Radiation Redistribution Research Articles

A Practical Algorithm for Correcting Topographical Effects on Global GPP Products

AbstractVegetation in mountainous areas contributes about 36% to the global gross primary productivity (GPP). However, the influences of topography on radiation and water redistributions in mountain ecosystems are so far ignored in existing global GPP data sets. Here, an eco‐hydrological model was adopted to simulate 30 m resolution mountain and flat GPP over 16 watersheds. Then, a topographical correction index (TCI) was developed based on simulated soil water redistribution (TCIwater), radiation redistribution (TCIrad), and redistribution of climate factors (TCIclim). Finally, the proposed TCI was applied to four GPP data sets. The mean‐bias‐error (MBE), determination coefficient (R2), and Root‐Mean‐Square‐Error (RMSE) between mountain GPP and flat GPP (or GPP data sets) were used for evaluation. Results showed that the MBE of flat GPP before correction (194 g C m−2 yr−1) was reduced to 126, 94, and 2 g C m−2 yr−1 after the corrections of TCIwater, TCIrad, and TCIclim, highlighting the effectiveness of integrated redistribution information in correcting the topographical effect on GPP estimation. The relationship between mountain and flat GPP after the TCI correction was improved at the 30 m resolution (increasing R2 by 0.09 and reducing RMSE by 90 g C m−2 yr−1) and 480 m resolution (increasing R2 by 0.13 and reducing RMSE by 178 g C m−2 yr−1). Regarding the four GPP data sets after the TCI correction, the MBE of 183 g C m−2 yr−1 was averagely reduced to 17 g C m−2 yr−1, and RMSE was reduced by 118 g C m−2 yr−1 at 480 m resolution. This study suggests that integrating topography‐induced interactions into current GPP data sets is a feasible way to understand the carbon budget in mountain ecosystems.

Collisional redistribution of hydrogen line radiation in low- and moderate-density magnetized plasmas.

A computer simulation technique has been applied to the modeling of radiation redistribution functions in low- and moderate-density magnetized hydrogen plasmas. The radiating dipole is described within the Heisenberg picture, and perturbations by the plasma microfield are accounted for through a time-dependent Stark effect term in the Hamiltonian. Numerical applications are presented for the first Lyman and Balmer lines at plasma conditions relevant to tokamak divertors and magnetized white dwarf atmospheres. In both cases, the collisional redistribution of the radiation frequency is shown to be incomplete. Comparisons with a previously developed impact model are performed, and results are discussed.

Spatial Scaling of Gross Primary Productivity Over Sixteen Mountainous Watersheds Using Vegetation Heterogeneity and Surface Topography

AbstractLand surface models intended for large‐scale applications are often executed at coarse resolutions, and the sub‐grid heterogeneity is usually ignored. Here, a spatial scaling algorithm that integrates the information of vegetation heterogeneity (land cover type and leaf area index) and surface topography (elevation, slope, relative azimuth (Raz) between the sun and the slope background, sky‐view factor, and topographic wetness index), was proposed to correct errors in gross primary productivity (GPP) estimates at a coarse spatial resolution. An eco‐hydrological model named BEPS‐TerrainLab was used to simulate GPP at 30 and 480 m resolutions for 16 mountainous watersheds selected globally. Results showed that an obvious improvement on GPP estimates at 480 m resolution was achieved after the correction in comparison with GPP modeled at 30 m resolution, with the determination coefficient increased by 0.38 and mean bias error reduced by 203gCm−2 yr−1. The combination of all the seven factors made the largest improvement for GPP estimation at 480 m resolution, suggesting that a larger improvement would be achieved when more factors of surface heterogeneity are considered. More specifically, our results indicated that five factors, including land cover type and leaf area index regarded as integrated outcomes of all the environmental conditions, Raz and sky‐view factor associated with radiation redistribution, and slope related to soil water redistribution, were especially important in the spatial scaling procedure. This study suggests that incorporating the information of surface heterogeneity into the spatial scaling algorithm is useful for improving coarse resolution GPP estimates over mountainous areas.

Role of Dislocations in the Process of Degradation of Semiconductor Lasers with Electronic Energy Pumping. Experimental Research

Light self-destruction-degradation of the second type has been observed in samples of semiconductor lasers with electronic energy pumping with high optical homogeneity and good quality of surface treatment. In these samples, damage appeared in the form of cords perpendicular to the ends of the resonator. According to the current understanding of the passage of powerful light streams through various media, the emergence of narrow light channels is due to the phenomenon of self-focusing. It refers to the fundamental physical mechanisms of propagation of laser radiation and is caused by nonlinear phenomena arising in a medium under the influence of high-power laser radiation. The physical reason for self-focusing is an increase in the refractive index n in a strong light field. Thermal self-focusing is the most probable cause of radiation redistribution in the active region of the crystal. However, it is possible that in the initial stage of the appearance of light channels a certain role is played by the growth of the intensity of radiation in certain sections of the crystal because of the instability of generation or small fluctuations in the pump current density. Then the process acquires an avalanche character, since the localization of the ray in the channel increases the density of light radiation which can lead to overheating of the substance and the activation of the thermal self-focusing mechanism. The experiments performed in this paper have shown that optically homogeneous crystals possess maximum resistance to degradation processes. In them, the critical power of light destruction is determined by the self-focusing threshold of radiation in a material. Since the nonlinear addition to the refractive index Δn = n2E2 at the self-focusing threshold is determined by the change in the concentration of non-equilibrium carriers ΔN(E2), the value of the maximum fluctuation DΔNmax itself is proportional to the value of the non-equilibrium carrier concentration at the generation threshold ΔNpores and the relative excess of the generation threshold J = (j – jn)/jn. Thus, a low threshold concentration of non-equilibrium carriers is one of the conditions for increasing material resistance to degradation processes. In doped crystals ΔNpores is less than in pure materials. This, perhaps, explains the rather higher value of Pcritial in the optimally doped homogeneous n-GaAs. Smaller values of Pcritial in p-type samples doped with zinc can be associated not only with the inhomogeneity of these crystals, but also with large generation thresholds. In addition, the cross section for absorption of radiation by holes is about 3–4 times larger than by electrons, which can also reduce the self-destruction threshold of lasers. At Т = 300 K, the lasing thresholds are higher that naturally reduces the value of the self-focusing threshold.

AUTOMATED ECOLOGICAL TERRAIN MORPHOLOGY CLASSIFICATION OF STRETCH OF UPPER DNISTER RIVER VALLEY

Modern technological developments can induce substantial changes not only in research methods, but also in theoretical concepts and approaches in Earth sciences. Recent developments in the technologies of remote sensing, GIS data processing and mapping now make possible to more directly consider ecologically relevant properties in the process of spatial units delineation. The concept of morphotop has been proposed by author meaning spatial units mapped taking into account ecologically relevant properties of terrain. It is different from the commonly used concept of natural complex in that ecological and not genetic criteria are at the base of spatial units differentiation. The ecological approach for terrain morphology classification has been applied for the 4.5 to 2 km study area located at the upper part of Dnister river valley. The 10 m spatial resolution DEM was obtained for the study area by the interpolation of digitized topographic map layers with ANUDEM algorithm. Three groups of ecologically meaningful factors of landscape differentiation have been taken into account: 1) solar radiation redistribution; 2) water and soil moisture redistribution; 3) erosion potential of terrain. For each of these, the appropriate index was proposed and derived from DEM by the respective formula. The method of iterative cluster analysis with ISODATA algorithm has been applied to these variables complemented with absolute elevation. This method distinguishes a predefined number of classes by revealing the natural groupings of data in attribute space. Arbitrary presetting the number of classes allows to classify data with the different levels of detail and to analyze the changes in classification output as a function of classification scale and detalization. The study area has been successively classified into 12 and 8 classes, with 100 algorithm iteration in each case. Each class has been given a descriptive characteristic; an average values of certain terrain morphometric parameters for each class were also calculated and given in a table. The map of the distribution of the distinguished classes was produced. Key words: terrain morphology, unsupervised classification, morphotop, ecological geomorphology.

A method to calculate Fresnel lenses

In solar engineering, in contrast to image optics, Fresnel lenses are intended for securing the required concentrations of solar radiation and its distribution over a receiver’s surface. It is also important to secure a high use coefficient of the concentrated flux. In particular, this defines the features of calculation of Fresnel lenses: it is necessary to take into account inaccuracies in fabrication of Fresnel lenses and solar radiation redistribution by means of selecting the respective parameters of Fresnel lens belts. In the present work, we examine the procedure for the calculating geometrical parameters of Fresnel lenses on a flat base by considering the mentioned requirements. A corresponding software for calculating the geometrical parameters and concentrating characteristics of the Fresnel lenses is developed, and examples of calculation are given. For a constant refractive index of Fresnel lens material, it is shown that the Fresnel lens can secure a concentration of about 1000, but in this case the optical efficiency of the Fresnel lens will not be higher than 70%. The procedure that has been developed may be the basic one for determining the parameters and concentrating characteristics of Fresnel lenses by considering refractive index variance.

Study of x-ray radiant characteristics and thermal radiation redistribution in CH foam filling cylindrical cavities

Experiments are presented, which demonstrate the properties of x-ray radiation and redistribution of radiant thermal energy in high Z cylindrical cavities filled with low Z CH foam. Time integrated spectra records were obtained by a calibrated space-resolved transmission grating spectrometer. The x-ray radiation became weaker in intensity and was changed to a softer near-Planckian radiation light after a 1500 μm long transport in the foam filling cavity. The experimental redistribution of the radiant thermal energy was plotted and compared to the numerical results of a simplified model. Good agreements have been achieved.

Mapping Glacier Variations at Regional Scale through Equilibrium Line Altitude Interpolation: GIS andStatistical Application in Massif des Écrins (French Alps)

Glacier variation is one of the best indicators of climate change in mountainous environment. In French Alps, many temporal data are acquired by glaciologists at glaciers scale: geometrical parameters (surface area, thickness, length and front altitude) are surveyed since the end of the 19th century. Those parameters are necessary to estimate the mass-balance of glaciers and, then, an accurate temporal signal of glacier variation. However, the time-response of the glaciers can be highly variable because of the topoclimate, and more generally the local settings of the glaciers. Moreover, climatologists and hydrologists are requiring estimation of glacier variations at regional scale and not only at local scale. In this paper, we highlight that the Equilibrium Line Altitude (ELA) is a parameter prone to spatio-temporal reconstructions at regional scale. ELA can indeed be interpolated at a region scale from local data: for instance, many geographers have reconstructed spatial trends during 1980s. Here, we try to interpolate ELA from multi-dimensionnal regression analysis: ELA is explained by many local parameters (Incoming solar radiation, topographic indexes, snow-redistribution by wind, etc.). Regression model was adjusted from a spatio-temporal database of 50 glaciers, located in the Massif des Ecrins. ELA was estimated for each glacier thanks to the Accumulation Area Ratio (ratio = 0.65) at two stages: LIA maximum and at present. Results first show that the multiple regression analysis is efficient to interpolate ELA through space: the adjusted r2 is about 0.49 for the reconstruction during the LIA, and 0.47 at present. Moreover, the RMSE error is about 50 meters for the LIA period, 55 meters at present. Finally, a high spatial variability (standard deviation of about 150 meters) is highlighted: incoming solar radiation and snow redistribution by wind mostly explain the observed differences. We can also assess a rise of the ELA of about 250 meters during the 20th century.

Solar radiation redistribution peculiarities in ice hummocks of the Arctic basin

The problem of the solar radiation heat assimilation in the stratum of the ice hummock sail is considered within the frameworks of the problem of quantitative description of hummocky formation evolution. The technique of experimental investigations and the measuring means are described. The results are given of observations on the solar radiation weakening in the stratum of ice hummocks and level ice carried out at the North Pole-35 drifting station and during the Arctic-2008 expedition on board the scientific-research vessel Akademik Fedorov. It is demonstrated that the ice hummock sail stratum assimilates 20–50% of solar radiation more than the level sea ice. The possible explanation of this phenomenon is proposed based on morphometric peculiarities of ice hummock formation.

X-ray micro-imaging by capillary optics

In this work the results on X-ray micro-imaging by means of novel polycapillary optical elements will be presented. To simulate various radiation propagation processes in both single capillary and polycapillary systems, a PolyCAD code was developed. The new experimental results on radiation redistribution by novel capillary lenses in comparison with simulated data will be reported. The images of characterized extended samples (~ 3 mm) were recorded with 6 μm resolution, the maximum provided by CCD. Polycapillary Optics CAD software X-ray tracing Imaging Confocal 02.60.Cb 02.70.-c 41.50. + h 42.15.-i 42.15.Dp 42.30.-d.

Ground-based secondary eclipse detection of the very-hot Jupiter OGLE-TR-56b

We report on the detection of the secondary eclipse of the very-hot Jupiter OGLE-TR-56b from combined z-band time series photometry obtained with the VLT and Magellan telescopes. We measure a flux decrement of 0.0363+/-0.0091 percent from the combined Magellan and VLT datasets, which indicates a blackbody brightness temperature of 2718 (+127/-107) K, a very low albedo, and a small incident radiation redistribution factor, indicating a lack of strong winds in the planet's atmosphere. The measured secondary depth is consistent with thermal emission, but our precision is not sufficient to distinguish between a black-body emitting planet, or emission as predicted by models with strong optical absorbers such as TiO/VO. This is the first time that thermal emission from an extrasolar planet is detected at optical wavelengths and with ground-based telescopes.

An analytical model for the Ly α redistribution function in conditions of tokamak edge plasmas

Radiation redistribution is investigated for applications to magnetic fusion studies. An analytical model, suitable for Monte Carlo simulations of radiative transfer, is developed for the redistribution function of the resonance line of hydrogen isotopes. The model retains Zeeman and Stark effects in the atom's rest frame and in the impact approximation. The Zeeman effect is shown to play a major role on redistribution. Discussions are given on consequences of the Doppler effect in the laboratory frame.

Influence of X-radiation in receiver system on reconstruction performance of projection tomography

It is investigated tomogram recovery accuracy dependences on radiation redistribution layer between receiver system parts. Developed model of multi-unit receiving system allows to change its characteristics. We have calculated boundary redistribution characteristics, that provides one-valuedness of tomogram restoration.

The divertor program in stellarators

Two significant problems that need to be solved for any future fusion device are heat removal and particle control. A very promising method to attack these problems in tokamaks and helical devices is the use of a divertor, providing a controlled interaction zone between plasma and wall. By carefully designing a divertor, conditions can be created in front of the divertor targets, which lead to a sufficient reduction of the power load on the targets by strong radiation redistribution. Any solution of course needs to allow for an energy confinement which is at least sufficient for the realization of a fusion reactor. Since energy confinement has been found to be strongly related to edge anomalous transport and edge plasma profiles, the ultimate aim is to find an integral solution which is optimum with respect to exhaust, heat load and energy confinement.Two different types of divertors are presently being investigated in helical devices: the `helical divertor' and the `island divertor'. So far divertor concepts have been investigated only in a few helical devices. Theoretical and experimental efforts have mainly concentrated on the suitability of divertor magnetic field structures, while detailed studies of the divertor plasma properties for the two types of divertor configurations have only recently begun. In the course of this exploration, a promising new high-density H-mode (HDH) plasma operational regime has been discovered on the Wendelstein stellarator W7-AS. It benefits from high-energy (up to twice the value of the International Stellarator Scaling ISS95) and low impurity confinement times, complemented by edge radiated power fractions of up to 90% in detached regimes. This allowed quasi-steady-state operation for up to 50 energy confinement times and so far was only constrained by machine operability.

Analytical axial view factors and thermal radiation distribution inside a cylindrical hohlraum

Thermal radiation redistribution inside a cylindrical hohlraum is discussed for uniform disc and two-ring sources. The flux conservation equation, coupled with self-similar scaling relation for the re-emitted flux, is solved to obtain the radiation temperature profile inside a gold capillary hohlraum at various times. The axial view factors required for the calculations are derived analytically in a closed form, which not only exactly reproduce the numerical results [G. D. Tsakiris, Phys. Fluids B 4, 992 (1992)] but also simplifies the overall problem enormously, both in terms of computational time and effort.

Quantum Interference in Radiation Redistribution of Highly Charged Ions in Plasmas

The influence of quantum interference effects induced by mixing of coherences and populations in the fluctuating plasma microfield on the redistribution of resonance radiation by HCI is studied in terms of the atomic density matrix. The thermal ion motion is considered within the model microfield method. Results show that the thermal ion motion (ion dynamics) induces QIEF as well, and both are essential in line centres and nearest wings of the scattered radiation.

Model microfield method for partial redistribution of resonance radiation in dense plasmas

The influence of nonlinear interference effects (NIEF) on the radiation redistribution functions is investigated in terms of the atomic density matrix formalism. The ion motion is considered within the model microfield method. The particular calculations have been performed for the spectral doublet , of helium-like ion in hot dense plasmas (T = 350 eV, ). Taking account of both NIEF and ion dynamics is essential in the line centre and the nearest wings of the scattered radiation.

Numerical method for finding uniform irradiation conditions of a fusion capsule driven by X-ray radiation

A three-dimensional model to calculate X-ray intensity distribution on an indirectly driven fusion target is presented. The model includes conversion of laser light into X rays, radiation reemission from X-ray-heated wall of a cavity, and influence of an inner pellet (i.e., a fuel capsule) on radiation redistribution. Intensity distribution of an X ray inside a cylindrical cavity heated by intense blue laser light (wavelength 351 nm, energy 5.2 kJ, duration 0.7 ns) was determined by measuring a burn-through signal from a diagnostic foil integrated onto the cavity. The experimental result is well replicated by the model calculation. By using this model, optimum conditions for uniform irradiation of afusion capsule by X-ray radiation are evaluated for use in Gekko XII laser fusion experiments.

The spectra of radiation redistribution in the presence of velocity-changing collisions

The authors present an approach that allows the study of the influence of velocity-changing collisions (VCC) on the spectrum of resonance fluorescence. They give a theoretical framework yielding general, though quite complicated results. Working in the dressed-atom basis and describing the VCC by a strong-collision model, they focus their attention on the particular case of well separated spectral lines, which leads to relatively simple expressions. The results allow the authors to compare the effects of Doppler shifts and VCC on the profiles of the central line and on the spectra sidebands. They predict that VCC cause a narrowing of the spectral lines, which they attribute to Dicke narrowing. This prediction is also confirmed by numerical results. The adopted method of dealing with VCC in terms of collision operators can be applied to a larger class of collision models than just the strong-collision model used here.

Spectrum and polarization of collision-induced fluorescence and rayleigh components of Na D lines at quasiresonant excitation

A theory for radiation redistribution was tested by observing the fluorescence-emission spectrum obtained when sodium atoms, in collision with perturber gas atoms and molecules, were excited within the absorption line-width. A narrow band tunable CW dye laser was used as an irradiating source. Intensities and polarizations of the collision-induced fluorescence and the Rayleigh component were found to be in good agreement with the values expected from theory.