Velocity Doppler Shift Research Articles

Rethinking Doppler Effect for Accurate Velocity Estimation With Commodity WiFi Devices

Enabling pervasive WiFi devices with non-contact sensing capability is an important topic in the field of integrated sensing and communication. Doppler effect has been widely exploited to estimate targets’ velocity from wireless signals. However, the separation of signal sources and receivers complicates the relationship between Doppler frequency shift (DFS) and target velocity in WiFi-based non-contact sensing systems. In contrast to existing works that rely on either approximated relations or coarse-grained information such as whether a target is moving toward or away from WiFi transceivers, this paper investigates rigorously the dependency of velocity estimation accuracy on target locations and headings in WiFi sensing systems. The theoretical insights allow us to derive a closed-form solution and understand the fundamental limitation of velocity estimation. To optimize velocity estimation performance, we devise a receiving device selection scheme that dynamically chooses the optimal set of receivers among multiple available WiFi devices. A prototype real-time target tracking system has been implemented using commodity WiFi devices. Extensive experimental results show that the proposed system outperforms state-of-the-art approaches in velocity estimation and tracking, and is able to achieve <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.38cm/s$ </tex-math></inline-formula> , 13.42°, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$31.08cm$ </tex-math></inline-formula> median errors in speed, heading and location estimation amongst experiments conducted in three indoor environments with three device placements and eight human subjects over 15 trajectories.

Methods for coherent optical Doppler orbitography

Doppler orbitography uses the Doppler shift in a transmitted signal to determine the orbital parameters of satellites including range and range rate (or radial velocity). We describe two techniques for atmospheric-limited optical Doppler orbitography measurements of range rate. The unstabilised technique determines the Doppler shift directly from a heterodyne measurement of the returned optical signal. The stabilised technique aims to improve the precision of the first by suppressing atmospheric phase noise imprinted on the transmitted optical signal. We demonstrate the performance of each technique over a $$2.2\,\hbox {km}$$ horizontal link with a simulated in-line velocity Doppler shift at the far end. A horizontal link of this length has been estimated to exhibit nearly half the total integrated atmospheric turbulence of a vertical link to space. Without stabilisation of the atmospheric effects, we obtained an estimated range rate precision of $$17\,{\upmu }\hbox {m}\,\hbox {s}^{-1}$$ at $$1\,\hbox {s}$$ of integration. With active suppression of atmospheric phase noise, this is improved by three orders of magnitude to an estimated range rate precision of $$9.0\,\hbox {nm}\,\hbox {s}^{-1}$$ at $$1\,\hbox {s}$$ of integration, and $$1.1\,\hbox {nm}\,\hbox {s}^{-1}$$ when integrated over $$60\,\hbox {s}$$ . This represents four orders of magnitude improvement over the typical performance of operational ground to space X-Band systems in terms of range rate precision at the same integration time. The performance of this system is a promising proof of concept for coherent optical Doppler orbitography. There are many additional challenges associated with performing these techniques from ground to space that were not captured within the preliminary experiments presented here. In the future, we aim to progress towards a $$10\,\hbox {km}$$ horizontal link to replicate the expected atmospheric turbulence for a ground to space link.

An Improved Method for Determining Near‐Surface Currents From Wave Dispersion Measurements

AbstractA new inversion method for determining near‐surface shear currents from a measured wave spectrum is introduced. The method is straightforward to implement and starts from the existing state‐of‐the‐art technique of assigning effective depths to measured wavenumber‐dependent Doppler shift velocities. A polynomial fit is performed, with the coefficients scaled based on a simple derived relation to produce a current profile that is an improved estimate of the true profile. The method involves no user‐input parameters, with the optimal parameters involved in the polynomial fit being chosen based on a simple criterion involving the measured Doppler shift data only. The method is tested on experimental data obtained from a laboratory where current profiles of variable depth dependence could be created and measured by particle image velocimetry, which served as “truth” measurements. Applying the new inversion method to experimentally measured Doppler shifts resulted in a &gt;3 times improvement in accuracy relative to the state of the art for current profiles with significant near‐surface curvature. The experiments are dynamically similar to typical oceanographic flows such as wind‐drift profiles, and our laboratory thus makes a suitable and eminently useful scale model of the real‐life setting. Our results show that the new method can achieve improved accuracy in reconstructing near‐surface shear profiles from wave measurements by a simple extension of methods, which are currently in use, incurring little extra complexity and effort. A novel adaptation of the normalized scalar product method has been implemented, able to extract Doppler shift velocities as a function of wavenumber from the measured wave spectrum.

The Effect of Drifter GPS Errors on Estimates of Submesoscale Vorticity

AbstractDifferential kinematic flow properties (DKP), such as vertical vorticity, have been estimated from surface drifters. However, previous DKP error estimates were a posteriori and did not include correlated errors across drifters. To accurately estimate submesoscale (≤1 km) DKPs from drifters, errors must be better understood. Here, the a priori vorticity standard error is derived that depends upon the number of drifters in the cluster, the drifter cluster major and minor axes lengths, the instrument velocity error, and the cross-drifter error correlation. Two stationary GPS experiments, with zero vorticity, were performed at separations of O(101–103) m to understand vorticity error and test the derivation using 1 Hz position differences and Doppler shift velocities. Vorticity errors of ±5f (where f is the local Coriolis parameter)were found for ≈40 m separations. The frequency-dependent velocity variances and GPS-to-GPS correlations are quantified. Vorticity estimated with a “blended” velocity has reduced error. The stationary vorticity error can be well predicted given velocity error, correlation, and minor axis length. Vorticity error analysis is applied to submesoscale-sampling in situ GPS drifters near Point Sal, California. The derivation predicts when large high-frequency vorticity fluctuations (indicating noise) occur. Previously, cluster area or ellipticity were used as criteria to distinguish error. We show that the drifter cluster minor axis (narrowness) is a key time-dependent factor affecting vorticity error, and even for velocity errors &lt;0.004 m s−1, the vorticity error exceeds ±5f when cluster minor axis &lt;50 m. These results will aid submesoscale drifter deployment planning.

Moving target detection based on velocity compensation methods in a coherent continuous wave lidar

Light Detection and Ranging (lidar) technology has been applied in military and civil areas and shows great potential. However, in coherent lidar detection, significant Doppler Effect and velocity uncertainty result a bad influence on moving target ranging. In this study, the authors demonstrate a velocity compensation method based on both Doppler shift evaluation and velocity searching and matching method. The authors used dot-linear frequency modulation signal for detection in order to achieve both velocity and distance information in the same period. Further by using searching and matching processing based on Shannon entropy can give a better-compensated velocity to extract more accurate distance information of targets. The authors applied this method on passive and self-driving moving targets, which fit the actual characteristics of both kinds of targets. Especially in self-driving moving target, there exists a significant target fluctuation in movement during detection that causes the splitting of Doppler peaks. The blurry in velocity estimation restricts the accuracy of sensing. The authors found the Shannon entropy searching method could reduce this effect. On the other hand, the feature of fluctuation in micro movement may give a way to identify the targets in the future.

Frequency-domain waveform approximants capturing Doppler shifts

Gravitational wave astrophysics has only just begun, and as current detectors are upgraded and new detectors are built, many new, albeit faint, features in the signals will become accessible. One such feature is the presence of time-dependent Doppler shifts, generated by the acceleration of the center of mass of the gravitational-wave emitting system. We here develop a generic method that takes a frequency-domain, gravitational-wave model devoid of Doppler shifts and introduces modifications that incorporate them. Building upon a perturbative expansion that assumes the Doppler-shift velocity is small relative to the speed of light, the method consists of the inclusion of a single term in the Fourier phase and two terms in the Fourier amplitude. We validate the method through matches between waveforms with a Doppler shift in the time domain and waveforms constructed with our method for two toy problems: constant accelerations induced by a distant third body and Gaussian accelerations that resemble a kick profile. We find mismatches below $\sim\!10^{-6}$ for all of the astrophysically relevant cases considered, and improve further at smaller velocities. The work presented here will allow for the use of future detectors to extract new, faint features in the signal from the noise.

Spatially resolved evolution of the local H2O production rates of comet 67P/Churyumov-Gerasimenko from the MIRO instrument on Rosetta

Aims. Using spectroscopic and continuum data measured by the MIRO instrument on board Rosetta of comet 67P/Churyumov-Gerasimenko, it is possible to derive and track the change in the water production rate, to learn how the outgassing evolves with heliocentric distance. The MIRO data are well suited to investigate the evolution of 67P, in unprecedented spatial and temporal detail.Methods. To obtain estimates of the local effective Haser production rates we developed an efficient and reliable retrieval approach with precalculated lookup tables. We employed line area ratios (H2 16 O/H2 18 O) from pure nadir observations as the key variable, along with the Doppler shift velocity, and continuum temperature. This method was applied to the MIRO data from August 2014 until April 2016. Perihelion occurred on August 13, 2015 when the comet was 1.24 AU from the Sun.Results. During the perihelion approach, the water production rates increased by an order of magnitude, and from the observations, the derived maximum for a single observation on August 29, 2015 is (1.42 ± 0.51) ×1028 . Modeling the data indicates that there is an offset in the peak outgassing, occurring 34 ± 10 days after perihelion. During the pre-perihelion phase, the production rate changes with heliocentric distance as r h −3.8±0.2 ; during post-perihelion, the dependence is r h −4.3±0.2 . The comet is calculated to have lost 0.12 ± 0.06 % of its mass during the perihelion passage, considering only water ice sublimation. Additionally, this method provides well sampled data to determine the spatial distribution of outgassing versus heliocentric distance. The time evolution is definitely not uniform across the surface. Pre- and post-perihelion, the surface temperature on the southern hemisphere changes rapidly, as does the sublimation rate with an exponent of ~−6. There is a strong latitudinal dependence on the r h exponent with significant variation between northern and southern hemispheres, and so the average over the comet surface may only be of limited importance. We present more detailed regional variation in the outgassing, demonstrating that the highest derived production rates originate from the Wosret, Neith and Bes regions during perihelion.

A SEARCH FOR SUBMILLIMETER H2O MASERS IN ACTIVE GALAXIES: THE DETECTION OF 321 GHz H2O MASER EMISSION IN NGC 4945

ABSTRACT We present further results of a search for extragalactic submillimeter H2O masers using the Atacama Large Millimeter/submillimeter Array (ALMA). The detection of a 321 GHz H2O maser in the nearby type 2 Seyfert galaxy, the Circinus galaxy, has previously been reported, and here the spectral analysis of four other galaxies is described. We have discovered H2O maser emission at 321 GHz toward the center of NGC 4945, a nearby type 2 Seyfert. The maser emission shows Doppler-shifted velocity features with velocity ranges similar to those of the previously reported 22 GHz H2O masers; however, the non-contemporaneous observations also show differences in velocity offsets. The subparsec-scale distribution of the 22 GHz H2O masers revealed by earlier very long baseline interferometry observations suggests that the submillimeter masers could arise in an edge-on rotating disk. The maser features remain unresolved by the synthesized beam of ∼0.″54 (∼30 pc) and are located toward the 321 GHz continuum peak within errors. A marginally detected (3σ) high-velocity feature is redshifted by 579 km with respect to the systemic velocity of the galaxy. Assuming that this feature is real and arises from a Keplerian rotating disk in this galaxy, it is located at a radius of ∼0.020 pc (∼1.5 × 105 Schwarzschild radii), which would enable molecular material closer to the central engine to be probed than the 22 GHz H2O masers. This detection confirms that submillimeter H2O masers are a potential tracer of the circumnuclear regions of active galaxies, which will benefit from higher angular resolution studies with ALMA.

MODELING OF REFLECTIVE PROPAGATING SLOW-MODE WAVE IN A FLARING LOOP

Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in EUV images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by the synthesized \textit{Solar Dynamics Observatory}/Atmospheric Imaging Assembly (AIA) 131, 94~\AA~emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km/s in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps of the \textit{Solar and Heliospheric Observatory}/Solar Ultraviolet Measurement of Emitted Radiation (SUMER) Fe XIX line emission, we confirm that these reflected slow mode waves are propagating waves.

Synthesis of Vortex Rossby Waves. Part I: Episodically Forced Waves in the Inner Waveguide

Abstract Spiral cloud bands dominate tropical cyclones’ appearance in satellite and radar images. It is generally accepted that at least some of them are vortex Rossby waves that propagate on the radial gradient of mean-flow-relative vorticity. This study models these features in Fourier and time domains as linear, barotropic, nondivergent waves on a maintained mean vortex scaled to resemble tropical cyclones. This formulation is the simplest one imaginable that encompasses the essential rotational dynamics. The modeled waves are episodically forced by a rotating annular train of sinusoidal vorticity sources and sinks that crudely represents eyewall convection. Substantial quiescent time intervals separate forced intervals. The waves propagate wave energy predominantly outward and converge angular momentum inward. Waves’ energy is absorbed as their perturbation vorticity becomes filamented near the outer critical radii where their Doppler-shifted frequencies and radial group velocities approach zero. The waves can propagate spatially only in narrow annular waveguides because of their slow tangential phase velocity and the restricted Rossby wave frequency domain. Although radial shear of the mean flow distorts their velocity field into tightly wound spirals, their streamfunction and geopotential fields assume the form of elliptical gyres or broad trailing spirals that do not resemble observed hurricane rainbands.

SIMULATED PHOTOEVAPORATIVE MASS LOSS FROM HOT JUPITERS IN 3D

ABSTRACT Ionizing stellar photons heat the upper regions of planetary atmospheres, driving atmospheric mass loss. Gas escaping from several hot, hydrogen-rich planets has been detected using UV and X-ray transmission spectroscopy. Because these planets are tidally locked, and thus asymmetrically irradiated, escaping gas is unlikely to be spherically symmetric. In this paper, we focus on the effects of asymmetric heating on local outflow structure. We use the Athena code for hydrodynamics to produce 3D simulations of hot Jupiter mass loss that jointly model wind launching and stellar heating via photoionization. Our fiducial planet is an inflated, hot Jupiter with radius R p = 2.14 R Jup ?> and mass M p = 0.53 M Jup ?> . We irradiate the initially neutral, atomic hydrogen atmosphere with 13.6 eV photons and compute the outflow’s ionization structure. There are clear asymmetries in the atmospheric outflow, including a neutral shadow on the planet’s nightside. Given an incident ionizing UV flux comparable to that of the Sun, we find a steady-state mass loss rate of &sim; 2 &times; 10 10 ?> g s−1. The total mass loss rate and the outflow substructure along the substellar ray show good agreement with earlier 1D models, for two different fluxes. Our 3D data cube can be used to generate the outflow’s extinction spectrum during transit. As a proof of concept, we find absorption of stellar Lyα at Doppler-shifted velocities of up to ±50 km s−1. Our work provides a starting point for further 3D models that can be used to predict observable signatures of hot Jupiter mass loss.

Doppler shift and ambiguity velocity caused by relative motion in quantum-enhanced measurement.

We study the effect of relative motion on a frequency-entangled-based ranging scheme. Two major puzzles arise, i.e., Doppler shift and ambiguity velocity. During condition of rapid relative motion, Doppler shift invalidates the measurement result of this scheme; while during condition of slow relative motion, the ambiguity velocity turns into a major limitation. If relative speed between targets and measurement platform exceeds the ambiguity velocity, an accumulated profile obtained by the coincidence measurement will be distorted, which causes a lower ranging accuracy. Theoretical analysis shows a time-varying delay can be introduced to solve the two major puzzles.

FORWARD MODELING OF STANDING SLOW MODES IN FLARING CORONAL LOOPS

Standing slow mode waves in hot flaring loops are exclusively observed in spectrometers and are used to diagnose the magnetic field strength and temperature of the loop structure. Due to the lack of spatial information, the longitudinal mode cannot be effectively identified. In this study, we simulate standing slow mode waves in flaring loops and compare the synthesized line emission properties with SUMER spectrographic and SDO/AIA imaging observations. We find that the emission intensity and line width oscillations are a quarter period out of phase with Doppler shift velocity both in time and spatial domain, which can be used to identify a standing slow mode wave from spectroscopic observations. However, the longitudinal overtones could be only measured with the assistance of imagers. We find emission intensity asymmetry in the positive and negative modulations, this is because the contribution function pertaining to the atomic emission process responds differently to positive and negative temperature variations. One may detect \textbf{half} periodicity close to the loop apex, where emission intensity modulation is relatively small. The line-of-sight projection affects the observation of Doppler shift significantly. A more accurate estimate of the amplitude of velocity perturbation is obtained by de-projecting the Doppler shift by a factor of $1-2\theta/\pi$ rather than the traditionally used $\cos\theta$. \textbf{If a loop is heated to the hotter wing, the intensity modulation could be overwhelmed by background emission, while the Doppler shift velocity could still be detected to a certain extent.

A new paradigm for E × B velocity shear suppression of gyro-kinetic turbulence and the momentum pinch

Detailed studies of the non-linear radial wavenumber spectrum of electric potential fluctuations in gyro-kinetic plasma turbulence simulations have led to a new paradigm that is capable of computing the momentum pinch quasilinearly. It is found that shear in the E × B velocity Doppler shift suppresses turbulence by inducing a shift in the peak of the radial wavenumber spectrum, and a reduction in the amplitude. An analytic model of the process is used to understand the roles of the sheared velocity and the non-linear mode coupling. The analytic model leads to a simple formula that fits the non-linear spectrum and only depends on the spectral average shift in the radial wavenumber. This ‘spectral shift’ model is a new paradigm that radial parity breaking is the fundamental mechanism that suppresses the turbulence through a radial wavenumber shift. The E × B velocity shear is one of a number of radial parity breaking mechanisms. Using a model of the spectral shift the toroidal Reynolds stress due to the E × B velocity shear can be computed for the first time with a quasilinear model. It is shown that, when diamagnetic and neoclassical contributions to the parallel flows are included, the E × B velocity shear term in the toroidal Reynolds stress allows the sign of the intrinsic toroidal rotation to change. Simulations of the co-current and balanced neutral beam injection phase of a DIII-D discharge using the quasilinear model show good agreement with experiment.

High time resolution observations of HF cross‐modulation within the D region ionosphere

High‐frequency cross‐modulation is employed to probe the D region ionosphere during HF heating experiments at the High‐frequency Active Auroral Research Program (HAARP) observatory. We have adapted Fejer's well‐known cross‐modulation probing method to determine the extent of ionospheric conductivity modification in the D region ionosphere with high (5 μsec) time resolution. We demonstrate that the method can be used to analyze D region conductivity changes produced by HF heating both during the initial stages of heating and under steady state conditions. The sequence of CW probe pulses used allow the separation of cross‐modulation effects that occur as the probe pulse propagates upward and downward through the heated region. We discuss how this probing technique can be applied to benefit ELF/VLF wave generation experiments and ionospheric irregularities experiments at higher altitudes. We demonstrate that large phase changes equivalent to Doppler shift velocities &gt;60 km/s can be imposed on HF waves propagating through the heated D region ionosphere.

New Paradigm for Suppression of Gyrokinetic Turbulence by Velocity Shear

The shear in the mean field velocity Doppler shift is shown to suppress the amplitude of electric potential fluctuations by inducing a shift in the peak of the radial wave number spectrum. An analytic model of the process shows that the fluctuation spectrum shifts in the direction where the velocity shear is linearly destabilizing but that nonlinear mixing causes a recentering of the spectrum about a shifted radial wave number at reduced amplitude A model for the 2D nonlinear spectrum is used in a quasilinear calculation of the transport that is shown to accurately reproduce the suppression of energy and particle transport and the Reynolds stress due to the velocity shear.

ATMOSPHERIC ESCAPE FROM HOT JUPITERS

Photoionization heating from ultraviolet (UV) radiation incidents on the atmospheres of hot Jupiters may drive planetary mass loss. Observations of stellar Lyman-α (Lyα) absorption have suggested that the hot Jupiter HD 209458b is losing atomic hydrogen. We construct a model of escape that includes realistic heating and cooling, ionization balance, tidal gravity, and pressure confinement by the host star wind. We show that mass loss takes the form of a hydrodynamic (Parker) wind, emitted from the planet's dayside during lulls in the stellar wind. When dayside winds are suppressed by the confining action of the stellar wind, nightside winds might pick up if there is sufficient horizontal transport of heat. A hot Jupiter loses mass at maximum rates of ~2 × 1012 g s–1 during its host star's pre-main-sequence phase and ~2 × 1010 g s–1 during the star's main-sequence lifetime, for total maximum losses of ~0.06% and ~0.6% of the planet's mass, respectively. For UV fluxes F UV 104 erg cm–2 s–1, the mass-loss rate is approximately energy limited and scales as . For larger UV fluxes, such as those typical of T Tauri stars, radiative losses and plasma recombination force to increase more slowly as F 0.6 UV. Dayside winds are quenched during the T Tauri phase because of confinement by overwhelming stellar wind pressure. During this early stage, nightside winds can still blow if the planet resides outside the stellar Alfven radius; otherwise, even nightside winds are stifled by stellar magnetic pressure, and mass loss is restricted to polar regions. We conclude that while UV radiation can indeed drive winds from hot Jupiters, such winds cannot significantly alter planetary masses during any evolutionary stage. They can, however, produce observable signatures. Candidates for explaining why the Lyman-α photons of HD 209458 are absorbed at Doppler-shifted velocities of ±100 km s–1 include charge-exchange in the shock between the planetary and stellar winds.

Reliability of P mode event classification using contemporaneous BiSON and GOLF observations

We carried out a comparison of the signals seen in contemporaneous BiSON and GOLF data sets. Both instruments perform Doppler shift velocity measurements in integrated sunlight, although BiSON perform measurements from the two wings of potassium absorption line and GOLF from one wing of the NaD1 line. Discrepancies between the two datasets have been observed. We show,in fact, that the relative power depends on the wing in which GOLF data observes. During the blue wing period, the relative power is mugh higher than in BiSON datasets, while a good agreement has been observed during the red period.

Twin Jets as a Potential Distance Detector

Abstract A preview study of using observational data of the proper motions and Doppler-shifted velocities of twin jets to determine the distance of sources inside and outside our Galaxy is made. We investigate the feasibility of this method by studying the uncertainty of the distance caused by the uncertainties of the measured quantities. It shows that, when the motion of components of the jet is relativistic, the uncertainty of the distance is within the same order of the uncertainties of the measured values of the proper motions and Doppler-shifted velocities. In particular, when assuming that the pattern speed equals the flow speed in the jet, for 10% uncertainties of the measured quantities, the uncertainty of the distance caused by them would be well within 13%. With the current technique, this method is realizable. For the convenience of choosing the sources to observe, some sources as potential targets are also listed in this paper.

Determination of the line-of-sight velocities in the dark penumbral fibrils

High resolution observations of an isolated sunspot located near the centre of the solar disk (NOAA/AR 7783) were obtained on October 3, 1994. They were performed with the Multichannel Subtractive Double Pass (MSDP) Spectrograph installed at the focus of the VTT at Tenerife and operating in the H α line. The penumbra and superpenumbra are made up of an apparently well-ordered pattern of elongated dark fibrils. Line profiles were reconstructed and monochromatic images and Doppler shift velocities were derived at several depths in the H α line over a two dimensional field of view. Apart from the Doppler velocities the H α line profiles are used for the computation of the line-of-sight velocities of the dark fibrils by two other methods. The first one involves the well-known Beckers' cloud model. The second is the photographic subtraction method based on the cloud model and expressing the “Doppler signal”. This method using the monochromatic intensities at two wavelengths on either side of the H α line profile can give, in the general case, a quantitative picture of the velocity field, but under some assumptions, values of the velocities at different depths can be obtained. The values of the velocities obtained by this method are compared to those given by the Doppler shift method and by the cloud model, while comparison of the velocities at different depths can give a picture of the gradient of the velocity inside the dark penumbral fibrils.