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Littérature scientifique sur le sujet « High-Frequency RADARs »

Auteur : Grafiati

Publié le 25 janvier 2025

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Articles de revues sur le sujet "High-Frequency RADARs"

Dussol, Abïgaëlle, et Cédric Chavanne. « Estimation of the Wind Field with a Single High-Frequency Radar ». Remote Sensing 16, n^o 13 (21 juin 2024) : 2258. http://dx.doi.org/10.3390/rs16132258.

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Over several decades, high-frequency (HF) radars have been employed for remotely measuring various ocean surface parameters, encompassing surface currents, waves, and winds. Wind direction and speed are usually estimated from both first-order and second-order Bragg-resonant scatter from two or more HF radars monitoring the same area of the ocean surface. This limits the observational domain to the common area where second-order scatter is available from at least two radars. Here, we propose to estimate wind direction and speed from the first-order scatter of a single HF radar, yielding the same spatial coverage as for surface radial currents. Wind direction is estimated using the ratio of the positive and negative first-order Bragg peaks intensity, with a new simple algorithm to remove the left/right directional ambiguity from a single HF radar. Wind speed is estimated from wind direction and de-tided surface radial currents using an artificial neural network which has been trained with in situ wind speed observations. Radar-derived wind estimations are compared with in situ observations in the Lower Saint-Lawrence Estuary (Quebec, Canada). The correlation coefficients between radar-estimated and in situ wind directions range from 0.84 to 0.95 for Wellen Radars (WERAs) and from 0.79 to 0.97 for Coastal Ocean Dynamics Applications Radars (CODARs), while the root mean square differences range from 8° to 12° for WERAs and from 10° to 19° for CODARs. Correlation coefficients between the radar-estimated and the in situ wind speeds range from 0.89 to 0.93 for WERAs and from 0.81 to 0.93 for CODARs, while the root mean square differences range from 1.3 m.s−1 to 2.3 m.s−1 for WERAs and from 1.6 m.s−1 to 3.9 m.s−1 for CODARs.

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Baranov, G., R. Gabruk et I. Gorishna. « Features of Usіng Pulse-Doppler Radars for Determіnatіon Low-Altіtude Targets ». Metrology and instruments, n^o 2 (3 mai 2019) : 62–66. http://dx.doi.org/10.33955/2307-2180(2)2019.62-66.

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In this paper, we analyzed the features of Doppler processing in radars. In ground based radars, the amount of clutter in the radar receiver depends heavily on the radar-to-target geometry. The amount clutter is considerably higher when the radar beam has to face toward the ground. Furthermore, radars employing high PRFs have to deal with an increased amount of clutter due to folding in range. Clutter introduces additional difficulties for airborne radars when detecting ground targets and other targets flying at low altitudes. This is illustrated in Fig. 10.5. Returns from ground clutter emanate from ranges equal to the radar altitude to those which exceed the slant range along the main-beam, with considerable clutter returns in the side-lobes and main-beam. The presence of such large amounts of clutter interferes with radar detection capabilities and makes it extremely difficult to detect targets in the look-down mode. This difficulty in detecting ground or low altitude targets has led to the development of pulse Doppler radars where other targets, kinematics such as Doppler effects are exploited to enhance detection. Pulse Doppler radars utilize high PRFs to increases the average transmitted power and rely on target's Doppler frequency for detection. The increase in the average transmitted power leads to an improved SNR which helps the detection process. However, using high PRFs compromise the radar's ability to detect long range target because of range ambiguities associated with high PRF applications. Techniques such as using specialized Doppler filters to reject clutter are very effective and are often employed by pulse Doppler radars. Pulse Doppler radars can measure target Doppler frequency (or its range rate) fairly accurately and use the fact that ground clutter typically possesses limited Doppler shift when compared with moving targets to separate the two returns. Clutter filtering is used to remove both main-beam and altitude clutter returns, and fast moving target detection is done effectively by exploiting its Doppler frequency. In many modern pulse Doppler radars the limiting factor in detecting slow moving targets is not clutter but rather another source of noise referred to as phase noise generated from the receiver local oscillator instabilities.

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Roarty, Hugh J., Erick Rivera Lemus, Ethan Handel, Scott M. Glenn, Donald E. Barrick et James Isaacson. « Performance Evaluation of SeaSonde High-Frequency Radar for Vessel Detection ». Marine Technology Society Journal 45, n^o 3 (1 mai 2011) : 14–24. http://dx.doi.org/10.4031/mtsj.45.3.2.

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AbstractHigh-frequency (HF) surface wave radar has been identified to be a gap-filling technology for Maritime Domain Awareness. Present SeaSonde HF radars have been designed to map surface currents but are able to track surface vessels in a dual-use mode. Rutgers and CODAR Ocean Sensors, Ltd., have collaborated on the development of vessel detection and tracking capabilities from compact HF radars, demonstrating that ships can be detected and tracked by multistatic HF radar in a multiship environment while simultaneously mapping ocean currents. Furthermore, the same vessel is seen simultaneously by the radar based on different processing parameters, mitigating the need to preselect a fixed set and thereby improving detection performance.

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Silva, Murilo Teixeira, Weimin Huang et Eric W. Gill. « Bistatic High-Frequency Radar Cross-Section of the Ocean Surface with Arbitrary Wave Heights ». Remote Sensing 12, n^o 4 (18 février 2020) : 667. http://dx.doi.org/10.3390/rs12040667.

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The scattering theory developed in the past decades for high-frequency radio oceanography has been restricted to surfaces with small heights and small slopes. In the present work, the scattering theory for bistatic high-frequency radars is extended to ocean surfaces with arbitrary wave heights. Based on recent theoretical developments in the scattering theory for ocean surfaces with arbitrary heights for monostatic radars, the electric field equations for bistatic high-frequency radars in high sea states are developed. This results in an additional term related to the first-order electric field, which is only present when the small-height approximation is removed. Then, the radar cross-section for the additional term is derived and simulated, and its impact on the total radar cross-section at different radar configurations, dominant wave directions, and sea states is assessed. The proposed term is shown to impact the total radar cross-section at high sea states, dependent on radar configuration and dominant wave direction. The present work can contribute to the remote sensing of targets on the ocean surface, as well as the determination of the dominant wave direction of the ocean surface at high sea states.

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Kirincich, Anthony, Brian Emery, Libe Washburn et Pierre Flament. « Improving Surface Current Resolution Using Direction Finding Algorithms for Multiantenna High-Frequency Radars ». Journal of Atmospheric and Oceanic Technology 36, n^o 10 (octobre 2019) : 1997–2014. http://dx.doi.org/10.1175/jtech-d-19-0029.1.

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AbstractWhile land-based high-frequency (HF) radars are the only instruments capable of resolving both the temporal and spatial variability of surface currents in the coastal ocean, recent high-resolution views suggest that the coastal ocean is more complex than presently deployed radar systems are able to reveal. This work uses a hybrid system, having elements of both phased arrays and direction finding radars, to improve the azimuthal resolution of HF radars. Data from two radars deployed along the U.S. East Coast and configured as 8-antenna grid arrays were used to evaluate potential direction finding and signal, or emitter, detection methods. Direction finding methods such as maximum likelihood estimation generally performed better than the well-known multiple signal classification (MUSIC) method given identical emitter detection methods. However, accurately estimating the number of emitters present in HF radar observations is a challenge. As MUSIC’s direction-of-arrival (DOA) function permits simple empirical tests that dramatically aid the detection process, MUSIC was found to be the superior method in this study. The 8-antenna arrays were able to provide more accurate estimates of MUSIC’s noise subspace than typical 3-antenna systems, eliminating the need for a series of empirical parameters to control MUSIC’s performance. Code developed for this research has been made available in an online repository.

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Greenwald, Raymond A. « History of the Super Dual Auroral Radar Network (SuperDARN)-I : pre-SuperDARN developments in high frequency radar technology for ionospheric research and selected scientific results ». History of Geo- and Space Sciences 12, n^o 1 (11 mai 2021) : 77–93. http://dx.doi.org/10.5194/hgss-12-77-2021.

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Abstract. Part I of this history describes the motivations for developing radars in the high frequency (HF) band to study plasma density irregularities in the F region of the auroral zone and polar cap ionospheres. French and Swedish scientists were the first to use HF frequencies to study the Doppler velocities of HF radar backscatter from F-region plasma density irregularities over northern Sweden. These observations encouraged the author of this paper to pursue similar measurements over northeastern Alaska, and this eventually led to the construction of a large HF-phased-array radar at Goose Bay, Labrador, Canada. This radar utilized frequencies from 8–20 MHz and could be electronically steered over 16 beam directions, covering a 52∘ azimuth sector. Subsequently, similar radars were constructed at Schefferville, Quebec, and Halley Station, Antarctica. Observations with these radars showed that F-region backscatter often exhibited Doppler velocities that were significantly above and below the ion-acoustic velocity. This distinguished HF Doppler measurements from prior measurements of E-region irregularities that were obtained with radars operating at very high frequency (VHF) and ultra-high frequency (UHF). Results obtained with these early HF radars are also presented. They include comparisons of Doppler velocities observed with HF radars and incoherent scatter radars, comparisons of plasma convection patterns observed simultaneously in conjugate hemispheres, and the response of these patterns to changes in the interplanetary magnetic field, transient velocity enhancements in the dayside cusp, preferred frequencies for geomagnetic pulsations, and observations of medium-scale atmospheric gravity waves with HF radars.

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Wang, Li, Xiongbin Wu et Weihua Ai. « A Scheme for Credibility of Surface Currents Derived From High Frequency Radars ». Journal of Physics : Conference Series 2718, n^o 1 (1 mars 2024) : 012009. http://dx.doi.org/10.1088/1742-6596/2718/1/012009.

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Abstract Large amount of real-time ocean currents measured by HF radar have been included into the ocean observation database in many countries and regions, in support of applications for various marine activities such as marine research, Oil spill detection, tsunami warning, search and rescue. However, due to the performance of inversion algorithms and radar antennas, and other reasons, there are differences in the credibility of ocean current results at different times and locations, which brings on difficulties to applications of ocean currents. This letter proposes a method for developing a credibility model of ocean current results, mainly for all-digital multi-input and multi-output (MIMO) HF radar. By comparing the model with field experimental results, it is confirmed that the method is feasible. It will be very beneficial for radar users to select and use ocean current results, greatly reducing the work of verification of newly installed radars, and will be an innovation in the application technology of over-the-horizon marine radars.

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Choi, Mun Gak, Dong Sik Woo, Hyun Chul Choi et Kang Wook Kim. « High-Accuracy AM-FM Radar with an Active Reflector ». Journal of Sensors 2017 (2017) : 1–8. http://dx.doi.org/10.1155/2017/8589469.

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An amplitude-modulated and frequency-modulated (AM-FM) radar with an active reflector to produce high-accuracy distance measurements is proposed and demonstrated in this paper. The proposed radar consists of an AM-FM base module and an active reflector. The combination of AM and FM modulations resolves ambiguity of the absolute distance in typical AM radars, while improving range accuracy in typical FM radars with narrow bandwidth. Also, the active reflector, which translates the frequency of the received signal, resolves the problem of phase detection interference due to the direct Tx-to-Rx leakage in AM radars. In this paper, the operating principle, experimental tests, and analysis are presented. The implemented AM-FM radar operates in X-band (Tx: 10.5 GHz, Rx: 8.5 GHz) with the 620 MHz bandwidth. The measured range accuracy of less than ±10 mm at a distance of 70 m is obtained.

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Leinonen, Jussi, Matthew D. Lebsock, Simone Tanelli, Ousmane O. Sy, Brenda Dolan, Randy J. Chase, Joseph A. Finlon, Annakaisa von Lerber et Dmitri Moisseev. « Retrieval of snowflake microphysical properties from multifrequency radar observations ». Atmospheric Measurement Techniques 11, n^o 10 (5 octobre 2018) : 5471–88. http://dx.doi.org/10.5194/amt-11-5471-2018.

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Abstract. We have developed an algorithm that retrieves the size, number concentration and density of falling snow from multifrequency radar observations. This work builds on previous studies that have indicated that three-frequency radars can provide information on snow density, potentially improving the accuracy of snow parameter estimates. The algorithm is based on a Bayesian framework, using lookup tables mapping the measurement space to the state space, which allows fast and robust retrieval. In the forward model, we calculate the radar reflectivities using recently published snow scattering databases. We demonstrate the algorithm using multifrequency airborne radar observations from the OLYMPEX–RADEX field campaign, comparing the retrieval results to hydrometeor identification using ground-based polarimetric radar and also to collocated in situ observations made using another aircraft. Using these data, we examine how the availability of multiple frequencies affects the retrieval accuracy, and we test the sensitivity of the algorithm to the prior assumptions. The results suggest that multifrequency radars are substantially better than single-frequency radars at retrieving snow microphysical properties. Meanwhile, triple-frequency radars can retrieve wider ranges of snow density than dual-frequency radars and better locate regions of high-density snow such as graupel, although these benefits are relatively modest compared to the difference in retrieval performance between dual- and single-frequency radars. We also examine the sensitivity of the retrieval results to the fixed a priori assumptions in the algorithm, showing that the multifrequency method can reliably retrieve snowflake size, while the retrieved number concentration and density are affected significantly by the assumptions.

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Zhu, Langfeng, Tianyi Lu, Fan Yang, Chunlei Wei et Jun Wei. « Performance Assessment of a High-Frequency Radar Network for Detecting Surface Currents in the Pearl River Estuary ». Remote Sensing 16, n^o 1 (3 janvier 2024) : 198. http://dx.doi.org/10.3390/rs16010198.

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The performance of a high-frequency (HF) radar network situated within the Pearl River Estuary from 17 July to 13 August 2022 is described via a comparison with seven acoustic Doppler current profilers (ADCPs). The radar network consists of six OSMAR-S100 compact HF radars, with a transmitting frequency of 13–16 MHz and a direction-finding technique. Both the radial currents and vector velocities showed good agreement with the ADCP results (coefficient of determination r2: 0.42–0.78; RMS difference of radials: 11–21.6 cm s−1; bearing offset Δθ: −4.8°–16.1°; complex correlation coefficient γ: 0.62–0.96; and phase angle α: −24.3°–17.8°). For these radars, the Δθ values are not constant but vary with azimuthal angles. The relative positions between the HF radar and ADCPs, as well as factors such as the presence of island terrain obstructing the signal, significantly influence the errors. The results of spectral analysis also demonstrate a high level of consistency and the capability of HF radar to capture diurnal and semidiurnal tidal frequencies. The tidal characteristics and the Empirical Orthogonal Function (EOF) results measured by the HF radars also resemble the ADCPs and align with the characteristics of the estuarine current field.

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Thèses sur le sujet "High-Frequency RADARs"

Woodfield, Emma Elizabeth. « Studies of nightside spectral with behaviour from coherent high frequency radars ». Thesis, University of Leicester, 2002. http://hdl.handle.net/2381/30664.

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The work presented in this thesis is aimed to improving our understanding of the HF Doppler spectral width parameter and how it can be used to identify ionospheric and magnetospheric boundaries, specifically the use of the frequently observed gradient between high (>200 m s-1) and low (<200 m s-1) spectral width. Locating the boundaries between regions is important to the study of how the magnetosphere responds to the solar wind and interplanetary magnetic field conditions. Three case studies and a statistical investigation are presented herein which investigate the nature of these regions. Data from the Co-operative U.K. Twin Located Auroral Sounding System (CUTLASS) HF radars and the European Incoherent SCATter (EISCAT) radars from the primary observations. The cases presented show that high spectral width can be observed both on open and closed magnetic field lines, and that there is a relationship between elevated electron temperature and high spectral width (although the reverse is not true) which appears to be restricted to the post 0300 MLT nightside region. The data also show that high spectral widths can be associated with both single- and multiple-peak HF spectra. The statistical study compares three years of data from the CUTLASS radars and the Syowa East radar (part of the Super Dual Auroral Radar Network, SuperDARN), magnetically conjugate to Iceland East. It is found that the mean spectral width is dependent on latitude, magnetic local time (MLT) and season. The data from the two hemispheres show similar dependence on these factors, although the Syowa East spectral widths are larger in general (instrumental variations are discounted). These results suggest that the physical mechanism(s) creating the high spectral widths must work both on open and closed field lines, be dependent upon latitude and MLT, and be less prevalent (or attenuated) in summer months.

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Burger, Johann. « High frequency surface wave radar demonstrator ». Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29408.

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High Frequency Surface Wave Radar (HFSWR) is used around the globe for the mapping of sea currents and coastal monitoring of the Exclusive Economic Zone. Decision to build an HF radar at the University of Cape Town (UCT) was made by Daniel O’Hagan and Andrew Wilkinson in February 2015 immediately after seeing a demonstration of the CODAR system at IMT. Their intention was subsequently discussed at several meetings, including a South African Radar Interest Group (SARIG) meeting and one at IMT in order to gauge interest and raise funding. There was both interest (mainly for ocean current monitoring) and scepticism (expressed by CSIR and SARIG members) of the value of HF radar for ship monitoring. This reports the design, construction, test, and evaluation of the UCT HFSWR demonstrator. A modular approach was taken in its design and construction making it easy to replicate and upscale. A pillar of this work is to prove the feasibility of a software defined radar (SDR) based HF radar demonstrator. Every part of the demonstrator was designed and constructed from scratch as UCT had no prior HF activities, and therefore no legacy antennas or components to utilise. A low-cost RF frontend follows the HF antennas, which were also designed for this project. Combined with an SDR platforn known as the Red Pitaya (RP), a complete HF radar demonstrator was assembled and trials were conducted at the UCT rugby field and at the IMT facilities in Simon’s Town. A preliminary assessment of the results reveal the effects of Bragg resonance scatter and detection of two stationary targets (mountains) distinguishable by both range and azimuth. This assessment of the results indicates that the demonstrator is operational.

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Middleditch, Andrew. « Spectral analysis in high frequency radar oceanography ». Thesis, University of Sheffield, 2006. http://etheses.whiterose.ac.uk/3590/.

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High Frequency radar systems provide a unique opportunity to measure evolving littoral oceanic dynamics at high temporal and spatial resolution. Backscattered electromagnetic signals from ocean waves are modulated by Bragg resonant scattering. A perturbation analysis yields an expression for the spectral content of radar signals which can be exploited to provide estimates of oceanographic parameters: the radial component of surface current can be extracted from the frequency locations of the first order peaks; the ocean wave directional spectrum is related to the second order continuum via a non-linear integral equation. The periodogram, based on a Fourier decomposition of radax data, is the standard method used to derive frequency spectra. Limitations in this approach, caused by inhomogeneities in the underlying ocean field, are investigated. An instantaneous frequency technique is proposed in this thesis which mitigates the spectral distortion by demodulating the backscattered radax signals -a filtering procedure is developed which measures the temporally varying Bragg components. Alternative spectral techniques are analysed in order to validate the filter: an autoregressive paxa, metric modelling approach and an eigendecomposition method. The filter is evaluated, using radar and in situ data, which establishes its potential for ocean remote sensing. Significant improvements in the quantity and accuracy of wave measurements are demonstrated. Properties and constraints of the filter are derived using simulated data. Finally, the generic structure of the extracted instantaneous frequency signals is investigated and related to oceanographic processes.

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Paulose, Abraham Thomas. « High radar resolution with the step frequency waveform ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA284611.

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Warren, Craig. « Numerical modelling of high-frequency ground-penetrating radar antennas ». Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4074.

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Ground-Penetrating Radar (GPR) is a non-destructive electromagnetic investigative tool used in many applications across the fields of engineering and geophysics. The propagation of electromagnetic waves in lossy materials is complex and over the past 20 years, the computational modelling of GPR has developed to improve our understanding of this phenomenon. This research focuses on the development of accurate numerical models of widely-used, high-frequency commercial GPR antennas. High-frequency, highresolution GPR antennas are mainly used in civil engineering for the evaluation of structural features in concrete i. e., the location of rebars, conduits, voids and cracking. These types of target are typically located close to the surface and their responses can be coupled with the direct wave of the antenna. Most numerical simulations of GPR only include a simple excitation model, such as an infinitesimal dipole, which does not represent the actual antenna. By omitting the real antenna from the model, simulations cannot accurately replicate the amplitudes and waveshapes of real GPR responses. Numerical models of a 1.5 GHz Geophysical Survey Systems, Inc. (GSSI) antenna and a 1.2 GHz MALÅ GeoScience (MALÅ) antenna have been developed. The geometry of antennas is often complex with many fine features that must be captured in the numerical models. To visualise this level of detail in 3d, software was developed to link Paraview—an open source visualisation application which uses the Visualisation Toolkit (VTK)—with GprMax3D—electromagnetic simulation software based on the Finite-Difference Time-Domain (FDTD) method. Certain component values from the real antennas that were required for the models could not be readily determined due to commercial sensitivity. Values for these unknown parameters were found by implementing an optimisation technique known as Taguchi’s method. The metric used to initially assess the accuracy of the antenna models was a cross-corellation of the crosstalk responses from the models with the crosstalk responses measured from the real antennas. A 98 % match between modelled and real crosstalk responses was achieved. Further validation of the antenna models was undertaken using a series of laboratory experiments where oil-in-water (O/W) emulsions were created to simulate the electrical properties of real materials. The emulsions provided homogeneous liquids with controllable permittivity and conductivity and enabled different types of targets, typically encountered with GPR, to be tested. The laboratory setup was replicated in simulations which included the antenna models and an excellent agreement was shown between the measured and modelled data. The models reproduced both the amplitude and waveshape of the real responses whilst B-scans showed that the models were also accurately capturing effects, such as masking, present in the real data. It was shown that to achieve this accuracy, the real permittivity and conductivity profiles of materials must be correctly modelled. The validated antenna models were then used to investigate the radiation dynamics of GPR antennas. It was found that the shape and directivity of theoretically predicted far-field radiation patterns differ significantly from real antenna patterns. Being able to understand and visualise in 3d the antenna patterns of real GPR antennas, over realistic materials containing typical targets, is extremely important for antenna design and also from a practical user perspective.

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Svensson, Johan. « High Resolution Frequency Estimation in an FMCW Radar Application ». Thesis, Linköpings universitet, Reglerteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-148526.

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FMCW radars are widely used in the process industry for range estimation, usu- ally for estimating the liquid level in a tank. Since the tank system, often is an automatically controlled system, reliable estimates of the surface level are re- quired, e.g. to avoid the tank from pouring over or become empty. The goal of this thesis is to investigate methods which can distinguish fre- quencies closer to each other than the FFT resolution limit. Two properties are of interest, the accuracy and the resolution performance. Three such methods have been evaluated: one that tries to compensate for the leakage and interference of close frequencies, one subspace-based method and one deconvolution method. The deconvolution is performed with the iterative Lucy Richardson algorithm. The methods are evaluated against each other and against a typical FFT based algorithm. The methods sensitivity to amplitude differences is examined together with the robustness against noise and disturbances which appear due to imperfections in the radar unit. The deconvolution algorithm is the one that performs the best. The subspace-based method SURE requires prior knowledge of the number of ingoing frequencies which is difficult to know for real data from an FMCW radar. The leakage compensation method main weakness is the influence of the phase difference between close frequencies. The deconvolution algorithm is evaluated on some real data, and it is proven that it has better resolution performance than the FFT. However, the accuracy of the estimates are dependent on the number of iterations used. With a large num- ber of iterations, the algorithm finds peaks with small amplitude nearby the large peaks and they will thus interact and hence contribute to a worse accuracy even in the undisturbed case. If too few iterations are used in the deconvolution algo- rithm the resolution performance is about the same as the FFT algorithm. With a suitable choice of iterations about 40–50 mm, extra of continuous measurements are achieved. However, the estimation error of the gained resolution can in the worst case be about 40–50 mm.

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Green, Sean David. « Improving the range information of high frequency over-the-horizon skywave radar ». Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268265.

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Delgado, Raymond R. « Mapping coastal surface winds in Monterey Bay using high frequency radar ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA362924.

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Thesis (M.S. in Meteorology and M.S. in Physical Oceanography) Naval Postgraduate School, March 1999.
"March 1999". Thesis advisor(s): Jeffrey D. Paduan, Carlyle H. Wash. Includes bibliographical references (p. 121-122). Also available online.

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Chang, Paul Chinling. « Near zone radar imaging and feature capture of building interiors ». Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1197399599.

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Palmer, David J. « Topside sounding on a microsatellite ». Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/844211/.

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An ionospheric topside sounder is a high frequency radar system that is located above the ionosphere, ideally on-board a polar orbiting satellite to provide global coverage. The previous eight satellite sounders have measured the critical frequency of the F2 ionosphere region using traditional swept frequency methods. The most expensive part of these missions however is considered to be the large network of ground support stations required for collecting and processing data. This information has been invaluable in improving our global understanding of the upper ionosphere and the accuracy of critical frequency maps used by HF radio engineers to calculate communications routes and the optimum frequencies for early warning OTH radars. A new technique for the direct detection of critical frequency has been developed, which is called the 'Dispersion Method'. Real data from previous sounders is used in the development and verification of this method. This sounder will not only provide traditional lonograms but detects critical frequency and spread echoes directly from the dispersion of a returning radar pulse. This new method does not use traditional lonograms with their inherent processing complexity and is an order faster than any previous sounder. The 'Dispersion Method' therefore resolves the problems encountered with the past topside sounder missions and produces large quantities of real time data autonomously when required. Previous sounding satellites had little memory capacity, no on-board processing capability, required large antennas and transmitters on satellites with a mass of between 150 and 250 kg. This meant power requirements of about 60 watts per orbit average. A feasibility study to place a third generation topside sounder into low Earth orbit on a 50 kg microsatellite with an orbit average power capacity of only 20 watts has been successfully completed.

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Livres sur le sujet "High-Frequency RADARs"

Madden, J. M. Adaptive interference suppression in high frequency groundwave radar. Birmingham : University ofBirmingham, 1986.

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Paulose, Abraham Thomas. High radar resolution with the step frequency waveform. Monterey, Calif : Naval Postgraduate School, 1994.

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Kouteas, Dimitrios. Investigation of high frequency ship radar cross section reduction by means of shaping. Monterey, Calif : Naval Postgraduate School, 1998.

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Balanis, Constantine A. High-frequency techniques for RCS prediction of plate geometries : Semiannual progress report. Tempe, AZ : Telecommunications Research Center, College of Engineering and Applied Science, Arizona State University, 1992.

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A, Polka Lesley, et United States. National Aeronautics and Space Administration., dir. High-frequency techniques for RCS prediction of plate geometries : Semiannual progress report. Tempe, AZ : Telecommunications Research Center, College of Engineering and Applied Science, Arizona State University, 1992.

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Balanis, Constantine A. High-frequency techniques for RCS prediction of plate geometries : Semiannual progress report, August 1, 1990 - January 31, 1991. Tempe, Ariz : Dept. of Electrical Engineering, Telecommunications Research Center, Arizona State University, 1991.

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A, Polka Lesley, Arizona State University. Dept. of Electrical Engineering. et Langley Research Center, dir. High-frequency techniques for RCS prediction of plate geometries : Semiannual progress report, February 1, 1991 - July 31, 1991. Tempe, Ariz : Dept. of Electrical Engineering, Telecommunications Research Center, Arizona State University, 1991.

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Balanis, Constantine A. High-frequency techniques for RCS prediction of plate geometries : Semiannual progress report, February 1, 1991 - July 31, 1991. Tempe, Ariz : Dept. of Electrical Engineering, Telecommunications Research Center, Arizona State University, 1991.

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Balanis, Constantine A. High-frequency techniques for RCS prediction of plate geometries : Semiannual progress report, August 1, 1991 - January 31, 1992. Tempe, Ariz : Telecommunications Research Center, College of Engineering and Applied Science, Arizona State University, 1992.

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Chapitres de livres sur le sujet "High-Frequency RADARs"

Liu, Kai, Yang Wang, Qilong Song et Xi Liao. « Spectrum Modulation of Smart-Surfaces for Ultra High Frequency Radars ». Dans Communications and Networking, 405–13. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-06161-6_40.

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Liu, Yonggang, Clifford R. Merz, Robert H. Weisberg, Benjamin K. O’Loughlin et Vembu Subramanian. « Data Return Aspects of CODAR and WERA High-Frequency Radars in Mapping Currents ». Dans Observing the Oceans in Real Time, 227–40. Cham : Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-66493-4_11.

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Park, Sangwook, Chul Jin Cho, Younglo Lee, Andrew Da Costa, SangHo Lee et Hanseok Ko. « Bayesian Estimator Based Target Localization in Ship Monitoring System Using Multiple Compact High Frequency Surface Wave Radars ». Dans Lecture Notes in Electrical Engineering, 157–67. Cham : Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-90509-9_9.

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Horstmann, Jochen, et Anna Dzvonkovskaya. « High Frequency Radar ». Dans Springer Handbook of Atmospheric Measurements, 953–68. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-52171-4_33.

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Ma, Xiaoyu, Kunmei Li, Zhiwei Wang, Wei Xu, Zheng Bian, Zicheng Du et Longbo Deng. « Hybrid Noise Eliminating Algorithm for Radar Target Images Based on the Time-Frequency Domain ». Dans Lecture Notes in Civil Engineering, 408–20. Singapore : Springer Nature Singapore, 2024. http://dx.doi.org/10.1007/978-981-97-4355-1_38.

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AbstractThe radar target imaging effect directly affects the resolution of the radar target, which affects the commander’s decision. However, the hybrid noise composed of speckle and Gaussian noise is one of the main affecting factors. The existing methods for image denoising are hard to eliminate the hybrid noise in radar images. Hence, this paper proposes a new hybrid noise elimination algorithm for the radar target image. Based on the strong correlation between wavelet coefficients, this algorithm first uses the wavelet coefficient correlation denoising algorithm (WCCDA) to filter the high-frequency information and high-frequency part of low-frequency information for different directions of the three channels of the image. Then, an improved adaptive median filtering algorithm (IAMF) is proposed to perform fine-grained filtering on each re-constructed channel. Finally, the radar target image is reconstructed. The results show that the proposed algorithm outperforms the comparison approaches in the peak signal-to-noise ratio (PSNR) and mean-square error (MSE) indexes with better denoising effects.

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Wang, Linwei, Changjun Yu et Haorong Wang. « Seawater Antenna for High-Frequency Surface Wave Radar ». Dans Lecture Notes in Electrical Engineering, 776–83. Singapore : Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-6508-9_94.

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Zhou, Hao, et Biyang Wen. « Portable High Frequency Surface Wave Radar OSMAR-S ». Dans Intelligent Environmental Sensing, 79–110. Cham : Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-12892-4_4.

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Miyashita, Toyokatsu. « High Precision Acoustic Radar by Unequally Spaced Frequency Array ». Dans Acoustical Imaging, 519–24. Boston, MA : Springer US, 1996. http://dx.doi.org/10.1007/978-1-4419-8772-3_84.

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Linwei, Wang, Li Bo, Yu Changjun et Ji Xiaowei. « Slow-Time MIMO in High Frequency Surface Wave Radar ». Dans Wireless and Satellite Systems, 751–61. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-93398-2_65.

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Grilli, Stéphan T., Samuel Grosdidier et Charles-Antoine Guérin. « Tsunami Detection by High-Frequency Radar Beyond the Continental Shelf ». Dans Pageoph Topical Volumes, 3895–934. Cham : Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-55480-8_13.

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Actes de conférences sur le sujet "High-Frequency RADARs"

Iswandi, Risanuri Hidayat et Sigit Basuki Wibowo. « Comparison of Ship Tracking Algorithms on Dual Overlapping High Frequency Surface Wave Radars ». Dans 2024 16th International Conference on Information Technology and Electrical Engineering (ICITEE), 457–62. IEEE, 2024. https://doi.org/10.1109/icitee62483.2024.10808939.

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Bekar, Ali, Michail Antoniou et Christopher J. Baker. « High-Resolution Drone-Borne SAR using Off-the-Shelf High-Frequency Radars ». Dans 2021 IEEE Radar Conference (RadarConf21). IEEE, 2021. http://dx.doi.org/10.1109/radarconf2147009.2021.9455342.

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Bourges, A., et R. Guinvarc'h. « Perspectives of the use of high frequency radars on buoys ». Dans Oceans 2005 - Europe. IEEE, 2005. http://dx.doi.org/10.1109/oceanse.2005.1513239.

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Sabet-Peyman, F., R. L. Cohoon et J. S. Finnigan. « Time–frequency processing of high-range resolution radar returns ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.thu1.

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The properties of the returned signals associated with high range resolution (HRR) radars are influenced by Doppler and constantly vary according to the target aspect relative to the radar line of sight. To effectively sort and classify the returned signals the spectral and temporal contents must be measured simultaneously. A 2-D processor implementing the Wigner transform of the received signals is designed and demonstrated. This architecture is based on acoustooptics and provides the time–frequency information related to the scattered chirped signals in real time at the output plane. In this architecture the returned signals modulate the laser beam via a Bragg cell. A cylindrical lens of appropriate focal length is used to dechirp the returned signals and a second Bragg cell to generate the time base, followed by Fourier transform optics. In this paper we discuss the architecture, its performance, and present the results of recent experiments. System performance is discussed in terms of unintentional signal variation, the dechirping lens and Bragg cell aperture and bandwidth.

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Goutelard, C. « STUDIO father of NOSTRADAMUS. Some considerations on the limits of detection possibilities of HF radars ». Dans 8th International Conference on High-Frequency Radio Systems and Techniques. IEE, 2000. http://dx.doi.org/10.1049/cp:20000174.

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Dussol, Abigaelle, Cedric Chavanne et Dany Dumont. « Wave-Induced Stokes Drift Measurement by High-Frequency Radars : Preliminary Results ». Dans 2019 IEEE/OES Twelfth Current, Waves and Turbulence Measurement (CWTM). IEEE, 2019. http://dx.doi.org/10.1109/cwtm43797.2019.8955276.

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Sil, Sourav, Shouvik Dey et Samiran Mandal. « Seasonal Circulation of Gulf of Khambhat, India using High Frequency Radars ». Dans OCEANS 2022 - Chennai. IEEE, 2022. http://dx.doi.org/10.1109/oceanschennai45887.2022.9775249.

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Park, Sangwook, Chul Jin Cho, Younglo Lee, Andrew Da Costa, SangHo Lee et Hanseok Ko. « Coastal ship monitoring based on multiple compact high frequency surface wave radars ». Dans 2017 IEEE International Conference on Multisensor Fusion and Integration for Intelligent Systems (MFI). IEEE, 2017. http://dx.doi.org/10.1109/mfi.2017.8170381.

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Cruz, Febus Reidj G., Mark Rommel L. Collado, Francis C. Penetrante et Jesse Michael E. Baltazar. « Background-Dependent Adaptive Composite CFAR Detector for Compact High Frequency Surface Wave Radars ». Dans TENCON 2018 - 2018 IEEE Region 10 Conference. IEEE, 2018. http://dx.doi.org/10.1109/tencon.2018.8650494.

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YOUNG, NICHOLAS, et GEORGE BOHANNON. « Verification and validation of algorithms for obtaining debris data using high frequency radars ». Dans Space Programs and Technologies Conference. Reston, Virigina : American Institute of Aeronautics and Astronautics, 1990. http://dx.doi.org/10.2514/6.1990-3869.

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Rapports d'organisations sur le sujet "High-Frequency RADARs"

Rubio, Anna, Emma Reyes, Carlo Mantovani, Lorenzo Corgnati, Pablo Lorente, Lohitzune Solabarrieta, Julien Mader et al. European High Frequency Radar network governance. EuroSea, mai 2021. http://dx.doi.org/10.3289/eurosea_d3.4.

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This report describes the governance of the European HF radar network including: the landscape of the Ocean observation networks and infrastructures, the role and links between operators of observational systems and stakeholders, the role and activities of the EuroGOOS HF radar Task Team in building a sound community strategy, the roadmap of the community with current achievements and future work lines.

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Monk, Virginia C., et Fred W. Sedenquist. High Frequency Radar Target Modeling. Fort Belvoir, VA : Defense Technical Information Center, janvier 1995. http://dx.doi.org/10.21236/ada290955.

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Monk, Virginia C., et Fred W. Sedenquist. High-Frequency Radar Target Modeling. Fort Belvoir, VA : Defense Technical Information Center, janvier 1995. http://dx.doi.org/10.21236/ada290965.

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Solabarrieta, Lohitzune. HF-Radar Tools. EuroSea, 2023. http://dx.doi.org/10.3289/eurosea_d3.14.

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This report provides a description of the different tools developed for tackling key issues of the High Frequency Radar (HFR) community: advanced delayed time QC of HFR historical data, implementation of Best Practices, enhancing the application of HFR observations in NRT modelling assessment and Ocean State indicators

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Schmitt, R. L., R. J. Williams et J. D. Matthews. High-frequency scannerless imaging laser radar for industrial inspection and measurement applications. Office of Scientific and Technical Information (OSTI), novembre 1996. http://dx.doi.org/10.2172/419074.

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Atkinson, Larry P. Oceanography - High Frequency Radar and Ocean Thin Layers, Volume 10, No. 2. Fort Belvoir, VA : Defense Technical Information Center, mars 1999. http://dx.doi.org/10.21236/ada361115.

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Vesecky, John F. Mapping of Ocean Surface Currents and Vertical Shear by High Frequency Radar. Fort Belvoir, VA : Defense Technical Information Center, septembre 1997. http://dx.doi.org/10.21236/ada628156.

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Polyakov, S. V. The Use of High Frequency Solar Radar to Detect Coronal Mass Ejections. Fort Belvoir, VA : Defense Technical Information Center, janvier 1998. http://dx.doi.org/10.21236/ada353482.

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Goldman, Geoffrey H., et Frank J. Crowne. High-frequency Radar Cross Section (RCS) Approximation of a Thin Dielectric Spherical Shell. Fort Belvoir, VA : Defense Technical Information Center, juillet 2012. http://dx.doi.org/10.21236/ada562481.

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Mathew, Jijo K. Speed Enforcement in Work Zones and Synthesis on Cost-Benefit Assessment of Installing Speed Enforcement Cameras on INDOT Road Network. Purdue University, 2023. http://dx.doi.org/10.5703/1288284317639.

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Work zone safety is a high priority for transportation agencies across the United States. High speeds in construction zones are a well-documented risk factor that increases the frequency and severity of crashes. It is therefore important to understand the extent and severity of high-speed vehicles in and around construction work zones. This study uses CV trajectory data to evaluate the impact of several work zone speed compliance measures, such as posted speed limit signs, radar-based speed feedback displays, and automated speed enforcement on controlling speeds inside the work zone. This study also presents several methodologies to characterize both the spatial and temporal effects of these control measures on driver behavior and vehicle speeds across the work zones.

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