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1
van der Struijf, C., T. Ph Pelupessy, E. E. van Faassen, and Y. K. Levine. "Rotational Motion of Ca-ATPase Monitored by Electron Spin Echoes." Journal of Magnetic Resonance, Series B 111, no. 2 (May 1996): 158–67. http://dx.doi.org/10.1006/jmrb.1996.0074.
2
Karlsson, Torgny, Michael Helmle, N. D. Kurur, and Malcolm H. Levitt. "Rotational resonance echoes in the nuclear magnetic resonance of spinning solids." Chemical Physics Letters 247, no. 4-6 (December 1995): 534–40. http://dx.doi.org/10.1016/s0009-2614(95)01257-5.
3
Rosenberg, Dina, Ran Damari, Shimshon Kallush, and Sharly Fleischer. "Rotational Echoes: Rephasing of Centrifugal Distortion in Laser-Induced Molecular Alignment." Journal of Physical Chemistry Letters 8, no. 20 (October 6, 2017): 5128–35. http://dx.doi.org/10.1021/acs.jpclett.7b02215.
4
Lu, Jian, Yaqing Zhang, Harold Y. Hwang, Benjamin K. Ofori-Okai, Sharly Fleischer, and Keith A. Nelson. "Nonlinear two-dimensional terahertz photon echo and rotational spectroscopy in the gas phase." Proceedings of the National Academy of Sciences 113, no. 42 (October 4, 2016): 11800–11805. http://dx.doi.org/10.1073/pnas.1609558113.
Анотація:
Ultrafast 2D spectroscopy uses correlated multiple light−matter interactions for retrieving dynamic features that may otherwise be hidden under the linear spectrum; its extension to the terahertz regime of the electromagnetic spectrum, where a rich variety of material degrees of freedom reside, remains an experimental challenge. We report a demonstration of ultrafast 2D terahertz spectroscopy of gas-phase molecular rotors at room temperature. Using time-delayed terahertz pulse pairs, we observe photon echoes and other nonlinear signals resulting from molecular dipole orientation induced by multiple terahertz field−dipole interactions. The nonlinear time domain orientation signals are mapped into the frequency domain in 2D rotational spectra that reveal J-state-resolved nonlinear rotational dynamics. The approach enables direct observation of correlated rotational transitions and may reveal rotational coupling and relaxation pathways in the ground electronic and vibrational state.
5
SHARMA, BL. "Hailstorms near Nagpur -A radar study." MAUSAM 18, no. 2 (April 30, 2022): 255–66. http://dx.doi.org/10.54302/mausam.v18i2.4446.
Анотація:
In the present study, which has been made by a Decca type 41 radar, it has been shown that the hailstorms over Kamptee situated at a distance of 10 n, miles towards northeast of the radar station had occurred due to the presence of a rotational echo with characteristic hook features, An attempt has been made to find out (a) the speed and direction of the movement of the rotational and non-rotational echoes and their collision courses in directional convergence, (b) to calculate the terminal velocity of the precipitation particles and the corresponding particle size from the streamers, associated with a prominent hook echo and (()) to suggest the probable time of occurrence and end of the hailstorm over Kamptee.
6
Watanabe, Jun-Ichi. "RADAR Observations of Leonids in Japan." Highlights of Astronomy 11, no. 2 (1998): 1020. http://dx.doi.org/10.1017/s153929960001950x.
Анотація:
We are observing meteor showers using the MU radar located at Shigaraki, Japan. This is a Mesosphere, Stratosphere and Troposphere radar, belonging to the Kyoto University, with a frequency and a peak power of 46.5M.ffz and 1MW, respectively. This system is characterized by the versatility of the antenna array. By using four antennas out of 475 Yagi arrays together with four receiver channels, we can observe more than several hundred meteor echoes per hour. The beam applied at the meteor observation is a static “doughnut beam”, which is the rotational symmetrical pattern to the vertical line. This beam is effective enough to detect meteor echoes of which the zenith angle is smaller than about 50°, which characterizes the MU radar as an all sky monitoring radar of meteor echoes. For the low velocity meteors, most of the echoes satisfy a condition of the perpendicular reflection, and we can derive the position of the radiant point statistically, and succeeded its application for the Geminids (Watanabe et al. 1992a). For the high velocity meteors, most of the echoes are in the overdense condition. However, we can discriminate the echoes of a specific meteor shower out of the data by checking the echo duration, the height, the strength or the combination of them. We have been monitoring the Perseids from 1990, and succeeded to reveal the unusual activity in 1991 (Watanabe et al. 1992b). For the Leonids, we are continuing the observation from 1991. The drastic increase of the activity has been detected around 23h UT on November 17, 1994. The number of the observed long duration echoes, which came from possibly bright Leonids meteors, were 80 per hour. This should be the beginning of the Leonids activity toward the 1998-1999. We are planning to continue this observation until the end of the activity in the 2000’s.
7
Zhou, Zibo, Libing Jiang, and Zhuang Wang. "A novel image registration method for InISAR 3D imaging." MATEC Web of Conferences 232 (2018): 02044. http://dx.doi.org/10.1051/matecconf/201823202044.
Анотація:
Image registration is a key intermediate step for Interferometric Inverse Synthetic Aperture Radar (InISAR) three-dimensional (3D) imaging. It arranges the same scatterers of the target on the same pixel cell in different ISAR images, which makes the interferometric processing carried on between the same scatterers to obtain its 3D coordinates. This paper proposes a novel ISAR image registration method of three steps. Firstly, chirp Fourier transform is used to estimate the rotational angular velocity of the target. Secondly, the compensation phase is constructed, according to the rotational angular velocity, to eliminate the wave path difference between different radars echoes. Finally, two-dimensional (2D) Fourier transform is used to yield registered ISAR images. The proposed method achieves the ISAR image registration through phase compensation in echo field, therefore, no extra computation is needed in image field. The experiment results demonstrate the advantages of the proposed method in precision, computation efficiency and practicability.
8
Karlsson, Torgny, and Malcolm H. Levitt. "Longitudinal rotational resonance echoes in solid state nuclear magnetic resonance: Investigation of zero quantum spin dynamics." Journal of Chemical Physics 109, no. 13 (October 1998): 5493–507. http://dx.doi.org/10.1063/1.477168.
9
Bertmer, Marko, and Hellmut Eckert. "Dephasing of spin echoes by multiple heteronuclear dipolar interactions in rotational echo double resonance NMR experiments." Solid State Nuclear Magnetic Resonance 15, no. 3 (December 1999): 139–52. http://dx.doi.org/10.1016/s0926-2040(99)00050-8.
10
Di Girolamo, Paolo, Noemi Franco, Marco Di Paolantonio, Donato Summa, and Davide Dionisi. "Atmospheric Thermodynamic Profiling through the Use of a Micro-Pulse Raman Lidar System: Introducing the Compact Raman Lidar MARCO." Sensors 23, no. 19 (October 6, 2023): 8262. http://dx.doi.org/10.3390/s23198262.
Анотація:
It was for a long time believed that lidar systems based on the use of high-repetition micro-pulse lasers could be effectively used to only stimulate atmospheric elastic backscatter echoes, and thus were only exploited in elastic backscatter lidar systems. Their application to stimulate rotational and roto-vibrational Raman echoes, and consequently, their exploitation in atmospheric thermodynamic profiling, was considered not feasible based on the technical specifications possessed by these laser sources until a few years ago. However, recent technological advances in the design and development of micro-pulse lasers, presently achieving high UV average powers (1–5 W) and small divergences (0.3–0.5 mrad), in combination with the use of large aperture telescopes (0.3–0.4 m diameter primary mirrors), allow one to presently develop micro-pulse laser-based Raman lidars capable of measuring the vertical profiles of atmospheric thermodynamic parameters, namely water vapor and temperature, both in the daytime and night-time. This paper is aimed at demonstrating the feasibility of these measurements and at illustrating and discussing the high achievable performance level, with a specific focus on water vapor profile measurements. The technical solutions identified in the design of the lidar system and their technological implementation within the experimental setup of the lidar prototype are also carefully illustrated and discussed.
11
Bu, Xiangxi, Zhuo Zhang, Xingdong Liang, Longyong Chen, Haibo Tang, Zheng Zeng, and Jie Wang. "A Novel Scheme for MIMO-SAR Systems Using Rotational Orbital Angular Momentum." Sensors 18, no. 10 (October 18, 2018): 3511. http://dx.doi.org/10.3390/s18103511.
Анотація:
The vortex electromagnetic (EM) wave with orbital angular momentum (OAM) brings a new degree of freedom for synthetic aperture radar (SAR) imaging, although to date, its application to multi-input multi-output (MIMO) SAR has not yet been widely reported. In this paper, an orbital angular momentum (OAM)-based MIMO-SAR system is proposed. The rotational Doppler Effect (RDE) of vortex EM waves offers a novel scheme for an OAM-based MIMO-SAR system. By transmitting the rotational vortex EM waves, echoes of different OAM modes can be discriminated by a bandpass filter in the range-Doppler domain. The performance of the proposed scheme is independent of the time-variant channel responses, and the wider beam width of the vortex EM waves delivers, for the same antenna aperture size, better performance in terms of swath width and azimuth resolution, in contrast to the plane EM waves. Moreover, the spatial diversity of vortex EM waves shows great potential to enhance the MIMO-SAR system applications, which involve high-resolution wide-swath remote sensing, 3-D imaging, and radar-communication integration. The proposed scheme is verified by proof-of-concept experiments. This work presents a new application of vortex EM waves, which facilitates the development of new-generation and forthcoming SAR systems.
12
Sud, Seema. "Noise and Interference Suppression in Sonar Echoes Using the Fractional Fourier Transform." European Journal of Engineering Research and Science 2, no. 7 (July 25, 2017): 40. http://dx.doi.org/10.24018/ejers.2017.2.7.422.
Анотація:
The Fractional Fourier Transform (FrFT) enables separation of signals from noise and interference by utilizing the entire time-frequency space. Signals are filtered by rotating to a new time axis ‘ta’, with rotational parameter ‘a’, selected using some metric such as mean-square error (MSE) between a desired signal-of-interest (SOI) and its estimate. The FrFT has been applied to numerous problems, but it is most suited for applications such as sonar and radar, when the time-frequency distribution of the SOI and the undesired environment are different. It can greatly outperform the conventional fast Fourier Transform (FFT), which is solely a frequency domain method (a=1), as well as conventional time-based MMSE adaptive filtering (a=0). In this paper, we present a simple FrFT-based algorithm that separates sonar echoes of a desired SOI, e.g. a chirp, from the cluttered background, which could be noise or interference (i.e. another signal). We exploit the fact that we can find the best time axis ‘ta’ in which the SOI becomes a tone, or close to it, with the FrFT, enabling easy notching (zeroing) of the clutter. By searching for the tone peak and notching everywhere except the peak, we can successfully and easily remove the clutter. This algorithm is robust because clutter typically does not correlate with the signal in the FrFT domain, and thus does not impair our ability to estimate the peaks and notch the clutter. We compute the MSE between the true transmitted signal and the received echo with and without this algorithm as a function of signal-to-noise ratio (SNR) and show that 5 dB reduction in MSE is possible with the FrFT.
13
Sud, Seema. "Noise and Interference Suppression in Sonar Echoes Using the Fractional Fourier Transform." European Journal of Engineering and Technology Research 2, no. 7 (July 25, 2017): 40–44. http://dx.doi.org/10.24018/ejeng.2017.2.7.422.
Анотація:
The Fractional Fourier Transform (FrFT) enables separation of signals from noise and interference by utilizing the entire time-frequency space. Signals are filtered by rotating to a new time axis ‘ta’, with rotational parameter ‘a’, selected using some metric such as mean-square error (MSE) between a desired signal-of-interest (SOI) and its estimate. The FrFT has been applied to numerous problems, but it is most suited for applications such as sonar and radar, when the time-frequency distribution of the SOI and the undesired environment are different. It can greatly outperform the conventional fast Fourier Transform (FFT), which is solely a frequency domain method (a=1), as well as conventional time-based MMSE adaptive filtering (a=0). In this paper, we present a simple FrFT-based algorithm that separates sonar echoes of a desired SOI, e.g. a chirp, from the cluttered background, which could be noise or interference (i.e. another signal). We exploit the fact that we can find the best time axis ‘ta’ in which the SOI becomes a tone, or close to it, with the FrFT, enabling easy notching (zeroing) of the clutter. By searching for the tone peak and notching everywhere except the peak, we can successfully and easily remove the clutter. This algorithm is robust because clutter typically does not correlate with the signal in the FrFT domain, and thus does not impair our ability to estimate the peaks and notch the clutter. We compute the MSE between the true transmitted signal and the received echo with and without this algorithm as a function of signal-to-noise ratio (SNR) and show that 5 dB reduction in MSE is possible with the FrFT.
14
Wang, Jiakun, Min Zhang, Pengbo Wei, and Panpan Jiang. "ISAR imaging of moving satellite based on GO–PO scattering model." International Journal of Microwave and Wireless Technologies 9, no. 7 (February 10, 2017): 1499–507. http://dx.doi.org/10.1017/s1759078717000083.
Анотація:
An efficient algorithm is proposed for the radar cross-section (RCS) prediction of complex target with electronically large size, which is a combination of geometrical optics and physical optics (GO–PO) method. The method taking the multiple reflections into account is applied to the electromagnetic scattering analysis of a satellite model. Then RCS curves of entire satellite model and the model without antenna structure are figured out. Based on the simulated echoes, the traditional inverse synthetic aperture radar (ISAR) images are discussed. Moreover, an application of motion compensation technique based on the joint time-frequency analysis is presented for ISAR imaging of the moving satellite that has both translational and rotational movements. Numerical results show good performance of GO–PO method in accuracy and efficiency and the great influence of the antenna with corner structures on the scattering characteristic of the satellite.
15
Chung, Kao-Shen, and I.-An Yao. "Improving Radar Echo Lagrangian Extrapolation Nowcasting by Blending Numerical Model Wind Information: Statistical Performance of 16 Typhoon Cases." Monthly Weather Review 148, no. 3 (February 25, 2020): 1099–120. http://dx.doi.org/10.1175/mwr-d-19-0193.1.
Анотація:
Abstract Severe weather nowcasting is a crucial mission of atmospheric science for the betterment of society to save life, limb, and property. In this study, composite radar data from the Central Weather Bureau of 16 typhoons are collected to examine the statistical performance of the McGill Algorithm for Precipitation nowcasting using Lagrangian Extrapolation (MAPLE) over Taiwan, an extrapolation algorithm that predicts future precipitation based on current radar echoes. In addition, instead of mixing the precipitation between radar extrapolation and numerical model forecast as in previous studies, a blending system is formed by synthesizing the wind information from model forecast with the echo extrapolation motion field via a variational algorithm to improve the nowcasting system. The statistical results of the radar echo extrapolation for 16 typhoon cases show that while the quantitative precipitation nowcasting skill can persist for up to 2 h, significant distortion for the rotational system is found after 2 h. On the other hand, the blending system helps to capture and maintain the rotation of typhoon rainband structures. The blending system extends the nowcasting skill by 1 h to a total of 3 h. Furthermore, the blending scheme performs especially well after the typhoon makes landfall in Taiwan. For disaster prevention and mitigation, this blending nowcasting technique may provide effective weather information immediately.
16
Gullion, Terry, and Shimon Vega. "A simple magic angle spinning NMR experiment for the dephasing of rotational echoes of dipolar coupled homonuclear spin pairs." Chemical Physics Letters 194, no. 4-6 (July 1992): 423–28. http://dx.doi.org/10.1016/0009-2614(92)86076-t.
17
Benzeroual, Hajar, Abdellatif Khamlichi, and Alia Zakriti. "Detection of Transverse Defects in Rails Using Noncontact Laser Ultrasound." Proceedings 42, no. 1 (November 14, 2019): 43. http://dx.doi.org/10.3390/ecsa-6-06556.
Анотація:
Rail inspections are required and used to ensure safety and preserve the availability of railway infrastructure. According to the statistics published by railroad administrations worldwide, the transverse fissure appearing in railhead is the principal cause of rail accidents. These particular defects are initiated inside the railhead. Detection of these cracks has always been challenging because a defect signature remains mostly small until the defect size reaches a significant value. The present work deals with the theoretical analysis of an integrated contact-less system for rail diagnosis, which is based on ultrasounds. The generation of these waves was performed through non-ablative laser sources. Rotational laser vibrometry was used to achieve the reception of the echoes. Detection of flaws in the rail was monitored by considering special ultrasound wave signal based indicators. Finite element modeling of the rail system was performed, and transverse defect detection of the rail was analyzed.
18
Benzeroual, Hajar, Abdellatif Khamlichi, and Alia Zakriti. "Reliability of rail transverse flaw detection by means of an embedded ultrasonic based device." MATEC Web of Conferences 191 (2018): 00005. http://dx.doi.org/10.1051/matecconf/201819100005.
Анотація:
The main causes of train derailment are related to rail defects such as head surface defects, horizontal defects, vertical longitudinal split defects, star cracks at colt holes and diagonal crack in web. The most adverse form of these defects consists of transverse flaws that are either opened or internal. These flaws are developed generally in a plane which is orthogonal to the rail direction. Detection of these defects is essential in order to improve security of rail roads and to prevent catastrophic failures. Most of the inspection techniques of rails relay on eddy currents, electromagnetic induction and ultrasounds. Unlike some conventional inspection tests based on contact excitation probes that roll on the rail head, this work deals with theoretical analysis of an integrated contact-less system based on ultrasound waves. Generation of these waves was performed by using a non-ablative laser source. A rotational laser vibrometer was used to perform reception of the echoes. Through finite element modelling of the rail system under specific ultrasound excitation of the rail head, detection of transverse rail flaws was studied. Reliability of defect detection was then assessed by considering various sources of perturbations.
19
Chen, Pinhui, Brice J. Albert, Chukun Gao, Nicholas Alaniva, Lauren E. Price, Faith J. Scott, Edward P. Saliba, et al. "Magic angle spinning spheres." Science Advances 4, no. 9 (September 2018): eaau1540. http://dx.doi.org/10.1126/sciadv.aau1540.
Анотація:
Magic angle spinning (MAS) is commonly used in nuclear magnetic resonance of solids to improve spectral resolution. Rather than using cylindrical rotors for MAS, we demonstrate that spherical rotors can be spun stably at the magic angle. Spherical rotors conserve valuable space in the probe head and simplify sample exchange and microwave coupling for dynamic nuclear polarization. In this current implementation of spherical rotors, a single gas stream provides bearing gas to reduce friction, drive propulsion to generate and maintain angular momentum, and variable temperature control for thermostating. Grooves are machined directly into zirconia spheres, thereby converting the rotor body into a robust turbine with high torque. We demonstrate that 9.5–mm–outside diameter spherical rotors can be spun at frequencies up to 4.6 kHz with N2(g) and 10.6 kHz with He(g). Angular stability of the spinning axis is demonstrated by observation of 79Br rotational echoes out to 10 ms from KBr packed within spherical rotors. Spinning frequency stability of ±1 Hz is achieved with resistive heating feedback control. A sample size of 36 μl can be accommodated in 9.5-mm-diameter spheres with a cylindrical hole machined along the spinning axis. We further show that spheres can be more extensively hollowed out to accommodate 161 μl of the sample, which provides superior signal-to-noise ratio compared to traditional 3.2-mm-diameter cylindrical rotors.
20
Brown, Rodger A., Bradley A. Flickinger, Eddie Forren, David M. Schultz, Dale Sirmans, Phillip L. Spencer, Vincent T. Wood, and Conrad L. Ziegler. "Improved Detection of Severe Storms Using Experimental Fine-Resolution WSR-88D Measurements." Weather and Forecasting 20, no. 1 (February 1, 2005): 3–14. http://dx.doi.org/10.1175/waf-832.1.
Анотація:
Abstract Doppler velocity and reflectivity measurements from Weather Surveillance Radar-1988 Doppler (WSR-88D) radars provide important input to forecasters as they prepare to issue short-term severe storm and tornado warnings. Current-resolution data collected by the radars have an azimuthal spacing of 1.0° and range spacing of 1.0 km for reflectivity and 0.25 km for Doppler velocity and spectrum width. To test the feasibility of improving data resolution, National Severe Storms Laboratory’s test bed WSR-88D (KOUN) collected data in severe thunderstorms using 0.5°-azimuthal spacing and 0.25-km-range spacing, resulting in eight times the resolution for reflectivity and twice the resolution for Doppler velocity and spectrum width. Displays of current-resolution WSR-88D Doppler velocity and reflectivity signatures in severe storms were compared with displays showing finer-resolution signatures. At all ranges, fine-resolution data provided better depiction of severe storm characteristics. Eighty-five percent of mean rotational velocities derived from fine-resolution mesocyclone signatures were stronger than velocities derived from current-resolution signatures. Likewise, about 85% of Doppler velocity differences across tornado and tornadic vortex signatures were stronger than values derived from current-resolution data. In addition, low-altitude boundaries were more readily detected using fine-resolution reflectivity data. At ranges greater than 100 km, fine-resolution reflectivity displays revealed severe storm signatures, such as bounded weak echo regions and hook echoes, which were not readily apparent on current-resolution displays. Thus, the primary advantage of fine-resolution measurements over current-resolution measurements is the ability to detect stronger reflectivity and Doppler velocity signatures at greater ranges from a WSR-88D.
21
Gong, Rui, Ling Wang, Bin Wu, Gong Zhang, and Daiyin Zhu. "Optimal Space-Borne ISAR Imaging of Space Objects with Co-Maximization of Doppler Spread and Spacecraft Component Area." Remote Sensing 16, no. 6 (March 14, 2024): 1037. http://dx.doi.org/10.3390/rs16061037.
Анотація:
The Inverse Synthetic Aperture Radar (ISAR) has been proven to be an effective tool for space target sensing due to its capability of performing high-resolution imaging. Since the component information of the spacecraft is key to the identification of the target and diagnosis of its status, ISAR images with a clear and complete representation of the typical components are much desired. This requires a selection of the imaging time, during which a certain spacecraft component has a good projection on the ISAR image plane with the shape feature well conserved and a high resolution. In addition, a fully automated implementation with a high computational efficiency is also highly preferred for on-orbit operations so as to improve the intelligence level of the space-borne system. We propose a bicriterion-based automated optimal imaging time-selection method for the space-borne ISAR, which is seeking the slow time section of the data that result in the best image. A good image means a high azimuth resolution and the best presentation of the solar panels. One criterion is the Maximum Doppler Spread (MDS), which indicates the maximum Effective Rotational Velocity (ERV) leading to high image resolution, but it is influenced by the satellite attitude. of the spacecraft. The other is the Maximum Component Area (MCA), which is defined to indicate the completeness of the component considered. The radar echoes are processed sequentially by way of a sliding window. The interval with the co-maximization of the DS and CA is selected, and fine processing is performed further to obtain the best images. The results of the simulation experiments show that the proposed method can achieve spacecraft images with the solar panels presented the best. The computational complexity is low.
22
Ma, Xiangchao, Junmin Meng, Chenqing Fan, and Ping Chen. "Effects of Wave-Induced Doppler Velocity on the Sea Surface Current Measurements by Ka-Band Real-Aperture Radar with Small Incidence Angle." Remote Sensing 15, no. 4 (February 18, 2023): 1127. http://dx.doi.org/10.3390/rs15041127.
Анотація:
The Doppler shift of microwave radar sea surface echoes serves as the foundation for sea surface current field retrieval; it includes the shift caused by satellite platform motion, ocean waves, and sea surface currents. The Doppler shift caused by ocean waves is known as the wave-induced Doppler velocity (UWD), and its removal is critical for the accurate retrieval of sea surface current fields. The low-incidence Ka-band real-aperture radar rotary scan regime has the capability of directly observing wide-swath two-dimensional current fields, but as a new regime to be further explored and validated, simulation and analysis of UWD in this regime have a significant influence on the hardware design and currently observed applications of this satellite system in its conceptual stage. In this study, we simulated and investigated the impacts of radar parameters and sea-state conditions on the UWD obtained from small-incidence-angle Ka-band rotational scanning radar data and verified the simulation results with the classical analytical solution of average specular scattering point velocity. Simulation results indicate that the change in the azimuth direction of platform observation affects UWD accuracy. Accuracy is the lowest when the antenna is in a vertical side-view. The UWD increases slowly with the incidence angle. Ocean waves are insensitive to polarization in the case of small-incidence-angle specular scattering. The increase in wind speed and the development of wind waves result in a substantial increase in UWD. We classified swell by wavelength and wave height and found that UWD increases with swell size, especially the contribution of swell height to UWD, which is more significant. The contribution of the swell to UWD is smaller than that of wind waves to UWD. Furthermore, the existence of sea surface currents changes the contribution of ocean waves to UWD, and the contribution weakens with increasing wind speed and increases with wind wave development.
23
Yi, Xianzhou. "Three DOF Rotation Compensation in Floating HFSWR for Ocean Current Inversion." Journal of Physics: Conference Series 2718, no. 1 (March 1, 2024): 012017. http://dx.doi.org/10.1088/1742-6596/2718/1/012017.
Анотація:
Abstract High-frequency surface wave radar (HFSWR) has been widely used for ocean surface current inversion. Floating this radar can realize the ocean surface inversion among large areas far away from the coastline. However, six degree-of-freedom (DOF) movements will set the barrier for the ocean current inversion on its radial velocity estimation and direction of arrival estimation. Among these movements, three DOF rotations can cause both Doppler modulation and azimuth modulation while three DOF translations only cause Doppler modulation which is dependent on the arrival direction of echoes. Hence, the analysis and compensation for three DOF rotations are first to be solved. In this paper, we analyse the Doppler modulation and azimuth modulation of three DOF rotations and further develop the global adaptive beamforming method to compensate for these rotations. Adaptive beamforming is used to compensate for rotations to make the real-time beams fixed to the ground when the platform is rotating. Simulations indicate that the global adaptive beamforming can perfectly compensate for the reasonable rotations, among which the yaw rotation is the dominant factor for both Doppler spectrum modulation and azimuth modulation. The rotation compensation using global adaptive beamforming can greatly improve the precision of ocean surface inversion.
24
SHARIFF, KARIM, and ALAN WRAY. "Analysis of the radar reflectivity of aircraft vortex wakes." Journal of Fluid Mechanics 463 (July 25, 2002): 121–61. http://dx.doi.org/10.1017/s0022112002008674.
Анотація:
Radar has been proposed as a way of tracking wake vortices to reduce aircraft spacing and tests have revealed radar echoes from aircraft wakes in clear air. The mechanism causing refractive index gradients in these tests is thought to be the same as that for homogeneous and isotropic atmospheric turbulence in the Kolmogorov inertial range, for which there is a scattering analysis due to Tatarski. In reality, however, the structure of aircraft wakes has a significant coherent part superimposed with turbulence, about whose structure very little is known. This work adopts a picture of a coherent (in fact two-dimensional) wake to perform a scattering analysis and calculate the reflected power. In particular, two simple mechanisms causing refractive index gradients are considered: (A) radial pressure (and therefore density) gradient in a columnar vortex arising from the rotational flow; (B) adiabatic transport of atmospheric fluid within a descending oval surrounding a vortex pair. In the scattering analysis, Tatarski's weak scattering approximation is kept but the usual assumptions of a far field and a uniform incident wave are dropped. Neither assumption is generally valid for a wake that is coherent across the radar beam. For analytical insight, an approximate analysis that invokes, in addition to weak scattering, the far-field and wide cylindrical beam assumptions, is also developed and compared with the more general analysis. Reflectivities calculated for the oval (mechanism B) are within 2–13 dB m2 of the measurements (≈−70 dB m2) of MIT Lincoln Laboratory at Kwajalein atoll. However, the present predictions have a cut-off away from normal incidence which is not present in the measurements. This implies that the two-dimensional picture is not entirely complete. Estimates suggest that the thin layer of vorticity which is baroclinically generated at the boundary of the oval is turbulent and this may account for reflectivity away from normal incidence. The reflectivity of a vortex (mechanism A) is comparable to that of the oval (mechanism B) but occurs at a frequency (about 50 MHz) that is lower than those considered in all the experiments to date. This result may be useful because: (i) existing atmospheric radars (known as ST radars) already operate at this frequency and so the present prediction could be verified; (ii) rain clutter is not a problem at this frequency; (iii) mechanism A is more robust because it is independent of atmospheric stratification.
25
Wang, Cheng, Wulong Guo, Haisheng Zhao, Liang Chen, Yiwen Wei, and Yuanyuan Zhang. "Improving the Topside Profile of Ionosonde with TEC Retrieved from Spaceborne Polarimetric SAR." Sensors 19, no. 3 (January 26, 2019): 516. http://dx.doi.org/10.3390/s19030516.
Анотація:
Signals from spaceborne polarimetric synthetic aperture radar will suffer from Faraday rotations when they propagate through the ionosphere, especially those at L-band or lower frequencies, such as signals from the Phased Array type L-band Synthetic Aperture Radar (PALSAR). For this reason, Faraday rotation compensation should be considered. On the other hand, Faraday rotation could also be retrieved from distorted echoes. Moreover, combining Faraday rotation with the radar parameters and the model of magnetic field, we could derive the total electron content (TEC) along the signal path. Benefiting from the high spatial resolution of the SAR system, TEC obtained from PALSAR could be orders of magnitude higher in spatial resolution than that from GPS. Besides, we demonstrated that the precision of TEC from PALSAR is also much higher than that from GPS. With the precise TEC available, we could fuse it with data from other ionosphere detection devices to improve their performances. In this paper, we adopted it to help modify the empirically modeled topside profile of ionosonde. The results show that the divergence between the modified profile and the referenced incoherent scattering radar profile reduced by about 30 percent when compared to the original ionosonde topside profile.
26
Yang, Shenghui, Shiqiang Li, Xiaoxue Jia, Yonghua Cai, and Yifei Liu. "An Efficient Translational Motion Compensation Approach for ISAR Imaging of Rapidly Spinning Targets." Remote Sensing 14, no. 9 (May 5, 2022): 2208. http://dx.doi.org/10.3390/rs14092208.
Анотація:
For inverse synthetic aperture radar (ISAR) imaging of rapidly spinning targets, the large migration through range cells (MTRC) results in weak coherence between adjacent echoes, which makes the conventional envelope alignment method unable to be applied. By analyzing the correlation between the echoes, a translational motion compensation (TMC) method for rapidly spinning targets is proposed. Firstly, the rotation period of the target is estimated by the incoherent accumulation method for the echo signal after range compression. Secondly, Kalman filtering is performed on the shift values required to maximize the correlation coefficient of the echoes with one rotation period difference in azimuth time to obtain the relative translational motion of the radar and the target. Finally, a translational compensation function is constructed according to the results of Kalman filtering to compensate the phase items caused by translational motion. Furthermore, the covariance matrix of observation noise required by Kalman filtering is also provided. This method is used to achieve high-precision envelope alignment, and the effectiveness of the proposed method is validated by simulations.
27
Sergeev, N. A. "Influence of Molecular Hindered Rotations on NQR Spin Echoes." Zeitschrift für Physikalische Chemie 219, no. 8 (August 2005): 1107–19. http://dx.doi.org/10.1524/zpch.2005.219.8.1107.
28
Su, Aifang, Han Li, Liman Cui, and Yungang Chen. "A Convection Nowcasting Method Based on Machine Learning." Advances in Meteorology 2020 (January 27, 2020): 1–13. http://dx.doi.org/10.1155/2020/5124274.
Анотація:
In this study, a convection nowcasting method based on machine learning was proposed. First, the historical data were back-calculated using the pyramid optical flow method. Next, the generated optical flow field information of each pixel and the Red-Green-Blue (RGB) image information were input into the Convolutional Long Short-Term Memory (ConvLSTM) algorithm for training purposes. During the extrapolation process, dynamic characteristics such as the rotation, convergence, and divergence in the optical flow field were also used as predictors to form an optimal nowcasting model. The test analysis demonstrated that the algorithm combined the image feature extraction ability of the convolutional neural network (CNN) and the sequential learning ability of the long short-term memory network (LSTM) model to establish an end-to-end deep learning network, which could deeply extract high-order features of radar echoes such as structural texture, spatial correlation, and temporal evolution compared with the traditional algorithm. Based on learning through the above features, this algorithm can forecast the generation and dissipation trends of convective cells to some extent. The addition of the optical flow information can more accurately simulate nonlinear trends such as the rotation, or merging, or separation of radar echoes. The trajectories of radar echoes obtained through nowcasting are closer to their actual movements, which prolongs the valid forecasting period and improves forecast accuracy.
29
Uspensky, M., P. Eglitis, H. Opgenoorth, G. Starkov, T. Pulkkinen, and R. Pellinen. "On auroral dynamics observed by HF radar: 1. Equatorward edge of the afternoon-evening diffuse luminosity belt." Annales Geophysicae 18, no. 12 (December 31, 2000): 1560–75. http://dx.doi.org/10.1007/s00585-001-1560-x.
Анотація:
Abstract. Observations and modelling are presented which illustrate the ability of the Finland CUTLASS HF radar to monitor the afternoon-evening equatorward auroral boundary during weak geomagnetic activity. The subsequent substorm growth phase development was also observed in the late evening sector as a natural continuation of the preceding auroral oval dynamics. Over an 8 h period the CUTLASS Finland radar observed a narrow (in range) and persistent region of auroral F- and (later) E-layer echoes which gradually moved equatorward, consistent with the auroral oval diurnal rotation. This echo region corresponds to the subvisual equatorward edge of the diffuse luminosity belt (SEEL) and the ionospheric footprint of the inner boundary of the electron plasma sheet. The capability of the Finland CUTLASS radar to monitor the E-layer SEEL-echoes is a consequence of the nearly zero E-layer rectilinear aspect angles in a region 5–10° poleward of the radar site. The F-layer echoes are probably the boundary blob echoes. The UHF EISCAT radar was in operation and observed a similar subvisual auroral arc and an F-layer electron density enhancement when it appeared in its antenna beam.Key words: Ionsophere (ionospheric irregularities) · Magnetospheric physics (auroral phenomena; magnetosphere–ionosphere interactions)
30
Liang, Mengning, Ross Harder, and Ian K. Robinson. "Brownian motion studies of viscoelastic colloidal gels by rotational single particle tracking." IUCrJ 1, no. 3 (April 14, 2014): 172–78. http://dx.doi.org/10.1107/s2052252514006022.
Анотація:
Colloidal gels have unique properties due to a complex microstructure which forms into an extended network. Although the bulk properties of colloidal gels have been studied, there has been difficulty correlating those properties with individual colloidal dynamics on the microscale due to the very high viscosity and elasticity of the material. We utilize rotational X-ray tracking (RXT) to investigate the rotational motion of component crystalline colloidal particles in a colloidal gel of alumina and decanoic acid. Our investigation has determined that the high elasticity of the bulk is echoed by a high elasticity experienced by individual colloidal particles themselves but also finds an unexpected high degree of rotational diffusion, indicating a large degree of freedom in the rotational motion of individual colloids even within a tightly bound system.
31
Zhang, Lingling, Yongzhong Zhu, Yijun Chen, Wenxuan Xie, and Hang Yuan. "Parameter Extraction of Accelerated Moving Targets under Non-Quasi-Axial Incidence Conditions Based on Vortex Electromagnetic Wave Radar." Remote Sensing 16, no. 11 (May 27, 2024): 1931. http://dx.doi.org/10.3390/rs16111931.
Анотація:
Vortex electromagnetic wave radar carrying orbital angular momentum can compensate for the deficiency of planar electromagnetic wave radar in detecting motion parameters perpendicular to the direction of electromagnetic wave propagation, thus providing more information for target recognition, which has become a hot research field in recent years. However, existing research makes it difficult to obtain the acceleration and rotation centers of targets under non-quasi-axial incidence conditions of vortex electromagnetic waves. Based on this, this article proposes a variable speed motion target parameter extraction method that combines single element and total element echoes. This method can achieve three-dimensional information extraction of radar targets based on a uniform circular array (UCA). Firstly, we establish a non-quasi-axis detection echo model for variable-speed moving targets and extract echoes from different array elements. Then, a single element echo is used to extract the target’s range slow time profile and obtain the target’s rotation center z coordinate. We further utilize the target linear, angular Doppler frequency shift extremum, and median information to extract parameters such as target acceleration, tilt angle, rotation radius, and rotation center x and y coordinates. We analyzed the impact of different signal-to-noise ratios and motion states on parameter extraction. The simulation results have verified the effectiveness of the proposed algorithm.
32
Liebmann, Max, Alexander Treffer, Martin Bock, Thomas Seiler, Jürgen Jahns, Thomas Elsaesser, and Ruediger Grunwald. "Self-imaging of tailored vortex pulse arrays and spectral Gouy rotation echoes." Optics Letters 44, no. 4 (February 15, 2019): 1047. http://dx.doi.org/10.1364/ol.44.001047.
33
He, Zhang, Yi, Jin, and Dong. "Suppressing Paired Echoes Caused by Stair-Step Antenna Steering in TOPS SAR Imaging." Remote Sensing 11, no. 21 (October 29, 2019): 2544. http://dx.doi.org/10.3390/rs11212544.
Анотація:
The use of electronically steered antennas in the azimuth dimension typically leads to a staircase-like antenna beam steering law in the Terrain Observation by Progressive Scan (TOPS) wide-swath synthetic aperture radar (SAR) data acquisition mode, which will introduce paired echoes in the focused images. This paper proposes a new approach for removing such paired echoes from TOPS SAR images based on the generalization of the ideal optimum filtering concept, which can be implemented easily in the SAR data processing. Modeling the amplitude-modulated azimuth signal shows that the absolute phase of the introduced paired echoes cannot be determined due to the random rotation angle jump time for each target, which will prevent the precise use of optimum filtering. An extended optimum filtering approach, which is originally proposed for suppressing the azimuth ambiguities in SAR images, is reintroduced in this particular case, and a new approximated and generalized form of the deconvolving filtering in the approach is redefined to accommodate the undetermined phase for both the strongest paired distortion peaks and the other peripheral peaks in the distorted impulse response function (IRF). Simulated data from a TOPS SAR mode with staircase-like beam steering are used to verify the improvement in image quality by using the new method.
34
Bell, Michael M., Wen-Chau Lee, Cory A. Wolff, and Huaqing Cai. "A Solo-Based Automated Quality Control Algorithm for Airborne Tail Doppler Radar Data." Journal of Applied Meteorology and Climatology 52, no. 11 (November 2013): 2509–28. http://dx.doi.org/10.1175/jamc-d-12-0283.1.
Анотація:
AbstractAn automated quality control preprocessing algorithm for removing nonweather radar echoes in airborne Doppler radar data has been developed. This algorithm can significantly reduce the time and experience level required for interactive radar data editing prior to dual-Doppler wind synthesis or data assimilation. The algorithm uses the editing functions in the Solo software package developed by the National Center for Atmospheric Research to remove noise, Earth-surface, sidelobe, second-trip, and other artifacts. The characteristics of these nonweather radar returns, the algorithm to identify and remove them, and the impacts of applying different threshold levels on wind retrievals are presented. Verification was performed by comparison with published Electra Doppler Radar (ELDORA) datasets that were interactively edited by different experienced radar meteorologists. Four cases consisting primarily of convective echoes from the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX), Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX), Hurricane Rainband and Intensity Change Experiment (RAINEX), and The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC)/Tropical Cyclone Structure-2008 (TCS08) field experiments were used to test the algorithm using three threshold levels for data removal. The algorithm removes 80%, 90%, or 95% of the nonweather returns and retains 95%, 90%, or 85% of the weather returns on average at the low-, medium-, and high-threshold levels. Increasing the threshold level removes more nonweather echoes at the expense of also removing more weather echoes. The low threshold is recommended when weather retention is the highest priority, and the high threshold is recommended when nonweather removal is the highest priority. The medium threshold is a good compromise between these two priorities and is recommended for general use. Dual-Doppler wind retrievals using the automatically edited data compare well to retrievals from interactively edited data.
35
Sheng, L. Q., J. H. Pei, and X. Y. Liu. "Self-affine Fractal Modelling of Aircraft Echoes from Low-resolution Radars." Defence Science Journal 66, no. 2 (March 23, 2016): 151. http://dx.doi.org/10.14429/dsj.66.8423.
Анотація:
<p>For complex targets, the non rigid vibration of an aircraft as well as its attitude changes and the rotation of its rotating parts will induce complex nonlinear modulation on its echo from low-resolution radars. If one performs the fractal analysis of measures on an aircraft echo, it may offer a fine description of the dynamic characteristics which induce the echo structure. On basis of introducing self-affine fractal theory, the paper models real recorded aircraft echo data from a low-resolution radar using the self-affine fractal representation, and investigates the application of echo self-affine fractal characteristics in aircraft target classification. Results analysis shows that aircraft echoes from low-resolution radars can be modelled by using the self-affine fractal method, and the self-affine fractal features can be effectively applied to target classification and recognition.</p><p> </p>
36
Costa, Andreu F., Daniel W. Petrie, Yi-Fen Yen, and Maria Drangova. "Using the axis of rotation of polar navigator echoes to rapidly measure 3D rigid-body motion." Magnetic Resonance in Medicine 53, no. 1 (2004): 150–58. http://dx.doi.org/10.1002/mrm.20306.
37
Ghasemi Azar, A., H. Rezaei, and H. Moradpour. "Some applications of the Shapiro time delay." Serbian Astronomical Journal, no. 207 (2023): 1–7. http://dx.doi.org/10.2298/saj2307001g.
Анотація:
Listening to echoes has long been a way to estimate distances, a technique whose backbone is the time delay. The gravitational field also creates a time delay, called Shapiro time delay, that helps us extract some information from the field and is indeed due to the photon journey through the field. Here, the ability of the Shapiro effect to distinguish naked singularities from non-naked ones (black holes) is discussed. It is also inferred that this time delay may be hired to compare the various types of singularities with different dimensions. Besides them, the possibility of detecting the rotation of the assumed objects through surveying the gravitational time delay is also addressed.
38
Vasiliev, A. Yu, E. B. Petrova, M. V. Fedorova, S. B. Efimova, and P. N. Kordatov. "The results of standard echocardiography and use of Velocity Vector Imaging technology after surgical revascularization in patients with coronary artery disease." Bulletin of Siberian Medicine 18, no. 2 (August 11, 2019): 31–43. http://dx.doi.org/10.20538/1682-0363-2019-2-31-43.
Анотація:
The aim of the study was to assess the impact of surgical revascularization on left ventricular function using standard echocardiographic study and Velocity Vector Imaging technology. Materials and methods. 40 patients with ischemic heart disease were examined before and 12 days, 6, 12 and 24 months after coronary artery bypass grafting (CABG). A standard echocardiographic (EchoCG) study was performed on ultrasound scanner Acuson Х 300 (Siemens, USA) with a 5–1 MHz sector multifrequency sensor. For objective assessment of myocardial function, the analysis of left ventricular (LV) deformation and rotational properties was performed using Syngo VVI (Siemens Medical Solutions USA Inc., США) in 720 LV segments. Results. Standard EchoCG showed a stable systolic, diastolic and contractile LV function during 2 years of follow-up. The study of global values of strain (S) and strain rate (SR) showed a decrease in longitudinal S 6 months after CABG in the right coronary artery (RCA) area in the group of patients with complaints compared to those who had no complaints (p = 0.004), in addition, in this zone there was a tendency to a difference in longitudinal SR between these two groups (p = 0.07). In anterior descending artery area was a tendency to decreased strain of longitudinal fibers (p = 0.06) during the same period of observation. 1 year after CABG, strain decreased in patients with complaints (p = 0.04) in the circumference artery area only in circular fibers. Positive dynamics were noted in the diastolic function of left ventricular fibers and rotation indices. Conclusion. The use of Velocity Vector Imaging after coronary bypass surgery shows a change in the function of myocardial fibers in the areas of coronary arteries, which is important in patients complaining of angina pain.
39
Hysell, D. L., J. Drexler, E. B. Shume, J. L. Chau, D. E. Scipion, M. Vlasov, R. Cuevas, and C. Heinselman. "Combined radar observations of equatorial electrojet irregularities at Jicamarca." Annales Geophysicae 25, no. 2 (March 8, 2007): 457–73. http://dx.doi.org/10.5194/angeo-25-457-2007.
Анотація:
Abstract. Daytime equatorial electrojet plasma irregularities were investigated using five distinct radar diagnostics at Jicamarca including range-time-intensity (RTI) mapping, Faraday rotation, radar imaging, oblique scattering, and multiple-frequency scattering using the new AMISR prototype UHF radar. Data suggest the existence of plasma density striations separated by 3–5 km and propagating slowly downward. The striations may be caused by neutral atmospheric turbulence, and a possible scenario for their formation is discussed. The Doppler shifts of type 1 echoes observed at VHF and UHF frequencies are compared and interpreted in light of a model of Farley Buneman waves based on kinetic ions and fluid electrons with thermal effects included. Finally, the up-down and east-west asymmetries evident in the radar observations are described and quantified.
40
Lee, Yasuharu, Naoki Mori, Daisuke Nakamura, Takahiro Yoshimura, Masayuki Taniike, Nobuhiko Makino, Hiroyasu Kato, et al. "New Approach for Rotational Dyssynchrony Using Three-Dimensional Speckle Tracking Echocardiography." Echocardiography 31, no. 4 (October 18, 2013): 492–98. http://dx.doi.org/10.1111/echo.12406.
41
Doeleman, S. S., C. J. Lonsdale, and L. J. Greenhill. "86 GHz VLBI Imaging of the SiO Masers in VX Sgr." International Astronomical Union Colloquium 164 (1998): 363–64. http://dx.doi.org/10.1017/s0252921100045942.
Анотація:
AbstractWe present the first 86 GHz spectral line VLBI map. Strong SiO masers in the late type star VX Sgr are mapped with a relative astrometry of 0.15 mas revealing an irregular ring of maser emission that echos structure seen at 43 GHz. A surprising feature of this map is the detection of a large (0.5 km s−1 AU−1 ) linear velocity gradient that can be interpreted as rigid rotation of the circumstellar envelope.
42
Kroh, Patrick K., Ralph Simon, and Stefan J. Rupitsch. "Classification of Sonar Targets in Air—A Neural Network Approach." Proceedings 2, no. 13 (November 29, 2018): 929. http://dx.doi.org/10.3390/proceedings2130929.
Анотація:
Ultrasonic sonar sensors are commonly used for contactless distance measurements in application areas such as automotive and mobile robotics. They can also be used to identify and classify sound reflecting objects. In the presented work, we classify simple sonar targets of different geometric shape and size. For this purpose, we built a test stand for echo measurements that facilitates defined arbitrary translation and rotation of the targets. Artificial neural networks (ANNs) with multiple hidden layers were used as classifiers and different features were evaluated. The focus was on two features that were derived from the echoes’ cross-correlation functions with their excitation chirp signals. We could distinguish different target geometries with our features and also evaluated the ANNs’ capabilities for size discrimination of targets with the same geometric shape.
43
Elford, W. G., and A. D. Taylor. "Measurement of Faraday rotation of radar meteor echoes for the modelling of electron densities in the lower ionosphere." Journal of Atmospheric and Solar-Terrestrial Physics 59, no. 9 (June 1997): 1021–24. http://dx.doi.org/10.1016/s1364-6826(96)00083-1.
44
Rebull, L. M., J. R. Stauffer, L. A. Hillenbrand, A. M. Cody, Ethan Kruse, and Brian P. Powell. "Rotation of Low-mass Stars in Upper Centaurus–Lupus and Lower Centaurus–Crux with TESS." Astronomical Journal 164, no. 3 (August 3, 2022): 80. http://dx.doi.org/10.3847/1538-3881/ac75f1.
Анотація:
Abstract We present stellar rotation rates derived from Transiting Exoplanet Survey Satellite (TESS) light curves for stars in Upper Centaurus–Lupus (UCL; ∼136 pc, ∼16 Myr) and Lower Centaurus–Crux (LCC; ∼115 pc, ∼17 Myr). We find spot-modulated periods (P) for ∼90% of members. The range of light-curve and periodogram shapes echoes that found for other clusters with K2, but fewer multiperiod stars may be an indication of the different noise characteristics of TESS, or a result of the source selection methods here. The distribution of P as a function of color as a proxy for mass fits nicely in between that for both older and younger clusters observed by K2, with fast rotators being found among both the highest and lowest masses probed here, and a well-organized distribution of M-star rotation rates. About 13% of the stars have an infrared excess, suggesting a circumstellar disk; this is well matched to expectations, given the age of the stars. There is an obvious pileup of disked M stars at P ∼ 2 days, and the pileup may move to shorter P as the mass decreases. There is also a strong concentration of disk-free M stars at P ∼ 2 days, hinting that perhaps these stars have recently freed themselves from their disks. Exploring the rotation rates of stars in UCL/LCC has the potential to help us understand the beginning of the end of the influence of disks on rotation, and the timescale on which stars respond to unlocking.
45
Alizadehasl, Azin, Anita Sadeghpour, Reza Hali, Hooman Bakhshandeh Abkenar, and Luigi Badano. "Assessment of left and right ventricular rotational interdependence: A speckle tracking echocardiographic study." Echocardiography 34, no. 3 (January 25, 2017): 415–21. http://dx.doi.org/10.1111/echo.13452.
46
Hiraga, Takahiro, Yasufumi Yamada, and Ryo Kobayashi. "Theoretical investigation of active listening behavior based on the echolocation of CF-FM bats." PLOS Computational Biology 18, no. 10 (October 7, 2022): e1009784. http://dx.doi.org/10.1371/journal.pcbi.1009784.
Анотація:
Bats perceive the three-dimensional environment by emitting ultrasound pulses from their nose or mouth and receiving echoes through both ears. To determine the position of a target object, it is necessary to know the distance and direction of the target. Certain bat species that use a combined signal of long constant frequency and short frequency modulated ultrasounds synchronize their pinnae movement with pulse emission, and this behavior has been regarded as helpful for localizing the elevation angle of a reflective sound source. However, the significance of bats’ ear motions remains unclear. In this study, we construct a model of an active listening system including the motion of the ears, and conduct mathematical investigations to clarify the importance of ear motion in direction detection of the reflective sound source. In the simulations, direction detection under rigid ear movements with interaural level differences was mathematically investigated by assuming that bats accomplish direction detection using the amplitude modulation in the echoes caused by ear movements. In particular, the ear motion conditions required for direction detection are theoretically investigated through exhaustive simulations of the pseudo-motion of the ears, rather than simulations of the actual ear motions of bats. The theory suggests that only certain ear motions, namely three-axis rotation, allow for accurate and robust direction detection. Our theoretical analysis also strongly supports the behavior whereby bats move their pinnae in the antiphase mode. In addition, we suggest that simple shaped hearing directionality and well-selected uncomplicated ear motions are sufficient to achieve precise and robust direction detection. Our findings and mathematical approach have the potential to be used in the design of active sensing systems in various engineering fields.
47
French, Michael M., Donald W. Burgess, Edward R. Mansell, and Louis J. Wicker. "Bulk Hook Echo Raindrop Sizes Retrieved Using Mobile, Polarimetric Doppler Radar Observations." Journal of Applied Meteorology and Climatology 54, no. 2 (February 2015): 423–50. http://dx.doi.org/10.1175/jamc-d-14-0171.1.
Анотація:
AbstractPolarimetric radar observations obtained by the NOAA/National Severe Storms Laboratory mobile, X-band, dual-polarization radar (NOXP) are used to investigate “hook echo” precipitation properties in several tornadic and nontornadic supercells. Hook echo drop size distributions (DSDs) were estimated using NOXP data obtained from 2009 to 2012, including during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). Differences between tornadic and nontornadic hook echo DSDs are explored, and comparisons are made with previous observations of estimated hook echo DSDs made from stationary S- and C-band Doppler radars. Tornadic hook echoes consistently contain radar gates that are characterized by small raindrops; nontornadic hook echoes are mixed between those that have some small-drop gates and those that have almost no small-drop gates. In addition, the spatial distribution of DSDs was estimated using the high-spatial-resolution data afforded by NOXP. A unique polarimetric signature, an area of relatively low values of differential radar reflectivity factor ZDR south and east of the tornado, is observed in many of the tornadic cases. Also, because most data were obtained using 2-min volumetric updates, the evolution of approximated hook echo precipitation properties was studied during parts of the life cycles of three tornadoes. In one case, there is a large decrease in the percentage of large-raindrop gates and an increase in the percentage of small-raindrop gates in the minutes leading up to tornado formation. The percentage of large-drop gates generally increases prior to and during tornado dissipation. Near-storm environmental data are used to put forth possible relationships between bulk hook echo DSDs and tornado production and life cycle.
48
Zhou, Bi, Shen, Wang, and Wang. "Hough Transform-Based Large Dynamic Reflection Coefficient Micro-Motion Target Detection in SAR." Sensors 19, no. 14 (July 22, 2019): 3227. http://dx.doi.org/10.3390/s19143227.
Анотація:
Special phase modulation of SAR echoes resulted from target rotation or vibration, is a phenomenon called the micro-Doppler (m-D) effect. Such an effect offers favorable information for micro-motion (MM) target detection, thereby improving the performance of the synthetic aperture radar (SAR) system. However, when there are MM targets with large differences in reflection coefficient, the weak reflection components will be difficult to be detected. To find a solution to this problem, we propose a novel algorithm. First, we extract and detect the strongest reflection component. By removing the strongest reflection component from the original azimuth echo one by one, we realize the detection of reflection components sequentially, from the strongest to the weakest. Our algorithm applies to detecting MM targets with different reflection coefficients and has high precision of parameter estimation. The results of simulation and field experiments verify the advantages of the algorithm.
49
Wakimoto, Roger M., Hanne V. Murphey, Christopher A. Davis, and Nolan T. Atkins. "High Winds Generated by Bow Echoes. Part II: The Relationship between the Mesovortices and Damaging Straight-Line Winds." Monthly Weather Review 134, no. 10 (October 1, 2006): 2813–29. http://dx.doi.org/10.1175/mwr3216.1.
Анотація:
Abstract Airborne radar analysis of a mesovortex that developed near the apex of a bow echo is presented. The mesovortex was shown to play a critical role in determining the location of intense “straight-line” wind damage at the surface. The perturbation pressure gradient force (in natural coordinates) along the parcel path accelerated the horizontal winds; however, intense mesovortices modified the low-level outflow and largely determined the locations where the strongest winds occurred. Regions of maximum winds are accounted for as a superposition of the vortex and the flow in which it is embedded. The strongest winds occur on the side of the vortex where translation and rotation effects are in the same direction. This model explains the observed tongue of high wind speeds that were confined to the periphery of the mesovortex. The origin of the mesovortex is also examined. Similarities and differences of this bow echo event with recent modeling studies are presented.
50
Prsa, Mario, Steven Gale, and Olaf Blanke. "Self-motion leads to mandatory cue fusion across sensory modalities." Journal of Neurophysiology 108, no. 8 (October 15, 2012): 2282–91. http://dx.doi.org/10.1152/jn.00439.2012.
Анотація:
When perceiving properties of the world, we effortlessly combine multiple sensory cues into optimal estimates. Estimates derived from the individual cues are generally retained once the multisensory estimate is produced and discarded only if the cues stem from the same sensory modality (i.e., mandatory fusion). Does multisensory integration differ in that respect when the object of perception is one's own body, rather than an external variable? We quantified how humans combine visual and vestibular information for perceiving own-body rotations and specifically tested whether such idiothetic cues are subjected to mandatory fusion. Participants made extensive size comparisons between successive whole body rotations using only visual, only vestibular, and both senses together. Probabilistic descriptions of the subjects' perceptual estimates were compared with a Bayes-optimal integration model. Similarity between model predictions and experimental data echoed a statistically optimal mechanism of multisensory integration. Most importantly, size discrimination data for rotations composed of both stimuli was best accounted for by a model in which only the bimodal estimator is accessible for perceptual judgments as opposed to an independent or additive use of all three estimators (visual, vestibular, and bimodal). Indeed, subjects' thresholds for detecting two multisensory rotations as different from one another were, in pertinent cases, larger than those measured using either single-cue estimate alone. Rotations different in terms of the individual visual and vestibular inputs but quasi-identical in terms of the integrated bimodal estimate became perceptual metamers. This reveals an exceptional case of mandatory fusion of cues stemming from two different sensory modalities.