Tall Objects Research Articles

Arch fulcrum

A beam balanced on an arch provides a stable platform for investigating the principle of moments (law of levers), and for using it to weigh tall objects.

Validation and revision of far-field-current relationship for the lightning strike to electrically short objects

In this paper we have validated and revised the general expressions for far-field-current factors presented by Bermudez et al. (2005, 2007) for lightning strike to tall objects on perfectly and finitely conducting ground, respectively. For the perfectly conducting ground, it is found that when the risetime of lightning return stroke current (RT) is larger than 5h/c (h is the height of tall object and c is the light speed), the overestimation caused by the traditional method predicting the lightning current peak is within 10% beyond a distance of 20km from the lightning channel, and with the decrease of observed horizontal distance d, the error will increase due to the effect of induction field component. For example, when d is 10km, the overestimation is about 20% for strike to a 300-m-tall object. For the finite conductivity ranging from 0.01S/m to 0.001S/m, when the lightning strikes the 300-m-tall object, the lightning current peak predicted from the measured magnetic field peak according to the traditional method is overestimated ranging from about +5% to +20% (positive means overestimation while negative means underestimation) and the derivation value is more within a distance of 20km because of induction field component; When the lightning strikes the 50-m-tall object, the predicted current peak according to the traditional method has an error ranging from about +5% to −15%.

Synoptic scale outbreak of self‐initiated upward lightning (SIUL) from tall structures during the central U.S. blizzard of 1–2 February 2011

AbstractA major central U.S. winter cyclone on 1–2 February 2011 produced a band of high winds, up to 75 cm of snow, and numerous reports of thundersnow from Oklahoma into Ontario over a 26 h period. The National Lightning Detection Network (NLDN) recorded 282 flashes comprised of 1153 events which were >96% negative polarity. Hopes of imaging winter sprites associated with energetic positive cloud‐to‐ground events that sometimes accompany such winter storms did not materialize. However, the lack of lightning over the Great Lakes waters, plus media reports of numerous thundersnow events in downtown Chicago, prompted a detailed analysis of the NLDN data. This revealed that >93% of all lightning in the snow band was likely or possibly associated with self‐initiated upward lightning (SIUL) events from a variety of tall, and some not so tall, structures. In addition to 43 events from two Chicago skyscrapers, many shorter structures were involved, including wind turbines (13.1% of the total) and transmission line towers (6.7%). Wind speeds for all events exceeded the 8 m s−1 minimum threshold associated with SIULs in Japanese winter lightning storms. Radar reflectivities at the event locations had a mean of 28 dBZ and were almost always <35 dBZ. While conventional radar displays suggested stratiform precipitation in the thundersnow region, detailed analysis of 3‐D‐gridded NMQ (National Mosaic and Multi‐Sensor Quantitative Precipitation Estimation) radar reflectivity data confirmed elevated embedded cellular convection spanning the −10°C region associated with isentropic lifting above a frontal surface, evidence of noninductive charge generation sufficient to allow upward leader initiation from tall objects.

A new approach to calculate electric fields and charge density distribution when lightning strikes a tall object

We derive electric field expressions, associated with lightning strikes to a tall object, using the monopole (Continuity Equation) technique which is distinctly different from the traditional dipole (Lorentz Condition) technique. Expressions to calculate the charge density along the tall object and lightning channel based on the assumptions of the transmission line model of the lightning strikes to a tall object and a series point current source placed at the object top, are also derived. These expressions are used to calculate the very close-range electric fields in the monopole (Continuity Equation) technique in terms of the retarded current and charge density along the tower and lightning channel and their results are compared with those calculated from the traditional dipole (Lorentz Condition) technique in terms of the retarded current along the tower and lightning channel. Alternative explanations are provided to the inversion of polarity of the vertical electric field at very close range based on distribution of charge density along the tower and lightning channel.

A Study of Parameters of the Counterpropagating Leader and its Influence on the Lightning Protection of Objects Using Large-Scale Laboratory Modeling

UDC 537.86 In this work, the results of experiments on initiating the upward and descending leaders during the development of a long spark when studying lightning protection of objects with the help of large-scale models are shown. The influence of the counterpropagating leaders on the process of the lightning strike of ground-based and insulated objects is discussed. In the first case, the upward negative leader is initiated by the positive downward leader, which propagates from the high-voltage electrode of the “rod–rod”-type Marx generator (the rod is located on the plane and is 3-m high) in the gap with a length of 9–12 m. The positive-voltage pulse with a duration of 7500 µs had an amplitude of up to 3 MV. In the second case, initiation of the positive upward leader was performed in the electric field created by a cloud of negatively charged aerosol, which simulates the charged thunderstorm cell. In this case, all the phases characteristic of the ascending lightnings initiated by the tall ground-based objects and the triggered lightnings during the experiments with an actual thunderstorm cloud were observed in the forming spark discharge with a length of 1.5– 2.0 m. The main parameters of the counterpropagating leader, which is initiated by the objects during the large-scale model experiments with a long spark, are shown.

The influence of object height on maximum grip aperture in empirical and modeled data.

During a grasping movement, the maximum grip aperture (MGA) is almost linearly scaled to the dimension of the target along which it is grasped. There is still a surprising uncertainty concerning the influence of the other target dimensions on the MGA. We asked healthy participants to grasp cuboids always along the object's width with their thumb and index finger. Independent from variations of object width, we systematically varied height and depth of these target objects. We found that taller objects were generally grasped with a larger MGA. At the same time, the slope of the regression of MGA on object width decreased with increasing target height. In contrast, we found no effect of varying target depth on the MGA. Simulating these movements with a grasping model in which the objective to avoid contact of the digits with the target object at positions other than the goal positions was implemented yielded larger effects of target height than of target depth on MGA. We concluded that MGA does not only depend on the dimension of the target object along which it is grasped. Furthermore, the effects of the other 2 dimensions are considerably different. This pattern of results can partially be explained by the aim to avoid contacting the target object at positions other than the goal positions.

A stereo image matching method to improve the DSM accuracy inside building boundaries

In a digital surface model derived from high-resolution stereo images, the accuracies of building rooftop elevations are usually much lower than that of open areas without tall objects. This problem makes building height estimation difficult from the stereo images. The inaccuracy of building rooftop elevation is caused by many factors including shadows, occlusions, smoothing constraints in the matching algorithms, and the mismatch on extremely high buildings. To improve the accuracy of building rooftop elevations, this study enhances the existing image matching methods by adding building footprint maps as a constraint. The proposed image matching method consists of three steps. First, a building footprint was used to identify the corresponding building rooftop locations in the stereo images. Second, the left and right stereo images were matched according to color and shape. Third, the left and right sub-images of the building were further matched at pixel level to generate detailed roof elevations. Validation using surveyed rooftop elevations demonstrated that the proposed method can estimate building rooftop elevation with a one-third error using the current commercial software. In addition, the errors for low-rise and high-rise buildings were consistent in the proposed method.

Glow corona generation and streamer inception at the tip of grounded objects during thunderstorms: revisited

The initiation of streamers prior to a lightning strike can be reportedly inhibited by glow corona discharges generated from tall objects. In contrast to previous studies based on a simplified one-dimensional model of glow corona, a two-dimensional evaluation of the corona ion drift from tall objects is used here to analyse this effect quantitatively. Proper estimates for the corona space charge distribution generated during both the charging process of a thundercloud and the descent of the downward stepped leader are thus calculated. It is found that the shielding effect of the corona space charge on the streamer inception is not as severe as previously reported. Estimations of the effective height of the downward leader tip at which streamer inception takes place are presented and discussed for lightning rods and dissipation array systems.

Productivity of TerraSAR-X 3D Data In Urban Areas: A Case Study In Trento

TerraSAR-X (TSX) is supposed to be a revolution for synthetic aperture radar (SAR) imaging because it offers the highest resolution spatial data and is suitable for interferometry. This study aims to validate the performance of TSX high-resolution spotlight (HS) mode data in 3D representations of urban areas. Therefore, a digital surface model (DSM) with a 3-m grid was generated over Trento, Italy, and its quality was validated by comprehensive analyses. The TSX HS DSM matches the reference model well, and the absolute vertical accuracy is ±7-8 m. The quality of the topographic estimation is satisfactory due to the suitable normal baseline which yields a more sensitive SAR signal to height differences, transformed into a lower value for the height of ambiguity. The DSM has distortions because of foreshortening, layover and shadows caused by terrain inclination and tall objects on the ground. Dense forests have a negative influence on the results because they are not penetrated by the short wavelengths of the X-band.

Urban Tree Cover Mapping with Relief-corrected Aerial Imagery and Lidar

This article discusses how urban tree canopy cover is often mapped by classifying high-resolution multispectral imagery. However, it can be difficult to differentiate low-lying vegetation from tree cover using optical data alone. Combining a lidar-derived normalized digital surface model (NDSM) improves classification accuracy, but the optical imagery is often imperfectly aligned with the NDSM. Aerial imagery is normally orthorectified using the ground elevation. However, tall objects in the orthorectified imagery still suffer from relief displacement and this can cause classification errors when lidar and the aerial imagery are combined. This article presents an approach for urban tree cover mapping that is composed of two parts. The first part is a method for correcting the relief displacement of trees in previously orthrectified aerial imagery, and the second part is an object-based classification method that combines relief-corrected multispectral aerial imagery with a lidar-derived NDSM. Using these methods, tree cover was mapped for a 1,600 ha region of London, Ontario, Canada with improved positional and classification accuracy.

Evaluation of visual cues of three-dimensional virtual environments for helicopter simulators

Visual cues are an essential part of helicopter flight simulators. The required cues for hover are particularly large, due to closeness to the ground and small movements. However, the research on low-altitude helicopter flight is limited. In this research, the density and height of the three-dimensional (3D) objects in the scene are analysed to find their effect on hovering and low-altitude helicopter flight. An experiment is conducted using a personal computer-based flight simulator on 10 professional military pilots. The results revealed that 3D object density and 3D object height affect both horizontal and vertical hovering performance. In hover and low-altitude flight, altitude control is positively affected by smaller object height. Paradoxically, the pilots preferred the scenes composed of tall and mixture objects. Pilot distance estimation was significantly affected by the knowledge of both object density and object height, but these factors do not individually improve distance estimation.

Observations of simultaneous upward lightning leaders from multiple tall structures

We present high-speed camera observations (up to 7200 images per second) and correlated electric field measurements of upward lightning leaders initiated simultaneously from multiple tall towers. Four towers spanning a horizontal distance of 2.9km and ranging in height from 121 to 191m, developed upward leaders following a nearby positive cloud-to-ground (+CG) flash on 7/16/09 UT in Rapid City, South Dakota, USA during the summer thunderstorm season. The optical and electric field observations suggest that all four upward propagating leaders were positive polarity (i.e., upward negative lightning) and initiated simultaneously approximately 2ms following the +CG return stroke. There was significant intracloud flash activity prior to the return stroke, and upward leader initiation coincided with the passage of horizontally extensive in-cloud negative breakdown following the +CG return stroke. This observation supports the idea that downward positive cloud-to-ground lightning can trigger upward negative lightning from multiple tall objects. Specifically, the triggering component is an area of horizontally propagating negative breakdown following the +CG return stroke that influences a broad area resulting in simultaneous or near-simultaneous, positive polarity upward leader initiation from multiple tall objects.

Investigation on the Interaction of Secondary Current Pulses with the Main Wavefront

Additional current pulses get injected into the lightning channel from branches and/or from successive reflections within struck Tall Grounded Objects (TGOs). These pulses termed here as current waves/pulses affect the lightning Electro-Magnetic Fields (EMFs). With regard to these, an important question arises on whether or not these pulses get reflected at the main wavefront and there seems to be uncertainty in the pertinent literature. A particular case involving only the first ground end reflection from a struck TGO has been fully dealt in our earlier work. However, the same for subsequent reflections from TGO and that for the current fed by the branches were not dealt and this forms the main goal of present work. As the main objective is to ascertain the status of these secondary current pulses after they have reached the main wavefront, dynamics at the point of injection assumes lesser importance. In view of this, a lumped voltage source is employed for the injection of secondary current pulses at appropriate time instants. The main stroke evolution is emulated by a macroscopic physical model, which was developed in our earlier work. Investigation showed that these secondary pulses merge with the main wavefront without any sign of reflection whatsoever. Analysis showed that the spatial dynamic resistance/conductance profile at the main wavefront is basically responsible for the same with distributed source providing additional support. These findings are in line with the observations made in our earlier work for the first ground end reflected current.

Atomic Force Microscopy of Connexin40 Gap Junction Hemichannels Reveals Calcium-dependent Three-dimensional Molecular Topography and Open-Closed Conformations of Both the Extracellular and Cytoplasmic Faces

Atomic force microscopy was used to study the three-dimensional molecular topography and calcium-sensitive conformational changes of Connexin40 hemichannels (connexons) reconstituted in 1,2-dioeloyl-sn-glycero-3-phosphatidylcholine lipid bilayers. Two classes of objects were observed that differed in their protrusion heights above the bilayer (2.6 versus 4.2 nm). Comparison to reconstituted connexons containing Connexin40 truncated to eliminate most of its C-terminal cytoplasmic domain showed that the two height classes corresponded to the shorter extracellular and taller cytoplasmic aspects of the hemichannels and that the C-terminal tail of Connexin40 contributes ∼1.6 nm in thickness. Hemichannels imaged in solutions containing < 10 μm Ca(2+) showed 3.1-3.2 nm depressions (openings) in 30% of the cytoplasmic faces and 65% of the extracellular faces, and high-resolution three-dimensional topography of extracellular or cytoplasmic aspects of some connexons was observed. After addition of 3.6 mm Ca(2+), > 75% of the connexons in either orientation adopted closed conformations. In contrast, hemichannels imaged in the presence of 0.1 mm EDTA showed large (5.6- to 5.8-nm diameter) openings in nearly all hemichannels regardless of orientation, and detailed topography was visible in many connexons. Real-time imaging following the addition of 3.6 mm Ca(2+) showed transitions of both extracellular and cytoplasmic orientations from "open" into "closed" conformations within several minutes. These studies provide the first high-resolution topographic information regarding a connexin with a large cytoplasmic domain and suggest that the extramembranous portions of Connexin40 contribute to a channel entrance that is relaxed by chelation of residual divalent cations.

Determination of Current Within the Lightning Path in the Case of Lightning to a Tall Object

Four model types that could be used to theoretically approximate lightning events currently exist. These are namely gas dynamic (physical) models, electromagnetic models, distributed-circuit models, and “engineering” models. In this paper, a modified transmission line (TL) “engineering” modeling approach, which incorporates the presence of a tall object in the lightning path is adopted. The associated discontinuity at the lightning channel front is treated by introducing reflected and transmitted components, with constituents that are less influential omitted. All computations are performed in the time domain. The considered tall structure is the CN Tower and it is represented by either one, three, or five transmission line sections connected in series. The lightning channel is represented by two more transmission line sections of variable length. The models allow for calculation of current at any height of the CN Tower or the lightning channel and at any time, as needed for determination of the electric and magnetic fields at a distance. The approach is applicable to any other tall structure.

Does planning a different trajectory influence the choice of grasping points?

We examined whether the movement path is considered when selecting the positions at which the digits will contact the object’s surface (grasping points). Subjects grasped objects of different heights but with the same radius at various locations on a table. At some locations, one digit crossed to the side of the object opposite of where it started. In doing so, it moved over a short object whereas it curved around a tall object. This resulted in very different paths for different objects. Importantly, the selection of grasping points was unaffected. That subjects do not appear to consider the path when selecting grasping points suggests that the grasping points are selected before planning the movements towards those points.

Lightning-Induced Voltage Over Lossy Ground by a Hybrid Electromagnetic Circuit Model Method With Cooray–Rubinstein Formula

This paper presents the calculation of lightning-induced voltages over lossy ground, generated by a lightning strike to a flat ground and a tall object. A hybrid electromagnetic circuit model method adopting an approximation formula, i.e., Cooray-Rubinstein expression, is employed in this paper. A comparison of the simulation results with experimental data shows that the Cooray-Rubinstein formula is still good enough for the calculation of a lightning-induced voltage. Electric fields calculated by the proposed method, and by equations derived by Master and Uman and a conventional dipole technique, are compared. The two approaches yield the same total electrical fields but different components of electrostatic, induction and radiation.

A new concept in lightning parameters measurement

Nowadays the electrical activity measured in tall objects has been widely characterized, but the collected data of lightning rods installed in buildings do not amount to enough to obtain reliable statistics. The measures stored at relatively few points are not representative of the different types of installations. Furthermore, the protection model applied for lightning air terminal installations is based on theoretical models. This paper describes the design of a micro-station to measure some lightning parameters in real lightning air terminal installations correlated to the nature of emplacement instead of triggering lightning or choosing points with a high number of lightning impacts.

Missing in action: the effect of obstacle position and size on avoidance while reaching

When reaching to objects, our hand and arm rarely collide with non-target objects, even if our workspace is cluttered. The simplicity of these actions hides what must be a relatively sophisticated obstacle avoidance system. Recent studies on patients with optic ataxia and visual form agnosia have demonstrated that obstacle avoidance is an automatic process, likely governed by the dorsal stream (Schindler et al. 2004; Rice et al. 2006). The current study sought to quantify how normal participants react to changes in the size and position of non-target objects in and around their workspace. In the first experiment, 13 right-handed subjects performed reaches to a target strip in the presence of two non-target objects, which varied in depth and horizontal configuration. We found that objects with horizontal alignments that were asymmetric about midline created systematic deviations in reach trajectory away from midline, with participants seeming to maximize the distance away from the two objects. These deviations were significantly greater for objects nearer in depth and nearly disappeared when the objects were placed beyond the target strip. Accompanying this pattern of deviation were other significant obstructing effects whereby reaches were executed more slowly when objects were close in depth and close to the participants reaching (right) hand. In the second experiment, we varied the height of the two objects, as well as the depth. Object pairs were now both tall, both short, or one-short/one-tall. We replicated the significant depth effects of the first experiment, extending the finding to include sensitivity to the size of the objects. Here the obstructing effect caused by short objects was similar to tall objects when those objects were placed at the depth of the reach target, but less than the tall objects when placed at mid-reach. Taken together, these experiments suggest that humans possess a sophisticated obstacle avoidance system that is extremely sensitive and conservative in evaluating potential obstacles and adjusting the reach accordingly.

Influences of the Presence of a Tall Grounded Strike Object and an Upward Connecting Leader on Lightning Currents and Electromagnetic Fields

Using a generalized transmission line model of the lightning return stroke, we have investigated the influences of the presence of a tall strike object and an upward connecting leader on the magnitude of lightning current and on associated electric and magnetic fields. For a typical subsequent lightning return stroke, the peak current at the bottom of a 100-m-high object is 1.5 times larger than the channel base peak current for the same strike to the flat ground, regardless of the presence of a 20-m-long upward connecting leader, while the lightning peak current at the top of the strike object is not much different from the current in the absence of the object. The vertical electric field due to a lightning strike to a 100-m-high object E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z-tall</sub> is reduced relative to that due to the same strike to the flat ground E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">flat</sub> at distances ranging from 30 m to 200 m from the object and enhanced at distances greater than 200 m. The azimuthal magnetic field for the tall object case H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">phi-tall</sub> is larger than that for the flat ground case H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">phi-flatt</sub> at any distance. Beyond about 3 km, E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z-tall</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">/</sub> E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">flat</sub> becomes insensitive to distance change and is equal to H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">phi-tall</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">/</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">phi-flatt</sub> .