measuring accuracy and effective number of look for satellite synthetic aperture altimeter.These must be considered in the delay compensation,system design and signal processing.

Application of Adaptive Wavelet Thresholding to Ultrasonic Signal Compression of Aluminum Alloy Forgings

In this paper, for the purpose of ultrasonic signal compression and the coherent noise depressing in nondestructive test of aluminum alloy forging, the mathematical model of defect echoes is discussed and confirmed. And then the wavelet kernel is also confirmed according the waveform of the defect echoes. As the algorithms of standard hard thresholding and soft thresholding of wavelet transform can not bring out effective compression and depression to the coherent noise, an adaptive wavelet thresholding algorithm is introduced. Experimental results indicate that the adaptive wavelet thresholding algorithm can offer effective signal compression and depression to the coherent noise.

Dolphins use “packets” of broadband clicks during long range echolocation tasks

When echolocating, dolphins typically emit a single short duration, high-frequency, broadband “click,” then wait for the echo to return before emitting another click. However, previous studies have shown that dolphins and belugas performing long-range echolocation tasks may instead emit a burst, or “packet,” of several clicks, then wait for the packet of echoes to return before emitting another packet of clicks. The exact reasons for the use of packets, rather than individual clicks, is unknown. In this study, the use of packets by dolphins was examined by having trained bottlenose dolphins perform long-range echolocation tasks. The tasks featured the use of “phantom” echoes produced by capturing the dolphin’s outgoing echolocation clicks, convolving the clicks with the impulse response of a physical target to create an echo waveform, then broadcasting the delayed, scaled echo waveform back to the dolphin. Dolphins were trained to report the presence of phantom echoes or a change in phantom echoes. At ranges below 75 m, the dolphins rarely used packets of clicks. For ranges greater than 75 m, the likelihood of packet use was related to both target range and echo strength. [Work supported by the SSC Pacific Naval Innovative Science and Engineering (NISE) program.]

Realtime face recognition system with ultrasonic sensing

Unlike vision-based approaches, ultrasonic sensing systems have the ability to obtain the object distance and echo energy information. With the development of airborne ultrasonic detection, ultrasonic face recognition has been discussed. However, the existing ultrasonic face recognition systems store the echo waveform data and make processing and analysis afterwards. Seperated acquisition and analysis procedures make these systems non-realtime. In this paper, a realtime ultrasonic face recognition system is proposed. The system has the following functions: signal generation, transmitting, receiving, amplification, demodulation, spectral analysis, and feature extraction. A continuous wideband ultrasonic signal is transmitted, then the geometrical information can be extracted from the echo signal, and suitable pattern recognition methods are used to recognize human face. The system can implement realtime face recognition with ultrasonic sensing, and a considerable recognition rate is achieved.

Small calcification indicator in ultrasonography using correlation of echoes with a modified Wiener filter.

The purpose of this study is to improve the calcification depiction ability in ultrasonography using correlation of echoes with a modified Wiener filter. The waveform of an ultrasound pulse changes when it passes through the location of a calcification. Since the change in echo waveform caused by a calcification decreases the correlation of waveforms in adjacent scan lines, we have proposed a calcification depiction method using the decorrelation of echoes. However, the low signal-to-noise ratio of echoes also decreases the correlation of the echoes. In this study, we employ the correlation of echoes with a modified Wiener filter to suppress the effect of noise, as an indicator of a calcification. The proposed calcification indicator depicted copper cylindrical rods 0.2mm in size at a depth of 2cm with a sensitivity of 80% and a positive predictive value of 80%, despite being hardly depicted at all on B-mode ultrasound imaging. This study suggests the potential of the proposed method to improve the performance of calcification depiction by ultrasound devices.

High-Resolution Imaging of the Ocean Surface Backscatter by Inversion of Altimeter Waveforms

Abstract This paper presents a new method to analyze high-resolution altimeter waveforms in terms of surface backscatter. Over the ocean, a basic assumption of modeling altimeter echo waveforms is to consider a homogeneous sea surface within the altimeter footprint that can be described by a mean backscatter coefficient. When the surface backscatter varies strongly at scales smaller than the altimeter footprint size, such as in the presence of surface slicks, rain, small islands, and altimeter echoes can be interpreted as high-resolution images of the surface whose geometry is annular and not rectangular. A method based on the computation of the imaging matrix and its pseudoinverse to infer the surface backscatter at high resolution (~300 m) from the measured waveforms is presented. The method is tested using synthetic waveforms for different surface backscatter fields and is shown to be unbiased and accurate. Several applications can be foreseen to refine the analysis of rain patterns, surface slicks, and lake surfaces. The authors choose here to focus on the small-scale variability of backscatter induced by a submerged reef smaller than the altimeter footprint as the function of tide, significant wave height, and wind.