Diffuse Ultraviolet Radiation Research Articles

Components of the diffuse ultraviolet radiation at high latitudes

ABSTRACT We have used data from the Galaxy Evolution Explorer to study the different components of the diffuse ultraviolet background in the region between the Galactic latitudes 70°–80°. We find an offset at zero dust column density (E(B − V) = 0) of 240 ± 18 photon units in the FUV (1539 Å) and 394 ± 37 photon units in the NUV (2316 Å). This is approximately half of the total observed radiation with the remainder divided between an extragalactic component of 114 ± 18 photon units in the FUV and 194 ± 37 photon units in the NUV and starlight scattered by Galactic dust at high latitudes. The optical constants of the dust grains were found to be a = 0.4 ± 0.1 and g = 0.8 ± 0.1 (FUV) and a = 0.4 ± 0.1 and g = 0.5 ± 0.1 (NUV). We cannot differentiate between a Galactic or extragalactic origin for the zero-offset but can affirm that it is not from any known source.

Development of a model for calculating the solar ultraviolet protection factor of small to medium sized built shade structures

A method was proposed for calculating the ultraviolet protection factor (PF) of small to medium built shade structures. The method takes into account the amount of sky view visible from under the structure, the transmittance of the roof material, the relative amount of diffuse ultraviolet radiation (UV), the measurement position under the structure and the albedo of the relevant surfaces. The PF of four different shade structure designs was measured 90 cm above ground-level at the centre of the widest diameter of each structure. Measurements were only made on cloud-free days. Three structures had a thin metal roof and the fourth had shade-cloth. The proportion of sky view ranged from 4.6% to 15.4% for these structures. The influence of position was investigated for one structure, with the PF evaluated 50 cm in from each of the sides at 90 cm above ground-level. The reliability of the method was tested by comparing calculated and measured PF values for solar zenith angles ranging from 7° to 49°. The mean absolute difference between the calculated and the measured PF for these small to medium structures was 1.4 PF (14%). The proposed method is more likely to be widely used to measure the PF in situ compared to measuring UV in full sun and in the shade with a UV meter because many stakeholders do not have access to UV meters due to the cost or the degree of specialization required to use these meters effectively.

Multi-wavelength correlation studies of diffuse emission from the Aquila Rift

We present a multi-wavelength correlation study of diffuse ultraviolet radiation using GALEX observations towards the Aquila Rift. Apart from airglow and zodiacal emissions, we find a diffuse background of 1300 - 3700 \photu\ in the far-ultraviolet (FUV: 1350 - 1750 \AA) band and 1300 - 2800 \photu\ in the near-ultraviolet (NUV: 1750 - 2850 \AA) band. The observed diffuse UV emissions are saturated with total as well as neutral hydrogen column density in the region due to high optical depth in UV ($\tau$: 0.91-23.38). Higher values of FUV/NUV ratio in the region, greater than the threshold value of 0.6, along with the positive correlation between the ratio and FUV intensity are due to excess emission in the FUV band which is absent in the NUV band. We estimated the excess emission to be in the range $\sim$ 400 - 2700 \photu, plausibly due to H$_2$ fluorescence, ion line emissions and two-photon continuum emissions from the region in the FUV band, which also shows saturation in optically thick regions with N(H$_{2}$) as well as H$\alpha$ emissions. Since N(H$_{2}$) and H$\alpha$ emissions spread all over the region, the excess emission from the field is composite in nature and a detailed spectroscopic analysis is needed to disentangle the contribution from individual components.

Ultraviolet and Infrared Correlation Studies in Orion

Abstract We have studied the variation of diffuse ultraviolet (UV) radiation in the northern part of the Orion constellation using a set of eight areas of the GALEX All-Sky Imaging Survey in the far and near UV. Different components of diffuse UV radiation, like dust scattered emission and H2 fluorescence, were quantified and separated after removing the point sources and the foreground emission in each of the fields. Then the dependence of the individual UV components on the infrared 100 μm dust emission was studied. We did not find any positive correlation between the diffuse-UV and IR-100 micron intensities, probably due to the high optical depth of the region or the entire dust column not contributing to the diffuse UV radiation. However, in the far UV we noticed the presence of an excess emission in addition to the dust scattered radiation, which is clearly absent in the near UV. This excess emission, identified as the H2 fluorescence, is produced by the Trapezium stars in the surrounding molecular clouds. We also compare our results with those of previous studies in the region, based on Far Ultraviolet Spectroscopic Explorer (FUSE) observations.

Shadow‐band correction for diffuse ultraviolet radiation measurements

AbstractAlthough the correction of shadow‐band solar total diffuse measurements has been extensively studied, the case of diffuse ultraviolet measurements has not been properly addressed. This study analyzes the correction factor to be applied to experimental measurements performed adapting a shadow‐band to a UV radiometer at a radiometric station in Badajoz (Spain). Three different models, based on approaches widely used for correcting total diffuse measurements, have been revised and adapted for the ultraviolet spectral range. Results reveal that some aspects of the correction proposed for total diffuse radiation are not suitable for ultraviolet diffuse radiation. The mathematical expressions are consequently modified to match the behavior in the ultraviolet range. Thus, three correction models particularized for ultraviolet diffuse measurements are proposed and validated against experimental data. The two models adapted from the original expressions proposed by Battles et al., and Steven show the best performance, with rRMSE of 2.74% and 2.20% and rMBE of 1.53% and 0.46%, respectively.

Anatomical exposure patterns of skin to sunlight: relative contributions of direct, diffuse and reflected ultraviolet radiation

The dose-response between ultraviolet (UV) exposure patterns and skin cancer occurrence is not fully understood. Sun-protection messages often focus on acute exposure, implicitly assuming that direct UV radiation is the key contributor to the overall UV exposure. However, little is known about the relative contribution of the direct, diffuse and reflected radiation components. To investigate solar UV exposure patterns at different body sites with respect to the relative contribution of the direct, diffuse and reflected radiation. A three-dimensional numerical model was used to assess exposure doses for various body parts and exposure scenarios of a standing individual (static and dynamic postures). The model was fed with erythemally weighted ground irradiance data for the year 2009 in Payerne, Switzerland. A year-round daily exposure (08:00-17:00 h) without protection was assumed. For most anatomical sites, mean daily doses were high (typically 6.2-14.6 standard erythemal doses) and exceeded the recommended exposure values. Direct exposure was important during specific periods (e.g. midday during summer), but contributed moderately to the annual dose, ranging from 15% to 24% for vertical and horizontal body parts, respectively. Diffuse irradiation explained about 80% of the cumulative annual exposure dose. Acute diffuse exposures were also observed during cloudy summer days. The importance of diffuse UV radiation should not be underestimated when advocating preventive measures. Messages focused on avoiding acute direct exposures may be of limited efficiency to prevent skin cancers associated with chronic exposure.

Modelling the diffuse ultraviolet radiation observed by Dynamics Explorer 1

The Dynamics Explorer spacecraft, DE-1, has undertaken two sky surveys in the far-ultraviolet regime, covering a wide variety of Galactic latitudes. We have used a single scattering dust model to probe into the optical constants and the distance of the interstellar dust clouds. We find that, in agreement with most other observations, the dust grains are strongly forward scattering with a relatively high albedo and, in addition, that the scattering is from dust sheets within 100 pc of the Sun.

Observations of the near and far ultraviolet background

The diffuse ultraviolet radiation field is seen over the entire sky and is a tracer of both the hot (in the form of lines such as CIV and OVI) and cold component (in the form of interstellar dust or molecular hydrogen) of the interstellar medium. Observations over the last 40 years have been continually pushing the boundaries of the available instrumentation but are now bearing fruit in a much better definition of the radiation and an understanding of its constituents, both foreground, such as airglow or zodiacal light, and cosmic. I present a review of the current state of observations of the far and near ultraviolet background.

Optimizing Solar UV-Radiation Exposures for Vitamin D3: Comparing Global and Diffuse Spectral UV Radiation

Currently, there is a major gap in the knowledge that is needed to optimize the beneficial effects related to ultraviolet (UV) radiation at wavelengths that induce vitamin D(3) synthesis (UV(D3)) compared to reducing the biologically damaging overexposure to UV radiation. The aim of this study was to investigate the use of diffuse (radiation that is scattered from all directions) UV radiation to optimize exposures to UV(D3) radiation and maximize the reduction of exposure to UVA radiation. Data on global and diffuse solar UV-radiation spectra were collected at 10-min intervals in the Southern Hemisphere in the late spring and summer from 1 November 2006 to 28 February 2007. For a solar zenith angle (SZA) of approximately 5 degrees , the observed maximum UV(D3) irradiances were 0.80 W/m(2) and 0.46 W/m(2) for global and diffuse UV radiation, respectively. The observed maximum UVA irradiances were 79.0 W/m(2) and 36.2 W/m(2) for global and diffuse UV radiation, respectively. For diffuse UV radiation, the maximum ratio of vitamin D(3) to UVA radiation was 1.75% at a SZA of approximately 10 degrees , whereas the maximum ratio for global UV was 1.27% at 10 degrees . For SZAs of 25 degrees and less, more UV radiation is in the wavelength region contributing to vitamin D(3) synthesis (UV(D3)) than in the UVA region for diffuse UV radiation than for global UV radiation.

Use of UV-protective windows and window films to aid in the prevention of skin cancer.

People are exposed to ambient solar ultraviolet (UV) radiation throughout their daily routine, intentionally and unintentionally. Cumulative and excessive exposure to UV radiation is the behavioral cause to skin cancers, skin damage, premature skin aging, and sun-related eye disorders. More than one million new cases of skin cancer were diagnosed in the United States this year. UV radiates directly and diffusely scattered by the various environmental and atmospheric conditions and has access to the skin from all directions. Because of this diffuse UV radiation, a person situated under a covering, such as the roof of a car or house, is not completely protected from the sun's rays. Because shade structures do not protect effectively against UV radiation, there have been major advances in photoprotection of glass by the development of specially designed photoprotective windows and films. It is the purpose of this collective review to highlight the photoprotective windows and films that should be incorporated into residential, commercial, and school glass windows to reduce sun exposure. Low-emittence (low-E) coatings are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface to reduce the U-factor by suppressing radiative heat flow as well as to limit UV radiation. The exclusive Thermaflect coating uses the most advanced, double-layer soft coat technology to continue to deliver top performance for UV protection as well as prevent heat loss in the home. This product blocks 87% of UV radiation and has an Energy Star certification in all climate zones. Tints and films have been another important advance in glass photoprotection, especially in automobiles. Quality widow film products are high-tech laminates of polyester and metallized coatings bonded by distortion-free adhesives. The International Window Film Association provides members with accreditation in solar control films, safety films, and automotive films in an effort to increase consumer awareness and demand for all professionally installed film window products. The Skin Cancer Foundation has also played a leadership role in certifying window films that limit UV transmission. The Panorama Designer and Safety Films are currently recommended for UV photoprotection by The Skin Cancer Foundation. On the basis of these innovative scientific and industrial advances in window and film photoprotective products, we recommend that they be used in all residential, commercial, and school facilities to provide photoprotection in an effort to reduce skin cancer.

The ortho- to para- ratio of H2 in the starburst of NGC 253

We present measurements of several near-infrared emission lines from the nearby galaxy NGC 253. We have been able to measure four H2 lines across the circumnuclear starburst, from which we estimate the ortho- to para- ratio of excited H2 to be ∼2. This indicates that the bulk of the H2 emission arises from photodissociation regions (PDRs), rather than from shocks. This is the case across the entire region of active star formation. As the H2 emission arises from PDRs, it is likely that the ratio of H2 to Brγ (the bright hydrogen recombination line) is a measure of the relative geometry of O and B stars and PDRs. Towards the nucleus of NGC 253 the geometry is deduced to be tightly clustered O and B stars in a few giant H II regions that are encompassed by PDRs. Away from the nuclear region, the geometry becomes that of PDRs bathed in a relatively diffuse ultraviolet radiation field. The rotation curves of 1–0 S(1) and Brγ suggest that the ionized gas is tracing a kinetic system different from that of the molecular gas in NGC 253, particularly away from the nucleus.

A Model of the Diffuse Ultraviolet Radiation Field

A Model of the Diffuse Ultraviolet Radiation Field

Measurements of the Diffuse Ultraviolet Radiation

We have used the imaging instrumentation on the Dynamics Explorer 1 (DE) satellite to measure the intensity of the diffuse ultraviolet (UV) radiation on two great circles about the sky. We find that the isotropic component of the diffuse UV radiation (possibly of extragalactic origin) has an intensity of 530 ±80 units (a unit is one photon cm−2 s−1 sr−1 A−1) at a wavelength of 150 nm. The galactic component of the diffuse UV radiation has a dependence on galactic latitude, which requires strongly forward-scattering particles if it is produced by dust above the galactic plane.

Measurements of the diffuse ultraviolet radiation

The imaging instrumentation on the Dynamics Explorer 1 satellite has been used to measure the intensity of the diffuse ultraviolet radiation on two great circles about the sky. It is found that the isotropic component of the diffuse ultraviolet radiation (possibly of extragalactic origin) has an intensity of 530 + or - 80 units (a unit is 1 photon per sq cm s A sr) at a wavelength of 150 nm. The Galactic component of the diffuse ultraviolet radiation has a dependence on Galactic latitude which requires strongly forward scattering particles if it is produced by dust above the Galactic plane.

On detecting diffuse ultraviolet radiation of cosmological origin

The intensity of diffuse extragalactic background radiation is determined by the integrated emission of all sources along a given line of sight through the Universe and by absorption due to intervening cool gas and dust. Due to red-shift and lookback-time effects, more distant objects contribute at a given wave-length today with light emitted at earlier epochs at shorter wave-lengths. Possible sources of ultraviolet (100÷3000) A emission include, but may not be restricted to, galaxies and quasars, a lukewarm or photoionized dense intergalactic medium and a cosmological sea of decaying massive neutrinos and photinos formed in the hot big bang. The resultant complex spatial intensity pattern and spectral distribution will appear superimposed on an intense galactic emission source whose main characteristics have yet to be clearly and satisfactorily established. Although substantial progress has been made recently in understanding galactic emission mechanisms, the remaining uncertainties substantially limit the accuracy with which a cosmologically significant signal may be disentangled from the diffuse galactic background «noise».

The penetration of diffuse ultraviolet radiation into interstellar clouds

view Abstract Citations (102) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The penetration of diffuse ultraviolet radiation into interstellar clouds Flannery, B. P. ; Roberge, W. ; Rybicki, G. B. Abstract It is shown that the solution of the transfer equation appropriate for models of the penetration of diffuse UV radiation into interstellar clouds, subject to attenuation by coherent, nonconservative, anisotropic scattering from grains, can be expressed analytically, with arbitrary accuracy, by means of the spherical harmonics method. Models of plane-parallel and homogeneous spherical clouds are given as functions of three parameters: the central optical depth, the single scattering albedo, and the parameter in the Henyey-Greenstein phase function. These models qualitatively confirm the results of earlier Monte Carlo simulations of dust scattering, but reveal quantitative discrepancies: the earlier results overestimated the actual mean intensity, often by more than an order of magnitude. Publication: The Astrophysical Journal Pub Date: March 1980 DOI: 10.1086/157778 Bibcode: 1980ApJ...236..598F Keywords: Clouds; Diffuse Radiation; Interstellar Matter; Radiative Transfer; Spherical Harmonics; Ultraviolet Radiation; Asymptotic Methods; Legendre Functions; Monte Carlo Method; Transfer Functions; Astrophysics full text sources ADS |