Search Results (16)

Against the backdrop of high-quality urbanization in cities, the rapid expansion of metro networks has led to severe spatial mismatches in land use around station areas, which seriously restricts the full exertion of the comprehensive benefits of the transit-oriented development (TOD) model. Taking 139 operational metro stations in Xi’an in 2024 as the research sample, this study constructs a multi-objective land use optimization model with the richness of public services, transportation accessibility and population distribution balance as the three core maximization objectives. A hierarchically adaptive improved NSGA-III algorithm is proposed, with the following four key technical optimizations implemented: multi-dimensional adaptive reference point adjustment, design of real-integer hybrid coding genetic operators, construction of an enhanced multi-criteria environmental selection mechanism, and dynamic regulation of algorithm iteration. Experimental results show that the performance of the improved algorithm is significantly superior to that of the traditional NSGA-III algorithm: the values of the three core objectives are increased by 59.58%, 12.94% and 7.35% respectively compared with the original data; the algorithm achieves stable convergence after 25 iterations, with the convergence efficiency improved by 30%. The obtained Pareto optimal front features good uniformity (U = 0.92) and coverage (C = 0.95), and all the 80 non-dominated solutions meet all constraint conditions, with the solution set highly coupled with the urban functional zoning and spatial planning of Xi’an. This study proposes a zoned, prioritized and phased hierarchical land use optimization strategy for the areas around metro stations in Xi’an. The research findings provide a replicable research framework and methodological reference for the TOD practice and land use optimization of metro station areas in other rapidly urbanizing central cities in China and developing countries worldwide with the characteristic of rapid rail transit expansion. Full article

A two-dimensional segmentation model based on the P-matrix array was developed to simulate surface acoustic wave (SAW) delay-line devices under irregular loading. Building on coupling-of-modes (COM) theory and P-matrix model, a channelization approach was introduced to enhance conventional response simulation, enabling the systematic extraction of frequency and phase characteristics under varying spatial load distributions. Experimental verification was conducted using SAW devices fabricated by depositing aluminum interdigital transducers (IDTs) on Y-cut 35° quartz crystals through semiconductor lithography. The results demonstrate that the two-dimensional segmentation method effectively and accurately simulates the response of SAW delay line devices under various non-uniform and irregular mass loading distributions, both the phase shift and frequency shift exhibit linear proportionality to the loaded area (R² > 0.99), while the amplitude-frequency characteristics remain stable with increasing load coverage, showing no observable distortion or aberration. Quantitative mass detection experiments employing polystyrene microspheres further demonstrate that the device response increases linearly with the number of sample injections, and the shift magnitude is directly proportional to the amount injected per loading event. Full article

Unmanned Aerial Vehicles (UAVs) are integral components of future 6G networks, offering rapid deployment, enhanced line-of-sight communication, and flexible coverage extension. However, UAV communications in low-altitude environments face significant challenges, including rapid link variations due to attitude instability, severe signal blockage by urban obstacles, and critical sensitivity to transmitter–receiver alignment. While traditional planar reconfigurable intelligent surfaces (RIS) show promise for mitigating these issues, they exhibit inherent limitations such as angular sensitivity and beam squint in wideband scenarios, compromising reliability in dynamic UAV scenarios. To address these shortcomings, this paper proposes and evaluates a spherical-cap reflective intelligent surface (ScRIS) specifically designed for dynamic low-altitude communications. The intrinsic curvature of the ScRIS enables omnidirectional reflection capabilities, significantly reducing sensitivity to UAV attitude variations. A rigorous analytical model founded on Generalized Sheet Transition Conditions (GSTCs) is developed to characterize the electromagnetic scattering of the curved metasurface. Three distinct 1-bit RIS unit cell coding arrangements, namely alternate, chessboard, and random, are investigated via numerical simulations utilizing CST Microwave Studio and experimental validation within a mechanically stirred reverberation chamber. Our results demonstrate that all tested ScRIS coding patterns markedly enhance electromagnetic field uniformity within the chamber and reduce the lowest usable frequency (LUF) by approximately 20% compared to a conventional metallic spherical reflector. Notably, the random coding pattern maximizes phase entropy, achieves the most uniform scattering characteristics and substantially reduces spatial field autocorrelation. Furthermore, the combined curvature and coding functionality of the ScRIS facilitates simultaneous directional focusing and diffuse scattering, thereby improving multipath diversity and spatial coverage uniformity. This effectively mitigates communication blind spots commonly encountered in UAV applications, providing a resilient link environment despite UAV orientation changes. To validate these findings in a practical context, we conduct link-level simulations based on a reproducible system model at 3.5 GHz, utilizing electromagnetic scale invariance to bridge the fundamental scattering properties observed in the RC to the application band. The results confirm that the ScRIS architecture can enhance link throughput by nearly five-fold at a 10 km range compared to a baseline scenario without RIS. We also propose a practical deployment strategy for urban blind-spot compensation, discuss hybrid planar-curved architectures, and conduct an in-depth analysis of a DRL-based adaptive control framework with explicit convergence and complexity analysis. Our findings validate the significant potential of ScRIS as a passive, energy-efficient solution for enhancing communication stability and coverage in multi-band 6G networks. Full article

The deployment of wireless sensor networks (WSNs) is fundamental for smart buildings, industrial automation, and healthcare. However, achieving uniform wireless coverage in complex indoor environments remains a significant challenge due to structural obstructions and non-line-of-sight areas. As an example of this problem and of the proposed solution, this paper addresses the signal coverage issue in an L-shaped corridor. We present a novel solution based on a double, entirely passive Reflective Intelligent Surface (RIS) configuration. This setup significantly improves both the amplitude and the spatial uniformity of the received power in the shadowed region, effectively overcoming the limitations of the single-RIS configuration, which often leaves coverage gaps in Non-Line-of-Sight areas. To model realistic multipath propagation, we developed a custom ray-tracing algorithm that takes advantage of the regular geometry of indoor environments to improve processing speed. The field response of an RIS is then evaluated by analyzing possible reflecting-surface configurations and comparing the performance of single- and double-RIS configurations. Additionally, a statistical analysis of the power received by an observer located anywhere in the corridor, considering RIS positioning uncertainties across various deployment scenarios, has been performed. Results show that the double-RIS solution increases the covered area by $76\%$, considering a receiver sensitivity of $-100$ dBm. The proposed approach can be easily generalized to other typical indoor environments with similar structural characteristics. Full article

Trailing suction hopper dredgers (TSHDs) are widely used in port subgrade reinforcement and land reclamation layered backfilling, with construction quality relying on sediment settling paths and deposition characteristics. To tackle the lack of guidance on key parameters like bottom door opening, sailing speed, and related problems, a multiphase settling model based on coupled CFD–DEM is developed. This model analyzes sediment particle settling trajectories, distribution patterns, and uniformity responses under different conditions. Through orthogonal simulations of bottom door openings (22%, 50%, 100%) and sailing speeds (0.02, 0.045, 0.07 kn), the coupling relationships among particle settling velocity, main deposition layer thickness, and spatial extension are revealed, clarifying how parameter variations affect deposition uniformity and coverage. The results indicate that, relative to a small opening (22%), a moderate bottom door opening (50%) simultaneously increases layer thickness and markedly improves deposition uniformity (minimum uniformity index), whereas a very large opening (100%) further increases thickness at the expense of a modest loss of uniformity relative to the moderate case; higher sailing speeds cause long-range migration and local deposition irregularities. Engineering validation using field data from the Junyang 1 TSHD in the Manila Pasay project shows that a moderate bottom door opening of about 15% (selected based on the 22–50% simulation trend), combined with a medium sailing speed of about 0.4 kn, achieves a good balance between thickness control and uniformity. A coupled multi-physics analysis framework and a parameter–response map are established, systematically revealing the influence of operational parameters on sediment settling and deposition uniformity and providing quantitative support for TSHD backfilling operations. Full article

The accurate point cloud completion of individual tree crowns is critical for quantifying crown complexity and advancing precision forestry, yet it remains challenging in dense plantations due to canopy occlusion and LiDAR limitations. In this study, we extended the scope of conventional point cloud completion techniques to artificial planted forests by introducing a novel approach called Multi−feature Fusion Completion of Populus (MFCPopulus). Specifically designed for Populus Tomentosa plantations with uniform spacing, this method utilized a dataset of 1050 manually segmented trees with expert−validated trunk−canopy separation. Key innovations include the following: (1) a hierarchical adversarial framework that integrates multi−scale feature extraction (via Farthest Point Sampling at varying rates) and biologically informed normalization to address trunk−canopy density disparities; (2) a structural characteristics split−collocation (SCS−SCC) strategy that prioritizes crown reconstruction through adaptive sampling ratios, achieving a 94.5% canopy coverage in outputs; (3) a cross−layer feature integration enabling the simultaneous recovery of global contours and a fine−grained branch topology. Compared to state−of−the−art methods, MFCPopulus reduced the Chamfer distance variance by 23% and structural complexity discrepancies (ΔD_b) by 33% (mean, 0.12), while preserving species−specific morphological patterns. Octree analysis demonstrated an 89−94% spatial alignment with ground truth across height ratios (HR = 1.25−5.0). Although initially developed for artificial planted forests, the framework generalizes well to diverse species, accurately reconstructing 3D crown structures for both broadleaf (Fagus sylvatica, Acer campestre) and coniferous species (Pinus sylvestris) across public datasets, providing a precise and generalizable solution for cross−species trees’ phenotypic studies. Full article

This study investigates the dynamic changes in wheat canopy spectral characteristics across seven critical growth stages (Tillering, Pre-Jointing, Jointing, Post-Jointing, Booting, Flowering, and Ripening) using UAV-based multispectral remote sensing. By analyzing four key spectral bands—green (G), red (R), red-edge (RE), and near-infrared (NIR)—and their combinations, we identify spectral features that reflect changes in canopy activity, health, and structure. Results show that the green band is highly sensitive to chlorophyll activity and low canopy coverage during the Tillering stage, while the NIR band captures structural complexity and canopy density during the Jointing and Booting stages. The combination of G and NIR bands reveals increased canopy density and spectral concentration during the Booting stage, while the RE band effectively detects plant senescence and reduced spectral uniformity during the ripening stage. Time-series analysis of spectral data across growth stages improves the accuracy of growth stage identification, with dynamic spectral changes offering insights into growth inflection points. Spatially, the study demonstrates the potential for identifying field-level anomalies, such as water stress or disease, providing actionable data for targeted interventions. This comprehensive spatio-temporal monitoring framework improves crop management and offers a cost-effective, precise solution for disease prediction, yield forecasting, and resource optimization. The study paves the way for integrating UAV remote sensing into precision agriculture practices, with future research focusing on hyperspectral data integration to enhance monitoring models. Full article

Understanding the flow processes and pattern optimization of ecosystem services (ESs) supply and demand is crucial for integrated regional ecological management. However, the understanding of the flow process of ESs at the 1 km grid scale is still limited, especially in areas dominated by mineral resource development. The landscape in these areas has undergone significant changes due to mining activities. It is urgent to construct a regional management model that integrates the flow of ecosystem services and mine restoration. This study developed a framework that links ecosystem service flows (ESFs) and ecological security patterns (ESP) based on multi-source ecological monitoring data, constructed an ES supply-demand flow network through the flow properties, and determined the sequence and optimization strategies for mine rehabilitation to achieve integrated regional management. The results show that, except for food production (FP), other services were in surplus overall, mostly in synergistic relationships, but the spatial distribution of their supply and demand was not coordinated. Surplus areas were located mainly in the eastern woodlands, and deficit areas were located in the northwestern production agglomeration centers, suggesting that areas of supply-demand imbalance can be mitigated through ecological integration. Among these, water yield (WY) had a small number of sources and sinks and is limited in area range. Habitat quality (HQ) sources and sinks had the largest area coverage and the highest number. The distribution of ESF corridors, influenced by factors such as the number of sources and sinks, flow characteristics, and spatial resistance, varied significantly. HQ exhibited a more uniform distribution range, while WY had a longer average length of flow path. Overlaying ecological and mining factors, we identified ecological strategic spots, important supply areas, beneficiary areas, and mine priority restoration areas to further optimize the overall layout and rationally allocate the intrinsic structure of the patches based on ES supply and demand. Full article

The recharge of karst aquifers is significant for the effective management of groundwater resources, and its estimation should be tailored to accommodate their specific hydrogeological characteristics. This study provides a two-step methodological approach for the determination of karst aquifer recharge. Initially, mean annual recharge rates were estimated in the karst system of Ziria (Southern Greece) utilizing the APLIS and modified APLIS methods in order to decipher which was the most suitable version for recharge assessments. The results indicated similar mean recharge rate values at 42.7% and 41.4%, respectively, but significant differences in the spatial distribution. The modified methodology emerged as a more accurate and realistic approach, mainly due to the incorporation of permeability assessments. The final phase of the methodological approach involved the application of modified APLIS in two additional karst hydrosystems, Planitero and Xiromero, while a quantitative cross-comparison of the recharge rates was obtained for a deeper understanding of the factors controlling the groundwater recharge process. In Ziria, recharge rates exhibit a relatively uniform distribution throughout the area, with a median value of 46.7%. Conversely, in Planitero, High recharge rates (60–80%) occupy 56.8% of the surface, while in Xiromero, Moderate recharge rates (40–60%) dominate, representing 53.4% of the land coverage. These variations underscore the spatial heterogeneity of recharge within the karst systems, highlighting the importance of considering local geological and hydrological conditions in its assessments. The methodological approach of this study is flexible and can be adapted to different karst sites for the determination of recharge regimes, contributing to the alleviation of the groundwater depletion issue. Full article

With its ecological, economic, and social benefits, urban green space (UGS) plays an important role in urban planning. Accordingly, it is also an important indicator in the evaluation of urban liveability. However, the extraction and statistical analysis of UGS are difficult because urban land use involves complex types and UGS exhibits fragmented distribution and common vegetation extraction models such as the NDVI model and pixel bipartite model. In addition, there are few studies that analyze UGS in Hangzhou with a pixel decomposition model. Therefore, applying the mixed pixel decomposition model with GF-1 data, the following three objectives were set in this study: (1) analyzing the temporal changes of UGS in Shangcheng District, Hangzhou from 2018 to 2020; (2) analyzing the spatial distribution characteristics of UGS in the six main urban areas of Hangzhou in 2020; (3) analyzing the rationality and influencing factors of UGS distribution in Hangzhou. In Shangcheng District, the overall UGS area increased from 2018 to 2020 due to the increase in forest area rather than grassland area. As for the main built-up area in Hangzhou, medium and high coverage of UGS were primarily observed, with an overall high level of greening and a relatively uniform vegetation cover. Only a few areas showed very low UGS coverage. Some differences were observed among administrative regions under the influence of topography, but the overall coverage is high. At the same time, the distribution of UGS in Hangzhou is closely related to policy guidance, the needs of urban residents, and the requirements of economic development. This research not only can provide a new way to analyze UGS features in Hangzhou but also provides scientific guidance for governments in urban planning. Full article

The southern portion of the Qinghai–Tibet Plateau (QTP) and the central Himalayan region are home to the Mt. Qomolangma (Everest) National Nature Reserve (QNNR), which is the world’s highest nature reserve and is distinguished by delicate natural ecosystems and unique geographic features. Analyzing regional vegetation trends, as well as the impacts of natural and anthropogenic variables on vegetation coverage, is crucial for local environmental protection and sustainable development. In this study, the variation patterns of the MOD13Q1 Normalized Difference Vegetation Index (NDVI) data were explored, and the responses of vegetation development to both natural and anthropogenic parameters were investigated by applying trend analysis and partial correlation analysis, as well as the partial least squares-structural equation model (PLS-SEM). To better comprehend the spatial characteristics and interrelationships between NDVI and various parameters under different vegetation types, the Uniform Manifold Approximation and Projection (UMAP) was employed for dimensionality reduction and visualization. The results illustrated that between 2000 and 2018, the reserve greened up at a rate of 0.00073/a (p < 0.05), with vegetation improvement areas accounting for 49.46%. The major climatic driver for the greening trend of vegetation was temperature. Topography (especially elevation) remains dominant in regulating vegetation development in the QNNR, despite a progressively growing impact of hydrothermal conditions on vegetation development. Additionally, the implementation of environmental initiatives has stifled the adverse impacts of human activity. Full article

To achieve uniform spatial coverage characteristics in optical signals in an underwater wireless optical communication (UWOC) system, and therefore reduce the requirement of the alignment between the receiver and the transmitter, we propose an optimized scheme of optical signal coverage based on a light-emitting diode (LED) array in this paper. For high-efficiency coverage of the optical signals, the pitch angle of the LED light source is first optimized on the basis of the light beam geometry. Then, the layout of the LED array and the horizontal deflection angle of the light source are jointly optimized by an improved particle swarm optimization (PSO) algorithm. Taking a 16-LED array as an example, the performances of the spatial coverage characteristics with three different LED array layouts are analyzed in detail under four typical seawater environments. The results show that the LED array with the PSO-optimized layout can achieve better uniformity in the power distribution for the received optical signals, and enhance the robustness of the UWOC system in complex seawater environments. Full article

For the sustainable development of marine fishery resources, it is essential to comprehensively, accurately, and objectively obtain the spatial characteristics and evolution law of fishing intensity. However, previous studies have focused more on the use of single data sources, such as AIS (Automatic Information System) and VBD (VIIRS boat detection), to obtain fishing intensity information and, as such, have encountered some problems, such as insufficient comprehensive data coverage for ships, non-uniform spatial distribution of data signal acquisition, and insufficient accuracy in obtaining fishing intensity information. The development of big data and remote sensing Earth observation technology has provided abundant data sources and technical support for the acquisition of fishing intensity data for marine fisheries. Based on this situation, this paper proposes a framework that integrates the data of fishing vessels from two sources (AIS, with high space-time granularity, and VBD, with short revisit cycle and high sensitivity), in order to obtain such information based on closely matching and fusing the vector point data of ship positions. With the help of this framework and the strategy of indirectly representing fishing intensity by data point density after fusion, the spatial characteristics and rules of fishing intensity in typical seasons (February, April, September, and November) in the northern South China Sea in 2018 were systematically analyzed and investigated. The results revealed the following: (1) Matching and fusing AIS and VBD data can provide a better perspective to produce robust and accurate marine fishery intensity data. The two types of data have a low proximity match rate (approximately 1.89% and 6.73% of their respective inputs) and the matching success for fishing vessels in the data was 49.42%. (2) Single AIS data can be used for nearshore (50 to 70 km) marine fishery analysis research, while VBD data reflect the objective marine fishing in space, showing obvious complementarity with AIS. (3) The fishing intensity grid data obtained from the integrated data show that high-intensity fishing in the study area was concentrated in the coastal area of Maoming City, Guangdong (0–50 km); the coastal area of Guangxi Beihai (10–70 km); around Hainan Island in Zhangzhou (10–30 km); and the Sanya nearshore area (0–50 km). However, it did not decay with increasing offshore distance, such as at the Trans-Vietnamese boundary in the Beibu Gulf, near the China–Vietnam Common Fisheries Area (50 km) and high-intensity fishing areas. (4) The obtained fishing intensity data (AIS, VBD, and AIS + VBD) were quantitatively analyzed, showing that the CV (Coefficient of Variation) of the average for each month (after fusing the two types of data) was 0.995, indicating that the distribution of the combined data was better than that before fusion (before fusion: AIS = 0.879, VBD = 1.642). Therefore, the integration of AIS and VBD can meet the need for a more effective, comprehensive, and accurate fishing intensity analysis in marine fishery resources. Full article

Advances in synthetic aperture radar (SAR) interferometry have enabled the seamless monitoring of the Earth’s crust deformation. The dense archive of the Sentinel-1 Copernicus mission provides unprecedented spatial and temporal coverage; however, time-series analysis of such big data volumes requires high computational efficiency. We present a parallelized-PSI (P-PSI), a novel, parallelized, and end-to-end processing chain for the fully automated assessment of line-of-sight ground velocities through persistent scatterer interferometry (PSI), tailored to scale to the vast multitemporal archive of Sentinel-1 data. P-PSI is designed to transparently access different and complementary Sentinel-1 repositories, and download the appropriate datasets for PSI. To make it efficient for large-scale applications, we re-engineered and parallelized interferogram creation and multitemporal interferometric processing, and introduced distributed implementations to best use computing cores and provide resourceful storage management. We propose a new algorithm to further enhance the processing efficiency, which establishes a non-uniform patch grid considering land use, based on the expected number of persistent scatterers. P-PSI achieves an overall speed-up by a factor of five for a full Sentinel-1 frame for processing in a 20-core server. The processing chain is tested on a large-scale project to calculate and monitor deformation patterns over the entire extent of the Greek territory—our own Interferometric SAR (InSAR) Greece project. Time-series InSAR analysis was performed on volumes of about 12 TB input data corresponding to more than 760 Single Look Complex Sentinel-1A and B images mostly covering mainland Greece in the period of 2015–2019. InSAR Greece provides detailed ground motion information on more than 12 million distinct locations, providing completely new insights into the impact of geophysical and anthropogenic activities at this geographic scale. This new information is critical to enhancing our understanding of the underlying mechanisms, providing valuable input into risk assessment models. We showcase this through the identification of various characteristic geohazard locations in Greece and discuss their criticality. The selected geohazard locations, among a thousand, cover a wide range of catastrophic events including landslides, land subsidence, and structural failures of various scales, ranging from a few hundredths of square meters up to the basin scale. The study enriches the large catalog of geophysical related phenomena maintained by the GeObservatory portal of the Center of Earth Observation Research and Satellite Remote Sensing BEYOND of the National Observatory of Athens for the opening of new knowledge to the wider scientific community. Full article

Rock fragments in soil strongly increase the complexity of hydrological processes. Spatial variability of preferential flow and infiltration characteristics, especially along a rocky-mountain hillslope are poorly understood. In this study, five rainfall–dye tracer experiments were performed in the rocky Taihang Mountains, northern China, to investigate the spatial variability of preferential flow and infiltration redistribution on different hillslope positions. Tracers were used to distinguish macropore flow and actual water flow patterns, and preferential flow indices and spatial non–uniformity of the infiltration redistribution were calculated using image analysis. Results showed increasing trends in the dye coverage, maximum infiltration depth, and steady infiltration rate with increased hillslope position, with a preferential flow fraction of 0.10, 0.11, 0.15, 0.29, and 0.26 for the bottom–, down–, mid–, upper–, and top–slope positions, respectively. With increased hillslope position, the spatial non–uniformity of the infiltration redistribution gradually increased in orthogonal and parallel directions to the stained section, and was supported by the fractal dimensions. Positive (gravel mass ratio, saturated water content, altitude, hydraulic conductivity and roots) and negative (bulk density and clay content) impacts on preferential flow and infiltration redistribution were quantitatively emphasized. The characteristic and mechanism of infiltration process were further identified along a rocky-mountain hillslope. Full article