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In underwater communications, reciprocal motion between transmitter and receiver has a significant impact on reception quality. In orthogonal broadband systems that provide high bit rates, this problem becomes more important, especially in the higher frequency range, where the absolute Doppler shift is the greatest. Due to the low propagation speed of acoustic wave underwater, a substantial difference exists between the Doppler shift for lower and upper frequencies of the utilized spectrum. Consequently, a frequency-independent Doppler shift factor is employed. One of the most popular methods for determining the Doppler shift is the use of pilots. The problem of selecting the number and determining the frequency of pilots in such a way as to obtain the lowest possible error rate was identified. Real-world testing was conducted in a multipath propagation environment with relative speeds of up to 1.5 m/s. The effectiveness of Doppler shift determination was evaluated by analyzing the bit error rate. The results of the conducted tests indicate that, based on the achieved error rate, it is sufficient to employ 7 pilots positioned at low frequencies.

Space-based opportunistic positioning is a crucial component of resilient positioning, navigation, and timing (PNT) systems, and it requires the acquisition of orbit information for non-cooperative low Earth orbit (LEO) satellites. Traditional methods for orbit determination (OD) of non-cooperative LEO satellites have difficulty in achieving a balance between reliability, hardware costs, and availability duration. To address these challenges, this study proposes a framework for single-station orbit determination of non-cooperative LEO satellites. By utilizing signals of opportunity (SOPs) captured by a single ground station, the system performs initial orbit determination (IOD), precise orbit determination (POD), and orbit prediction (OP), enabling the long-term determination of satellite positions and velocities. Under the proposed framework, the reliability and real-time performance are dependent on the initial orbit determination and the orbit calculation based on the dynamical model. To achieve initial orbit determination, a three-step algorithm is designed. (1) An improved search method is employed to estimate a coarse orbit using single-pass Doppler measurements. (2) Data association is conducted to obtain multi-pass Doppler observations. (3) The least squares (LS) is implemented to determine the initial orbit using the associated multi-pass Doppler measurements and the coarse orbit. Additionally, to enhance computational efficiency, two fast orbit calculation algorithms are devised. These algorithms leverage the numerical stability of the Runge–Kutta integrator to reduce computations and exploit the strong correlation among nearby time intervals of orbits with small eccentricities to minimize redundant calculations, thereby achieving orbit calculation efficiently. Finally, through positioning experiments, the determined orbits are demonstrated to have accuracy comparable to that of two-line elements (TLE) updated by the North American Aerospace Defense Command (NORAD). [ABSTRACT FROM AUTHOR]

For a better understanding of atmospheric dynamics, it is very important to know the general condition (dynamics and chemistry) of the atmosphere. Planetary waves (PWs) are global scale waves, which are well-known as main drivers of the large-scale weather patterns in mid-latitudes on time scales from several days up to weeks in the troposphere. When PWs break, they often cut pressure cells off the jet stream. A specific example are so-called streamer events, which occur predominantly in the lower stratosphere at mid-and high latitudes. For streamer events we check, whether there are any changes of gravity wave (GW) or infrasound characteristics related to these events in ionospheric and surface measurements (continuous Doppler soundings, array of microbarometers) in the Czech Republic. First order signatures of streamer events were not identified in infrasound data at stations WBCI and PVCI. Supplementary ground-based measurements of GW using the WBCI array in the troposphere showed that GW propagation azimuths were more random during streamer and streamer-like events compared to those observed during calm conditions. GW propagation characteristics observed in the ionosphere by continuous Doppler soundings during streamer events did not differ from those expected for the given time period. [ABSTRACT FROM AUTHOR]

Background Malaria in pregnancy (MiP) has been associated with fetal growth restriction, the underlying pathogenic mechanisms of which remain poorly understood. Malaria in pregnancy is suspected to induce abnormalities in placental vascularization, leading to impaired placental development. Our study evaluated MIP's effect on uterine artery (UtA) and umbilical artery (UA) blood flow. Methods The analysis included 253 Beninese women followed throughout pregnancy and screened monthly for submicroscopic and microscopic malaria. Uterine artery Doppler measurement was performed once between 21 and 25 weeks' gestation (wg), and UA Doppler measurement was performed 1–3 times from 28 wg. Linear and logistic regression models were used to assess the effect of malaria infections on UtA Doppler indicators (pulsatility index and presence of a notch), whereas a logistic mixed model was used to assess the association between malaria infections and abnormal UA Doppler (defined as Z-score ≥2 standard deviation or absent/reversed UA end-diastolic flow). Results Primigravidae represented 7.5% of the study population; 42.3% of women had at least 1 microscopic infection during pregnancy, and 29.6% had at least 1 submicroscopic infection (and no microscopic infection). Both microscopic and submicroscopic infections before Doppler measurement were associated with the presence of a notch (adjusted odds ratio [aOR] 4.5, 95% confidence interval [CI] = 1.2–16.3 and aOR 3.3, 95% CI =.9–11.9, respectively). No associations were found between malaria before the Doppler measurement and abnormal UA Doppler. Conclusions Malaria infections in the first half of pregnancy impair placental blood flow. This highlights the need to prevent malaria from the very beginning of pregnancy. [ABSTRACT FROM AUTHOR]

Abstract Smoothing process can effectively improve the accuracy of the Global Navigation Satellite System (GNSS) position estimation algorithm. In this study, a Doppler‐aided GNSS position estimation algorithm with a B‐spline smoothing strategy is proposed. B‐spline signal processing is used to smoothen the code measurements with Doppler measurements, which were selected because they are more robust and immune to cycle slips than carrier phase measurements. Next, the mathematical expressions of the smoothing process and position estimation are derived. The smoothing process is based on the structure of a digital filter, which is especially suitable for real‐time applications. The Cramer–Rao lower bound of the proposed algorithm is derived. Moreover, a complete implementation structure of the proposed algorithm is presented. The validity of the proposed algorithm is verified through scenario simulation in terms of static, kinematic, and adverse environments. The advantages of the proposed algorithm are demonstrated by comparison with existing algorithms.

Smoothing process can effectively improve the accuracy of the Global Navigation Satellite System (GNSS) position estimation algorithm. In this study, a Doppler‐aided GNSS position estimation algorithm with a B‐spline smoothing strategy is proposed. B‐spline signal processing is used to smoothen the code measurements with Doppler measurements, which were selected because they are more robust and immune to cycle slips than carrier phase measurements. Next, the mathematical expressions of the smoothing process and position estimation are derived. The smoothing process is based on the structure of a digital filter, which is especially suitable for real‐time applications. The Cramer–Rao lower bound of the proposed algorithm is derived. Moreover, a complete implementation structure of the proposed algorithm is presented. The validity of the proposed algorithm is verified through scenario simulation in terms of static, kinematic, and adverse environments. The advantages of the proposed algorithm are demonstrated by comparison with existing algorithms. [ABSTRACT FROM AUTHOR]

Parameter estimation of multiple sinusoids is one of the fundamental problems of signal processing having numerous application areas, including wireless communications and array signal processing. This article proposes an iterative, fast, and efficient algorithm to estimate the frequencies and amplitudes of multiple sinusoids in noisy environments. The proposed approach interpolates on the q-shifted DFT coefficients of multiple sinusoids. We theoretically demonstrate that the performance of the proposed algorithm depends on DFT-shift, number of iterations and minimum DFT frequency separation parameters. Further, mean square error of the proposed algorithm achieves the Cramér-Rao lower bound when these parameters are selected appropriately. We also propose solid bounds regarding how these parameters can be selected for optimum overall performance. The total computational cost of the proposed algorithm is in the order of O(K N log N), where K is the number of sinusoidal components and N is the signal length. We provide comprehensive numerical simulations that confirm the correctness of our theoretical deductions. [ABSTRACT FROM AUTHOR]

This paper presents a pulse radar system to detect drones based on a target fluctuation model, specifically the Swerling target model. Because drones are small atypical objects and are mainly composed of non‐conducting materials, their radar cross‐section value is low and fluctuating. Therefore, determining the target fluctuation model and applying a proper integration method are important. The proposed system is herein experimentally verified and the results are discussed. A prototype design of the pulse radar system is based on radar equations. It adopts three different pulse modes and a coherent pulse integration to ensure a high signal‐to‐noise ratio. Outdoor measurements are performed with a prototype radar system to detect Doppler frequencies from both the drone frame and blades. The results indicate that the drone frame and blades are detected within an instrumental maximum range. Additionally, the results show that the drone's frame and blades are close to the Swerling 3 and 4 target models, respectively. By the analysis of the Swerling target models, proper integration methods for detecting drones are verified and can thus contribute to increasing in detectability.

Attitude and heading estimation methods using the global navigation satellite system (GNSS) are generally based on multi-antenna deployment, where the installation space and system cost increase with the increase in the number of antennas. Since the single-antenna receiver is still the major choice of the mass market, we focus on precise and reliable heading and pitch estimation using a low-cost GNSS receiver. Carrier phase observations are precise but have an ambiguity problem. A single difference between consecutive epochs can eliminate ambiguity and reduce the measurement errors. In this work, a measurement model based on the time-differenced carrier phases (TDCPs) is utilized to estimate the precise delta position of the antenna between two consecutive epochs. Then, considering the motion constraint, the heading and pitch angles of a moving land vehicle can be determined by the components of the estimated receiver delta position. A threshold on the length of the delta position is selected to avoid large errors in static periods. To improve the reliability of the algorithm, the Doppler-aided cycle slip detection method is applied to exclude carrier phases with possible cycle slips. A real vehicular dynamic experiment using a low-cost, single-frequency GNSS receiver is conducted to evaluate the proposed algorithm. The experimental results show that the proposed algorithm is capable of providing precise vehicular heading and pitch estimates, with both the root mean square errors being better than 1.5°. This also indicates that the cycle slip exclusion is indispensable to avoid unexpected large errors.

The initial Gaussian mixture cardinality balanced multi-target multi-Bernoulli (GM-CBMeMBer) filter does not provide track information and assumes that the target birth intensity is known as a priori, but in reality the target may appear anywhere in the detection area. Therefore, the study proposes a labelled GM-CBMeMBer filter with adaptive track initiation. First, the filter introduces track label information and selects the measurements of newborn targets in the prediction process. In addition, it also makes full use of the Doppler information of the airborne Doppler radar. Then, the position estimate and velocity estimate of newborn targets are calculated by using position measurements converted and Doppler measurements, respectively. Further the label information in the prediction process is inherited during the update process, and the target states are updated sequentially with the Doppler measurements after having been updated by using position measurements. Monte–Carlo experiments show that the proposed filter can perform adaptive track initiation effectively, with good tracking performance, and provide target track information well.

Acoustical Driving Forces (ADF), induced by propagating waves in a homogeneous and inhomogeneous lossy fluid (suspension), are determined and compared depending on the concentration of suspended particles. Using integral equations of the scattering theory, the single particle (inclusion) ADF was calculated as the integral of the flux of the momentum density tensor components over the heterogeneity surface. The possibility of negative ADF was indicated. Originally derived, the total ADF acting on inclusions only, stochastically distributed in ambient fluid, was determined as a function of its concentration. The formula for the relative increase in ADF, resulting from increased concentration was derived. Numerical ADF calculations are presented. In experiments the streaming velocities in a blood-mimicking starch suspension (2 μm radius) in water and Bracco BR14 contrast agent (SF6 gas capsules, 1 μm radius) were measured as the function of different inclusions concentration. The source of the streaming and ADF was a plane 2 mm diameter 20 MHz ultrasonic transducer. Velocity was estimated from the averaged Doppler spectrum obtained from originally developed pulsed Doppler flowmeter. Numerical calculations of the theoretically derived formula showed very good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The initial Gaussian mixture cardinality balanced multi-target multi-Bernoulli (GM-CBMeMBer) filter does not provide track information and assumes that the target birth intensity is known as a priori, but in reality the target may appear anywhere in the detection area. Therefore, the study proposes a labelled GM-CBMeMBer filter with adaptive track initiation. First, the filter introduces track label information and selects the measurements of newborn targets in the prediction process. In addition, it also makes full use of the Doppler information of the airborne Doppler radar. Then, the position estimate and velocity estimate of newborn targets are calculated by using position measurements converted and Doppler measurements, respectively. Further the label information in the prediction process is inherited during the update process, and the target states are updated sequentially with the Doppler measurements after having been updated by using position measurements. Monte–Carlo experiments show that the proposed filter can perform adaptive track initiation effectively, with good tracking performance, and provide target track information well. [ABSTRACT FROM AUTHOR]

In this paper, Bragg and non-Bragg scattering mechanisms and frequency shifts from time-varying periodic water wave are studied from three aspects: wave tank measurements with an ultrahigh frequency radar, numerical simulation using the method of moments, and theoretical derivation applying the small perturbation method. The scattering field, radar cross section (RCS), and frequency shifts are discussed in both horizontal and vertical polarizations. The wave tank observations show that backscattering enhancement occurs when water wavelength is an integer multiple of Bragg wavelength, and there are several Doppler harmonics with frequency shifts of water-wave frequency and its integer multiples. Numerical simulations indicate that these Doppler harmonics except the one associated with the water-wave phase velocity are caused by the water surface edge effect. Moreover, theoretical analyses, numerical simulations, and wave tank experiments all show a clear exponential relationship between backscattering RCS and wave height. In addition, we further analyze the bistatic scattering and find that the scattering field is composed of plane waves propagating in the directions determined by water wavelength and radio wavelength, the bistatic frequency shift is the harmonic frequency of water wave, and the bistatic RCS also has an exponential relation with water-wave height. [ABSTRACT FROM AUTHOR]

This paper presents a pulse radar system to detect drones based on a target fluctuation model, specifically the Swerling target model. Because drones are small atypical objects and are mainly composed of non‐conducting materials, their radar cross‐section value is low and fluctuating. Therefore, determining the target fluctuation model and applying a proper integration method are important. The proposed system is herein experimentally verified and the results are discussed. A prototype design of the pulse radar system is based on radar equations. It adopts three different pulse modes and a coherent pulse integration to ensure a high signal‐to‐noise ratio. Outdoor measurements are performed with a prototype radar system to detect Doppler frequencies from both the drone frame and blades. The results indicate that the drone frame and blades are detected within an instrumental maximum range. Additionally, the results show that the drone's frame and blades are close to the Swerling 3 and 4 target models, respectively. By the analysis of the Swerling target models, proper integration methods for detecting drones are verified and can thus contribute to increasing in detectability. [ABSTRACT FROM AUTHOR]

Intrauterine growth restriction (IUGR) is a serious pregnancy complication with short- and long-term health consequences. The mechanisms underlying this condition are not well understood. Animal models are the basis for understanding the causes of IUGR and for developing useful therapeutic strategies. Here, we aimed to ascertain the in utero growth of fetuses from NK (natural killer cells)/MC (mast cells)-deficient mothers that give birth to growth-restricted pups and to determine the time point at which IUGR starts. We used high frequency ultrasound imaging to follow-up fetal and placenta size and employed Doppler measurements to document blood supply to the fetus in females that were deficient for NK cells and MCs. In mice lacking NKs and MCs, we observed significantly reduced implantation sizes from mid gestation onward, which was further associated with smaller placentas. Additionally, NK/MC-deficiency was associated with absent and reversed end diastolic flow in umbilical arteries of the fetuses and an increased systolic/ diastolic ratio as well as an elevated resistance index. Together, our results indicate that NKs/MCs promote blood flow, placental growth, and subsequent fetal development. The results of this study offer new insights as to how fetal growth is affected in vivo in NK/MC-deficient mice, whose pups are growth restricted at birth. The use of IUGR models and modern technologies enabling the in vivo follow-up of fetal development are important tools for understanding mechanisms behind pregnancy complications that in the future may lead to the development of effective therapies. [ABSTRACT FROM AUTHOR]

Results of a coastal measurement campaign called MediterraneAn Rfc and cLutter ENvironmental Experiment (MARLENE) are presented and studied. The campaign was held in spring 2014, on a DGA site in the Mediterranean Sea region of Toulon, France. Three coastal measurement radar systems, Millimeter wave Experimental Multifrequency Polarimetric High Resolution Interferometric System (Fraunhofer FHR), MARSIG (WTD 71), and MEDYCIS (ONERA), were deployed to simultaneously acquire sea clutter measurements. During the campaign, the in situ oceanic and meteorological conditions were characterized from the RV PLANET meteorological ship deployed by WTD 71 and by modeling from WAVEWATCH III and SWAN wave models. Radar measurements were performed at the C-, X-, Ku-, Ka-, and W-bands. The measurement results are presented in terms of reflectivity and mean Doppler spectrum according to low grazing angle and azimuth variations. Reflectivity variations are compared with the empirical GIT model and close results are obtained at the C- and Ka-bands. At the same frequency bands, mean Doppler Spectrum velocity is presented and analyzed according to grazing and azimuth angles. Physical interpretations of electromagnetic interaction with sea surface are discussed. [ABSTRACT FROM PUBLISHER]

Dead-reckoning (DR) algorithms, which use self-contained inertial sensors combined with gait analysis, have proven to be effective for pedestrian navigation purposes. In such DR systems, the primary error is often due to accumulated heading drifts. By tightly integrating global navigation satellite system (GNSS) Doppler measurements with DR, such accumulated heading errors can usually be accurately compensated. Under weak signal conditions, high sensitivity GNSS (HSGNSS) receivers with block processing techniques are often used, however, the Doppler quality of such receivers is relatively poor due to multipath, fading and signal attenuation. This often limits the benefits of integrating HSGNSS Doppler with DR. This paper investigates the benefits of using Doppler measurements from a novel direct vector HSGNSS receiver with pedestrian dead-reckoning (PDR) for indoor navigation. An indoor signal and multipath model is introduced which explains how conventional HSGNSS Doppler measurements are affected by indoor multipath. Velocity and Doppler estimated by using direct vector receivers are introduced and discussed. Real experimental data is processed and analyzed to assess the veracity of proposed method. It is shown when integrating HSGNSS Doppler with PDR algorithm, the proposed direct vector method are more helpful than conventional block processing method for the indoor environments considered herein.

A Doppler centroid \boldsymbolD c model based on the generalized curvature ocean surface scattering model (generalized curvature model or GCM) is presented. Two key features are included in this model: a skewness-related phase coefficient based on empirical skewness coefficients of sea-surface-slope probability density function (pdf) for wind speed less than 10 m/s and effects from wave breaking for wind speed greater than 10 m/s. Simulated \boldsymbolD\mathbf{c} values are exclusively compared with the empirical geophysical Doppler model function named CDOP, for \mathbfhh and \mathbfvv polarizations, various wind conditions, and incidence angles. Good agreement is found overall between CDOP and simulated \boldsymbolD\mathbf{c} values. The overall bias for simulated \boldsymbolD\mathbf{c-hh} with and without skewness are 2.63 versus −0.51 Hz (14.6 versus −2.8 cm/s), respectively; overall standard deviations are 2.76 versus 3.53 Hz (15.3 versus 19.6 cm/s). For simulated \boldsymbolD\mathbf{c-vv}, overall bias values with and without skewness are −0.16 versus −2.52 Hz (−0.9 versus −14 cm/s); standard deviations are 3.56 versus 4.32 Hz (19.7 versus 24 cm/s). The overall bias for simulated \boldsymbolD\mathbf{c-hh} with and without the wave breaking component are −0.08 versus 0.12 Hz (−0.4 versus 0.7 cm/s), respectively; corresponding standard deviations are 3.32 versus 4.75 Hz (18.4 versus 26.3 cm/s). Bias values for simulated \boldsymbolD\mathbf{c-vv} with and without the wave breaking component are −1.83 versus −2.02 Hz (−10.2 versus −11.2 cm/s), with corresponding overall standard deviations of 3.43 versus 4.87 Hz (19 versus 27 cm/s). The largest deviation from CDOP, of about 18 Hz (0.99 m/s), is found in the upwind direction for a 26° incidence angle, 10-m/s wind speed, and \mathbfhh polarization. [ABSTRACT FROM PUBLISHER]

Using data from the Envisat Advanced Synthetic Aperture Radar (ASAR) instrument, this paper demonstrates how the high-precision radial surface velocity product, which will become available with the European Space Agency's Sentinel-1 satellite, can complement the analysis of sea ice motion. High-resolution Doppler frequency measurements are used to estimate the subsecond line-of-sight motion of drifting sea ice in Fram Strait. We compare the method with buoy measurements and a recent cross-correlation algorithm for tracking ice between pairs of images. Maximum speeds measured from the time series were on the order of 20 cm/s. Using our method, we measured instantaneous speeds reaching 40–60 cm/s. [ABSTRACT FROM PUBLISHER]

In this paper, a new radar waveform based on wavelet packets is proposed. This waveform shows significant advantages over conventional linear frequency modulated waveforms for range and velocity detections of moving targets. The proposed waveform can decouple its envelope and carrier for range and velocity estimations, respectively, because of which the Doppler spread term can be totally removed when estimating velocity and the Doppler effect ignored when estimating range. This way, the proposed waveform produces higher resolution in range or velocity detection. The proposed waveform can be applied to the synthetic aperture radar for improved performance. [ABSTRACT FROM PUBLISHER]

An alternative approach to sea surface wind retrieval using synthetic aperture radar (SAR) stripmap (SM) data is explored in this paper, using both the polarization residual Doppler frequency (PRDF) - the difference between the VV and HH Doppler centroids - and the normalized radar cross section (NRCS). The PRDF not only enables the possible elimination of unwanted biases present in both VV and HH Doppler estimates but also helps decrease the number of wind ambiguities down to two. In order to successfully infer the wind field from the PRDF, the use of a geophysical Doppler model function, such as the general curvature model (GCM)-Dop, is necessary. Using such a function, a simulated version of the PRDF at X-band is analyzed in terms of the sea surface wind field at various incidence angles. Simulations first show that the PRDF increases with increasing incidence angle regardless of wind field conditions. Actual PRDF measurements also exhibit strong correlation with radial components of the wind speed. An alternate SAR wind retrieval procedure, incorporating both the PRDF and the NRCS, is tested on a series of dual-polarized SM TerraSAR-X scenes carefully selected along the Norwegian coast. The geophysical model functions used for this analysis are the GCM-NRCS and GCM-Dop. A 1.13-m/s bias, with a correlation of 0.85 and a 1.86-m/s rmse, exists between the mean estimated wind speeds and in situ measurements, while a 15.43° bias, with a 0.93 correlation coefficient and a 34.1° rmse, is found between the mean estimated wind directions and in situ measurements. [ABSTRACT FROM PUBLISHER]

In clinical practice, echocardiographers are often unkeen to make the significant time investment to make additional multiple measurements of Doppler velocity. Main hurdle to obtaining multiple measurements is the time required to manually trace a series of Doppler traces. To make it easier to analyze more beats, we present the description of an application system for automated aortic Doppler envelope quantification, compatible with a range of hardware platforms. It analyses long Doppler strips, spanning many heartbeats, and does not require electrocardiogram to separate individual beats. We tested its measurement of velocity-time-integral and peak-velocity against the reference standard defined as the average of three experts who each made three separate measurements. The automated measurements of velocity-time-integral showed strong correspondence (R^2 =0.94) and good Bland–Altman agreement (SD = 1.39~\ cm) with the reference consensus expert values, and indeed performed as well as the individual experts (R^2 = 0.90 to 0.96, SD = 1.05 to 1.53 cm). The same performance was observed for peak-velocities; (R^2 =0.98, SD = 3.07~cm/s) and (R^2 = 0.93 to 0.98, SD = 2.96 to 5.18 cm/s). This automated technology allows > 10 times as many beats to be analyzed compared to the conventional manual approach. This would make clinical and research protocols more precise for the same operator effort. [ABSTRACT FROM PUBLISHER]

Scattering signals on wind turbines may lead to degradation problems on the communication systems provided in the UHF band, such as terrestrial television broadcasting, broadband wireless systems or public safety services. To date, despite the continuous requests from the International Telecommunication Union for studies on this field, no channel model has been developed to characterize signal propagation under these particular conditions. In response to this necessity, this paper presents a complete Tapped Delay Line (TDL) channel model to characterize multipath propagation in presence of a wind farm, including novel scattering modeling and Doppler spectra characterization. As proved later, this channel model, which is based on both theoretical development and empirical data obtained in the surroundings of a real wind farm, is adaptable to the particular features of any case under study: wind turbine dimensions, working frequency, and relative location of the wind farm, transmitter and receivers. [ABSTRACT FROM AUTHOR]

Dead-reckoning (DR) algorithms, which use self-contained inertial sensors combined with gait analysis, have proven to be effective for pedestrian navigation purposes. In such DR systems, the primary error is often due to accumulated heading drifts. By tightly integrating global navigation satellite system (GNSS) Doppler measurements with DR, such accumulated heading errors can usually be accurately compensated. Under weak signal conditions, high sensitivity GNSS (HSGNSS) receivers with block processing techniques are often used, however, the Doppler quality of such receivers is relatively poor due to multipath, fading and signal attenuation. This often limits the benefits of integrating HSGNSS Doppler with DR. This paper investigates the benefits of using Doppler measurements from a novel direct vector HSGNSS receiver with pedestrian dead-reckoning (PDR) for indoor navigation. An indoor signal and multipath model is introduced which explains how conventional HSGNSS Doppler measurements are affected by indoor multipath. Velocity and Doppler estimated by using direct vector receivers are introduced and discussed. Real experimental data is processed and analyzed to assess the veracity of proposed method. It is shown when integrating HSGNSS Doppler with PDR algorithm, the proposed direct vector method are more helpful than conventional block processing method for the indoor environments considered herein. [ABSTRACT FROM AUTHOR]

The problem of Doppler-based target position and velocity estimation using a sensor network is outlined. The minimum number of Doppler-shift measurements at distinct generic sensor positions in order to have a finite number of solutions, and later, a unique solution for the unknown target position and velocity are stated analytically. Furthermore we study the same problem, where not only Doppler-shift measurements are collected, but also other types of measurements are available, e.g,. bearing or distance to the target from each of the sensors. Later we study the Cramer-Rao inequality associated with the Doppler-shift measurements to a target in a sensor network, and we use the Cramer-Rao bound to illustrate some results on optimal placements of the sensors when the goal is to estimate the velocity of the target. Some simulation results are presented at the end. [ABSTRACT FROM PUBLISHER]

In contrast to carrier-phase measurements, receiver-generated Doppler measurements have much better availability, even in severe urban canyons or high-dynamic movement applications, while providing centimeter-level precision. Thus, the Doppler-aided approach may improve the positioning accuracy of the receiver. Some Kalman-filter-based applications have been developed in recent years, but the theoretical error analysis is still missing. In this paper, we propose a model-free Doppler-aided position estimation approach. The Doppler measurements are modeled together with the code pseudoranges and then solved as a weighted least square (WLS) problem. In addition, we analyze the lower bound of errors of the approach based on the Cramér–Rao bound (CRB). Simulation results and the error analysis show that the proposed approach may improve accuracy in position estimation. [ABSTRACT FROM PUBLISHER]

The processing steps and error corrections needed to retrieve estimates of sea surface range Doppler velocities from Envisat Advanced Synthetic Aperture Radar Wide Swath Medium resolution image products are presented. Retrieval accuracies based on examination of the corrected Doppler shift measurements are assessed. The root-mean-square errors of the Doppler shift after bias corrections are found to be 4.7 and 3.9 Hz in VV and HH polarizations, respectively. At 35^\circ incidence angle, this corresponds to horizontal Doppler velocities of 23 and 19 cm/s. [ABSTRACT FROM AUTHOR]

Precision of two-way satellite time and frequency transfer (TWSTFT) highly depends on the residual nonreciprocity delays; one of them is caused by the Sagnac effect. In this paper, we employ the satellite ephemeris data to compute the precise Sagnac effect and discuss the possible additive effect related to the Sagnac effect. We also describe a method to calculate the diurnal correction based on the time derivative of the Sagnac effect. Through the analysis of the link between the National Institute of Information and Communications Technology in Japan and the Telecommunication Laboratories in Taiwan, we demonstrate that the correction was useful to improve the TWSTFT data. The time deviation at an 8-h averaging time is reduced from 346 to 156 ps after the correction. [ABSTRACT FROM AUTHOR]

In this paper, we present an all-electronic rain gauge that uses microwave sensors operating at either 10 or 24 GHz and measures the Doppler shift caused by falling raindrops. It is straightforward to interface the microwave rain gauge with conventional data loggers. A disadvantage of the microwave rain gauge is that it consumes significant power when operating. However, this may be partially negated by using the data loggers' sleep--wake--sleep mechanism. Advantages of the microwave rain gauge are that it is robust, does not clog, and does not have mechanical parts that wear out. Prototype microwave rain gauges were collocated with tipping-bucket rain gauges, and data were collected for several seasons. At higher rain rates, microwave rain gauge measurements compare well with tipping bucket measurements. At lower rain rates, the microwave rain gauge provides more detailed information than widely used tipping buckets, which inherently quantize measurements. [ABSTRACT FROM AUTHOR]

In order to study the vibration characterization of a spindle motor, the rotor runout must be measured accurately. In this paper, a method based on measurement uncertainty is presented to evaluate different measurement systems and measurement confidence. The principle optic interferometer (iRVM) system is introduced in this paper, which is based on optical interference technology. The results of the iRVM are compared with another two methods that make use of capacitance probe and laser Doppler velocimetry. [ABSTRACT FROM AUTHOR]

Polynomial-phase signals have numerous applications including radar, sonar, geophysics, and radio communication. Many techniques for estimating the parameters of polynomial-phase signals have been described in the literature. Despite the significant interest, aliasing of polynomial-phase parameters has not been fully clarified. We address the problem of identifiability and aliasing in polynomial-phase signals. We fully describe the region in which aliasing does not occur for polynomial-phase signals of any order. We call this the identifiable region. We find that this region is the Voronói region of a lattice generated by the coefficients of a set of polynomials known as the integer-valued polynomials. We show how aliasing can be resolved by solving the nearest lattice point probleni. We discuss some of the consequences of these results on a popular estimator for polynomial-phase signals that is based on the discrete polynomial phase transform (DPPT). It is shown that the range of parameters suitable for the DPPT estimator is very small compared to the identifiable region. [ABSTRACT FROM AUTHOR]