Ground Topography Research Articles

A Comparison of a Three Blade and Five Blade Wind Turbine in Terms of the Mechanical Properties Using the Q-Blade Software

يمكن لتوربينات الرياح المنتشرة في مزارع الرياح على نطاق المرافق أن تدعم تلبية رغبات الطاقة المستقبلية وتقليل انبعاثات ثاني أكسيد الكربون عن طريق تقليل متطلبات الطاقة من الوقود الأحفوري. مع ارتفاع درجة حرارة الهواء على مدار اليوم، تزداد سرعة الرياح بسبب تدرجات درجة الحرارة، والتي تنتج تدرجًا في الكثافة / الضغط، مما يؤدي إلى حركة الهواء التي تواجهها توربينات الرياح. اعتمادًا على تضاريس الأرض، يمكن أن تواجه الرياح وتوجه في الوديان بين التلال وفوقها حيث تتدفق وتتبع منحنيات الأرض. تنتج هذه التضاريس زيادة في سرعة الرياح في القمم والتلال. في هذا العمل، تم تصميم شفرة دوار توربينات الرياح الأفقية الصغيرة للعمل في ظل سرعة الرياح المنخفضة، باستخدام برنامج (Q-Blade). استنادًا إلى نظرية عنصر الشفرة (BEM). مع الجنيح NACA3712. تم استخدام دوار ثلاثي الشفرات ودوار بخمس شفرات بناءً على نوع التوربين وحجم الدوار لتوليد الطاقة الميكانيكية من طاقة الرياح. تم إجراء مقارنة وتحليل قوة التوربين ومعامل القدرة ومعامل عزم الدوران عند سرعة رياح منخفضة ((1m/s-8m/s وتم الحصول على نتائج دقيقة للغاية. وجد أن أفضل أداء يمكن أن يعمل فيه دوار توربيني ثلاثي الشفرات بقدرة توربينية تبلغ (955W) كما تم الحصول على قدرة التوربين ((582W للدوار خماسي الشفرات. وجد أن تصميم توربينة رياح أفقية صغيرة بخمس ريش أفضل من التوربين بثلاث ريش ومناسب للعمل في المناطق ذات سرعة الرياح المنخفضة وبكفاءة عالية مقارنة بحجم التوربين.

Models for topographic ground motion amplification based on finite element analyses considering topographic features and ground motions in Japan

Models for topographic ground motion amplification based on finite element analyses considering topographic features and ground motions in Japan

Contribution of Geometric Feature Analysis for Deep Learning Classification Algorithms of Urban LiDAR Data.

The use of a Machine Learning (ML) classification algorithm to classify airborne urban Light Detection And Ranging (LiDAR) point clouds into main classes such as buildings, terrain, and vegetation has been widely accepted. This paper assesses two strategies to enhance the effectiveness of the Deep Learning (DL) classification algorithm. Two ML classification approaches are developed and compared in this context. These approaches utilize the DL Pipeline Network (DLPN), which is tailored to minimize classification errors and maximize accuracy. The geometric features calculated from a point and its neighborhood are analyzed to select the features that will be used in the input layer of the classification algorithm. To evaluate the contribution of the proposed approach, five point-clouds datasets with different urban typologies and ground topography are employed. These point clouds exhibit variations in point density, accuracy, and the type of aircraft used (drone and plane). This diversity in the tested point clouds enables the assessment of the algorithm's efficiency. The obtained high classification accuracy between 89% and 98% confirms the efficacy of the developed algorithm. Finally, the results of the adopted algorithm are compared with both rule-based and ML algorithms, providing insights into the positioning of DL classification algorithms among other strategies suggested in the literature.

Consumer‐grade UAV solid‐state LiDAR accurately quantifies topography in a vegetated fluvial environment

AbstractUnoccupied aerial vehicles (UAVs) with passive optical sensors have become popular for reconstructing topography using Structure from Motion (SfM) photogrammetry. Advances in UAV payloads and the advent of solid‐state LiDAR have enabled consumer‐grade active remote sensing equipment to become more widely available, potentially providing opportunities to overcome some challenges associated with SfM photogrammetry, such as vegetation penetration and shadowing, that can occur when processing UAV‐acquired images. We evaluate the application of a DJI Zenmuse L1 solid‐state LiDAR sensor on a Matrice 300 RTK UAV to generate digital elevation models (DEMs). To assess flying height (60–80 m) and speed parameters (5–10 ms−1) on accuracy, four point clouds were acquired at a test site. These point clouds were used to develop a processing workflow to georeference, filter and classify the point clouds to produce a raster DEM product. A dense control network showed that there was no significant difference in georeferencing from differing flying height or speed. Building on the test results, a 3 km reach of the River Feshie was surveyed, collecting over 755 million UAV LiDAR points. The Multiscale Curvature Classification algorithm was found to be the most suitable classifier of ground topography. GNSS check points showed a mean vertical residual of −0.015 m on unvegetated gravel bars. Multiscale Model to Model Cloud Comparison (M3C2) residuals compared UAV LiDAR and Terrestrial Laser Scanner point clouds for seven sample sites demonstrating a close match with marginally zero residuals. Solid‐state LiDAR was effective at penetrating sparse canopy‐type vegetation but was less penetrable through dense ground‐hugging vegetation (e.g. heather, thick grass). Whilst UAV solid‐state LiDAR needs to be supplemented with bathymetric mapping to produce wet–dry DEMs, by itself, it offers advantages to comparable geomatics technologies for kilometre‐scale surveys. Ten best practice recommendations will assist users of UAV solid‐state LiDAR to produce bare earth DEMs.

A two-dimensional effective sound speed parabolic equation model for infrasound propagation with ground topography.

A terrain capable parabolic equation (PE) propagation algorithm for long range infrasound propagation modeling has been implemented using Padé approximations for the various operator valued functions that arise in PE algorithms. In this work, the influence of the winds are captured by the effective sound speed approximation and propagation is restricted to the range-altitude plane. The ground topography is included by the addition of an impenetrable fluid below the ground surface. The impedance condition at the ground is handled explicitly, including both vertical and radial components. It is found that including terrain can have a large influence on long range propagation. In particular, reflections from a sufficiently steep slope can change the inclination angle enough to move the propagation path from one atmospheric duct to another.

Assessment of flow characteristics over complex terrain covered by the heterogeneous forest at slightly varying mean flow directions: (A case study of a Swedish wind farm)

The impact of heterogeneous forest canopies and complex terrain on the horizontal distortion of the inflow is studied. Large-Eddy Simulation (LES) of the neutral Atmospheric Boundary Layer (ABL) flow is performed for a wind farm in Sweden for three cases associated with three different wind directions at the range of the static yaw misalignment (≃±6∘) where the yaw control system is not activated. The ground topography and forest properties for the numerical modeling are extracted from the Airborne Laser Scanning (ALS) 3D data. The wind turbines within the wind farm are introduced using the actuator disk model. To focus on the airflow deflection only by the complex terrain and vegetation, the study is limited to upstream wind turbines without any wake interaction. The predicted mean wind speed and turbulence intensity for the upstream wind turbines are compared against the nacelle-mounted anemometers taken from the wind farm’s turbine SCADA data. To quantify the additional load and moments induced at the rotor blades by the horizontal misalignment of the incoming flow, aero-structural simulation of the upstream wind turbines in the wind farm for all three cases is performed. The results show that the horizontal distortion of the inflow over the rotor swept area is usually kept below the range of static yaw misalignment (≃6∘) for the majority of the upstream wind turbines for all three cases. However, the impact of a large vertical shear exponent leading to misinterpretation of the results must be taken into consideration. Furthermore, the load imbalance of the rotor due to the vertical wind shear has the least direct contribution to the yaw moment. However, for a mean vertical shear exponent larger than α=0.25, contrary to expectation, a positive mean yaw moment under the positive-yawed inflow may be observed.

Playing in 'The Backyard': Environmental Features and Conditions of a Natural Playspace Which Support Diverse Outdoor Play Activities among Younger Children.

Outdoor play in nature-rich spaces has been associated with healthy development among young children. The diverse play opportunities afforded to children by natural playspaces can scaffold health benefits, appreciation of nature, and pro-environmental behaviors into adulthood. Environmental features and conditions of outdoor playspaces significantly influence the diversity and quality of play opportunities. Understanding how the physical environment can support high-quality play experiences can inform the design of stimulating, health-promoting playscapes for children. An observational behavior mapping framework was utilized to examine the environmental features of The Backyard, a large natural playscape, associated with play activities among young children. The Tool for Observing Play Outdoors was used to capture outdoor play types OPT), along with associated behavioral and environmental data, during seven days of field observation. While the playspace supported most OPTs, Physical and Exploratory play were most prevalent. Associations with activity intensity and risk play are also presented. Loose parts, particularly natural loose parts, were highly involved in most OPTs, but especially associated with Exploratory play. Ground topography showed some association with several OPTs and warrants further investigation. The environmental features of The Backyard supported an abundant and diverse range of outdoor play activities for young children and families.

A comprehensive numerical analysis of EQ-induced lateral earth pressure on structures basement walls

Due to soil-structure interaction, dynamic lateral earth pressures on building embedded walls affect the dynamic performance of the building. Classic relations such as Mononobe-Okabe (M − O) and Seed & Withman (S–W) are applied to determine these dynamic lateral earth pressures in conventional design methods. Considering these relations' assumptions and their neglect of soil-structure interactions during an earthquake, using these relations may result in erroneous and inaccurate estimation of dynamic earth pressure. This paper attempts to understand this phenomenon better and estimate dynamic earth pressure on basement walls. Structure and soil mass are simulated simultaneously, using numerical models. Numerical (finite element) dynamic analyses are carried out for qualitative and quantitative evaluation of dynamic earth pressures on buildings with basements. Different excavation depths, ground topography, geotechnical parameters, and building stories above ground have been considered in these analyses. Finally, the soil-structure interaction response has been discussed using the obtained results, and approximate relations are derived to estimate the dynamic earth pressure.

2D electromagnetic simulation for ground penetrating radar with a topographic ground surface by the curvilinear collocated-grid finite-difference method combined with equivalent field method

In this paper, we extend the curvilinear collocated-grid finite-difference method, which has been developed in the study of seismology, to the 2D electromagnetic simulation of ground penetrating radar (GPR). The method combines curvilinear coordinate and collocated grid, so it can better describe the geometry of the irregular interfaces than traditional finite difference method and is more efficient than finite element method which is suitable for complex geometries. Due to the differences in interfacial condition between elastic waves and electromagnetic waves, a novel scheme of equivalent electromagnetic fields is introduced to explicitly ensure discontinuous interfacial boundary conditions with collocated grid. Furthermore, this approach eliminates the need for orthogonality of the grid at the interface, which reduces the complexity of mesh generation. The proposed method is verified for a series of ground penetrating radar application models, by comparing synthetic waveforms with independent reference solutions. The perfect consistency of the comparisons indicates the accuracy of our new method in the simulation of GPR. Compared with the second-order gprMax, the proposed method is proved to be more efficient in terms of computing time and memory. Combination of collocated grid and the novel equivalent field method leads to reliable and accurate solutions of EM fields even on the ground surface.

Locality of Topographic Ground Truth Data for Salt Marsh Lidar DEM Elevation Bias Mitigation

Lidar-derived digital elevation models (DEMs) are crucial for modeling salt marsh evolution, forecasting inundation depth, frequency and duration, and simulating sea level rise (SLR). Advances in lidar acquisition and data processing techniques have led to increased accuracy, however in densely vegetated coastal salt marsh areas, lidar-derived DEMs are generally unreliable without adjustment. In this paper, we investigate the need for local topographic ground truth data to train Random Forest (RF) DEM adjustment models for two similar Northern Gulf of Mexico salt marshes. Two GNSS-RTK field surveys were conducted to acquire ground truth topographic elevations near St. Marks, Florida (n=377) and Pascagoula, Mississippi (n=610). These elevations, along with Sentinel-2A MSI reflectance values and lidar DEM elevations, were used to validate and train local and combined RF salt marsh DEM adjustment models. The local RF models achieved MAE values of 0.054 m and 0.045 m in the leave-one-out cross-validation for St. Marks and Pascagoula, respectively. Elevation bias predictions using remote RF models were far worse and those using the combined RF model were marginally worse. Using the local RF predictions to mitigate the bias in the lidar DEMs improved their accuracy by 69.1% for St. Marks and 90.9% for Pascagoula. The DEM elevation was identified as the most important predictor. This evidence suggests that local ground truth data are necessary for mitigating bias in salt marsh lidar DEMs, although it remains to be seen if increasing the data set size and incorporating additional hydrologic predictor variables could narrow the accuracy gap.

Terrain Adaptability and Optimum Contact Stiffness of Vibro-bot with Arrayed Soft Legs.

The terrain adaptability of the state-of-the-art robot is far behind natural animals, partly because of limited sensing, intelligence, controlling, and actuating ability. One possible solution is to explore the flexible locomotion structure and locomotion mode with good adaptability and fault tolerance. Based on this idea, we presented a type of vibro-bot with arrayed soft legs (VBASL) with excellent terrain adaptability by utilizing the rapid vibration of the soft belt array. With the resistance to local terrain blocking and combing the vibrational actuation, the VBASL has an advantage of multi-leg collaboration, so that very simple structure can achieve good terrain adaptability, such as steady locomotion on complex terrains like steep slope, ladders, steps, discrete pillars, and soft sands. Besides, the effects of soft leg geometry, stiffness, and ground topography on terrain adaptability and locomotion speed were also studied, indicating the similar contact stiffness to maximize the locomotion speed on different grounds. Then, a theoretical model was developed to describe the experiments well, which can guide the design of optimum contact stiffness of VBASL to achieve fast locomotion speed and good load capacity. By further modifying the robot structure, more practical functions such as turning, climbing, and anti-impacting were easily realized. The resistance to local terrain blocking and optimum contact stiffness are two important factors to improve the performance of VBASL, which may address the terrain adaptability challenge of robots working in practical unstructured environments.

Redescription of Paracles vulpina (Hübner, [1825]) (Lepidoptera: Erebidae), with comments of the aquatic habit of larval instars

The genus Paracles Walker, 1855 is one of the most diverse genera present in Arctiinae and some species have larvae with aquatic habits. Several larvae were found swimming in flooded areas in different grasslands and were bred to adults to identify the species: Paracles vulpina (Hübner, [1825]). The current knowledge of immature stages of this species is not useful to identify and discriminate from other species of Paracles. For this reason, we proposed to redescribe adults of P. vulpina, showing for the first time the male and female genitalia, and improve the information on the immature stages and their habits. The adults can be recognized by the whitish paler brown band in the costal area in the forewing and whitish paler brown antenna. The final larval stage of P. vulpina can be differentiated from other species because it shows a body with a black pubescence except for a ferruginous subventral pubescence, blue dorsal verrucae, red lateral verrucae, and dorsal plastron with longest white setae. Because of its polyphagous feeding habit on aquatic and non aquatic plants we consider the aquatic larval habit is not a necessary strategy and could depend on the ground topography or weather of the locality.

Axisymmetric BEM analysis of layered elastic halfspace with volcano-shaped mantle and cavity under internal gas pressure

This paper presents an axisymmetric BEM analysis of layered elastic halfspace with volcano-shaped mantle and cavity under internal gas pressure. The problem is of interest to understand the behavior of volcanoes, tectonic earthquakes and other oil and gas reservoirs. The volcano-shaped mantle ground topography and the internal spherical or ellipsoidal cavity are added to the conventional model of layered halfspace. The analysis uses the axisymmetric boundary element method (BEM) associated with the fundamental solution of a multilayered elastic fullspace subject to the concentrated ring-body force. The BEM is further verified for its high efficiency and accuracy by comparing its result with the analytical and FEM solutions for the problem of a homogeneous elastic halfspace whose spherical cavity is under internal pressure. The BEM is used to examine the effect of the volcano-shaped mantle, the cavity shape, the layered material properties and the internal pressure on the elastic behavior of the halfspace under the internal pressure loading within the cavity. The displacements and stresses at the external and internal boundaries and within the layered halfspace are presented and analyzed in detail. The presence of the volcano-shaped mantle can reduce significantly the swelling ground movement induced by the expansive pressure in the cavity in the layered halfspace. The cavity shape can have significant effect to the location and magnitude of the maximum tensile principal hoop stress on the cavity surface induced by its internal pressure.

TomoSAR Mapping of 3D Forest Structure: Contributions of L-Band Configurations

Synthetic Aperture Radar (SAR) measurements are unique for mapping forest 3D structure and its changes in time. Tomographic SAR (TomoSAR) configurations exploit this potential by reconstructing the 3D radar reflectivity. The frequency of the SAR measurements is one of the main parameters determining the information content of the reconstructed reflectivity in terms of penetration and sensitivity to the individual vegetation elements. This paper attempts to review and characterize the structural information content of L-band TomoSAR reflectivity reconstructions, and their potential to forest structure mapping. First, the challenges in the accurate TomoSAR reflectivity reconstruction of volume scatterers (which are expected to dominate at L-band) and to extract physical structure information from the reconstructed reflectivity is addressed. Then, the L-band penetration capability is directly evaluated by means of the estimation performance of the sub-canopy ground topography. The information content of the reconstructed reflectivity is then evaluated in terms of complementary structure indices. Finally, the dependency of the TomoSAR reconstruction and of its structural information to both the TomoSAR acquisition geometry and the temporal change of the reflectivity that may occur in the time between the TomoSAR measurements in repeat-pass or bistatic configurations is evaluated. The analysis is supported by experimental results obtained by processing airborne acquisitions performed over temperate forest sites close to the city of Traunstein in the south of Germany.

Numerical and test study on vertical vibration characteristics of pile group in slope soil topography

Topography effects on the vertical vibration responses of pile group are revealed though numerical analysis and model tests. First, a series of model tests with different topography of ground and bedrock are conducted. The results indicate that displacement amplitude of the pile head in sloping ground topography is larger than in horizontal ground. Differential displacement at various positions of the pile cap is observed in non-horizontal topography. Afterwards, a numerical algorithm is employed to further explore the essential response characteristics in group piles of different topography configurations, which has been verified by the test results. The lengths of the exposed and frictional segment, together with the thickness of the subsoil layer, are the dominant factors which cause non-axisymmetric vibration at the pile cap.

Adaptable Flight Line Planning for Airborne Photogrammetry Using DEM

Flight line planning is the first step in an aerial photography campaign. Its two key parameters, ground sampling distance (GSD), and overlap should be designed carefully as they will impact subsequent flying workload and even the final mapping accuracy. For a flat terrain region, flight line planning is easy using a traditional method with fixed baseline, flight spacing, and flight altitude. But for a steep terrain region, photo overlap and GSD will change greatly with topography, and thus a flight line planning using the traditional method is not sufficient. This article presents a novel adaptable flight line planning method for frame camera with four application modes. The flight line planning procedure is implemented through rigorous imaging geometry model using digital elevation data, where actual overlap and GSD can be calculated precisely. Using the desired overlap and GSD as constraint conditions, the flight spacing, baseline, and flight altitude can be adjusted adaptively according to ground topography. To assess the effect, a hypothetical test in a rugged terrain region was conducted to compare the project workload, GSD, and overlap of the four modes. The results show that Mode 2, Mode 3, and Mode 4 can realize better overlap with lower workload than the traditional method Mode 1. Mode 3 and Mode 4 have better GSD distribution than Mode 1 and Mode 2. The Mode 3 method was also validated in an actual project, showing a favorable performance in final reality 3D model result.

Height map-based social force model for stairway evacuation

The stairway is ubiquitous in public places like shopping mall, theater and stadium. Due to the unevenness of the ground, the staircase often brings about undesirable effects in emergency evacuation, such as stumble, trampling and falling. Therefore, it is necessary to study the evacuation dynamics of pedestrians on the stairway in-depth. However, the widely studies social force model fails to take into account the effect of ground topography on stair movement. In this paper, an extended social force model based on height map is proposed. This kind of model can accurately reproduce the temporal-spatial pedestrian dynamics on the stairway. Simulations indicate that the pedestrian flow on the stairway is not only constrained by geometric narrowing, but also restricted by the ground topography. Most of all, the discontinuous feature of height variance led to the fluctuation of velocity and further constrain the traffic capacity of stairs. Higher aspiration levels result in speed variance during emergency evacuation, and further induce congestion near the transitions between horizontal way and the stairs. The danger of clogging induced by transitions can be minimized by replacing staircases with ramps.

Estimation of RVoG Scene Parameters by Means of PolInSAR With TanDEM-X Data: Effect of the Double-Bounce Contribution

This article evaluates the effect of the double-bounce (DB) decorrelation term that appears in single-pass bistatic acquisitions, as in the TanDEM-X system, on the inversion of scene parameters by means of polarimetric SAR interferometry (PolInSAR). The retrieval of all scene parameters involved in the Random Volume over Ground (RVoG) model (i.e., ground topography, vegetation height, extinction, and ground-to-volume ratios) is affected by this term when the radar response from the ground is dominated by the DB. The estimation error in all these parameters is analyzed by means of simulations over a wide range of system configurations and scene variables for both agricultural crops and forest scenarios. Simulations demonstrate that the inclusion of the DB term, which complicates the inversion algorithm, is necessary for the angles of incidence shallower than 30° to achieve an estimation error below 10% in vegetation height and to avoid a significant underestimation in the ground-to-volume ratios. At steep incidences, this decorrelation term does not affect the estimation of vegetation height and ground-to-volume ratios. Regarding the extinction, this parameter is intrinsically not well estimated, since most retrieved values are close to the initial guesses employed for the optimization algorithm, regardless of the use or not of the DB decorrelation term. Finally, these findings are compared with the experimental results from the TanDEM-X data acquired over the rice fields in Spain for the available system parameters (baseline and incidence angle) of the acquired data set.

Evaluating P-Band TomoSAR for Biomass Retrieval in Boreal Forest

P-band synthetic aperture radar (SAR) is sensitive to above-ground biomass (AGB) but retrieval accuracy has been shown to deteriorate in topographic areas. In boreal forest, the signal penetrates through the canopy to interact with the ground producing variations in backscatter depending on ground topography, forest structure, and soil moisture. Tomographic processing of multiple SAR images Tomographic SAR (TomoSAR) provides information about the vertical backscatter distribution. This article evaluates the use of P-band TomoSAR data to improve AGB retrievals from backscattered intensity by suppressing the backscattered signal from the ground. This approach can be used even when the tomographic resolution is insufficient to resolve the vertical backscatter profile. The analysis is based on P-band data from two campaigns: BioSAR-1 (2007) in Remingstorp, southern Sweden, and BioSAR-2 (2008) in Krycklan (KR), northern Sweden. BioSAR airborne data were also processed to correspond as closely as possible to future BIOMASS TomoSAR acquisitions, with BioSAR-2-based results shown. A power law AGB model using volumetric HV polarized backscatter performs best in KR, with training residual root mean-squared error (RMSE) of 30%–36% (27–33 t/ha) for airborne data and 38%–39% for simulated BIOMASS data. Airborne TomoSAR data suggest that both vertical and horizontal tomographic resolution are of importance and that it is possible to greatly reduce AGB retrieval bias when compared with airborne P-band SAR backscatter intensity-based retrievals. A lack of significant ground slopes in Remningstorp reduces the benefit of using TomoSAR data which performs similar to retrievals based solely on P-band SAR backscatter intensity.

Pol-InSAR sensitivity to hemi-boreal forest structure at L- and P-bands

A dual-frequency approach is proposed to discriminate hemi-boreal forest species using L- and P-band data. First, it is shown that L-band is less sensitive to the forest structure than P-band. Second, the underlying ground topography is estimated using polarimetric sub-space decomposition at P-band to minimize any potential bias. Then, the Gaussian backscatter model is employed to extract the forest vertical backscatter at P-band. The inverted profiles differ significantly over the various forest stands and in the polarimetric channels, indicating important P-band sensitivity to the forest vertical structure. According to these measurements, it is shown that tree species, as pines and spruces, were presenting different signatures related to the vertical distribution of their structural elements. On the contrary, sensitivity to the forest vertical heterogeneity is low at L-band, allowing to accurately invert the forest height from an empirical structure function. A general workflow taking advantage of both frequencies is finally proposed to discriminate the forest species.