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The performance of Doppler velocity logs (DVLs) in terms of velocity estimate error is directly linked to the geometry of the beam and the pulse transmitted. Beyond a specific transmitted bandwidth, the phase‐shift beamformer can introduce significant errors in velocity estimation. To delineate the operating mechanism of phase‐shift errors within a phased array of acoustic DVLs, the correlation between bottom echo and velocity distribution, in conjunction with the power‐weighted function, was initially examined predicated on spectral estimation theory. Subsequently, numerical and analytical models of the Gaussian‐shaped Doppler spectrum were formulated. The models are employed to evaluate the velocity estimation inaccuracies attributed to phase shifts in extant DVLs, and the comparative results with field experiments corroborate the model's efficacy in forecasting errors. The theoretical findings evaluate the performance limitations of the current phased array transducer design and provide insights for developing new designs. Pool experimental results show that this design effectively reduces the velocity estimation error caused by phase shift under static conditions and in the presence of Doppler frequencies to a level of almost complete elimination of the error compared to conventional configurations. [ABSTRACT FROM AUTHOR]

Sea surface wind, waves, and currents are the three basic parameters that describe the dynamic process of sea surface, and they are coupled with each other. To more accurately describe large-scale ocean motion and extract the ocean dynamic parameters, we adopt the spaceborne Doppler measurement to estimate the radial Doppler velocity generated by the sea surface motion. Due to the presence of wind and waves, the Doppler spectrum will be formed, shifted and broadened. Pulse-pair phase interference is used to obtain the Doppler spectrum from the sea surface echo. We simulate the Doppler spectrum with different look geometry and ocean states in a spaceborne condition. In this paper, the Doppler centroid variations are estimated after reducing the platform Doppler velocity under different observation conditions. With the increase in wind speed, the measured Doppler shift increases, and the simulated Doppler centroid accuracy is estimated. In addition, the measurement error along the trace direction is at the maximum, and the error in the cross-track is the smallest. At moderate wind-wave conditions, the Doppler velocity offset can be less than 0.1 m/s. [ABSTRACT FROM AUTHOR]

Specifying parameters of high‐speed targets as range and velocity in radar systems operating with phase‐modulated signals is a problematic process because of the serious effect of high Doppler frequency on these types of waveforms. In the existence of a high‐speed target, its Doppler frequency will be very high such that it totally changes the phase sequence of the received signal. As a result, the matched filter output will be distorted. Therefore, estimating target parameters will be impossible. In this letter, a new method is proposed for detecting and estimating velocity of high speed targets using phase‐modulated signals. The suggested technique methodology depends on compensating the target high‐Doppler frequency for signal recovery using a customized waveform shape. Moreover, the Doppler frequency value is estimated without ambiguity from one pulse, and without the need for a range‐Doppler module. As such, the implementation of the proposed method is simple and inexpensive. The performance evaluation of the new method shows its superiority in compensation and estimation compared to other techniques when examined under higher Doppler frequency and noise compared to the conventional radar.The paper presents a new method for detecting high‐speed targets, and super‐sonic vehicles using phase‐modulated waveforms. The proposed technique depends on a customized waveform shape for compensating the target high‐Doppler frequency when received in the Doppler compensation module. Moreover, the Doppler frequency information is estimated from one pulse for determining the target velocity in the Doppler estimation module. [ABSTRACT FROM AUTHOR]

Abstract Specifying parameters of high‐speed targets as range and velocity in radar systems operating with phase‐modulated signals is a problematic process because of the serious effect of high Doppler frequency on these types of waveforms. In the existence of a high‐speed target, its Doppler frequency will be very high such that it totally changes the phase sequence of the received signal. As a result, the matched filter output will be distorted. Therefore, estimating target parameters will be impossible. In this letter, a new method is proposed for detecting and estimating velocity of high speed targets using phase‐modulated signals. The suggested technique methodology depends on compensating the target high‐Doppler frequency for signal recovery using a customized waveform shape. Moreover, the Doppler frequency value is estimated without ambiguity from one pulse, and without the need for a range‐Doppler module. As such, the implementation of the proposed method is simple and inexpensive. The performance evaluation of the new method shows its superiority in compensation and estimation compared to other techniques when examined under higher Doppler frequency and noise compared to the conventional radar.

For radar target tracking with non‐linear measurements, a sequential linear filtering method is proposed in this study, which includes a linear filter based on the position measurements and a linear sequential filter based on the range rate measurement. The linear radar measurement equation in the sequential filter is estimated based on the position filtering result. Furthermore, the feedback information during tracking is adaptively selected according to the quality of the angle measurements. When tracking the manoeuvring target, the proposed sequential linear filtering with adaptive information feedback is combined with the interacting multiple model (IMM) framework, and the IMM filter based on sequential linear filtering with adaptive model probability selection is proposed. Simulation results demonstrate the effectiveness of the proposed algorithms in non‐manoeuvring and manoeuvring target tracking. Compared with traditional algorithms, the tracking performance is improved by the proposed algorithms in both typical non‐manoeuvring and manoeuvring scenes. [ABSTRACT FROM AUTHOR]

• PSFBG-enhanced achieves an impressive enhancement of up to 800 times compared to unenhanced signals. • PSFBG is applied to detect surfaces with lower reflectivity. • The spatial measurement range has been improved, achieving long-distance detection. • Application of PSFBG-enhanced signal in non-contact Doppler measurement. In this paper, phase-shifted fiber Bragg grating (PSFBG) is introduced in an all-fiber laser self-mixing interferometry (SMI) for signal enhancement. PSFBG is used as an optical filter to enhance the signal to noise ratio (SNR) of SMI signal. When the laser wavelength locates at the edge of the filter, the frequency modulation (FM) can be mapped to the easy-to-detect amplitude modulation (AM) to enhance the SMI signal. Simulation and experimental comparison of unenhanced SMI signal, FBG-enhanced SMI signal and PSFBG-enhanced SMI signal are presented. The enhancement effects of different reflectivity surfaces are comparatively analyzed and the maximum spatial test ranges of lower reflectivity surfaces are compared between unenhanced and PSFBG-enhanced. As well as applying the PSFBG-enhanced to the Doppler effect experiment. Due to the extremely narrow linewidth of PSFBG, the PSFBG-based SMI has the better performance in longer detection range and lower backscattering light. PSFBG-enhanced achieves an impressive enhancement of up to 800 times compared to unenhanced signals. [ABSTRACT FROM AUTHOR]

Obtaining high‐precision Doppler frequencies for very weak and high‐dynamic signals in deep space exploration is challenging. Such signals are commonly encountered, including in soft landing of lunar probes and the entry, descent, and landing (EDL) phase of Mars probes. Phase‐locked loop (PLL) is a widely used method for measuring high‐precision Doppler frequencies. In this study, two major improvements are applied to PLL. The first is that high precision estimation of initial frequency is achieved by open loop maximum amplitude search algorithm. Second, a novel denoising method is proposed and a new type of phase detector is designed based on this new denoising method. By replacing arctangent phase detector with the novel phase detector, the tracking accuracy and weak‐signal tracking abilities of the PLL are improved. The actual data processing results of soft landing process of lunar probe further verify the excellent performance of the improved PLL. Key Points: A novel low pass denoising method is proposedA improved PLL with excellent performance is achievedThe proposed method is suitable for high‐precision carrier tracking in deep space exploration, especially for high‐dynamic and weak signals [ABSTRACT FROM AUTHOR]

Motion estimation is critical for the localization of autonomous underwater vehicles. Current SONAR-based techniques exclusively utilize either Doppler or spatial measurements. However, these measurement domains are complementary to each other; Doppler measurements directly measure radial motion, whereas spatial measurements uniquely observe angular motion. Therefore, this article presents SONARODO (SONAR Odometry), a novel real-time motion estimation algorithm for 2-D forward-looking SONARs. It depends on a largely decoupled motion estimation process that better utilizes each measurement domain for their respective strengths. Specifically, it estimates translational motion from Doppler-azimuth images and rotational motion from range-azimuth images. While this method does require a SONAR that can provide both image types, it was designed to ensure robustness to featureless seafloor environments and low-resolution images. This article's validation with high-fidelity simulation data demonstrated that SONARODO offers accuracy and computational cost advantages over related motion estimation techniques. [ABSTRACT FROM AUTHOR]

In this letter, a radar target simulator (RTS) for the generation of targets for frequency modulated continuous wave (FMCW) chirp sequence radar in the close range of a vehicles surroundings is presented. Key interest is the reproduction of micro-Doppler signatures of vulnerable road users, for example, pedestrians or cyclists. The received $E$ -band radar signal is first converted from the RF band to an IF band, in which the target is manipulated by modulating a range and velocity profile with an IQ modulator. To generate arbitrary signals forms, a PC controlled digital to analog converter (DAC) is used. The RTS has no delay lines to simulate the range, instead it is modulated directly. This allows the distance to be set individually for a large number of targets. In this contribution, the system itself and the underlying concept for the range generation are presented. Finally, measurements of generated static targets and micro-Doppler-signatures are shown. [ABSTRACT FROM AUTHOR]

The 2-D sparse arrays, in which a few hundreds of elements are distributed on the probe surface according to an optimization procedure, represent an alternative to full 2-D arrays, including thousands of elements usually organized in a grid. Sparse arrays have already been used in B-mode imaging tests, but their application to Doppler investigations has not been reported yet. Since the sparsity of the elements influences the acoustic field, a corresponding influence on the mean frequency (Fm), bandwidth (BW), and signal-to-noise ratio (SNR) of the Doppler spectra is expected. This article aims to assess, by simulations and experiments, to what extent the use of a sparse rather than a full gridded 2-D array has an impact on spectral Doppler measurements. Parabolic flows were investigated by a 3 MHz, 1024-element gridded array and by a sparse array; the latter was obtained by properly selecting a subgroup of 256 elements from the full array. Simulations show that the mean Doppler frequency does not change between the sparse and the full array while there are significant differences on the BW (average reduction of 17.2% for the sparse array, due to different apertures of the two probes) and on the signal power (Ps) (22 dB, due to the different number of active elements). These results are confirmed by flow phantom experiments, which also highlight that the most critical difference between sparse and full gridded array in Doppler measurements is in terms of SNR (−16.8 dB). [ABSTRACT FROM AUTHOR]

This paper presents new closed-form estimators for 3-D source localization using Doppler measurements collected by a moving sensor platform. Two estimators, based on bias compensation and instrumental variables, are developed with significant performance improvement over a previously proposed least-squares estimator (LSE). First, a refined variant of the LSE, called bias-compensated weighted LSE (BCWLSE), is presented utilizing a weighting matrix and a bias compensation step. A weighted instrumental variable estimator is then developed based on a modified pseudolinear equation for the LSE to avoid pseudolinear noise amplification that may deteriorate the BCWLSE performance at large noise. Comparative simulation studies are presented to demonstrate the performance advantages of the proposed estimators over the severely biased LSE and divergence-prone maximum likelihood estimator. The proposed estimators are observed to produce almost no bias and achieve a mean-squared-error performance close to the Cramér–Rao lower bound. [ABSTRACT FROM AUTHOR]

This paper shows initial results from estimating Doppler radial surface velocities (RVLs) over Arctic sea ice using the Sentinel-1A (S1A) satellite. Our study presents the first quantitative comparison between ice drift derived from the Doppler shifts and drift derived using time-series methods over comparable time scales. We compare the Doppler-derived ice velocities with global positioning system tracks from a drifting ice station as well as vector fields derived using traditional cross correlation between a pair of S1A and Radarsat-2 images with a time lag of only 25 min. A strategy is provided for precise calibration of the Doppler values in the context of the S1A level-2 ocean RVL product. When comparing the two methods, root-mean-squared errors (RMSEs) of 7 cm/s were found for the extra wide (EW4) and EW5 swaths, while the highest RMSE of 32 cm/s was obtained for the EW1 swath. Though the agreement is not perfect, our experiment demonstrates that the Doppler technique is capable of measuring a signal from the ice if the ice is fast moving. However, for typical ice speeds, the uncertainties quickly grow beyond the speeds we are trying to measure. Finally, we show how the application of an antenna pattern correction reduces a bias in the estimated Doppler offsets. [ABSTRACT FROM AUTHOR]

Laser Doppler velocimetry (LDV) is a high precision instrument based on the Doppler effect of a laser, and it would greatly improve the performance of vehicle navigation and vehicle velocity metrology for its advantages. To reduce the measurement error produced by a jolt of a vehicle, a novel Janus‐configured all fibre LDV is designed. The system comprising two independent interferometers is connected by 1.55 μm single mode fibre devices. Road experiments are carried out to compare the performances of the microwave radar, single beam LDV and Janus‐configured LDV. The Janus‐configured LDV is reliable to measure the velocity of the vehicle and its root‐mean‐square error is 0.0222 m/s, while it is 0.0284 m/s for the single beam LDV. The results validate that the designed LDV can achieve improved performance of vehicle velocity measurement. [ABSTRACT FROM AUTHOR]

The combination of celestial measurement and ground Doppler measurement has been successfully used for orbit determination in many deep-space exploration missions. However, one of the inherent drawbacks of ground tracking is the long communication delay. Using the Doppler measurement from the sun instead of the ground station is a feasible strategy for real-time navigation, but the accuracy of this Doppler measurement is affected by the frequency fluctuation of the solar spectrum. To solve this problem, a differential Doppler measurement-aided celestial navigation method is proposed in this paper, which uses the differential Doppler measurement to reduce the influence caused by instability of the solar spectrum frequency and improve the navigation accuracy. Simulations demonstrate the feasibility and effectiveness of this method. [ABSTRACT FROM PUBLISHER]

A Doppler shift measurement system based on four-wave mixing effect in a highly nonlinear fiber is demonstrated practically. The system exhibits two low-frequency voltages, which are functions of the Doppler shift, and therefore, low-cost low-frequency photodetectors can be employed in the system. No sophisticated electrical instrument is required to perform the measurement. The scheme is able to simultaneously and independently measure the Doppler frequency of a radar echo and its power level with carrier frequency up to 40 GHz. The system is suitable to be employed in any microwave photonics (MWP) radar system with broad frequency agility characteristics or the other MWP systems operating based on frequency hopping technique. [ABSTRACT FROM AUTHOR]

Ultrasonic Doppler-based systems for surface topography measurements are attractive alternatives to the transit-time-based methods. Sensors used in Doppler systems are less dependent on the speed of the sound in air, although contemporary Doppler measurement systems are sensitive to the amplitude variation of the received signal. Amplitude variation significantly affects the measurement accuracy when the surface axial displacement range is comparable with the ultrasonic wavelength. This paper presents a theoretical and experimental study of the effect of amplitude modulation on the performance of the Doppler measurement techniques. A modified Doppler measurement system that significantly improves the measurement accuracy is also presented. The fabricated sensor has 72- \mu \textm measurement accuracy using 40-kHz transducers. This technique can also be employed in cost-effective displacement measurement applications that require high axial resolution. [ABSTRACT FROM AUTHOR]

A moving target creates the Doppler effect on the transmitted signal, which can be exploited to improve the target localization accuracy in multistatic sonar that normally utilizes differential delay time measurements only. In this letter, we first examine the contribution of Doppler measurements via the Cr \acute\textamer–Rao lower bound (CRLB) study, and then develop an algebraic closed-form solution for the moving target localization problem. The proposed algorithm is shown in both theory and simulation to be able to reach the CRLB performance under Gaussian noise, when the measurement error is small. [ABSTRACT FROM PUBLISHER]

A standalone microwave photonics system for Doppler frequency measurement purposes is conceived and demonstrated practically. The system exhibits a maximum of 1.61% relative error in Doppler frequency estimation at the worst case. Utilization of all optical mixing has enabled RF frequency independent operation. The system is thus capable of operating at any radar carrier frequency up to 40 GHz. This makes it a perfect candidate for various types of photonic-based radars and frequency agility systems. [ABSTRACT FROM PUBLISHER]

Purpose: The objective of this project is to demonstrate the principle and operation for a simple, inexpensive, and highly portable Doppler ultrasound quality assurance (QA) phantom intended for routine QA testing. A prototype phantom has been designed, fabricated, and evaluated. The phantom described here is powered by gravity alone, requires no external equipment for operation, and produces a stable fluid velocity useful for quality assurance. Many commercially available Doppler ultrasound testing systems can suffer from issues such as a lengthy setup, prohibitive cost, nonportable size, or difficulty in use. This new phantom design aims to address some of these problems and create a phantom appropriate for assessing Doppler ultrasound stability. Methods: The phantom was fabricated using a 3D printer. The basic design of the phantom is to provide gravity-powered flow of a Doppler fluid between two reservoirs. The printed components were connected with latex tubing and then seated in a tissue mimicking gel. Spectral Doppler waveforms were sampled to evaluate variations in the data, and the phantom was evaluated using high frame rate video to find an alternate measure of mean fluid velocity flowing in the phantom. Results: The current system design maintains stable flow from one reservoir to the other for approximately 7 s. Color Doppler imaging of the phantom was found to be qualitatively consistent with laminar flow. Using pulsed spectral Doppler, the average fluid velocity from a sample volume approximately centered in the synthetic vessel was measured to be 56 cm/s with a standard deviation of 3.2 cm/s across 118 measurements. An independent measure of the average fluid velocity was measured to be 51.9 cm/s with a standard deviation of 0.7 cm/s over 4 measurements. Conclusions: The developed phantom provides stable fluid flow useful for frequent clinical Doppler ultrasound testing and attempts to address several obstacles facing Doppler phantom testing. Such an ultrasound phantom can make routine testing more approachable for institutions that wish to initiate a Doppler QA program or complement a previously existing QA program. [ABSTRACT FROM AUTHOR]

We demonstrate a new method to recover 4D blood flow over the entire ventricle from partial blood velocity measurements using multiple 3D+t colour Doppler images and ventricular wall motion estimated using 3D+t BMode images. We apply our approach to realistic simulated data to ascertain the ability of the method to deal with incomplete data, as typically happens in clinical practice. Experiments using synthetic data show that the use of wall motion improves velocity reconstruction, shows more accurate flow patterns and improves mean accuracy particularly when coverage of the ventricle is poor. The method was applied to patient data from 6 congenital cases, producing results consistent with the simulations. The use of wall motion produced more plausible flow patterns and reduced the reconstruction error in all patients. [ABSTRACT FROM AUTHOR]

Purpose: Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length. Methods: The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4; large ring: 6), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats. Results: In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as -0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02±0.31μl/min among four wild-type rats. The authors' measured flow rates were consistent with results in the literature. Conclusions: By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length. [ABSTRACT FROM AUTHOR]

Antenna-pointing techniques that rely on Earth's surface Doppler velocity measurements are expected to play a crucial role in enabling antenna mispointing corrections in spaceborne radar systems. Here, the impact of the EarthCARE cloud profiling radar (CPR) receiver saturation on the quality of the surface Doppler velocity measurements is discussed. The CPR linear receiver is expected to saturate always from surface echoes. Our results based on an I/Q simulation framework show that for the EarthCARE radar configuration: 1) biases introduced by saturation will be negligible; 2) the standard deviation of the velocity estimates will increase by 30-50% when moving from unsaturated to completely saturated surface return for a corresponding pulse repetition frequency in the range between 6.1 and 7.5 kHz. As a consequence longer integration times will be necessary to achieve the same accuracy in presence of complete saturation. [ABSTRACT FROM PUBLISHER]

This paper describes the development of a simple low-cost adjustable radar cross section (RCS) Doppler calibration target. It consists of a small metal sphere attached to the diaphragm of an ultrasound transducer. It is shown that the effective RCS of the target is a function of the physical RCS determined by the size of the sphere, and the magnitude of the displacement introduced by the transducer. A simple Michelson's interferometer was constructed to determine the magnitude of these displacements, and a linear relationship between the applied sinusoidal voltage (at resonance) and the displacement is determined. Measurements made using a sensitive Doppler radar confirm the calculated RCS to an accuracy of better than 2 dB, and show that it can be adjusted over 20 dB by adjusting the transducer excitation voltage through one decade. These low RCS targets are ideal for testing radio acoustic sounding systems and entomological radars. [ABSTRACT FROM PUBLISHER]

Pulmonary hypertension (PH) is a complex pathology, which affects the pulmonary circulatory system. The European Society of Cardiology (ESC)/European Respiratory Society (ERS) Guidelines on diagnosis and treatment of pulmonary hypertension represents the standard used in the clinical practice for the definition and the treatment of the pathology. At the moment, medical screenings used for the diagnosis of PH are both invasive and noninvasive. The noninvasive diagnostic tools use continuous-wave Doppler echocardiography to measure the tricuspid and/or pulmonary regurgitation velocity. Such parameter represents the input variable of the Bernoulli equation so as to estimate specific pulmonary hemodynamic variables used in the diagnosis. In detail, the PH diagnosis is positive when such hemodynamic variables exceed fixed cutoff values. Nevertheless the poor accuracy of Doppler-derived pressure estimations affects the diagnosis result negatively. Thus, false-negative and false-positive diagnoses are possible. We deal with such issue to provide physicians with useful and fault-tolerant diagnostic procedures. The aim is to guarantee a more reliable interpretation of the echocardiographic variables. In view of this, the criteria at present used in clinical practice for detecting the PH have been revised to improve the accuracy of diagnosis. The proposed procedure is based on the accurate and reliable interpretation of hemodynamic indexes by evaluating the uncertainty impact. In detail, the procedure is based on the analysis of the standard uncertainty associated with the hemodynamic parameters estimation. An algorithm has been implemented so to perform the data processing and the revised criteria. The proposed criteria have been validated both by numerical simulations and by experimentation on real clinical cases. Comparisons with the criteria of the ESC/ERS Guidelines have been carried out. Results are reported in the manuscript. Reliability and sensitivity of the computing algorithm have been tested. Experimental results and numerical simulations have shown interesting outcomes. During the tests, the algorithm has properly diagnosed the pathology. It has shown good tolerance to false-positive and false-negative diagnoses with respect to the standard criteria. [ABSTRACT FROM PUBLISHER]

In natural and urban canyon environments, Global Navigation Satellite System (GNSS) signals suffer from various challenges such as signal multipath, limited or lack of signal availability and poor geometry. Inertial sensors are often employed to improve the solution continuity under poor GNSS signal quality and availability conditions. Various fault detection schemes have been proposed in the literature to detect and remove biased GNSS measurements to obtain a more reliable navigation solution. However, many of these methods are found to be sub-optimal and often lead to unavailability of reliability measures, mostly because of the improper characterization of the measurement errors. A robust filtering architecture is thus proposed which assumes a heavy-tailed distribution for the measurement errors. Moreover, the proposed filter is capable of adapting to the changing GNSS signal conditions such as when moving from open sky conditions to deep canyons. Results obtained by processing data collected in various GNSS challenged environments show that the proposed scheme provides a robust navigation solution without having to excessively reject usable measurements. The tests reported herein show improvements of nearly 15% and 80% for position accuracy and reliability, respectively, when applying the above approach. [ABSTRACT FROM AUTHOR]

A reduced inertial measurement unit (RIMU) is ultratightly (UT) integrated with a vector-based Global Positioning System (GPS) receiver using two approaches; vector delay and frequency lock loops (VDLL/VFLL), and a VDLL with a cascaded phase lock loop (CaP). A CaP plus a frequency discriminator (CaPF) composite loop is developed to provide reliable Doppler measurements and improves navigation performance by up to 20% compared with other methods using real world data. [ABSTRACT FROM AUTHOR]

In this paper, a real-time algorithm that operates on data provided by a network of weather radars in the form of moments is presented. The algorithm implementation, performance, and abilities are presented and discussed. As part of this paper, a methodology for mapping from native spherical coordinates to a common network grid is developed and demonstrated. Metrics which gauge the quality of mapping and quality of data are derived, and their use from a network point of view is demonstrated. The main product of the algorithm, which is an implementation of a vector velocity estimation technique based on a maximum likelihood approach, is shown, and its results are displayed, compared, and discussed. The application of a methodology for velocity unfolding and reflectivity display enhancement is presented as well. [ABSTRACT FROM AUTHOR]

A method measuring Doppler parameters by joint time-frequency analysis is presented. Two-dimensional velocity retrieval can be achieved by estimation of the Doppler center frequency and Doppler frequency rate for the range and azimuth velocity components, respectively. The Doppler spectrum along a Doppler phase history line in the time-frequency domain was reconstructed and projected onto the frequency and time dimensions. The peak of the frequency axis projected spectrum corresponds to the Doppler center frequency, while that of the time axis indicates an azimuth time of closest approach. The Doppler frequency rate is obtained by measuring the slope of the Doppler spectrum in the time-frequency domain. Simulation using TerraSAR-X and Envisat ASAR parameters indicated that the velocity errors were less than 1 m/s or 5% for moving objects with a velocity higher than 3 m/s. While the measurement of Doppler center frequency was reliable over the entire velocity range, errors in Doppler frequency rate became large if the velocity was slower than 3 m/s (or 10.8 km/h). Range migration correction plays a key role for the precision of Doppler parameter estimation. An experiment using TerraSAR-X and truck-mounted corner reflectors validated the measurement accuracy of the approach. The absolute and percent errors of the range velocity (49.6 km/h) were 1.4 km/h and 2.8%, respectively, and the azimuth velocity (23.8 km/h) measurement was comparatively accurate, with a percent error of 1.8% under an assumption of zero acceleration. To apply the method to single-look complex data, the full Doppler bandwidth must be preserved. [ABSTRACT FROM PUBLISHER]

This paper extends the results of a previous work by combining hydrodynamic and electromagnetic analytical models for the simulation of the ocean Doppler spectrum at microwave frequencies. We consider weakly nonlinear sea surfaces after the choppy wave model and incorporate them in classical and unified scattering models, namely, the Kirchhoff and weighted curvature approximations. We show that statistical expressions can be obtained for the Doppler spectrum in a way similar to the case of linear surfaces. As expected, the nonlinear nature of the sea surface dramatically impacts the Doppler spectrum at moderate to large incidence angles, with a shift of the central frequency and a broadening of the spectrum. Monte Carlo comparisons are performed with the Creamer model, which is frequently used to describe weakly nonlinear sea surfaces but does not enjoy a statistical formulation for the Doppler characteristics. The same qualitative behavior is found but some quantitative differences are found and discussed. [ABSTRACT FROM PUBLISHER]

This paper discusses ways to avoid and/or mitigate biases in polarimetric variables inherent to agile-beam planar phased-array radars. Two bias-avoiding schemes produce unbiased estimates of the polarimetric backscattering covariance matrix which are then combined into bias-free polarimetric variables. One concerns full polarimetric measurements and calls for adjusting the amplitudes and phases of the array elements so that the transmitted field equals that generated by a mechanically steered polarimetric weather radar antenna; this is followed by an additional adjustment of the received fields. The second scheme is also applicable to full polarimetric measurements but involves adjustments only of the received fields. Crucial to both schemes is decoupling of the Doppler effects from the terms of the covariance matrix. It is a significant part of the bias issue that had not been previously addressed. A scheme to reduce bias applicable to nondepolarizing media (i.e., diagonal backscattering matrix) is also addressed; it calls for multiplication of the fields received by each dipole as opposed to a combination of multiplication and addition required for full correction. The schemes are applied to the alternate transmission and simultaneous reception polarimetric mode and the simultaneous transmission and simultaneous reception mode. [ABSTRACT FROM AUTHOR]

Abstract: A potential candidate that can be used for emulating different propagation environments is the reverberation chamber (RVC). Since mobility is of primary concern for wireless communication systems, understanding of its consequences is crucial. Mobility causes spectral broadening whose impact is generally evaluated through the observation of Doppler spectrum. In this study, investigation of Doppler spectrum characteristics through the use of an RVC and the methods for the purpose of its manipulation are presented. This study verifies that the Doppler spectrum can be manipulated in various ways. However, unless a precise setup is established it is almost impossible to obtain very specific Doppler shapes in RVCs such as widely known Jakes’ spectrum. Also, a different interpretation of mobility for wireless channels is given by the use of a new concept called motion intensity. This concept is elaborated in terms of both its technical aspects and its impact on wireless channel characterization. [ABSTRACT FROM AUTHOR]

Abstract: Objective: To compare the efficacy of vaginal versus sublingual misoprostol for second-trimester pregnancy termination, and to evaluate the effect on the blood flow of the uterine and umbilical arteries. Methods: Forty-nine patients were randomized to receive either 200 μg of vaginal misoprostol every 6 hours or 200 μg of misoprostol sublingually every 6 hours. Doppler velocimetry studies were assessed immediately before and 60 minutes after the administration of the first dose. Standard descriptive calculations, Mann–Whitney U, Wilcoxon, and χ2 tests were performed. Results: The mean interval between induction and onset of active labor, induction and delivery, and the duration of oxytocin administration were significantly shorter in the sublingual misoprostol group. Both routes of administration increased the Doppler indices for the uterine arteries; however, misoprostol via the sublingual route did not affect the umbilical arteries. Conclusion: Sublingual administration of misoprostol for second-trimester medical abortion results in a higher success rate and does not affect umbilical blood flow. [Copyright &y& Elsevier]

In many wireless sensors, the target kinematic states include location and Doppler information that can be observed from a time series of range and velocity measurements. In this work, we present a tracking strategy for comprising target velocity components as part of the measurement supplement procedure and evaluate the advantages of the proposed scheme. Data association capability can be considered as the key performance for multi-target tracking in an active sonar system. Then, we proposed an enhanced Doppler data association (DDA) scheme which exploits target range and target velocity components for linear multi-target tracking. If the target velocity measurements are not incorporated into target kinematic state tracking, the linear filter bank for the combination of target velocity components can be implemented. Finally, a significant enhancement in the multi-target tracking capability provided by the proposed DDA scheme with the linear multi-target combined probabilistic data association method is demonstrated in a sonar underwater scenario. [ABSTRACT FROM AUTHOR]

Ultrasound Doppler techniques are widely employed in detecting the velocity of moving fluids both in medical and industrial applications. Echo Doppler electronics systems include a highly sensitive front-end suitable to processing the very low power ultrasound echoes received by the transducer. Moreover, the front-end input bandwidth typically ranges between 100 kHz and 10 MHz, which is the same frequency range where modern switching regulators work. Thus, the front-end is particularly prone to the noise produced by the suppliers that power the board itself. Electromagnetic interference (EMI) filters and spread-spectrum modulation of the switching regulator frequency help, but the results are often not optimal, and unacceptable artifacts are visible in the Doppler spectrum. In this paper a spread-spectrum modulation is proposed that concentrates the switching noise in the low-frequency range of the Doppler spectrum (e.g., 0–100 Hz). This range is removed by the high-pass clutter filter normally used in velocity Doppler investigations, thus switching noise and artifacts are eliminated. The method is verified through mathematical simulations and tested in measurements carried out with a research Doppler system. An example is presented in which the artifacts present during the investigation of a 0.4-m/s flow in a 25.4-mm diameter pipe are effectively removed by the proposed method. [ABSTRACT FROM AUTHOR]

Purpose: There is a lot of speculation about the role of nitric-oxide (NO) in the improvement usually noticed in microcirculatory function, following exercise. The knowledge of the underlying mechanisms leading to such an improvement is important as it may help in targeting and implementing therapies for microcirculatory diseases. Through a laser Doppler flowmetry (LDF) signal processing study, the authors' goal is to compare multifractal spectra of LDF data recorded in both lower leg and forearm, during different exercise conditions, in an older, untrained but healthy population. Methods: Using the method suggested by Halsey et al. [Phys. Rev. A 33, 1141-1151 (1986)], multifractal spectra of LDF signals recorded on lower leg and forearm before and after exercise (arm-cranking), before and after acetylcholine (ACh) iontophoresis, were determined on scales in relation with the NO-dependent endothelial activity. The width of each multifractal spectrum was then computed through the maximum and minimum Hölder exponent values for which the multifractal spectrum reaches its minimal values. The results were then compared. Results: Following exercise and on the scales studied, the average width of the multifractal spectra in both lower leg and forearm does not vary significantly before and after ACh iontophoresis. Similarly, following ACh iontophoresis and exercise, the average width of multifractal spectra remains statistically unchanged, when compared to that measured prior to exercise, in both upper and lower body, although negative trends can be observed. Conclusions: For the authors' population and for the type of exercise that the authors have chosen, the authors showed that the width of the multifractal spectra of LDF signals does not change significantly on scales in relation with the NO-dependent endothelial activity. Future studies may involve comparisons with signals obtained in patient populations. [ABSTRACT FROM AUTHOR]