Search results for "Forestry"
showing 10 items of 1998 documents
Pore-space characterization of an altered tonalite by X-ray computed microtomography and the14C-labeled-polymethylmethacrylate method
2012
[1] The structure of geological materials strongly affects migration processes that take place in them and are also important in their weathering and alteration processes. Further information of that structure will also be important for many applications that involve geological materials. The emphasis of this study was thus to characterize the pore structure and porosity of altered tonalite by combining different measuring techniques: X-ray tomography, the14C-polymethylmethacrylate method, electron microscopy, and argon pycnometry. Intragranular porosities were determined using chemical staining of rock surfaces. Three-dimensional distributions of minerals and porosities were evaluated with…
Influence of ice crystal shape on retrieval of cirrus optical thickness and effective radius: A case study
2009
Airborne measurements of spectral upwelling radiances (350A¢Â�Â�2200 nm) reflected by cirrus using the Spectral Modular Airborne Radiation measurement sysTem (SMART)-Albedometer were made over land and water surfaces. Based on these data, cloud optical thickness tau and effective radius Reff of the observed cirrus were retrieved. By using different crystal shape assumptions (hexagonal plates, solid and hollow columns, rough aggregates, planar and spatial rosettes, ice spheres, and a mixture of particle habits) in the retrieval, the influence of crystal shape on the retrieved tau and Reff was evaluated. With relative differences of up to 70%, the influence of particle habit on t is larger th…
Approaches to partitioning the global UVER irradiance into its direct and diffuse components in Valencia, Spain
2012
[1] The paper explores methods of partitioning the hourly average UV erythemal flux into its direct and diffuse components for Valencia, Spain. It is shown that the cloud modification factor, the ratio of measured to cloudless erythemal flux relates linearly to the fraction of the measured irradiance that is diffuse. This relationship was developed further into two simple models- a linear and nonlinear one. The models are characterized by an effective cloud cover to partition the global erythemal flux. The diffuse fraction increases linearly with cloud cover in the linear model, but exponentially in the nonlinear one. The models may be used to partition the direct and diffuse irradiance wit…
Intercomparison of spectroradiometers and Sun photometers for the determination of the aerosol optical depth during the VELETA-2002 field campaign
2006
In July 2002 the VELETA-2002 field campaign was held in Sierra Nevada (Granada) in the south of Spain. The main objectives of this field campaign were the study of the influence of elevation and atmospheric aerosols on measured UV radiation. In the first stage of the field campaign, a common calibration and intercomparison between Licor-1800 spectroradiometers and Cimel-318 Sun photometers was performed in order to assess the quality of the measurements from the whole campaign. The intercomparison of the Licor spectroradiometers showed, for both direct and global irradiances, that when the comparisons were restricted to the visible part of the spectrum the deviations were within the instrum…
On the direct and semidirect effects of Saharan dust over Europe: A modeling study
2007
[1] On the basis of a new regional dust model system, the sensitivity of radiative forcing to dust aerosol properties and the impact on atmospheric dynamics were investigated. Uncertainties in optical properties were related to uncertainties in the complex spectral refractive index of mineral dust. The climatological-based distribution of desert-type aerosol in the radiation scheme of the nonhydrostatic regional model LM was replaced by dust optical properties from spectral refractive indices, derived from in situ measurements, remote sensing, bulk measurements, and laboratory experiments, employing Mie theory. The model computes changes in the solar and terrestrial irradiance from a spatia…
Stratosphere-troposphere exchange: A review, and what we have learned from STACCATO
2003
[1] This paper provides a review of stratosphere-troposphere exchange (STE), with a focus on processes in the extratropics. It also addresses the relevance of STE for tropospheric chemistry, particularly its influence on the oxidative capacity of the troposphere. After summarizing the current state of knowledge, the objectives of the project Influence of Stratosphere-Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity (STACCATO), recently funded by the European Union, are outlined. Several papers in this Journal of Geophysical Research– Atmospheres special section present the results of this project, of which this paper gives an overview. STACCATO deve…
Comparison of ERA40 cloud top phase with POLDER-1 observations
2008
[1] A detailed grid-point-based comparison of the cloud top phase derived from the 40-year reanalyses (ERA40) of the European Centre for Medium-Range Weather Forecasts (ECMWF) with satellite measurements is presented. For this purpose an algorithm is implemented to extract a two-dimensional “satellite-like” field of the cloud top phase from ERA40 data. This field is compared with cloud top phase data from the Polarization and Directionality of the Earth Reflectances (POLDER-1) instrument which was in orbit from November 1996 to June 1997. The thermodynamic cloud phase in ERA40 data is parameterized as a function of temperature with pure liquid clouds above 0°C, pure ice clouds below −23°C a…
Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing site to Backstay Rock in the Columbia Hills
2006
Spirit landed on the floor of Gusev Crater and conducted initial operations on soil covered, rock-strewn cratered plains underlain by olivine-bearing basalts. Plains surface rocks are covered by wind-blown dust and show evidence for surface enrichment of soluble species as vein and void-filling materials and coatings. The surface enrichment is the result of a minor amount of transport and deposition by aqueous processes. Layered granular deposits were discovered in the Columbia Hills, with outcrops that tend to dip conformably with the topography. The granular rocks are interpreted to be volcanic ash and/or impact ejecta deposits that have been modified by aqueous fluids during and/or after…
Geochemical properties of rocks and soils in Gusev Crater, Mars: Results of the Alpha Particle X-Ray Spectrometer from Cumberland Ridge to Home Plate
2008
Geochemical diversity of rocks and soils has been discovered by the Alpha Particle X-Ray Spectrometer (APXS) during Spirit’s journey over Husband Hill and down into the Inner Basin from sol 470 to 1368. The APXS continues to operate nominally with no changes in calibration or spectral degradation over the course of the mission. Germanium has been added to the Spirit APXS data set with the confirmation that it occurs at elevated levels in many rocks and soils around Home Plate. Twelve new rock classes and two new soil classes have been identified at the Spirit landing site since sol 470 on the basis of the diversity in APXS geochemistry. The new rock classes are Irvine (alkaline basalt…
Multilayer modelling of ozone fluxes on winter wheat reveals large deposition on wet senescing leaves
2015
Understanding how ozone is deposited on vegetation canopies is needed to perform tropospheric greenhouse gas budgets and evaluate the associated damage on vegetation. In this study, we propose a new multilayer scheme of ozone deposition on vegetation canopies that predicts stomatal, cuticular and soil deposition pathways separately. This mechanistic ozone deposition scheme is based on the multi-layer, multi-leaf mass and energy transfer model MuSICA. This model was chosen because it explicitly simulates the processes of rain interception, through fall and evaporation at different depths within the vegetation canopy, so that ozone deposition on wet leaf cuticles can be explicitly modelled wi…