Reducing Emissions from Deforestation and Forest Degradation (REDD) in efforts to combat climate change requires participating countries to periodically assess their forest resources on a national scale. Such a process is particularly challenging in the tropics because of technical difficulties related to large aboveground forest biomass stocks, restricted availability of affordable, appropriate remote-sensing images, and a lack of accurate forest inventory data. In this paper, we apply the Fourier-based FOTO method of canopy texture analysis to Google Earth's very-high-resolution images of the wet evergreen forests in the Western Ghats of India in order to (1) assess the predictive power of the method on aboveground biomass of tropical forests, (2) test the merits of free Google Earth images relative to their native commercial IKONOS counterparts and (3) highlight further research needs for affordable, accurate regional aboveground biomass estimations. We used the FOTO method to ordinate Fourier spectra of 1436 square canopy images (125 x 125 m) with respect to a canopy grain texture gradient (i.e., a combination of size distribution and spatial pattern of tree crowns), benchmarked against virtual canopy scenes simulated from a set of known forest structure parameters and a 3-D light interception model. We then used 15 1-ha ground plots to demonstrate that both texture gradients provided by Google Earth and IKONOS images strongly correlated with field-observed stand structure parameters such as the density of large trees, total basal area, and aboveground biomass estimated from a regional allometric model. Our results highlight the great potential of the FOTO method applied to Google Earth data for biomass retrieval because the texture-biomass relationship is only subject to 15% relative error, on average, and does not show obvious saturation trends at large biomass values. We also provide the first reliable map of tropical forest aboveground biomass predicted from free Google Earth images. 相似文献
Objective: With 16 percent of the total road user fatalities, motorcyclists represent the second highest rate of road fatalities in France after car occupants. Regarding road accidents, a large proportion of trauma was on the lower cervical spine. According to different clinical studies, it is postulated that the cervical spine fragility areas are located on the upper and lower cervical spine. In motorcycle crashes, impact conditions occur on the head segment with various orientations and impact directions, leading to a combination of rotations and compression. Hence, motorcyclist vulnerability was investigated considering many impact conditions. Method: Using the human model for safety (HUMOS), a finite element model, this work aims to provide an evaluation of the cervical spine weaknesses based on an evaluation of injury mechanisms. This evaluation consisted of defining 2 injury risk factors (joint injury and bone fracture) using a design of experiment including various velocities, impact directions, and impact orientations. Results: The results confirmed previously reported clinical and epidemiological work on the fragility of the lower cervical spine and the upper cervical spine segments. Joint injuries appeared before bone fractures on both the upper and lower cervical spine. Bone fracture risk was greater on the lower cervical spine than on the upper cervical spine. The compression induced by a high impact angle was identified as an important injury severity factor. It significantly increased the injury incidence for both joint injuries and bone fractures. It also induced a shift in injury location from the lower to the upper cervical spine. The impact velocity exhibited a linear relationship with injury risks and severity. It also shifted the bone fracture risk from the lower to upper spinal segments. 相似文献
To determine whether stable isotope measurements of body feathers can be used to investigate the isotopic niche of moulting
(inter-nesting) adult seabirds, we examined the stable carbon (δ13C) and nitrogen (δ15N) isotopic composition of body feathers of breeding wandering albatrosses (Diomedea exulans) from Crozet Islands, southern Indian Ocean. First we showed that the isotopic composition of body feathers was not significantly
different from that of wing feathers, being thus a safe alternative to flight feathers whose collection impairs the birds’
flying ability. Second, we looked at the variances in δ13C and δ15N values resulting from the isotopic measurement of a single feather, four different feathers, and a pool of four feathers
per bird, to delineate the best isotopic analytical procedure. A two-step protocol is proposed that allows investigating both
the intra- and inter-individual components of the niche width of the species. In a first step, isotopic measurements on a
single feather per bird are used to define isotopic specialist from isotopic generalist populations. In a second step and
for generalist populations only, measurements on additional (three) feathers per bird are used to delineate type A from type
B isotopic generalists (Bearhop et al. in J Anim Ecol 73:1007–1012, 2004). Third, from a biological point of view, our data
showed different moulting isotopic niches for adult males and females, and also within female wandering albatrosses. Since
the isotopic composition of body feathers in this species reflects that of wing feathers, our results suggest that, after
validation, body feathers have the potential for investigating the foraging ecology of other Procellariiforms and seabirds
during the poorly known inter-nesting period. 相似文献
In two articles, we present ‘coregionalization analysis with a drift’ (CRAD), a method to assess the multi-scale variability
of and relationships between ecological variables from a multivariate spatial data set. In phase I of CRAD (the first article),
a deterministic drift component representing the large-scale pattern and a random component modeled as a second-order stationary
process are estimated for each variable separately. In phase II (this article), a linear model of coregionalization (LMC)
is fitted by estimated generalized least squares to the direct and cross experimental variograms of residuals (i.e., after
the removal of estimated drifts). Structural correlations and coefficients of determination at smaller scales are then computed
from the estimated coregionalization matrices, while the estimated drifts are used to calculate pseudo coefficients at large
scale. The performance of five procedures in estimating correlations and coefficients of determination was compared using
a Monte Carlo study. In four CRAD procedures, drift estimation was based on local polynomials of order 0, 1, 2 (L0, L1, L2) or a global polynomial with forward selection of the basis functions; the fifth procedure was coregionalization analysis
(CRA), in which large-scale patterns were modeled as a supplemental component in the LMC. In bivariate and multivariate analyses,
the uncertainty in the estimation of correlations and coefficients of determination could be related to the interference between
spatial components within a bounded sampling domain. In the bivariate case, most procedures provided acceptable estimates
of correlations. In regionalized redundancy analysis, uncertainty was highest for CRA, while L1 provided the best results overall. In a forest ecology example, the identification of scale-specific correlations between
plant species diversity and soil and topographical variables illustrated the potential of CRAD to provide unique insight into
the functioning of complex ecosystems. 相似文献
Agricultural crops can be either a source or a sink of ammonia (NH3). Most NH3 exchange models developed so far do not account for the plants nitrogen (N) metabolism and use prescribed compensation points. We present here a leaf-scale simplified NH3 stomatal compensation point model related to the plants N and carbon (C) metabolisms, for C3 plants. Five compartments are considered: xylem, cytoplasm, apoplasm, vacuole and sub-stomatal cavity. The main processes accounted for are the transport of ammonium (NH4+), NH3 and nitrate (NO3−) between the different compartments, NH4+ production through photorespiration and NO3− reduction, NH4+ assimilation, chemical and thermodynamic equilibriums in all the compartments, and stomatal transfer of NH3.The simulated compensation point is sensitive to paramaters related to the apoplastic compartment: pH, volume and active transport rate. Determining factors are leaf temperature, stomatal conductance and NH4+ flux to the leaf. Atmospheric NH3 concentration seem to have very little effect on the compensation point in conditions of high N fertilization. Comparison of model outputs to experimental results show that the model underestimates the NH3 compensation point for high N fertilization and that a better parametrisation of sensitive parameters especially active trasport rate of NH4+ may be required. 相似文献
A tidal bore is a natural and fragile phenomenon, which is of great importance for the ecology of an estuary. The bore development
is closely linked with the tidal range and the river mouth shape, and its existence is sensitive to any small change in boundary
conditions. Despite their ecological and cultural value, little is known on the flow field, turbulent mixing and sediment
motion beneath tidal bores. Indeed, some striking features can be highlighted in two-dimensional simulations, such as large
velocity fluctuations and flow recirculation structures. Using Large Eddy Simulation method, the numerical results emphasised
the complicated turbulent structures and their unsteadiness under a tidal bore. 相似文献
An analytical methodology was developed to characterize the colloidal distribution of trace elements of interest in environmental waters sampled in a same site and enables the different colloidal distributions from waters to be compared. The purpose was to provide consistent information related to the origin and nature of colloids responsible for the transport of trace element(s). The work was motivated by the observed enhanced mobility of uranium in soil. The colloidal size continuum was investigated by a multi-technique approach involving asymmetric flow field-flow fractionation (AF4) coupled with ultraviolet spectroscopy (UV), multi angle light scattering (MALS), and atomic mass spectrometry (ICPMS). To take into consideration the size and shape variability specific to each sample, the size distributions were established from the gyration radii measured from MALS, also considering the size information from standard nanospheres fractionated by AF4. A new parameter called “shape index” was proposed. It expresses the difference in hydrodynamic behavior between analytes and spherical particles taken as reference. Under AF4 diffusion conditions, it can be considered as an evaluator of the deviation from the sphericity of the fractionated analytes. AF4-UV-MALS-ICPMS enabled the dimensional and chemical characteristics of the colloidal size continuum to be obtained. As a “proof of concept”, the developed methodology was applied at a field scale, in a reference study site. In order to have a “dynamic understanding”, the investigation was based on the joint characterization of colloids from surface waters and soil leachates from static and dynamic processes. In the water samples of the study site, the continuum of gyration radius ranged from a few nanometers up to 200 nm. Colloids containing iron, aluminum, and organic carbon were involved in the uranium transport in the soil column and surface waters. The colloidal uranium concentration in the surface water increased from the upstream location (approximately 13 ng (U) L?1) to the downstream location (approximately 60 ng (U) L?1).