Modeling of the influence of snow reflectance on ultraviolet irradiance for cloudless sky

The amplification of UV irradiance at the Earth's surface that is due to successive reflections between the snow-covered ground and the scattering atmosphere is analyzed by a method based on decoupling the atmosphere and the surface functions. For a uniform Lambertian surface the amplification factor for the global irradiance depends only on the product of the surface reflectance and the atmospheric backscatter. It varies with wavelength, reaching a maximum near 320 nm; this maximum is close to 50% for clean snow. In UV-B the amplification depends strongly on tropospheric ozone. For non-Lambertian, nonuniform surfaces it is possible, by the same method, to define effective or average reflectances.     

Using shaded filter instruments for measurements of sky radiance: retrieval of the apparent sky-view factor from ultraviolet radiation measurements

There is a growing need for sky radiometric measurements that encapsulate spatial as well as temporal variability. Since the advent of fast data acquisition systems in the 1980s, recent studies have utilized radiation filter instruments deployed in various sky-shading platforms. One cost effective method provides azimuthally averaged sky radiance distribution data at time scales down to fractions of a minute. Successful operation of this scheme requires knowledge of the apparent sky-view factor of the deployed sensor--an artifact of the instrument input optics, instrument filter design, and the instrument shading device employed. We provide a methodology for a determination of the sensor sky-view factor by using the employed shading device and the sun as a light source. The effect of an incorrect determination of instrument sky-view factor is also analyzed in context of the measurements.     

Bandpass-resampling effects on the retrieval of radiance and surface reflectance

Radiative transfer models are often employed to derive the surface reflectance for Earth-looking multispectral scanners or imaging spectrometers. For this purpose the calculated radiances have to be resampled with the spectral channel response functions of the instrument. Three methods of bandpass resampling the product terms of the radiative transfer equation are compared: the exact method and two commonly used approximations. Error budgets for the two approximate methods are given for typical multispectral and hyperspectral sensors. The error depends on the wavelength, bandwidth, atmospheric parameters, and atmospheric path length.     

Effect of molecular anisotropy on backscattered ultraviolet radiance

The effect of molecular anisotropy on backscattered UV (BUV) radiances is computed by accounting for it in both Rayleigh optical thickness and the scattering-phase matrix. If the effect of molecular anisotropy is included only in the optical thickness and not in the phase matrix, then for high sun (θ(0) ～ 0°), the nadir radiance (I(0)) leaving the top of the atmosphere is approximately 1.8% higher than the radiance (I(op)) computed with the effect included in the phase matrix. For very low sun (θ(0) > 80°), I(0) is approximately 2.3% lower than I(op). For off-nadir radiances the relative increase (decrease) depends on both the local zenith angle as well as the azimuth angle. Also, an increase in the surface reflectivity decreases the effect of molecular anisotropy on the upwelling radiances. Exclusion of the anisotropy factor in the Rayleigh-phase matrix has very little effect (<1%) on ozone retrieval from the BUV-type instruments. This is because of the ratio technique used in the retrieval algorithm, which practically cancels out the anisotropy effect.     

Charge-coupled device spectrograph for direct solar irradiance and sky radiance measurements

The characterization of a charged-coupled device (CCD) spectrograph developed at the Laboratory of Atmospheric Physics, Thessaloniki is presented. The absolute sensitivity of the instrument for direct irradiance and sky radiance measurements was determined, respectively, with an uncertainty of 4.4% and 6.6% in the UV-B, and 3% and 6% in the UV-A, visible and near-infrared (NIR) wavelength ranges. The overall uncertainty associated with the direct irradiance and the sky radiance measurements is, respectively, of the order of 5% and 7% in the UV-B, increasing to 10% for low signals [e.g., at solar zenith angles (SZAs) larger than 70 degrees ], and 4% and 6% in the UV-A, visible, and NIR. Direct solar spectral irradiance measurements from an independently calibrated spectroradiometer (Bentham DTM 300) were compared with the corresponding CCD measurements. Their agreement in the wavelength range of 310-500nm is within 0.5% +/- 1.1% (for SZA between 20 degrees and 70 degrees ). Aerosol optical depth (AOD) derived by the two instruments using direct Sun spectra and by a collocated Cimel sunphotometer [Aerosol Robotic network (AERONET)] agree to within 0.02 +/- 0.02 in the range of 315-870 nm. Significant correlation coefficients with a maximum of 0.99 in the range of 340-360 nm and a minimum of 0.90 at 870 nm were found between synchronous AOD measurements with the Bentham and the Cimel instruments.     

Island perturbation to the sky radiance over the ocean: simulations

Sky-radiance measurements at the sea surface can be used to estimate radiative properties of aerosols over water. We demonstrate, through Monte Carlo simulations, that significant perturbations to sky radiance over the ocean can occur when measurements are carried out with radiometers located on islands. In particular, we present examples of the influence of the physical and optical thicknesses of an aerosol layer, the azimuth of observation relative to the Sun, the size of the island, the location of the radiometer on the island, and the albedo of the island on the magnitude of the perturbation for a circular island of uniform albedo. Relative errors in sky radiance of as high as 39% were found in the blue. Simulated (perturbed) sky radiances were combined with an algorithm for retrieving the aerosol phase function P(θ), where θ is the scattering angle, and with the single-scattering albedo ω(0), to demonstrate how the perturbation can influence the retrieved values. It was found that the fractional error in the retrieved values of the product ω(0)P(θ) can be significantly greater than the fractional error in the sky radiance, because of the effects of multiple scattering. This underscores the importance of removing the island perturbation before an inversion algorithm is used. A first-order procedure for removing the island perturbation based on the values of ω(0)P(θ) retrieved from the perturbed sky radiance is proposed and is found to be effective if the island perturbation is not too large. A simplified Monte Carlo procedure that is applicable to an island of arbitrary shape and albedo distribution is presented. The procedure could be used to assess the suitability of a given island as a measurement site, and to provide a first-order correction to actual experimental measurements.     

Effects of ocean surface reflectance variation with solar elevation on normalized water-leaving radiance

Effects of the ocean surface reflection for solar irradiance on the normalized water-leaving radiance in the visible wavelengths are evaluated and discussed for various conditions of the atmosphere, solar-zenith angles, and wind speeds. The surface reflection effects on water-leaving radiance are simply due to the fact that the radiance that is backscattered out of the water is directly proportional to the downward solar irradiance just beneath the ocean surface. The larger the solar-zenith angle, the less the downward solar irradiance just beneath the ocean surface (i.e., more photons are reflected by the ocean surface), leading to a reduced value of the radiance that is backscattered out of the ocean. For cases of large solar-zenith angles, the effects of surface irradiance reflection need to be accounted for in both the satellite-derived and in situ measured water-leaving radiances.     

Retrieval of elements of the columnar aerosol scattering phase matrix from polarized sky radiance over the ocean: simulations

We have extended the Wang-Gordon [Appl. Opt. 32, 4598-4609 (1993)] and Gordon-Zhang [Appl. Opt.34, 5552-5555 (1995)] algorithms for retrieval of omega(0)P(?, where omega(0) is the aerosol single-scattering albedo and P(?) is the aerosol phase function for scattering through an angle ?, from measurement of the radiances exiting the top and the bottom of the atmosphere over the ocean, to include polarization. This permits derivation of the P(11)(?) and P(12)(?) elements of the Mueller scattering phase matrix P(?) from measurement of the linear polarization portion of the Stokes vectors associated with the radiance exiting the top and the bottom of the atmosphere. Simulations show that good retrievals are possible for aerosol optical thicknesses as large as 2; however, the atmosphere is required to be horizontally homogeneous. We study the influence of the elements of P(?) that cannot be determined in this manner. It is shown that including surface measurements of the linear polarization of the sky radiance improves the estimation of the radiance simultaneously exiting the top of the atmosphere (TOA) and also allows reasonably accurate estimates of the TOA polarization. This is important for in-orbit calibration of ocean-color sensors.     

Sub-quarter-wave multilayer coatings with high reflectance in the extreme ultraviolet

Multilayer coatings with a small number of layers were designed and prepared to provide an increase in normal-incidence reflectance in the extreme ultraviolet compared with the reflectance of available single-layer coatings, namely, SiC, B4C, and Ir. Multilayers were designed to produce coatings with the highest possible reflectance at 91.2 and at 58.4 nm. At these wavelengths all the materials absorb radiation strongly, but still a reflectance enhancement can be obtained by means of sub-quarter-wave multilayer coatings with two or more different materials. Sub-quarter-wave multilayer coatings based on Al, MgF2, diamondlike carbon, B4C, SiC, and Ir showed higher reflectance than single-layer coatings of SiC and B4C not only at the target wavelength but in a wide band ranging from 50 nm to the 121.6-nm H Lyman-alpha line. Multilayer coatings suffered some reflectance degradation over time. However, after approximately 80-100 days of aging in a desiccator, the reflectance for the multilayer coatings was greater than for the single-layer coatings.     

Bidirectional reflectance distribution function of diffuse extreme ultraviolet scatterers and extreme ultraviolet baffle materials

Bidirectional reflectance distribution function (BRDF) measurements of a number of diffuse extreme ultraviolet (EUV) scatterers and EUV baffle materials have been performed with the Goddard EUV scatterometer. BRDF data are presented for white Spectralon SRS-99 at 121.6 nm; the data exhibit a non-Lambertian nature and a total hemispherical reflectance lower than 0.15. Data are also presented for an evaporated Cu black sample, a black Spectralon SRS-02 sample, and a Martin Optical Black sample at wavelengths of 58.4 and 121.6 nm and for angles of incidence of 15 degrees and 45 degrees. Overall Martin Optical Black exhibited the lowest BRDF characteristic, with a total hemispherical reflectance of the order of 0.01 and measured BRDF values as low as 2 x 10(-3) sr(-1).     

Assessment of a bidirectional reflectance distribution correction of above-water and satellite water-leaving radiance in coastal waters

Water-leaving radiances, retrieved from in situ or satellite measurements, need to be corrected for the bidirectional properties of the measured light in order to standardize the data and make them comparable with each other. The current operational algorithm for the correction of bidirectional effects from the satellite ocean color data is optimized for typical oceanic waters. However, versions of bidirectional reflectance correction algorithms specifically tuned for typical coastal waters and other case 2 conditions are particularly needed to improve the overall quality of those data. In order to analyze the bidirectional reflectance distribution function (BRDF) of case 2 waters, a dataset of typical remote sensing reflectances was generated through radiative transfer simulations for a large range of viewing and illumination geometries. Based on this simulated dataset, a case 2 water focused remote sensing reflectance model is proposed to correct above-water and satellite water-leaving radiance data for bidirectional effects. The proposed model is first validated with a one year time series of in situ above-water measurements acquired by collocated multispectral and hyperspectral radiometers, which have different viewing geometries installed at the Long Island Sound Coastal Observatory (LISCO). Match-ups and intercomparisons performed on these concurrent measurements show that the proposed algorithm outperforms the algorithm currently in use at all wavelengths, with average improvement of 2.4% over the spectral range. LISCO's time series data have also been used to evaluate improvements in match-up comparisons of Moderate Resolution Imaging Spectroradiometer satellite data when the proposed BRDF correction is used in lieu of the current algorithm. It is shown that the discrepancies between coincident in-situ sea-based and satellite data decreased by 3.15% with the use of the proposed algorithm. This confirms the advantages of the proposed model over the current one, demonstrating the need for a specific case 2 water BRDF correction algorithm as well as the feasibility of enhancing performance of current and future satellite ocean color remote sensing missions for monitoring of typical coastal waters.     

Influence of nonuniform ground reflectance on horizontal visibility

One of the assumptions made in calculating the horizontal visibility of black targets is that every volume element of the atmosphere or medium is illuminated by the same amount of light. This assumption has always been interpreted as a homogeneous illumination, without considering the importance of the reflectance properties of the ground extending between observer and horizon along the path of sight. This paper is a theoretical and experimental study of the effect of ground, with varying reflectance properties, on the horizontal visibility. The laboratory simulation shows that, if that part of the ground extending between observer and target has a higher reflectance than the one extending between target and horizon, the visibility may decrease by up to 15%. In the opposite case, the visibility increases.     

Ground-based zenith sky abundances and in situ gas cross sections for ozone and nitrogen dioxide with the Earth Observing System Aura Ozone Monitoring Instrument

High-accuracy spectral-slit-function calibration measurements, in situ ambient absorption gas cell measurements for ozone and nitrogen dioxide, and ground-based zenith sky measurements with the Earth Observing System Aura Ozone Monitoring Instrument (OMI) flight instrument are reported and the results discussed. For use of high-spectral-resolution gas absorption cross sections from the literature in trace gas retrieval algorithms, accurate determination of the instrument's spectral slit function is essential. Ground-based measurements of the zenith sky provide a geophysical determination of atmospheric trace gas abundances. When compared with other measurements, they can be used to verify the performance of the OMI flight instrument. We show that the approach of using published high-resolution absolute absorption cross sections convolved with accurately calibrated spectral slit functions for OMI compares well with in situ gas absorption cell measurements made with the flight instrument and that use of these convolved cross sections works well for reduction of zenith sky data taken with the OMI flight instrument for ozone and nitrogen dioxide that are retrieved from measured spectra of the zenith sky with the differential optical absorption spectroscopy technique, the same method to be used for the generation of in-flight data products. Finally, it is demonstrated that the spectral stability and signal-to-noise ratio performance of the OMI flight instrument, as determined from preflight component and full instrument tests, are sufficient to meet OMI mission objectives.     

铁镁电气石的红外发射率研究

用化学分析、X射线衍射(XRD)、傅立叶红外吸收(FTIR)和低温红外发射率测试等实验手段,以东北产的花岗岩为对比,研究热处理对铁镁电气石红外发射率的影响.实验发现分别经过550、750、850、950、1010和1100℃2h处理的陕西汉中地区电气石,80℃时波长在2～18μm间的全红外发射率在0.91～0.93间.电气石的结构破坏和晶型转变对红外发射率影响不大,即电气石的晶体结构不是其具有高红外发射率的原因;但热处理会影响晶格常数,晶胞体积增大发射率略有降低;跟电气石的化学元素组成相近,以α二氧化硅和钠长石为主要物相的花岗岩红外发射率也较高(0.93),所以该电气石具有较高的红外发射率和成分有关.     

Development and study of a radiance measurement system based on a CCD array in the vacuum and near ultraviolet region

We describe methods and instrumentation that we have developed for measuring the radiance distribution over the emitting region of plasma emitters in the extreme vacuum ultraviolet region. The radiance comparator for vacuum and near ultraviolet radiation includes a reflecting telescope based on highly reflective nanostructures, a set of filters to eliminate the effect of scattered light and higher orders of diffraction, and a cooled CCD array.     

Influence of pyrometallurgical copper production on the environment

In this paper the influence of pyrometallurgical treatment of copper sulphide minerals and pyrite on the environment from the aspect of ambient air pollutions is considered. Results of emission of SO(2) and particulate matter from the location with the most pollution are presented. According to the results it could be seen that the Bor's citizen were exposed to the high concentration of SO(2) and arsenic which were found to be multiple over the Serbian legislative limits during 2007. Also, the reasons and consequences of this pollution were analysed.     

系统环境对化学光源发光效率的影响

介绍了化学光源的特点、组成及化学发光机理,详细讨论了系统环境对化学发光效率的影响,述评了相关研究的进展.     

Influence of the angular shape of the volume-scattering function and multiple scattering on remote sensing reflectance

Scattering phase functions derived from measured (volume-scattering meter, VSM) volume-scattering functions (VSFs) from Crimean coastal waters were found to have systematic differences in angular structure from Fournier-Forand (FF) functions with equivalent backscattering ratios. Hydrolight simulations demonstrated that differences in the angular structure of the VSF could result in variations in modeled subsurface radiance reflectances of up to +/-20%. Furthermore, differences between VSM and FF simulated reflectances were found to be nonlinear as a function of scattering and could not be explained with the single-scattering approximation. Additional radiance transfer modeling demonstrated that the contribution of multiple scattering to radiance reflectance increased exponentially from a minimum of 16% for pure water to a maximum of approximately 94% for turbid waters. Monte Carlo simulations demonstrated that multiple forward-scattering events were the dominant contributors to the generation of radiance reflectance signals for turbid waters and that angular structures in the shape of the VSF at forward angles could have a significant influence in determining reflectance signals for turbid waters.