An object-based approach for mapping forest structural types based on low-density LiDAR and multispectral imagery

Mapping forest structure variables provides important information for the estimation of forest biomass, carbon stocks, pasture suitability or for wildfire risk prevention and control. The optimization of the prediction models of these variables requires an adequate stratification of the forest landscape in order to create specific models for each structural type or strata. This paper aims to propose and validate the use of an object-oriented classification methodology based on low-density LiDAR data (0.5 m^?2) available at national level, WorldView-2 and Sentinel-2 multispectral imagery to categorize Mediterranean forests in generic structural types. After preprocessing the data sets, the area was segmented using a multiresolution algorithm, features describing 3D vertical structure were extracted from LiDAR data and spectral and texture features from satellite images. Objects were classified after feature selection in the following structural classes: grasslands, shrubs, forest (without shrubs), mixed forest (trees and shrubs) and dense young forest. Four classification algorithms (C4.5 decision trees, random forest, k-nearest neighbour and support vector machine) were evaluated using cross-validation techniques. The results show that the integration of low-density LiDAR and multispectral imagery provide a set of complementary features that improve the results (90.75% overall accuracy), and the object-oriented classification techniques are efficient for stratification of Mediterranean forest areas in structural- and fuel-related categories. Further work will be focused on the creation and validation of a different prediction model adapted to the various strata.     

Statistical estimation of runoff characteristics of watersheds in central Chile

Abstract

Estimation of monthly runoff statistical properties, such as monthly means and variances, is usually needed to design and evaluate water resource systems. If no local recorded data are available, a transfer of information through different alternative procedures can be used. In this paper, the use of linear Transfer Function (TF) models with precipitation series as inputs is proposed to estimate statistical properties of the resulting runoff series. Empirical relationships based on data from watersheds in the mountainous zone of central Chile are suggested to estimate parameters of low-order TF models and some of their properties.     

An extended finite element framework for slow‐rate frictional faulting with bulk plasticity and variable friction

We present an extended finite element (FE) approach for the simulation of slow‐rate frictional faulting in geologic media incorporating bulk plasticity and variable friction. The method allows the fault to pass through the interior of FEs without remeshing. The extended FE algorithm for frictional faulting, advocated in two recent articles, emanates from a variational equation formulated in terms of the relative displacement on the fault. In the present paper we consider the combined effects of bulk plasticity and variable friction in a two‐dimensional plane strain setting. Bulk plasticity is localized to the fault tip and could potentially be used as a predictor for the initiation and propagation of new faults. We utilize a variable velocity‐ and state‐dependent friction, known as the Dieterich–Ruina or ‘slowness’ law, formulated in a slip‐weakening format. The slip‐weakening/variable friction model is then time‐integrated according to the generalized trapezoidal rule. We present numerical examples demonstrating the convergence properties of a global Newton‐based iterative scheme, as well as illustrate some interesting properties of the variable friction model. Copyright © 2009 John Wiley & Sons, Ltd.     

Changes in fault length distributions due to fault linkage

Fault linkage plays an important role in the growth of faults. In this paper we analyze a published synthetic model to simulate fault linkage. The results of the simulation indicate that fault linkage is the cause of the shallower local slopes on the length–frequency plots. The shallower local slopes lead to two effects. First, the curves of log cumulative number against log length exhibit fluctuating shapes as reported in literature. Second, for a given fault population, the power-law exponents after linkage are negatively related to the linked length scales. Also, we present datasets of fault length measured from four structural maps at the Cantarell oilfield in the southern Gulf of Mexico (offshore Campeche). The results demonstrate that the fault length data, corrected by seismic resolution at the tip fault zone, also exhibit fluctuating curves of log cumulative frequency vs. log length. The steps (shallower slopes) on the curves imply the scale positions of fault linkage. We conclude that fault linkage is the main reason for the fluctuating shapes of log cumulative frequency vs. log length. On the other hand, our data show that the two-tip faults are better for linear analysis between maximum displacement (D) and length (L). Evidently, two-tip faults underwent fewer fault linkages and interactions.     

Periodic and quasi-periodic motions of a solar sail close to SL 1 in the Earth–Sun system

Solar sails are a proposed form of spacecraft propulsion using large membrane mirrors to propel a satellite taking advantage of the solar radiation pressure. To model the dynamics of a solar sail we have considered the Earth–Sun Restricted Three Body Problem including the Solar radiation pressure (RTBPS). This model has a 2D surface of equilibrium points parametrised by the two angles that define the sail orientation. In this paper we study the non-linear dynamics close to an equilibrium point, with special interest in the bounded motion. We focus on the region of equilibria close to SL ₁, a collinear equilibrium point that lies between the Earth and the Sun when the sail is perpendicular to the Sun–sail direction. For different fixed sail orientations we find families of planar, vertical and Halo-type orbits. We have also computed the centre manifold around different equilibria and used it to describe the quasi-periodic motion around them. We also show how the geometry of the phase space varies with the sail orientation. These kind of studies can be very useful for future mission applications.     

Continuity and facies heterogeneities of shallow carbonate ramp cycles (Sinemurian,Lower Jurassic,North‐east Spain)

The lateral continuity and facies heterogeneities of metre‐scale cycles in a greenhouse Lower Jurassic (Sinemurian) carbonate ramp from the northern Iberian Basin (Spain) was evaluated from extensive field analysis carried out on a well‐exposed 12 km long outcrop. Eleven high‐frequency continuous cycles and their bounding surfaces are traceable laterally through the entire outcrop. However, three of these cycles are found to split laterally into discontinuous cycles of more limited distribution (up to 3 to 5 km of lateral extent). The continuous and discontinuous cycles have a similar field expression in one‐dimensional logs. As a consequence, the number of cycles that can be differentiated is variable along the logged sections (i.e. from 11 to 16). Cycles have variable facies heterogeneities and sedimentary trends depending on the environment of formation: shallowing‐upward and symmetrical cycles occur in protected lagoon–tidal flat areas and in the open‐marine, high‐energy domain. These cycles show significant facies heterogeneities, which were controlled mainly by lateral migration of a mosaic of facies over an irregular topography. Deepening‐upward and aggradational cycles are generated in low‐energy, sub wave‐base, open‐marine areas. Facies are laterally homogeneous, reflecting low potential for carbonate accumulation and inability to fill the created accommodation space in this low‐relief and relatively deep area. Cycle boundaries are generated by stages of rapid accommodation gain, involving the flooding of the carbonate ramp; they are more likely to originate from regional tectonic pulses (related to the extensional tectonics operating in the northern Iberian Basin) rather than greenhouse low‐amplitude eustacy. Discontinuous cycles tend to occur in thickened areas and are interpreted as originating from the infill of wedge‐shaped accommodation space resulting from differential subsidence (i.e. local tectonic pulses). In conclusion, where thickness variations occur in extensional settings lateral continuity of cycles should not be expected. In less well‐exposed, or in one‐dimensional sections and in wells, it would not be possible to distinguish continuous from discontinuous cycles, or to understand such two‐dimensional heterogeneities. Identification of unique cycle‐forming mechanisms or attempting cyclostratigraphic long‐distance correlation of cycles is unrealistic without a detailed analysis of the architecture of cycles in laterally continuous outcrops.     

Effects of coastal orientation and depth on the distribution of subtidal benthic assemblages

A better understanding of biological systems can only be gained if we understand what processes are important and how they operate to determine the distribution of organisms. Coastal orientation and depth can influence environmental conditions, including the degree of water motion and availability of light, which in turn may influence the horizontal and vertical patterns of organism distribution. Here, we used a mixed‐model design to examine the effects of coastal orientation and depth on the structure of benthic assemblages by comparing the abundance and distribution of macroalgae and invertebrates in shallow and deep waters on the opposing coasts of São Miguel. Generally, coastal orientation had little influence on the distribution of most taxa. In contrast, significant differences were generally associated with depth, although patterns were spatially variable at the scale of locations. This study suggests that depth, and processes operating at the scale of location, but not at the scale of the coast, have an important influence on these assemblages, and that failure to recognise such a scale of variability may hamper our ability to better understand the processes that structure these communities.     

CH4/N2/H2-spark hydrophobic tholins: A systematic approach to the characterisation of tholins. Part II

Two different simulation experiments of prebiotic synthesis were carried out in a CH₄/N₂/H₂ atmosphere with spark discharge activation of aqueous aerosols and liquid water. In both cases, a hydrophilic tholin and a hydrophobic tholin were obtained. The methodology developed by our group for the characterisation of hydrophilic tholins [Ruiz-Bermejo, M., Menor-Salván, C., Mateo-Martí, E., Osuna-Esteban, S., Martín-Gago, J.A., Veintemillas-Verdaguer, S., 2008. Icarus 198, 232-241] was used in order to study the hydrophobic tholins. The gas precursors of the tholins from mixtures containing CH₄, with and without H₂, were studied. We propose that the formation of the hydrophobic tholins involves the formation of unsaturated oligomeric hydrocarbon chains from vinyl and acetylene monomers, as well as allene derivatives formed in the gas phase after the incorporation of polar groups into these hydrocarbon chains. Finally, we compare our results concerning hydrophobic tholins with HCN polymers, since it is generally suggested that the polymeric material formed in spark experiments are possible oligomers of HCN, and that Titan’s tholins could be poly-HCN.     

Ccd Photometry of Neglected Eclipsing Binaries – Kz Dra, Lr Cam and Im Vul

We present ephemerides and solutions of one Algol-type (KZ Dra) and two overcontact systems (LR Cam and IM Vul) based on V(RI)_C CCD observations obtained in the project Prosper (network of amateur observers).