Visible Radiative Transfer Research Articles

Inter-Comparison Campaign of Solar UVR Instruments under Clear Sky Conditions at Reunion Island (21°S, 55°E).

Measurement of solar ultraviolet radiation (UVR) is important for the assessment of potential beneficial and adverse impacts on the biosphere, plants, animals, and humans. Excess solar UVR exposure in humans is associated with skin carcinogenesis and immunosuppression. Several factors influence solar UVR at the Earth’s surface, such as latitude and cloud cover. Given the potential risks from solar UVR there is a need to measure solar UVR at different locations using effective instrumentation. Various instruments are available to measure solar UVR, but some are expensive and others are not portable, both restrictive variables for exposure assessments. Here, we compared solar UVR sensors commercialized at low or moderate cost to assess their performance and quality of measurements against a high-grade Bentham spectrometer. The inter-comparison campaign took place between March 2018 and February 2019 at Saint-Denis, La Réunion. Instruments evaluated included a Kipp&Zonen UVS-E-T radiometer, a Solar Light UV-Biometer, a SGLux UV-Cosine radiometer, and a Davis radiometer. Cloud fraction was considered using a SkyCamVision all-sky camera and the Tropospheric Ultraviolet Visible radiative transfer model was used to model clear-sky conditions. Overall, there was good reliability between the instruments over time, except for the Davis radiometer, which showed dependence on solar zenith angle. The Solar Light UV-Biometer and the Kipp&Zonen radiometer gave satisfactory results, while the low-cost SGLux radiometer performed better in clear sky conditions. Future studies should investigate temporal drift and stability over time.

The Impact of Smoke on the Ultraviolet and Visible Radiative Forcing Under Different Fire Regimes

The quantification of the UV characteristics of smoke aerosols is valuable to UV Index forecasting, air quality studies, air chemistry studies, and assessments of the impacts on regional and global environmental changes. The wavelength dependence of the light absorption by smoke aerosol has been researched throughout the UV and visible spectral region and varies with fire type and aerosol composition. An objective of this study is to investigate the spectral optical properties (eg, extinction coefficient, single-scattering albedo, and asymmetry parameter), UV actinic fluxes, and radiative forcing of smoke of different fire regimes. The smoke aerosol information (eg, simulated smoke fields from biomass burning emission and vertical distribution of the mass concentration of smoke components) from WRF-Chem is used to distinguish 2 smoke types: flaming and smoldering. To compute the spectral optical properties for the fire regimes, the representative size distribution and spectral refractive index have been implemented into the Mie code, and the optical properties are used to run the tropospheric ultraviolet and visible radiative transfer model. We make comparisons between simulated model and measured actinic flux in the UV and visible spectra under smoke aerosol laden conditions. The WRF-Chem-SMOKE model simulates the smoke plume matched with fire locations and comparable aerosol optical depth (AOD) with satellite measurements. However, the correlation between the simulated and observed AOD is small, which implies that adjusting the fire size for the emission inputs and improving meteorological fields are required for further research. The smoke at selected locations reduces the UV actinic flux and increases the visible actinic flux above the plume at small solar zenith angles. The specific spectral response is dependent on the smoke type. Overall, the results of this investigation show that this approach is valuable to estimate the impact of smoke on UV and visible radiative fluxes.

First aerosol optical thickness measurements at Dome C (East Antarctica), summer season 2003–2004

In the framework of a calibration project concerning satellite sensors over a remote site of inland Antarctica, the temporal variations of atmospheric aerosol properties have been investigated in relation to their strong influence on the transfer of visible radiation. For this, a sunphotometer was installed at Concordia station (75°S, 123°E, 3200 m a.s.l.) on the Antarctic plateau during summer season 2003–2004. Meteorological parameters were recorded for the same period. Very low aerosol optical thickness values were observed with a mean AOT of 0.02 at 440 nm and 0.007 at 870 nm for clear sky conditions, and a small standard deviation. Angstrom coefficients were high with an average of 1.65 at 440 nm. These values reflect the high purity of the atmosphere and the small size of particles, mainly sulfate aerosols. Higher AOT values are observed under diamond dust conditions (0.025 at 440 nm and 0.013 at 870 nm). Temporal variations are also observed at the daily and seasonal levels. Dome C, therefore, appears to be an excellent site for satellite sensor calibration as well as investigations concerning the background atmospheric composition and global atmosphere changes caused by human activities.

A Time-Dependent Model of Radiative and Conductive Thermal Energy Transport in Planetary Regoliths with Applications to the Moon and Mercury

Modeling thermal energy transfer in planetary regoliths involves treating four processes: visible radiative transfer, thermal radiative transfer, conductive transfer, and heat storage. We explicitly treat these processes while considering time-dependent problems, and we apply this model to the regoliths of the Moon and Mercury. Fitting the model to observational data allows us to constrain the radiative resistivity and thermal inertia parameters of these regoliths and hence constrain their conductivities, thermal extinction coefficients, and average grain sizes. It is also found that water ice would be stable in the polar subsurfaces of both bodies, even in areas which receive sunlight during the day.

Transfer of visible radiation in the atmosphere

Transfer of visible radiation in the atmosphere

Transfer of visible radiation in the atmosphere

The problem of the transfer of visible radiation in the terrestrial atmosphere is addressed from the visual-air-quality point-of-view. Attention is therefore focused on computations of the luminance, dominant wavelength, and spectral purity of the sky radiation requiring radiance values for a number of wavelengths in the 0.38–0.78 μm interval of the electromagnetic spectrum. These colorimetric parameters are determined, for five different plane-parallel atmospheric models, from values of the radiances at 23 unequally spaced wavelengths. The diffuse radiation is evaluated after taking into account all orders of scattering, but after neglecting the polarization aspects of the scattered radiation. The atmospheric models studied are for average, cloudfree, mid-latitude summer conditions, and vary from an aerosol-free, absorption-free model at one end to a model with a very large amount of aerosols and absorption by ozone, water vapor and oxygen at the other. These models are assumed to rest on a ground obeying Lambert's law of reflection. Discussion of results is confined to variations of the aforementioned colorimetric parameters as a function of the zenith angle of observation in a vertical plane passing through the sun and the observer, but for several positions of the sun, and for several atmospheric conditions. For a few selected cases, results obtained after including all orders of scattering are compared with those obtained after consideration of the first scattering of the incoming solar, and outgoing ground-reflected radiation. The main features of the sunlit sky for various cloud free atmospheric conditions and for various sun's positions are, qualitatively speaking, well-reproduced by the model calculations. Attention is drawn to the need for a detailed comparison of the colorimetric measurements taken simultaneously with the observations of various atmospheric parameters of crucial importance, and computations carried out with the input parameters representative of the experimental conditions; and also to the need for including absorption by other gases and sphericity of the earth-atmosphere system in future modeling studies.

Polar nephelometer for atmospheric particulate studies

A unique polar nephelometer was designed and constructed for the measurement of atmospheric particulate characteristics. The nephelometer produces visible light from a self-contained laser to irradiate an air sample drawn into the instrument. The light scattered from the particulates and molecules in the sample is detected as a function of scattering angle for each of four different incident light polarizations. These measurements are used to determine the particulate scattering matrix which is a function of the size, shape, and index of refraction of the particles. The region of sensitivity for the measurements corresponds to the size range of particles that strongly affects visible radiative transfer in the atmosphere, which is the primary application for the derived information.

The Transfer of Visible Radiation through Clouds

Visible radiation reflection, transmission and inside intensities of terrestrial clouds calculated by Monte Carlo program utilizing scattering phase function

On the Transfer of Visible Radiation through Sea Ice and Snow

Abstract Coefficients of absorption of visible radiation are determined for sea ice and snow as a function of porosity of the medium and wave-length of energy refracted into it. A comparison is made between the values derived and those obtained by other investigators under similar snow conditions. A difference in results suggests a significant rôle of crystal size and orientation in the absorption properties of sea ice and snow.

On the Transfer of Visible Radiation through Sea Ice and Snow

AbstractCoefficients of absorption of visible radiation are determined for sea ice and snow as a function of porosity of the medium and wave-length of energy refracted into it. A comparison is made between the values derived and those obtained by other investigators under similar snow conditions. A difference in results suggests a significant rôle of crystal size and orientation in the absorption properties of sea ice and snow.