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Shvets, S., O. Kipriianov, F. Yermolenko y I. Haidak. "SUGGESTIONS FOR TYPICAL METHODS OF USING DOPPLER RADAR SYSTEMS OF TRAJECTORY MEASUREMENTS DURING TESTS OF ARTYLLERY ARMAMENT AND ITS AMMUNITION". Наукові праці Державного науково-дослідного інституту випробувань і сертифікації озброєння та військової техніки, n.º 7 (21 de mayo de 2021): 94–100. http://dx.doi.org/10.37701/dndivsovt.7.2021.11.
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The article analyzes the report documentation of the tests in which the Doppler radar trajectory measurement system MFTR–2100/40 and the muzzle velocity measurement system SL-520PE were used to determine the trajectory parameters of artillery armament.
The purpose of the article is to provide proposals for standard methods of using Doppler radar systems of trajectory measurements when testing artillery armament and its ammunition.
The proposals for these standard methods are based on the experience of using the MFTR–2100/40 radar system and the SL–520PE muzzle velocity measurement system during the tests of the latest specimens of artillery and ammunition and relate to typical Doppler radar systems. When choosing the position and mode of operation of such Doppler radar trajectory measurement systems, it is always necessary to take into account safety measures, instructions for their operation, technical features (capabilities) of radar systems specified in this article, considering the interference environment during firing (shot) of artillery armament and experiment (test) conditions. Placing typical Doppler radar systems when taking measurements in unplanned places is dangerous for the crew and measuring instruments and leads to partial or complete loss of measuring trajectory information and reduced measurement accuracy.
Abovementioned proposals are offered to be taken into account when developing methods of trajectory measurements using typical Doppler radar systems during testing artillery armament and its ammunition.
Methods of measurements using standard Doppler radar systems of trajectory measurements should be developed in accordance with current standards (GOST 8.010-99, GOST V 15.211-78 and others) for a particular test, taking into account the results of analysis of the characteristics of samples to be evaluated, measuring instruments used, conditions and locations of measurements.
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Heymsfield, Andrew J., Alain Protat, Dominique Bouniol, Richard T. Austin, Robin J. Hogan, Julien Delanoë, Hajime Okamoto et al. "Testing IWC Retrieval Methods Using Radar and Ancillary Measurements with In Situ Data". Journal of Applied Meteorology and Climatology 47, n.º 1 (1 de enero de 2008): 135–63. http://dx.doi.org/10.1175/2007jamc1606.1.
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Abstract Vertical profiles of ice water content (IWC) can now be derived globally from spaceborne cloud satellite radar (CloudSat) data. Integrating these data with Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data may further increase accuracy. Evaluations of the accuracy of IWC retrieved from radar alone and together with other measurements are now essential. A forward model employing aircraft Lagrangian spiral descents through mid- and low-latitude ice clouds is used to estimate profiles of what a lidar and conventional and Doppler radar would sense. Radar reflectivity Ze and Doppler fall speed at multiple wavelengths and extinction in visible wavelengths were derived from particle size distributions and shape data, constrained by IWC that were measured directly in most instances. These data were provided to eight teams that together cover 10 retrieval methods. Almost 3400 vertically distributed points from 19 clouds were used. Approximate cloud optical depths ranged from below 1 to more than 50. The teams returned retrieval IWC profiles that were evaluated in seven different ways to identify the amount and sources of errors. The mean (median) ratio of the retrieved-to-measured IWC was 1.15 (1.03) ± 0.66 for all teams, 1.08 (1.00) ± 0.60 for those employing a lidar–radar approach, and 1.27 (1.12) ± 0.78 for the standard CloudSat radar–visible optical depth algorithm for Ze > −28 dBZe. The ratios for the groups employing the lidar–radar approach and the radar–visible optical depth algorithm may be lower by as much as 25% because of uncertainties in the extinction in small ice particles provided to the groups. Retrievals from future spaceborne radar using reflectivity–Doppler fall speeds show considerable promise. A lidar–radar approach, as applied to measurements from CALIPSO and CloudSat, is useful only in a narrow range of ice water paths (IWP) (40 < IWP < 100 g m−2). Because of the use of the Rayleigh approximation at high reflectivities in some of the algorithms and differences in the way nonspherical particles and Mie effects are considered, IWC retrievals in regions of radar reflectivity at 94 GHz exceeding about 5 dBZe are subject to uncertainties of ±50%.
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Azizi, Mussyazwann Azizi Mustafa, Mohammad Nazrin Mohd Noh, Idnin Pasya, Ahmad Ihsan Mohd Yassin y Megat Syahirul Amin Megat Ali. "Pedestrian detection using Doppler radar and LSTM neural network". IAES International Journal of Artificial Intelligence (IJ-AI) 9, n.º 3 (1 de septiembre de 2020): 394. http://dx.doi.org/10.11591/ijai.v9.i3.pp394-401.
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<span lang="EN-US">Integration of radar systems as primary sensor with deep learning algorithms in driver assist systems is still limited. Its implementation would greatly help in continuous monitoring of visual blind spots from incoming pedestrians. Hence, this study proposes a single-input single-output based Doppler radar and long short-term memory (LSTM) neural network for pedestrian detection. The radar is placed in monostatic configuration at an angle of 45 degree from line of sight. Continuous wave with frequency of 1.9 GHz are continuously transmitted from the antenna. The returning signal from the approaching subjects is characterized by the branching peaks higher than the transmitted frequency. A total of 1108 spectrum traces with Doppler shifts characteristics is acquired from eight volunteers. Another 1108 spectrum traces without Doppler shifts are used for control purposes. The traces are then fed to LSTM neural network for training, validation and testing. Generally, the proposed method was able to detect pedestrian with 88.9% accuracy for training and 87.3% accuracy for testing.</span>
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Lyashenko, V., V. Kuznecov, O. Kipriianov, F. Yermolenko y T. Pavliuk. "RECOMMENDATIONS ON INTEGRATED APPLICATION OF DOPPLER RADAR SYSTEMS OF EXTERNAL TRACTORY MEASUREMENTS IN THE MOBILE TESTING GROUND MEASURING AND COMPUTING COMPLEX". Наукові праці Державного науково-дослідного інституту випробувань і сертифікації озброєння та військової техніки, n.º 8 (29 de junio de 2021): 72–79. http://dx.doi.org/10.37701/dndivsovt.8.2021.08.
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Testing ground measuring and computing complex (TGMCC) is a set of interconnected hardware and software designed to perform measurements and processing of measuring information to determine the tactical and technical characteristics of objects in different conditions of their application, objective evaluation of test results of armament and military equipment (AME).
For radar measurements of trajectory parameters of moving objects, mobile and stationary radar stations of trajectory measurements are used, including Doppler radar systems of external trajectory measurements. Such radar stations of trajectory measurements are one of the components of TGMCC. They are designed to measure, process and record the parameters of the trajectories of moving objects in a given spatial volume with a given accuracy and reliability during testing of a wide range of new and upgraded samples of AME, as well as perform measurements along with optoelectronic stations of trajectory measurements, or they could be used separately from them.
Therefore, currently there is a problem of creation of mobile testing ground measuring and computing complex which consists in its equipping by modern means of external trajectory measurements, both domestic and foreign.
Thus, the proposed recommendations for the integrated application of Doppler radar systems of external trajectory measurements as a part of a mobile testing ground measuring and computing complex will allow to conduct testing and certification of armament and military equipment offered for supply to the Armed Forces of Ukraine more efficiently and with increased quality.
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Zou, Tao, Xian Lin Zeng y Jian Hua Peng. "Research on the Airborne Pulse Doppler Radar Jamming System Tester". Applied Mechanics and Materials 654 (octubre de 2014): 250–53. http://dx.doi.org/10.4028/www.scientific.net/amm.654.250.
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This paper introduces the design of an airborne pulse Doppler radar jamming system tester. Based on a detailed analysis of the functional structure of the radar-jamming system, we summarize the important failure mode. To achieve fault location and performance testing, we have developed an automatic detector for the radar-jamming system, the device uses a mode of hardware platform and software platform, and it can reach the purpose of fault location by a method of encouraging input and measuring the output of each of the radar-jamming system failure mode individually. The automatic test instrument has the features of simple operation, high degree of automation, real-time, scalable, and actual use of running proves it to reach the required design specifications, the test with good results.
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Diewald, Andreas R., Manuel Steins y Simon Müller. "Radar target simulator with complex-valued delay line modeling based on standard radar components". Advances in Radio Science 16 (18 de diciembre de 2018): 203–13. http://dx.doi.org/10.5194/ars-16-203-2018.
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Abstract. With increasing radar activities in the automotive, industrial and private sector, there is a need to test radar sensors in their environment. A radar target simulator can help testing radar systems repeatably. In this paper, the authors present a concept of low-cost hardware for radar target simulation. The theoretical foundations are derived and analyzed. An implementation of a demonstrator operating in the 24 GHz ISM band is shown for which the dynamical range simulation was implemented in a FPGA with fast sampling ADCs and DACs. By using a FIR filtering approach a fine discretization of the range could be reached which will furthermore allow an inherent and automatic Doppler simulation by moving the target.
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Dubosclard, G., R. Cordesses, P. Allard, C. Hervier, M. Coltelli y J. Kornprobst. "First testing of a volcano Doppler radar (Voldorad) at Mount Etna, Italy". Geophysical Research Letters 26, n.º 22 (15 de noviembre de 1999): 3389–92. http://dx.doi.org/10.1029/1999gl008371.
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Muscarella, Philip, Kelsey Brunner y David Walker. "Estimating Coastal Winds by Assimilating High-Frequency Radar Spectrum Data in SWAN". Sensors 21, n.º 23 (24 de noviembre de 2021): 7811. http://dx.doi.org/10.3390/s21237811.
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Many activities require accurate wind and wave forecasts in the coastal ocean. The assimilation of fixed buoy observations into spectral wave models such as SWAN (Simulating Waves Nearshore) can provide improved estimates of wave forecasts fields. High-frequency (HF) radar observations provide a spatially expansive dataset in the coastal ocean for assimilation into wave models. A forward model for the HF Doppler spectrum based on first- and second-order Bragg scattering was developed to assimilate the HF radar wave observations into SWAN. This model uses the spatially varying wave spectra computed using the SWAN model, forecast currents from the Navy Coastal Ocean Model (NCOM), and system parameters from the HF radar sites to predict time-varying range-Doppler maps. Using an adjoint of the HF radar model, the error between these predictions and the corresponding HF Doppler spectrum observations can be translated into effective wave-spectrum errors for assimilation in the SWAN model for use in correcting the wind forcing in SWAN. The initial testing and validation of this system have been conducted using data from ten HF radar sites along the Southern California Bight during the CASPER-West experiment in October 2017. The improved winds compare positively to independent observation data, demonstrating that this algorithm can be utilized to fill an observational gap in the coastal ocean for winds and waves.
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Foth, Andreas, Janek Zimmer, Felix Lauermann y Heike Kalesse-Los. "Evaluation of micro rain radar-based precipitation classification algorithms to discriminate between stratiform and convective precipitation". Atmospheric Measurement Techniques 14, n.º 6 (21 de junio de 2021): 4565–74. http://dx.doi.org/10.5194/amt-14-4565-2021.
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Abstract. In this paper, we present two micro rain radar-based approaches to discriminate between stratiform and convective precipitation. One is based on probability density functions (PDFs) in combination with a confidence function, and the other one is an artificial neural network (ANN) classification. Both methods use the maximum radar reflectivity per profile, the maximum of the observed mean Doppler velocity per profile and the maximum of the temporal standard deviation (±15 min) of the observed mean Doppler velocity per profile from a micro rain radar (MRR). Training and testing of the algorithms were performed using a 2-year data set from the Jülich Observatory for Cloud Evolution (JOYCE). Both methods agree well, giving similar results. However, the results of the ANN are more decisive since it is also able to distinguish an inconclusive class, in turn making the stratiform and convective classes more reliable.
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Beckwith, Dana M. y Katharine M. Hunter-Zaworski. "Passive Pedestrian Detection at Unsignalized Crossings". Transportation Research Record: Journal of the Transportation Research Board 1636, n.º 1 (enero de 1998): 96–103. http://dx.doi.org/10.3141/1636-16.
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The city of Portland, Oregon, is researching ways to provide safe unsignalized crossings for pedestrians. A concept that shows promise is known as passive pedestrian detection. Passive pedestrian detection is the detection of pedestrians in a stationary or moving state at the curbside of or in a pedestrian crossing by means other than those requiring physical response by the pedestrian. Research was conducted to find sensor technologies that can be used to passively detect pedestrians. Five technologies were found to be options for this type of detection: passive infrared, ultrasonic, microwave radar, video imaging, and piezometric. Of these five technologies, passive infrared, ultrasonic, and microwave radar were selected for testing. An unbiased selection of sensors was made by using a decision matrix in the form of the quality function deployment method, which also provides a record of sensor information for future research. Preliminary testing was conducted on the sensors to ensure that the detection of pedestrians was possible and to determine sensor operating characteristics. Sensors then went through secondary tests to ensure proper operation at an unsignalized crossing. The secondary test site was retrofitted with reflective pedestrian crossing signs, yellow beacons, Doppler radar, and passive infrared sensors chosen from the preliminary tests. Initial secondary tests have shown promising results for the Doppler radar and especially for the passive infrared sensors. Future applications of passive pedestrian detection in Portland will involve installation of sensors at signalized pedestrian crossings.
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Unal, Christine. "Spectral Polarimetric Radar Clutter Suppression to Enhance Atmospheric Echoes". Journal of Atmospheric and Oceanic Technology 26, n.º 9 (1 de septiembre de 2009): 1781–97. http://dx.doi.org/10.1175/2009jtecha1170.1.
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Abstract The clutter present in the Doppler spectra of atmospheric targets can be removed by using polarimetry. The purpose is to suppress the Doppler velocity bins where spectral polarimetric parameters have atypical values. This procedure largely improves profiles of moments and polarimetric parameters of atmospheric targets. Several spectral polarimetric clutter-reduction techniques, which are based on thresholding and intended for real-time processing, are discussed in this paper. A new method, the double spectral linear depolarization ratio clutter-suppression technique, is proposed. Very satisfactory performances are obtained with this method, which can be used in the full range of elevations (0°–90°). Spectral polarimetric clutter-suppression techniques for real-time processing were studied for the S-band high-resolution Transportable Atmospheric Radar (TARA) profiler. For this study, precipitation, cloud, and clear-air scattering are considered examples of atmospheric echoes. After successful testing in 2008, the double spectral linear depolarization ratio filter was implemented in the real-time processing of the X-band scanning drizzle radar (IDRA).
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Scheiblhofer, Werner, Reinhard Feger, Andreas Haderer y Andreas Stelzer. "Concept and realization of a low-cost multi-target simulator for CW and FMCW radar system calibration and testing". International Journal of Microwave and Wireless Technologies 10, n.º 2 (13 de febrero de 2018): 207–15. http://dx.doi.org/10.1017/s1759078718000028.
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AbstractWe present the realization of an frequency-modulated continuous-wave radar target simulator, based on a modulated-reflector radar system. The simulator, designed for the 24 GHz frequency band, uses low-cost modulated-reflector nodes and is capable to simultaneously generate multiple targets in a real-time environment. The realization is based on a modular approach and thus provides a high scalability of the whole system. It is demonstrated that the concept is able to simulate multiple artificial targets, located at user-selectable ranges and even velocities, utilized within a completely static setup. The characterization of the developed hardware shows that the proposed concept allows to dynamically and precisely adjust the radar cross-section of each single target within a dynamic range of 50 dB. Additionally, the provided range-proportional target frequency bandwidth makes the system perfectly suitable for fast and reliable intermediate frequency-chain calibration of multi-channel radar systems. Within this paper we demonstrate the application of the concept for a linear sweeped frequency-modulated continuous-wave radar. The presented approach is applicable to any microwave-based measurement system using frequency differences between transmit- and receive signals for range- and velocity evaluation, such as (non-)linear sweeped as well as pure Doppler radar systems.
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Tucker, Sara C., Carl S. Weimer, Sunil Baidar y R. Michael Hardesty. "The Optical Autocovariance Wind Lidar. Part I: OAWL Instrument Development and Demonstration". Journal of Atmospheric and Oceanic Technology 35, n.º 10 (octubre de 2018): 2079–97. http://dx.doi.org/10.1175/jtech-d-18-0024.1.
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AbstractWe present the motivation, instrument concept, hardware descriptions, and initial validation testing for a Doppler wind lidar (DWL) system that uses optical autocovariance (OA) in a field-widened quadrature Mach–Zehnder interferometer lidar to measure Doppler shifts from atmospheric-aerosol-backscattered laser light. We describe system architectures for three different generations of the direct-detection aerosol Optical Autocovariance Wind Lidar (OAWL) system, including the current two-line-of-sight, dual-wavelength (355 and 532 nm) airborne configuration, designed to be an airborne demonstrator for potential space-based global wind measurement applications. We provide meter-per-second-precision results from a ground-based 355-nm OAWL aerosol winds measurement validation study alongside another DWL, results from an autumn 2011 airborne validation testing performed with radar wind profiler data, and wind measurement results from airborne validation flight testing using the 532-nm wavelength in spring 2016.
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Narayanan, Ram M., Michael J. Harner, John R. Jendzurski y Nicholas G. Paulter. "Analysis of a Dynamic Calibration Target for Through-Wall and Through-Rubble Motion Sensing Doppler Radar". Instruments 5, n.º 4 (3 de diciembre de 2021): 37. http://dx.doi.org/10.3390/instruments5040037.
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Through-wall and through-barrier motion-sensing systems are becoming increasingly important tools to locate humans concealed behind barriers and under rubble. The sensing performance of these systems is best determined with appropriately designed calibration targets, which are ones that can emulate human motion. The effectiveness of various dynamic calibration targets that emulate human respiration, heart rate, and other body motions were analyzed. Moreover, these targets should be amenable to field deployment and not manifest angular or orientation dependences. The three targets examined in this thesis possess spherical polyhedral geometries. Spherical geometries were selected due to their isotropic radar cross-sectional characteristics, which provide for consistent radar returns independent of the orientation of the radar transceiver relative to the test target. The aspect-independence of a sphere allows for more accurate and repeatable calibration of a radar than using a nonspherical calibration artifact. In addition, the radar cross section (RCS) for scattering spheres is well known and can be calculated using far-field approximations. For Doppler radar testing, it is desired to apply these calibration advantages to a dynamically expanding-and-contracting sphere-like device that can emulate motions of the human body. Monostatic RCS simulations at 3.6 GHz were documented for each geometry. The results provide a visual way of representing the effectiveness of each design as a dynamic calibration target for human detection purposes.
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Chipengo, Ushemadzoro, Peter M. Krenz y Shawn Carpenter. "From Antenna Design to High Fidelity, Full Physics Automotive Radar Sensor Corner Case Simulation". Modelling and Simulation in Engineering 2018 (27 de diciembre de 2018): 1–19. http://dx.doi.org/10.1155/2018/4239725.
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Advanced driver assistance systems (ADAS) have recently been thrust into the spotlight in the automotive industry as carmakers and technology companies pursue effective active safety systems and fully autonomous vehicles. Various sensors such as lidar (light detection and ranging), radar (radio detection and ranging), ultrasonic, and optical cameras are employed to provide situational awareness to vehicles in a highly dynamic environment. Radar has emerged as a primary sensor technology for both active/passive safety and comfort-advanced driver-assistance systems. Physically building and testing radar systems to demonstrate reliability is an expensive and time-consuming process. Simulation emerges as the most practical solution to designing and testing radar systems. This paper provides a complete, full physics simulation workflow for automotive radar using finite element method and asymptotic ray tracing electromagnetic solvers. The design and optimization of both transmitter and receiver antennas is presented. Antenna interaction with vehicle bumper and fascia is also investigated. A full physics-based radar scene corner case is modelled to obtain high-fidelity range-Doppler maps. Finally, this paper investigates the effects of inclined roads on late pedestrian detection and the effects of construction metal plate radar returns on false target identification. Possible solutions are suggested and validated. Results from this study show how pedestrian radar returns can be increased by over 16 dB for early detection along with a 27 dB reduction in road construction plate radar returns to suppress false target identification. Both solutions to the above corner cases can potentially save pedestrian lives and prevent future accidents.
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Song, Nuan, Yang Jiao, Ya Ji Song y Chun Hui Liu. "The Doppler Radar Bomb Chamber Volume Speed Measurement System Research Based on LabView". Advanced Materials Research 571 (septiembre de 2012): 692–95. http://dx.doi.org/10.4028/www.scientific.net/amr.571.692.
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This article in view of the firing range and speed of ballistic test parameters, follow the "virtual instrument" thought to design a multi-function weapon test system, establishing a uniform platform development and complete Doppler radar speed module, meet a variety of ballistic speed needs. In the system, we realize intelligent control, real time collection of signal in time and frequency domain, result display at the same time and data analyze, Based on hardware realize, system realize testing of chamber volume.
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Iukhno, Artem, Sergei Buzmakov y Alisa Zorina. "DOPPLER NON-CONTACT RADAR SENSORS FOR WATER DISCHARGE ESTIMATION: ADVANTAGES AND LIMITATIONS". ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference 3 (16 de junio de 2021): 124–29. http://dx.doi.org/10.17770/etr2021vol3.6616.
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The use of non-contact doppler flow radars to determine water discharge is a widespread trend in hydrometeorological surveying and monitoring. However, is it reasonable to consider such an instrument as one of the most suitable and perspective for the hydrological observation network? In-situ testing have been carrying out by authors of this article and the analysis performed in scientific papers cannot provide a single-valued positive conclusion on this issue. Obvious advantage of these radars as independent safe mode of operation seems to overweight their obvious weak points. Many "undercurrents" do not allow this method to be recognized as reliable, such as the problem of transition from surface to medium flow velocities, which consists in the data processing apparatus, reliable positioning of the device, blanking distance task and etc. All in all, this article discusses the main advantages and "vulnerabilities" of the use of such an instrument as non-contact doppler radars to determine water discharge from a scientific and practical points of view.
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Michaels, J. F. "An approach to radiated testing of installed airborne Doppler radar with weather/windshear detection capability". IEEE Aerospace and Electronic Systems Magazine 10, n.º 12 (diciembre de 1995): 25. http://dx.doi.org/10.1109/62.480827.
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Darnitskyi, Y., V. Lyashenko, S. Shvets y T. Pavliuk. "ANALYSIS OF PECULIARITIES FOR USE OF MUZZLE VELOCITY MEASUREMENT SYSTEM SL – 520PЕ AND DOPPLER RADAR TRAJECTORY MEASUREMENT SYSTEM MFTR–2100/40 DURING TESTS OF ROCKET AND ARTILLERY ARMAMENT". Наукові праці Державного науково-дослідного інституту випробувань і сертифікації озброєння та військової техніки, n.º 12 (5 de julio de 2022): 29–40. http://dx.doi.org/10.37701/dndivsovt.12.2022.04.
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The article presents a comparative analysis of test results in which the SL–520PЕ muzzle velocity measurement system and the MFTR – 2100/40 Doppler radar system were used. A set of recommendations is proposed, which are aimed at improving the efficiency of the organization and the quality of tests during which the parameters of the initial (muzzle) velocity of the measured objects are determined.
Qualitative testing of a wide range of new and modernized models of rocket and artillery armament largely depends on modern radar measurement systems.
Recently, the Armed Forces of Ukraine (Armed Forces of Ukraine) have been using the SL – 520PЕ muzzle velocity measurement system and the Doppler radar system MFTR – 2100/40 to determine the initial (muzzle) velocity and trajectory measurements of rocket and artillery armament.
The issue of checking the compliance of the parameters of modern models of rocket and artillery armament with the stated specifications is well-timed and is constantly in the focus of attention of the leadership of the Armed Forces of Ukraine.
The above mentioned determines the relevance of scientific research to solve the problem of testing rocket and artillery armament by developing a set of recommendations aimed at improving the efficiency of the organization and quality of tests during which the parameters of the initial (muzzle) velocity of measured objects are determined.
Thus, anticipating the urgency of this issue there was an initiation of research on the feasibility for use of SL–520PЕ muzzle velocity measurement system and the MFTR – 2100/40 Doppler radar system, taking into account their practical employment. Therefore, the author's team considers it appropriate to contemplate certain test methods using the above measurement systems.
The conducted research makes it possible to offer recommendations on setting the options Maximum Velocity, Tracking Time; to determine the magnitude of the minimum value of the start signal level, source of signal, and the optimal value of the angle (Elevation) of the SL–520PЕ antenna for reliable measurement of the initial (muzzle) velocity of artillery shells (mines) during a single shot or a series of shots of the artillery system; determination of the average initial (muzzle) velocity of artillery shells (min) in a series of shots; ensuring the transmission of measured data to the automated fire control system for calculation of ballistic range correction in the process of artillery firing and more efficient testing and certification of artillery weapons offered for procurement to the Armed Forces of Ukraine.
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Gao, Jidong, Travis M. Smith, David J. Stensrud, Chenghao Fu, Kristin Calhoun, Kevin L. Manross, Jeffrey Brogden et al. "A Real-Time Weather-Adaptive 3DVAR Analysis System for Severe Weather Detections and Warnings". Weather and Forecasting 28, n.º 3 (1 de junio de 2013): 727–45. http://dx.doi.org/10.1175/waf-d-12-00093.1.
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Abstract A real-time, weather-adaptive three-dimensional variational data assimilation (3DVAR) system has been adapted for the NOAA Warn-on-Forecast (WoF) project to incorporate all available radar observations within a moveable analysis domain. The key features of the system include 1) incorporating radar observations from multiple Weather Surveillance Radars-1988 Doppler (WSR-88Ds) with NCEP forecast products as a background state, 2) the ability to automatically detect and analyze severe local hazardous weather events at 1-km horizontal resolution every 5 min in real time based on the current weather situation, and 3) the identification of strong circulation patterns embedded in thunderstorms. Although still in the early development stage, the system performed very well within the NOAA's Hazardous Weather Testbed (HWT) Experimental Warning Program during preliminary testing in spring 2010 when many severe weather events were successfully detected and analyzed. This study represents a first step in the assessment of this type of 3DVAR analysis for use in severe weather warnings. The eventual goal of this real-time 3DVAR system is to help meteorologists better track severe weather events and eventually provide better warning information to the public, ultimately saving lives and reducing property damage.
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Rahnemoonfar, Maryam, Jimmy Johnson y John Paden. "AI Radar Sensor: Creating Radar Depth Sounder Images Based on Generative Adversarial Network". Sensors 19, n.º 24 (12 de diciembre de 2019): 5479. http://dx.doi.org/10.3390/s19245479.
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Significant resources have been spent in collecting and storing large and heterogeneous radar datasets during expensive Arctic and Antarctic fieldwork. The vast majority of data available is unlabeled, and the labeling process is both time-consuming and expensive. One possible alternative to the labeling process is the use of synthetically generated data with artificial intelligence. Instead of labeling real images, we can generate synthetic data based on arbitrary labels. In this way, training data can be quickly augmented with additional images. In this research, we evaluated the performance of synthetically generated radar images based on modified cycle-consistent adversarial networks. We conducted several experiments to test the quality of the generated radar imagery. We also tested the quality of a state-of-the-art contour detection algorithm on synthetic data and different combinations of real and synthetic data. Our experiments show that synthetic radar images generated by generative adversarial network (GAN) can be used in combination with real images for data augmentation and training of deep neural networks. However, the synthetic images generated by GANs cannot be used solely for training a neural network (training on synthetic and testing on real) as they cannot simulate all of the radar characteristics such as noise or Doppler effects. To the best of our knowledge, this is the first work in creating radar sounder imagery based on generative adversarial network.
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Victoria, Dr A. Helen, S. V. Manikanthan, Dr Varadaraju H R, Muhammad Alkirom Wildan y Kakarla Hari Kishore. "Radar Based Activity Recognition using CNN-LSTM Network Architecture". International Journal of Communication Networks and Information Security (IJCNIS) 14, n.º 3 (11 de enero de 2023): 303–12. http://dx.doi.org/10.17762/ijcnis.v14i3.5630.
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Human Activity Recognition based research has got intensified based on the evolving demand of smart systems. There has been already a lot of wearables, digital smart sensors deployed to classify various activities. Radar sensor-based Activity recognition has been an active research area during recent times. In order to classify the radar micro doppler signature images we have proposed a approach using Convolutional Neural Network-Long Short Term Memory (CNN-LSTM). Convolutional Layer is used to update the filter values to learn the features of the radar images. LSTM Layer enhances the temporal information besides the features obtained through Convolutional Neural Network. We have used a dataset published by University of Glasgow that captures six activities for 56 subjects under different ages, which is a first of its kind dataset unlike the signals captured under controlled lab environment. Our Model has achieved 96.8% for the training data and 93.5% for the testing data. The proposed work has outperformed the existing traditional deep learning Architectures.
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Marks, David A., David B. Wolff, Lawrence D. Carey y Ali Tokay. "Quality Control and Calibration of the Dual-Polarization Radar at Kwajalein, RMI". Journal of Atmospheric and Oceanic Technology 28, n.º 2 (1 de febrero de 2011): 181–96. http://dx.doi.org/10.1175/2010jtecha1462.1.
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Abstract The dual-polarization weather radar on the Kwajalein Atoll in the Republic of the Marshall Islands (KPOL) is one of the only full-time (24/7) operational S-band dual-polarimetric (DP) radars in the tropics. Through the use of KPOL DP and disdrometer measurements from Kwajalein, quality control (QC) and reflectivity calibration techniques were developed and adapted for use. Data studies in light rain show that KPOL DP measurements are of sufficient quality for these applications. While the methodology for the development of such applications is well documented, the tuning of specific algorithms to the particular regime and observed raindrop size distributions requires a comprehensive testing and adjustment period. Presented are algorithm descriptions and results from five case studies in which QC and absolute reflectivity calibration were performed and assessed. Also described is a unique approach for calibrating the differential reflectivity field when vertically pointing observations are not available. Results show the following: 1) DP-based QC provides superior results compared to the legacy Tropical Rainfall Measuring Mission (TRMM) QC algorithm (based on height and reflectivity thresholds), and 2) absolute reflectivity calibration can be performed using observations of light rain via a published differential phase–based integration technique; results are within ±1 dB compared to independent measurements. Future extension of these algorithms to upgraded Weather Surveillance Radar-1988 Doppler (WSR-88D) polarization diverse radars will benefit National Aeronautics and Space Administration’s (NASA’s) Precipitation Measurement Missions (PMM) validation programs.
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Päschke, E., R. Leinweber y V. Lehmann. "An assessment of the performance of a 1.5 μm Doppler lidar for operational vertical wind profiling based on a 1-year trial". Atmospheric Measurement Techniques 8, n.º 6 (3 de junio de 2015): 2251–66. http://dx.doi.org/10.5194/amt-8-2251-2015.
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Abstract. We present the results of a 1-year quasi-operational testing of the 1.5 μm StreamLine Doppler lidar developed by Halo Photonics from 2 October 2012 to 2 October 2013. The system was configured to continuously perform a velocity-azimuth display scan pattern using 24 azimuthal directions with a constant beam elevation angle of 75°. Radial wind estimates were selected using a rather conservative signal-to-noise ratio based threshold of −18.2 dB (0.015). A 30 min average profile of the wind vector was calculated based on the assumption of a horizontally homogeneous wind field through a Moore–Penrose pseudoinverse of the overdetermined linear system. A strategy for the quality control of the retrieved wind vector components is outlined for ensuring consistency between the Doppler lidar wind products and the inherent assumptions employed in the wind vector retrieval. Quality-controlled lidar measurements were compared with independent reference data from a collocated operational 482 MHz radar wind profiler running in a four-beam Doppler beam swinging mode and winds from operational radiosonde measurements. The intercomparison results reveal a particularly good agreement between the Doppler lidar and the radar wind profiler, with root mean square errors ranging between 0.5 and 0.7 m s−1 for wind speed and between 5 and 10° for wind direction. The median of the half-hourly averaged wind speed for the intercomparison data set is 8.2 m s−1, with a lower quartile of 5.4 m s−1 and an upper quartile of 11.6 m s−1.
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Mahale, Vivek N., Guifu Zhang y Ming Xue. "Fuzzy Logic Classification of S-Band Polarimetric Radar Echoes to Identify Three-Body Scattering and Improve Data Quality". Journal of Applied Meteorology and Climatology 53, n.º 8 (agosto de 2014): 2017–33. http://dx.doi.org/10.1175/jamc-d-13-0358.1.
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AbstractThe three-body scatter signature (TBSS) is a radar artifact that appears downrange from a high-radar-reflectivity core in a thunderstorm as a result of the presence of hailstones. It is useful to identify the TBSS artifact for quality control of radar data used in numerical weather prediction and quantitative precipitation estimation. Therefore, it is advantageous to develop a method to automatically identify TBSS in radar data for the above applications and to help identify hailstones within thunderstorms. In this study, a fuzzy logic classification algorithm for TBSS identification is developed. Polarimetric radar data collected by the experimental S-band Weather Surveillance Radar-1988 Doppler (WSR-88D) in Norman, Oklahoma (KOUN), are used to develop trapezoidal membership functions for the TBSS class of radar echo within a hydrometeor classification algorithm (HCA). Nearly 3000 radar gates are removed from 50 TBSSs to develop the membership functions from the data statistics. Five variables are investigated for the discrimination of the radar echo: 1) horizontal radar reflectivity factor ZH, 2) differential reflectivity ZDR, 3) copolar cross-correlation coefficient ρhv, 4) along-beam standard deviation of horizontal radar reflectivity factor SD(ZH), and 5) along-beam standard deviation of differential phase SD(ΦDP). These membership functions are added to an HCA to identify TBSSs. Testing is conducted on radar data collected by dual-polarization-upgraded operational WSR-88Ds from multiple severe-weather events, and results show that automatic identification of the TBSS through the enhanced HCA is feasible for operational use.
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Lolli, S., A. Delaval, C. Loth, A. Garnier y P. H. Flamant. "0.355 μm direct detection wind lidar under testing during a field campaign in consideration of ESA's ADM-Aeolus Mission". Atmospheric Measurement Techniques Discussions 6, n.º 3 (23 de mayo de 2013): 4551–75. http://dx.doi.org/10.5194/amtd-6-4551-2013.
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Abstract. The atmospheric wind field information is a key issue to Numerical Weather Prediction (NWP) and climate studies. A space based Wind Doppler lidar mission so-called ADM-Aeolus is currently developed by the European Space Agency for a launch in 2015. Such a Doppler lidar will provide accurate direct measurements of horizontal wind velocity in the depth of atmosphere. The wind data will be evenly distributed at a global scale. The goal is to enhance the present meteorological observation system over sparse wind data regions, and more important to provide direct wind information in the tropics where no geostrophic wind can be derived from passive radiometer satellite. ADM-Aeolus is basically a 0.355 μm high spectral resolution backscatter lidar. This concept was under test during a field campaign conducted at the Haute Provence Observatory in France 1999. It was the opportunity to address the self-consistency of wind measurements made by different active remote sensors i.e. lidars and a 72-MHz radar, and balloon radio soundings.
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Morris, M. P., P. B. Chilson, T. J. Schuur y A. Ryzhkov. "Microphysical retrievals from simultaneous polarimetric and profiling radar observations". Annales Geophysicae 27, n.º 12 (7 de diciembre de 2009): 4435–48. http://dx.doi.org/10.5194/angeo-27-4435-2009.
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Abstract. The character of precipitation detected at the surface is the final product of many microphysical interactions in the cloud above, the combined effects of which may be characterized by the observed drop size distribution (DSD). This necessitates accurate retrieval of the DSD from remote sensing data, especially radar as it offers large areal coverage, high spatial resolution, and rigorous quality control and testing. Combined instrument observations with a UHF wind profiler, an S-band polarimetric weather radar, and a video disdrometer are analyzed for two squall line events occuring during the calendar year 2007. UHF profiler Doppler velocity spectra are used to estimate the DSD aloft, and are complemented by DSDs retrieved from an exponential model applied to polarimetric data. Ground truth is provided by the disdrometer. A complicating factor in the retrieval from UHF profiler spectra is the presence of ambient air motion, which can be corrected using the method proposed by Teshiba et al. (2009), in which a comparison between idealized Doppler spectra calculated from the DSDs retrieved from KOUN and those retrieved from contaminated wind profiler spectra is performed. It is found that DSDs measured using the distrometer at the surface and estimated using the wind profiler and polarimetric weather radar generally showed good agreement. The DSD retrievals using the wind profiler were improved when the estimates of the vertical wind were included into the analysis, thus supporting the method of Teshiba et al. (2009). Furthermore, the the study presents a method of investigating the time and height structure of DSDs.
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Hasebe, F., T. Tsuda, T. Nakamura y M. D. Burrage. "Validation of HRDI MLT winds with meteor radars". Annales Geophysicae 15, n.º 9 (30 de septiembre de 1997): 1142–57. http://dx.doi.org/10.1007/s00585-997-1142-7.
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Abstract. A validation study of the mesospheric and lower-thermospheric (MLT) wind velocities measured by the High-Resolution Doppler Imager (HRDI) on board the Upper-Atmosphere Research Satellite (UARS) has been carried out, comparing with observations by meteor radars located at Shigaraki, Japan and Jakarta, Indonesia. The accuracy of the HRDI winds relative to the meteor radars is obtained by a series of simultaneous wind measurements at the time of UARS overpasses. Statistical tests on the difference in the wind vectors observed by HRDI and the meteor radars are applied to determine whether the wind speed has been overestimated by HRDI (or underestimated by the MF radars) as previously noticed in HRDI vs. MF radar comparisons. The techniques employed are the conventional t-test applied to the mean values of the paired wind vector components as well as wind speeds, and two nonparametric tests suitable for testing the paired wind speed. The square-root transformation has been applied before the t-tests of the wind speed in order to fit the wind-speed distribution function to the normal distribution. The overall results show little evidence of overestimation by HRDI (underestimation by meteor radars) of wind velocities in the MLT region. Some exceptions are noticed, however, at the altitudes around 88 km, where statistical differences occasionally reach a level of significance of 0.01. The validation is extended to estimate the precision of the wind velocities by both HRDI and meteor radars. In the procedure, the structure function defined by the mean square difference of the observed anomalies is applied in the vertical direction for the profile data. This method assumes the isotropy and the homogeneity of variance for the physical quantity and the homogeneity of variance for the observational errors. The estimated precision is about 6ms–1 for the Shigaraki meteor radar, 15ms–1 for the Jakarta meteor radar, and 20ms–1 for HRDI at 90-km altitude. These values can be used to confirm the statistical significance of the wind field obtained by averaging the observed winds.
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Elmore, Kimberly L., Pamela L. Heinselman y David J. Stensrud. "Using WSR-88D Data and Insolation Estimates to Determine Convective Boundary Layer Depth". Journal of Atmospheric and Oceanic Technology 29, n.º 4 (1 de abril de 2012): 581–88. http://dx.doi.org/10.1175/jtech-d-11-00043.1.
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Abstract Prior work shows that Weather Surveillance Radar-1988 Doppler (WSR-88D) clear-air reflectivity can be used to determine convective boundary layer (CBL) depth. Based on that work, two simple linear regressions are developed that provide CBL depth. One requires only clear-air radar reflectivity from a single 4.5° elevation scan, whereas the other additionally requires the total, clear-sky insolation at the radar site, derived from the radar location and local time. Because only the most recent radar scan is used, the CBL depth can, in principle, be computed for every scan. The “true” CBL depth used to develop the models is based on human interpretation of the 915-MHz profiler data. The regressions presented in this work are developed using 17 summer days near Norman, Oklahoma, that have been previously investigated. The resulting equations and algorithms are applied to a testing dataset consisting of 7 days not previously analyzed. Though the regression using insolation estimates performs best, errors from both models are on the order of the expected error of the profiler-estimated CBL depth values. Of the two regressions, the one that uses insolation yields CBL depth estimates with an RMSE of 208 m, while the regression with only clear-air radar reflectivity yields CBL depth estimates with an RMSE of 330 m.
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Päschke, E., R. Leinweber y V. Lehmann. "A one year comparison of 482 MHz radar wind profiler, RS92-SGP Radiosonde and 1.5 μm Doppler Lidar wind measurements". Atmospheric Measurement Techniques Discussions 7, n.º 11 (19 de noviembre de 2014): 11439–79. http://dx.doi.org/10.5194/amtd-7-11439-2014.
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Abstract. We present the results of a one-year quasi-operational testing of the 1.5 μm StreamLine Doppler lidar developed by Halo Photonics from 2 October 2012 to 2 October 2013. The system was configured to continuously perform a velocity-azimuth display (VAD) scan pattern using 24 azimuthal directions with a constant beam elevation angle of 75°. Radial wind estimates were selected using a rather conservative signal-to-noise ratio (SNR) based threshold of −18.2 dB (0.015). A 30 min average wind vector was calculated based on the assumption of a horizontally homogeneous wind field through a singular-value decomposed Moore–Penrose pseudoinverse of the overdetermined linear system. A strategy for a quality control of the retrieved wind vector components is outlined which is used to ensure consistency between the retrieved winds and the assumptions inherent to the employed wind vector retrieval. Finally, the lidar measurements are compared with operational data from a collocated 482 MHz radar wind profiler running in a four-beam Doppler beam swinging (DBS) mode and winds from operational radiosonde measurements. The intercomparisons show that the Doppler lidar is a reliable system for operational wind measurements in the atmospheric boundary layer (ABL).
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Davies-Jones, Robert, Vincent T. Wood y Mark A. Askelson. "Ray Curvature on a Flat Earth for Computing Virtual WSR-88D Signatures of Simulated Supercell Storms". Monthly Weather Review 147, n.º 3 (1 de marzo de 2019): 1065–75. http://dx.doi.org/10.1175/mwr-d-18-0356.1.
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Abstract Two accepted postulates for applications of ground-based weather radars are that Earth’s surface is a perfect sphere and that all the rays launched at low-elevation angles have the same constant small curvature. To accommodate a straight vertically launched ray, we amend the second postulate by making the ray curvature dependent on the cosine of the launch angle. A standard atmospheric stratification determines the ray-curvature value at zero launch angle. Granted this amended postulate, we develop exact formulas for ray height, ground range, and ray slope angle as functions of slant range and launch angle on the real Earth. Standard practice assumes a hypothetical equivalent magnified earth, for which the rays become straight while ray height above radar level remains virtually the same function of the radar coordinates. The real-Earth and equivalent-earth formulas for height agree to within 1 m. Our ultimate goal is to place a virtual Doppler radar within a numerical or analytical model of a supercell and compute virtual signatures of simulated storms for development and testing of new warning algorithms. Since supercell models have a flat lower boundary, we must first compute the ray curvature that preserves the height function as the earth curvature tends to zero. Using an approximate height formula, we find that keeping planetary curvature minus the ray curvature at zero launch angle constant preserves ray height to within 5 m. For standard refraction the resulting ray curvature is negative, indicating that rays bend concavely upward relative to a flat earth.
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Heinselman, Pamela L. y Alexander V. Ryzhkov. "Validation of Polarimetric Hail Detection". Weather and Forecasting 21, n.º 5 (1 de octubre de 2006): 839–50. http://dx.doi.org/10.1175/waf956.1.
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Abstract This study describes, illustrates, and validates hail detection by a simplified version of the National Severe Storms Laboratory’s fuzzy logic polarimetric hydrometeor classification algorithm (HCA). The HCA uses four radar variables: reflectivity, differential reflectivity, cross-correlation coefficient, and “reflectivity texture” to classify echoes as rain mixed with hail, ground clutter–anomalous propagation, biological scatterers (insects, birds, and bats), big drops, light rain, moderate rain, and heavy rain. Diagnostic capabilities of HCA, such as detection of hail, are illustrated for a variety of storm environments using polarimetric radar data collected mostly during the Joint Polarimetric Experiment (JPOLE; 28 April–13 June 2003). Hail classification with the HCA is validated using 47 rain and hail reports collected by storm-intercept teams during JPOLE. For comparison purposes, probability of hail output from the Next-Generation Weather Radar Hail Detection Algorithm (HDA) is validated using the same ground truth. The anticipated polarimetric upgrade of the Weather Surveillance Radar-1988 Doppler network drives this direct comparison of performance. For the four examined cases, contingency table statistics show that the HCA outperforms the HDA. The superior performance of the HCA results primary from the algorithm’s lack of false alarms compared to the HDA. Statistical significance testing via bootstrapping indicates that differences in the probability of detection and critical success index between the algorithms are statistically significant at the 95% confidence level, whereas differences in the false alarm rate and Heidke skill score are statistically significant at the 90% confidence level.
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Lothon, Marie, Bernard Campistron, Michel Chong, Fleur Couvreux, Françoise Guichard, Catherine Rio y Earle Williams. "Life Cycle of a Mesoscale Circular Gust Front Observed by a C-Band Doppler Radar in West Africa". Monthly Weather Review 139, n.º 5 (mayo de 2011): 1370–88. http://dx.doi.org/10.1175/2010mwr3480.1.
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On 10 July 2006, during the Special Observation Period (SOP) of the African Monsoon Multidisciplinary Analysis (AMMA) campaign, a small convective system initiated over Niamey and propagated westward in the vicinity of several instruments activated in the area, including the Massachusetts Institute of Technology (MIT) C-band Doppler radar and the Atmospheric Radiation Measurement (ARM) mobile facility. The system started after a typical convective development of the planetary boundary layer. It grew and propagated within the scope of the radar range, so that its entire life cycle is documented, from the precluding shallow convection to its traveling gust front. The analysis of the observations during the transitions from organized dry convection to shallow convection and from shallow convection to deep convection lends support to the significant role played by surface temperature heterogeneities and boundary layer processes in the initiation of deep convection in semiarid conditions. The analysis of the system later in the day, of its growth and propagation, and of its associated density current allows the authors to estimate the wake available potential energy and demonstrate its capability to trigger deep convection itself. Given the quality and density of observations related to this case, and its typical and quasi-textbook characteristics, this is considered a prime case for the study of initiation and evolution of deep convection, and for testing their parameterizations in single-column models.
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Medlin, Jeffrey M., Sytske K. Kimball y Keith G. Blackwell. "Radar and Rain Gauge Analysis of the Extreme Rainfall during Hurricane Danny’s (1997) Landfall". Monthly Weather Review 135, n.º 5 (1 de mayo de 2007): 1869–88. http://dx.doi.org/10.1175/mwr3368.1.
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Abstract As a minimal hurricane, Danny moved over Mobile Bay around 0900 UTC 19 July 1997 and became stationary by midmorning, while situated within a synoptic col. Danny then evolved into an asymmetric storm with an intensely convective rainband that produced torrential rainfall through 1200 UTC 20 July 1997. Danny’s center remained <100 km from the National Weather Service (NWS) Weather Surveillance Radar-1988 Doppler (WSR-88D) in Mobile, Alabama, for over 48 h, allowing long-term surveillance of the storm’s inner core. This event marked the first time the tropical Z–R relationship was employed on an operational WSR-88D system during tropical cyclone landfall. A radar-estimated maximum rainfall accumulation of 1097 mm (43.2 in.) was analyzed over southwestern Mobile Bay. A NWS cooperative rain gauge located on Dauphin Island, Alabama, measured 896 mm (35.28 in.). An adjacent standard rain gauge measured the highest rainfall amount of 932 mm (36.71 in.). This paper investigates the spatial and temporal distribution and potential magnitude of Danny’s torrential rainfall episode over coastal Alabama. It is shown that both gauges and radar seriously underestimated event rainfall. An estimate is given for what could have been the true event rainfall amount. In the case of the radar, the WSR-88D Algorithm Testing and Display System is used to obtain a better estimate of rainfall using higher dBZ caps than the operational 50 dBZ. In the case of the tipping-bucket rain gauge, wind and mechanical error estimates were applied in order to quantify rainfall underestimation.
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Chandra, Arunchandra S., Pavlos Kollias, Scott E. Giangrande y Stephen A. Klein. "Long-Term Observations of the Convective Boundary Layer Using Insect Radar Returns at the SGP ARM Climate Research Facility". Journal of Climate 23, n.º 21 (1 de noviembre de 2010): 5699–714. http://dx.doi.org/10.1175/2010jcli3395.1.
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Abstract A long-term study of the turbulent structure of the convective boundary layer (CBL) at the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) Climate Research Facility is presented. Doppler velocity measurements from insects occupying the lowest 2 km of the boundary layer during summer months are used to map the vertical velocity component in the CBL. The observations cover four summer periods (2004–08) and are classified into cloudy and clear boundary layer conditions. Profiles of vertical velocity variance, skewness, and mass flux are estimated to study the daytime evolution of the convective boundary layer during these conditions. A conditional sampling method is applied to the original Doppler velocity dataset to extract coherent vertical velocity structures and to examine plume dimension and contribution to the turbulent transport. Overall, the derived turbulent statistics are consistent with previous aircraft and lidar observations. The observations provide unique insight into the daytime evolution of the convective boundary layer and the role of increased cloudiness in the turbulent budget of the subcloud layer. Coherent structures (plumes–thermals) are found to be responsible for more than 80% of the total turbulent transport resolved by the cloud radar system. The extended dataset is suitable for evaluating boundary layer parameterizations and testing large-eddy simulations (LESs) for a variety of surface and cloud conditions.
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Fedorov, Roman y Oleg Berngardt. "Monitoring observations of meteor echo at the EKB ISTP SB RAS radar: algorithms, validation, statistics". Solar-Terrestrial Physics 7, n.º 1 (29 de marzo de 2021): 47–58. http://dx.doi.org/10.12737/stp-71202107.
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The paper considers the implementation of algorithms for automatic search for signals scattered by meteor trails according to EKB ISTP SB RAS radar data. In general, the algorithm is similar to the algorithms adopted in specialized meteor systems. The algorithm is divided into two stages: detecting a meteor echo and determining its parameters. We show that on the day of the maximum Geminid shower, December 13, 2016, the scattered signals detected by the algorithm are foreshortening and correspond to scattering by irregularities extended in the direction of the meteor shower radiant. This confirms that the source of the signals detected by the algorithm is meteor trails. We implement an additional program for indirect trail height determination. It uses a decay time of echo and the NRLMSIS-00 atmosphere model to estimate the trail height. The dataset from 2017 to 2019 is used for further testing of the algorithm. We demonstrate a correlation in calculated Doppler velocity between the new algorithm and FitACF. We present a solution of the inverse problem of reconstructing the neutral wind velocity vector from the data obtained by the weighted least squares method. We compare calculated speeds and directions of horizontal neutral winds, obtained in the three-dimensional wind model, and the HWM-14 horizontal wind model. The algorithm allows real-time scattered signal processing and has been put into continuous operation at the EKB ISTP SB RAS radar.
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Bu, Jinwei, Kegen Yu, Yongchao Zhu, Nijia Qian y Jun Chang. "Developing and Testing Models for Sea Surface Wind Speed Estimation with GNSS-R Delay Doppler Maps and Delay Waveforms". Remote Sensing 12, n.º 22 (16 de noviembre de 2020): 3760. http://dx.doi.org/10.3390/rs12223760.
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This paper focuses on sea surface wind speed estimation based on cyclone global navigation satellite system reflectometry (GNSS-R) data. In order to extract useful information from delay-Doppler map (DDM) data, three delay waveforms are presented for wind speed estimation. The delay waveform without Doppler shift is defined as central delay waveform (CDW), and the integral of the delay waveforms with different Doppler shift values is defined as integral delay waveform (IDW), while the difference between normalized IDW (NIDW) and normalized CDW (NCDW) is defined as differential delay waveform (DDW). We first propose a data filtering method based on threshold setting for data quality control. This method can select good-quality DDM data by adjusting the root mean square (RMS) threshold of cleaned DDW. Then, the normalized bistatic radar scattering cross section (NBRCS) and the leading edge slope (LES) of IDW are calculated using clean DDM data. Wind speed estimation models based on NBRCS and LES observations are then developed, respectively, and on this basis, a combination wind speed estimation model based on determination coefficient is further proposed. The CYGNSS data and ECMWF reanalysis data collected from 12 May 2020 to 12 August 2020 are used, excluding data collected on land, to evaluate the proposed models. The evaluation results show that the wind speed estimation accuracy of the piecewise function model based on NBRCS is 2.3 m/s in terms of root mean square error (RMSE), while that of the double-parameter and triple-parameter models is 2.6 and 2.7 m/s, respectively. The wind speed estimation accuracy of the double-parameter and triple-parameter models based on LES is 3.3 and 2.5 m/s. The results also demonstrate that the RMSE of the combination method is 2.1 m/s, and the coefficient of determination is 0.906, achieving a considerable performance gain compared with the individual NBRCS- and LES-based methods.
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Kollias, Pavlos y Bruce Albrecht. "Vertical Velocity Statistics in Fair-Weather Cumuli at the ARM TWP Nauru Climate Research Facility". Journal of Climate 23, n.º 24 (15 de diciembre de 2010): 6590–604. http://dx.doi.org/10.1175/2010jcli3449.1.
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Abstract Fair-weather cumuli are fundamental in regulating the vertical structure of water vapor and entropy in the lowest 2–3 km of the earth’s atmosphere over vast areas of the oceans. In this study, a long record of profiling cloud radar observations at the Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) at Nauru Island is used to investigate cloud vertical air motion statistics over an 8-yr observing period. Appropriate processing of the observed low radar reflectivities provides radar volume samples that contain only small cloud droplets; thus, the Doppler velocities are used as air motion tracers. The technique is applied to shallow boundary layer clouds (less than 1000 m thick) during the 1999–2007 period when radar data are available. Using the boundary layer winds from the soundings obtained at the Nauru ACRF, the fair-weather cumuli fields are classified in easterly and westerly boundary layer wind regimes. This distinction is necessary to separate marine-forced (westerlies) from land-forced (easterlies) shallow clouds because of a well-studied island effect at the Nauru ACRF. The two regimes exhibit large diurnal differences in cloud fraction and cloud dynamics as manifested by the analysis of the hourly averaged vertical air motion statistics. The fair-weather cumuli fields associated with easterlies exhibit a strong diurnal cycle in cloud fraction and updraft strength and fraction, indicating a strong influence of land-forced clouds. In contrast over the fair-weather cumuli with oceanic origin, land-forced clouds are characterized by uniform diurnal cloudiness and persistent updrafts at the cloud-base level. This study provides a unique observational dataset appropriate for testing fair-weather cumulus mass flux and turbulence parameterizations in numerical models.
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Yi, Qiang, Stanley Chien, Lingxi Li, Wensen Niu, Yaobin Chen, David Good, Chi-Chih Chen y Rini Sherony. "Development of test scenarios and bicyclist surrogate for the evaluation of bicyclist automatic emergency braking systems". Journal of Intelligent and Connected Vehicles 1, n.º 1 (5 de febrero de 2018): 15–27. http://dx.doi.org/10.1108/jicv-02-2018-0005.
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Purpose To support the standardized evaluation of bicyclist automatic emergency braking (AEB) systems, test scenarios, test procedures and test system hardware and software tools have been investigated and developed by the Transportation Active Safety Institute (TASI) at Indiana University-Purdue University Indianapolis. This paper aims to focus on the development of test scenarios and bicyclist surrogate for evaluating vehicle–bicyclist AEB systems. Design/methodology/approach The harmonized general estimates system (GES)/FARS 2010-2011 crash data and TASI 110-car naturalistic driving data (NDD) are used to determine the crash geometries and environmental factors of crash scenarios including lighting conditions, vehicle speeds, bicyclist speeds, etc. A surrogate bicyclist including a bicycle rider and a bicycle surrogate is designed to match the visual and radar characteristics of bicyclists in the USA. A bicycle target is designed with both leg pedaling and wheel rotation to produce proper micro-Doppler features and generate realistic motion for camera-based AEB systems. Findings Based on the analysis of the harmonized GES/FARS crash data, five crash scenarios are recommended for performance testing of bicyclist AEB systems. Combined with TASI 110-car naturalistic driving data, the crash environmental factors including lighting conditions, obscuring objects, vehicle speed and bicyclist speed are determined. The surrogate bicyclist was designed to represent the visual and radar characteristics of the real bicyclists in the USA. The height of the bicycle rider mannequin is 173 cm, representing the weighted height of 50th percentile US male and female adults. The size and shape of the surrogate bicycle were determined as 26-inch wheel and mountain/road bicycle frame, respectively. Both leg pedaling motion and wheel rotation are suggested to produce proper micro-Doppler features and support the camera-based AEB systems. Originality/value The results have demonstrated that the developed scenarios, test procedures and bicyclist surrogate will provide effective objective methods and necessary hardware and software tools for the evaluation and validation of bicyclist AEB systems. This is crucial for the development of advanced driver assistance systems.
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Fedorov, Roman y Oleg Berngardt. "Monitoring observations of meteor echo at the EKB ISTP SB RAS radar: algorithms, validation, statistics". Solnechno-Zemnaya Fizika 7, n.º 1 (29 de marzo de 2021): 59–73. http://dx.doi.org/10.12737/szf-71202107.
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The paper considers the implementation of algorithms for automatic search for signals scattered by meteor trails according to EKB ISTP SB RAS radar data. In general, the algorithm is similar to the algorithms adopted in specialized meteor systems. The algorithm is divided into two stages: detecting a meteor echo and determining its parameters. We show that on the day of the maximum Geminid shower, December 13, 2016, the scattered signals detected by the algorithm are foreshortening and correspond to scattering by irregularities extended in the direction of the meteor shower radiant. This confirms that the source of the signals detected by the algorithm is meteor trails. We implement an additional program for indirect trail height determination. It uses a decay time of echo and the NRLMSIS-00 atmosphere model to estimate the trail height. The dataset from 2017 to 2019 is used for further testing of the algorithm. We demonstrate a correlation in calculated Doppler velocity between the new algorithm and FitACF. We present a solution of the inverse problem of reconstructing the neutral wind velocity vector from the data obtained by the weighted least squares method. We compare calculated speeds and directions of horizontal neutral winds, obtained in the three-dimensional wind model, and the HWM-14 horizontal wind model. The algorithm allows real-time scattered signal processing and has been put into continuous operation at the EKB ISTP SB RAS radar.
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Foster, James, Ning Li y Kwok Fai Cheung. "Sea State Determination from Ship-Based Geodetic GPS". Journal of Atmospheric and Oceanic Technology 31, n.º 11 (noviembre de 2014): 2556–64. http://dx.doi.org/10.1175/jtech-d-13-00211.1.
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AbstractOcean waves have a profound impact on navigation, offshore operations, recreation, safety, and the economic vitality of a nation’s maritime and coastal communities. This study demonstrates that ships equipped with geodetic GPS and a radar gauge can provide accurate estimates of sea state. The Research Vessel (R/V) Kilo Moana recorded 1-Hz data for the entire period of a 10-day cruise around the Hawaiian Islands. Solving for precise kinematic positions for the ship and combining these solutions with the ranges from the ship to the sea surface provided by the radar gauge, it was possible to retrieve 1-Hz estimates of the sea surface elevation along the cruise track. Converting these into estimates of significant wave height, strong agreement was found with wave buoy measurements and hindcast wave data. Comparison with buoy data indicates the estimates have errors on the order of 0.22 m, or less than 11% of the wave height. Using wave model predictions of the dominant directions, the data were processed further to correct for the Doppler shift and to estimate the dominant wave period. Although relatively noisy in locations where the predicted wave directions are expected to be poor, in general these estimates also show a good agreement with the wave buoy observations and hindcast wave estimates. A segment of the cruise that formed a circuit allowed for testing the consistency of the ship-based estimates and for determining a dominant wave direction, which was found to agree closely with model predictions.
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Lolli, S., A. Delaval, C. Loth, A. Garnier y P. H. Flamant. "0.355-micrometer direct detection wind lidar under testing during a field campaign in consideration of ESA's ADM-Aeolus mission". Atmospheric Measurement Techniques 6, n.º 12 (9 de diciembre de 2013): 3349–58. http://dx.doi.org/10.5194/amt-6-3349-2013.
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Abstract. The atmospheric wind field information is a key issue to numerical weather prediction (NWP) and climate studies. The Atmospheric Dynamic Mission-Aeolus is currently developed by the European Space Agency (ESA) to launch a wind sensing Doppler lidar in mid-2015. The high spectral resolution lidar concept is using backscattered laser signals from molecules and particles to provide accurate horizontal wind velocity measurements in the depth of atmosphere. The Aeolus lidar, so-called ALADIN, will operate in UV at 0.355 μm. The combination of air molecules and UV laser light is intended to provide wind data evenly distributed everywhere in the lower atmosphere (below 30 km altitude). The goal of the ESA's Aeolus mission is to enhance the present meteorological observations system over sparse wind data regions, and more importantly to provide direct wind information in the tropics where no geostrophic wind can be derived from mass fields obtained from passive radiometer satellite. The 0.355 μm lidar concept was under testing during a field campaign conducted at the Haute-Provence Observatory, France, in 1999. Several active remote sensors were deployed on the site, and it was the opportunity to address the self-consistency of wind measurements made by different lidars, a 72 MHz radar, and conventional balloon radio soundings. The paper presents the comparison of different remote sensors using two criteria: Pearson cross-correlation coefficient and root mean square error. The methodology discussed here may be useful in future ESA Aeolus validation campaigns involving different kinds of instruments.
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Parate, Bhupesh Ambadas. "Propellant Actuated Device for Parachute Deployment during Seat Ejection for an Aircraft Application". HighTech and Innovation Journal 1, n.º 3 (1 de septiembre de 2020): 112–20. http://dx.doi.org/10.28991/hij-2020-01-03-03.
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Propellant Actuated Devices (PAD) are installed on various combat aircraft of Air Force and Naval bases to perform extremely important operations such as parachute deployment, harness and leg restrain, cable cutting, pullers, seat ejection, bomb release or fuel tanks etc. They are basically called as gas generators. Such devices produce the high temperature and pressure combustion gases on initiation and used to perform different operations. These cartridges are single-shot operating devices. The performance of such kind of PADs cannot be tested by non-destructive techniques. Hence, cartridges are designed to function with high reliability and stringent quality control checks at all levels during entire development cycle. The safety features required during handling, storage and transportation are built in the design of PAD. The cartridges are required to undergo different exhaustive design qualification tests to qualify design aspects. Total life of 6 years is assigned to cartridge after performance degradation study of the propellant which includes 2 years installed life. This paper explains about the development aspects of PAD, its use, function, testing and performance evaluation methodology in a suitable fabricated Velocity Test Rig (VTR). The maximum slug velocity is 121.14 m/s in hot condition and minimum slug velocity is 99.14 m/s in cold condition. The main objective of this paper is to device a novel method to measure actual slug velocity of the aircraft gun inside a cartridge using VTR and Doppler RADAR.
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Johnson, Victoria, Richard Jeffries, Greg Byrd, Wendy Schreiber-Abshire, Elizabeth Page, Bruce Muller y Tim Alberta. "Celebrating COMET’s 25 Years of Providing Innovative Education and Training". Bulletin of the American Meteorological Society 96, n.º 12 (1 de diciembre de 2015): 2183–94. http://dx.doi.org/10.1175/bams-d-14-00276.1.
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Abstract The Cooperative Program for Operational Meteorology, Education, and Training (COMET)’s mission when it began in 1990 was to deliver professional development opportunities to U.S. government forecasters during the National Weather Service (NWS) modernization program. Since then, COMET has emerged as a worldwide leader in geoscience education. Its original objectives were to provide forecasters with classroom and distance learning training based on state-of-the-art science; support development and testing of new forecast methods; promote collaboration between the forecasting, research, and academic communities; and to advance forecasting and nowcasting by encouraging research. Over the years, COMET’s mission has expanded to disseminating and enhancing scientific knowledge in the environmental sciences, particularly meteorology, but also including diverse areas such as oceanography, hydrology, space weather, and emergency management. This paper reviews COMET’s evolution from a primary focus on educating U.S. forecasters on the application of new technologies (such as Doppler radar) to mesoscale meteorology problems into a program with a much broader scope. Those changes include offering learning opportunities that now cover a wider variety of topics and support the educational needs of diverse audiences worldwide. The history of COMET is a story of adaptation to technological changes, funding cycles, partner requirements, and service opportunities as well as taking on a more global mission. We will look at how COMET’s activities in geoscience education have changed, how its adaptability has contributed to the longevity of the program that was only supposed to exist until the NWS modernization was complete, and expectations and plans for the future.
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Roueche, David B. y David O. Prevatt. "Residential Damage Patterns Following the 2011 Tuscaloosa, AL and Joplin, MO Tornadoes". Journal of Disaster Research 8, n.º 6 (1 de diciembre de 2013): 1061–67. http://dx.doi.org/10.20965/jdr.2013.p1061.
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Damage survey data was collected following the destruction caused by tornadoes in Tuscaloosa, AL and Joplin, MO that together destroyed over 13,000 buildings, caused over $5 billion in economic losses and left 226 persons dead. Using geotagged photographs for 1,814 residential structures in the two cities, damage ratings were assigned using the Enhanced Fujita Scale and mapped for each building, in an effort to establish the wind field for each tornado. The results depict the physical distribution of the damaging forces away from the centerline of the tornado. The spatial distribution of wind velocities estimated using the EF-Scale were in agreement with measured wind velocity distributions using Doppler radar in other violent tornadoes. A second part of the study identified common failure mechanisms within a data set of 365 light-framed wood residential structures from the Tuscaloosa tornado. The results of this analysis showed that tornado forces rapidly attenuate with distance away from the center of the tornado, as EFratings can be reduced from EF-4 to EF-2 within 100 meters. In addition, the seven most prevalent failure mechanisms were identified and the correlations among them are presented. Catastrophic failures are most common at or near the center of the tornado’s path (below the vortex). Buildings further away from the center experience damage patterns that are similar to structures subjected to straight-line hurricane force winds. These field studies and analyses are being used to inform the development of full-scale structural testing wall components with the goal of developing structural retrofits and improving design practices for tornado-resilient houses.
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Ellender, Claire M., Syeda Farah Zahir, Hailey Meaklim, Rosemarie Joyce, David Cunnington y John Swieca. "Prospective cohort study to evaluate the accuracy of sleep measurement by consumer-grade smart devices compared with polysomnography in a sleep disorders population". BMJ Open 11, n.º 11 (noviembre de 2021): e044015. http://dx.doi.org/10.1136/bmjopen-2020-044015.
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ObjectivesConsumer-grade smart devices are now commonly used by the public to measure waking activity and sleep. However, the ability of these devices to accurately measure sleep in clinical populations warrants more examination. The aim of the present study was to assess the accuracy of three consumer-grade sleep monitors compared with gold standard polysomnography (PSG).DesignA prospective cohort study was performed.SettingAdults undergoing PSG for investigation of a suspected sleep disorder.Participants54 sleep-clinic patients were assessed using three consumer-grade sleep monitors (Jawbone UP3, ResMed S+ and Beddit) in addition to PSG.OutcomesJawbone UP3, ResMed S+ and Beddit were compared with gold standard in-laboratory PSG on four major sleep parameters—total sleep time (TST), sleep onset latency (SOL), wake after sleep onset (WASO) and sleep efficiency (SE).ResultsThe accelerometer Jawbone UP3 was found to overestimate TST by 28 min (limits of agreement, LOA=−100.23 to 157.37), with reasonable agreement compared with gold standard for TST, WASO and SE. The doppler radar ResMed S+ device underestimated TST by 34 min (LOA=−257.06 to 188.34) and had poor absolute agreement compared with PSG for TST, SOL and SE. The mattress device, Beddit underestimated TST by 53 min (LOA=−238.79 to 132) on average and poor reliability compared with PSG for all measures except TST. High device synchronisation failure occurred, with 20% of recordings incomplete due to Bluetooth drop out and recording loss.ConclusionPoor to moderate agreement was found between PSG and each of the tested devices, however, Jawbone UP3 had relatively better absolute agreement than other devices in sleep measurements compared with PSG. Consumer grade devices assessed do not have strong enough agreement with gold standard measurement to replace clinical evaluation and PSG sleep testing. The models tested here have been superseded and newer models may have increase accuracy and thus potentially powerful patient engagement tools for long-term sleep measurement.
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Giangrande, Scott E., Edward P. Luke y Pavlos Kollias. "Automated Retrievals of Precipitation Parameters Using Non-Rayleigh Scattering at 95 GHz". Journal of Atmospheric and Oceanic Technology 27, n.º 9 (1 de septiembre de 2010): 1490–503. http://dx.doi.org/10.1175/2010jtecha1343.1.
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Abstract Automated retrievals of vertical air motion and the drop size distribution (DSD) slope parameter from the surface to the base of the melting layer are presented using a technique for W-band (95 GHz) profiling radars. The technique capitalizes on non-Rayleigh resonance signatures found in the observed Doppler spectra to estimate the mean vertical air motion. The slope parameter of the DSD for an assumed exponential form is retrieved through an inversion of the Doppler spectra. Extended testing is performed in central Oklahoma for a monthlong period of observation that includes several midlatitude convective line trailing stratiform events featuring low to moderate rainfall rates (<1 to 30 mm h−1). Low-level DSD slope parameter retrievals are shown in agreement (bias of −1.48 cm−1 and rms error of 4.38 cm−1) with collocated surface disdrometer DSD observations. Velocity retrievals indicate a net downward motion in stratiform rain of 0.05 m s−1 with a standard deviation of 0.24–0.3 m s−1. Time–height examples drawn from the available dataset illustrate finescale structures, as well as evidence of drop sorting due to differential terminal velocity and wind shear.
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Koskinen, Jarkko T., Jani Poutiainen, David M. Schultz, Sylvain Joffre, Jarmo Koistinen, Elena Saltikoff, Erik Gregow et al. "The Helsinki Testbed: A Mesoscale Measurement, Research, and Service Platform". Bulletin of the American Meteorological Society 92, n.º 3 (1 de marzo de 2011): 325–42. http://dx.doi.org/10.1175/2010bams2878.1.
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Abstract The Finnish Meteorological Institute and Vaisala have established a mesoscale weather observational network in southern Finland. The Helsinki Testbed is an open research and quasi-operational program designed to provide new information on observing systems and strategies, mesoscale weather phenomena, urban and regional modeling, and end-user applications in a high-latitude (~60°N) coastal environment. The Helsinki Testbed and related programs feature several components: observing system design and implementation, small-scale data assimilation, nowcasting and short-range numerical weather prediction, public service, and commercial development of applications. Specifically, the observing instrumentation focuses on meteorological observations of meso-gamma-scale phenomena that are often too small to be detected adequately by traditional observing networks. In particular, more than 40 telecommunication masts (40 that are 120 m high and one that is 300 m high) are instrumented at multiple heights. Other instrumentation includes one operational radio sounding (and occasional supplemental ones), ceilometers, aerosol-particle and trace-gas instrumentation on an urban flux-measurement tower, a wind profiler, and four Doppler weather radars, three of which have dual-polarimetric capability. The Helsinki Testbed supports the development and testing of new observational instruments, systems, and methods during coordinated field experiments, such as the NASA Global Precipitation Measurement (GPM). Currently, the Helsinki Testbed Web site typically receives more than 450,000 weekly visits, and more than 600 users have registered to use historical data records. This article discusses the three different phases of development and associated activities of the Helsinki Testbed from network development and observational campaigns, development of the local analysis and prediction system, and testing of applications for commercial services. Finally, the Helsinki Testbed is evaluated based on previously published criteria, indicating both successes and shortcomings of this approach.
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Ran, Yuanbo, Haijiang Wang, Li Tian, Jiang Wu y Xiaohong Li. "Precipitation cloud identification based on faster-RCNN for Doppler weather radar". EURASIP Journal on Wireless Communications and Networking 2021, n.º 1 (1 de febrero de 2021). http://dx.doi.org/10.1186/s13638-021-01896-5.
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AbstractPrecipitation clouds are visible aggregates of hydrometeor in the air that floating in the atmosphere after condensation, which can be divided into stratiform cloud and convective cloud. Different precipitation clouds often accompany different precipitation processes. Accurate identification of precipitation clouds is significant for the prediction of severe precipitation processes. Traditional identification methods mostly depend on the differences of radar reflectivity distribution morphology between stratiform and convective precipitation clouds in three-dimensional space. However, all of them have a common shortcoming that the radial velocity data detected by Doppler Weather Radar has not been applied to the identification of precipitation clouds because it is insensitive to the convective movement in the vertical direction. This paper proposes a new method for precipitation clouds identification based on deep learning algorithm, which is according the distribution morphology of multiple radar data. It mainly includes three parts, which are Constant Altitude Plan Position Indicator data (CAPPI) interpolation for radar reflectivity, Radial projection of the ground horizontal wind field by using radial velocity data, and the precipitation clouds identification based on Faster-RCNN. The testing result shows that the method proposed in this paper performs better than the traditional methods in terms of precision. Moreover, this method boasts great advantages in running time and adaptive ability.
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Potylitsyn, Vadim S., Danil S. Kudinov y Ekaterina A. Kokhonkova. "Investigation of the Influence of a Cavity Type Defect on the Frequencies of the Natural Rail Oscillations by the Radar Method". Journal of Siberian Federal University. Engineering & Technologies, diciembre de 2019, 1006–12. http://dx.doi.org/10.17516/1999-494x-0201.
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Currently, the problem of non-destructive testing of rail lashes or rolling stock is quite acute, as the demands of both speed characteristics and vehicle safety increase every year. Thus, the purpose of this study was to determine the possibility of recording frequencies of natural oscillations by the radar method for rail lashes and the influence of the dimensions of the cavity-type defect. For this purpose, a laboratory bench was created with a standard rail, the length of 1.19 m of the P-65 brand, in which free oscillations were excited using a shock impulse load. Measurements of natural oscillation frequencies of the rail were recorded on a 24-bit ADC and a specialized accelerometer ZETLAB BC110. To register the oscillations, a Doppler radar with a frequency of 10 GHz was used, which was installed at the focus of a parabolic mirror offset antenna with a 1.6-meter diameter. It was found that a “field” defect shifts the frequency mode of oscillation 750 Hz upwards. It is shown that the hole in the rail neck with a diameter of 10 mm makes a change in the frequency of about 14 Hz