Search results for "Radiance"
showing 10 items of 284 documents
Quantum Backreaction on Three-Dimensional Black Holes and Naked Singularities
2016
We analytically investigate backreaction by a quantum scalar field on two rotating Ba\~nados-Teitelboim-Zanelli (BTZ) geometries: that of a black hole and that of a naked singularity. In the former case, we explore the quantum effects on various regions of relevance for a rotating black hole space-time. We find that the quantum effects lead to a growth of both the event horizon and the radius of the ergosphere, and to a reduction of the angular velocity, compared to the unperturbed values. Furthermore, they give rise to the formation of a curvature singularity at the Cauchy horizon and show no evidence of the appearance of a superradiant instability. In the case of a naked singularity, we f…
Flux heterogeneity and evapotranspiration partitioning in a sparse canopy: the fallow savanna
1997
Abstract This paper focuses on in situ measurements obtained during the intensive observation period of the HAPEX-Sahel experiment. Micrometeorological measurements and trunk sap flow monitoring were combined to analyse transfer characteristics of a fallow savanna site within the East Central Supersite. Results show that the shrub canopy heterogeneity induces a large spatial variability of solar irradiance, soil heat flux and sensible and latent heat fluxes at the grassland level. This variability is induced by both a “shade effect” and a “wake effect”. Both shrubs and grassland provide sources of vapour, but the partitioning of evapotranspiration between these two components varies conside…
Mapping burns and natural reforestation using thematic Mapper data
1991
Abstract Remote sensing techniques are specially suitable to detect and to map areas affected by forest fires. In this work, Landsat 5 Thematic Mapper (TM) data has been used to study a number of forest fires that occurred in the province of Valencia (Spain) and to monitor the vegetation regeneration over burnt areas. A reference area (non‐burnt forest) was established to assess the change produced by fire. The radiance in the thermal band (10.4–12.5 μm) and the normalized difference in reflectance between near 1R (0.76–0.90 μm) and middle IR (2.08–2.35 μm) were the most suitable parameters to map burnt areas. This index can also be used for monitoring vegetation regeneration in burnt areas…
Sensitivity of scope modelled GPP and fluorescence for different plant functional types
2014
This study addresses the question which factors are responsible for reported positive correlations between solar induced fluorescence (SIF) and gross primary production (GPP). A sensitivity analysis of the model SCOPE, which simulates photosynthesis, fluorescence emission and radiative transfer in canopies, has been carried out for four different plant functional types (PFT): tropical rainforest, C4 crops, C3 crops, and tundra, located in distinct climate zones: tropical everwet (Af), tropical with seasonal drought (savannah, Aw), temperate (Cf), and continental tundra (Dfd). Literature values for structural and physiological parameters and climate reanalysis data were used as input. The ef…
Climate change and Ecotone boundaries: Insights from a cellular automata ecohydrology model in a Mediterranean catchment with topography controlled v…
2014
Abstract Regions of vegetation transitions (ecotones) are known to be highly sensitive to climate fluctuations. In this study, the Cellular-Automata Tree Grass Shrub Simulator (CATGraSS) has been modified, calibrated and used with downscaled future climate scenarios to examine the role of climate change on vegetation patterns in a steep mountainous catchment (1.3 km2) located in Sicily, Italy. In the catchment, north-facing slopes are mostly covered by trees and grass, and south-facing slopes by Indian Fig opuntia and grass, with grasses dominating as elevation grows. CATGraSS simulates solar radiation, evapotranspiration, and soil moisture in space and time. Each model cell can hold a sing…
Assessment of the Usability and Accuracy of Two-Diode Models for Photovoltaic Modules
2017
Many diode-based equivalent circuits for simulating the electrical behaviour of photovoltaic (PV) cells and panels are reported in the scientific literature. Two-diode equivalent circuits, which require more complex procedures to calculate the seven model parameters, are less numerous. The model parameters are generally calculated using the data extracted from the datasheets issued by the PV panel manufactures and adopting simplifying hypotheses and numerical solving techniques. A criterion for rating both the usability and accuracy of two-diode models is proposed in this paper with the aim of supporting researchers and designers, working in the area of PV systems, to select and use a model…
A Criterion for Rating the Usability and Accuracy of the One-Diode Models for Photovoltaic Modules
2016
In selecting a mathematical model for simulating physical behaviours, it is important to reach an acceptable compromise between analytical complexity and achievable precision. With the aim of helping researchers and designers working in the area of photovoltaic systems to make a choice among the numerous diode-based models, a criterion for rating both the usability and accuracy of one-diode models is proposed in this paper. A three-level rating scale, which considers the ease of finding the data used by the analytical procedure, the simplicity of the mathematical tools needed to perform calculations and the accuracy achieved in calculating the current and power, is used. The proposed criter…
Assessment of the Usability and Accuracy of the Simplified One-Diode Models for Photovoltaic Modules
2016
Models for photovoltaic (PV) cells and panels, based on the diode equivalent circuit, have been widely used because they are effective tools for system design. Many authors have presented simplified one-diode models whose three or four parameters are calculated using the data extracted from the datasheets issued by PV panel manufactures and adopting some simplifying hypotheses and numerical solving techniques. Sometimes it may be difficult to make a choice among so many models. To help researchers and designers working in the area of photovoltaic systems in selecting the model that is fit for purpose, a criterion for rating both the usability and accuracy of simplified one-diode models is p…
Effect of light intensity, light duration and photoperiods in the performance of an outdoor photobioreactor for urban wastewater treatment
2019
[EN] A series of eight experiments were carried out to analyse the effects of light intensity, light duration and photoperiods on a microalgae culture for treating AnMBR effluent at an outdoor photobioreactor (PBR) plant. Improved performance was achieved in terms of nutrient recovery rates, biomass productivity and effluent nutrient concentrations at a higher net photon flux. However, the higher irradiance was also responsible for lower biomass productivity:light irradiance ratios. None of the experiments with different lighting regimes and the same net photon flux showed any significant differences. The data obtained suggest that microalgae performance in this system did not depend on the…
A Color Image Database for Haze Model and Dehazing Methods Evaluation
2016
International audience; One of the major issues related to dehazing methods (single or multiple image based) evaluation is the absence of the haze-free image (ground-truth). This is also a problem when it concerns the validation of Koschmieder model or its subsequent dehazing methods. To overcome this problem, we created a database called CHIC (Color Hazy Image for Comparison), consisting of two scenes in controlled environment. In addition to the haze-free image, we provide 9 images of different fog densities. Moreover, for each scene, we provide a number of parameters such as local scene depth, distance from the camera of known objects such as Macbeth Color Checkers, their radiance, and t…