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Literatura académica sobre el tema "Spectral Doppler measurements"

Autor: Grafiati

Publicado: 10 de marzo de 2023

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Artículos de revistas sobre el tema "Spectral Doppler measurements"

Moisseev, Dmitri N. y V. Chandrasekar. "Nonparametric Estimation of Raindrop Size Distributions from Dual-Polarization Radar Spectral Observations". Journal of Atmospheric and Oceanic Technology 24, n.º 6 (junio de 2007): 1008–18. http://dx.doi.org/10.1175/jtech2024.1.

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This paper presents a method to retrieve raindrop size distributions (DSD) from slant profile dual-polarization Doppler spectra observations. It is shown that using radar measurements taken at a high elevation angle raindrop size distributions can be retrieved without making an assumption on the form of a DSD. In this paper it is shown that drop size distributions can be retrieved from Doppler power spectra by compensating for the effect of spectrum broadening and mean velocity shift. To accomplish that, spectrum deconvolution is used where the spectral broadening kernel width and wind velocity are estimated from spectral differential reflectivity measurements. Since convolution kernel is estimated from dual-polarization Doppler spectra observations and does not require observation of a clear-air signal, this method can be used by most radars capable of dual-polarization spectra measurements. To validate the technique, sensitivity of this method to the underlying assumptions and calibration errors is evaluated on realistic simulations of radar observations. Furthermore, performance of the method is illustrated on Colorado State University–University of Chicago–Illinois State Water Survey radar (CSU–CHILL) measurements of stratiform precipitation.

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Chaxel, Y., E. M. Griffin y N. P. Meredith. "Spectral analysis techniques for doppler lidar measurements". Advances in Space Research 21, n.º 10 (enero de 1998): 1441–44. http://dx.doi.org/10.1016/s0273-1177(97)00657-1.

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Панчук, В. Е., В. Л. Афанасьев, А. Г. Пельменев, М. В. Юшкин, Г. С. Жуклевич y С. В. Ларионов. "Doppler measurements of stars: evolution of accuracy and some perspectives". Научные труды Института астрономии РАН, n.º 4 (31 de diciembre de 2021): 129–35. http://dx.doi.org/10.51194/inasan.2021.6.4.006.

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Перечислены основные этапы повышения точности доплеровских измерений спектров звезд и связанные с этимтехнологические прорывы. Упоминаются методы интерференционной спектроскопии, ориентированные как на сни-жение стоимости массовых доплеровских измерений, так и на увеличение спектрального разрешения до значений,превосходящих спектральное разрешение согласованного спектрографа высокого разрешения. The main stages of increasing the accuracy of Doppler measurements of stellar spectra and related technological break-throughs are listed. Methods of interference spectroscopy are mentioned, which are aimed at both reducing the cost of massDoppler measurements and increasing the spectral resolution to values exceeding the spectral resolution of a conventionalhigh-resolution spectrograph.

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Gómez Vega, Carlos A., Carlos A. Gutiérrez, Jose J. Jaime Rodriguez, Javier Vazquez Castillo, Daniel U. Campos Delgado, Jose M. Luna Rivera y Miguel A. Díaz Ibarra. "Doppler spectrum measurements of vehicular radio channels using a narrowband sounder". Revista Facultad de Ingeniería Universidad de Antioquia, n.º 93 (23 de agosto de 2019): 32–40. http://dx.doi.org/10.17533/10.17533/udea.redin.20190405.

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This paper describes the implementation of a narrowband sounder for Doppler power spectrum (DPS) measurements of vehicular communication channels. The narrowband channel sounder is implemented using general purpose equipment, making such measurement platform easy to replicate for didactic and research purposes. To demonstrate the practical value of this framework, a measurement campaign was conducted to obtain empirical information about the spectral characteristics of vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) multipath radio channels in the 700 MHz band. The collected data wasprocessed to compute the average Doppler shift and the Doppler spread of the measured channels. The obtained results show that the spectral properties of frequency-dispersive vehicular radio channels can be effectively analyzed using narrowband sounding principles.

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Cifuentes-Lorenzen, Alejandro, James B. Edson, Christopher J. Zappa y Ludovic Bariteau. "A Multisensor Comparison of Ocean Wave Frequency Spectra from a Research Vessel during the Southern Ocean Gas Exchange Experiment". Journal of Atmospheric and Oceanic Technology 30, n.º 12 (1 de diciembre de 2013): 2907–25. http://dx.doi.org/10.1175/jtech-d-12-00181.1.

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Abstract Obtaining accurate measurements of wave statistics from research vessels remains a challenge due to the platform motion. One principal correction is the removal of ship heave and Doppler effects from point measurements. Here, open-ocean wave measurements were collected using a laser altimeter, a Doppler radar microwave sensor, a radar-based system, and inertial measurement units. Multiple instruments were deployed to capture the low- and high-frequency sea surface displacements. Doppler and motion correction algorithms were applied to obtain a full 1D (0.035–1.3 ± 0.2 Hz) wave spectrum. The radar-based system combined with the laser altimeter provided the optimal low- and high-frequency combination, producing a frequency spectrum in the range from 0.035 to 1.2 Hz for cruising speeds ≤3 m s−1 with a spectral rolloff of f−4 Hz and noise floor of −20/−30 dB. While on station, the significant wave height estimates were comparable within 10%–15% among instrumentation. Discrepancies in the total energy and in the spectral shape between instruments arise when the ship is in motion. These differences can be quantified using the spectral behavior of the measurements, accounting for aliasing and Doppler corrections. The inertial sensors provided information on the amplitude of the ship’s modulation transfer function, which was estimated to be ~1.3 ± 0.2 while on station and increased while underway [2.1 at ship-over-ground (SOG) speed; 4.3 m s−1]. The correction scheme presented here is adequate for measurements collected at cruising speeds of 3 m s−1 or less. At speeds greater than 5 m s−1, the motion and Doppler corrections are not sufficient to correct the observed spectral degradation.

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Mattesini, Paolo, Alessandro Ramalli, Lorena Petrusca, Olivier Basset, Herve Liebgott y Piero Tortoli. "Spectral Doppler Measurements With 2-D Sparse Arrays". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 67, n.º 2 (febrero de 2020): 278–85. http://dx.doi.org/10.1109/tuffc.2019.2944090.

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Wang, Yadong, Tian-You Yu, Alexander V. Ryzhkov y Matthew R. Kumjian. "Application of Spectral Polarimetry to a Hailstorm at Low Elevation Angle". Journal of Atmospheric and Oceanic Technology 36, n.º 4 (abril de 2019): 567–83. http://dx.doi.org/10.1175/jtech-d-18-0115.1.

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AbstractSpectral polarimetry has the potential to be used to study microphysical properties in relation to the dynamics within a radar resolution volume by combining Doppler and polarimetric measurements. The past studies of spectral polarimetry have focused on using radar measurements from higher elevation angles, where both the size sorting from the hydrometeors’ terminal velocities and polarimetric characteristics are maintained. In this work, spectral polarimetry is applied to data from the 0° elevation angle, where polarimetric properties are maximized. Radar data collected by the C-band University of Oklahoma Polarimetric Radar for Innovations in Meteorology and Engineering (OU-PRIME) during a hailstorm event on 24 April 2011 are used in the analysis. The slope of the spectral differential reflectivity exhibits interesting variations across the hail core, which suggests the presence of size sorting of hydrometeors caused by vertical shear in a turbulent environment. A nearby S-band polarimetric Weather Surveillance Radar-1988 Doppler (KOUN) is also used to provide insights into this hailstorm. Moreover, a flexible numerical simulation is developed for this study, in which different types of hydrometeors such as rain and melting hail can be considered individually or as a combination under different sheared and turbulent conditions. The impacts of particle size distribution, shear, turbulence, attenuation, and mixture of rain and melting hail on polarimetric spectral signatures are investigated with the simulated Doppler spectra and spectral differential reflectivity.

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Anandan, V. K., C. J. Pan, T. Rajalakshmi y G. Ramachandra Reddy. "Multitaper spectral analysis of atmospheric radar signals". Annales Geophysicae 22, n.º 11 (29 de noviembre de 2004): 3995–4003. http://dx.doi.org/10.5194/angeo-22-3995-2004.

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Abstract. Multitaper spectral analysis using sinusoidal taper has been carried out on the backscattered signals received from the troposphere and lower stratosphere by the Gadanki Mesosphere-Stratosphere-Troposphere (MST) radar under various conditions of the signal-to-noise ratio. Comparison of study is made with sinusoidal taper of the order of three and single tapers of Hanning and rectangular tapers, to understand the relative merits of processing under the scheme. Power spectra plots show that echoes are better identified in the case of multitaper estimation, especially in the region of a weak signal-to-noise ratio. Further analysis is carried out to obtain three lower order moments from three estimation techniques. The results show that multitaper analysis gives a better signal-to-noise ratio or higher detectability. The spectral analysis through multitaper and single tapers is subjected to study of consistency in measurements. Results show that the multitaper estimate is better consistent in Doppler measurements compared to single taper estimates. Doppler width measurements with different approaches were studied and the results show that the estimation was better in the multitaper technique in terms of temporal resolution and estimation accuracy.

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Bascom, Peter A. J., K. Wayne Johnston, Richard S. C. Cobbold y Matadial Ojha. "Defining the limitations of measurements from Doppler spectral recordings". Journal of Vascular Surgery 24, n.º 1 (julio de 1996): 34–45. http://dx.doi.org/10.1016/s0741-5214(96)70142-8.

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Lee, Bor-Ray, Huihua Kenny Chiang, Yi-Hong Chou, Cheng-Deng Kuo, Jia-Horng Wang y San-Kan Lee. "Implementation of spectral width Doppler in pulsatile flow measurements". Ultrasound in Medicine & Biology 25, n.º 8 (octubre de 1999): 1221–27. http://dx.doi.org/10.1016/s0301-5629(99)00083-6.

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Tesis sobre el tema "Spectral Doppler measurements"

Brooks, Donald Ray. "Development of Specialized Laser Doppler Velocimeters for High Resolution Flow Profile and Turbulence Spectral Measurements". Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/78089.

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Fluid dynamicists are always in need of innovative instruments for flow velocity measurements. An ideal instrument would be non-intrusive, have a very fine spatial resolution as well as a very fine temporal resolution, be able to measure three-components of velocity, and be compact. Through recent advancements, laser Doppler velocimetry can now meet all of those requirements making it an important part of aerodynamicist's research toolbox. The first paper presented in this manuscript style thesis explains the development of an advanced three-velocity component, spatially-resolving laser-Doppler velocimetry (LDV) system for highly resolved velocity measurements in situations with limited optical access. The new instrument, a next generation version of the previously developed 'comprehensive' LDV technology, enables measurements of three components of velocity and particle position in the axial direction all through a single transceiving lens. Described here is the design process and the final design for the 'compact, comprehensive' LDV (Comp²LDV). The probe was designed to achieve ± 10 micron root-mean-square uncertainties in axial particle position, which combined with the long measurement volume, allow researchers to obtain a three-velocity-component velocity statistics profiles over a span of approximately 1.5mm without the need for traversing. Results from measurements in a flat plate turbulent boundary layer very near the wall have compared favorably to data from previous studies. The second paper focuses on the motion and evolution of coherent structures in supersonic jet flows and how that relates to the intense noise the flows generate. As a preliminary study to experimentally address these relationships, novel non-intrusive measurements using two-component laser Doppler velocimetry (LDV) have been conducted at exceptionally high data rates to lend insight into the statistical behavior of noise-generating flow structures. A new heated supersonic jet facility has been constructed to provide supersonic flow at total temperatures ratios (T₀/Tₐ) up to 3. In the present work, the instrumentation is validated via comparison of LDV measurements along the centerline of a screeching cold jet with microphone and high-speed shadowgraph results. Reynolds stress spectra are presented for an over-expanded case (nozzle pressure ratio of 3.2) of a design Mach number 1.65 nozzle operated cold (T₀/Tₐ = 1). A preliminary study was then conducted in the near-nozzle shear layer, up to x/d = 4.0, at design nozzle pressure ratio (4.58) and total temperature ratio of 2.0. Results are presented for Reynolds stress time-delay correlations and power spectra at Re_d = 1.1M for this case. The stream-wise Reynolds normal stress spectra are compared with published spectral behavior reported by other researchers, indicating a similar spectral shape in the downstream stations as previously measured with LDV and hot wire anemometry for cold jets, but which differ in shape from density-based techniques.
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David, Jean-Yves. "Modern spectral analysis techniques for blood flow velocity and spectral measurements with a 20 MHZ pulsed doppler ultrasound catheter". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/17791.

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Walther, Julia y Edmund Koch. "Lateral resonant Doppler flow measurement by spectral domain optical coherence tomography". SPIE, 2017. https://tud.qucosa.de/id/qucosa%3A34981.

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In spectral domain optical coherence tomography (SD-OCT), any transverse motion component of a detected obliquely moving sample results in a nonlinear relationship between the Doppler phase shift and the axial sample velocity restricting phase-resolved Doppler OCT. To circumvent the limitation, we propose the lateral resonant Doppler flow quantification in spectral domain OCT, where the scanner movement velocity is matched to the transverse velocity component of the sample motion.

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Sundaram, Preethi. "New Results For Characterization Of Indoor Channels In Two Ism Bands (900-928 Mhz And 2.4-2.5 Ghz)". Ohio University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1140462634.

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Jouette, Christian. "Conception d'un appareil de mesure du débit sanguin tissulaire par effet doppler optique : choix des paramètres d'échantillonnage et d'analyse spectrale, et détermination d'un indice débit métrique". Nancy 1, 1994. http://www.theses.fr/1994NAN10106.

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La mesure du débit sanguin tissulaire par effet doppler optique est une idée séduisante. L'utilisation d'une source laser, par la cohérence spatiale et géométrique qu'elle offre, en simplifie la réalisation pratique. La vitesse des différentes composantes, notamment les hématies, n'est pas uniforme. Il en résulte donc une distribution spectrale image de cette répartition. De plus, l'environnement du faisceau laser étant constitué par de la matière vivante, de nombreux paramètres influencent les résultats. Dans un premier temps, nous décrivons l'évolution des doppler-lasers, et nous exposons les problèmes qu'ils soulèvent. Ceci nous amène à considérer ensuite, que seule une étude fine du spectre peut nous conduire à un appareil fiable et réellement utilisable en routine. Nous présentons ici un doppler-laser à traitement numérique. La distribution spectrale est calculée par un processeur de signaux numérique (dsp) grâce à un algorithme de transformée de Fourier rapide. Nous donnons les paramètres caractéristiques qui nous paraissent optimaux, et relevons les difficultés qui subsistent avant de pouvoir réaliser un système performant

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Lee, Christopher Francis. "Use of wind profilers to quantify atmospheric turbulence". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/use-of-wind-profilers-to-quantify-atmospheric-turbulence(d6a12ed2-533a-4dae-9f0d-747bc0b4c725).html.

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Doppler radar wind profilers are already widely used to measure atmospheric winds throughout the free troposphere and stratosphere. Several methods have been developed to quantify atmospheric turbulence with such radars, but to date they have remained largely un-tested; this thesis presents the first comprehensive validation of one such method. Conventional in-situ measurements of turbulence have been concentrated in the surface layer, with some aircraft and balloon platforms measuring at higher altitudes on a case study basis. Radars offer the opportunity to measure turbulence near continuously, and at a range of altitudes, to provide the first long term observations of atmospheric turbulence above the surface layer. Two radars were used in this study, a Mesosphere-Stratosphere-Troposphere (MST) radar, at Capel Dewi, West Wales, and the Facility for Ground Based Atmospheric Measurements (FGAM) mobile boundary layer profiler. In-situ measurements were made using aircraft and tethered-balloon borne turbulence probes. The spectral width method was chosen for detailed testing, which uses the width of a radar's Doppler spectrum as a measure of atmospheric velocity variance. Broader Doppler spectra indicate stronger turbulence. To obtain Gaussian Doppler spectra (a requirement of the spectral width method), combination of between five and seven consecutive spectra was required. Individual MST spectra were particularly non-Gaussian, because of the sparse nature of turbulence at its observation altitudes. The width of Gaussian fits to the Doppler spectrum were compared to those from the `raw' spectrum, to ensure that non-atmospheric signals were not measured. Corrections for non-turbulent broadening, such as beam broadening, and signal processing, were investigated. Shear broadening was found to be small, and the errors in its calculation large, so no corrections for wind shear were applied. Beam broadening was found to be the dominant broadening contribution, and also contributed the largest uncertainty to spectral widths. Corrected spectral widths were found to correlate with aircraft measurements for both radars. Observing spectral widths over time periods of 40 and 60 minutes for the boundary layer profiler and MST radar respectively, gave the best measure of turbulence intensity and variability. Median spectral widths gave the best average over that period, with two-sigma limits (where sigma is the standard deviation of spectral widths) giving the best representation of the variability in turbulence. Turbulent kinetic energies were derived from spectral widths; typical boundary layer values were 0.13 m 2.s (-2) with a two-sigma range of 0.04-0.25 m 2.s (-2), and peaked at 0.21 m 2.s (-2) with a two-sigma range of 0.08-0.61 m 2.s (-2). Turbulent kinetic energy dissipation rates were also calculated from spectral widths, requiring radiosonde measurements of atmospheric stability. Dissipation rates compared well width aircraft measurements, reaching peaks of 1x10 (-3) m 2.s (-3) within 200 m of the ground, and decreasing to 1-2x10 (-5) m 2.s (-3) near the boundary layer capping inversion. Typical boundary layer values were between 1-3x10 (-4) m 2.s (-3). Those values are in close agreement with dissipation rates from previous studies.

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Rossi, Stefano y Piero Tortoli. "Development and validation of novel approaches for real-time ultrasound vector velocity measurements". Doctoral thesis, 2021. http://hdl.handle.net/2158/1239650.

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Ultrasound imaging techniques have become increasingly successful in the medical field as they provide relatively low cost and totally safe diagnosis. Doppler methods focus on blood flow for the diagnosis and follow-up of cardiovascular diseases. First Doppler methods only measured the axial component of the motion. More recently, advanced methods have solved this problem, by estimating two or even all three velocity components. In this context, high frame rate (HFR) imaging techniques, based on the transmission of plane waves (PW), lead to the reconstruction of 2-D and 3-D vector maps of blood velocity distribution. The aim of this Ph.D. project was to develop novel acquisition schemes and processing methods for advanced ultrasound Doppler systems. Each development step was based on simulations and experimental tests. Simulations were based on Field II©, while experiments were conducted by using the ULA OP 256 open scanner. In particular, the recently proposed 2-D HFR vector flow imaging (VFI) method (DOI: 10.1109/TUFFC.2014.3064), based on the frequency domain for displacement estimation, was thoroughly investigated. Three main issues were addressed: the high underestimation of blood flow velocity observed when examining vessels at great depths, the high computational load, which hindered any real-time implementation and the lack of information about the third velocity component. Specifically, the progressive broadening of the transmitted beam on the elevation plane due to the acoustic lens was demonstrated to be responsible for the underestimation. The computational cost was reduced by processing demodulated and down-sampled baseband data instead of radiofrequency data, and a preliminary real time version of the 2-D VFI method was implemented. It was also found that a more efficient implementation could be obtained by exploiting parallel computing and graphic processing units (GPUs). An expansion circuit board for the ULA-OP 256 hardware, which allocates GPU resources, was thus designed and built. This new system architecture may allow the implementation of even more complex algorithms, such as the 3-D VFI methods. In particular, it will be possible to implement the novel method for 3D VFI that was developed and tested during this Ph.D. project. Such method suitably extended the 2D VFI approach by proposing an efficient estimation strategy that considerably limits the overall computational load.

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Mattesini, Paolo, Piero Tortoli, Enrico Boni, Hervé Liebgott y Olivier Basset. "Development of methods and electronic circuits for ultrasound imaging based on innovative probes". Doctoral thesis, 2020. http://hdl.handle.net/2158/1186186.

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I sistemi di imaging ad ultrasuoni (US), sebbene siano stati oggetto di intense indagini da parte di molti gruppi di ricerca in tutto il mondo, non hanno ancora raggiunto la piena maturità. Le sonde ad ultrasuoni, in particolare, hanno ampi margini di miglioramento, non solo in termini di materiali e configurazione degli elementi, ma anche di modalità di eccitazione. Il mio lavoro di dottorato è stato impegnato nello sviluppo di circuiti elettronici e metodi per l'imaging ad ultrasuoni basati su sonde innovative. In primo luogo, ho sviluppato i circuiti elettronici necessari per rendere compatibile un sistema di ricerca a ultrasuoni per scopi di ricerca (ULA-OP 256) con le sonde CMUT. La tecnologia CMUT è sempre più utilizzata perché offre ampia banda, elevata sensibilità e grande flessibilità nella progettazione della geometria degli elementi ma, a differenza della tecnologia piezoelettrica, necessita di alte tensioni di polarizzazione (dell’ordine delle centinaia di Volt). Poiché ULA-OP 256 è stato originariamente progettato per funzionare solo con sonde piezoelettriche, ho contribuito allo sviluppo di circuiti in grado di adattare questo scanner aperto per lavorare anche con sonde CMUT. Inoltre, in collaborazione con ST Microelectronics, ho sviluppato una scheda elettronica che permette di testare un nuovo amplificatore di potenza a nove livelli per la trasmissione di segnali sia alle sonde piezoelettriche che alle sonde CMUT. La seconda parte del mio lavoro è stata dedicata allo studio del possibile utilizzo di sonde ad array "sparse" per ecografie 3D Doppler e ad alto frame rate. Le sonde sparse sono array 2D in cui un numero limitato di elementi, paragonabile al numero di canali presenti nella maggior parte degli scanner ad ultrasuoni, è distribuito secondo specifiche geometrie, progettate per ottimizzare il fascio acustico in trasmissione e ricezione. CMUT è la tecnologia ideale per l'implementazione di sonde sparse array, in quanto garantisce la massima flessibilità nella distribuzione degli elementi in posizioni arbitrarie. Il mio lavoro con gli Sparse Array ha incluso prima di tutto lo studio di possibili limitazioni legate al loro utilizzo quando sono usati per trasmettere onde divergenti (DWs). Si tratta di onde non focalizzate che permettono di aumentare notevolmente il frame rate nell'imaging volumetrico (3D). In questa attività, ho fatto simulazioni ed esperimenti nel laboratorio CREATIS (Lione) per confrontare le prestazioni ottenibili in termini di contrasto e risoluzione quando si utilizzano diverse configurazioni di DW e di elementi sparsi. Infine, una parte consistente del mio dottorato di ricerca è stata focalizzata sulla valutazione dell'uso di array sparse in applicazioni Doppler spettrali. L'intenzione di questo studio era di valutare in che misura la dispersione degli elementi sulla superficie della sonda può influenzare le prestazioni del Doppler spettrale. Per raggiungere questo obiettivo, l'uso di un array 2D a 1024 elementi a griglia completa è stato confrontato con l'uso di array sparse ottenuti selezionando opportunamente 256 elementi sulla stessa matrice completa. Gli esperimenti sono stati sviluppati sia su un disco di agar rotante (dove sono raggiungibili alti SNR) che su un phantom di flusso (per testare una condizione più realistica) al CREATIS. I risultati di questo lavoro confermano quantitativamente l'idoneità degli array sparse per misure di velocità Doppler spettrali, a condizione che la perdita di rapporto segnale/rumore dovuto all'utilizzo di meno elementi attivi sia adeguatamente compensata. Ultrasound (US) imaging systems, although intensively investigated by many research groups worldwide, have not achieved full maturity yet. US probes, in particular, have wide margins of improvement, not only in terms of materials and elements configuration but also of excitation modalities. This PhD work has been committed to the development of electronic circuits and methods for US imaging based on innovative ultrasound probes. First, I’ve developed the electronic circuits necessary to make an open ultrasound research system (ULA-OP 256) compatible with CMUT probes. CMUT technology is increasingly used because it offers wide band, high sensitivity and great flexibility in the design of elements geometry but, differently from the piezoelectric technology, needs high polarization and peak-to-peak voltages (hundreds of Volt). Since ULA-OP 256 was originally designed to work only with piezoelectric probes, I contributed to the development of circuits capable of adapting this open scanner to work also with CMUT array probes. Furthermore, within a collaboration with ST Microelectronics, I’ve developed an electronic board that allows to test a new 9-level power amplifier for the transmission of signals to both piezoelectric and CMUT probes. The second part of my work has been dedicated to the investigation of possible use of “sparse” array probes for 3D high-frame rate and Doppler imaging. Sparse probes are 2D arrays in which a limited number of elements, comparable to the number of channels present in most US scanners, is distributed according to specific geometries, designed to optimize the transmit/receive acoustic beam. CMUT is the ideal technology for implementing sparse array probes, since it guarantees maximum flexibility in distributing the elements into arbitrary positions. My work with sparse arrays has first included the investigation of possible limitations related to their use when they are committed to transmit Diverging Waves (DWs). These are unfocused waves that may notably increase the frame rate in volumetric (3D) imaging. In this activity, I’ve done simulations and experiments at CREATIS (Lyon) to compare the achievable performance in terms of contrast and resolution when different DWs and sparse elements configurations are used. Finally, a consistent part of my PhD has been focused on the evaluation of the use of sparse arrays in spectral Doppler applications. The intention of this study was to evaluate at which extent the sparsification of probe elements may affect the spectral Doppler performance. To achieve this goal, the use of a full-gridded 1024-element 2D array was compared with the use of a sparse arrays obtained by properly selecting 256 elements out of the same full array. The experiments were developed on both a rotating agar disc (where high SNR are achievable) and on a flow phantom (to test a more realistic condition) at CREATIS. The results of this work quantitatively confirm the suitability of sparse arrays for spectral Doppler velocity measurements, provided the poor signal-to-noise ratio due to the use of few active elements is properly compensated.

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Libros sobre el tema "Spectral Doppler measurements"

Gossard, Earl E. Automated editing of spectra from wind profilers. Boulder, Colo: U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Environmental Technology Laboratory, 1997.

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Woodahl, Brian Arvid. On obtaining auto-spectral-density from non-uniformly sampled data using signal reconstruction. 1993.

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Kasprzak, Jaroslaw D., Anita Sadeghpour y Ruxandra Jurcut. Doppler echocardiography. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780198726012.003.0003.

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Doppler examination is an integral part of the echocardiogram. Current systems are equipped with spectral Doppler in continuous wave mode (offering measurements of high velocities with limited spatial specificity due to integration of signal along the scan line), pulsed wave mode (high spatial specificity with maximal recordable velocity reduced by the Nyquist limit), and colour Doppler flow mapping (allowing rapid identification of flow pattern within a cross-sectional B-mode sector). Tissue Doppler echocardiography emerged as a basic tool for sampling regional myocardial velocities, in pulsed wave or colour velocity mapping mode. Finally, three-dimensional systems improve spatial presentation of flow phenomena by integrating Doppler-derived flow patterns in three-dimensional datasets.

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Choi, Seong Jong. Parametric spectral analysis of ultrasound doppler signal. 1992.

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Capítulos de libros sobre el tema "Spectral Doppler measurements"

Matera, Riccardo, David Vilkomerson y Stefano Ricci. "Ultrasound Measurement of the Peak Blood Flow Based on a Doppler Spectrum Model". En Lecture Notes in Electrical Engineering, 383–89. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-11973-7_45.

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Bao, S. L., F. Z. Huang, J. Q. Liu, G. Y. Tang, H. Y. Zhou, G. Y. Fan, C. L. Wen y M. Hua. "Measurement of 7Li(n,n′γ) (478 keV) Inelastic Angular Distribution Derived via the Shape Analysis of the Doppler Shifted γ-Ray Spectrum (DSM) at 14.9 MeV". En Nuclear Data for Science and Technology, 323–25. Berlin, Heidelberg: Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-58113-7_92.

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Sidebotham, David, Alan Merry, Malcolm Legget y Gavin Wright. "Quantitative Doppler echocardiography". En Practical Perioperative Transoesophageal Echocardiography. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780198759089.003.0003.

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Quantitative echocardiography refers to using spectral Doppler measurements of blood velocity, in combination with 2D imaging, to obtain calculated values for flow (e.g. stroke volume, regurgitant volume), area (stenotic valve area, regurgitant orifice area), and pressure (e.g. pulmonary artery pressure, transvalvular gradient). Relevant formulae used by the echocardiography machine software for calculating these parameters are provided. Physical phenomena, such jets, the Venturi effect, and the Coanda effect, are explained, along with applications of the continuity principle, the Bernoulli equation, and pressure half-time measurements. The emphasis throughout the chapter is on practical calculations that can be performed rapidly with TOE in the operating room. The concept of pressure recovery is touched on but discussed in more detail in Chapter 13: Prosthetic valves.

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Gray, P. H., E. A. Griffin, J. E. Drumm, D. E. Fitzgerald y N. M. Duignan. "Doppler spectral analysis of cerebral blood flow in preterm infants and the relationship to intraventricular haemorrhage". En Neonatal Physiological Measurements, 117–23. Elsevier, 1986. http://dx.doi.org/10.1016/b978-0-407-00451-1.50019-9.

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Binder, Thomas. "Transthoracic echocardiography and the standard examination of specific cardiac structures". En ESC CardioMed, editado por Frank Flachskampf, 425–31. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780198784906.003.0085.

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Transthoracic echocardiography is by far the most frequently used imaging procedure in cardiology. Adherence to a standard protocol is essential for a comprehensive evaluation of cardiac structures and function. The protocol must include the minimal requirements outlined in this chapter. Two-dimensional imaging is performed from specific windows, such as the parasternal, apical, and subcostal ones. A number of standard cut planes are needed for a full understanding of the entire heart. M-mode, spectral, and colour Doppler are used to obtain additional anatomical and functional information. Advanced techniques such as deformation imaging, three-dimensional, or contrast echocardiography may be used if needed. A set of standard measurements, as outlined in this chapter, are equally important.

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Goody, R. M. y Y. L. Yung. "Band Models". En Atmospheric Radiation. Oxford University Press, 1989. http://dx.doi.org/10.1093/oso/9780195051346.003.0006.

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Radiative heating calculations in the atmosphere involve four distinguishable scales of frequency. First, there is the comparatively slow variation with frequency of the Planck function and its derivative with respect to temperature. About one-half of the radiation from a black body at terrestrial temperatures lies in a wave number range of 500 cm-1. The second scale is that of the unresolved contour of a band. For atmospheric molecules other than water vapor, the Planck function is effectively constant over a single band; water vapor bands must be divided into sections of the order of 50 cm-1 wide before this is so. For a rotating molecule, the next relevant scale of frequency is that of the spacing between rotation lines, approximately 1-5 cm-1. Finally, there is the monochromatic scale on which the absorption coefficient may be treated as a constant, and for which Lambert’s absorption law is obeyed: of the order of one-fifth of a line width ≃ 2 x 10-2 cm-1 for a gas at atmospheric pressure, down to 2 x 10-4cm-1 for a Doppler line in the middle atmosphere. This step takes us to a division of the frequency scale that, when taken together with other features of the calculation, presents a formidable computation task. Calculations can, of course, be made and are made at this limiting spectral resolution (line-by-line calculations) but, despite the fact that they are technically feasible with modern computers, such calculations are rare and are usually performed to provide a few reference cases. The great majority of investigations make use of averages over many lines, embracing spectral ranges that are small compared to a band contour (narrow-band models), or over complete bands (wide-band models), or over the entire thermal spectrum (emissivity models.) There are a number of reasons for working with spectral averages. Practical considerations are that important classes of laboratory measurements, and most atmospheric observations (e.g., satellite radiometry) are made with some spectral averaging, often comparable to that of narrow-band models.

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Huang, Stephen. "Basic Doppler principles". En Oxford Textbook of Advanced Critical Care Echocardiography, editado por Anthony McLean, Stephen Huang y Andrew Hilton, 2–20. Oxford University Press, 2020. http://dx.doi.org/10.1093/med/9780198749288.003.0001.

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Basic two-dimensional echocardiography alone is inadequate for advanced diagnosis and treatment monitoring in critically ill patients because of haemodynamic complexities. To cope with such demands, a critical care physician will also need to be competent in Doppler echocardiography, which provides accurate measurements of blood flows. Experienced echocardiographers are able to draw inference about the cardiac function, intracardiac and intravascular pressures, and other abnormalities from the Doppler flow spectra. Doppler echocardiography also provides objective measurements that can be used for bedside diagnosis or for longitudinal monitoring. Learning Doppler echocardiography has a steep learning curve and has several hurdles to overcome. First, one needs to develop high-level transducer navigation skills to make sure a proper insonation angle is obtained for all Doppler measurements. Second, an understanding of medical ultrasound physics is required not only for knobology purposes, but also for appreciation of the pros and cons of various Doppler modalities. Third, recognition of the limitations of Doppler echocardiography is necessary to avoid misapplications and misinterpretations. Fourth, the operator needs to be able to identify Doppler artefacts so as not to mistake artefacts for real findings. Finally, an understanding of haemodynamic principles is important to execute proper interpretations of Doppler measurements. This chapter will cover mainly the second and third aspects of these. Doppler artefacts will be covered in Chapter 2 and haemodynamic principles in Chapter 3.

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Huang, Stephen. "Common Doppler artefacts and pitfalls". En Oxford Textbook of Advanced Critical Care Echocardiography, editado por Anthony McLean, Stephen Huang y Andrew Hilton, 21–36. Oxford University Press, 2020. http://dx.doi.org/10.1093/med/9780198749288.003.0002.

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Artefacts are spurious signals that do not represent true signals or physical structures. It is important to differentiate artefacts from genuine signals in ultrasound studies as this may help avoid misinterpretations and measurement errors. The nature of many Doppler ultrasound artefacts is similar to 2D echocardiography artefacts, including inappropriate gain settings, mirror artefacts, and reverberation artefacts. However, as Doppler ultrasound is used to detect blood flow and myocardial velocity, it is susceptible to insonation (Doppler) angle error, aliasing, and other velocity-related artefacts. These will be presented in this chapter as two main types of artefacts: one that is related to spectral Doppler, and the other related to colour-flow Doppler ultrasound.

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Karadimas, Petros. "Stochastic Modeling of Narrowband Fading Channels with Three Dimensional Diffuse Scattering". En Handbook of Research on Heterogeneous Next Generation Networking, 361–81. IGI Global, 2009. http://dx.doi.org/10.4018/978-1-60566-108-7.ch016.

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This chapter studies a composite stochastic model, in which the diffuse component arises from three dimensional (3-D) multipath scattering. That case occurs especially in dense scattering environments, in which the tall obstacles cause arrival of multipath power in the elevation plane, besides that arriving in the azimuth one. Also the multipath components are assumed to arrive at the mobile receiver in specific angular sectors at the azimuth receiver’s plane. The last is physically justified by multipath power blocking due to the channel obstacles (shadow fading), or/and lack of scattering objects at specific angular directions, or/and directional antennas utilization. An extended Suzuki model, where the Rician process for the diffuse scattering component is multiplied by a lognormal one, is considered as an appropriate composite model. The most important metrics of the model are presented, according to its assumptions. More specifically, from the closed form autocorrelation function, the Doppler power spectral density (PSD) of the diffuse component can be analytically derived. Afterwards exact solutions for the envelope and phase probability density functions (PDF’s) are presented. Exact solutions are also derived for the second order statistics, i.e. the level crossing rate (LCR) and the average duration of fades (ADF’s). An efficient deterministic simulation scheme will be presented, which implements the analytical model on a digital computer. Finally a curve fitting of the LCR to real world data, drawn from channel measurements, will demonstrate the flexibility and usefulness of the extended Suzuki model.

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Huang, Stephen. "Haemodynamics for echocardiography". En Oxford Textbook of Advanced Critical Care Echocardiography, editado por Anthony McLean, Stephen Huang y Andrew Hilton, 37–52. Oxford University Press, 2020. http://dx.doi.org/10.1093/med/9780198749288.003.0003.

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Haemodynamics is the study of the physics of blood flows through the cardiovascular system, and is mainly concerned with the physical factors that controls the blood flow. Experienced clinicians and echocardiographers can deduce the haemodynamic status of a patient from examining the shapes, velocities, timings, and durations of the Doppler spectrum without performing any sophisticated measurements. If accurate measurements are needed, the operators need recourse to advanced concepts in fluid dynamics. For example, the simplified Bernoulli equation and continuity equation are often used for pressure gradient and orifice size estimations. Although these equations are used in everyday echocardiography, misunderstanding and misuses of the equations are common because the assumptions and limitations of these equations are fully appreciated. Further, haemodynamics is not a single concept. Rather, it is a collection of different concepts and that makes learning and teaching haemodynamics as one of least appealing but most challenging area in echocardiography. This chapter revisits the basic concepts of haemodynamics and their applications in echocardiography.

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Actas de conferencias sobre el tema "Spectral Doppler measurements"

Mattesini, Paolo, Alessandro Ramalli, Emmanuel Roux, Lorena Petrusca, Herve Liebgott, Olivier Basser y Piero Tortoli. "Spectral Doppler Measurements with 2-D Sparse Arrays". En 2018 IEEE International Ultrasonics Symposium (IUS). IEEE, 2018. http://dx.doi.org/10.1109/ultsym.2018.8579909.

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Eloranta, E. W. y P. Piironen. "High Spectral Resolution Lidar Measurements of Extinction and Particle Size in Clouds". En Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/orsa.1995.wa1.

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The spectral width of light backscattered from molecules is increased due to Doppler shifts caused by the thermal motion of the molecules. The thermal motion of aerosol and cloud particles is much slower and the backscatter spectrum is nearly unchanged. The University of Wisconsin High Spectral Resolution Lidar (HSRL) measures optical properties of the atmosphere by separating the Doppler-broadened molecular backscatter return from the unbroadened aerosol return1. The molecular backscatter cross section can be calculated from the molecular density profile. Thus, observing the magnitude of the measured molecular signal relative to the computed profile allows unambiguous measurement of the atmospheric extinction profile. The ratio of the aerosol return to the molecular return along with the computed molecular cross section provides direct measurement of the aerosol backscatter cross section.

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Kathpalia, Aditi, Yucel Karabiyik, Bente Simensen, Eva Tegnander, Sturla Eik-Nes, Hans Torp, Ingvild Kinn Ekroll y Gabriel Kiss. "A robust Doppler spectral envelope detection technique for automated blood flow measurements". En 2015 IEEE International Ultrasonics Symposium (IUS). IEEE, 2015. http://dx.doi.org/10.1109/ultsym.2015.0419.

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Fuchs, J., T. Lamont-Smith y M. P. Tulin. "Laboratory measurements of LGA Doppler spectral components and their physical sources unveiled". En IGARSS '98. Sensing and Managing the Environment. 1998 IEEE International Geoscience and Remote Sensing. Symposium Proceedings. (Cat. No.98CH36174). IEEE, 1998. http://dx.doi.org/10.1109/igarss.1998.703811.

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Grund, C. J. y E. W. Eloranta. "High Spectral Resolution Lidar Measurements of Cirrus Cloud Optical Properties". En Laser and Optical Remote Sensing: Instrumentation and Techniques. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/lors.1987.mc9.

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Lidar backscatter signals are generated by scattering from both molecules and particles. The spectral distribution of light scattered by molecules is Doppler-broadened by rapid, thermally induced, molecular motions. Light scattered by aerosols and cirrus particles is essentially unshifted because of the relatively slow Brownian motion of particles. Using this difference, the High Spectral Resolution Lidar (HSRL)1,2 interferometrically separates particulate from molecular backscatter. By using the distribution of molecular scattering as a known target, the HSRL achieves unambiguous, calibrated measurements of atmospheric extinction, backscatter cross section, and backscatter phase function.

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Gentry, Bruce M. y C. Laurence Korb. "Doppler velocimetry with sub-meter-per-second accuracy using the edge technique". En OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.tup3.

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The edge technique is a powerful new method for the measurement of small frequency shifts. When applied to the measurement of Doppler shifts, the edge technique can be used to obtain high accuracy remote measurements of instantaneous velocity. In the edge technique the laser frequency is located on the edge of the spectral response function of a high resolution optical filter. Because of the steep slope of the edge, very small frequency shifts cause large changes in filter transmission. The Doppler shift is determined from a differential measurement of the frequency of the unshifted laser beam and the Doppler-shifted frequency of the laser energy scattered from the target. The differential nature of the measurement makes the Doppler shift determination essentially insensitive to the initial location of the laser on the edge and also to frequency jitter and drift. The high sensitivity and accuracy of the edge technique and the insensitivity to frequency jitter and drift have been demonstrated in recent laboratory experiments. The velocity of a calibrated target was measured using a He-Ne laser and the edge technique. A Fabry-Perot etalon with a spectral resolving power of 8.9 × 106 (Airy width of 54 MHz) was used as the edge filter. Velocity accuracy varied from 0.19 to 0.3 m/sec depending on the initial location of the laser on the edge. This corresponds to a Doppler shift measurement accuracy of 600 kHz which is ~1 % of the spectral bandwidth (combined laser and filter spectral widths) of the measurement.

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Martinsen, Robert J., Andrew J. Jankevics, Charles P. Plum y John H. Flint. "Clear Air Turbulence Detection with a 2 μm Lidar Employing Velocity Width Processing". En Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/orsa.1993.tud.20.

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We describe in this paper results of a system study for an airborne lidar system that makes real-time, range-resolved measurements of clear air turbulence (CAT) to several kilometers forward of an aircraft's projected flight path. Exploiting the width of the IF signal Doppler spectrum (σf) is central to the system concept. Since broadening of the Doppler spectrum beyond the transform limit is a function of the mixture of velocities (velocity width, σv) in the pulse scattering volume, any combination of shear and/or turbulence in the flight path is immediately revealed by the broadened spectra. Hence, σf relates to a property of the velocity field that is particularly important to aircraft anti other aerospace vehicles. Explicit spectral width processing is quite powerful for CAT detection lidars because complex atmospheric wind patterns can be characterized in terms of a single observable σv for subsequent reckoning against a hazard index.

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Johnson, Steve. "Laboratory Measurements of the Performance of a Poly Pulse Pair Signal Processor". En Coherent Laser Radar. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/clr.1987.tua8.

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A signal processor has been developed to perform estimations of the parameters associated with the signal return from a coherent CO2 pulsed Doppler lidar. The processor is based on a variation of the pulse pair technique utilized in conventional Doppler radar signal processing. The variation, termed poly-pulse pair processing, was developed in an attempt to provide an optimized method of estimating the mean frequency, intensity and spectral width associated with the lidar return signal. In order to ascertain the performance of the processor, a test program was undertaken in which simulated lidar returns of known spectral characteristics were input and the signal processor output was evaluated as a function of input signal to noise ratio. These results were then compared to the signal processor performance using actual lidar signals from hard targets and clear air.

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Prasad, Varanasi. "Spectral Absorption Coefficient Measurements in CFC Bands Relevant to Atmospheric Remote Sensing†". En Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/orsa.1991.owe13.

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The so-called line-by-line procedure is an impractical procedure in the case of several chlorofluorocarbons (CFCs). Positions, strengths and widths of individual lines are practically impossible to catalogue since there are literally (densely packed) thousands of them. Lines belonging to hot bands, which are transitions from excited vibrational levels, and isotopic bands further complicate the problem. A proper approach to take in such instances would be to measure the absorption coefficient itself over the range of wavenumbers, temperatures and pressures that are relevant to atmospheric remote sensing experiments. The ultimate goal in the line-by-line scheme is, after all, that of computing the absorption coefficient, a computation that is so desperately dependent on our knowledge, which we can never hope to possess totally adequately in the near future, of all of the parameters mentioned above and of their temperature and pressure dependence. Why not measure the absorption coefficient itself in the laboratory ? To illustrate the atttractiveness of this idea we present below two examples involving CFC-12 (CF2Cl2) and CFC-22 (CHClF2). The spectra were measured with the Doppler-limited spectral resolution of a tunable diode laser spectrometer and using a cryogenically cooled absorption cell, both of which are adequately described in some of our publications.1

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Schwiesow, R. L. y S. D. Mayor. "Coherent Optical Signal Processing for a Doppler Lidar using a Michelson Interferometer". En Coherent Laser Radar. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/clr.1995.wa5.

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There are a number of reasons to consider operating a Doppler lidar at wavelengths near 1 µm rather than at 10.6 µm. A very important one for NCAR applications is that the shorter-wavelength lidar offers better range and velocity resolution for measurements in the turbulent boundary layer because the product of range resolution and spectral width of the velocity spectrum is proportional to the wavelength. In addition, the quantized backscattering coefficient (number of photons backscattered for a given transmitted pulse energy) may be greater near 1 µ than at 10.6 µm for particle size distributions with a relatively small mean particle size.

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Informes sobre el tema "Spectral Doppler measurements"

Naguib, Ahmed M. A Doppler Sensor Array for High-Resolution Measurements of the Wavenumber-Frequency Spectrum of the Turbulent Wall Pressure at High Reynold Numbers. Fort Belvoir, VA: Defense Technical Information Center, octubre de 2003. http://dx.doi.org/10.21236/ada417457.

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Tire Experimental Characterization Using Contactless Measurement Methods. SAE International, agosto de 2021. http://dx.doi.org/10.4271/2021-01-1114.

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In the frame of automotive Noise Vibration and Harshness (NVH) evaluation, inner cabin noise is among the most important indicators. The main noise contributors can be identified in engine, suspensions, tires, powertrain, brake system, etc. With the advent of E-vehicles and the consequent absence of the Internal Combustion Engine (ICE), tire/road noise has gained more importance, particularly at mid-speed driving and in the spectrum up to 300 Hz. At the state of the art, the identification and characterization of Noise and Vibration sources rely on pointwise sensors (microphones, accelerometers, strain gauges). Optical methods such as Digital Image Correlation (DIC) and Laser Doppler Vibrometer (LDV) have recently received special attention in the NVH field because they can be used to obtain full-field measurements. Moreover, these same techniques could also allow to characterize the tire behavior in operating conditions, which would be practically impossible to derive with standard techniques. In this paper we will demonstrate how non-contact full-field measurement techniques can be used to reliably and robustly characterize the tire behavior up to 300 Hz, focusing on static conditions. Experimental modal analysis will extract the modal characteristic of the tire in both free-free and statically preloaded boundary conditions, using both DIC and LDV. The extracted natural frequencies, damping ratios and full-field mode shapes will be used on one side to improve the accuracy of tire models (either by deriving FRF based models or updating FE ones) but also as a reference for future investigation on the tire behavior characterization in rotating conditions.

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