Search results for " mineralogy"
showing 10 items of 69 documents
The First Precise Determination of an Optical–Far‐Ultraviolet Extinction Curve Beyond the Local Group ( \documentclass{aastex} \usepackage{amsbsy} \u…
2005
We present the optical-far-ultraviolet extinction curve of the dust in the lens galaxy of the gravitational lens system SBS 0909+532 (z = 0.83). Extending our previous optical-UV estimate (from λ ~ 2 to 5 μm-1) into the far ultraviolet (from λ ~ 5 to 8 μm-1) is crucial for comparing with the extinction curves measured for Local Group galaxies in the spectral region where the differences are greatest. The SBS 0909+532 curve is similar to that of the LMC2 supershell, with a weaker 2175 A feature and a steeper rise into the UV than that observed in the Milky Way. The shapes of the extinction curve inferred from the quasar continuum and emission lines are in very good agreement. There is, howev…
Sensitivity of UVER enhancement to broken liquid water clouds: A Monte Carlo approach
2016
The study uses a Monte Carlo radiative transfer model to examine the sensitivity of the UV erythemal radiation (UVER) enhancement to broken liquid water clouds of the cumulus and stratocumulus type. The model uses monochromatic radiation at 310 nm corresponding approximately to the peak of the product between irradiance and the erythemal curve. All scattering, absorption, extinction coefficients, and spectral albedos are tuned to this wavelength. In order of importance, fractional cloud cover, the area of individual cloud patches, and cloud thickness exert a strong influence on the enhancement, with smaller contributions from cloud optical depth, cloud base height, and solar zenith angle. I…
The ratio of primary scattering to total scattering of sky radiance
1974
Recently Eschelbach has computed from theory spectral radiance values for a turbid atmosphere taking into account the effect of multiple scattering. In the present work these computational data were used to investigate the ratio of primary to total scattering. This quotient is a measure of multiple scattering because of the relation: Total Scattering (TS) is equal to Primary Scattering (PS) plus Multiple Scattering (MS), i.e. PS/TS = 100 - MS/TS (%). It is discussed in which way multiple scattering in the solar almucantar depends on the solar elevation, turbidity, scattering angle, wavelength and albedo. The present work shows in which way multiple scattering is related to the optical thick…
Light Propagation in Clouds: From Digital Holography to Non-Exponential Extinction
2019
Optical propagation is strongly influenced b y t he n umber concentration, size distribution, thermodynamic phase, and spatial distribution of particles in atmospheric clouds. These properties have been investigated in the field using an airborne digital holographic instrument. A laboratory facility has also been developed, in which optical propagation is being investigated in steady-state turbulent-cloud conditions.
Extinction law classification and lens redshift estimate by means of the principal component analysis
2007
Aims. We propose a method based on the Principal Component Analysis (PCA) to classify and estimate the redshift of an extinction law in a distant gravitational lens galaxy. Such extinction laws are very poorly known and an efficient method to characterize them is badly needed. Methods. We first compute the principal axes of an exhaustive collection of redshifted theoretical extinction laws. Then, we project on these new axes the extinction law we wish to classify. The position of its projection among those redshifted extinction laws from the collection allows us to characterize it and to estimate its redshift. Results. Monte Carlo simulations show that the method is efficient and relatively…
Der Einflu� einer inhomogenen Verteilung auf die Messung der Extinktion an monoerythrocyt�ren Schichten und an einzelnen Erythrocyten
1969
Bei der Messung der Extinktion an einzelnen Erythrocyten oder an monoerythrocytaren Schichten ist eine wesentliche Voraussetzung fur die Gultigkeit des Lambert-Beerschen Gesetzes, namlich die der homogenen Verteilung der gelosten Substanz, nicht erfullt. Es wird gezeigt, welchen Einflus eine solche Inhomogenitat auf den Meswert hat und welche Moglichkeiten bestehen, bei bekannter Inhomogenitat eine Korrektur des Meswertes durchzufuhren. Besonders eingehend wird ein einfaches und anschauliches Zwei-Kompartiment-System diskutiert und der Einflus der Inhomogenitat mit Hilfe von zwei Diagrammen dargestellt, wobei als Mas fur die Inhomogenitat der Bedeckungsfaktor α eingefuhrt wird. Es wird fern…
FRAM—The Robotic Telescope for the Monitoring of the Wavelength Dependence of the Extinction: Description of Hardware, Data Analysis, and Results
2010
FRAM-F/(Ph)otometric Robotic Atmospheric Monitor is one of the atmospheric monitoring instruments at the Pierre Auger Observatory in Argentina. FRAM is an optical telescope equipped with CCD cameras and photometer, and it automatically observes a set of selected standard stars. Primarily, FRAM observations are used to obtain the wavelength dependence of the light extinction. FRAM telescope is also able to observe secondary astronomical targets, and namely the detection of optical counterparts of gamma-ray bursts has already proven to be successful. Finally, a wide-field CCD camera of FRAM can be used for rapid monitoring of atmospheric conditions along the track of particularly interesting …
The Influence of Absorption on the Extinction of Solar and Sky Radiation
1965
The purpose of this paper is to investigate the influence of absorption of the aerosol particles on the extinction of solar and sky radiation. The efficiency factors have been computed as well as the extinction, the scattering, the absorption, and the scattering function for the whole turbid atmosphere with help of the Mie theory for a complex index of refraction for a more or less absorbent medium. From these values the intensities of diffuse sky radiation have been obtained. The extinction and absorption coefficients increase for a more absorbent atmosphere, whereas the scattering coefficient decreases. The imaginary part of the complex index of refraction effects an increasing attenuatio…
Determination of Aerosol Size Distributions from Spectral Attenuation Measurements
1971
An iteration method for the determination of size distributions of aerosols from spectral attenuation data, similar to the one previously published for clouds, is presented. The basis for this iteration is to consider the extinction efficiency factor of particles as a set of weighting functions covering the entire radius region of a distribution. The weighting functions were calculated exactly from the Mie theory. Aerosol distributions are shown derived from tests with analytical size distributions and also generated from measured aerosol extinction data in seven spectral channels from 0.4-microto 10-micro wavelength in continental aerosols. The influence of relative humidity on the complex…
Mineralogical and chemical variability of fluvial sediments 2. Suspended-load silt (Ganga–Brahmaputra, Bangladesh)
2011
Sediments carried in suspension represent a fundamental part of fluvial transport. Nonetheless, largely because of technical problems, they have been hitherto widely neglected in provenance studies. In order to determine with maximum possible precision the mineralogy of suspended load collected in vertical profiles from water surface to channel bottom of Rivers Ganga and Brahmaputra, we combined Raman spectroscopy with traditional heavy-mineral and X-ray diffraction analyses, carried out separately on low-density and dense fractions of all significant size classes in each sample (multiple-window approach). Suspended load resulted to be a ternary mixture of dominant silt enriched in phyllosi…