Doppler Correction Research Articles

Development of a charged particle-[formula omitted] coincidence system for nuclear structure and reaction studies at TIFR

A new detector system for measurements of charged particles and γ-rays in coincidence has been developed at TIFR Mumbai, by coupling an annular double-sided segmented Si detector with an array of Compton-suppressed clover HPGe detectors. Digital data acquisition system has been configured for the setup, which has been calibrated and tested using the 229Th radioactive source that emits α-particles along with γ-rays. The functionality and performance of the coincidence apparatus for Doppler correction of γ-transitions emitted during the in-flight de-excitation of the projectile and the target in the 30Si + 197Au Coulomb excitation experiment have been demonstrated.

Conceptual design and simulated performance of the Barrel part of gamma array for the experimental terminal at HFRS of HIAF

The Barrel of γ array, consisting of 640 CsI(Tl) crystals and covering a polar angle range from 36.4° to 135.6°, has been designed for the experimental terminals at High energy FRagment Separator of High-Intensity heavy-ion Accelerator Facility in Huizhou. Together with the existing Endcap, consisting of 1024 CsI(Tl) crystals and covering a polar angle from 15.6° to 36.4°, at the External Target Facility in Lanzhou to form a new γ array, it is expected to meet the experimental requirements for in-beam γ-ray spectroscopy technique. A Monte Carlo code based on Geant4 was implemented to study the performance of the new γ array. Taking into account the Doppler correction and the intrinsic energy resolution of the detector, the energy resolution is 5.4% (FWHM) for the Endcap and 9.8% (FWHM) for the Barrel when the energy of the emitted γ-ray is 1 MeV in the Center-of-Mass frame with the beam energy of 500 MeV/u (beam velocity β = 0.759). The full-space photopeak efficiency is greater than 40% when the energy of the emitted γ-ray is less than 5 MeV in the Center-of-Mass frame and the beam energy is less than 700 MeV/u (β = 0.821). Such performance can satisfy most of the physics requirements for in-beam γ-ray spectroscopy experiments.

Precision spectroscopy of fast, hot, exotic isotopes using machine-learning-assisted event-by-event Doppler correction

We propose an experimental scheme for performing sensitive, high-precision laser spectroscopy studies on fast exotic isotopes. By inducing a stepwise resonant ionization of the atoms traveling inside an electric field and subsequently detecting the ion and the corresponding electron, time-, and position-sensitive measurements of the resulting particles can be performed. Using a mixture density network, we can leverage this information to predict the initial energy of individual atoms and thus apply a Doppler correction of the observed transition frequencies on an event-by-event basis. We conduct numerical simulations of the proposed experimental scheme and show that kHz-level uncertainties can be achieved for ion beams produced at extreme temperatures (>108 K), with energy spreads as large as 10 keV and nonuniform velocity distributions. The ability to perform in-flight spectroscopy, directly on highly energetic beams, offers unique opportunities to study short-lived isotopes with lifetimes in the millisecond range and below, produced in low quantities, in hot and highly contaminated environments, without the need for cooling techniques. Such species are of marked interest for nuclear structure, astrophysics, and new physics searches. Published by the American Physical Society 2024

Wave measurements using open source ship mounted ultrasonic altimeter and motion correction system during the one ocean circumnavigation

This study reviews the design and signal processing of ship borne ultrasonic altimeter wave measurements. The system combines a downward facing ultrasonic altimeter to capture the sea surface elevation as a time series, and an inertial measurement unit to compensate for the ship’s motion. The methodology is cost-effective, open source, and adaptable to various ships and platforms. The system was installed on the barque Statsraad Lehmkuhl and recorded data continuously during the 20-month One Ocean Expedition. Results from 1-month crossing of the Tropical Atlantic are presented here. The one-dimensional wave spectrum and associated wave parameters are obtained from the sea surface elevation time series. The observed significant wave height agrees well with satellite altimetry and a spectral wave model. The agreement between observations and the spectral wave model is better for the mean wave period than the peak period. We perform Doppler shift corrections to improve wave period estimates by accounting for the speed of the ship relative to the waves. This correction enhances the accuracy of the mean period, but not the peak period. We suggest that the Doppler correction could be improved by complementing the data sources with directional wave measurements from a marine X-band radar.

Further Evidence for the ∼9 s Pulsation in LS 5039 from NuSTAR and ASCA

The present study aims to reinforce the evidence for the ∼9 s pulsation in the gamma-ray binary LS 5039, derived from a Suzaku observation in 2007 and a NuSTAR observation in 2016. Through a reanalysis of the NuSTAR data incorporating the orbital Doppler correction, the 9.0538 s pulsation was confirmed successfully even in the 3–10 keV range, where it was undetectable previously. This was attained by perceiving an energy-dependent drift in the pulse phase below 10 keV and correcting the pulse timing of individual photons for that effect. Similarly, an archival 0.7–12 keV data set of LS 5039, taken with the ASCA Gas Imaging Spectrometer in 1999 October, was analyzed. The data showed possible periodicity at about 8.882 s, but again the energy-dependent phase drift was noticed below 10 keV. By correcting for this effect, and for the orbital Doppler delays in the LS 5039 system, the 2.8–12 keV periodicity became statistically significant at 8.891 ± 0.001 s. The periods measured with ASCA, Suzaku, and NuSTAR approximately follow an average period derivative of s s−1. These results provide further evidence for the pulsation in this object and strengthen the scenario proposed by Yoneda et al. that the compact object in LS 5039 is a strongly magnetized neutron star.

Parametric Doppler correction for wayside array acoustic signal via short-time reconstruction

The trackside acoustic detection system (TADS) plays a vital role in vehicle bearings condition monitoring. However, the inevitable Doppler distortion embedded in collected data will bring considerable difficulties to defect inspection and diagnosis in the system. The distortion elimination approaches mainly achieve spectrum recovery based on time-domain interpolation resampling (TIR) in a data-driven way. These will be further limited by the requirement to signal to noise ratio (SNR) or calculation speed. Considering the principle of wayside acoustic physical model and the benefits of array acoustic in practice, this study proposes an adaptive parametric Doppler correction (PDC) scheme based on short-time reconstruction (STR), including perception modeling, inverse perception optimization and Doppler correction. Firstly, mathematical modeling with multiple perception operators, including acoustic amplitude modulation operator, frequency modulation operator and array time delay operator, a wayside acoustic physical model based on array sensing is established. Secondly, through the corresponding inverse multiple perception operators, a transition signal with frequency-domain energy concentrated is obtained for the optimal moving parameters searching. Thirdly, within short-time sequence segments of the sound source, the real-time position recovery is realized via the proposed STR with formulaic propagation delay compensation. Theoretically, it can be seen that the proposed PDC scheme can simultaneously recover the amplitude, frequency distribution and phase of the Doppler signal, which can be applicable to all wayside acoustic diagnosis scenarios. With the correction analysis of simulation and experimental array defect signals, it can be confirmed that the proposed STR-based PDC scheme is effective for Doppler signal recovery in high fidelity, and has great potential to the real-time diagnosis of TADS.

A γ-Ray Detector Based on a 3” LaBr3:Ce:Sr Crystal With SiPM Readout for 80 keV–16 MeV Energy Range With Position Sensitivity for Doppler Correction

A <i>γ</i>-Ray Detector Based on a 3” LaBr₃:Ce:Sr Crystal With SiPM Readout for 80 keV–16 MeV Energy Range With Position Sensitivity for Doppler Correction

On the Blackbody Spectrum of Kilonovae

The early spectra of the kilonova AT2017gfo have a remarkably smooth blackbody continuum, which reveals information on the thermal properties and radioactive heating within the ejecta. However, the widespread use of a single-temperature blackbody to fit kilonova data is theoretically invalid, because (1) the significant travel-time delays for a rapidly cooling surface result in a broad distribution of temperatures and (2) the relativistic Doppler correction varies across different surface elements. Thus, the observed spectrum should be a modified blackbody with a range of temperatures over the surface. In this paper we quantify the impact of these effects and illustrate the typical wavelength-dependent spectral corrections. We apply the multitemperature blackbody framework to the first-epoch X-shooter AT2017gfo spectrum, to deconvolve the underlying physical temperature at the photosphere from the relativistic Doppler shift. We show that the cooling and Doppler effects individually result in a variation of temperatures over the photosphere of up to 30%, but in combination these effects nearly cancel and produce the single-temperature blackbody observed. Finally, we show that fitting the UV, optical, or near-infrared separately yields blackbody temperatures consistent at the percent level, which puts stringent limits on any proposed modification of the spectral continuum.

Gamma-ray spectroscopy of exotic neutron-rich nuclei in the doubly magic 132Sn region

An experiment with the aim to obtain information on the excited states of neutron-rich nuclei with N~82 was performed at RIBF/RIKEN as part of the HiCARI campaign. The method to identify nuclei on ion-by-ion basis, including charge-state identification, is presented. The Doppler correction technique was validated using the test case of 131In, based on the prompt πp3/2 → πp1/2 transition at 988 keV. Preliminary analysis of the 130Cd spectrum is also presented.

AGATA: performance of $$\gamma $$-ray tracking and associated algorithms

AGATA is a modern $$\gamma $$ -ray spectrometer for in-beam nuclear structure studies, based on $$\gamma $$ -ray tracking. Since more than a decade, it has been operated performing experimental physics campaigns in different international laboratories (LNL, GSI, GANIL). This paper reviews the obtained results concerning the performances of $$\gamma $$ -ray tracking in AGATA and associated algorithms. We discuss $$\gamma $$ -ray tracking and algorithms developed for AGATA. Then, we present performance results in terms of efficiency and peak-to-total for AGATA. The importance of the high effective angular resolution of $$\gamma $$ -ray tracking arrays is emphasised, e.g. with respect to Doppler correction. Finally, we briefly touch upon the subject of $$\gamma $$ -ray imaging and its connection to $$\gamma $$ -ray tracking.

Towards an Intrinsic Doppler Correction for X-ray Spectroscopy of Stored Ions at CRYRING@ESR

We report on a new experimental approach for the Doppler correction of X-rays emitted by heavy ions, using novel metallic magnetic calorimeter detectors which uniquely combine a high spectral resolution with a broad bandwidth acceptance. The measurement was carried out at the electron cooler of CRYRING@ESR at GSI, Darmstadt, Germany. The X-ray emission associated with the radiative recombination of cooler electrons and stored hydrogen-like uranium ions was investigated using two novel microcalorimeter detectors positioned under 0∘ and 180∘ with respect to the ion beam axis. This new experimental setup allowed the investigation of the region of the N, M → L transitions in helium-like uranium with a spectral resolution unmatched by previous studies using conventional semiconductor X-ray detectors. When assuming that the rest-frame energy of at least a few of the recorded transitions is well-known from theory or experiments, a precise measurement of the Doppler shifted line positions in the laboratory system can be used to determine the ion beam velocity using only spectral information. The spectral resolution achievable with microcalorimeter detectors should, for the first time, allow intrinsic Doppler correction to be performed for the precision X-ray spectroscopy of stored heavy ions. A comparison with data from a previous experiment at the ESR electron cooler, as well as the conventional method of conducting Doppler correction using electron cooler parameters, will be discussed.

Performance Evaluation of Random Access Methods for IoT-over-Satellite

Low Earth orbit (LEO) satellite constellations are currently being explored to provide global and seamless coverage for IoT-over-Satellite applications. Random access techniques require low transmission overhead providing a compatible route for IoT-over-Satellite applications, however, coming at the expense of the offered quality-of-service. In this paper, we develop a realistic uplink performance framework that incorporates many practical parameters such as the satellite availability, packet collision and interference, Doppler shift, and impairments experienced in a typical Satellite-to-Ground channel. The framework is capable of assessing multiple key performance indicators of the overall IoT-over-Satellite random access system. The performance is presented in terms of the bit error rate, packet error rate, and the energy wasted per IoT device. To emulate a realistic IoT-over-Satellite network, LoRa modulated traffic is first generated and injected into the Satellite-to-Ground channel. The results indicate high resistance to Doppler shifts even without any Doppler correction and provide some resistance to highly congested environments.

A Low-Complexity Underwater Acoustic Coherent Communication System for Small AUV

While underwater acoustic (UWA) communication offers a practical way to establish a wireless link with underwater vehicles, designing a UWA communication system onboard a small autonomous underwater vehicle (AUV) still poses significant challenges. As the adoption of the low-complexity, robust noncoherent communication technology is limited by low bandwidth efficiency and a low data rate, coherent UWA communication requires Doppler mitigation and channel equalization measures to achieve a relatively high data rate in a moving state. Due to the strict constraints of a small-scale AUV in terms of resources and energy consumption, it is not appropriate to use high-complexity Doppler/multipath compensation technology from the prospect of system implementation. In this paper, an efficient and low-complexity UWA differential binary phase-shift keying (DBPSK) system onboard a small AUV is proposed by simplifying the Doppler and multipath compensation. Specifically, for Doppler, the delay of the adjacent DBPSK symbols is calculated according to the Doppler estimate to facilitate delay-tuning Doppler correction. For multipath, low-complexity LMS channel equalization is incorporated with error correction coding to enable multipath mitigation. With a simple structure and low computational complexity, the proposed scheme facilitates the practical hardware implementation and system integration in the small AUV platform. The numerical simulations are conducted to assess the validity of the proposed scheme under different channel conditions and the effectiveness of the proposed scheme is further verified by two UWA communication field tests, which are performed at a practical shallow water sea and lake, respectively.

Signal processing ocean ambient sound for environmental awareness

Signal processing methods have been developed that use ocean ambient sound to estimate environmental parameters such as the seabed properties. The techniques are straightforward, but in realistic environments there are a variety of complications. The methods considered use a vertically oriented hydrophone line array and practical issues arise such as array motion and deformation. These array parameters are often unknown and represent mismatch with the processing assumptions (e.g., a stationary, straight array). If ignored, performance can degrade significantly so robust signal processing techniques are needed to mitigate. Further, when using ambient sound, as opposed to a sound projector, additional averaging time is needed; this is typically on the order of one or two minutes. Stability in the measurements is essential to obtain the necessary coherent gain. Motion-correcting averaging methods, Doppler correction, adaptive beamforming and supergain are applied to ambient sound processing and will be discussed. Further, data will be analyzed to illustrate the relevant issues and potential remedies in real acoustic environments. Measurements from recent experiments will be presented to illustrate the performance including data collected on the New England Shelf Break in April/May 2021. [Work supported by the Office of Naval Research.]

Parametric Doppler correction analysis for wayside acoustic bearing fault diagnosis

Wayside acoustic system plays a crucial role in monitoring and diagnosing the status of train wheel bearings. However, due to the signal distortion caused by Doppler effect, the diagnosis accuracy will be seriously disturbed. In this manner, this paper proposes a model-driven Doppler distortion self-tuning method in theory, named as parametric Doppler correction analysis (PDCA). Different from traditional methods, such as instantaneous frequency tracking and Doppler distortion sparse representation, the proposed method aims to abstractly construct a physical model of acoustic signal distortion propagation based on Morse acoustic theory, where the acoustic forward propagation model and reverse reconstruction model are simultaneously built. The scheme consists of four basic steps. Firstly, the physical model with amplitude modulation operator and frequency shift operator is described for the distortion process. Secondly, the pseudo transition signal with the characteristics of energy accumulation and no distortion is obtained via a construction of frequency rearrangement operator and amplitude demodulation operator. Then, pseudo Doppler correction (PDC) is presented to solve the frequency distortion of the received signal, where a high energy accumulation for frequency distribution is designed as optimization function. Especially, quasi Newton algorithm L-BFGS is used to realize the adaptive learning for distortion parameters. Finally, through time-domain interpolation resampling (TIR) technique, the corrected signal can be analytically reconstructed with the optimal parameters. Applying the PDCA scheme to simulated signals and experimental signals, its validity is verified. The comparison with the instantaneous frequency ridge extraction approach further indicates the proposed model-driven method can reach a more accurate correction result in a faster and adaptive process.

Random Stepped-Frequency SAR Imagery With Full Cell Doppler Coherent Processing

Random stepped-frequency chirp waveform (RSFCW) is capable of achieving high-resolution synthetic aperture radar (SAR) imagery as well as certain electronic countermeasure capabilities. The Doppler-dependent phase incoherence due to the platform motion leads to degradation of the frequency synthesis of RSFCW. In this letter, a coherence processing algorithm for RSFCWSAR is developed with full cell Doppler correction (FCDC). The waveform structure of RSFCW is exploited to decompose the signal into different Doppler cells, which paves a way to the FCDC in phase alignment for frequency synthesis. Extensive simulation has confirmed the superiority of our method&#x2019;s performance in comparison to those of traditional techniques.

From the Fermi Blazar Sequence to the Relation between Fermi Blazars and γ-Ray Narrow-line Seyfert 1 Galaxies

Abstract We use the third catalog of blazars detected by Fermi/LAT (3LAC) and γ-ray narrow-line Seyfert 1 Galaxies (γ-NLSy1s) to study the blazar sequence and relationship between them. Our results are as follows. (i) There is a weak anticorrelation between synchrotron peak frequency and peak luminosity for both Fermi blazars and γ-NLSy1s, which supports the blazar sequence. However, after Doppler correction, the inverse correlation disappeared, which suggests that anticorrelation between synchrotron peak frequency and peak luminosity is affected by the beaming effect. (ii) There is a significant anticorrelation between jet kinetic power and synchrotron peak frequency for both Fermi blazars and γ-NLSy1s, which suggests that the γ-NLSy1s could fit well into the original blazar sequence. (iii) According to previous work, the relationship between synchrotron peak frequency and synchrotron curvature can be explained by statistical or stochastic acceleration mechanisms. There are significant correlations between synchrotron peak frequency and synchrotron curvature for whole sample, Fermi blazars and BL Lac objects, respectively. The slopes of the correlation are consistent with statistical acceleration. For FSRQs, LBLs, IBLs, HBLs, and γ-NLS1s, we also find a significant correlation, but in these cases the slopes cannot be explained by previous theoretical models. (iv) The slope of the relation between synchrotron peak frequency and synchrotron curvature in γ-NLS1s is larger than that of FSRQs and BL Lac objects. This result may imply that the cooling dominates over the acceleration process for FSRQs and BL Lac objects, while γ-NLS1s is the opposite.

A Modified Factorized Geometrical Autofocus Method for Wide Angle SAR

Wide-Angle (WA) synthetic aperture radar (SAR) has shown remarkable performance in high-resolution mapping, and its mostly used imaging algorithm, fast factorized back projection (FFBP), is efficient, robust, and of low computational complexity. However, trajectory deviations and the system calibration error, introduced by low measurement accuracy, dramatically degrade FFBP's performance. This article proposes the modified factorized geometrical autofocus (MFGA) method for WA-SAR to address the above problems in FFBP. MFGA implements the phase gradient algorithm on defocus subimages at first. Then, a factorized geometrical error hypothesis between subimages is proposed. And the corresponding defocus factors are classified as three independent parts: image distortion, spectrum migration, and phase error. To deal with those problems, MFGA introduces image registration techniques and a maximum sharpness method to calibrate image distortion and phase error. Moreover, in MFGA, based on minimum entropy and least square method, a Doppler spectrum migration correction algorithm is proposed to correct spectrum migration. In the FFBP chain, MFGA is used on subimages refocus and fusion until obtaining a full-resolution image. In our experiments, we compared MFGA and other time-domain autofocus algorithms using simulated data and real data obtained by helicopter and airship with false trajectory and system calibration parameters. The results show that MFGA performs better in terms of the peak to side-lobe ratio, the azimuth resolution, the refocused images' entropy, and processing time consumption. The better performance demonstrates MFGA's advantages in addressing trajectory deviations and the system calibration error for WA-SAR.

A Doppler-modulation based veto to discard false continuous gravitational-wave candidates

In this paper we present a chain-of-vetoes algorithm designed to filter out false-positive continuous gravitational-wave candidates returned by all sky searches, such as the frequencyHough pipeline []. The underlying idea is to use the correlation among candidates (produced by the Earth Doppler effect) in the Hough map to discriminate candidates caused by noise from real continuous-wave signals. Indeed, in presence of a signal, a wrong Doppler correction (due to a mismatch in the sky) can create a candidate with high detection statistic and a small error in estimated frequency and frequency time derivative (s). The current veto scheme allows us to discard 60% of the candidates (with respect to the standard method in []) as not belonging to a continuous-wave signal, thus reducing the false alarm probability, as well as the computational cost needed to follow up interesting candidates.

Doppler Correction in Moving Narrowband Ultrasonic Ranging Sensors for Small-Scale Motion Tracking

Narrowband ultrasonic sensors can be used for motion tracking and small-scale localization. Moving sensor nodes emitting ultrasonic waves produce a Doppler shift in the received signals. Doppler correction methods in narrowband ultrasonic motion tracking systems are explained in this letter. Two methods are suggested for Doppler compensation for small-scale localization using ultrasonic sensors. One of the methods requires a pilot carrier to be added to the transmitted signal and the other method exploits range-Doppler coupling for Doppler correction. In the simulation experiments, we compare the performance of the two methods with the traditional methods. We implement both the methods on hardware and compare the performance of the methods for ranging and localization in the presence of Doppler shift.