Angle Resolution Research Articles

Estimating the parameters of the seabed using the spatial characteristics of ocean ambient noise

When solving traditional underwater problems, the boundary condition is always used to calculate the sound field. In practice, however, it is hard to get the boundary conditions of the seabed. So geoacoustics inversion is needed to acquire the parameters of the seabed. In this paper, a method estimating seabed parameters by using the spatial characteristics of ocean ambient noise is demonstrated without using matched-field processing. For the reason of the limit of the resolution of conventional beamforming (CBF), a method of synthetic array processing (SAP) is used because of some characters of cross-spectrum density matrix (CSDM). The result shows that the method of synthetic array processing enhanced the resolution of critical angle to some degree. By comparing the true bottomloss calculated by OASR, the result of traditional beamforming and the synthetic array processing, the result of synthetic array processing is closer to the true bottomloss than the result of traditional beamforming. After ensuring a range of critical angle, the sound speed of the seabed can be estimated by using Snell law. And then, an experimental data collected in Qingdao, China, 2016 is used to prove the validity of the method of synthetic array processing and estimate the local seabed parameters.

Target Recognition of Synthetic Aperture Radar Images Based on Matching and Similarity Evaluation Between Binary Regions

This work uses the binary target region for synthetic aperture radar (SAR) automatic target recognition (ATR). Due to the differences of physical sizes and target shapes, the region residuals among the same classes and those between different targets are distributed in different manners. The Euclidean distance transform is then performed on the region residuals to further enhance such differences, which is beneficial for correctly discriminating different targets. Based on the results, a similarity measure is formed according to the distribution characteristics of the region residuals. In addition, the designed similarity measure considers the possible variations of the target region caused by the nuisance conditions like noise corruption, partial occlusion, etc. Owing to its robustness and comprehensiveness, the similarity measure is applied to target recognition by comparing the test sample with different kinds of template classes. Experiments are undertaken on the Moving and Stationary Target Acquisition and Recognition (MSTAR) dataset under standard operating condition (SOC) and some representative extended operating conditions (EOCs), i.e., configuration variants, depression angle variation, noise corruption, resolution variation and partial occlusion. Moreover, the proposed method is examined under reduced training size and possible azimuth estimation errors for a comprehensive evaluation. The experimental results demonstrate the superiority of the proposed method in comparison with several baseline algorithms in SAR ATR.

Application of Ps Scattering Kernels to Imaging the Mantle Transition Zone With Receiver Functions

AbstractSeismic imaging of the global boundaries of the mantle transition zone provides important constraints regarding mantle composition and convection. Additionally, modern hypotheses about mantle convection and increasing seismic data resources motivate attempts to image more complex regional transition zone structures such as dipping and discontinuous interfaces. Here we extend a 3‐D prestack migration method to make it more applicable for transition zone imaging with Ps receiver functions. After validation with 1‐D synthetic data, two types of hypothetical structures are adopted to demonstrate the strengths and weaknesses of different practical imaging parameters with 2‐D synthetic tests. The results show that the method can resolve dipping anomalies and laterally discontinuous low velocity layers. However, receiver spacing of 0.5° is inadequate to accurately migrate scattering from all possible angles in the transition zone at ~0.3 Hz. Application of a slowness cutoff window about the Ps raypath can mitigate artifacts due to low receiver density, but the tradeoff is a decrease in the maximum resolvable dip angle. Further synthetic tests evaluate source wavelet effects, addition of observed seismic noise to synthetic data, and imaging grid dimensions. Cumulatively, the tests indicate that generic application of migration algorithms to the limited source‐receiver distributions relevant for the transition zone should be treated cautiously. Imaging parameters, such as the slowness cutoff and wavelet, should be chosen based on synthetic tests for hypothetical targets and realistic source‐receiver geometries. Finally, observational Ps receiver functions from the USArray are migrated with the new method.

High-Resolution Imaging of Multi-Channel Forward-Looking Synthetic Aperture Radar Under Curve Trajectory

Forward-looking synthetic aperture radar is an essential tool in modern remote sensing applications, but its imaging is a challenging task. Few existing methods consider the curve trajectory. Aiming at the difficulty of resolution and the Doppler ambiguity in forward-looking SAR under the curve trajectory, this paper establishes a forward-looking multi-channel SAR system model and proposes a novel approach for the forward-looking SAR imaging under the curve trajectory. The approach is implemented by a two-step process: 1) The Doppler ambiguity under forward-looking mode is solved by adaptive beam-forming processing; and 2) A sparsity-driven optimization imaging algorithm is developed to enhance the azimuth angle resolution in the forward-looking direction, where the resolution gain aroused by the curve trajectory is exploited. The extensive simulation confirms the validity of the proposed approach.

Angular Motion Decoupling and Attitude Determination Based on High Dynamic Gyro

Aiming at the problem of attitude angular motion coupling of a high-spinning rigid body, the model of the compound regular precession and the random angular motion is constructed by studying the angular motion characteristics of the high-spinning rigid body. This paper presents a new decoupling method with least squares angular rate zero-crossing detection. This method can estimate the coupling parameters in the model by estimating the angular motion period, and then, it extracts the real angular velocity information. In order to improve the attitude solution accuracy, a new four-subsample quaternion attitude algorithm is proposed by combining the angular velocity polynomial fitting and the attitude quaternion high-order Taylor series expansion. The self-developed high dynamic gyro and Missile-borne computer and simulation software are used to verify the attitude angle resolution accuracy between the traditional method and the new method proposed in this paper. The results show that the method is superior to the traditional algorithm, and increase by an order of magnitude. Finally, the flight test with the high dynamic gyro and Missile-borne computer is carried out to verify the real-time decoupling and attitude angle real-time solving ability of the proposed algorithm in the flight test.

Disappearance of Superconductivity and a Concomitant Lifshitz Transition in Heavily Overdoped Bi2Sr2CuO6 Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy**Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0300300 and 2017YFA0302900, the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant Nos XDB07020300 and XDB25000000, the National Basic Research Program of China under Grant

By partially doping Pb to effectively suppress the superstructure in single-layered cuprate Bi2Sr2CuO6+δ (Pb-Bi2201) and annealing them in vacuum or in high pressure oxygen atmosphere, a series of high quality Pb-Bi2201 single crystals are obtained with Tc covering from 17 K to non-superconducting in the overdoped region. High resolution angle resolved photoemission spectroscopy measurements are carried out on these samples to investigate the evolution of the Fermi surface topology with doping in the normal state. Clear and complete Fermi surfaces are observed and quantitatively analyzed in all of these overdoped Pb-Bi2201 samples. A Lifshitz transition from hole-like Fermi surface to electron-like Fermi surface with increasing doping is observed at a doping level of ∼0.35. This transition coincides with the change that the sample undergoes superconducting-to-non-superconducting states. Our results reveal the emergence of an electron-like Fermi surface and the existence of a Lifshitz transition in heavily overdoped Bi2201 samples. This provides important information in understanding the connection between the disappearance of superconductivity and the Lifshitz transition in the overdoped region.

Deep ultraviolet tip-enhanced fluorescence

Theoretical calculations were performed for the deep ultraviolet (DUV) tip-enhanced fluorescence (TEF) using Al@Al2O3 core–shell tips. Fluorescence enhancement, spatial resolution and surface plasmon coupled emission (SPCE) of DUV-TEF were quantitatively studied by finite-difference time-domain (FDTD) method. FDTD results demonstrate that the enhancement factor (EF) of TEF can be as high as 3 orders of magnitudes in the optimal TEF geometry. At the DUV excitation wavelength of 244 nm, the spatial resolution and SPCE angles are 6 nm and ±23°, respectively, showing maximum EF of 7.4 × 102. Our results not only help understanding the underlying physical mechanism for developing high-sensitivity and high-resolution DUV-TEF platform, but also contribute to expanding TEF technology from visible to UV range.

Compton polarimetry with a multi-layer CdTe focal plane prototype

In high-energy astrophysics, polarimetry is a promising subject with a wide scientific potential that is relatively unexplored due to the complexity of the design and technical requirements of the sensors. Often gamma-ray telescope proposals are based on multi-layer spectro-imager instruments with polarimetric capabilities. Herein we study a new Compton polarimeter prototype based on a two-layer CdTe pixelized spectro-imager operated in coincidence. The two CdTe detectors are 2 mm thick anode 8×8 pixels’ segmented matrices with 2 mm pitch. This detection system configuration allows an assessment of the polarimetric potential of multi-layer solution focal planes as well as the polarimetric potential of a possible 3D spectro-imager by analysing the polarimetric performance when varying the distance between the two CdTe detection layers. The polarimetric modulation factors for single-layer (Q∼0.4) and two-layer (up to 0.13) double-events were measured for 6 mm and for 10 mm distance between planes. The measured polarization angle resolution was lower than 10°. The potential of CdTe spectro-imager focal plane solutions with polarimetric capabilities for the next generation space missions based on both Laue lenses and 3D segmented focal planes is also discussed.

Rotation sensing and gesture control of a robot joint via triboelectric quantization sensor

In human-machine interaction, robotic hands are expected to work like human's hands and to be even more powerful or delicate in certain situations. To operate robotic hands via human gesture instead of handle or button will make this human-robot interface more natural and precise. Here, we designed a joint motion triboelectric quantization sensor (jmTQS) for constructing a robotic hand synchronous control system. Based on the ultrahigh sensitivity of a triboelectric nanogenerator (TENG) to mechanical displacement, the jmTQS designed as grating-sliding mode realized directly quantifying a joint's flexion-extension degree/speed. Through counting the pulses induced by jmTQS and signing the positive/negative of the pulses to represent flexion/extension, the joint's angular position can be determined with absolute value on the basis of the initial human-robotic synchronizing position value. In the whole operating course, the intuitionistic human-robotic hand two-dimensional motion mapping can be preserved. The minimum resolution angle of the fabricated jmTQSs is 3.8° and can be further improved by decreasing the grating width. This direct quantization and intuitionistic mapping at the sensing stage greatly simplified the signal processing and classification algorithms, which contributes to achieving the natural, high-precision and real-time interface.

Constraining the Dip of Shallow, Shallowly Dipping Thrust Events Using Long‐Period Love Wave Radiation Patterns: Applications to the 25 October 2010 Mentawai, Indonesia, and 4 May 2018 Hawaii Island Earthquakes

AbstractConstraining precise faulting geometry for shallow, shallowly dipping thrust earthquakes is a common challenge. Plate boundary megathrust faults near the trench and décollement faults beneath volcanic islands and nappes may dip only a few degrees. Long‐period point source moment tensor waveform inversions provide limited resolution of shallow fault dip angle. The possibility of splay faulting requires precise dip estimation. High sensitivity to dip is provided by long‐period Love wave amplitude azimuthal radiation patterns, which undergo rapid change from four lobed to two lobed as dip decreases from 10° to 0°. Modeling variability in Love wave nodal amplitudes allows the dip to be determined to within a few degrees. This is demonstrated for the 25 October 2010 Mentawai (MWW 7.8) tsunami earthquake, which ruptured the 2.0–5.0° dipping megathrust beneath the shallow sedimentary wedge offshore of Indonesia, and the 4 May 2018 Hawaii Island (MWW 6.9) thrust earthquake, which ruptured the 2.5–7.5° dipping décollement under the island flank.

Combination of global and local filters for robust SAR target recognition under various extended operating conditions

In this paper, a robust synthetic aperture radar (SAR) automatic target recognition (ATR) method is proposed by combining the global and local filters, especially aiming to improve the recognition performance under various extended operating conditions (EOCs). Due to the cleanness of the Moving and Stationary Target Acquisition and Recognition (MSTAR) dataset, which is the prevalent benchmark for SAR ATR, extremely high performance has been reported in many literatures. However, in the real-world scenarios, there exist many types of EOCs such as noise corruption, partial occlusion, sensor variation, etc. Therefore, this study focuses on the SAR ATR problem under several typical EOCs. The intensities of the test image to be classified is taken as the global filter. The spatial correlation between the test image and its corresponding template is calculated as the global response, which describes the global consistency. To depict the local properties of the target, the attributed scattering centers (ASCs) are employed as local filters. Each ASC of the test image is matched with its counterpart from the template ASC set. Then, the local response is evaluated based on the attributes’ differences. The global response and local responses are linearly combined using a random weight matrix. Afterwards, a judgment variable is designed as the measure for target recognition. Experiments are conducted on the MSTAR dataset under the standard operating condition (SOC) and various EOCs including configuration variance, depression angle variance, noise corruption, resolution variance, and partial occlusion. Compared with several state-of-the-art SAR ATR methods, the validity and robustness of the proposed method is fully demonstrated.

X-ray spectrometer throughput model for (selected) flat Bragg crystal spectrometers on laser plasma facilities.

At large laser faculties, such as OMEGA and the National Ignition Facility (NIF), x-ray spectrometers are provided by the facility to diagnose plasma conditions or monitor backlighters. Often the calibration of these spectrometers is unknown or out of date. As a remedy to this situation, we present a simple ray trace method to calibrate flat crystal spectrometers using only basic information regarding the optical design of the spectrometer. This model is then used to output photometric throughput estimates, dispersion, solid angle, and spectral resolution estimates. This model is applied to the mono angle crystal spectrometer and Super Snout I at the NIF and the X-Ray Spectrometer at the OMEGA laser facility.

A compact, high resolution tracker for cosmic ray muon scattering tomography using semiconductor sensors

A semiconductor tracker for muon scattering tomography is presented. The tracker contains silicon strip sensors with an 80 μm pitch, precision mechanics and integrated cooling. The electronic readout of the sensors is performed by a scalable, inexpensive, flexible, FPGA-based system, which is demonstrated to achieve an event rate of 30 kHz. The tracker performance is compared with a Geant4 simulation. A scattering angle resolution compatible with 1.5 mrad at the 4 GeV average cosmic ray muon energy is demonstrated. Images of plastic, iron and lead samples are obtained using an Angle Statistics Reconstruction algorithm. The images demonstrate good contrast between low and high atomic number materials.

Sudakov suppression of jets in QCD media

We compute modifications to the jet spectrum in the presence of a dense medium. We show that in the large-$N_c$ approximation and at leading logarithmic accuracy the jet nuclear modification factor factorizes into a quenching factor associated to the total jet color charge and a Sudakov suppression factor which accounts for the energy loss of jet substructure fluctuations. This factor, called the jet collimator, implements the fact that subjets, that are not resolved by the medium, lose energy coherently as a single color charge, whereas resolved large angle fluctuations suffer more quenching. For comparison, we show that neglecting color coherence results in a stronger suppression of the jet nuclear modification factor.

Low‐complexity range and angle two‐dimensional gold‐MUSIC for multi‐carrier frequency MIMO radar

Two-dimensional (2D) gold multiple signal classification (gold-MUSIC) is proposed in order to reduce the complexity of MUSIC and make real-time processing possible for joint range and angle estimation by multi-carrier frequency multiple-input multiple-output radar. 2D gold-MUSIC evaluates the MUSIC spectrum at coarse intervals, then determines peaks by narrowing the 2D search area iteratively based on a simultaneous gold-section of range and angle to find accurate localisation of the peaks. The proposed method eliminates huge computation burden caused by a grid-by-grid spectral search of classical MUSIC and obtains remarkable resolution in range and angle with no dependence on array configurations. Numerical studies demonstrate the effectiveness and efficiency of the proposed method.

Performance Analysis of Space-Time Array Processing Using Ultrawideband-Throb Signals for High-Resolution Imaging

In this paper, performance analysis is conducted to demonstrate that the combination of employing ultrawideband (UWB) throb signals and array beamforming can enhance the resolution performance as well as the robustness of imaging radar systems, i.e., airborne and spaceborne synthetic aperture radar. A mathematical model for the response of an array beamforming system, with systematic faults and channel instability, to received UWB-throb signals is derived. The effect of parametric random errors associated with this array beamforming system on the processing gain is analyzed for the UWB-throb signal and the linear FM chirp signal. Space–time resolution function, an essential tool for waveform design, is derived for the UWB-throb signal corrupted by parametric random errors. By using the Monte Carlo computer simulation technique, plots are generated for the space–time resolution function, temporal profile, array factor, and energy beampattern, for different values of the signals’ design parameters and the statistical parameters of the random errors. The plots reveal the degradations in the beamforming performance due to the presence of parametric random errors, i.e., drop in the central peak amplitude, rise of sidelobe level, generation of spurious sidelobes, and beam-shape loss affecting beamwidth and beam-pointing accuracy. In the presence of parametric random errors, the robustness of array beamforming using the UWB-throb signal is superior to that achievable by array beamforming using the linear-FM chirp signal. The resolution angle obtained from the energy pattern of the UWB-throb signal provides a tradeoff between signal design parameters and array size for improving the angular-resolution capability. Such a tradeoff is desirable in practice to achieve a balance between system complexity and cost effectiveness.

An extension of the Gluckstern formulae for multiple scattering: Analytic expressions for track parameter resolution using optimum weights

Momentum, track angle and impact parameter resolution are key performance parameters that tracking detectors are optimised for. This report presents analytic expressions for the resolution of these parameters for equal and equidistant tracking layers. The expressions for the contribution from position resolution are based on the Gluckstern formulae and are well established. The expressions for the contribution from multiple scattering using optimum weights are discussed in detail.

Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure

For the first time, an ultrahigh degree of optical polarization (DOP) of 81.8% in AlGaN-based deep ultraviolet LED (DUV-LED) operated at 286 nm has been experimentally demonstrated. The very high DOP was obtained by introducing the novel moth-eye microstructure fabricated on the backside of a sapphire substrate. Compared with conventional DUV-LED with a DOP of 64.7%, a significant 1.26-fold enhancement was obtained. It was worth mentioning that the DOP was accurately measured via self-built full spatial transverse electric (TE) and transverse magnetic (TM) mode light intensity test system, which was mainly composed of angle resolution bracket, Glan-Taylor prism, and spectrometer. For both TE and TM mode light, the extraction angle inside the semiconductor was extended from conventional (−26°, 26°), (−52°, −41°), (41°, 52°) to (−52°, 52°). Combined with finite difference time domain simulation, it was further confirmed that the novel moth-eye microstructure could notably weaken the total internal reflectio...

Development of a Portable Muography Detector for Infrastructure Degradation Investigation

A portable muography detector was developed for measuring infrastructure degradation and its performance was tested. The detector consists of two muon position sensitive detectors (mu-PSDs) of the area of 140 mm $\times \,\, 140$ mm, placed in a compact light-shielding box. Each mu-PSD consists of plastic scintillating fibers connected to multipixel photon counters (MPPCs). To suppress the gain deviation of the MPPCs, the box was heat insulated and its inner air temperature was maintained by Peltier cooling–heating modules. The mu-PSD pixel size was 8.75 mm $\times \,\, 8.75$ mm and the distance between the two mu-PSDs was set to 100 mm in order to achieve a solid angle resolution of 8 msr when measuring typical pieces of infrastructure at thicknesses of several tens of centimeters. The intensity of cosmic-ray muons was measured as a function of zenith angle on the ground and was found to be in good agreement with the well-known empirical formula for muon intensity at Earth’s surface. The structural interior of a seven-story concrete building was then successfully imaged with the muography detector placed in the building’s basement.

Airport low-level wind shear lidar observation at Beijing Capital International Airport

The low-level wind shear is defined as a sharply change of the wind speed or wind direction within 600 m above the ground level. Due to affecting the airspeed of aircraft during take-off and landing phases, the wind shear can result in the disastrous aircraft accidents. The lidar team at Ocean University of China (OUC) carried out the particular research of the low-level wind shear at Beijing Capital International Airport (BCIA) in 2015 and 2016 by operating a pulse coherent Doppler lidar (PCDL) system. In this field experiment, the radial resolution is 30 m while the angle resolution is 0.1° and the updating rate of observation data is 4 Hz. On account of the high spatial and temporal resolution, the small-scale meteorological phenomenon can be captured. The low-level wind shear is observed by different scanning modes including 5-Doppler beam swing (5-DBS), step-wise plane-position indicator (PPI), multi-elevation PPI, range-height indicator (RHI) and glide path scan. The experiment configuration, the PCDL system, the observation modes and the case study of the wind shear are proposed and experimentally demonstrated. The quick-look algorithms which identifies the wind shear alarm based on the radial velocity data have been developed and tested. A case study of the wind shear shows that the events of low-level wind shear at the southern end of 18R/36L are suspected to be caused by buildings and rows of trees along the glide path under strong northwest wind conditions. Meanwhile, more than 2000 PPI scans have been analyzed to indicate the relationship between wind shear intensity and ramp length. Preliminary validations of the algorithms against wind shear reports from the crew and the terminal control office indicated positive skill. Totally, 14 wind shear cases have been validated by reports from the crew during field observation campaign.