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Search Results: 1 - 10 of 134009 matches for " Andrew T. Hudak "
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Using Satellite and Airborne LiDAR to Model Woodpecker Habitat Occupancy at the Landscape Scale
Lee A. Vierling, Kerri T. Vierling, Patrick Adam, Andrew T. Hudak
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0080988
Abstract: Incorporating vertical vegetation structure into models of animal distributions can improve understanding of the patterns and processes governing habitat selection. LiDAR can provide such structural information, but these data are typically collected via aircraft and thus are limited in spatial extent. Our objective was to explore the utility of satellite-based LiDAR data from the Geoscience Laser Altimeter System (GLAS) relative to airborne-based LiDAR to model the north Idaho breeding distribution of a forest-dependent ecosystem engineer, the Red-naped sapsucker (Sphyrapicus nuchalis). GLAS data occurred within ca. 64 m diameter ellipses spaced a minimum of 172 m apart, and all occupancy analyses were confined to this grain scale. Using a hierarchical approach, we modeled Red-naped sapsucker occupancy as a function of LiDAR metrics derived from both platforms. Occupancy models based on satellite data were weak, possibly because the data within the GLAS ellipse did not fully represent habitat characteristics important for this species. The most important structural variables influencing Red-naped Sapsucker breeding site selection based on airborne LiDAR data included foliage height diversity, the distance between major strata in the canopy vertical profile, and the vegetation density near the ground. These characteristics are consistent with the diversity of foraging activities exhibited by this species. To our knowledge, this study represents the first to examine the utility of satellite-based LiDAR to model animal distributions. The large area of each GLAS ellipse and the non-contiguous nature of GLAS data may pose significant challenges for wildlife distribution modeling; nevertheless these data can provide useful information on ecosystem vertical structure, particularly in areas of gentle terrain. Additional work is thus warranted to utilize LiDAR datasets collected from both airborne and past and future satellite platforms (e.g. GLAS, and the planned IceSAT2 mission) with the goal of improving wildlife modeling for more locations across the globe.
Discrete Return Lidar in Natural Resources: Recommendations for Project Planning, Data Processing, and Deliverables
Jeffrey S. Evans,Andrew T. Hudak,Russ Faux,Alistair M. S. Smith
Remote Sensing , 2009, DOI: 10.3390/rs1040776
Abstract: Recent years have seen the progression of light detection and ranging (lidar) from the realm of research to operational use in natural resource management. Numerous government agencies, private industries, and public/private stakeholder consortiums are planning or have recently acquired large-scale acquisitions, and a national U.S. lidar acquisition is likely before 2020. Before it is feasible for land managers to integrate lidar into decision making, resource assessment, or monitoring across the gambit of natural resource applications, consistent standards in project planning, data processing, and user-driven products are required. This paper introduces principal lidar acquisition parameters, and makes recommendations for project planning, processing, and product standards to better serve natural resource managers across multiple disciplines.
Utility of Remotely Sensed Imagery for Assessing the Impact of Salvage Logging after Forest Fires
Sarah A. Lewis,Peter R. Robichaud,Andrew T. Hudak,Brian Austin,Robert J. Liebermann
Remote Sensing , 2012, DOI: 10.3390/rs4072112
Abstract: Remotely sensed imagery provides a useful tool for land managers to assess the extent and severity of post-wildfire salvage logging disturbance. This investigation uses high resolution QuickBird and National Agricultural Imagery Program (NAIP) imagery to map soil exposure after ground-based salvage operations. Three wildfires with varying post-fire salvage activities and variable ground truth data were used to evaluate the utility of remotely sensed imagery for disturbance classification. The Red Eagle Fire in northwestern Montana had intensive ground truthing with GPS-equipment logging equipment to map their travel paths, the Tripod Fire in north central Washington had ground truthed disturbance transects, and the School Fire in southeastern Washington had no salvage-specific ground truthing but pre-and post-salvage images were available. Spectral mixture analysis (SMA) and principle component analysis (PCA) were used to evaluate the imagery. Our results showed that soil exposure (disturbance) was measureable when pre-and post-salvage QuickBird images were compared at one site. At two of the sites, only post-salvage imagery was available, and the soil exposure correlated well to salvage logging equipment disturbance at one site. When ground disturbance transects were compared to NAIP imagery two years after the salvage operation, it was difficult to identify disturbance due to vegetation regrowth. These results indicate that soil exposure (ground disturbance) by salvage operation can be detected with remotely sensed imagery especially if the images are taken less than two years after the salvage operation.
A Comparison of Two Open Source LiDAR Surface Classification Algorithms
Wade T. Tinkham,Hongyu Huang,Alistair M. S. Smith,Rupesh Shrestha,Michael J. Falkowski,Andrew T. Hudak,Timothy E. Link,Nancy F. Glenn,Danny G Marks
Remote Sensing , 2011, DOI: 10.3390/rs3030638
Abstract: With the progression of LiDAR (Light Detection and Ranging) towards a mainstream resource management tool, it has become necessary to understand how best to process and analyze the data. While most ground surface identification algorithms remain proprietary and have high purchase costs; a few are openly available, free to use, and are supported by published results. Two of the latter are the multiscale curvature classification and the Boise Center Aerospace Laboratory LiDAR (BCAL) algorithms. This study investigated the accuracy of these two algorithms (and a combination of the two) to create a digital terrain model from a raw LiDAR point cloud in a semi-arid landscape. Accuracy of each algorithm was assessed via comparison with >7,000 high precision survey points stratified across six different cover types. The overall performance of both algorithms differed by only 2%; however, within specific cover types significant differences were observed in accuracy. The results highlight the accuracy of both algorithms across a variety of vegetation types, and ultimately suggest specific scenarios where one approach may outperform the other. Each algorithm produced similar results except in the ceanothus and conifer cover types where BCAL produced lower errors.
LiDAR Utility for Natural Resource Managers
Andrew Thomas Hudak,Jeffrey Scott Evans,Alistair Matthew Stuart Smith
Remote Sensing , 2009, DOI: 10.3390/rs1040934
Abstract: Applications of LiDAR remote sensing are exploding, while moving from the research to the operational realm. Increasingly, natural resource managers are recognizing the tremendous utility of LiDAR-derived information to make improved decisions. This review provides a cross-section of studies, many recent, that demonstrate the relevance of LiDAR across a suite of terrestrial natural resource disciplines including forestry, fire and fuels, ecology, wildlife, geology, geomorphology, and surface hydrology. We anticipate that interest in and reliance upon LiDAR for natural resource management, both alone and in concert with other remote sensing data, will continue to rapidly expand for the foreseeable future.
Magnetic Nanoparticles with Core Shell: Macroscopic Model and Coercive Field
O. Hudak,M. Hudak
Advances in Materials Science and Engineering , 2010, DOI: 10.1155/2010/909810
Abstract: There exists nonhomogeneous structure in mechanosynthesized nanoparticles consisting of an ordered core surrounded by the shell. The shell may be structurally and magnetically disordered, or it may be ordered. These nanoparticles are found to be roughly spherical. We formulate the macroscopic model for the description of magnetic properties of nanoparticles with core-shell structure. The case of spheroids oriented in the same direction of polar axes is considered. There exits two coercive fields: and . They are depending on quantities o and x, where ), and , here is the volume of the nanoparticle, and is the volume of the core. is the magnetization of the core, and is the magnetization of the shell. There exists a transition from one type of the coercive field to another, changing x and o. We have found qualitative explanation of observed enhancement of coercive field and of its d-dependence in nanoparticles. 1. Introduction Ferromagnetic and (ferri-) or antiferromagnetic nanoparticles, mechanochemically prepared, have a shell structuredifferent from the core structure. The shell has mostly disordered structural and magnetic properties, while the core is magnetically ordered. In this paper, we formulate a model describing interaction of ellipsoid with ferromagnetic/antiferro- (ferri-)magnetic/ordering with shell (ellipsoid part which is not in the volume of the core ellipsoid). We study here the description of coercive fields of magnetic nanoparticles with spheroid shape with polar axes in the same direction for both spheroids. Due to fact that nanoparticles are small (smaller than ), we consider a single domain magnetic system. While porosity of ceramics prepared from such nanoparticles is in the range up to nearly 33 percents, and such pores do not disappear during further sintering, they undergo coalescence together with grain growth. Only subsurface pores have the possibility to go out in the surface, see in [1]. For the case of a spheroid with a pore, it can be easily shown that the pore may enhance the coercive field, or the coercive field is smaller than the bulk coercive field. Mechanosynthesized nanocrystalline nanoparticles were studied in [2]. There exists nonhomogeneous structure in these nanoparticles consisting of an ordered core surrounded by a disordered grain boundary-surface region. The core has a fully inverse spinel structure with a collinear spin alignment. The surface layer (shell) is structurally and magnetically disordered due to nearly random distribution of cations and the canted spin structure. It exhibits a reduced
Anisotropic Vortices in High-Temperature Superconductors and the Onset of Vortex-like Excitations above the Critical Temperature
O. Hudak
Physics , 2005,
Abstract: Recently we have found that a three-dimensional superconducting state with anisotropic vortices localized at the vortex-lattice points is a stable state in zero external magnetic field for the layered high temperature uperconductivity materials. There exists a phase transition at the temperature $T_{c}^{v}$ from the normal phase to the vortex superconducting state which is of the first order. The first order phase transition shows overheating and overcooling effects. Nucleation of the superconducting phase in the normal phase thus may occur at temperatures higher than the transition temperature $T_{c}^{v}$. Then the onset of the vortex-like excitations above the transition temperature $T_{c}^{v}$ occurs in our theory. The onset of the vortex-like excitations in Nerst signal and some other experimental evidence for these excitations above the transition temperature $T_{c}^{v}$ in LSCO, YBCO and in other high-temperature materials may be explained thus by our theory. The vortex-like excitations above and below the transition temperature $T_{c}^{v}$ in high temperature materials continuously evolve. This fact may be explained within our theory.
Landau theory of 180 degrees domain walls in BaTiO3 type ferroelectric particles: microcomposite materials
O. Hudak
Physics , 2005,
Abstract: The Landau theory of 180 degrees domain walls in BaTiO3 type ferroelectric particles is presented. Results of exact description of domain walls in bulk enabled us to formulate variational approach to theory of domain walls in corresponding small particles. The depolarization field effects and the space-charge layers are taken into account in the samples of the cube form. It was found that at low temperatures well known hyperbolic tangent wall profile is a good approximation for description of domain walls. Near the transition temperature it is more appropriate to speak about two walls separating ferroelectric-paraelectric-ferroelectric domains correspondingly as a result of splitting of a single ferroelectric wall in small BaTiO3 particles. Domain wall energy density, average interwall distance and change of the dielectric response of thick walls in small ferroelectric particles in microcomposites is found. Our results describe observed dependencies better than those theories which exist up to date. In temperature region near transition from the ferroelectric to paraelectric phase in micrcomposites our new quantitative results for response, for Curie-like transition temperature and other properties may be verified.
Social Behaviour of Agents: Capital Markets and Their Small Perturbations
O. Hudak
Physics , 2005,
Abstract: We study social behaviour of agents on capital markets when these are perturbed by small perturbations. We use the mean field method. Social behaviour of agents on capital markets is described: volatility of the market, aversion constant and equilibrium states are discussed. Relaxation behaviour of agents on the capital market is studied. Equation of motion for the agent average number is of the relaxation type. Development of the group of agents in the states corresponding to minimum of the aim function is either linear either exponentially damped. There exist characteristic volatility constants $ V_{c3} $ and $ V_{c3} $. The constant b of verification of information contribution to the aversion constant A and the $ A_{0} $ constant of aversion are distinguishing three types of dependencies of the minimum of the aim function on the expected volatility EV and on the expected returns E. Arbitrage trades and group forces lead the group into the equilibrium state. Verification of information intensity influences return back to the equilibrium state. The linear in time damping to the equilibrium state is characterized with the characteristic time $ T_{3}$ and $ T_{6} $, the exponential with a characteristic time $ \tau $. Their dependence on the expected volatility, on the expected profit and characteristics of agents is discussed.
Paraelectric - Ferroelectric Phase Transitions in Particles of the Sphere Shape
O. Hudak
Physics , 2005,
Abstract: A transition in a spheroidal particle from the paraelectric to the ferroelectric phase as well as dynamic susceptibility are studied without approximation in the paraphase. It is assumed that the surface charge is compensated and the boundary condition for the polarisation is P=0, i. e. with zero polarisation at the surface of the particle. There is an infinite number of resonance frequencies in the dynamic dielectric function within the quasistatic approximation. The paraphase properties of the dielectric response of the particle are discussed. The transition temperature decreases with decreasing diameter d of the particles inverse quadratically. There exists such a critical diameter that for the particles with the diameter below the critical one the ferroelectric phase is absent. Comparison of the experiment with theoretical results is carried out. Introduction of a dead layer thickness leads to a very good agreement of theory with the experiment for $PbTiO_{3}$ and to a good agreement with the experimentfor $BaTiO_{3}$.
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