Shadow Area Research Articles

Urban skies safeguarded: innovative drone detection with programmable metasurface periscope

Programmable metasurfaces (PMSs) exhibit great potentials in target detection techniques, because they can take actions to change channel propagation characteristics which introduces further degrees of freedom for system optimizations. However, responses of most traditional PMSs are sensitive to incident angles of impinging electromagnetic waves, resulting in a failure of angular estimation to dynamic targets coming from different directions. Herein, by proposing a fully resonant structure and introducing a mode-alignment technology, we report an isotropic angle-insensitive PMS whose phase response is stable with respect to different incident angles in both elevation- and azimuth-planes. A radar scheme that uses such a PMS as a periscope is also demonstrated, to detect drones in a non-line-of-sight (N-LOS) scenario which usually happens in an urban environment. Our proposed scheme enables those targets even falling in shadow areas caused by high buildings to be successfully detected and tracked, which shows promising potentials in N-LOS target detections.

RIS-assisted differential transmitted spatial modulation design

In this paper, we propose a novel reconfigurable intelligent surface (RIS)-assisted wireless communication design called the RIS-assisted differential transmitted spatial modulation (DTSM) scheme. The encoding process of the differential spatial modulation (DSM) is integrated into the DTSM scheme, where only one transmit antenna is activated per time slot to transmit the M-ary phase shift keying (PSK) modulation symbol through the RIS. Due to the detection characteristics of DSM, the bit error rate (BER) performance remains satisfactory without requiring channel state information estimation, thereby enhancing robustness. The RIS application in the proposed scheme mitigates the effects of shadow area fading by adjusting the phase of the reflected signals to improve the signal-to-noise ratio at the receiver. In simulation results by comparing to other RIS-assisted spatial modulation schemes, we can find that the proposed DTSM scheme demonstrates good BER performance across various scenarios, including Nakagami-m fading, which also indicates its potential for practical applications.

Image shadow removal via multi-scale deep Retinex decomposition

In recent years, deep learning has emerged as an important tool for image shadow removal. However, existing methods often prioritize shadow detection and, in doing so, they oversimplify the lighting conditions of shadow regions. Furthermore, these methods neglect cues from the overall image lighting when re-lighting shadow areas, thereby failing to ensure global lighting consistency. To address these challenges in images captured under complex lighting conditions, this paper introduces a multi-scale network built on a Retinex decomposition model. The proposed approach effectively senses shadows with uneven lighting and re-light them, achieving greater consistency along shadow boundaries. Furthermore, for the design of network, we introduce several techniques for boosting shadow removal performance, including a shadow-aware channel attention module, local discriminative and Retinex decomposition loss functions, and a multi-scale mechanism for guiding Retinex decomposition by concurrently capturing both fine-grained details and large-scale contextual information. Experimental results demonstrate the superiority of our proposed method over existing solutions, particularly for images taken under complex lighting conditions.

A Shadow Imaging Bilinear Model and Three-Branch Residual Network for Shadow Removal.

The current shadow removal pipeline relies on the detected shadow masks, which have limitations for penumbras and tiny shadows, and results in an excessively long pipeline. To address these issues, we propose a shadow imaging bilinear model and design a novel three-branch residual (TBR) network for shadow removal. Our bilinear model reveals the single-image shadow removal process and can explain why simply increasing the brightness of shadow areas cannot remove shadows without artifacts. We considerably shorten the shadow removal pipeline by modeling illumination compensation and developing a single-stage shadow removal network without additional detection and refinement networks. Specifically, our network consists of three task branches, i.e., shadow image reconstruction, shadow matte estimation, and shadow removal. To merge these three branches and enhance the shadow removal branch, we design a model-based TBR module. Multiple TBR modules are cascaded to generate an intensive information flow and facilitate feature integration among the three branches. Thus, our network ensures the fidelity of nonshadow areas and restores the light intensity of shadow areas through three-branch collaboration. Extensive experiments demonstrate that our method outperforms the state-of-the-art methods. The model and code are available at https://github.com/nachifur/TBRNet.

Shoreline Behavior in Response to Coastal Structures: A Case Study in Haikou Bay, China

The rapid development of coastal structures on sandy coastlines raises concerns about their impacts on the shoreline’s evolution and the sediment transport dynamics. This study utilized a numerical modeling approach to simulate the multi-year response of Haikou Bay’s coastline to various nearshore structures, including piers and a large artificial island. The LITLINE module of the MIKE21 (v2020) software was employed to analyze the sediment transport patterns across three distinct coastal segments. The simulation results indicated that the sediment transport directions varied significantly: from west to east in the western segment, from east to west in the middle segment, and convergence toward the center in the eastern segment, divided by a construction trestle. The net sediment transport rates were quantified as 2000 m3/year for the western segment, 8000 m3/year for the middle segment, and 13,000 m3/year (west) and 10,000 m3/year (east) for the eastern segment. Due to the conflicting sediment transport directions on each side of the breakwater, noticeable deposition occurred on both sides. The presence of the artificial island created notable deposition in its wave shadow area, while the overall impact on the shoreline changes diminished over time. These findings underscore the significant influence of human activities, particularly coastal structures, on the natural evolution of shorelines.

Gaussian in the Dark: Real‐Time View Synthesis From Inconsistent Dark Images Using Gaussian Splatting

Abstract3D Gaussian Splatting has recently emerged as a powerful representation that can synthesize remarkable novel views using consistent multi‐view images as input. However, we notice that images captured in dark environments where the scenes are not fully illuminated can exhibit considerable brightness variations and multi‐view inconsistency, which poses great challenges to 3D Gaussian Splatting and severely degrades its performance. To tackle this problem, we propose Gaussian‐DK. Observing that inconsistencies are mainly caused by camera imaging, we represent a consistent radiance field of the physical world using a set of anisotropic 3D Gaussians, and design a camera response module to compensate for multi‐view inconsistencies. We also introduce a step‐based gradient scaling strategy to constrain Gaussians near the camera, which turn out to be floaters, from splitting and cloning. Experiments on our proposed benchmark dataset demonstrate that Gaussian‐DK produces high‐quality renderings without ghosting and floater artifacts and significantly outperforms existing methods. Furthermore, we can also synthesize light‐up images by controlling exposure levels that clearly show details in shadow areas.

Automated Cloud Shadow Detection from Satellite Orthoimages with Uncorrected Cloud Relief Displacements

Clouds and their shadows significantly affect satellite imagery, resulting in a loss of radiometric information in the shadowed areas. This loss reduces the accuracy of land cover classification and object detection. Among various cloud shadow detection methods, the geometric-based method relies on the geometry of the sun and sensor to provide consistent results across diverse environments, ensuring better interpretability and reliability. It is well known that the direction of shadows in raw satellite images depends on the sun’s illumination and sensor viewing direction. Orthoimages are typically corrected for relief displacements caused by oblique sensor viewing, aligning the shadow direction with the sun. However, previous studies lacked an explicit experimental verification of this alignment, particularly for cloud shadows. We observed that this implication may not be realized for cloud shadows, primarily due to the unknown height of clouds. To verify this, we used Rapideye orthoimages acquired in various viewing azimuth and zenith angles and conducted experiments under two different cases: the first where the cloud shadow direction was estimated based only on the sun’s illumination, and the second where both the sun’s illumination and the sensor’s viewing direction were considered. Building on this, we propose an automated approach for cloud shadow detection. Our experiments demonstrated that the second case, which incorporates the sensor’s geometry, calculates a more accurate cloud shadow direction compared to the true angle. Although the angles in nadir images were similar, the second case in high-oblique images showed a difference of less than 4.0° from the true angle, whereas the first case exhibited a much larger difference, up to 21.3°. The accuracy results revealed that shadow detection using the angle from the second case improved the average F1 score by 0.17 and increased the average detection rate by 7.7% compared to the first case. This result confirms that, even if the relief displacement of clouds is not corrected in the orthoimages, the proposed method allows for more accurate cloud shadow detection. Our main contributions are in providing quantitative evidence through experiments for the application of sensor geometry and establishing a solid foundation for handling complex scenarios. This approach has the potential to extend to the detection of shadows in high-resolution satellite imagery or UAV images, as well as objects like high-rise buildings. Future research will focus on this.

Simulation of lunar soil compressive strength performance test based on grey correlation analysis

Detecting water ice in the permanent shadow area of the lunar south pole is an important task of China's Chang'e-7. For this purpose, a simulation study was carried out under the earth environment, and a test sample of polar water-containing simulated lunar soil was prepared. The mechanical properties of the lunar soil simulant were tested under ultra-low temperature conditions, and the changes in water content, relative density, temperature, loading rate, and base material ratio with compressive strength were analyzed. The results show that the compressive strength of the frozen lunar soil simulant increases with the increase of water content, increases with the increase of density, and increases with the decrease of temperature. It is less affected by the change of loading rate. The order of compressive strength affected by different base material ratios is: 100%anorthosite, <90%anorthosite, +10%basalt <70%, +30%anorthosite <100%, basalt, lunar soil simulant. Finally, the correlation between the basic physical properties of lunar soil simulant such as water content, relative density, temperature, loading rate, and ratio and compressive strength is explored through grey correlation analysis. The correlation order is: water content> density> temperature> ratio> loading rate. This paper prepared and tested the mechanical properties of hydrated lunar soil, and proposed a more systematic and standardized implementation plan. It serves as the basis for studying the properties of hydrated lunar soil in the polar region, and provides a theoretical basis and reference for subsequent lunar soil simulation research.

A higher shadow ratio of the living environment on the remote sensing digital image is possibly protective for adolescent myopia

This study aims to assess how the construction patterns within residential communities influence the adolescent myopia using general survey. In a private high school from a megacity in mid-west China, a questionnaire gathered data on the 10th-grade students’ level of myopia, home address, and some potential confounding factors. Additionally, satellite digital images were utilized to calculate the proportion of shadow area (PSA) and the proportion of greenness area (PGA) within a 500 m×500 m area centered on each student’s home address. Correlations between myopia levels and PSA, along with other variables, were analyzed. The prevalence of mild, moderate, and high myopia were 39.2%, 32.5%, and 8.3%, respectively. A negative correlation was observed between myopia levels and PSA, albeit marginally significant (r=-0.189*, P = 0.05). Upon dividing the sample into higher and lower PSA groups using a cut-off point of 20%, a significant difference in myopia levels was evident (χ2 = 8.361, P = 0.038), while other confounding factors remained comparable. In conclusion, high-rise apartment constructions, which often cast more shadows on digital satellite maps, may not exacerbate myopia progression. Instead, they could potentially serve as a protective factor against adolescent myopia in densely populated megacities, as they allow for more ground space allocation.

Angle-dependent ion-beam etching of RuAl thin films for structuring GHz-frequency electronics

The ruthenium aluminide (RuAl) alloy is a promising electrode material for wireless surface acoustic wave sensors working under harsh conditions at high temperatures. However, during the structuring of RuAl thin films using ion-beam etching, etched material can redeposit at the edges of the electrodes and form objects, so-called fences, on top of the structured features. These decrease the high-temperature stability and lead to an undesired alteration of the sensor performance. In this work, the angle-dependent ion-beam etching of RuAl thin films was investigated to inhibit the formation of such fence structures. The etch rate was determined as a function of the etching angle between ion-beam and sample surface in a range between 90° and 40°. Furthermore, finger structures with pitches below 500 nm, which are required for devices working in the intended GHz regime, were patterned to study the influence of the etching angle on the profile of the RuAl electrode fingers using transmission electron microscopy and energy-dispersive x-ray spectroscopy. The results show that an etching angle of 50° results in the highest etch rate. For etching angles of 50° and below, the width of the fences is reduced below 10 nm, so they break off during standard resist removal procedures. Such low etching angles lead to shadowed areas on the side of structured features in which unetched material remains. However, this material can be removed by using a two-step etching process combining a 50° step with a 90° step. This process is capable of structuring fence-free trapezoidal-shaped electrode finger profiles. Therefore, the developed process is well suited for the fabrication of high-temperature GHz-frequency RuAl electrodes.

Silicon nitride shadowed selective area growth of low defect density vertical GaN mesas via plasma-assisted molecular beam epitaxy

Ion bombardment during inductively coupled plasma reactive-ion etching and ion-implantation introduces irreparable crystalline damage to gallium nitride (GaN) power devices, leading to early breakdown and high leakage current. To circumvent this, a bi-layer selective area growth mask was engineered to grow up to 3.0 µm thick epitaxy of GaN using plasma-assisted molecular beam epitaxy as an ion-damage-free alternative to standard epitaxial processing routes. The masks and regrown architectures are characterized via SEM, conductive-atomic force microscopy (AFM), x-ray photo electron spectroscopy, Raman, and cathodoluminescence. Mask deposition conditions were varied to modulate and minimize the stress induced during thermal cycling. The resulting mesas exhibit low leakage, attributed to naturally terminated sidewalls as measured by an innovative perpendicular AFM measurement of the regrown sidewall. The regrown sidewall exhibited RMS (root mean square) roughness of 1.50 (±0.34) nm and defect density of 1.36 × 106 (±1.11 × 106) cm−2. This work provides a method to eliminate defect-inducing steps from GaN vertical epitaxial processing and stands to enhance GaN as a material platform for high-efficiency power devices.

Double-Exposure Algorithm: A Powerful Approach to Address the Accuracy Issues of Fractional Vegetation Extraction under Shadow Conditions

When recording the vegetation distribution with a camera, shadows can form due to factors like camera angle and direct sunlight. These shadows result in the loss of pixel information and texture details, significantly reducing the accuracy of fractional vegetation coverage (FVC) extraction. To address this issue, this study proposes an efficient double-exposure algorithm. The method reconstructs the pixel information in shadow areas by fusing normal-exposure and overexposed images. This approach overcomes the limitations of the camera’s dynamic range in capturing pixel information in shadowed regions. The study evaluates images with five levels of overexposure combined with five vegetation extraction indices. The aim is to determine the best-performing double-exposure combination under shadow conditions and the most suitable vegetation index. Experimental results reveal that the R² value between the best vegetation index and the FVC calculated from the fused double-exposure images and the ground truth FVC increases from 0.750 to 0.969. The root mean square error (RMSE) reduces from 0.146 to 0.046, and the intersection over union (IOU) increases from 0.856 to 0.943. These results demonstrate the excellent vegetation extraction capability of the double-exposure algorithm under shadow conditions, offering a straightforward and effective solution to low accuracy of FVC in shadowed areas.

Thermal Environments of Residential Areas: Sunlight and Building Shadow in a Chinese City with Hot and Humid Summers

With a primary focus on sunlight and building shadows, we studied the impact of residential building orientation angles, building heights, and area combinations, as well as the underlying surface materials, on the outdoor thermal environment in Changsha, a city located north of the Tropic of Cancer. On the basis of Changsha’s regulations, the research results indicate that building orientation angles of 15–45° and 315–345° can generate more building-shadow areas and have a better effect on improving the outdoor thermal environment. Based on the study of many common residential block building layouts in Changsha, we believe that, for point-pattern residential blocks, an increase in building lengths can be very effective for increasing building-shadow areas and thermal comfort. For row-pattern residential blocks, an increase in building heights can be regarded as more effective for increasing building-shadow areas and reducing air temperatures. Shadow areas formed on impervious surface material areas, such as concrete pavements, reduce the air temperature more than shadow areas formed on natural surfaces, such as grasslands. For the planning and regeneration of residential areas, urban planners should focus on placing more green spaces in areas which are seldom or never covered by building shadows; they should also focus on installing more impervious surfaces in areas covered by building shadows. These strategies are beneficial for making full use of building shadows to reduce air temperatures in residential areas.

The Infinite Corridor.

Description This photograph was chosen as a visual representation of the poem "Theory of a Well Mind" to capture the essence of the poem's exploration of the human psyche and the journey toward mental wellness. The corridor, with its repeating arches and vanishing point, symbolizes the cyclical nature of thoughts, emotions, and actions that the poem delves into. Just as the corridor seems to stretch into infinity, the poem reflects on the seemingly endless and challenging process of personal growth and self-discovery. The contrast between light and shadow within the image mirrors the poem's themes of introspection, uncertainty, and the pursuit of clarity amidst the complexities of the mind. The light that filters through the arches and windows represents moments of insight and hope, while the shadowed areas evoke the difficulties and unknowns that one encounters on the path to wellness.

Exploring perfect fluid dark matter with EHT results of Sgr A* through rotating 4D-EGB black holes

We investigate the rotating 4D Gauss–Bonnet (GB) black holes surrounded by Perfect Fluid Dark Matter (PFDM) using the Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*). This rotating black hole, influenced by an additional GB parameter α and a DM parameter β, deviates from the Kerr black hole geometry, offering a more complex horizon structure. Our findings reveal that the shadow size decreases and oblateness increases with higher values of α, β, and the spin parameter a. By plotting the shadow area A and oblateness D as functions of α and β for various a values, we determine the unique black hole parameters through the intersection points of the A and D curves. We constrain the GB and DM parameters with the EHT shadow observational results of Sgr A* for an inclination angle of 90° and 50°. The results, which align with EHT observations of Sgr A*, suggest that dark matter may exist in significant quantities around the galactic centre, challenging the traditional Kerr black hole model and offering new avenues for understanding complex interactions. Thus, It is essential to consider that rotating 4D GB black holes surrounded by PFDM could be strong candidates for astrophysical black holes.

Increasing the Beam Width and Intensity with Refraction Power Effect Using a Combination of Beam Mirrors and Concave Mirrors for Surgical-Fluorescence-Emission-Guided Cancer Monitoring Method.

The primary goal during cancer removal surgery is to completely excise the malignant tumor. Because the color of the tumor and surrounding tissues is very similar, it is difficult to observe with the naked eye, posing a risk of damaging surrounding blood vessels during the tumor removal process. Therefore, fluorescence emission is induced using a fluorescent contrast agent, and color classification is monitored through camera imaging. LEDs must be irradiated to generate the fluorescent emission electromotive force. However, the power and beam width of the LED are insufficient to generate this force effectively, so the beam width and intensity must be increased to irradiate the entire lesion. Additionally, there should be no shaded areas in the beam irradiation range. This paper proposes a method to enhance the beam width and intensity while eliminating shadow areas. A total reflection beam mirror was used to increase beam width and intensity. However, when the beam width increased, a shadow area appeared at the edge, limiting irradiation of the entire lesion. To compensate for this shadow area, a concave lens was combined with the beam mirror, resulting in an increase in beam width and intensity by more than 1.42 times and 18.6 times, respectively. Consequently, the beam width reached 111.8°, and the beam power was 13.6 mW. The proposed method is expected to be useful for observing tumors through the induction of fluorescence emission during cancer removal surgery or for pathological examination in the pathology department.

Digital twin based DDPG reinforcement learning for sum-rate maximization of AI-UAV communications

Construction of wireless infrastructure using unmanned aerial vehicle (UAV) can effectively expand the coverage and support high-density traffic of next-generation communication systems. Designing wireless systems including UAVs as aerial base stations (ABSs) is a challenging task, due to the mobility of ABSs causing time-varying nature of environmental surroundings and relative propagation paths to user equipment (UE) devices. Therefore, it is essential to have an accurate estimate of the channel for varying positioning of the UAVs. In this paper, we propose to adopt a digital twin based performance evaluation procedure for wireless systems including ABSs, providing enhanced accuracy of channel modeling for specific target deployment areas. Using ray-tracing channel models reflecting detailed building and terrain information of the transmission environment, an UAV position optimization algorithm based on reinforcement learning is presented. By utilizing deep deterministic policy gradient (DDPG), the proposed algorithm calculates the overall throughput in the digital twin and determines the desired states of the UAV. Performance evaluation results demonstrate the trajectory training ability of the algorithm and the performance advantage of the system with a reduced amount of shadow area compared to those with ground base stations (GBSs).

Residents' Perceptions of Passive Design Responding to Climate Change in Simple Houses in Depok, West Java, Indonesia

Since the last few years, environmental issues related to global warming and increasing earth surface temperatures have had an influence on various fields. This environmental issue also affects the micro and macro climate. Architecturally, design can respond to changes in microclimate with passive design and active design. Passive design has long been applied to vernacular architecture, namely responding to local conditions in buildings. Meanwhile, active design is related to the latest technology and developments, such as energy-saving technology, as well as the use of natural elements as energy sources. This research uses quantitative methods. Primary data was collected using a questionnaire to determine the tendency of residents' perceptions of passive design. The analysis of this research is descriptive statistics, based on the answers of 35 respondents who live in simple houses in Depok, West Java, Indonesia. The research results showed that respondents' tendency towards passive design was shown in several things, namely: additional elements of the building at the front (canopy) can reduce heat and create shadow areas, the location and size of openings can support natural lighting and ventilation. Openings can be doors, windows, grilles, rosters and other elements. The existence of open space at the front and back of the house can reduce heat and cool the microclimate.

Research on Temperature Distribution and Gradient Prediction of U-Shaped Girder Bridge under Solar Radiation Effect

With the development of bridge engineering, U-shaped girder bridges have been applied in numerous bridge designs due to their structural characteristics. However, the U-shaped girder bridge is sensitive to solar radiation effects, leading to uneven temperature distributions that can affect the service performance of the structure. Thus, this study proposes an analysis method for the temperature distribution of U-shaped girder bridges and develops a prediction model to estimate temperature gradients. First, an improved ASHRAE clear sky model is proposed to calculate the structural shadow areas under sunlight, which provides a basis for the numerical simulation of U-shaped girder bridges under solar radiation effect. Then, a three-dimensional finite element model of the U-shaped girder bridge is established, and its correctness is verified by comparing with the actual temperature data. The temperature distribution of the U-shaped girder bridge under solar radiation is simulated using the verified model to obtain the maximum temperature difference and temperature variation characteristics. Finally, a prediction model for the temperature gradient is developed using nonlinear fitting approaches, and its accuracy is confirmed through comparison with actual data. The results indicate that the temperature distribution of the U-shaped girder bridge has minor changes along the longitudinal direction, while there are significant changes in the transverse distribution; the temperature distribution exhibits nonlinear changes in the height direction of the two side webs and the lateral direction of the bottom slab, with the maximum temperature difference reaching 17 °C; the fitting effect of the prediction model is very good, the correlation coefficients of the fitting curve and the actual data are all greater than 88%, providing a basis for the analysis of the temperature effects on U-shaped girder bridges and its application in design specifications.

Modeling the Role of Courtyards with Clusters of Buildings in Enhancing Sustainable Housing Designs

As urbanization increases, buildings require greater amounts of energy for heating and cooling, thereby necessitating the search for effective solutions. The courtyard is often considered a viable option; however, the limited availability and high cost of land resulting from rapid urbanization hinder its widespread use. Consequently, a courtyard with a cluster of buildings is proposed as a feasible solution to address land scarcity. Nonetheless, further investigation is required to effectively integrate this solution into neighborhood urban planning. This study examines the influence of three variables—courtyard orientation, courtyard size, and the arrangement of buildings around the courtyard—on the provision of cooling and heating for buildings. The research focuses on 216 experimental scenarios simulated using Revit software, which excels in its ability to accurately interpret input data and conduct real-time analysis depending on the variables of the building design. The results were recorded for the facades and ground, and the shaded area was computed for each scenario; following these measurements, the shadow areas on both the facade and ground were converted into percentages. The testing involved a group of buildings surrounding courtyards of four different shapes (square, rectangle, triangle, and circle). This approach aimed to identify the most efficient design for implementation in neighborhood planning contexts. The findings indicate that the shape of the courtyard significantly impacts cooling and heating of buildings. Specifically, the square courtyard is unsuitable for countries with Mediterranean climates, such as Jordan, as it can reduce shade coverage by 30%, leading to higher temperatures. Conversely, employing a rectangular courtyard results in a higher proportion of shadows compared to other shapes. The study further demonstrates the influence of the examined variables on the efficacy of the courtyard in cooling and heating of buildings.