Search

We have observed that Variational Mode Decomposition (VMD) exhibits instability in the denoising and separation of noisy multitone signals. Specifically, minor changes in factors such as signal-to-noise ratio, frequency spacing, sampling rate, and probability distribution can significantly impact the decomposition results. To address this issue, we have developed the Dual-VMD-correlation algorithm. This algorithm effectively mitigates the impact of beat effects when harmonics of closely spaced frequencies are superimposed, enabling stable denoising of noisy multitone signals and the separation of each individual tone signal. The algorithm holds promise for applications in frequency-modulated continuous wave laser detection. It can address challenges related to denoising laser echo signals interfered with by aerosols and the difficulty in separating backscatter interference from the target reflected signal spectrum. [ABSTRACT FROM AUTHOR]

We report a two-layer Mueller matrix model of polarized light propagation through layered human skin. Our model is based on single scattering approximation and the fact that the main scatterers in the top layer are various types of cells and the scatterers beneath it consist of fibers. By modeling the first layer mainly with spherical particles inducing the characteristics represented by Mueller matrices of depolarization and diattenuation, the second layer mainly with cylindrical scatterers inducing the retardance caused by scattering and birefringence, and considering the effects of the first layer to the second one, and the equal weight of contributions from both layers to a scatterer, it is possible to separate polarization properties of the medium induced by light propagation and scattering processes. One advantage of our model is that its extension to multi-layer tissues is straightforward. Polarization effects of human nail fold are identified. [ABSTRACT FROM AUTHOR]

In this paper, the effect of heat input on the temperature of bobbin tool friction stir welding (BT-FSW) joint in 16-mm-thickness 6061-T6 aluminum alloy plate is investigated by means of COMSOL Multiphysics 5.6 multi-physics field simulation software and K-sheathed thermocouple. Furthermore, the effect of heat input on the microstructure and mechanical properties of the joint is explored through the use of confocal laser scanning microscope (CLSM), electron back scatter diffraction (EBSD), and hardness and tensile measurements. The thermal impact factor (f) is regarded as a representation of heat input, and the experimental results show that when the f-value increases from 1.5 to 2.5, the simulated peak temperature increases from 426.85 to 467.85 °C, and the simulated temperature is higher about 10℃ than the measured temperature. Hole-type defects are observed at the junction of advancing side (AS) thermal-mechanically affected zone (TMAZ) and stirred zone (SZ) of the joint when f-value is 2, and the size of the defect increases when f-value is 2.5. The average grain size and the degree of recrystallization of SZ increase, but the dislocation density decreases as the f-value increases. Comparing the microhardness curves of the three groups of joints, it is found that the microhardness of each region decreases with the increase of f-value, with the microhardness of SZ decreasing from 88 to 72 HV. The tensile strength of the joints decreases from 225 to 199 MPa, the elongation increases from 8.33 to 10.32%, and the fracture morphology changes from equiaxial dimple to parabolic dimple. [ABSTRACT FROM AUTHOR]

Satellite radar altimeters like CryoSat‐2 estimate sea ice thickness by measuring the return‐time of transmitted radar pulses, reflected from the sea ice and ocean surface, to measure the radar freeboard. Converting freeboard to thickness requires an assumption regarding the fractional depth of the snowpack from which the radar waves backscatter (α) $(\alpha)$. We derive sea ice thickness from CryoSat‐2 radar freeboard data with incremental values for α $\alpha $, for the 2010–2021 winter periods. By comparing these to sea ice thickness estimates derived from upward‐looking sonar moorings, we find that α $\alpha $ values between 35%–80% result in the best representation of interannual variability observed over first‐year ice, reduced to < ${< } $55% over multi‐year ice. The underestimating bias in retrievals caused by optimizing this metric can be removed by reducing the waveform retracking threshold to 20%–50%. Our results pave the way for a new generation of 'partial penetration' sea ice thickness products from radar altimeters. Plain Language Summary: Satellite altimeters like CryoSat‐2 can be used to estimate sea ice thickness by estimating how far sea ice floes stick out above the waterline. This is done by measuring the time taken for radar waves to travel to the surface of the ice floe and back to the altimeter. All current winter sea ice thickness estimates assume that the radar waves return entirely from the sea ice surface, and not from the overlying snow cover. A growing body of research suggests this may not be the case, with weather and snow conditions affecting the fraction of the detected radar power that comes from the ice surface. We consider how well CryoSat‐2 estimates capture whether the ice is thicker or thinner than usual at a given time of year. We find that its skill is highest when we assume that 35%–80% of the radar power comes from the sea ice surface, and 20%–65% comes from the snow surface. However, improving this aspect of skill makes the sea ice thickness estimates too low. To address this, we show that a simple change in the waveform processing method can counter this bias. Key Points: CryoSat‐2 retrievals of sea ice thickness have historically been tuned to minimize bias rather than to capture interannual variabilityWe use upward‐looking sonar moorings to tune the treatment of both waveform retracking and snowpack penetration by radar wavesTuning to optimize interannual variability indicates partial penetration for all retracking thresholds [ABSTRACT FROM AUTHOR]

This study aims to explore the forest aboveground biomass relationship to C-band backscatter. A one-hectare area in Wytham Woods, located west of Oxford, was selected for this research. The area has a total of 525 trees of seven different tree species. The Michigan Microwave Canopy Scattering Model (MIMICS), a two-layer radiative transfer model, was applied to simulate canopy backscatter responses in this deciduous UK forest. Model parameters related to forest structure were derived from previously published terrestrial laser (LiDAR) data. Simulated backscatter was performed for co-polarized and cross-polarized modes at a C-band frequency range and incidence angles (20° to 45° at 5° increments). The research includes five objectives: i) backscatter sensitivity analysis from the variation of different model parameters; ii) backscatter seasonal effect under spring–summer (leaf-on) and autumn–winter (leaf-off) periods; iii) backscatter comparison between species as well as between simulated and satellite observations in a spatial pattern; iv) relationship between simulated backscatter and aboveground biomass; and v) relationship between MIMICS forest structure parameters and simulated backscatter. Sensitivity analysis results showed significant differences in backscatter from changes in leaf distribution, leaf thickness and water content (leaf, trunk and soil) for both polarization modes in leaf-on scenarios. Leaf-off scenarios presented significant differences from changes in branch distribution but only for the co-polarized mode. Seasonal variations presented significant backscatter differences between spring–summer and autumn–winter scenarios; additionally, backscatter differences among species for each seasonality in the co-polarized mode were observed. The computation of the grid resolution (20 m × 20 m) showed a range of backscatter values depending on the grid and incidence angle. Higher backscatter values were observed for the satellite data than for the simulated data. Finally, the aboveground biomass and the MIMICS input parameters presented high random variability and little systematic co-variation with the total backscatter on both simulated seasons, suggesting that more robust allometric equations for biomass estimation are required. [ABSTRACT FROM AUTHOR]

Backscatter and derived parameters from Synthetic Aperture Radar (SAR) may vary across the swath as the incident angle increases from the near to the far range, especially in the ScanSAR mode. Previous studies characterize this angular variation in the form of linear regression for commonly used ice types, namely first-year (FYI) and multi-year (MYI). The present study took advantage of the appearance of three grounded multi-year ice floes, viewed at different radar incidence angles, in a series of 22 RADARSAT-2 fully-polarimetric images, acquired over the Resolute Passage in the Canadian Arctic, during the period from 21 October to 28 December 2017. The ice properties remained invariant during the observation period; hence, variation of radar parameters of MYI can be attributed to change of incidence angle only. Quantification of angular variation of the selected SAR parameters was performed. They include conventional orthogonal backscatter coefficients, derived parameters from the incoherent decomposition of Cloude-Pottier, Yamaguchi, and Touzi, as well as a set of parameters from the compact polarimetry mode. Results specify the parameters that reveal variation with incidence angle and present the linear regressions equations. The explanation for the behaviour of each parameter, in terms of showing or not showing an angular trend, is offered. Results will be useful when using the polarimetric parameters in the sea ice classification scheme. [ABSTRACT FROM AUTHOR]

Rapid acquisition of millimeter‐resolution subterranean images can significantly improve the efficiency of archaeological excavation and facilitate the preservation of artifacts. For excavation sites with limited space, small and portable imaging equipment is necessary. Compton backscatter imaging (CBI) is a single‐sided non‐destructive testing technique, which typically requires a short scan time to obtain high‐resolution images. It has great potential in archaeological excavation, supporting archaeologists to make quick judgments. This research utilized a compact, easy‐to‐carry handheld backscatter system, making it particularly suitable and beneficial for on‐site archaeological excavation. Tests were performed in the framework of the excavation of a chariot pit at Dajuan Han Tomb in Xi'an (Shaanxi Province, China) to validate the applicability of this technique in imaging soil structure changes and detecting cultural artifacts. The experimental results show that CBI can clearly image bronze artifacts buried underground, which means practical value in archaeological excavation. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative multi-scale method for determining gas pressure parameters of superplastic forming, which is based on the quantitative relationship between the grain growth mechanism and fracture mechanism of Tie6Ale4V alloy. The high-temperature tensile tests were conducted on the material at temperatures ranging from 700, 800, 840, 890, 920, and 950 °C, strain rates were selected as 10-2~10-4/s. The grain size measurements were observed using electron back-scatter diffraction (EBSD). Particularly, the relation between grain size changes and fracture behaviour is specifically discovered using a physically-based dynamic material model (DMM), and the grain size thresholds for each forming limit are proposed. The physical fracture mechanism is named the "Grain growth based fracture (GGBF)" mechanism. Furthermore, an innovative method based on the GGBF mechanism is proposed to design the superplastic forming loading, and practical four-layer hollow structures experiments are applied to validate the fracture mechanism in superplastic forming. In total, A superplastic forming GGBF mechanism has been verified, and it is expected to be helpful for shape and property control in the forming process of complex structures. [ABSTRACT FROM AUTHOR]

Chirality, one of the universal phenomena in physics, forms the playground for fascinating phenomena in modern electromagnetism and industrial applications. Within the rapidly advancing technologies of integrated optoelectronic and all‐optical devices, controlling the light flow on a chip using optical chiral modes emerges as a crucial topic, which implies numerous counterintuitive chiroptical effects such as unidirectional emission, magnetic‐free non‐reciprocity, chiral switching, and enhanced sensitivity. Here strong yet reconfigurable mode chirality is demonstrated in integrated silicon‐based spiral microring resonators. Leveraging the adjustable azimuthal positions of two spiral edges as asymmetric local scatterers, the inter‐modal coupling can be manipulated, which bypasses the requirement of external off‐chip components in conventional schemes. Besides, an integrated phase shifter enables electrical reconfiguration of the non‐Hermiticity toward or away from exceptional points. Experimental results reveal post‐fabrication reconfiguration with a sign‐reversible chirality and chirality‐induced suppression of backscattering down to −24 dB. By virtue of demonstrations using standard silicon photonics foundry services, the findings provide a new design framework of microresonators as a building block for integrated chiral photonics in both classical and quantum regimes. [ABSTRACT FROM AUTHOR]

Objectives: Examine the histomorphometric bone composition, following alveolar ridge preservation techniques and unassisted socket healing. Materials and Methods: Forty‐two patients (42) requiring a single rooted tooth extraction were randomly allocated into three groups (n = 14 per group): Group 1: Guided Bone Regeneration (GBR) using deproteinised bovine bone mineral (DBBM) and a porcine collagen membrane; Group 2: Socket Seal (SS) technique using DBBM and a porcine collagen matrix; Group 3: Unassisted socket healing (Control). Trephined bone biopsies were harvested following a 4‐month healing period. Forty‐two samples underwent Back‐Scattered Electrons ‐Scanning Electron Microscopy (BSE‐SEM) imaging, with 15 samples examined using Xray Micro‐Tomography (XMT) (n = 6 for each GBR/SS and n = 3 Control). Images were analysed to determine the percentage (%) of connective tissue, new bone formation, residual DBBM particles and direct bone to DBBM particle contact (osseointegration). Results: BSE‐SEM analysis demonstrated that new bone formation was higher in the Control (45.89% ± 11.48) compared to both GBR (22.12% ± 12.7/p <.004) and SS (27.62% ± 17.76/p <.005) groups. The connective tissue percentage in GBR (49.72% ± 9), SS (47.81% ± 12.57) and Control (47.81% ± 12.57) groups was similar. GBR (28.17% ± 16.64) and SS (24.37% ± 18.61) groups had similar levels of residual DBBM particles. XMT volumetric analysis indicated a lower level of bone and DBBM particles in all test groups, when matched to the BSE‐SEM area measurements. Osseointegration levels (DBBM graft and bone) were recorded at 35.66% (± 9.8) for GBR and 31.18% (± 19.38) for SS. Conclusion: GBR and SS ARP techniques presented with less bone formation when compared to unassisted healing. GBR had more direct contact/osseointegration between the DBBM particles and newly formed bone. [ABSTRACT FROM AUTHOR]

In this study, the high-temperature deformation behaviour of the UNS S32750 Super Duplex Stainless Steel (SDSS) alloy was investigated by means of deformability and microstructure evolution in the (1050–1200) °C temperature (T) range. The deformability of the UNS S32750 SDSS alloy was investigated by the up-setting method using a gravity-drop hammer, with the following deformation energy/impact energy ( E ∗ ): 545.2 J, 1021.5 J, 1480.6 J, and 1905.3 J. Data referring to deformation resistance ( σ c ′ ) and mechanical work ( A ∗ ) as a function of deformation temperature (T) and deformation energy/impact energy ( E ∗ ) were obtained and analysed. It was shown that increasing the deformation temperature leads to an increase in the obtained deformation degree (degree of reduction in height). By analysing the rate of increase in the deformation degree as a function of the applied impact energy, it was shown that the rate of increase in the deformation degree rises with the increase in the applied impact energy. Also, it was observed that the evolution of the deformation resistance ( σ c ′ ) as a function of temperature (T) shows a decreasing tendency while increasing the deformation temperature for all impact energies and that the evolution of the mechanical work ( A ∗ ) as a function of temperature (T) shows a decreasing tendency while increasing the deformation temperature for all impact energies. The microstructure evolution of the UNS S32750 SDSS alloy was investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy-Electron Backscatter Diffraction (SEM-EBSD) techniques. It was observed that, in all cases, the microstructure shows intensely deformed grains, strongly elongated in the rolling direction in both ferrite (δ) and austenite (γ) intensely deformed grains. The intensity of grain deformation is increasing with the increase in the applied deformation degree. Also, it was observed that increasing the deformation temperature leads to a strong increase in the weight fraction of the dynamically recrystallised (DRX) ferrite (δ) grains. [ABSTRACT FROM AUTHOR]

Ionospheric oblique backscatter sounding is an effective means of monitoring the ionosphere which can be used as a frequency selection system to serve HF communication and ensure its quality and stability. But how to obtain effective information from the oblique backscatter ionogram is still a hot issue. Due to this situation, a frequency selecting method for HF communication based on ionospheric oblique backscatter sounding is proposed in this study. After obtaining the ionograms, pattern recognition is used to separate the vertical echoes and the oblique backscatter echoes. Next, the leading edge of the oblique backscatter echoes are extracted, and then a two-dimensional electron density profile can be reconstructed. Then, with the help of ray tracing, the usable frequency range can be estimated. Finally, according to the signal-to-noise ratio reflected by the ionograms, several optimal communication frequencies can be selected. In order to verify this method, oblique ionograms are obtained through oblique sounding experiments to evaluate its accuracy. The result indicates that the usable frequency range and the selected frequencies are in accordance with the echo of the oblique ionogram, so the practicability and accuracy of the method are validated. Eventually, the maximum usable frequencies (MUFs) obtained from oblique backscatter sounding are compared with the MUFs from the oblique sounding ionogram; its Mean Absolute Percentage Error (MAPE) is 7.8% and its root mean squared error (RMSE) is 1.34 MHz. [ABSTRACT FROM AUTHOR]

Multibeam echosounders provide ideal data for the semi-automated seabed feature extraction and accurate morphometric measurements. In this study, bathymetric and raw backscatter data were initially used to manually delimit the reef morphologies found in an insular semi-enclosed gulf in the northern Aegean Sea (Gera Gulf, Lesvos Island, Greece). The complexity of this environment makes it an ideal area to "crash test" (test to the limit) and compare the results of the delineation methods. A large number of (more than 7000) small but prominent reefs were detected, which made manual mapping extremely time-consuming. Three semi-automated tools were also employed to map the reefs: the Benthic Terrain Modeler (BTM), Confined Morphologies Mapping (CoMMa), and eCognition Multiresolution Segmentation. BTM did not function properly with irregular reef footprints, but by modifying both the bathymetry and slope, the outcome was improved, producing accurate results that appeared to exceed the accuracy of manual mapping. CoMMa, a new GIS morphometric toolbox, was a "one-stop shop" that, besides generating satisfactory reef delineation results (i.e., detecting the same total reef area as the manual method), was also used to extract the morphometric characteristics of the polygons resulting from all the methods. Lastly, the Multiresolution Segmentation also gave satisfactory results with the highest precision. To compare the final maps with the distribution of the reefs, mapcurves were created to estimate the goodness-of-fit (GOF) with the Precision, Recall, and F1 Scores producing values higher than 0.78, suggesting a good detection accuracy for the semi-automated methods. The analysis reveals that the semi-automated methods provided more efficient results in comparison with the time-consuming manual mapping. Overall, for this case study, the modification of the bathymetry and slope enabled the results' accuracy to be further enhanced. This study asserts that the use of semi-automated mapping is an effective method for delineating the geomorphometry of intricate relief and serves as a powerful tool for habitat mapping and decision-making. [ABSTRACT FROM AUTHOR]

Satellite-based estimation of forest variables including forest biomass relies on model-based approaches since forest biomass cannot be directly measured from space. Such models require ground reference data to adapt to the local forest structure and acquired satellite data. For wide-area mapping, such reference data are too sparse to train the biomass retrieval model and approaches for calibrating that are independent from training data are sought. In this study, we compare the performance of one such calibration approach with the traditional regression modelling using reference measurements. The performance was evaluated at four sites representative of the major forest biomes in Europe focusing on growing stock volume (GSV) prediction from time series of C-band Sentinel-1 and Advanced Land Observing Satellite Phased Array L-band Synthetic Aperture Radar (ALOS-2 PALSAR-2) backscatter measurements. The retrieval model was based on a Water Cloud Model (WCM) and integrated two forest structural functions. The WCM trained with plot inventory GSV values or calibrated with the aid of auxiliary data products correctly reproduced the trend between SAR backscatter and GSV measurements across all sites. The WCM-predicted backscatter was within the range of measurements for a given GSV level with average model residuals being smaller than the range of the observations. The accuracy of the GSV estimated with the calibrated WCM was close to the accuracy obtained with the trained WCM. The difference in terms of root mean square error (RMSE) was less than 5% units. This study demonstrates that it is possible to predict biomass without providing reference measurements for model training provided that the modelling scheme is physically based and the calibration is well set and understood. [ABSTRACT FROM AUTHOR]

Channel coefficient estimation is a challenging problem in ambient backscatter communication systems. In this paper, unique identification of channel coefficients using the Expectation-Maximization (EM) method is investigated. It is proven that the EM method is not able to always yield unique solutions to channel coefficients and therefore the tag symbol estimation accuracy can be compromised. A correct derivation of the hybrid Cramer-Rao Bound (HCRB) is also provided. [ABSTRACT FROM AUTHOR]

Study of gamma-backscattered peaks is important for the estimation of composition, density, defects and thickness of the scattering materials. In the present study, gamma rays from a point source of 137Cs were scattered onto materials of different atomic numbers and NaI(Tl) scintillator detector was used for collection of backscattered events. It is observed that the area under the backscattering peak is dissimilar for materials of different atomic numbers with variable thickness. Simulation of the experiment was carried out using GEANT4 for the validation of the experimental findings. [ABSTRACT FROM AUTHOR]

This paper presents a cognitive radio (CR)-enabled symbiotic ambient backscatter communication (AmBC) system with the help of a zero-energy reconfigurable intelligent surface (zeRIS). An adaptive transmission (AT) strategy for the zeRIS is devised based on the amount of harvested energy. Specifically, when energy reserve is insufficient, the zeRIS merely reflects signals without any phase adjustments (PAs), whereas under sufficient energy conditions, it reflects signals following precise PAs. Moreover, a segmented zeRIS is adopted by taking primary transmission (PT) and backscatter transmission (BT) into account. Following this, the coexistence outage probability and ergodic capacity are derived to assess the reliability and effectiveness of the proposed model, respectively. Their asymptotic performance is analyzed to gain insightful observations. Finally, simulation results are provided to verify the accuracy of the theoretical analysis, confirming that AT offers improved reliability, system rate, and energy efficiency over non-adaptive transmission. Furthermore, CR-aided AT demonstrates superior energy efficiency compared to non-CR-assisted AT. It is also crucial to note that the allocation of reflective elements between PT and BT must be reasonably managed to satisfy specific system requirements. [ABSTRACT FROM AUTHOR]

Particle scattering is a key factor affecting underwater light transport. The diffusion length (zD), defined as 1/[b(1 - g)], where b is the scattering coefficient and g is the asymmetry factor, is obtained from the volume scattering function (VSF) of the particle and plays a vital role in assessing the potential for underwater optical detection, imaging and communication. Owing to the lack of VSF datasets, the variation in zD at different wavelengths in various ocean areas remains unclear. In this study, we used a dual-wavelength (488 & 532 nm) VSFLab to conduct the VSF measurement experiments in the East China Sea (ECS) and the South China Sea (SCS), obtaining VSFs from 1.5° to 178.5° at 51 stations. Seven optical properties, including absorption (a), scattering (b), attenuation (c), diffuse attenuation coefficient (Kd), backscattering (bb), g, and zD, were calculated from the measured VSFs. A comparative analysis of the results was performed, which showed that the laser transmission capability at 532 nm was better than that at 488 nm in terms of the absorption or diffuse attenuation coefficient in the ECS, whereas superior performance was observed at 488 nm in the SCS. However, from the perspective of scattering, zD at 532 nm (zD(532)) demonstrated superior performance in both the ECS and SCS. This superiority was particularly noticeable in regions with exceptionally clear water, such as the eastern side of the Luzon Strait, where zD(532) exceeded zD(488) by approximately 20%. Overall, the findings of this study provide a new perspective for assessing underwater light transmission capabilities. [ABSTRACT FROM AUTHOR]

The Atmospheric Environment Monitoring Satellite (DQ-1) was successfully launched in April 2022, with the capability of providing continuous multi-sensor spatial and optical simultaneous observations of carbon dioxide, aerosols and clouds. The primary payload carried on DQ-1 is an Aerosol and Carbon dioxide Detection Lidar (ACDL). The instrument comprises a high-spectral-resolution channel at 532 nm, polarization channels at 532 nm, elastic scattering channel at 1064 nm, and integrated-path differential absorption (IPDA) channel at 1572 nm. The optical properties of aerosols and clouds measured by the ACDL promote a quantitative characterization of the uncertainties in the global climate system, hence the precise calibrations for the ACDL are necessary. This paper outlines the algorithms employed for calibrating the nighttime 532 nm measurements for the first spaceborne high-spectral-resolution lidar with an iodine vapor absorption filter. The nighttime calibrations of the 532 nm data are fundamental to the ACDL measurement procedure, as they are utilized to derive the calibrations over daytime orbits and the calibrations of the 1064 nm channel relative to the 532 nm channel. This paper provides a review of the theoretical foundations for molecular normalization techniques as applied to spaceborne lidar measurements, includes a detailed discussion of auxiliary data and theoretical parameters used in ACDL calibrations, as well as a comprehensive description of the calibration algorithm procedure. To mitigate large errors stemming from high-energy events during calibration, a data filter is designed to obtain valid calibration signals. The paper also assesses the results of the calibration procedure, by analyzing the errors of calibration coefficients and validating the attenuated backscatter coefficient results. The results indicate that the relative error of the calibrated attenuated backscatter coefficients is lower than 1 % in the calibration area, and the uncertainty of the clear-air scattering ratio was within anticipated range of 6 %. [ABSTRACT FROM AUTHOR]

In the 2023 hurricane season, the Hurricane Analysis and Forecast System (HAFS) based Ensemble Prediction System (EPS) was being ported to the Amazon Web Service cloud. This relocation aimed to provide real-time hurricane probabilistic forecast guidance for National Hurricane Center (NHC) forecasters. The system comprises Stochastically Perturbed Physics Tendencies (SPPT), Stochastically Kinetic Energy Backscatter (SKEB), and Stochastically Perturbed PBL Humidity (SHUM). Initial and boundary conditions are derived from the National Centers for Environmental Prediction (NCEP) operational Global Ensemble Forecast System (GEFS) 21-member forecast data. The performance of HAFS-EPS for 2023 Atlantic hurricane forecasts was compared with the global GEFS, global ECMWF ensemble, and operational HAFS-A/B forecasts. This comparison highlighted the advantages of higher-resolution regional ensemble forecasts for hurricane track, intensity, Rapid Intensification (RI) probability, and various hazards, including wind, wave, and storm surge probability guidance. [ABSTRACT FROM AUTHOR]

Effective observation of the ocean is vital for studying and assessing the state and evolution of the marine ecosystem and for evaluating the impact of human activities. However, obtaining comprehensive oceanic measurements across temporal and spatial scales and for different biogeochemical variables remains challenging. Autonomous oceanographic instruments, such as Biogeochemical (BGC)-Argo profiling floats, have helped expand our ability to obtain subsurface and deep-ocean measurements, but measuring biogeochemical variables, such as nutrient concentration, still remains more demanding and expensive than measuring physical variables. Therefore, developing methods to estimate marine biogeochemical variables from high-frequency measurements is very much needed. Current neural network (NN) models developed for this task are based on a multilayer perceptron (MLP) architecture, trained over point-wise pairs of input–output features. Although MLPs can produce smooth outputs if the inputs change smoothly, convolutional neural networks (CNNs) are inherently designed to handle profile data effectively. In this study, we present a novel one-dimensional (1D) CNN model to predict profiles leveraging the typical shape of vertical profiles of a variable as a prior constraint during training. In particular, the Predict Profiles Convolutional (PPCon) model predicts nitrate, chlorophyll, and backscattering (bbp700) starting from the date and geolocation and from temperature, salinity, and oxygen profiles. Its effectiveness is demonstrated using a robust BGC-Argo dataset collected in the Mediterranean Sea for training and validation. Results, which include quantitative metrics and visual representations, prove the capability of PPCon to produce smooth and accurate profile predictions improving upon previous MLP applications. [ABSTRACT FROM AUTHOR]

Laser range-gated underwater imaging technology, by removing most of the backscattering noise, can effectively increase image contrast and extend the detection range. The optical signal captured by a range-gated imaging system primarily comprises reflected light from the object and backscattered light from the surrounding water. Consequently, surfaces with low reflectivity or highly turbid water environments substantially constrain the applicability of the range-gated imaging system. To enhance the detection capability of underwater laser range-gated imaging, this paper proposes the incorporation of underwater polarized light imaging technology as an enhancement method. Based on polarization differences, backscattered light and reflected light from an object can be distinguished. Experimental results indicate that, compared to images obtained using a conventional range-gated laser imaging system, those captured with a polarization-enhanced system exhibit an increase of up to 47% for the corresponding Enhancement Measure Evaluation (EME) index. The proposed approach, which integrates polarization imaging with range-gated laser imaging, has the potential to broaden the applicability of underwater laser imaging scenarios, such as deep-sea exploration and military applications. [ABSTRACT FROM AUTHOR]

The radar-backscattering coefficient (σ0) depends on surface characteristics and instrumental parameters (wavelength, polarization, and incidence angle). For Sentinel-1 (S1), with incidence angles ranging from 25° to 45°, σ0 for similar targets typically differs by a few dB depending on their localization in the S1 swath. Overcoming this angular dependence is crucial for the operational applications of radar data. In theory, σ0 follows a cosine function with an exponent "N" that represents the degree of dependence between σ0 and the incidence angle. In order to reduce the effect of the incidence angle on σ0, dynamic N normalizations based on vegetation descriptors, NDVI and SAR Ratio (VV/VH), were applied and then compared to the results obtained with temporally fixed N normalizations. N was estimated at each S1 date during the period of the study for three main summer crops: corn, soybean, and sunflower. Analysis shows that the angular dependence of the S1 σ0 is similar for all three crops. N varies from 3.0 for low NDVI values to 2.0 for high NDVI values (stage of maximal vegetation development) in the VV polarization and from 2.5 to 1.5 for the VH polarization. Furthermore, N fluctuates strongly during the periods before plant emergence and after harvesting, due to variations in the soil roughness. Finally, the results demonstrated that the dynamic normalization of σ0 significantly reduces its angular dependence compared to fixed N (N = 1 and N = 2), with SAR ratio-based normalization performing similarly to NDVI-based normalization. [ABSTRACT FROM AUTHOR]

The backscatter characteristics of ocean surfaces are of great importance in active marine remote-sensing fields. This paper presents the high spatial and temporal resolution dual co-polarized (VV and HH) and cross-polarized (HV) Ka-band sea-surface backscattering measurements taken from the Yellow Sea research platform at incidence angles ranging from 30° to 50° and in the wind speed range from 5.8 to 8.6 m/s. The experimental results show that the backscattering coefficient in HH polarization is close to (or even surpassing) that in VV polarization within a wind speed range of 7.1 to 8.6 m/s for Ka band under high resolution at medium incidence angles (30°–50°). Further analysis of the 10-ms short-time observation samples found that the sea surface echoes in VV polarization are more sensitive to wave motions, exhibiting more complex scattering characteristics such as multi-peaks and reducing scattering energy, especially at high wind speeds and large incident angles. The Doppler velocity analysis also confirms that rapid ocean wave changes can be detected within a short observation period, especially in VV polarization. The research in this article not only demonstrates the high spatial and temporal resolution capabilities of Ka-band radar for ocean surface observation but also reveals its great potential in interpreting and inversing rapidly evolving marine phenomena. [ABSTRACT FROM AUTHOR]

We study the amount of backscattering of Valley-Hall modes in a classical topological insulator. In reciprocal systems, the conservation of the valley index has been argued to be at the root of the high transmission of Valley-Hall modes observed in many experimental realizations. Here, we reconsider this hypothesis by quantitatively analysing the canonical scattering problem of interface Valley-Hall modes impinging on sharp bends that may or may not conserve the valley index. We consider a tight binding model of graphene ribbons with an interface and compute the reflection and transmission coefficients using the transfer matrix formalism. We find that, in all configurations considered, the transmission of Valley-Hall modes is close to being maximal, even in cases where the valley index is not conserved. Hence, there appears to be no correlation between valley conservation and good transmission. Our results serve as a reference case for the design of Valley-Hall type metamaterial. [ABSTRACT FROM AUTHOR]

Fresnel reflection has been known for centuries to fundamentally impede efficient transmittance across planar interfaces, especially at grazing incidence. In this work, the generalized Huygens' condition (GHC) is introduced to resolve such intricacies in metasurface (MS) designs and allow omnidirectional transparency. Compared to common numerical metamaterial approaches, the analytical framework herein yields surprisingly simple closed‐form conditions, carefully leveraging the natural nonlocal mechanisms endowed in planar electromagnetic structures. At the meta‐atom level, the GHC is met by balancing traditional tangential susceptibilities of Huygens' MSs with their unconventional normal counterparts; the latter facilitates the key requisite of vanishing backscattering at the challenging grazing incidence scenario. At the MS level, this central insight is sheerly utilized to engineer realistic all‐angle transparent printed‐circuit‐board (PCB) cascaded admittance sheets. Thoroughly validated in simulation and experiment, this universal GHC demonstrates a resourceful venue for practical implementation of advanced nonlocal devices, e.g., flat optical components, optical analog computers, and spaceplates. [ABSTRACT FROM AUTHOR]

This study focuses on welding UNS R30155 alloy thin sheets using IN718 filler metal, employing two welding modes: pulsed current gas tungsten arc welding and constant current gas tungsten arc welding. The main goal was to examine the combined effects of pulsed current and optimal frequency on the microstructure and oxidation behavior across the weldment, comparing it to the constant current mode using electron backscatter diffraction. The results show that employing an optimal frequency of 240 Hz induces turbulence in the molten pool, limiting epitaxial grain growth by fragmenting dendritic arms and generating solid particles as modifiers. This phenomenon results in an expanded zone featuring equiaxed grains with random orientations, causing the weld metal's texture intensity to shift from the preferred growth direction, < 001> (with a texture intensity of about 0.92 mrd (multiples of random texture distribution)), to random orientations. In contrast, constant current welding ensures extensive growth of epitaxial grains, maintaining a high texture intensity of 2.61 mrd, aligned with the preferred growth direction, < 001>. Oxidation tests reveal that the sample welded with the optimal frequency of 240 Hz, facilitating uniform distribution of alloying elements during solidification, forms alternating protective layers of Cr2O3 and NiCr2O4. This reduces damage to the substrate, resulting in the thinnest oxide layer and a lower parabolic rate constant (Kp) compared to other welded specimens. Specifically, the Kp values for the sample were 0.158 × 10−10 g2 cm−4 s−1 for up to 4 hours and 0.027 × 10−10 g2 cm−4 s−1 after 4 hours. [ABSTRACT FROM AUTHOR]

Backscattering is a promising power-efficient communication technique providing sustainable wireless links with a low carbon footprint. This approach is a critical enabler for dense IoT networks, which are forecast to grow to 41 billion by 2025. However, existing backscatter designs are limited to the sub-6 GHz bands or narrowband operation in the millimeter-wave regime; therefore, they fail to concurrently support many interference-free low-power users. Enabling a frequency-agile wideband backscatter design in the sub-terahertz offers a two-pronged advantage for densely deployed backscatter networks: spatial reuse enabled by directionality and frequency multiplexing enabled by the large available bandwidth. We present the first sub-THz backscatter architecture that operates above 100 GHz. Our design relies on a detailed understanding of reciprocity in leaky-wave devices and offers a realistic joint localization and communication protocol for sub-THz backscatter networks. This study presents the first sub-THz retrodirective wideband backscatter. Instead of phased arrays, it uses key properties of leaky waveguides, i.e., frequency-angle dependency and reciprocity for wideband retro directivity with ultra-low power. [ABSTRACT FROM AUTHOR]

Topology is essential for achieving unchanged (or protected) quantum properties in the presence of perturbations. A challenge facing the application is the variable protection levels displayed in real systems associated with the reconstructive behaviors of the dissipationless modes. Despite various insights on potential causes of backscattering, the edge-state-based approach is incomplete because the bulk states also contribute indispensably. This study investigates sample-scale reconstruction where dissipationless modes are global objects instead of being restricted to the sample edge. An integer quantum Hall effect hosted in a Corbino geometry is adopted and brought to the verge of a breakdown. Two independent and simultaneous detections are performed to capture transport responses in both longitudinal and transverse directions. The real-time correspondence between orthogonal results confirms two facts. 1. Dissipationless modes undergo frequent reconstruction in response to electrochemical potential changes, causing dissipationless current paths to expand transversely into the bulk while preserving chirality. A breakdown only occurs when a backscattering emerges between reconstructed dissipationless current paths bridging opposite edge contacts. 2. Topological protection is subject to an interplay of disorder, electron-electron interaction, and topology. The proposed reconstruction mechanism qualitatively explains the robustness variations, beneficial for protection optimization. Understanding the mechanisms influencing the robustness of topologically protected states is of fundamental relevance. This experimental work demonstrates, through the observation of real-time longitudinal and transverse responses, the importance of transverse reconstruction of protected modes which is influenced by electron-electron interaction in addition to disorder. [ABSTRACT FROM AUTHOR]

We examine the ability of two dynamic turbulence closure models to simulate the diurnal development of convection and the transition from dry to shallow cumuli and then to deep convection. The dynamic models are compared with the conventional Smagorinsky scheme at a range of cloud‐resolving and grey‐zone resolutions. The dynamic schemes include the Lagrangian‐averaged, scale‐dependent dynamic Smagorinsky model and a Lagrangian‐averaged, dynamic mixed model. The conventional Smagorinsky model fails to reproduce the shallow convection stage beyond the large‐eddy simulation regime, continuously building up the convective available potential energy that eventually leads to an unrealistic deep convection phase. The dynamic Smagorinsky model significantly improves the representation of shallow and deep convection; however, it exhibits issues similar to the conventional scheme at coarser resolutions. In contrast, the dynamic mixed model closely follows the large‐eddy simulation results across the range of sub‐kilometre simulations. This is achieved by the combined effect of an adaptive length scale and the inclusion of the Leonard terms, which can produce counter‐gradient fluxes through the backscatter of energy from the subgrid to the resolved scales and enable appropriate non‐local contributions. A further sensitivity test on the inclusion of the Leonard terms on all hydrometeor fluxes reveals the strong interaction between turbulent transport and microphysics and the possible need for further optimisation of the dynamic mixed model coefficients together with the microphysical representation. [ABSTRACT FROM AUTHOR]

To study the influence of multiple scattering factors on the scattering characteristics, the scattering properties of a sizable double-spherical system at random orientations were analyzed by comparison of the T matrix and simple addition in the S-, C-, and X-bands, including the backscatter section (Cbak), attenuation section (Cext) and scattering section (Csca), asymmetry factor (g), and single scattering albedo (w), with the change in the spherical distance (d) and particle radius (r). It was found that the spacing between the spheres is four times the sphere's radius, which is a clear cut-off point for the influence of multiple scattering in a two-spherical system. Then, by fitting the relative difference multiples of the T matrix method and the simple addition method, the uniform expression of each optical parameter under multiple scattering conditions is obtained. [ABSTRACT FROM AUTHOR]

The rockfish (Sebastes schlegeli) and striped beakperch (Oplegnathus fasciatus) were released in marine ranching areas in Korea, Japan, and China to maintain fishery resources in coastal areas. To estimate the density and biomass of fishery resources, the target strength (TS) of target marine organisms is needed to scale integrated volume backscattering coefficients. In this study, the target strength–length (TS–L) relationship for live rockfish and striped beakperch was derived using ex situ methods at a frequency of 200 kHz. The TS-L function for rockfish and striped beakperch can be expressed as TSAvg. = 20logTL − 69.25 (R2 = 0.35) and TSAvg. = 20logFL − 67.01 (R2 = 0.31), respectively. These results can be used to assess the growth, density, and abundance of the two species using acoustics. [ABSTRACT FROM AUTHOR]

Ocean mesoscale eddies are often poorly represented in climate models, and therefore, their effects on the large scale circulation must be parameterized. Traditional parameterizations, which represent the bulk effect of the unresolved eddies, can be improved with new subgrid models learned directly from data. Zanna and Bolton (2020), https://doi.org/10.1029/2020gl088376 (ZB20) applied an equation‐discovery algorithm to reveal an interpretable expression parameterizing the subgrid momentum fluxes by mesoscale eddies through the components of the velocity‐gradient tensor. In this work, we implement the ZB20 parameterization into the primitive‐equation GFDL MOM6 ocean model and test it in two idealized configurations with significantly different dynamical regimes and topography. The original parameterization was found to generate excessive numerical noise near the grid scale. We propose two filtering approaches to avoid the numerical issues and additionally enhance the strength of large‐scale energy backscatter. The filtered ZB20 parameterizations led to improved climatological mean state and energy distributions, compared to the current state‐of‐the‐art energy backscatter parameterizations. The filtered ZB20 parameterizations are scale‐aware and, consequently, can be used with a single value of the non‐dimensional scaling coefficient for a range of resolutions. The successful application of the filtered ZB20 parameterizations to parameterize mesoscale eddies in two idealized configurations offers a promising opportunity to reduce long‐standing biases in global ocean simulations in future studies. Plain Language Summary: This research focuses on improving the accuracy of ocean models by addressing the challenges of representing the mesoscale eddies on coarse grids. These eddies play a crucial role in the Earth's climate system, but traditional climate models struggle to capture their effects. Here, we implemented a new data‐driven parameterization simulating the physics of the mesoscale eddies into the state‐of‐the‐art ocean model. The parameterization is interpretable and captures key physical processes related to the mesoscale eddies known as energy backscatter. We tested this parameterization in two idealized ocean scenarios and found that it significantly improves the biases in the representation of the mean state and energetics. We propose new filtering schemes which improve the physical and numerical properties of the parameterization. Accurate representation of the mesoscale eddies by the present scheme has the potential to resolve long‐standing biases present in global ocean models and thus allow for more reliable climate simulations. Key Points: A data‐driven mesoscale eddy parameterization is implemented and evaluated in different configurations of the GFDL MOM6 ocean modelWe introduce filtering schemes to reduce the generation of grid‐scale noise and enhance the large‐scale backscatterThe subgrid parameterization improves the representation of the energy distributions and the climatological mean state [ABSTRACT FROM AUTHOR]

This paper presents a low‐scattering 1 × 2 patch array antenna combining resistive and coding metasurfaces (MSs) for the reduction of wideband‐backscatter. An artificial magnetic conductor technology is used to validate the proposed technique, which is fundamentally based on scattering, phase cancellation, and absorptive property of the MS. By integration of coding MS elements and an absorbent unit cell, three different array blocks are utilized to significantly reduce the monostatic and bistatic backscattered energy level from 6.5 to 16.5 GHz, as well as overall reduction from 5 to 22 GHz. Under the incidence of plane waves, various reflection phases have been observed. The diffusion of the scattering energy from the surface can be achieved by carefully choosing the phase distributions for the reflected waves. Additionally, the bistatic backscattered energy level of the prototype is realized at various frequency points. This technique is validated using artificial magnetic conductors, which uniquely combine the effects of scattering, phase cancellation, and absorption in the MS's hybrid unit cells. Further, antenna array parameters are optimized for frequency, polarization, and angular diversity, S‐parameters, radiating efficiency, reducing radar cross section (RCS) in the wideband range and ensuring robust performance. The experimental results were substantiated by simulations of the reference and proposed prototypes suggesting that the proposed prototype can be a good candidate for applications that require a low monostatic and bistatic RCS platform. [ABSTRACT FROM AUTHOR]

The use of depolarization lidar to measure atmospheric volume depolarization ratio (VDR) is a common technique to classify cloud phase (liquid or ice). Previous work using a machine learning framework, applied to peak properties derived from co-polarized attenuated backscatter data, has been demonstrated to effectively detect supercooled-liquid-water-containing clouds (SLCCs). However, the training data from Davis Station, Antarctica, include no warm liquid water clouds (WLWCs), potentially limiting the model's accuracy in regions where WLWCs are present. In this work, we apply the same framework used on the Davis data to a 9-month micro-pulse lidar dataset collected in Ōtautahi / Christchurch, Aotearoa / New Zealand, a location which includes WLWC. We then evaluate the results relative to a reference VDR cloud-phase mask. We found that the Davis model performed relatively poorly at detecting SLCC with a recall score of 0.18, often misclassifying WLWC as SLCC. The performance of our new model, trained using data from Ōtautahi / Christchurch, displays recall scores as high as 0.88 for identification of SLCC, although it generally underestimates SLCC occurrence. The overall performance of the new model highlights the effectiveness of the machine learning technique when appropriate training data relevant to the location are used. [ABSTRACT FROM AUTHOR]

In August 2022, China successfully launched the Terrestrial Ecosystem Carbon Inventory Satellite (TECIS). The primary payload of this satellite is an onboard multi-beam lidar system, which is capable of observing aerosol optical parameters on a global scale. This pioneering study used the Fernald forward integration method to retrieve aerosol optical parameters based on the Level 2 data of the TECIS, including the aerosol depolarization ratio, aerosol backscatter coefficient, aerosol extinction coefficient, and aerosol optical depth (AOD). The validation of the TECIS-retrieved aerosol optical parameters was conducted using CALIPSO Level 1 and Level 2 data, with relative errors within 30%. A comparison of the AOD retrieved from the TECIS with the AERONET and MODIS AOD products yielded correlation coefficients greater than 0.7 and 0.6, respectively. The relative error of aerosol optical parameter profiles compared with ground-based measurements for CALIPSO was within 40%. Additionally, the correlation coefficients R2 with MODIS and AERONET AOD were approximately between 0.5 and 0.7, indicating the high accuracy of TECIS retrievals. Utilizing the TECIS retrieval results, combined with ground air quality monitoring data and HYSPLIT outcomes, a typical dust transport event was analyzed from 2 to 7 April 2023. The results indicate that dust was transported from the Taklamakan Desert in Xinjiang, China, to Henan and Anhui provinces, with a gradual decrease in the aerosol depolarization ratio and backscatter coefficient during the transport process, causing varying degrees of pollution in the downstream regions. This research verifies the accuracy of the retrieval algorithm through multi-source data comparison and demonstrates the potential application of the TECIS in the field of aerosol science for the first time. It enables the fine-scale regional monitoring of atmospheric aerosols and provides reliable data support for the three-dimensional distribution of global aerosols and related scientific applications. [ABSTRACT FROM AUTHOR]

Underwater wireless sensor networks play an important role in exploring the oceans as part of an integrated space–air–ground–ocean network. Because underwater energy is limited, the equipment's efficiency is significantly impacted by the battery duration. Underwater backscatter technology does not require batteries and has significant potential in positioning, navigation, communication, and sensing due to its passive characteristics. However, underwater backscatter signals are susceptible to being swamped by the excitation signal. Additionally, the signals from different reflection signals share the same frequency and overlap, and contain fewer useful features, leading to significant challenges in detection. In order to solve the above problems, this paper proposes a recurrent neural network that introduces time-frequency and reference signal features for underwater backscatter signal separation (TF-REF-RNN). In the feature extraction part, we design an encoder that introduces time-frequency domain features to learn more about the frequency details. Additionally, to improve performance, we designed a separator that incorporates the reference signal's pure global information features. The proposed TF-REF-RNN network model achieves metrics of 28.55 dB SI-SNRi and 19.51 dB SDRi in the dataset that includes shipsEar noise data and underwater simulated backscatter signals, outperforming similar classical methods. [ABSTRACT FROM AUTHOR]

In this letter, a novel integrated sensing and communication (ISAC) scenario with wireless power transfer (ISAC‐WPT) is investigated. In this new setup, an access point simultaneously employs communication and sensing beams to serve a communication user, detect an RFID tag, and power an energy receiver. The objective is to design the sensing and communication beams to minimize the total transmit power while satisfying the requirements of tag detection, communication, and energy harvesting. To address the corresponding non‐convex problem, the constraints are reformulated into convex second‐order cone constraints, thereby obtaining the globally optimal solution. To further reduce computational complexity, zero‐forcing is employed to design the beamforming vectors, followed by solving a convex optimization problem to determine the optimal power allocation between sensing and communication beams. The simulation results demonstrate the effectiveness of the proposed beamforming designs, highlighting the potential of ISAC‐WPT Backscatter RFID systems. [ABSTRACT FROM AUTHOR]

The rotating fan beam scanning observation mechanism of China-France oceanography satellite (CFOSAT) scatterometer provides more comprehensive ocean measurements. However, its data quality is often impacted by rain contamination. In this study, we analysed the effect of rain on CFOSAT SCATterometer (CSCAT) backscatter measurements by collocating CSCAT data, the Integrated Multi-satellitE Retrievals (IMERG) rain data, and the wind reanalysis from European Centre for Medium-Range Weather Forecasts (ECMWF). The research findings indicate that, rain exhibits an intensification effect on backscatter at low wind speeds, but this effect gradually diminishes with increasing wind speeds, eventually transitioning to an attenuation effect at a wind speed between 10–20 m·s−1. At extremely high wind speeds above 20 m·s−1, the rain initially increases and then decreases CSCAT normalized radar cross section (σ0) as the rain rate increases. The sensitivity of CSCAT σ0 to rain rate decreases as the incidence angle increases. Its sensitivity to wind speed decreases as the rain rate increases. The azimuthal modulation becomes more pronounced with higher wind speeds and smaller incidence angles. However, rain weakens the asymmetry and anisotropy. Furthermore, the HH polarization exhibits a more pronounced susceptibility to rain compared to the VV polarization. [ABSTRACT FROM AUTHOR]

In this study, we conducted a quantitative analysis of the factors affecting Sentinel-1 interferometric decorrelation in a typical agricultural region in China, where maize and rice, two of the three staple crops in the country, are the primary crop types. Bayesian network and random forest regression analysis were employed to examine the impact of temporal and spatial decorrelation, Doppler centroid differences, and surface cover variations. Among these factors, the temporal baseline is the most significant contributor to decorrelation. This finding opens up the possibility of utilizing Sentinel-1 coherence, which quantifies the degree of decorrelation, as a mapping feature for staple crops. Consequently, we conducted classification experiments for staple crops in this typical agricultural region, utilizing time-series Sentinel-1 coherence data and considering polarization modes. The highest overall accuracy achieved was 98.08 % for the shortest temporal baseline (12 days), with VV polarization outperforming VH polarization. In comparison, we conducted classification experiments using Sentinel-1 intensity backscatter data in VV and VH channels. The combined use of coherence and backscatter data yielded superior results compared to using either data source alone. Furthermore, we conducted classification experiments based on Sentinel-2 optical remote sensing features. To sum up, we compared the classification performance of Sentinel-1 coherence with that of intensity and optical remote sensing features, demonstrating the reliability of time-series Sentinel-1 coherence as a valuable tool for mapping staple crops in China's crucial grain-producing regions. [ABSTRACT FROM AUTHOR]

Purpose: The impact of various hip prosthesis materials on the amount of dose perturbation generated by 9 MeV electron and 18 MV photon beams during pelvic radiation therapy is analyzed in this research. Materials and Methods: The Varian 2100 C/D LINAC head for the electron (9 MeV) and photon (18 MV) modes and a water phantom with a realistic hip prosthesis were modeled using the Monte Carlo (MC) code; MCNPX (Ver. 2.6.0) and were benchmarked for measurement. Four different materials, including Cobalt-Chromium-Molybdenumalloy (CCM), Stainless Steel (SS), Titanium, and Titanium-alloy (Ti-alloy) were evaluated. The changes in electron and photon fluences and dose perturbations due to the presence of the hip prostheses were investigated. Results: An increased dose of 13.29%, 13.77%, 6.16%, and 5.93% for 9 MeV and 30.43%, 33.05%, 10.89%, and 11.27% for 18 MV was calculated for Ti-alloy, Ti, CCM, and SS prosthesis, respectively. At 0.5 mm distance from the prosthesis, the Electron Backscatter Factor (EBF) of 1.31, 1.33, 1.15, and 1.14 for 9 MeV and 1.32, 1.34, 1.11, and 1.12 for 18 MV was calculated for Ti-alloy, Ti, CCM, and SS prosthesis, respectively. Dose perturbation is higher at a near distance from the prosthesis; by reducing the distance from the Ti-alloy prosthesis (1.5 to 0.5 mm), an increased dose of 7.70% and 5.54% resulted in 18 MV and 9 MeV, respectively. The dose decreases of up to 21% behind the hip prosthesis were calculated for 18 MV. Conclusion: It is essential to consider the dose perturbation due to the presence of a hip prosthesis to achieve the optimal treatment planning in radiotherapy. [ABSTRACT FROM AUTHOR]

Diode-pumped multi-mode graded-index (GRIN) fiber Raman lasers provide prominent brightness enhancement both in linear and half-open cavities with random distributed feedback via natural Rayleigh backscattering. Femtosecond laser-inscribed random refractive index structures allow for the sufficient reduction in the Raman threshold by means of Rayleigh backscattering signal enhancement by +50 + 66 dB relative to the intrinsic fiber level. At the same time, they offer an opportunity to generate Stokes beams with a shape close to fundamental transverse mode (LP01), as well as to select higher-order modes such as LP11 with a near-1D longitudinal random structure shifted off the fiber axis. Further development of the inscription technology includes the fabrication of 3D ring-shaped random structures using a spatial light modulator (SLM) in a 100/140 μm GRIN multi-mode fiber. This allows for the generation of a multi-mode diode-pumped GRIN fiber random Raman laser at 976 nm with a ring-shaped output beam at a relatively low pumping threshold (~160 W), demonstrated for the first time to our knowledge. [ABSTRACT FROM AUTHOR]

Meteor speed is crucial in identifying key astronomical aspects of the meteoroid environment, including the influx of meteoric material and the distribution of meteoric radiants. This study investigates diurnal and seasonal variations of meteor speed from April 2014 to December 2023 observed by the Mengcheng meteor radar (MCMR; 33.4°N, 116.3°E). In addition to the expected diurnal variation of meteor speed, azimuth peak, zenith peak, and the azimuthal direction of maximum meteor speed due to the Earth's rotation, where the meteor speed peaks northward in the local morning and shifts clockwise, we find that the meteor speed distribution resembles a superposition of two Gaussian distributions, with the lower (higher) distribution mainly ranging from 20 to 40 (45–65) km/s. The two speed peaks are estimated using a double‐Gaussian fitting approach. In terms of seasonal variation, we find that (a) the low‐speed peak indicates a semi‐annual variation cycle, with maxima in June–July and December–January, and minima in February and August; (b) the high‐speed peak indicates an annual variation cycle, with maxima in September–December and minima in March. There is also a correlation between the seasonal variations in the meteor speed peaks and the occurrence of meteor showers. Statistical analysis provides a map of seasonal variations in the intensity, duration, and timing of meteor shower activities, which is supplemental to previous shorter‐duration studies using backscatter meteor radar observations. We also find notable shower events where the meteor counts exceed 45%–97% of the background count on corresponding event dates and speeds. Plain Language Summary: Meteor speed plays a crucial role in understanding the quantity and distribution of meteoroids in our environment, yet there are limited observations and investigations conducted at mid‐latitudes. In this study, we utilized a meteor radar located in Mengcheng (in the northern lower middle latitudes) to investigate diurnal and seasonal variations in meteor speed from April 2014 to June 2023. Our findings revealed that meteor speed is generally faster in the morning and slower in the afternoon and evening, and the angle of arrival of meteors varies with local time. Additionally, we discovered that meteor speed exhibits two peaks, with the lower one at about 28 km/s and the higher one at 54 km/s. Seasonal changes indicated a semi‐annual variation cycle in the low‐speed peak and an annual variation cycle in the high‐speed peak. Furthermore, we observed several noteworthy meteor showers and their interannual variations. Key Points: The meteor speed peaks northward in the local morning and shifts clockwise to southward by local eveningMeteor speed distribution has two Gaussian peaks at ∼28 and ∼54 km/s, revealing semi‐annual and annual variation cycles respectivelyMajor meteor showers occur with 45%–97% higher counts than the background, and are associated with increases in the peak speeds [ABSTRACT FROM AUTHOR]

Accurate and precise KDP estimates are essential for radar-based applications, especially in quantitative precipitation estimation and radar data quality control routines. The accuracy of these estimates largely depends on the post-processing of the radar's measured Φ DP , which aims to reduce noise and backscattering effects while preserving fine-scale precipitation features. In this study, we evaluate the performance of several publicly available KDP estimation methods implemented in open-source libraries such as PyArt and Wradlib, and the method used in the Vaisala weather radars. To benchmark these methods, we employ a polarimetric self-consistency approach that relates KDP to reflectivity and differential reflectivity in rain, providing a reference self-consistency KDP (K DPSC) for comparison. This approach allows for the construction of the reference KDP observations that can be used to assess the accuracy and robustness of the studied KDP estimation methods. We assess each method by quantifying uncertainties using C-band weather radar observations where the reflectivity values ranged between 20 and 50 dBZ. Using the proposed evaluation framework we could define optimized parameter settings for the methods that have user-configurable parameters. Most of such methods showed significant reduction in the estimation errors after the optimization with respect to the default settings. We have found significant differences in the performances of the studied methods, where the best performing methods showed smaller normalized biases in the high reflectivity values (i.e., ≥ 40 dBZ) and overall smaller normalized root mean squared errors across the range of reflectivity values. [ABSTRACT FROM AUTHOR]

The established relationships between the size, shape, and terminal velocity of raindrops, along with the spheroidal shape approximation (SSA), are commonly employed for calculating radar observables in rain. This study, however, reveals the SSA's limitations in accurately simulating spectral and integrated backscattering polarimetric variables in rain at the W-band. Improving existing models is a complex task that demands high-precision data from both laboratory settings and natural rain, enhanced stochastic shape approximation techniques, and comprehensive scattering simulations. To circumvent these challenges, this study introduces a simpler and more straightforward approach – the empirical scattering model (ESM). The ESM is derived from an analysis of high-quality, low-turbulence Doppler spectra, which were selected from measurements taken with a 94 GHz radar at three different locations between 2021 and 2024. The ESM's primary advantages over the SSA include superior accuracy and the direct incorporation of microphysical effects observed in natural rain. This study demonstrates that the ESM can potentially clarify issues in existing retrieval and calibration methods that use polarimetric observations at the W-band. The findings of this study are not only valuable for experts in cloud radar polarimetry but also for scattering modelers and laboratory experimenters since explaining the presented observations necessitates a more profound understanding of the microphysical properties and processes in rain. [ABSTRACT FROM AUTHOR]

ABSTRACT The design and setup of a novel and simple backscatter Raman optical activity (ROA) spectrometer with incident light circular polarization (ICP) is presented, constructed from commercially available components. Incident light polarization is controlled using a combination of waveplates, compensating for unwanted birefringence and beam offsets. Realignment of the spectra in post‐processing reduced artifacts caused by spatial offsets. Spurious signals from achiral solvents like toluene and water are almost completely removed. The setup was validated by measuring references samples, including α‐pinene, carvone, and glucose in aqueous solution. The spectra show very good agreement with previously published results. [ABSTRACT FROM AUTHOR]

Populus euphratica is a unique constructive tree species within riparian desert areas that is essential for maintaining oasis ecosystem stability. The Tarim River Basin contains the most densely distributed population of P. euphratica forests in the world, and obtaining accurate distribution data in the mainstream of the Tarim River would provide important support for its protection and restoration. We propose a new method for automatically extracting P. euphratica using Sentinel-1 and 2 and Landsat-8 images based on the Google Earth Engine cloud platform and the random forest algorithm. A mask of the potential distribution area of P. euphratica was created based on prior knowledge to save computational resources. The NDVI (Normalized Difference Vegetation Index) time series was then reconstructed using the preferred filtering method to obtain phenological parameter features, and the random forest model was input by combining the phenological parameter, spectral index, textural, and backscattering features. An active learning method was employed to optimize the model and obtain the best model for extracting P. euphratica. Finally, the map of natural P. euphratica forests with a resolution of 10 m in the mainstream of the Tarim River was obtained. The overall accuracy, producer's accuracy, user's accuracy, kappa coefficient, and F1-score of the map were 0.96, 0.98, 0.95, 0.93, and 0.96, respectively. The comparison experiments showed that simultaneously adding backscattering and textural features improved the P. euphratica extraction accuracy, while textural features alone resulted in a poor extraction effect. The method developed in this study fully considered the prior and posteriori information and determined the feature set suitable for the P. euphratica identification task, which can be used to quickly obtain accurate large-area distribution data of P. euphratica. The method can also provide a reference for identifying other typical desert vegetation. [ABSTRACT FROM AUTHOR]

Data transmission is one of the critical factors in the future of the Internet of Things (IoT). The techniques of a reconfigurable intelligent surface (RIS) and backscatter communication (BackCom) are in need of a solution of realizing low-power sustainable transmission, which shows great potential in wireless communication. Hence, this paper introduces an RIS-based BackCom system, where the RIS receives energy from a base station (BS) and sends information by backscattering the signals from the BS. To maximize the sum rate of all IoT devices (IoTDs), we jointly optimized the time allocation, the RIS-reflecting phase shifts and the transmit power of the BS by exploiting an alternative optimization algorithm. The simulation results illustrate the effectiveness and the feasibility of the proposed wireless communication scheme and the proposed algorithm in IoT networks. [ABSTRACT FROM AUTHOR]

In order to achieve an effective balance between SAR image simulation fidelity and efficiency, we proposed a ray-tracing-assisted SAR image simulation method under range doppler (RD) imaging geometry. This method utilizes the spatial traversal mode of RD imaging geometry to transmit discrete electromagnetic (EM) waves into the SAR radiation area and follows the Nyquist sampling law to set the density of transmitted EM waves to effectively identify the beam radiation area. The ray-tracing algorithm is used to obtain the backscatter amplitude and real-time slant range of the transmitted EM wave, which can effectively record the multiple backscattering among the components of the distributed target so that the backscattering subfields of each component can be correlated. According to the RD condition equation, the backscattering amplitude is assigned to the corresponding range gate, and the three-dimensional (3D) target is mapped into the two-dimensional (2D) SAR slant-range coordinate system, and the SAR target simulated image is directly obtained. Finally, the simulation images of the proposed method are compared qualitatively and quantitatively with those obtained by commercial simulation software, and the effectiveness of the proposed method is verified. [ABSTRACT FROM AUTHOR]