Velocity Estimation Research Papers - Academia.edu (original) (raw)

Using repeated high precision GPS measurements on existing monuments, we hope to accurately determine the present day crustal strain rates in the State of Colorado on a regional and/or local scale. We will provide the first modern, space-based crustal strain and surface velocity estimates for the southern Rocky Mountain region, including the Front Range and Rio Grande Rift. In addition,

- by
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- Seismic Hazard, Strain Rate, Velocity Estimation, Rocky Mountains

We have developed a numerical model of Small Target Motion Detector neurons, bio-inspired from electrophysiological experiments in the fly brain. These neurons respond selectively to small moving features within complex moving surrounds. Interestingly, these cells still respond robustly when the targets are embedded in the background, without relative motion cues. This model contains representations of neural elements along a proposed pathway to the targetdetecting neuron and the resultant processing enhances target discrimination in moving scenes. The model encodes high dynamic range luminance values from natural images (via adaptive photoreceptor encoding) and then shapes the transient signals required for target discrimination (via adaptive spatiotemporal high-pass filtering). Following this, a model for Rectifying Transient Cells implements a nonlinear facilitation between rapidly adapting, and independent polarity contrast channels (an 'on' and an 'off' pathway) each with center-surround antagonism. The recombination of the channels results in increased discrimination of small targets, of approximately the size of a single pixel, without the need for relative motion cues. This method of feature discrimination contrasts with traditional target and background motion-field computations. We improve the target-detecting output with inhibition from correlation-type motion detectors, using a form of antagonism between our feature correlator and the more typical motion correlator. We also observe that a changing optimal threshold is highly correlated to the value of observer ego-motion. We present an elaborated target detection model that allows for implementation of a static optimal threshold, by scaling the target discrimination mechanism with a model-derived velocity estimation of ego-motion.

- by Steven Wiederman
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- High Dynamic Range, Velocity Estimation, Biosensing, Target Detection

Accelerometer-based activity monitoring sensors have become the most suitable means for objective assessment of mobility trends within patient study groups. The use of minimal, low power, IC (integrated circuit) components within these sensors enable continuous (long-term) monitoring which provides more accurate mobility trends (over days or weeks), reduced cost, longer battery life, reduced size and weight of sensor. Using scripted activities of daily living (ADL) such as sitting, standing, walking, and numerous postural transitions performed under supervised conditions by young and elderly subjects, the ability to discriminate these ADL were investigated using a single tri-axial accelerometer, mounted on the trunk. Data analysis was performed using Matlab ® to determine the accelerations performed during eight different ADL. Transitions and transition types were detected using the scalar (dot) product technique and vertical velocity estimates on a single tri-axial accelerometer was compared to a proven discrete wavelet transform method that incorporated accelerometers and gyroscopes. Activities and postural transitions were accurately detected by this simplified low-power kinematic sensor and activity detection algorithm with a sensitivity and specificity of 86-92% for young healthy subjects in a controlled setting and 83-89% for elderly healthy subjects in a home environment.

- by Alan Bourke and +1
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- Engineering, Algorithms, Data Analysis, Physical Activity

This paper presents a Kalman filter (KF)-integrated optical flow method to measure the velocity of mobile robots using a downward-looking camera. Tests conducted earlier by the authors have shown that currently available differential optical flow methods (X. Song, L. D. Seneviratne, K. Althoefer, and Z. Song, "Vision-based velocity estimation for unmanned ground vehicles," Int. J. Inf. Acquis., vol. 4, no. 4, pp. 303-315, 2007) require large image overlap for accurate velocity estimation. This constraint significantly limits the usefulness of this approach in practical applications. To overcome the problem of dealing with large image displacements, a KF is incorporated to efficiently predict the image transformations. Reducing the feature search area, the KF enables the differential optical flow method to rapidly converge and give accurate velocity estimates. The proposed method has been validated on a linear test rig under laboratory conditions and on a mobile platform in an outdoor field. Test results show good performance of the proposed method in velocity measurements with large image displacements. With this improvement, the required image overlap for feature tracking can be reduced approximately from 80% to 20%, resulting in a fourfold increase of the maximum measurable velocity of the mobile platform. The proposed method has good potential in velocity sensing for mobile robots, particularly in cases, where GPS and inertial measurement unit fail or are unavailable.

- by Lakmal D. Seneviratne
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- Mechanical Engineering, Robot Vision, Integrated Optics, Kalman Filter

Using linear-array Doppler ultrasound (US) transducers, the measured maximum velocity may be in error and lead to incorrect clinical diagnosis. This study investigates the existence and cause of maximum velocity estimation errors for steady flow of a blood-mimicking fluid in a tissue-mimicking phantom. A specially designed system was used that enabled fine control of flow rate, transducer positioning and transducer angle relative to the flow phantom. Doppler machine settings (transducer aperture size, focal depth, beam-steering, gain) were varied to investigate a wide range of clinical applications. To estimate the maximum velocity, a new signal-tonoise ratio (SNR) independent method was developed to calculate the maximum frequency from an ensemble averaged Doppler power spectrum. This enabled the impact of each factor on the total Doppler error to be determined. When using the new maximum frequency estimator, it was found that the effect of transducer focal depth, intratransducer, intramachine, intermachine (that was tested) and beam-steering did not significantly contribute to maximum velocity estimation errors. Instead, it was the dependence of the maximum velocity on the Doppler angle that made, by far, the greatest contribution to the estimation error. Because our maximum frequency estimator took into account the effect of intrinsic spectral broadening, the degree of overestimation error was not as great as that previously published. Thus, the effects of Doppler angle and intrinsic spectral broadening are the chief sources of Doppler US error and should be the focus of future efforts to improve the accuracy. (

- by Aaron Steinman and +1
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- Transducers, Doppler Ultrasound, Velocity Estimation, Clinical Sciences

Knowledge of velocity is crucial to certain industrial applications involving high-bandwidth modeling and control. In conventional approaches, the velocities obtained from encoders or tachometers are quite noisy, and low-pass filters are usually engaged to generate usable velocity signals. The low-pass filter, however, causes significant phase lag that can severely affect both modeling and control accuracy in the mid-and high-frequency ranges. In this paper, two approaches using a combination of an encoder and an imperfect accelerometer are proposed to estimate velocities with high bandwidth. The two approaches, namely the two-channel approach and the observer-based approach, estimate velocities by applying proper frequency weightings to the encoder and accelerometer signals. The encoder mainly contributes to the low-frequency components of velocity estimation, and the accelerometer mainly contributes to the high-frequency components of velocity estimation. An adaptive mechanism for estimating the accelerometer gain is also presented. The effectiveness of the two velocity estimation approaches is verified experimentally with respect to a one-degree-of-freedom robot performing both rigid contact modeling and control. Extension to 3-D applications is discussed.

- by Wen-Hong Zhu
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- Engineering, Motion control, Low Frequency, Parameter estimation

Most CMOS image sensors collect image data row by row, analogous to an open slit that scans over the image sequentially. Each row integrates light when the slit passes over it. Therefore, the scanlines of the image are not exposed at the same time. This sensor architecture creates a geometric distortion, known as the rolling shutter effect, for moving objects. We address this problem by using digital image processing techniques. A mathematical model of the rolling shutter is developed, by which the relative image motion between the object and the camera is determined, and a polynomial fitting is applied to smooth the motion data thus obtained. The resulting motion data are used to align the scanlines. The accuracy of the alignment process is further improved by an iterative motion refinement procedure.

- by Li-Wen Chang
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- Cognitive Science, Algorithms, Computer Vision, Image Processing

Characterization of the shallow subsurface (0.25 to 10 m) is of growing importance for engineering activities, solutions of environmental problems, and archaeological investigations. Ground-penetrating radar (GPR) is an appropriate technique considering the depth range of interest, the strength of electric and magnetic contrasts between different subsurface layers and buried objects, and the required resolution. GPR surveys can detect subsurface structures by recording electromagnetic reflections from discontinuities. The detectability of objects and the delineation of subsurface structures increases with increasing wave velocity and conductivity differences between the object and its surroundings or between adjacent layers. However, unwanted reflections from objects above the surface influence the images. Shielded antennas can be used to avoid strong reflections from these objects. The data thus obtained are, however, more difficult to interpret. The fundamentals of GPR and two different acquisition setups for a GPR system are discussed. Basic interpretation tools for travel-time and velocity estimation are described, and finally, case studies are presented, followed by conclusions. gen10179.tex; 10/06/1999; 16:22; p.1

- by Jan Van der Kruk
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- Geology, Ground Penetrating Radar, Case Study, Field Survey

In a stereo configuration, the measurable disparity values are integral, therefore the measurable depths are discrete. This can create a trap for a safety system whose purpose is to estimate the trajectory of a moving object, and issue an early warning for the driver. Accuracy of this estimation is determined by the samples which have different measurable depths. Change in measurable depths becomes obvious for closer regions, however due the limited extent of stereo common field of view for these regions, the object might not be in the common field of view. A velocity estimation algorithm has been created, which takes into account the constraints of stereo, while determining an accurate estimate of object's trajectory. From examination of various scenarios, we show that a stereo system could be misleading while estimating the object trajectory. An approaching object on a collision course could be estimated as a non-collider by stereo.

- by Waqar Khan
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- Early Warning, Mobile Robots, Collision Avoidance, Velocity Estimation

1] For the first time in the history of the International Terrestrial Reference Frame, the ITRF2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model. Minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame (TRF). The ITRF2000 origin is defined by the Earth center of mass sensed by satellite laser ranging (SLR) and its scale by SLR and very long baseline interferometry. Its orientation is aligned to the ITRF97 at epoch 1997.0, and its orientation time evolution follows, conventionally, that of the no-net-rotation NNR-NUVEL-1A model. The ITRF2000 orientation and its rate are implemented using a consistent geodetic method, anchored over a selection of ITRF sites of high geodetic quality, ensuring a datum definition at the 1 mm level. This new frame is the most extensive and accurate one ever developed, containing about 800 stations located at about 500 sites, with better distribution over the globe compared to past ITRF versions but still with more site concentration in western Europe and North America. About 50% of station positions are determined to better than 1 cm, and about 100 sites have their velocity estimated to at (or better than) 1 mm/yr level. The ITRF2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the TRF orientation rate. A comparison to relative rotation poles of the NUVEL-1A plate motion model shows vector differences ranging between 0.03°and 0.08°/m.y. (equivalent to approximately 1-7 mm/yr over the Earth's surface). ITRF2000 angular velocities for four plates, relative to the Pacific plate, appear to be faster than those predicted by the NUVEL-1A model. The two most populated plates in terms of space geodetic sites, North America and Eurasia, exhibit a relative Euler rotation pole of about 0.056 (±0.005)°/m.y. faster than the pole predicted by NUVEL-1A and located about (10°N, 7°E) more to the northwest, compared to that model.

- by Zuheir Altamimi
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- Western Europe, Multidisciplinary, Velocity Estimation, North America

Solute (NaCl) miscible displacement experiments are performed on long disturbed soil columns to determine the hydrodynamic longitudinal dispersion coefficient and correlate it with the variability of the local permeability. The solute concentration, averaged over several cross-sections along the soil column, is monitored by measuring the electrical resistance between rod electrodes. The measured solute concentration breakthrough curves are fitted simultaneously with the one-region and two-region analytical models of the 1-D advection-dispersion equation to estimate the longitudinal dispersion coefficient, D L , as a function of Peclet number, Pe, for common groundwater flow velocities (2<Pe<50). Macroscopic simulations of miscible displacement in 2-D porous media described by a periodic permeability field with low, moderate and high variability are employed to evaluate the predictability of the one-region and two-region models, and the sensitivity of the dispersion coefficients and flow velocities estimated from soil column displacement tests to the variance of local permeability. When the variability of the local permeability becomes high, the one-region model fails, while the two-region model is capable of reproducing satisfactorily the breakthrough curves, and providing reliable values of dispersion coefficients. The two mean pore velocities estimated by the two-region model represent, on average, a fast and a slow mean velocity of the dispersion front, whereas their difference is a measure of the transient evolution of the width of the equiconcentration dispersion front.

- by C. Aggelopoulos
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- Multidisciplinary, Numerical Simulation, Porous Media, Electrical Resistance

Nonlinear observers for estimation of lateral and longitudinal velocity of automotive vehicles are proposed, based on acceleration and yaw rate measurements in addition to wheel speed and steering angle. The observer for lateral velocity uses a tyre-road friction model. Exponential stability of the observers are shown. A structural assumption on the friction model is discussed. The observer structure is validated using experimental data from cars.

- by Lars Imsland
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- Engineering, System Identification, Modeling, Vibration

The island of Ischia, located at the northwestern end of the Gulf of Napoli (Italy), is a volcanic area that is historically active (the Arso eruption, in 1302 and the Casamicciola earthquake, in 1883) and has diffuse hydrothermal phenomena. We present in this work a study of the surface deformation occurring in the island, which is based on applying the Differential Synthetic Aperture Radar Interferometry (DInSAR) algorithm referred to as Small BAseline Subset (SBAS) technique. This study is focused on the 1992-2003 time interval and SAR data acquired by the European Remote Sensing (ERS) satellites from ascending and descending orbits have been used, thus allowing us to discriminate the vertical and east-west components of the displacements. A validation of the DInSAR results has been carried out first by comparing the vertical deformations estimated from the SAR data with those measured from the spirit leveling network that is present in the area. In particular, we computed the difference between the mean vertical deformation velocities estimated from the SAR and the corresponding geodetic measurements along three main leveling lines; the maximum value of the root mean square difference is of about 1 mm/yr. The final discussion is dedicated to the interpretation of the detected displacements, benefiting from the overall information extracted from the ascending and descending DInSAR measurements. In particular, DInSAR data relative to the vertical deformation component show that the present-day subsidence of Ischia mainly develops in areas characterized by active landsliding and along faults; moreover, the deflation of the island, which is recorded by the horizontal displacement component, is probably related to the de-pressurization of the hydrothermal system. D

- by Carlo Del Gaudio
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- Geology, Geochemistry, Geophysics, Information Extraction

This paper presents a new mobile station velocity estimator based on the first moment of the instantaneous frequency (IF) of the received signal. The effects of shadowing, additive noise, and scattering distribution on the proposed velocity estimator are analyzed. We show that, unlike velocity estimators based on the envelope and quadrature components of the received signal, the proposed estimator is robust to shadowing. We also prove that the performance of the IF-based estimator is only mildly affected by the presence of additive noise. Finally, by using simulations we show that the performance of the proposed IF-based estimator is superior to that of existing velocity estimators.

- by Alam Shwab
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- Engineering, Technology, Velocity Estimation, Additive noise

A nonlinear observer for estimation of lateral and longitu- dinal velocity of automotive vehicles is proposed, based on acceleration and yaw rate measurements in addition to wheel speed and steering angle measurements. Sta- bility of the observer is proved in the form of input-to-state stability of the observer error dynamics, under an assump- tion on the friction model. This assumption

- by Lars Imsland
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- Nonlinear Observer, Velocity Estimation, Experimental Data

High performance speed sensorless control of induction motors (IMs) calls for estimation and control schemes that offer solutions to parameter uncertainties as well as to difficulties involved with accurate flux/velocity estimation at very low and zero speed. In this study, a new EKF based estimation algorithm is proposed for the solution of both problems and is applied in combination with speed sensorless direct vector control (DVC). The technique is based on the consecutive execution of two EKF algorithms, by switching from one algorithm to another at every n sampling periods. The number of sampling periods, n, is determined based on the desired system performance. The switching EKF approach, thus applied, provides an accurate estimation of an increased number of parameters than would be possible with a single EKF algorithm. The simultaneous and accurate estimation of rotor, R 0 r and stator, R s resistances, both in the transient and steady state, is an important challenge in speed sensorless IM control and reported studies achieving satisfactory results are few, if any. With the proposed technique in this study, the sensorless estimation of R 0 r and R s is achieved in transient and steady state and in both high and low speed operation while also estimating the unknown load torque, velocity, flux and current components. The performance demonstrated by the simulation results at zero speed, as well as at low and high speed operation is very promising when compared with individual EKF algorithms performing either R 0 r or R s estimation or with the few other approaches taken in past studies, which require either signal injection and/or a change of algorithms based on the speed range. The results also motivate utilization of the technique for multiple parameter estimation in a variety of control methods.

- by murat barut
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- System Identification, Modeling, Parameter estimation, Kalman Filter

The paper summarizes the main steps necessary for the definition of the odometry algorithm that can be used in the Automatic Train Protection and Control Systems. In this kind of devices the availability of a reliable speed and travelled distance estimation is essential for the efficiency and the safety of the whole system. The first step is the analysis and the choice of the sensors that can be used for the odometric estimation, a procedure that fuses the measures obtained from the sensor is defined. In the paper the main features of the developed solution will be summarized and its performance, in terms of precision in the speed and travelled distance estimation will be presented.

- by Benedetto Allotta
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- Engineering, Control system, Sensors, Distance

Field data on debris flows are of utmost importance for improving knowledge of these hazardous phenomena and for the development of attenuation measures. In alpine basins, debris flows generally occur with a frequency high enough to create serious risk to human settlements and transportation routes, but too low to justify monitoring activity capable of providing enough data in a sufficiently short time. The Moscardo Torrent, a small stream in the Eastern Italian Alps, is an exception to this general situation since it displays a high frequency of debris flows (commonly at least one event per year). In 1989, this torrent was instrumented and the results of the following 10 years (1989 -1998) of debris-flow monitoring are presented, with an analysis of collected data. The equipment installed allowed measurement of rainfall, flow stage and ground vibrations caused by debris flows. Other important debris-flow variables, that is, mean front velocity, peak discharge and flowing volume were estimated from instrumental records. Video pictures have proved to be useful for the visual interpretation of debris-flow waves and have made it possible to estimate the surface velocity of debris flows. Recorded data are compared with other experimental data sets collected and documented worldwide. Advantages and shortcomings of different types of sensors are discussed with relevance both for research monitoring purposes and for possible use in debris-flow warning systems. D

- by Massimo Arattano
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- Geology, Geomorphology, Vibration, High Frequency

Interest is growing in the application of coherent processing of synthetic aperture radar (SAR) data to the monitoring of complex urban or infrastructure areas. However, such scenarios are characterized by the layover phenomenon, in the presence of which conventional interferometric SAR techniques degrade or cannot operate. As a consequence, to monitor reliably a high number of ground structures, the identification, i.e., the detection and height and deformation velocity estimation, of both single and multiple scatterers interfering in the same SAR cell can be a key step. This issue is addressed here by means of differential tomography (Diff-Tomo), a recent multibaseline-multitemporal generalized interferometric framework which allows to resolve multiple moving scatterers at different heights in the same cell. In particular, superresolution adaptive Diff-Tomo is extensively tested and augmented with a new information extraction algorithm for the automated identification of the multiple scatterers. Experiments have been carried out with real C-band spaceborne data over urban areas; corresponding results are shown and discussed.

- by Matteo Pardini
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- Geophysics, Information Extraction, Tomography, Noise

Electrical resistivity tomography (ERI) and ground-penetrating radar (GPR) surveys have been combined to investigate different volcanic materials, their contacts (lava flows, pyroclastic deposits, dykes) and structures (lava tubes, faults) in Tenerife (Canary Islands). The EM waves mean velocities estimated for the different rocks range from 0.075 to 0.1 m ns − 1 . Nonconsolidated materials such as hydromagmatic, pyroclastic and airfall deposits display the lowest EM mean velocities, whereas massive and consolidated materials, mainly lava flows, show the fastest ones. The higher resistivity values (> 800-1000 Ω m) correspond to lava flows, the intermediate resistivity values (∼ 100-800 Ω m) are related to different types of non-consolidated deposits (pyroclastic or explosive deposits), and the lower resistivity values (5-50 Ω m) correspond to fine grained volcanic materials (altered ignimbrite and hydrovolcanic). ERI usually provides a good definition of the boundaries between the volcanic units, shows a better performance than GPR to locate structures such as lava tubes and faults, and also gives a direct estimation of depth. The resistivity models are better defined if two different datasets obtained from dipole-dipole and Wenner arrays are combined prior to the inversion procedure. On the other hand, due to its greater horizontal and vertical resolution, the GPR technique is the most effective to characterize the internal structure of the volcanic deposits. However, a very strong attenuation of the EM waves has been observed in relation to the pyroclastic deposits, which makes the GPR unable to locate internal boundaries at depths as shallow as 2 m. This problem may also derive from the choice of the frequency antennae. If this is correct, then different antenna frequencies would have produced different results.

- by Ivan Velazquez
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- Civil Engineering, Geophysics, Ground Penetrating Radar, Applied Geophysics

A one-dimensional intravascular MR (IVMR) technique for the measurement of pulsewave velocity in a single cardiac cycle is presented. The technique was used to measure pulsewave velocity in vivo in the intact rabbit model, where its sensitivity to different hemodynamic states was demonstrated using a pharmacological intervention with phenylephrine and nitroprusside. IVMR measurements of pulsewave velocity were found to increase with mean arterial pressure, as expected. Further, IVMR-based pulsewave velocity estimates were in agreement with those measured by pressure catheters and direct distensibility measurement. Because of their rapidity and highly localized nature, these measurements of vessel elasticity may complement the high-resolution vascular imaging information gained in an IVMR examination. This could allow assessment of atherosclerotic plaques and facilitate immediate treatment decisions. Magn Reson Med 45:53-60, 2001.

- by Ergin Atalar
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- Biomedical Engineering, Magnetic Resonance Imaging, Medicine, Catheterization
- by Chris Houser
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- Earth Sciences, Marine Geology, Velocity Estimation, Wave Breaking

This paper investigates algorithms for constructing velocity approximations from discrete position versus time data. The study is limited to algorithms suitable to provide velocity information in discrete-time feedback control systems such as microprocessor-based systems with a discrete position encoder. Velocity estimators based on lines per period, reciprocal-time, Taylor series expansions, backward difference expansions, and least-square curve fits are presented. Based on computer simulations, comparisons of relative accuracies of the different algorithms are made. The least-squares velocity estimators Htered the effect of imperfect measurements ("noise") best, whereas the Taylor series expansions and backward difference equation estimators respond better to velocity transients.

- by Ronald Brown
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- Engineering, Computer Simulation, Feedback Control, Velocity Estimation

Surface velocity estimates from wind and altimeter data, together with satellite-derived sea surface temperature and chlorophyll, were used to explore the advection patterns and environmental conditions using a simple Lagrangian model. Although the model is generic (only considering the physical transport), the results are of particular interest for sardine (Sardina pilchardus) early life stages, due to the spawning dynamics of the species off Iberia and NW Africa. Particles were released on the shelf of the Iberian and northern African Atlantic coasts every five days from 1998 to 2004 and advected for 27-days. Trajectories were computed using combinations of three surface velocity constituents: Ekman velocity, geostrophic velocity derived from sea level anomaly maps and mean geostrophic velocity derived from two mean dynamic topographies. Daily time series of sea surface temperature, chlorophyll-a concentration and water depth where constructed for each particle trajectory. The results showed strong regional and seasonal dependence of the transport due to wind, with average seasonal cycles of the percentage of particles found in the shelf reflecting the anticipated effect of the seasonal north-south migration of the trade wind belt. The addition of the geostrophic transport led to the attenuation of seasonal cycles and higher mean/maximum values in the probability of retention within the shelf. This increased capacity for retention even during strong upwelling conditions seems to have been overlooked by theories aiming to describe the reproductive strategies of pelagic fish and understand recruitment dynamics based primarily on wind variability. On the other hand, the average surface chlorophyll values indicated a distribution area with higher primary production for particles that never leave the shelf, in comparison to those that return to it or are found in the open sea a month after release, which is in agreement with existing hypotheses that offshore advection is detrimental to larval survival mainly due to the higher risk of starvation. Finally, the exchange between adjacent shelf areas was generally small (less than 5%) within the study period, with the exception of the Gulf of Cadiz. In the latter area, up to 50% of particles released in the southern Iberian shelf reached the Moroccan shelf in several events, contradicting previous suggestions that the Strait of Gibraltar acts as a physical barrier that promotes genetic differentiation among neighbouring sardine populations in the Atlantic. Overall, these results provide useful insights for the study of sardine dynamics in the northeast Atlantic but the unexpectedly high sensitivity of summary metrics (namely retention probability) to the choice of surface velocity field preclude firm conclusions and indicate alternative routes for future studies.

- by Paulo Oliveira
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- Time Series, Sea surface temperature, Population structure, Seasonality

We present a new global model for Recent plate velocities, REVEL, describing the relative velocities of 19 plates and continental blocks. The model is derived from publicly available space geodetic (primarily GPS) data for the period 1993-2000. We include an independent and rigorous estimate for GPS velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates. The velocity fields for North America, Eurasia, and Antarctica clearly show the effects of glacial isostatic adjustment, and Australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field. Two thirds of tested plate pairs agree with the NUVEL-1A geologic (3 Myr average) velocities within uncertainties. Three plate pairs (Caribbean-North America, Caribbean-South America, and North America-Pacific) exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in NUVEL-1A due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities. Most other differences probably reflect real velocity changes over the last few million years. Several plate pairs (Arabia-Eurasia, Arabia-Nubia, Eurasia-India) move more slowly than the 3 Myr NUVEL-1A average, perhaps reflecting long-term deceleration associated with continental collision. Several other plate pairs, including Nazca-Pacific, Nazca-South America and Nubia-South America, are experiencing slowing that began $25 Ma, the beginning of the current phase of Andean crustal shortening.

- by Timothy Dixon
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- Geodesy, Geology, Stress field, Multidisciplinary
- by Yiannis Aloimonos
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- Cognitive Science, Image Recognition (Computer Vision), Bias, Motion estimation

A novel approach to vehicle velocity estimation is proposed. To be cost effective, the estimation is based solely on wheel speed measurement without any additional information on vehicle acceleration. This is made possible by employing an adaptive nonlinear filter scheme which proves to be simple and efficient. Simulation results from field-testing data show that this method results in accurate and smooth vehicle velocity estimation and it is practically feasible.

- by Fangjun Jiang
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- Control Systems, Nonlinear filters, Parameter estimation, Cost effectiveness

Temperature and pressure drop data obtained from an air-cooled heat exchanger model with crosssectional flow areas of 0.56 m 2 , 1.00 m 2 and 2.25 m 2 operating under natural convection are presented that indicate significant cold inflow, resulting in the reduction of effective chimney height. Cold inflows encountered in actual applications where the Froude number is typically 0.2, may not be as severe as described in this paper, which was of the order of 10 −6 -10 −4 . Additional tests on smaller scale models appeared to favor the explanation that the occurrence of cold inflow in the air-cooled heat exchanger model was primarily due to the relative ease in either drawing cold air from inlet or from outlet, and to a lesser extent the Froude number of the chimney or the critical velocity estimated by Jörg and Scorer's (1967) formula. A CFD study will bring much understanding of the phenomenon for the different situations.

- by Sivakumar Kumaresan
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- Heat Exchanger, Natural Convection, Velocity Estimation, Cooling Tower

In this work, a sensorless control scheme was designed for permanent magnet synchronous motors based on a sampled model. The discrete-time model was obtained using the Symplectic Euler method. Taking such model along with voltage and current measurements, an observer is designed for rotor position and velocity estimation. Then, the rotor velocity is forced to track a desired reference signal by means of a discretetime quasi-sliding mode technique.

- by Jorge Rivera
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- Digital Control, Sliding mode control, Velocity Estimation, Mathematical Model
- by Sergey Fomel
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- Geophysics, Velocity Estimation, Inverse Problem

In this note numerical sensitivity of a wave finite element approach and its post processing for group velocities and energy velocities estimation is dealt with. Precisely, aliasing effects is discussed first. Calculation of guided waves group velocity through a numerical procedure is given. A wave track versus frequencies criteria is employed. Energetics of multimode guided wave propagation is also discussed. Analytical expressions of energy velocities are provided. Energy velocities are compared to group velocities, and the sensitivity of energy velocities to the finite element system characteristics is discussed. r

- by Jean-Mathieu Mencik
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- Engineering, Finite Element, Physical sciences, Sound and Vibration

In a dynamic situation like robot soccer any individual player can only observe a limited portion of their environment at any given time. As such to develop strategies based upon planning and cooperation between different players it is imperative that they be able to share information which may or may not be in any individual player’s field of vision. In this paper we propose a method for multi-agent cooperation for perception based upon the Extended Kalman Filter (EKF) which enables players to track objects absent from their field of vision and also to improve the accuracy of position and velocity estimates of objects in their field of vision.

- by Alankar Karol
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- Object Tracking, RoboCup, Sensor Fusion, Velocity Estimation

Because of the sub-meter spatial resolution of very high resolution (VHR) optical satellite imagery, vehicles can be identified in this type of imagery. Further, because there is a time lag in image collection between the Panchromatic (Pan) and multispectral (MS) sensors onboard VHR satellites, a moving vehicle is observed by the satellite at slightly different times. Consequently, its velocity information including speed and direction can be determined. The higher spatial resolution and more spectral bands of WorldView-2 (WV2) imagery, compared to those of previous VHR satellites such as QuickBird and GeoEye-1, together with the new sensors' configuration of WV2, i.e., 4 bands on each side of the Pan sensor (MS1 and MS2), adds an opportunity to improve both moving vehicles extraction and the velocity estimation. In this paper, a novel processing framework is proposed for the automatic extraction of moving vehicles and determination of their velocities using single-pass WV2 imagery. The approach contains three major components: a) object-based road extraction, b) moving vehicle extraction from MS1 and MS2, and c) velocity estimation. The method was tested on two different areas of a WV2 image, a high speed and a low speed traffic zone. The method resulted in a correctness of 92% and a completeness of 77% for the extraction of moving vehicles. Furthermore, the estimated speeds and directions are very realistic and are consistent with the speed limits posted on the roads. The results demonstrate a promising potential for automatic and accurate traffic monitoring using a single image of WV2.

- by Bahram Salehi
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- Data Mining, Information Extraction, Image segmentation, Object Recognition

Vision, our intuition tells us, is about recognizing objects and colours. However, with a little more insight we realize that understanding spatial relationships is also crucial. In particular, the displacement of objects with time carries vital information. How difficult can it be to see an object move? The principle seems simple: an object is first in one location, and then a moment later it is in another. In reality, motion detection is fraught with difficulties, such as how to distinguish between image noise and actual motion, and how to deal with several movements in the same part of an image. But at the core of motion processing is the aperture problem, a computational obstacle that is as abstruse as it is inconvenient . The aperture problem refers to the visual system's inability to sense the overall velocity of an object by sampling the velocity at just one location on the object's surface. Unless this problem is overcome, the velocity of objects cannot be computed. Therefore, a great deal of visual processing is dedicated to a problem that most of us have never heard of. This Review will cover the basic stages of velocity computation in the primate visual system, with emphasis on the mechanisms that create and solve the aperture problem. We aim to show how a combined theoretical and experimental approach can provide unique insights into computational neural systems.

- by David Bradley
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- Cognitive Science, Computational Neuroscience, Space perception, Primates

A new vision-based obstacle avoidance technique for indoor navigation of Micro Aerial Vehicles (MAVs) is presented in this paper. The vehicle trajectory is modified according to the obstacles detected through the Depth Map of the surrounding environment, which is computed online using the Optical Flow provided by a single onboard omnidirectional camera. An existing closed-form solution for the absolute-scale velocity estimation based on visual correspondences and inertial measurements is generalized and here employed for the Depth Map estimation. Moreover, a dynamic region-of-interest for image features extraction and a self-limitation control for the navigation velocity are proposed to improve safety in view of the estimated vehicle velocity. The proposed solutions are validated by means of simulations.

- by Vincenzo Lippiello
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- Optical Flow, Velocity Estimation, Obstacle Avoidance, Depth Map

A position-based visual servo control strategy is proposed for leader-follower formation control of unmanned ground vehicles (UGVs). The proposed control law only requires the knowledge of a single known length on the leader. The relative pose and the relative velocity of the leader are estimated with respect to the follower in the follower reference frame. The relative pose and the relative velocity are obtained using a geometric pose estimation technique and a nonlinear velocity estimation strategy, respectively. A ...

- by Ashwin Dani
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- Computational Geometry, Neural Networks, Motion estimation, Mobile Robots

Coded excitation is now a well-established technique in medical ultrasound for B-mode imaging applications. It enables a gain in depth of penetration, without sacrificing the spatial resolution and maintaining an acceptable peak intensity for patient safety. The rationale of this technique for velocity estimation applications still has to be formulated in more precise terms. In particular, differences in the situation that arise in color flow imaging (CFI) applications from typical B-mode imaging conditions, such as signal-to-noise ratio conditions, pulsing strategy, and safety requirements, need to be specifically addressed to assess more quantitatively the potential of this technique. This paper discusses the potential improvement in sensitivity, resolution, and statistical performance provided by coded excitation for CFI applications from theoretical considerations and simulations.

- by Tom Anderson
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- Engineering, Colorimetry, Rheology, Ultrasound

Streambed seepage can be predicted using an analytical solution to the one-dimensional heat transport equation to take advantage of the relationship between streambed thermal properties, seepage flux, and the amplitude ratio and phase shift associated with streambed temperature signals. This paper explores the accuracy of streambed-seepage velocity estimates from this method when uncertainty in input parameters exists. Uncertainty in sensor spacing, thermal diffusivity, and the accuracy of temperature sensors were examined both individually and in combination using Monte Carlo analysis. The analytical solution correctly reproduced known thermal front velocities above 1.25 m d À1 , using both the amplitude-ratio and phase-shift methods, despite introduced uncertainty in any of the variables. Noise in temperature measurements (because of sensor accuracy) caused erroneous prediction of velocity for gaining stream conditions using both the amplitude ratio and phase shift. Uncertainty in the thermal diffusivity and sensor spacing resulted in incorrect velocity, primarily under gaining conditions, when using the amplitude ratio and near-zero velocity using the phase shift. For a sensor accuracy of 0.15 C, we present combinations of parameters for which the resulting signal amplitude is sufficiently large for use with the Stallman equation.

- by Christine Hatch
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- Environmental Engineering, Civil Engineering, Geology, Materials Science

Two-dimensional angle-independent blood velocity estimates typically combine the Doppler frequencies independently measured by two ultrasound beams with known interbeam angle. A different dual-beam approach was recently introduced in which one (reference) beam is used to identify the flow direction, and the second (measuring) beam directly estimates the true flow velocity at known beam-flow angle. In this paper, we present a procedure to automatically steer the two beams along optimal orientations so that the velocity magnitude can be measured. The operator only takes care of locating the Doppler sample volume in the region of interest and, through the extraction of appropriate parameters from the Doppler spectrum, the reference beam is automatically steered toward right orientation to the flow. The velocity magnitude is thus estimated by the measuring beam, which is automatically oriented with respect to the (known) flow direction at a suitable Doppler angle. The implementation of the new angle tracking method in the ULtrasound Advanced Open Platform (ULA-OP), connected to a linear array transducer, is reported. A series of experiments shows that the proposed method rapidly locks the flow direction and measures the velocity magnitude with low variability for a large range of initial probe orientations. In vitro tests conducted in both steady and pulsatile flow conditions produced coefficients of variability (CV) below 2.3% and 8.3%, respectively. The peak systolic velocities have also been measured in the common carotid arteries of 13 volunteers, with mean CV of 7%.

- by Piero Tortoli
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- Biomedical Engineering, Ultrasound, Automation, Method

The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author's institution, sharing with colleagues and providing to institution administration.

- by Vlad Manea
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- Geology, Geomorphology, Risk assessment, Velocity Estimation

Avalanche measurements carried out at the Ryggfonn test site, Norway, during several winter seasons are analyzed with emphasis on recognizing different flow regimes and estimating flow densities. Measurements include impact pressure readings from load cells mounted at two locations within the track and stress readings from load plates flush with the upstream slope of a catching dam. Pressure measurements were combined with velocity estimates based on cross correlations between the load cell readings and, in several cases, on Doppler radar measurements. In most cases a saltation (fluidized) layer in front of a more dense part could be identified. Doppler radar measurements confirm a fast moving head, in some instants preceded by a slower snout, and decreasing speed from the head to the tail. Calculated accelerations (decelerations) indicate that the effective friction parameter varies strongly and depends on the flow regime.

- by Krister Kristensen
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- Civil Engineering, Seasonality, Cross Correlation, Shear Stress

Since 1999 six Sound Fixing and Ranging (SOFAR) hydrophones have been moored along the Mid-Atlantic Ridge (MAR) (15Њ-35Њ N). These hydrophones (8-bit data resolution) are designed for long-term monitoring of MAR seismicity using the acoustic T waves of seafloor earthquakes. The completeness level of the MAR Twave earthquake catalog estimated from size-frequency constraints is m b ϳ 3.0, a significant improvement in detection compared to the m b 4.6 completeness level estimated from National Earthquake Information Center magnitude-frequency data. The hydrophones also detect the acoustic phase of converted upper mantle P arrivals from regional earthquakes at epicentral distances of 374-1771 km and from events as small as m b 3.6. These regional P waves are used to estimate a Pn velocity of 8.0 ‫ע‬ 0.1 km sec ‫1מ‬ along the east and west MAR flanks. An unexpected result was the identification of P arrivals from earthquakes outside the Atlantic Ocean basin. The hydrophones detected P waves from global earthquakes with magnitudes of 5.8-8.3 at epicentral distances ranging from 29.6Њ to 167.2Њ. Examination of travel times suggests these teleseismic P waves constitute the suite of body-wave arrivals from direct mantle P to outer-and inner-core reflected/refracted phases. The amplitudes of the teleseismic P waves also exhibit the typical solid-earth wave field phenomena of a P shadow zone and caustic at D ϳ 144Њ. These instruments offer a long-term, relatively low-cost alternative to ocean-bottom seismometers that allows for observation of Pn velocities and mantle/core phases arriving at normally inaccessible deepsea locations.

- by Delwayne Bohnenstiehl and +1
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- Civil Engineering, Geophysics, Lower mantle, Velocity Estimation

- by Lars Imsland
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- Cybernetics, Control, Vehicle Dynamics, Stability

We present the extension of stereotomography to P-and S-wave velocity estimation from PP-and PS-reflected/diffracted waves. In this new context, we greatly benefit from the use of locally coherent events by stereotomography. In particular, when applied to S-wave velocity estimation from PS-data, no pairing of PP-and PS-events is a priori required. In our procedure the P-wave velocity model is obtained first using stereotomography on PP-arrivals. Then the S-wave velocity model is obtained using PS-stereotomography on PS-arrivals fixing the Pwave velocity model. We present an application to an 'ideal' synthetic data set demonstrating the relevance of the approach, which allows us to recover depth consistent P-and S-waves velocity models even if no pairing of PP-and PS-events is introduced. Finally, results to a real data set from the Gulf of Mexico are presented demonstrating the potential of the method in a noisy data context.

- by Reda Baina and +1
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- Geology, Geophysics, Geomatic Engineering, Velocity Estimation

In this paper, we present a method for computing velocity using a single camera onboard a road vehicle, i.e. an automobile. The use of computer vision provides a reliable method to measure vehicle velocity based on egomotion computation. By doing so, cumulative errors inherent to odometrybased systems can be reduced to some extent. Road lane markings are the basic features used by the algorithm. They are detected in the image plane and grouped in couples in order to provide geometrically constrained vectors that make viable the computation of vehicle motion in a sequence of images. The applications of this method can be mainly found in the domains of Robotics and Intelligent Vehicles.

- by Jacob Fokkema
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- Geology, Ground Penetrating Radar, Case Study, Field Survey