Reflection Characteristics Research Articles

Dual adaptive differential threshold method for automated detection of faint and strong echo features in radar observations of winter storms

Abstract. Radar observations of winter storms often exhibit locally enhanced linear features in reflectivity, sometimes labeled as snow bands. We have developed a new, objective method for detecting locally enhanced echo features in radar data from winter storms. In comparison to convective cells in warm season precipitation, these features are usually less distinct from the background echo and often have more fuzzy or feathered edges. This technique identifies both prominent, strong features and more subtle, faint features. A key difference from previous radar reflectivity feature detection algorithms is the combined use of two adaptive differential thresholds, one that decreases with increasing background values and one that increases with increasing background values. The algorithm detects features within a snow rate field rather than reflectivity and incorporates an underestimate and overestimate of feature areas to account for uncertainties in the detection. We demonstrate the technique on several examples from the US National Weather Service operational radar network. The feature detection algorithm is highly customizable and can be tuned for a variety of data sets and applications.

Reflection and transmission characteristics of plane-P-wave at the interface of anisotropic nonlocal poroelastic and thermoelastic solid half-spaces

Reflection and transmission characteristics of plane-P-wave at the interface of anisotropic nonlocal poroelastic and thermoelastic solid half-spaces

Frequency selective surface with a bistable auxetic geometry

AbstractTwo bistable auxetic array geometries have been considered as FSS arrays of conducting elements. A square base form auxetic array with a combination of vertical and horizontal IT‐poles and a triangular one with three legged elements. Both of these have exhibited FSS reflection and transmission band characteristics with close band ratios.

Pattern reconfigurable mm‐Wave leaky‐wave antenna array using contactless excitation

AbstractA novel contactless excitation method for leaky‐wave antennas (LWAs) is proposed based on near‐field coupling between a physically disconnected input feed section and input ports of LWAs. Periodic slot‐pairs in substrate‐integrated waveguides are used to implement a plurality of planar LWAs in the Ka‐band, where contactless excitation allows switching of the input port along an antenna array without any mechanical disconnection and reconnection of coaxial connectors, thereby opening the path for mechanical switching‐based pattern reconfiguration. To demonstrate the proposed principle of contactless excitation, prototypes are shown with detailed reflection characteristics and radiation pattern measurements.

Microwave reflective properties of core-shell FeNX@C/Fe4N composite

Abstract To improve the electromagnetic properties of iron nitride, the core-shell FeNX@C/Fe4N composite material was designed by microwave plasma technique. Within the frequency range of 2-18 GHz, the microwave reflective characteristics of the novel composites mixed with 50% wax were examined. The composition of the core-shell FeNX@C was analyzed by XRD, Raman, and TEM, and the complex permeability and complex permittivity with frequency change were discussed. The results show that the RLmin value (RLmin=-55.1 dB) of FeNx@C/Fe4N composite appears at 17.8 GHz with a thickness of 1.5 mm, and the RLmin value reaches -42.1 dB at the thickness of 3.5 mm corresponding to 6.6 GHz. This work demonstrates the potential prospects for the application of microwave absorbers in the range of 2-18 GHz.

Effect of different surface alignment layers and temperature changes on bandwidth of Bragg reflection in chiral nematic liquid crystal

In recent years, the practical properties of cholesteric liquid crystals (CLCs) have been widely studied due to their unique feature of selective Bragg reflection. In this study, we investigated the following aspects: (i) the effect of surface alignment using polyvinyl alcohol, polyamide, and polyimide as covering substrate, (ii) the impact of temperature changes on the reflection bandwidth and, consequently, variations in the cholesteric pitch. Furthermore, we extended Li’s four-parameter model to the cholesteric environment using Haller’s assumption and Vuk’s equations for nematic liquid crystals (NLCs) and Fergason’s theory for CLCs. The fit of the experimental data with this model demonstrated an excellent agreement. The experimental data revealed that the S5011 chiral dopant, with left-handedness, used in the NLC environment of the host, exhibits a significant helical twist power (HTP). This leads to the narrowing of the reflection band width with increasing temperature, without causing a noticeable change in the wavelength of the central reflection. This feature highlights the high potential of these types of chiral materials as thermally stable materials for creating selective-reflective optical filters that remain stable with temperature changes, particularly away from the cholesteric to isotropic transition point.

Synergizing theory and experiment: Enhancing solar distillation performance with external reflector in a passive 4-stage model

Passive multi-stage solar distillers are pivotal in sustainable water purification, effectively utilizing solar energy. This study addresses the underexplored impact of reflective characteristics by integrating an aluminum reflector with radiation-trapping properties into a passive 4-stage solar distiller leveraging both experimental and theoretical methodologies. The influence of reflector height and angle on solar input, water production rate, and the Gain Output Ratio (GOR) was examined. Findings revealed a water production rate of 5.98 kg∙m−2hr−1and a GOR enhancement to 156 % at an optimal reflector setup of 40 mm height and 120° angle. Theoretical analysis assessed heat distribution and thermal efficiency across various air gaps and solar radiation levels. Evaporation emerged as the dominant heat mechanism, achieving 91 % thermal efficiency in the first stage with a 6.5 mm air gap and 1.50 kW∙m−2 of reflected solar radiation. Conversely, a 16 mm gap significantly lowered efficiency to 72 % in the last stage due to increased lateral heat loss. Transient analysis of the newly defined dissipation percent showed that narrower air gaps boosted heat retention in the distiller for evaporation and greater heat dissipation through the last stage, optimizing heat recycling for thermal applications. Increasing the solar input leads to sustained dissipation capacity.

An asymmetric road lighting concept: Probeam

An asymmetric road lighting concept known as Probeam is investigated in this study for energy efficiency, contrast and visibility of vertical objects and road markings in highway lighting. Calculations based on road lighting standards, road surface and markings reflection characteristics and typical Dutch highway geometry, reveal that Probeam lighting improves the average visibility of objects and road markings over symmetrical lighting, however, with a 14% increase in luminous flux as per current road lighting standards. This increase in luminous flux is attributed to the symmetrical lighting’s advantage in specular road surface reflection, leading to a reduction in the Counterbeam lobe size in the light intensity distribution when designed to meet the current road luminance requirement. Notably, by designing the Probeam luminaire to match symmetrical lighting’s average visibility of vertical objects, for removing the road luminance requirement and dimming the luminaire, energy consumption is reduced by 52%. Halving the Probeam luminaire’s mounting height leads to an impressive 82% energy savings. The study highlights the possibility of a balance in energy use and road safety using the Probeam concept, considering advancements in road luminaires and retroreflective materials. Due to glare, the relevance of the proposed Probeam concept is restricted to one-directional traffic on highways.

Hyperspectral remote sensing of forage stoichiometric ratios in the senescent stage of alpine grasslands

Senescence is an important phenological stage in the life cycle of grassland plants, and estimating grass senescence in alpine grasslands is particularly crucial for animal husbandry and grazing the utilization of grassland resources for grazing. However, the application of proximal sensing technologies to capture the variations in forage growth parameters in the senescent stage, especially regarding some key stoichiometric ratios, still faces challenges associated with indiscernible spectral properties and indeterminate absorption and reflectance features. The present study aims to demonstrate the potential and effectiveness of applying hyperspectral data to assess the forage carbon-nitrogen (C:N) ratio and calcium-phosphorus (Ca:P) ratio during the senescent stage (September to November). A progressive variable dimensionality reduction strategy based on a genetic algorithm (GA) and hybrid optimization method (ant optimization colony (ACO) and extreme learning machine (ELM)) coupled with multiple linear and nonlinear statistical methods is applied to develop C:N ratio and Ca:P ratio estimation models via combination with data from 205 sample sites collected from six field campaigns (2016–2019) on the eastern Tibetan Plateau. The results show that the important spectral bands favorable for forage C:N ratio and Ca:P ratio retrieval are generally in the red and shortwave infrared (SWIR) regions, and the proposed model presents satisfactory performance in the estimation of the forage C:N ratio (V-R2 = 0.81, V-RMSE = 6.44) and Ca:P ratio (V-R2 = 0.64, V-RMSE = 2.54) during senescence. Moreover, the model can effectively overcome the spatial differences among sampling areas and perform optimally in capturing the variations in the forage C:N ratio and Ca:P ratio in the early and middle stages of senescence. Overall, our study demonstrates that it is feasible and promising to estimate these stoichiometric ratios using hyperspectral feature bands during grass senescence at the canopy level, with potential applications that may further enhance the monitoring of forage quality and quantity.

Design and Application of Bionic Camouflage Materials Simulating Spectral Reflection Characteristics of Plants: A Review

Hyperspectral remote sensing (RS) has rapidly developed in recent years and has been widely used in the military field. This technology not only brings huge opportunities for military reconnaissance but also poses unprecedented challenges to military camouflage, severely complicating the development of plant hyperspectral camouflage materials and technology. In this review, the spectral reflectance characteristics of plants and the application of hyperspectral RS in plant RS and military operations are reviewed. The development status of bionic camouflage materials that simulate the spectral reflection characteristics of plants is analyzed. With the existing hyperspectral camouflage materials and technology, bionic camouflage technology is limited by the inability of bionic materials to accurately imitate the characteristic absorption peaks of green vegetation, low stability and durability, and the large overall material thickness, which complicate actual large-scale application. On this basis, a future development direction and a trend of plant hyperspectral bionic camouflage materials and technology are proposed.

Fast-track development of an automated solar photovoltaic module detecting framework utilizing open-access multispectral satellite imagery

The southwest coast of Taiwan is an important habitat for migratory waterbirds. However, the use of fossil fuels has led to climate crises. As society's awareness of environmental issues increases, renewable energy including solar power has become an irreplaceable choice. Monitoring the spread of solar photovoltaic (PV) to mitigate its ecological impact has become an important task. Yet, acquiring information related to the geographic information of this renewable energy is often challenging. Remote sensing techniques for identifying the distribution of solar PV modules have been extensively discussed and published in recent years. However, the use of high-resolution imagery, powerful computational hardware, or high-precision but technically challenging frameworks, particularly in terms of computational costs, hinders the rapid updating and dissemination of information on solar PV distribution. The aim of this study is to rapidly develop a PVs detecting framework. To do so, by utilizing the spectral reflectance characteristics of PV modules, along with open-access Sentinel-2 satellite datasets, we selected false color images derived from Bands 8 (842 nm), 11 (1,610 nm), and 12 (2,190 nm). With the foundation of ArcGIS and the U-Net deep learning architecture, we developed a framework with low training costs, simple data processing, and short training time. Through syntheses of false color with different combinations of spectral bands, we achieved a PVs detecting framework with 94.5% accuracy, 0.94 F1 score, and 0.89 Kappa in aquaculture landscape. In our application in the southwest coast region, the overall accuracy reached 96%, with a 0.92 F1 score and 0.9 Kappa performance. This framework will facilitate the rapid monitoring of the spatial and temporal distribution of PV in Taiwan, accelerate social communication, and alleviate ecological impacts.

Impact of cellular structure on the thickness and light reflection properties of structural color layers on diverse wood surfaces

ABSTRACT This study employed microsphere self-assembly to fabricate structural color layers on surfaces of seven woods. The wood cell structure, thickness of structural color layers, and optical reflection characteristics were analyzed. It was found that the main reflection wavelengths of structural color layers were all located at 490–500 nm. However, differences were observed in the reflection curves, as the thickness of structural color layers affected the width of reflection peak and the background reflection intensity. The water transport cells on wood surface are vessels in hardwood and tracheids in softwood. When they have larger diameters, higher numbers, and better internal patency, they can transport the emulsion, resulting in overflow and seepage. This reduced the number of microspheres, and led to thinner structural color layers with flatter and lower reflection peaks. The theoretical thickness of structural color layers were also calculated. By comparing the theoretical thickness of the structural color layers in two different crystal forms with the measured thickness, the influence of microsphere filling in vessels/tracheids and emulsion overflow on the thickness and optical reflection characteristics of the structural color layer was verified. This provides support for the development of controllable construction for structural color layers suitable for different woods.

Pharo: A reflective language—Analyzing the reflective API and its internal dependencies

Reflective operations are powerful APIs (Application Programming Interface) that let developers build advanced tools and architectures. Reflective operations are used for implementing tools and development environments (e.g., compilers, debuggers, inspectors) or language features (e.g., distributed systems, exceptions, proxies, aspect-oriented programming). In addition, languages are evolving, introducing better concepts, and revising practices and APIs. Since 2008 Pharo has evolved from Squeak and its reflective API has evolved accordingly, diverging consequently from the original Smalltalk reflective API. With more than 500 reflective methods identified, Pharo has one of the largest reflective feature sets ranging from structural reflection to on-demand stack reification. Those operations are often built on top of the other, creating different layers of reflective operations, from low-level to high-level ones.There is a need to understand the current reflective APIs to understand their underlying use, potential dependencies, and whether some reflective features can be scoped and optional. Such an analysis is challenged by new metaobjects organically introduced in the system, such as first-class instance variables, and their mixture with the base-level API of objects and classes.In this article, we analyze the reflective operations used in Pharo 12 and their interdependencies. We propose a classification based on their semantics and we identify a set of issues of the current implementation. Such an analysis of reflective operations in Pharo is important to support the revision of the reflective layer and its potential redesign.

Multistage microcellular waterborne polyurethane composite with optionally low-reflection behavior for ultra-efficient electromagnetic interference shielding

Electromagnetic interference (EMI) shielding materials with superior shielding efficiency and low-reflection properties hold promising potential for utilization across electronic components, precision instruments, and fifth-generation communication equipment. In this study, multistage microcellular waterborne polyurethane (WPU) composites were constructed via gradient induction, layer-by-layer casting, and supercritical carbon dioxide foaming. The gradient-structured WPU/iron-cobalt loaded reduced graphene oxide (FeCo@rGO) foam serves as an impedance-matched absorption layer, while the highly conductive WPU/silver loaded glass microspheres (Ag@GM) layer is employed as a reflection layer. Thanks to the incorporation of an asymmetric structure, as well as the introduction of gradient and porous configurations, the composite foam demonstrates excellent conductivity, outstanding EMI SE (74.9 dB), and minimal reflection characteristics (35.28 %) in 8.2–12.4 GHz, implying that more than 99.99999 % of electromagnetic (EM) waves were blocked and only 35.28 % were reflected to the external environment. Interestingly, the reflectivity of the composite foam is reduced to 0.41 % at 10.88 GHz due to the resonance for incident and reflected EM waves. Beyond that, the composite foam is characterized by low density (0.47 g/cm3) and great stability of EMI shielding properties. This work offers a viable approach for crafting lightweight, highly shielding, and minimally reflective EMI shielding composites.

BRDF-Based Photometric Modeling of LEO Constellation Satellite from Massive Observations

BRDF-Based Photometric Modeling of LEO Constellation Satellite from Massive Observations

Polymer-based cascaded waveguide Bragg grating for blood glucose sensing.

Waveguide Bragg grating (WBG) blood glucose sensing, as a biological sensing technology with broad application prospects, plays an important role in the fields of health management and medical treatment. In this work, a polymer-based cascaded WBG is applied to glucose detection. We investigated photonic devices with two different grating structures cascaded-a crossed grating and a bilateral grating-and analyzed the effects of the crossed grating period, bilateral grating period, and number of grating periods on the sensing performance of the glucose sensor. Finally, the spectral reflectance characteristics, response time, and sensing specificity of the cascaded WBG were evaluated. The experimental results showed that the glucose sensor has a sensitivity of 175 nm/RIU in a glucose concentration range of 0-2 mg/ml and has the advantages of high integration, a narrow bandwidth, and low cost.

Experimental research on the reflection and response characteristics of pressure pulse waves for different gas pipeline blockage materials

AbstractNatural gas pipelines are exposed to complex production and transportation environments, leading to blockages of varying compositions and forms due to various factors. This paper proposes a pressure pulsing wave‐based pipe blockage detection method, and a series of pipeline blockage detection experiments of different materials are carried out, including hydrate blockage, ice blockage, paraffin blockage, and water blockage. Through the blockage detection calculation theory and the reflection and transmission characteristics during pressure wave emission, the blockage position, length, and section blockage rate under different blockage materials are obtained, and the influence of different blockage materials on the reflection and transmission signal characteristics of the pressure pulse wave is analyzed. The results show that the solid blocking material does not noticeably impact the reflectivity and reflective properties of pressure waves, and different cross‐sectional shapes have a noticeable impact on the reflectivity of the pressure wave. The reflected wave waveform of the liquid blockage material is visible but irregular. The average error of blockage location is 0.78%.

Janus structure design of polyimide composite foam for absorption-dominated EMI shielding and thermal insulation

In the present work, by virtue of the synergistic and independent effects of Janus structure, an asymmetric nickel-chain/multiwall carbon nanotube/polyimide (Ni/MWCNTs/PI) composite foam with absorption-dominated electromagnetic interference (EMI) shielding and thermal insulation performances was successfully fabricated through an ordered casting and directional freeze-drying strategy. Water-soluble polyamic acid (PAA) was chosen to match the oriented freeze-drying method to acquire oriented pores, and the thermal imidization process from PAA to PI exactly eliminated the interface of the multilayered structure. By controlling the electro-magnetic gradient and propagation path of the incident microwaves in the MWCNT/PI and Ni/PI layers, the PI composite foam exhibited an efficient EMI SE of 55.8 dB in the X-band with extremely low reflection characteristics (R = 0.22). The asymmetric conductive network also greatly preserved the thermal insulation properties of PI. The thermal conductivity (TC) of the Ni/MWCNT/PI composite foam was as low as 0.032 W/(m K). In addition, owing to the elimination of MWCNT/PI and Ni/PI interfaces during the thermal imidization process, the composite foam showed satisfactory compressive strength. The fabricated PI composite foam could provide reliable electromagnetic protection in complex applications and withstand high temperatures, which has great potential in cutting-edge applications such as advanced aircraft.

Effect of Surface Functional Groups on the Electronic Behavior and Optical Spectra of Mn2N Based MXenes.

The extensive applications of MXenes, a novel type of layered materials known for their favorable characteristics, have sparked significant interest. This research focuses on investigating the influence of surface functionalization on the behavior of Mn2NTx (Tx=O2, F2) MXenes monolayers using the "Density functional theory (DFT) based full-potential linearized augmented-plane-wave (FP-LAPW)" method. We elucidate the differences in the physical properties of Mn2NTx through the influence of F and O surface functional groups. We found that O-termination results in half-metallic behavior, whereas the F-termination evolves metallic characteristics within these MXene systems. Similarly, surface termination has effectively influenced their optical absorption efficiency. For instance, Mn2NO2 and Mn2NF2 effectively absorb UV light ~50.15×104 cm-1 and 37.71×104 cm-1, respectively. Additionally, they demonstrated prominent refraction and reflection characteristics, which are comprehensively discussed in the present work. Our predictions offer valuable perspectives into the optical and electronic characteristics of Mn2NTx-based MXenes, presenting the promising potential for implementing them in diverse optoelectronic devices.

Morphology reconstruction and defect detection of holes inner surface based on reflection characteristics

A reconstruction method is proposed based on the reflection characteristics to measure the defect profile and depth of the inner surface of the hole. In addition to capturing geometric information of the scene, this method decomposes the distortion in the endoscope image into circumferential and axial distortions, thereby improving correction accuracy and enabling accurate measurement of the defect contour. The bidirectional reflection distribution function (BRDF) is established based on reflection characteristic theory, allowing for mapping between image brightness and normal declination. By accumulating tangent values of normal deflection angles, the height of axial contour lines inside the hole can be reconstructed to achieve defect shape reconstruction and depth measurement. This approach overcomes convex-concave ambiguity in shape from shading (SFS), as demonstrated by experimental results. The proposed detection method offers equipment versatility and high measurement efficiency, making it suitable for machine vision-based detection of internal surface defects in holes.