Local Height Research Articles

A Boundary-Based Ground-Point Filtering Method for Photogrammetric Point-Cloud Data

Ground-point filtering from point-cloud data is an important process in remote sensing and the photogrammetric map-production line, especially in generating digital elevation models from airborne lidar and aerial photogrammetric point-cloud data. In this article, a new and simple boundary-based method is proposed for ground-point filtering from the photogrammetric point-cloud data. The proposed method uses the local height difference to extract the boundaries of objects. Then the extracted boundary points are traced to generate polygons around the borders of any objects on the ground. Finally, the points located inside these polygons, which are classified as non-ground points, are filtered. The experimental results on the photogrammetric point cloud show that the proposed method can adapt to complex environments. The total error of the proposed method is about 8.96%, which is promising in these challenging data sets. Moreover, the proposed method is compared with cloth simulation filtering, multi-scale curvature classification, and gLiDAR methods and gives better results.

Canonical heights on Pell conics over number fields

In "Higher descent on Pell conics. III. The first 2-descent", Lemmermeyer introduced the canonical heights on the groups of rational points on Pell conics, which are analogues of the canonical heights on elliptic curves. In this paper, we generalize this: We introduce the canonical heights on the groups of $\overline{\mathbb{Q}}$-rational points on Pell conics over number fields.

Transcendence of polynomial canonical heights

There are two fundamental problems motivated by Silverman’s conversations over the years concerning the nature of the exact values of canonical heights of \(f(z)\in \bar{\mathbb {Q}}(z)\) with \(d:=\deg (f)\ge 2\). The first problem is the conjecture that \(\hat{h}_f(a)\) is either 0 or transcendental for every \(a\in \mathbb {P}^1(\bar{\mathbb {Q}})\); this holds when f is linearly conjugate to \(z^d\) or \(\pm C_d(z)\) where \(C_d(z)\) is the Chebyshev polynomial of degree d since \(\hat{H}_f(a)\) is algebraic for every a. Other than this, very little is known: for example, it is not known if there exists even one rational number a such that \(\hat{h}_f(a)\) is irrational where \(f(z)=z^2+\displaystyle \frac{1}{2}\). The second problem asks for the characterization of all pairs (f, a) such that \(\hat{H}_f(a)\) is algebraic. In this paper, we solve the second problem and obtain significant progress toward the first problem in the case of polynomial dynamics. These are consequences of our main result concerning algebraic numbers that can be expressed as a multiplicative combination of values of Böttcher coordinates. The proof of our main result uses a certain auxiliary polynomial and the powerful Medvedev–Scanlon classification of preperiodic subvarieties of split polynomial maps.

The hydromechanical behavior of opalinus clay fractures: Combining roughness measurements with computer simulations

The role of surface roughness of fractures in Opalinus Clay and in rocks in general is relevant in understanding the hydromechanical behavior of fractures. Two different fracture surfaces of shear fractures in the Opalinus Clay were investigated. The fracture surfaces were characterized based on their roughness power spectrum. It was found that slickensides fracture surfaces are near fractal-like up to the longest scale with a fractal dimension Df ∼ 2.1 and in the absence of a roll-off region at long wavelengths. In contrast, the glassy fracture surfaces show a roll-off region, which is characteristic of a flat surface with rather small and local topographic height variations. The glassy fracture surface is near fractal like with Df ∼ 2.0. The measured roughness power spectra were used to create fracture models to study the behavior of different fracture closure mechanism: 1) increasing congruence (matedness), 2) closure by compression and 3) closure by swelling. It turned out that the relationship between permeability and mean aperture depends on the fracture closure mechanism. Concerning closure by compression, the root mean square (rms) value of the aperture (aper) distribution aperrms influences the contact formation behavior, which in turn controls the hydromechanical properties. The lower aperrms is, the lower the fracture compliance. Apart from aperrms, the simulations show that in clay rocks, plastic deformation plays an important role in the closure of fractures by compression. In agreement with the experiments, the simulations predict that the permeability falls below 10% of the initial value at a compressive stress of 5 MPa. The simulations predict that fracture closure by swelling is rather ineffective for confining pressures exceeding ∼1 MPa.

Mission Planning for Low Altitude Aerial Drones during Water Sampling

Mission planning for small uncrewed aerial systems (sUAS) as a platform for remote sensors goes beyond the traditional issues of selecting a sensor, flying altitude/speed, spatial resolution, and the date/time of operation. Unlike purchasing or contracting imagery collections from traditional satellite or manned airborne systems, the sUAS operator must carefully select launching, landing, and flight paths that meet both the needs of the remote sensing collection and the regulatory requirements of federal, state, and local regulations. Mission planning for aerial drones must consider temporal and geographic changes in the environment, such as local weather conditions or changing tidal height. One key aspect of aerial drone missions is the visibility of the aircraft and communication with the aircraft. In this research, a visibility model for low-altitude aerial drone operations was designed using a GIS-based framework supported by high spatial resolution LiDAR data. In the example study, the geographic positions of the visibility of an aerial drone used for water sampling at low altitudes (e.g., 2 m above ground level) were modeled at different levels of tidal height. Using geospatial data for a test-case environment at the Winyah Bay estuarine environment in South Carolina, we demonstrate the utility, challenges, and solutions for determining the visibility of a very low-altitude aerial drone used in water sampling.

Percolating transition from weak to strong turbulence in wind-induced water surface waves

Recent studies in hydrodynamic flows and nonlinear plasma waves have demonstrated the turbulent transitions from ordered laminar flows and ordered plane waves, respectively, with the formation of a large percolating turbulent cluster, after the sporadic emergence and decay of turbulent puffs in the spatiotemporal space. These transitions follow the similar order–disorder transition scenario in nonequilibrium extended systems, governed by percolation theory. Here, we experimentally investigate the unexplored issue of whether a similar transition scenario can be extended to wind-driven water waves, especially for the transition from weak to strong turbulent states. Localized sites in the y–t (y is normal to the wind direction) space are binarized into hot turbulent sites (HTSs) and cold turbulent sites depending on the instantaneous energy of the local wave height fluctuations. It is found that increasing the fetch (the distance x from the wind entrance) as increasing the effective drive leads to the transition from the weak to the strong turbulent state with a smooth rapid rise of the area fraction occupied by HTSs, and the formation of a large HTS cluster percolating through the y–t space after the sporadic emergence of HTS clusters. This generic transition behavior and the scaling exponents of the HTS fraction around the critical (percolating) fetch, and of the quiescent time and the quiescent distance between adjacent HTS clusters at the critical fetch, are akin to those around and at the critical point, respectively, for the 1 + 1D (dimensional) nonequilibrium system governed by the directed percolation theory.

Is 3D surface structuring always a prerequisite for effective SERS?

In this work, we systematically investigate and compare the need for 3D vis-‘a-vis 2D surface morphologies of SERS templates by considering all major aspects of uniformity, reproducibility, sensitivity and cost-effectiveness. Controlled Si nanostructured surfaces varying largely in their local height fluctuations are fabricated by adopting an effortless wet chemical etch process. To evaluate the SERS behavior, an Au (50%)-Ag (50%) alloy plasmonic layer is grown over these substrates owing to its high and stable SERS response. An initial assessment of the SERS activity is done by using Rh6G as a probe molecule. Apparently, the surface with 3D morphology shows a slightly higher response than the surface possessed with a few nm of surface roughness (2D). But from signal uniformity and reproducibility considerations the 2D morphology gives the lowest value of RSD of 5.56% in contrast to a high value of 27.13% for the 3D morphology. The 2D substrate also allows a LOD up-to 10−15 M and an EF of 7.1 × 107, thereby indicating a high sensitivity at par the best values reported till date. Further, detection of methylene blue and methyl parathion up to nM concentrations bear testimony to its universal applicability and ultra-sensitivity.

Pheochromocytoma: A Diagnosis Made More Difficult in the COVID-19 Era

ABSTRACT INTRODUCTION Pheochromocytomas and paragangliomas are rare neuroendocrine tumors that secrete catecholamines. Symptoms of these tumors are related directly to catecholamine excess but can be intermittent and easily misattributed to other more common pathologies. Identification in the Emergency Department is inherently difficult. In the COVID-19 pandemic physicians have had to account for both the disease itself as well as associated increased prevalence of cardiac, pulmonary, and vascular complications. Such shifting of disease prevalence arguably makes rarer diseases, like pheochromocytoma, less likely to be recognized. CASE REPORT We report a case of pheochromocytoma discovered in the emergency department in a patient who presented with fatigue, tachycardia, and diaphoresis. The differential included pulmonary embolism, cardiomyopathy, congestive heart failure and infectious causes. A broad workup was begun including serology, electrocardiogram, Computed Tomography Angiogram (CTA), and COVID-19 testing. This patient was evaluated in the winter of 2020, the local height of the COVID-19 pandemic, and was found to be positive. A tiny retroperitoneal tumor was reported on CTA as “incidental” in the setting of multifocal pneumonia from COVID-19 infection. But further history taking discovered many years of intermittent symptoms and suggested that the tumor may be more contributory to the patient’s presentation. Subsequent MRI and surgical pathology confirmed the pheochromocytoma. CONCLUSION This case presentation highlights the importance of careful history taking, keeping a broad differential, and examining incidental findings in the context of the patient’s presentation.

Direct use of large-footprint lidar waveforms to estimate aboveground biomass

Many studies have established the strong connections between aboveground biomass and lidar height metrics; however, these relationships are site-specific. Field data required to derive these relationships are not readily available in many cases. We developed a model to estimate plot-level aboveground biomass density (AGBD) directly from large-footprint lidar waveform measurements. An individual tree-based aboveground biomass (AGB)-height allometric relationship was scaled up to the plot level using lidar-waveform sensed tree height and crown size distribution characteristics. The AGBD was estimated based on a waveform/foliage profile-weighted height-based allometric equation. The AGBD-height scaling exponent was then built on the allometric relationships of tree height with stem diameter and crown volume with tree height. Global vegetation structure data analysis demonstrated that one general model (scaling exponent ~ 1.6–1.8) works reasonably well across all global forest biomes except boreal forests (scaling exponent ~ 0.9). We applied the model to estimate aboveground biomass in two distinct geographic regions: temperate deciduous/conifer forests in the northeastern USA and a montane conifer forest in Sierra National Forest in California. Local vegetation structural data analysis leads to a consistent height scaling exponent for these two distinct biomes, slightly different from the global data analysis results. This model produced optimal AGBD estimates using the local height scaling exponent value. Adequate AGBD estimates with the general height scaling exponent value were also provided by our model. Our analysis suggests one general allometric relationship between plot-level AGBD and large-footprint lidar waveforms. Integrating local structure allometric relationships improve the predictive accuracy of the model. Our model outperformed the lidar height metrics-based approach for AGBD estimates and overcame the biomass underestimation problem using height metrics for high biomass regions. This model could potentially serve as a general and robust model for monitoring forest carbon stocks using large-footprint lidar waveform measurements such as the Global Ecosystem Dynamics Investigation (GEDI) mission at the continental and global scales. The model could be a framework for integrating a demography-based terrestrial ecosystem model and GEDI global mission measurements to improve global carbon stock and flux estimates.

Optimization of safe navigability conditions in shallow inland waters: The Routinav app

Safe navigation in inland waters subjected to tide requires dedicated forecasts of meteorological and oceanographic variables, such as local tidal height, currents, wind and atmospheric pressure. Indeed, it is more difficult to navigate inland shallow waters subjected to intense morphologic dynamics, and therefore characterized by the non-linearity of the tidal height propagation throughout the channels, traduced by important changes in tidal amplitude and phase, especially when no navigation aids are installed. In this context, this work objective is a mobile application (Routinav) development that allows simulating the navigability conditions in inland shallow waters. Firstly, a monitoring system was installed on volunteer boats and validated in Ria de Aveiro, showing high accuracy in depth and position acquisition. Secondly, was designed and applied an algorithm allowing the identification of navigable and non-navigable route segments, according to the updated depth and forecasted tidal height by the hydrodynamic model. Based on this algorithm, was created an agile prototype used to build up the Routinav mobile application for iOS (iPhone OS) and Android operating systems.

Can Simultaneous PIV In The Gas And Liquid Phases Provide Insight Into The Transfer Of Momentum Between The Two Phases?

Understanding the interaction between a gas shearing over a liquid film and the liquid film is essential if we wish to use modeling to optimize systems to decrease environmental impact, increase efficiency, and hence productivity. To this end, PIV is used to simultaneously study the velocity fields in the gas and liquid fields to better understand the interaction between the two phases. The methodology is detailed in the paper, and initial results show that the film shape changes as the flow increases from 2.2 m/s to 4.7 m/s. This change can be seen to be from a 2D surface wave regime to a 3D wave regime. In the 2D regime, the liquid film is linear in shape, and the averaged and conditionally averaged velocity profiles of the gas and liquid velocity are equal at the interface. In the 3-D regime, the averaged liquid and gas velocity profiles are no longer equal at the average interface height. Instead, they coincide at the 2.5% percentile of the local height distribution. The conditionally averaged velocity profiles show significant differences as the film height changes. It is suggested that this would mean the use of average profiles for validating CFD in similar situations might need to be reviewed.

Transonic Buffet Active Control with Local Smart Skin

Transonic flight has high economic benefits, but the appearance of transonic buffet limits the flight envelope. The shock control bump currently used for transonic buffet suppression tends to degrade the aerodynamic performance of the non-buffeting state. In this study, a smart skin system is used to eliminate the fluctuating load of transonic buffet by measuring the airfoil lift coefficient as the feedback signal and adjusting the local skin height using data-driven, model-free adaptive control. Since the actuator height is dynamically adjusted only after the occurrence of transonic buffet, the smart skin can completely suppress the fluctuating load and does not affect the aerodynamic performance in the non-buffeting state. The suppression effect of the proposed smart skin on transonic buffet is verified by numerical simulation of the flow. The simulation results show that due to the introduction of closed-loop control, the fluctuating load of transonic buffet can be effectively suppressed for different positions and maximum heights of the actuator. Even when the flow state changes, the robust smart skin system can also achieve the control goal. Therefore, smart skins combining flexible materials and control technologies have the potential to effectively improve the aerodynamic performance of aircraft.

Impact of radiation and electron trapping on minority carrier transport in p-Ga2O3

Highly resistive undoped p-type gallium oxide samples were subjected to cumulative proton irradiation with energies ranging from 25 to 70 keV and doses in the 1.6 × 1014–3.6 × 1014 cm−2 range. Proton irradiation resulted in up to a factor of 2 reduction of minority electron diffusion length in the samples for temperatures between ∼ 300 and 400 K. Electron injection into the samples under test using a scanning electron microscope beam leads to pronounced elongation of diffusion length beyond the pre-irradiation values, thus demonstrating stable (days after injection) recovery of adverse radiation impact on minority carrier transport. The activation energy of 91 meV estimated from the temperature dependent diffusion length vs electron injection duration experiments is likely related to the local potential barrier height for native defects associated with the phenomenon of interest.

Height pairing on higher cycles and mixed Hodge structures

For a smooth, projective complex variety, we introduce several mixed Hodge structures associated to higher algebraic cycles. Most notably, we introduce a mixed Hodge structure for a pair of higher cycles which are in the refined normalized complex and intersect properly. In a special case, this mixed Hodge structure is an oriented biextension, and its height agrees with the higher archimedean height pairing introduced in a previous paper by the first two authors. We also compute a non-trivial example of this height given by Bloch–Wigner dilogarithm function. Finally, we study the variation of mixed Hodge structures of Hodge–Tate type, and show that the height extends continuously to degenerate situations.

Spatiotemporal climatology of the Arabian Subtropical Anticyclone

ABSTRACT The Arabian Subtropical Anticyclone (ASA) plays an essential role in regulating weather systems over the Arabian Peninsula (Arabia) and adjacent areas. A need exists to document specific details of the spatial and temporal climatology of the ASA. In order to identify the monthly ASA position/center, the local maximum geopotential height (gph) should be located at different vertical levels. The common automated method did not work for the ASA in the warm season and an approach involving wind flow patterns was needed. The ASA was better defined in the lower troposphere in the cool season and in the mid- to upper-troposphere during the warm season. The near surface ASA begins in Aug over northern Arabia and migrates southeast until it reaches the Arabian Sea in Feb. Apr is the onset of the middle-troposphere ASA. From May to Aug, this anticyclone moves to the north with increasing height. The upper-level ASA is located over northeast Arabia in May and goes north in Jun and Jul. Seasonal changes in energy fluxes and atmospheric circulation patterns linked with the Asian Monsoon are identified as possible drivers of the temporal changes in the ASA.

Tsunami Occurrence 1900–2020: A Global Review, with Examples from Indonesia

We present an overview of tsunami occurrences based on an analysis of a global database of tsunamis for the period 1900–2020. We evaluate the geographic and statistical distribution of various tsunami source mechanisms, high-fatality tsunamis, maximum water heights (MWHs) of tsunamis, and possible biases in the observation and recording of tsunami events. We enhance a global statistical overview with case studies from Indonesia, where tsunamis are generated from a diverse range of sources, including subduction zones, crustal faults, landslides, and volcanic islands. While 80% of global recorded tsunamis during 1900–2020 have been attributed to earthquake sources, the median MWH of earthquake tsunamis is just 0.4 m. In contrast, the median water height of landslide tsunamis is 4 m. Landslides have caused or contributed to 24% of fatal tsunamis. During 1900–2020, more tsunamis with water heights > 1 m occurred in Indonesia than in any other country. In this region fatal tsunamis are caused by subduction zone earthquakes, landslides, volcanos, and intraplate crustal earthquakes. Landslide and volcano tsunami sources, as well as coastal landforms such as narrow embayments have caused high local maximum water heights and numerous fatalities in Indonesia. Tsunami hazards are increased in this region due to the densely populated and extensive coastal zones, as well as sea level rise from polar ice melt and local subsidence. Interrelated and often extreme natural hazards in this region present both an opportunity and a need to better understand a broader range of tsunami processes.

Effect of blade contamination on power production of wind turbines

Wind turbines suffer from considerable power losses because of contamination on their blades, that can be due to erosion, wear, smog, insect, sand and dust particle impact. Blade contamination, its effects on the flows over the wind turbine blades and consequent power production losses form the main focus of the present study. These effects are mainly due to increased roughness on the blades leading to earlier laminar-turbulent transition and consequently, thicker boundary-layers on the blades. Early laminar-turbulent transition leads to a larger part of the flow over a blade being turbulent, thus increasing skin friction drag. Thicker boundary-layer on a blade results in blade profile being effectively modified, rendering the flow over the blade depart from ideal. In the present study, the effects of blade contamination on power output of contaminated wind turbine blades is investigated numerically using an in-house computational tool. Blade Element Momentum Method (BEM) combined with the Panel Method is used to calculate the local velocity and angle of attack at the blade sections, together with the power produced by the blade. Trajectories of particles causing contamination are calculated using Lagrangian approach, also yielding the impingement pattern of the particles on the blade surface, i.e. particle collection efficiency distribution. The effects of roughness on the boundary-layer flow are investigated by using an Integral Boundary-Layer Method, which yields the characteristics of the boundary-layer, i.e. laminar-turbulent transition location, increased skin-friction and thickening of the boundary-layer. The blade shape is modified due contamination thickness, the local height of which is assumed to be proportional to the local collection efficiency. Also, the roughness height distribution used in the boundary-layer calculations is assumed to be equal to the contamination thickness distribution on the blades. Power production and consequent losses of wind turbines with contaminated wind turbine blades are studied with respect to variations in particle size, wind speed and roughness height.

Comparison of Unipedicular and Bipedicular Percutaneous Kyphoplasty for Kummell's Disease.

Objective:To compare the clinical efficacy of unipedicular and bipedicular percutaneous kyphoplasty (PKP) for Kummell’s disease.Methods:A retrospective study was performed to review 40 patients with stage I and II Kummell’s disease who underwent PKP in our hospital from January 2015 to June 2018. Based on the transpedicular approach of PKP, those patients were randomly divided into unipedicular group (n = 19) and bipedicular group (n = 21). Operative time, bone cement injection volume and cement leakage rate were compared in the two groups. Pre- and post-operative visual analogue score (VAS), local kyphotic angle and average vertebral height were also evaluated.Results:All patients underwent surgery successfully. Compared with preoperative condition, VAS was significantly decreased at 1 day after operation and the last follow-up in both groups (P < .05), and local kyphotic angle and average vertebral height were restored markedly (P < .05). Operative time of both groups had no significant difference (P > .05). Bone cement injection volume was larger in bipedicular group (P < .05). At 1 day after operation and the last follow-up, the local kyphotic angle and average vertebral height in bipedicular group were restored better than those in unipedicular group (P < .05). There were 4 cases of cement leakage in both groups, with leakage rates of 21.1% and 19.0%, respectively, and the difference was not significant (P > .05).Conclusion:Both unipedicular and bipedicular PKP are effective for treating patients with stage I and II Kummell’s disease, while postoperative pain relief and imaging results in bipedicular group were better than those in unipedicular group.

The Shift from Energy to Water Limitation in Local Canopy Height from Temperate to Tropical Forests in China

Canopy height greatly affects the biomass stock, carbon dynamics, and maintenance of biodiversity in forests. Previous research reported that the maximum forest canopy height (Hmax) at global and regional scales could be explained by variations in water or energy availability, that is, the water- or energy-related hypothesis. However, fundamental gaps remain in our understanding of how different drivers (i.e., water and energy) contribute to the Hmax at the local scale. In this study, we selected eight dynamic forest plots (20–30 ha) across a latitudinal gradient (from 21.6° N to 48.1° N) in China and measured the canopy structure using airborne light detection and ranging (LiDAR) data. Based on the LiDAR point cloud data, we extracted the maximum tree height (Hmax) in a 20 × 20 m quadrat as a proxy for canopy height, and the topographic wetness index (TWI) and digital terrain model-derived insolation (DTMI) were calculated as proxies for water and energy conditions. We used a linear mixed model and spatial simultaneous autoregressive error model to quantify how TWI and DTMI contributed to variations in Hmax at the local scale. We found that the positive effect of TWI was stronger in subtropical and tropical forests, highlighting that water was the main factor that drives the canopy height pattern in these regions. In contrast, although the effects of DTMI can be both positive and negative, its relative contribution was higher in temperate forest plots than in other forest types, supporting the idea that energy input is more critical for Hmax in temperate forests. Overall, our study revealed the directional change from energy to water limitation from temperate to subtropical and tropical forests. Our findings can offer important insights into forest management, especially under global climate change in the Anthropocene.

A comparison of international and national references to measure the prevalence of stunting in Pakistani school-age girls

Epidemiology of stunting in < 5 years old is well characterized; however, its prevalence in adolescence is inconsistent in different geographical locations. We estimated the prevalence of stunting in schoolgirls of Punjab, Pakistan, to standardize local references according to international and national references. In this population-wide cross-sectional study, 10,050 schoolgirls aged 8–16 years from 12 different districts of northern, central, and southern Punjab were analyzed. The prevalence of stunting was calculated by applying Centres for Disease Control and Prevention (CDC) and World Health Organisation (WHO) height-for-age references and the local reference for the study population. We used Cohen’s kappa statistics to analyze the agreement of our data with reference values, and chi-square test was used as the test of trend. Marked overestimation of the prevalence of stunting was observed (22.72% and 17.49% according to CDC and WHO, respectively) in comparison to local reference (4.94%). According to CDC and WHO references, there was an increasing trend of prevalence of stunting with higher age; however, data was comparable across all the age groups when local references were applied. We recommend that the prevalence of stunting in school-age girls should be determined by applying local height references rather than international ones to plan health strategies and treatments in the local population.