Reflectance Albedo Research Articles

Albedo Reflection Modeling in Bifacial Photovoltaic Modules

This paper focuses on the analytical modeling of albedo reflection in bifacial photovoltaic modules, with particular emphasis on the backside. First, we critically examine the approaches proposed in the literature, presenting them with a tutorial style and a uniform nomenclature. These approaches are demonstrated to yield physically meaningless results, as they erroneously assume that the ground area shaded by the module acts as a source of reflected irradiance independent of the portion of sky dome visible to such an area. Then we introduce a correction based on the view factor between the shaded area and the sky. The result is a comprehensive and accurate analytical model that also describes the case of suspended panels and can be easily implemented into PV plant simulators.

Orbital variability of polarized X-ray radiation reflected from a companion star in X-ray binaries

The reflection of X-ray radiation produced near a compact object from its stellar companion contributes to the orbital variability of polarization in X-ray binaries. The X-rays are reflected mainly via Thomson scattering resulting in a high polarization. The orbital variability of the polarization strongly depends on the inclination and the orbital parameters allowing us to constrain them. To explore this phenomenon, we present analytical single-scattering models for the polarized reflection. We find that while diluted by the direct emission, the reflection can produce a polarization degree of about 1<!PCT!> in the case of a large reflection albedo. We fitted the orbital variations of the X-ray polarization observed by the Imaging X-ray Polarimetry Explorer from an accreting weakly magnetized neutron star "clocked burster" GS 1826$-$238 and found that the amplitude of the variations is too large to be primarily caused by the companion star. The polarized reflection is more significant if the compact object is obscured from the observer, and thus it should be more easily observable in certain high-inclination targets.

Effect of temperature and pH on the Millepora alcicornis and Mussismilia harttii corals in light of a spectral reflectance response

ABSTRACT The increase in carbon dioxide (CO2) atmospheric levels contributes to the rise in temperature and ocean acidification; consequently, it directly impacts coral reefs. The increase in seawater temperature is the primary factor that causes the collapse of coral-algal symbiosis, which can be followed by coral death and, generally, ocean acidification impairs biogenic calcification and promotes dissolution of carbonate substrata. These harmful effects on corals associated with the continuous increase in CO2 atmospheric levels raise widespread concerns about the coral reef decline, intensifying the efforts to understand/monitor their effects on these organisms. The objective of this study was to evaluate the physiological effect of temperature increase, water acidification (i.e. decrease in pH), and their effects combined (temperature increase with water acidification), through the reflectance analyses and maximum photosynthetic capacity of zooxanthellae (Fv/Fm) in two coral species: Millepora alcicornis and Mussismilia harttii. Fragments of four large colonies of each specie were collected, fragmented, and submitted to four different treatments for 15 days: (i) control treatment (under identical temperature and pH conditions observed in the sampling seawater site), (ii) temperature treatment (with an increase temperature of around ≅2ºC); (iii) water acidification treatment (with a decrease of nearly 0.3 in pH); and (iv) a treatment of combined effects from water temperature rising and acidification. Spectral reflectance and Fv/Fm were measured from samples of these species in a marine mesocosm. Data of reflectance, first and second-order derivative, area under the curve, full width at half maximum (FWHM), depth values and the Fv/Fm were used to classify the coral species and treatments through the linear discriminant analysis (LDA). Coral samples were exposed to the increased temperature bleached, whilst decreased pH caused a slight reduction in reflectance albedo with minimal effects on Fv/Fm. The combined factors (treatment iv) triggered a bleaching response, presenting spectral reflectance and colouring patterns similar to those observed in bleached corals, especially for M. alcicornis. The two-way ANOVA indicated statistically meaningful spectral differences between treatments for the second-order derivatives at 634 nm and for Fv/Fm values. However, there was no statistically meaningful interaction effect due to the treatment type and coral species response for the second-order derivative at 670 nm and to the Fv/Fm values. LDA classified the corals’ species and the corals in different treatment, using their spectral responses and Fv/Fm results, with high accuracy (96.7% and 73.3%, respectively), reinforcing its application for coral physiology evaluation and species classification. The control and combined groups achieved the best classification scores, with only one misclassification.

Simulated effects of plastic film-mulched soil on surface energy fluxes based on optimized TSEB model in a drip-irrigated cotton field

The value-added by plastic film mulches are numerous in agricultural productivity and its global acceptance is unprecedented. However, its disturbing effects on the natural water cycling, surface energy fluxes and partitioning of evapotranspiration (ET) in drip-irrigated fields with plastic film mulch are often overlooked or not investigated due to deficiencies in existing process-based ET models. This study optimized the simulation of plastic film-mulched soil effects on surface energy fluxes by incorporating a thermal contact resistance component into a satellite derived Land Surface Temperature-based Two-Source Energy Balance (i.e.,TSEBPM) model, in a drip-irrigated cotton field for two consecutive growing seasons (2009 and 2010). The optimized model agrees better with Eddy Covariance (EC) flux tower observation and showed reduced error biases than the original TSEB model. The RMSE values decreased for the net radiation, latent, sensible and ground heat fluxes by 10.85, 1.93, 4.84, 0. 81 (Wm−2), respectively. Moreover, ET partitioning by TSEBPM revealed the actual contribution of evaporation (E) and transpiration (T) in cotton water use at different growth stages. When cotton growth reaches the ball-opening stage (i.e., harvesting period or cotton canopy coverage > 75%), the mean E/ET value was 0.20 ± 0.05, while T/ET was 0.79 ± 0.05 during the irrigation seasons. Meanwhile, the plastic mulching altered the reflected shortwave radiation, thereby impacting on surface albedo reflectance under well saturated cotton canopy. As such, the transpiration sub-model parameters such as fractionalvegetationcover and vegetationgreenfraction had influential effects, and are the most sensitive in the TSEBPM model parameterization. This study showed that TSEBPM can provide robust insights into the effects of plastic mulching on surface energy fluxes and cotton ET, therefore can be explored further across arid agroecosystems.

Over 30% efficiency bifacial 4-terminal perovskite-heterojunction silicon tandem solar cells with spectral albedo

We developed and designed a bifacial four-terminal perovskite (PVK)/crystalline silicon (c-Si) heterojunction (HJ) tandem solar cell configuration albedo reflection in which the c-Si HJ bottom sub-cell absorbs the solar spectrum from both the front and rear sides (reflected light from the background such as green grass, white sand, red brick, roofing shingle, snow, etc.). Using the albedo reflection and the subsequent short-circuit current density, the conversion efficiency of the PVK-filtered c-Si HJ bottom sub-cell was improved regardless of the PVK top sub-cell properties. This approach achieved a conversion efficiency exceeding 30%, which is higher than those of both the top and bottom sub-cells. Notably, this efficiency is also greater than the Schockley–Quiesser limit of the c-Si solar cell (approximately 29.43%). The proposed approach has the potential to lower industrial solar cell production costs in the near future.

IN-SITU MEASUREMENT OF DIFFUSE ATTENUATION COEFFICIENT AND ITS RELATIONSHIP WITH WATER CONSTITUENT AND DEPTH ESTIMATION OF SHALLOW WATERS BY REMOTE SENSING TECHNIQUE

Diffuse attenuation coefficient, Kd(λ), has an empirical relationship with water depth, thus potentially to be used to estimate the depth of the water based on the light penetration in the water column. The aim of this research is to assess the relationship of diffuse attenuation coefficient with the water constituent and its relationship to estimate the depth of shallow waters of Air Island, Panggang Island and Karang Lebar lagoons and to compare the result of depth estimation from Kd model and derived from Landsat 8 imagery. The measurement of Kd(λ) was carried out using hyperspectral spectroradiometer TriOS-RAMSES with range 320 – 950 nm. The relationship between measurement Kd(λ) on study site with the water constituent was the occurrence of absorption by chlorophyll-a concentration at the blue and green spectral wavelength. Depth estimation using band ratio from Kd(λ) occurred at 442,96 nm and 654,59 nm, which had better relationship with the depth from in-situ measurement compared to the estimation based on Landsat 8 band ratio. Depth estimated based on Kd(λ) ratio and in-situ measurement are not significantly different statistically. Depth estimated based on Kd(λ) ratio and in-situ measurement are not significantly different statistically. However, depth estimation based on Kd(λ) ratio was inconsistent due to the bottom albedo reflection because the Kd(λ) measurement was carried out in shallow waters. Estimation of water depth based on Kd(λ) ratio had better results compared to the Landsat 8 band ratio.

Thermodynamic limit of bifacial double-junction tandem solar cells

A traditional single-junction solar panel cannot harness ground-scattered light (albedo reflectance, RA), and also suffers from the fundamental sub-band-gap and the thermalization losses. In this paper, we explain how a “bifacial tandem” panel would dramatically reduce these losses, with corresponding improvement in thermodynamic performance. Our study predicts (i) the optimum combination of the band-gaps, empirically given by Eg(t)opt≈Eg(b)opt(2+RA)/3+(1−RA) and the (ii) corresponding optimum normalized output power given by ηT(opt)*≈RA (2ηSJ(opt))+(1−RA)ηDJ(opt). Empirically, ηT(opt)* interpolates between the thermodynamic efficiency limit of classical double-junction tandem cell (ηDJ) and twice that of a single-junction cell (ηSJ). We conclude by explaining how the fundamental loss mechanisms evolve with RA in a bifacial tandem cell.

Bulk hydrogen abundances in the lunar highlands: Measurements from orbital neutron data

The first map of bulk hydrogen concentrations in the lunar highlands region is reported. This map is derived using data from the Lunar Prospector Neutron Spectrometer (LP-NS). We resolve prior ambiguities in the interpretation of LP-NS data with respect to non-polar hydrogen concentrations by comparing the LP-NS data with maps of the 750nm albedo reflectance, optical maturity, and the wavelength position of the thermal infrared Christiansen Feature. The best explanation for the variations of LP-NS epithermal neutron data in the lunar highlands is variable amounts of solar-wind-implanted hydrogen. The average hydrogen concentration across the lunar highlands and away from the lunar poles is 65ppm. The highest hydrogen values range from 120ppm to just over 150ppm. These values are consistent with the range of hydrogen concentrations from soils and regolith breccias at the Apollo 16 highlands landing site. Based on a moderate-to-strong correlation of epithermal neutrons and orbit-based measures of surface maturity, the map of highlands hydrogen concentration represents a new global maturity index that can be used for studies of the lunar soil maturation process. We interpret these hydrogen concentrations to represent a bulk soil property related to the long-term impact of the space environment on the lunar surface. Consequently, the derived hydrogen concentrations are not likely related to the surficial enhancements (top tens to hundreds of microns) or local time variations of OH/H2O measured with spectral reflectance data.

Study of the turbocharger shaft motion by means of infrared sensors

This work describes a technique for measuring the precession movement of the shaft of small automotive turbochargers. The main novelty is that the technique is based on infrared light diode sensors. With presented technique it is possible to perform secure mounting of electronics and also to measure, with good accuracy, far enough from the turbocharger shaft. Both advantages allow applying it even in critical lubrication conditions and when blade contact occurs. The technique׳s main difficulties arise from the small size of the turbocharger shaft and the high precession movement in critical conditions. In order to generate the optimum albedo reflection for infrared measurement, a special cylindrical nut with larger diameter than the original one is assembled at the shaft tip in the compressor side. Following, shaft balancing, the calibration of the sensors and the compensation of errors from different sources are needed steps before the method is able to identify the main frequencies of shaft motion. Once synchronous and sub-synchronous frequencies have been obtained it is possible to reconstruct the instantaneous position of the shaft to determine its precession movement.

Radiation field modeling and optimization of a compact and modular multi-plate photocatalytic reactor (MPPR) for air/water purification by Monte Carlo method

The radiation field in a multi-plate photocatalytic reactor (MPPR) for air or water purification was modeled and optimized using a Monte Carlo stochastic method. The MPPR consists of parallel photocatalytic plates irradiated by cylindrical UV lamps orthogonal to the plates. The photocatalyst titanium dioxide (TiO2) is supported on the plates as a thin film. The photoreactor design is compact and offers a large irradiated photocatalytic surface area, a high degree of photon utilization, low pressure drop and a modular design which can facilitate scale-up. These features are desirable for the decontamination of indoor air in ventilation ducts or for water detoxification. The Monte Carlo method was applied to determine three dimensionless reactor performance parameters: the photon absorption efficiency (ϕ), the uniformity of the distribution of the dimensionless radiation intensity (η) and the overall photonic efficiency (Φ). The emission of photons from the light sources was simulated by the extensive source with superficial emission (ESSE) model. Simulations were performed by varying the catalyst reflectivity albedo, the number and the diameter of lamps, and the dimensions and spacing of the photocatalytic plates. Optimal design for a basic reactor module with one lamp was accomplished for lamp-diameter-to-plate-height ratio (β) of 0.7, while the plate-spacing-to-plate-height ratio (α) was correlated by [αoptimum=0.191β2−0.5597β+0.3854]. A multilamp arrangement leads to a feasible increase in the size and number of the plates and the irradiated photocatalytic surface area. The optimum design was validated by measuring the apparent quantum yield of the oxidation of toluene (7ppmv) in a humidified air stream using immobilized TiO2 (Degussa P25). Experiments performed varying the geometrical parameter α correlated well with the model calculations, with maximum apparent quantum yield for α=0.137. The results are directly transferable to the treatment of water by photocatalysis.

Imaging a full set of optical scattering properties of biological tissue by inverse spectroscopic optical coherence tomography

We here develop a method to measure and image the full optical scattering properties by inverse spectroscopic optical coherence tomography (ISOCT). Tissue is modelled as a medium with continuous refractive index (RI) fluctuation and such a fluctuation is described by the RI correlation functions. Under the first-order Born approximation, the forward model is established for ISOCT. By measuring optical quantities of tissue including the scattering power of the OCT spectrum, the reflection albedo α defined as the ratio of scattering coefficient μ(s), and the backscattering coefficient μ(b), we are able to inversely deduce the RI correlation function and image the full set of optical scattering properties.

Reprocessing of X-rays in the outer accretion disc of the black hole binary XTE J1817−330

We build a simple model of the optical/ultraviolet (UV) emission from irradiation of the outer disc by the inner disc and coronal emission in black hole binaries. We apply this to the broad-band Swift data from the outburst of the black hole binary XTE J1817−330 to confirm previous results that the optical/UV emission in the soft state is consistent with a reprocessing a constant fraction of the bolometric X-ray luminosity. However, this is very surprising as the disc temperature drops by more than a factor of 3 in the soft state, which should produce a marked change in the reprocessing efficiency. The easiest way to match the observed constant reprocessed fraction is for the disc skin to be highly ionized (as suggested 30 yr ago by van Paradijs), so that the bulk of the disc flux is reflected and only the hardest X-rays heat the disc. The constant reprocessed fraction also favours direct illumination of the disc over a scattering origin as the optical depth/solid angle of any scattering material (wind/corona) over the disc should decrease as the source luminosity declines. By contrast, the reprocessed fraction increases very significantly (by a factor of ∼6) as the source enters the hard state. This dramatic change is not evident from X-ray/UV flux correlations as it is masked by bandpass effects. However, it does not necessarily signal a change in emission, for example, the emergence of the jet dominating the optical/UV flux as the reflection albedo must change with the dramatic change in spectral shape.

Mapping surface mineralogy and scattering behavior using backscattered reflectance from a hyperspectral midinfrared airborne CO/sub 2/ laser system (MIRACO/sub 2/LAS)

Airborne, high-spectral resolution, thermal-infrared (TIR) MIRACO/sub 2/LAS reflectance data were evaluated for mapping surface mineralogy and scattering behavior for a variety of semi-arid, geological test sites in Australia. MIRACO/sub 2/LAS is a rapidly tuned, airborne CO/sub 2/ laser system that measures backscattered (bidirectional) reflectance at 100 wavelengths between 9.1 and 11.2 /spl mu/m for 2-m footprints in line profile mode. An operational methodology is described that permits reduction of the raw airborne signal-to-ground reflectance. This ground reflectance has two major properties, namely, wavelength-dependent mineralogical variations and reflection albedo variations related to surface roughness. Comparisons between the airborne MIRACO/sub 2/LAS spectra and laboratory directional hemispherical reflectance (DHR) spectra show the same spectral shapes, though differences in average reflectance (albedo) occur for some types of rocks. The minerals identified using MIRACO/sub 2/LAS include silicates (for example, quartz, microcline, plagiodase, almandine, spessartine, talc, tremolite, and kaolinite) and carbonates (dolomite and magnesite) as well as vegetation (dry and green). Many of the diagnostic spectral features that allow identification of these materials are narrow (<0.2 /spl mu/m), making them difficult to detect with broadband TIR systems, like the airborne TIMS and satelliteborne ASTER. Based on an empirical relationship between the minimum and maximum reflectance established using laboratory DHR spectra, a method is proposed that allows the use of MIRACO/sub 2/LAS data to identify surfaces that are characterized by Lambertian or specular scattering. The MIRACO/sub 2/LAS results show that Lambertian-type scatterers include soils and many types of isotropic rocks.

Computer simulation of enhanced output from bifacial photovoltaic modules

AbstractA bifacial photovoltaic module can collect not only the light falling directly on its front but also light incident on its rear after reflection from natural surroundings, called the albedo reflection, and light scattered from the sky itself. the benefits of such bifacial response are analysed by modifying a standard computer photovoltaic simulation software package (PVFORM version 3.3). Results obtained from computer simulation and field experiments show that, without any special features, there is about a 20% increase in the total annual energy generated by a bifacial panel compared to a monofacial panel. There are also summer peaks caused by the morning and evening light falling directly on the rear side of the panel. This means that the bifacial panel allows extended operation during summer. There is also a slightly smaller reduction in relative output power for the bifacial module on cloudy days.

LIGHT-CURVE MODELING OF THE BINARY STAR AK HERCULIS.

ABSTRACT Light-curve modeling of the W UMa class of binary-star systems is now done by a number of authors. A solution of the photoelectric R and I observations of AK Her by Bookmyer and Kaitchuck (1979) are presented and compared to four different analyses of three different sets of photoelectric B and V observations. The set of parameters solved for in each case varies as do the limits of the numerical values of some of the parameters, most notably the reflection albedo. The results do differ but even though the methods are divergent, the results are fairly consistent.

Applicability of albedo-Sn transport method to analysis of radiation shielding problem.

Albedo-Sn method was developed to predict the angular flux near the coupling boundary in the bootstrap method, using the energy-and-angle dependent double differential albedo boundary condition. In order to verify the applicability of the method to the reactor shielding design, two types of shielding problem have been analyzed. First, the neutron skyshine dose rates measured at the YAYOI reactor in University of Tokyo are predicted within an accuracy of 20%. It is also found that the neutron spectrum in the air-over-ground is much affected by albedo reflection from the ground and is reproduced well by the albedo-Sn method. Second, as for the neutron streaming through a sodium pipe chase-way, the albedo-Sn calculation saves a computer time and gives the results which agree with those by the reference Sn calculation.

Information content of sky intensity and polarization measurements at right angles to the solar direction

This paper presents the results of a Monte Carlo simulation study of the brightness and polarization at right angles to the solar direction both for ground-based observations (looking up) and for satellite-based systems (looking down). Calculations have been made for a solar zenith angle whose cosine was 0.6 and wavelengths ranging from 3500 A to 9500 A. We have succeeded in demonstrating a sensitivity of signatures to total aerosol loading, aerosol particle size distribution and refractive index, and the surface reflectance albedo. For Lambertian type surface reflection the albedo effects enters solely through the intensity sensitivity, and we have found very high correlations between the polarization term signatures for the ground-based and satellite-based systems. Potential applications of these results for local albedo predictions and satellite imaging systems recalibrations are discussed.