Radiative Transfer Approach Research Articles

Wave propagation through a dense cluster of cylinders: a radiative transfer model

Clusters of cylinders are a useful way to model the wave propagation through several natural and complex media: crowds of people, forests, arrays of scatterers, or various materials. Depending on the absorption properties of the cylinders, as well as their size- and distance-to-wavelength ratio, different physical mechanisms are at play: scattering, viscous and thermal dissipation, absorption within the material of the cylinders themselves. We consider the low frequency case when the wavelength is larger than both the cylinder diameter and spacing. Most multiple scattering theories require larger than wavelength spacing and are not applicable in the case of dense clusters and at low frequencies. As a first approximation, a porous medium model is used to calculate the speed of sound in the cluster. However, this approach does not readily give access to the coherency of the signal. Recently, a radiative transfer approach was used to model forest acoustics to examine the transformation of the coherent sound field into an incoherent sound field. We use this approach to examine the coherent to incoherent field transition depending on the wavelength to diameter and spacing.

Evaluating Numerical Methods to Investigate Spectral Solar Radiative Transfer in Plant Canopies

AbstractThe disposition of spectral solar irradiance in plant canopies is crucially important to understand processes such as photolysis of molecules amenable to absorbing actinic light. Thus, one objective of this study is to evaluate the most commonly applied radiative transfer approaches to estimate spectral irradiance as a function of plant canopy depth. Eight radiative transfer approaches are ascertained. Another objective is to determine the impacts of the spectral resolution assumed in radiative transfer calculations and model choice on key processes such as canopy absorption and reflection of irradiance. By comparing results from broadband‐only and spectrally‐resolved canopy radiative transfer, we aim to quantitatively determine the uncertainties associated with failing to resolve the sunlight spectra. We determine the optimal spectral resolution required to estimate canopy radiative transfer results such as air‐chemistry‐specific quantities related to photolysis of a select group of molecules. In addition, we evaluate techniques for binning leaf and soil optical properties. Results showed that high spectral resolution is ideally desired to compute photolysis of molecules such as ozone, nitrogen dioxide, nitrate radical, nitrous acid, and formaldehyde. For in‐canopy photolysis of molecules, a waveband resolution of at least 10 nm is sufficient to obtain accurate estimates for most photochemical reactions. Positive reaction‐dependent uncertainties in canopy‐mean relative photolysis values for individual molecules can be as high as 30% compared to estimates derived with broad‐band solar irradiance.

Separation of source, attenuation and site parameters of 2 moderate earthquakes in France: an elastic radiative transfer approach

Summary An accurate magnitude estimation is necessary to properly evaluate seismic hazard, especially in low to moderate seismicity areas such as Metropolitan France. However, magnitudes of small earthquakes are subject to large uncertainties caused by major high-frequency propagation effects which are generally not properly considered. To address this issue, we developed a method to separate source, attenuation and site parameters from the elastic radiative transfer modeling of the full energy envelopes of seismograms. The key feature of our approach is the treatment of attenuation -both scattering and absorption- in a simple but realistic velocity model of the Earth’s lithosphere, including a velocity discontinuity at the Moho. To reach this goal, we developed a 2-step inversion procedure, allowing first to extract attenuation parameters for each source-station path from the whole observed energy envelope using the Levenberg-Marquardt and grid-search algorithms, then to determine site amplification and the source displacement spectrum from which the moment magnitude Mw is extracted. In the first step, we use the forward modeling procedure of Heller et al. (2022) in order to simulate energy envelopes by taking into account the full treatment of wave polarization, the focal mechanism of the source and the scattering anisotropy. The inversion procedure is then applied to the 2019 ML 5.2 Le Teil and 2014 ML 4.5 Lourdes earthquakes which both occurred in southern France. Data from 6 stations are selected for each event. The inversion results confirm a significant variability in the attenuation parameters (scattering and absorption) at regional scale and a strong frequency dependence. Scattering appears to be stronger towards the French Alps and Western Pyrenees. Absorption is stronger as frequency increases. Although not very resolvable, the mechanism of scattering appears to be forward or very forward. By inverting the source spectrum, we determine moment magnitudes Mw of 5.02 ± 0.17 for the Le Teil earthquake and 4.17 ± 0.15 for the Lourdes earthquake.

Numerical investigations and design optimization of cryogenic plate-fin heat exchanger in Electric Arc Furnace using radiative heat transfer model

The most crucial element affecting cryogenic systems’ energy efficiency is heat exchangers. In this article, a model for cryogenic plate-fin heat exchanger (PFHE) under thermal-hydraulic performance with various blends is proposed. To reduce five objective functions total heat transfer rate, total weight, total mass flow rate, number of entropy generating units, and whole annual cost the study carried out the PFHE’s optimal design. This study innovatively focuses on optimizing PFHE design for cryogenic conditions using Opposition Learning with the Beetle Swarm algorithm. The proposed geometry addresses non-uniform temperature distribution, emphasizing thermal-hydraulic properties in various blends. Additionally, a second-order semi-discretization radiative heat transfer approach enhances boiler simulation accuracy. A multi-objective optimization of Opposition Learning with Beetle Swarm (MO-OBBS) optimization approach was suggested in the article for the design of PFHE. Despite the significant potential for renewable energy the low-temperature waste heat treatment process is rarely examined from a sustainability perspective. Consequently, the study proposed a second-order semi-discretization radiative heat transfer method to simulate a furnace using a water heat recovery process. The cooling panel’s numerical analysis was conducted using computed temperature fields. The performance of the various algorithms is compared using the Freidman rank-sum test to determine the statistical significance of the findings obtained. In logarithmic coordinates, the proposed method’s faster convergence is compared to GQB-PSO, SLTLBO, Jaya, CKKO, and OLE-SCA algorithms. The proposed method exhibits a maximum average increase of 115.39% for PFHE design. When the numerical simulation results are compared to measurements of output water temperature, the accuracy is highly improved.

A new model-perspective on the threshold radius of lasing of a spherical random medium

This work extends the understanding of photon behavior in spherical diffusive gain-media that may inform random lasing. We assess the time-dependent photon fluence rate on the boundary of a spherical homogeneous diffusive gain-medium, when resulted from hypothetical synchronous impulsive photon generations distributed uniformly within. The combined temporal photon fluence rate at a boundary position is modeled by means of a geometric-distribution-probability (GDP) weighting of the pulse-spread-function, according to the line-of-sight distance between the boundary point and a model-source. The approach acts to transform between a time-dependent size issue and a size-dependent time issue. The integral manifests a bi-phasic pattern having a global minimum. The time of the onset of the phase-change multiplying with the speed of light equates to a line-of-sight length, which decreases monotonically as the size of the sphere increases. The line-of-sight length equaling the radius of the spherical medium is interpreted as the threshold-size of lasing. This threshold size associated with a spherical medium assessed over a gain/scattering ratio spanning seven orders of magnitude of [ 10 − 3 , 10 4 ] is in good agreement with the values given by the Letoknov's eigen-mode-decomposition in the diffusive regime and by the radiative transfer approach over the semi-ballistic regime.

The 2 stream-exact single scattering (2S-ESS) radiative transfer model

The plane-parallel two-stream approximation is a popular radiative transfer approach for the calculation of fluxes and heating rates. However, it is typically not accurate enough for remote sensing applications involving the analysis of hyperspectral radiances. We present the 2 stream-exact single scattering (2S-ESS) radiative transfer model, which performs an exact calculation of single scattering in a spherically curved medium using an accurate treatment of the phase function and curved ray-tracing of the solar and line-of-sight paths, while approximating multiple scattering with the plane-parallel two-stream approach.The 2S-ESS model has three important features. First, it can be deployed for calculations in vertically inhomogeneous atmospheres. Second, the sphericity capability makes it applicable to large solar and/or viewing zenith angle scenarios such as those encountered close to sunrise or sunset. Third, it is fully linearized: in addition to generating radiances, the model can also compute Jacobians analytically with respect to any atmospheric or surface property (e.g., trace gases, aerosols and surface reflectance). These features of the model are especially useful for remote sensing retrieval applications.We examine the accuracy of this model for homogeneous slab and inhomogeneous multi-layer scenarios. The results show that this methodology introduces less than a few percent error in most situations, with the exception of heavy aerosol or cloud loading events, while providing three orders of magnitude improvement in computational efficiency. The code is publicly available along with documentation and test cases to assist the user.

Polarized discrete ordinate adding approximation for infrared and microwave radiative transfer

A POLarized Discrete ordinate aDding Approximation (POLDDA) is proposed to solve the vector thermal radiative transfer equation in a vertically inhomogeneous plane-parallel atmosphere. The discrete ordinates method is employed to find the single-layer solution for vector thermal radiative transfer; this is an extension of the approach for scalar radiative transfer, with the I- and Q-components being dealt with in a parallel way by using a doubled dimension in the discrete ordinate space. Chandrasekhar’s invariance principle is used to drive the adding process for the connection of multiple layers. This adding process has no restriction on the layer optical properties. The accuracy and efficiency of POLDDA are evaluated under different atmospheric conditions for different number of computational quadrature angles (streams). It is shown that the relative differences between POLDDA (using 32 or 16 streams) and the benchmark calculations (PolRadtran/RT3 with 32 streams, a typical model based on the adding-doubling method) are negligible for both I- and Q-components. When 8 streams are used, the accuracy of POLDDA slightly decreases, but still higher than that of 8-stream RT3. The computational efficiency of POLDDA is much higher than RT3, especially for large optical depths and when a large number of streams (≥ 16) are used. Unlike RT3, the computational time of POLDDA is always the same regardless of the optical depth.

Thermal emission in the successive orders of scattering (SOS) radiative transfer approach

The Successive Orders of Scattering (SOS) approach [1] is one of the well known methods for solving the Radiative Transfer (RT) problem. Its efficiency in terms of speed and accuracy of computation was already demonstrated for scattering and absorbing atmospheres in Solar spectrum. Although there are no principle limitations to account for the emission processes, the application of the SOS method for atmospheres with thermal emission is not widely used yet. In this paper we present a SOS-based RT approach accounting for the full source function, which enables its application from the UV (UltraViolet) to the TIR (Thermal InfraRed) parts of the electromagnetic spectrum. The atmospheric vertical discretization in this extended SOS scheme is a key point in order to properly retain the scattering and emission processes. An analysis of different methodologies to perform this vertical discretization is presented. The numerical implementation has been included in GRASP (Generalized retrieval of Atmosphere and Surface Properties) RT code [2]. In comparison with the widely used code DISORT (DIScrete-ORdinatemethod for Radiative Transfer) [3], the developed SOS scheme achieves a mean accuracy of radiance calculation of −0.005 K (−0.003%) expressed in terms of brightness temperature. Under the same configuration and vertically inhomogeneous atmospheric conditions, GRASP SOS RT is approximately eight times faster than DISORT. The analysis of the sensitivity of GRASP TIR SOS scheme to the number of layers and the effect of polarization are also investigated in the paper.

A new analytical scattering phase function for interstellar dust

Context. Properly modelling scattering by interstellar dust grains requires a good characterisation of the scattering phase function. The Henyey-Greenstein phase function has become the standard for describing anisotropic scattering by dust grains, but it is a poor representation of the real scattering phase function outside the optical range. Aims. We investigate alternatives for the Henyey-Greenstein phase function that would allow the scattering properties of dust grains to be described. Our goal is to find a balance between realism and complexity: the scattering phase function should be flexible enough to provide an accurate fit to the scattering properties of dust grains over a wide wavelength range, and it should be simple enough to be easy to handle, especially in the context of radiative transfer calculations. Methods. We fit various analytical phase functions to the scattering phase function corresponding to the BARE-GR-S model, one of the most popular and commonly adopted models for interstellar dust. We weigh the accuracy of the fit against the number of free parameters in the analytical phase functions. Results. We confirm that the Henyey-Greenstein phase functions poorly describe scattering by dust grains, particularly at ultraviolet (UV) wavelengths, with relative differences of up to 50%. The Draine phase function alleviates this problem at near-infrared (NIR) wavelengths, but not in the UV. The two-term Reynolds-McCormick phase function, recently advocated in the context of light scattering in nanoscale materials and aquatic media, describes the BARE-GR-S data very well, but its five free parameters are degenerate. We propose a simpler phase function, the two-term ultraspherical-2 (TTU2) phase function, that also provides an excellent fit to the BARE-GR-S phase function over the entire UV-NIR wavelength range. This new phase function is characterised by three free parameters with a simple physical interpretation. We demonstrate that the TTU2 phase function is easily integrated in both the spherical harmonics and the Monte Carlo radiative transfer approaches, without a significant overhead or increased complexity. Conclusions. The new TTU2 phase function provides an ideal balance between being simple enough to be easily adopted and realistic enough to accurately describe scattering by dust grains. We advocate its application in astrophysical applications, in particular in dust radiative transfer calculations.

Non-equilibrium radiation modeling in a gas kinetic simulation code

Radiation modeling is implemented in the highly parallel gas kinetic, open-source plasma simulation suite PICLas. A photon Monte Carlo approach for three-dimensional radiative energy transfer is developed. Since these kind of solvers have the disadvantage of high computational costs and statistical fluctuations, these points are addressed by specific adaptations to the solver. An approach to simulate axisymmetric problems is presented as well as noise reducing methods. Results are compared to a semi-infinite black body radiating cylinder, where an analytical solution is known, and a good agreement for both, three-dimensional and axisymmetric simulations is demonstrated. It is also shown that the implemented noise reducing methods can reduce statistical fluctuations. To calculate radiative properties in terms of emission and absorption coefficients, a line-by-line method is implemented and compared with good agreement to results obtained with other well-established radiation codes. The FIRE II reentry is used as a test case for a simulation combined with DSMC. Unidirectional coupling with the developed radiation modules shows good results compared to measured values as well as in performance scaling.

Modeling solar-induced fluorescence of forest with heterogeneous distribution of damaged foliage by extending the stochastic radiative transfer theory

Solar Induced chlorophyll Fluorescence (SIF) has been used as a novel proxy of photosynthetic activity, which carries information about plant physiological state from the remote sensing observations. It is of great interest and potential to use SIF to detect forest stresses, but the approach requires accurate modeling of the SIF emission within stressed forests. However, the existing radiative transfer approaches of SIF generally ignore the within-crown heterogeneity caused by pests. To account for within-canopy scattering with both high accuracy and efficiency, FluorESRT was proposed as a new model for simulating the SIF of forests with heterogeneous distribution of damaged foliage, which was the synergy of the SIF radiative transfer and the Stochastic Radiative Transfer (SRT) model for forest with vertical distribution of damage. The performance of FluorESRT for both homogeneous and heterogeneous cases were well validated not only by the one-dimensional (1D) model SCOPE but also by the three-dimensional (3D) model DART. As an analytically simple approach, FluorESRT can evaluate the sensitivity of canopy SIF and apparent reflectance to the level of pest damage. The impact of structural properties of damaged foliage on canopy fluorescence, as well as the response of hyperspectral signals on the pest damage was analyzed. According to our study, hyperspectral vegetation indices with the consideration of SIF showed higher sensitivity to pest damage in the early stage when the response of broad band vegetation indices was hardly detectable. The results indicated that the potential of FluorESRT to simulate SIF and hyperspectral apparent reflectance should play a critical role in early monitoring of pest damage.

Performance Assessment of Global Horizontal Irradiance Models in All-Sky Conditions

Solar irradiance models contribute to mitigating the lack of measurement data at a ground station. Conventionally, the models relied on physical calculations or empirical correlations. Recently, machine learning as a sophisticated statistical method has gained popularity due to its accuracy and potential. While some studies compared machine learning models with other models, a study has not yet been performed that compares them side-by-side to assess their performance using the same datasets in different locations. Therefore, this study aims to evaluate the accuracy of three representative models for estimating solar irradiance using atmospheric variables measurement and cloud amount derived from satellite images as the input parameters. Based on its applicability and performance, this study selected the fast all-sky radiation model for solar applications (FARMS) derived from the radiative transfer approach, the Hammer model that simplified atmospheric correlation, and the long short-term memory (LSTM) model specialized in sequential datasets. Global horizontal irradiance (GHI) data were modeled for five distinct locations in South Korea and compared with hourly measurement data of two years to yield the error metrics. When identical input parameters were used, LSTM outperformed the FARMS and the Hammer model in terms of relative root mean square difference (rRMSD) and relative mean bias difference (rMBD). Training an LSTM model using the input parameters of FARMS, such as ozone, nitrogen, and precipitable water, yielded more accurate results than using the Hammer model. The result shows unbiased and accurate estimation with an rRMSD and rMBD of 23.72% and 0.14%, respectively. Conversely, the FARMS has a faster processing speed and does not require significant data to make a fair estimation.

Passive microwave algorithms for refractive index of Arctic sea ice: a comparison of two approaches and interpretations

ABSTRACT The refractive index of sea ice can be estimated using the Debye relaxation model. However, the practical use of this model is difficult because it requires a large amount of information as inputs. To resolve this issue, two different approaches have been developed to retrieve the Arctic basin-scale refractive index from satellite passive microwave measurements using the bulk radiative transfer concept. One is the simplified three-layer sea ice radiative transfer (3SRT) approach and the other is the Brewster’s angle approximation (BAA) approach. Although these methods are different, both find polarized emissivities for the microwave emitting layer of sea ice to estimate the refractive index using a relationship between polarized emissivities and the refractive index. A typographical erroneous version of the equation for this relationship has been used in numerous studies without noting the errors. This study provides the correct equations for the relationship. The refractive index obtained using the 3SRT method is within a reasonable range of 1.2–1.8. However, the refractive index obtained using the BAA approach shows too high values ranging from 1.2 to 3.2. The sensitivity of the approaches to variation in the emissivity is analysed. The BAA method is sensitive to the surface emissivity because of the assumptions considered. The refractive index of sea ice obtained from the 3SRT approach is compared with that obtained from the Debye relaxation model. The results show that a plausible refractive index over Arctic sea ice can be estimated from satellite passive microwave measurements using the 3SRT method.

Influence of atmospheric adjacency effect on top-of-atmosphere radiances and its correction in the retrieval of Lambertian surface reflectivity based on three-dimensional radiative transfer

In satellite-based and airborne imagery, the observed radiances reflected by a certain pixel at the surface are additionally influenced by reflections from the neighboring surface pixels and multiple scatterings due to atmospheric components (mainly cloud and aerosol particles) into the observational solid angle of the imaging camera. This phenomenon is commonly referred to as the atmospheric adjacency effect. This three-dimensional (3D) radiative transfer effect is caused by spatial inhomogeneities of the surface reflectivity and the atmospheric properties. Based on the recently published 3D radiative transfer code LEIPSIC (Light Estimator Including Polarization, Surface Inhomogeneities, and Clouds), a new atmospheric correction (AC) algorithm is proposed to consider for the atmospheric adjacency effect when estimating the surface reflectivity from satellite or airborne imagery. The effectiveness of the new AC algorithm is quantified and compared to the results based on the independent pixel approximation (IPA) radiative transfer approach. It is shown that the image blurring caused by the atmospheric adjacency effect and the error of reflectivity retrievals are reduced by 80% using the new AC algorithm. Furthermore, the simulations demonstrate that the vertical profile of the atmospheric properties is crucial in determining the quality of the AC.

Temperature non-uniformity in the radiative cooler and its effect on performance under various humidity conditions

Sub-ambient diurnal radiative cooling is an effective, environment-friendly and energy-saving passive cooling approach as it cools a surface without anthropogenic energy input. The cooling power of a radiative cooler is strongly influenced by the meteorological conditions, in particular humidity, on which quite a few investigations have been conducted so far. However, the cooling power evaluation of a radiative cooler usually considers the radiative cooler to be isothermal, which ignores the interior temperature difference resulted from the low thermal conductivity of the prevalent radiative materials, leading to an overestimation of the cooling power. Therefore, this work focuses on the theoretical evaluation of the radiative cooling power along with the interior temperature distribution under varying humidity conditions through incorporating coupled heat and radiation transfer approach. The results show that higher relative humidity leads to less cooling power and minor interior temperature difference in the radiative cooler. In addition, the position of the lowest temperature inside the radiative cooler, which is usually taken at the bottom of the radiative cooler, gradually approaches the surface facing outer space with the increase in humidity during the diurnal time. Our work provides a unique viewpoint for predicting the cooling power by taking interior temperature non-uniformity resulted from the low thermal conductivity into account, which elaborates a vivid picture of the evolution of radiative cooling power as well as the internal temperature distribution with the variation of humidity. Such an approach is beneficial for the further design, efficiency enhancement and on-site deployment of radiative coolers.

Influence of Thermodynamic State Changes on Surface Cloud Radiative Forcing in the Arctic: A Comparison of Two Approaches Using Data From AFLUX and SHEBA

AbstractThe cloud radiative forcing (CRF) quantifies the warming or cooling effects of clouds. To derive the CRF, reference values of net (downward minus upward) irradiances in cloud‐free conditions are required. There are two groups of techniques to estimate these reference values; one is based on radiative transfer modeling, and a second group uses measurements in cloud‐free situations. To compare both approaches, we first look at a case study from the airborne measurements of radiative and turbulent FLUXes of energy and momentum in the Arctic boundary layer (AFLUX) campaign, where a moving cloud field with a sharp edge separating a cloudy boundary layer from an adjacent evolving cloud‐free area was probed. These data enabled the quantification of the impact of changing atmospheric and surface properties relevant for the reference net irradiances in cloud‐free conditions. The systematically higher surface albedo below clouds compared to cloud‐free conditions, results in a 11 W·m−2 smaller shortwave cooling effect by clouds estimated from the radiative transfer approach compared to the measurement‐based one. Due to the transition of thermodynamic parameters between the cloudy and cloud‐free atmospheric states, a 20 W·m−2 stronger warming effect is estimated by the radiative transfer approach. In a second step, radiative transfer simulations based on radiosoundings from the Surface Heat Budget of the Arctic Ocean campaign are used to quantify the impact of the vertical profiles of thermodynamic properties on the CRF. The largest difference between the longwave CRF estimated by the two methods is found in autumn with up to 25 W·m−2.

On the engineering of a laboratory LED‐based photocatalytic reactor for radiative and kinetic studies

AbstractThis contribution aims at developing engineering approaches to characterize radiative transfer and kinetics of a catalyst to be activated by electromagnetic radiation, one of the main bottlenecks when evaluating materials in heterogeneous photocatalytic processes. A specialized LED‐based photoreactor is engineered to obtain reliable information on the aforementioned mechanisms. The radiative transfer approach serves as a criterion to elucidate the capability of a catalyst to be activated or not by visible light or UV‐A light. When the catalyst favours the absorption of photons rather than their scattering or transmission, the experimental methodology allows the determination of intrinsic optical information being independent of fluid dynamics, and catalyst concentration. Radiative characterization, along with a mass transfer analysis, guides the proposal of the operational design of the photoreactor to carry out intrinsic kinetic studies. Thus, the operation of the photoreactor under pseudo‐isoactinic and differential reaction conditions leads to the determination of intrinsic initial reaction rates, enabling the understanding of the complex interaction among the optical properties of the catalyst, the reaction rate for the production of hydroxyl radicals (•OH), and the oxidation of a recalcitrant organic pollutant. The procedures assessed are worthy of being used for evaluating other materials, activated at different wavelength ranges or designed for different photocatalytic applications, paving the way for the scale‐up of the reactor, another of the main challenges in photocatalysis.

Extending the stochastic radiative transfer theory to simulate BRF over forests with heterogeneous distribution of damaged foliage inside of tree crowns

Within-crown heterogeneity exists in multiple vegetation scenes including forest stands with heterogeneous distribution of damaged foliage. The existing radiative transfer approaches implement the within-crown heterogeneity either using complicated three-dimensional (3D) scenes with excessive amounts of parameters, or simplifying the scenes to homogeneous cases by averaging canopy optical properties. In order to ascertain the optical response to within-crown heterogeneity both efficiently and accurately, we proposed a method for simulating bi-directional reflectance factor (BRF) of forests infected by pests based on the stochastic radiative transfer (SRT) theory. Each damaged tree crown was classified into one of the three types: top-only damage, bottom-only damage and random damage. The statistical properties of such canopy structures were described with extended definitions of the stochastic moments of the SRT model, including the probabilities of finding different foliage classes and the conditional pair-correlation functions between healthy and damaged foliage. Field measurements and remote sensing data from unmanned aerial vehicle (UAV) over infected Yunnan Pine (Pinus yunnanensis) forests, and simulations of two 3D models were utilized to evaluate the performance. Results showed that the extended SRT agreed well with 3D models and field measurements, which means it has the capability to model BRF over forests with heterogeneous foliage within crowns based on one-dimensional (1D) theory. The extended SRT provides a framework to analyze the sensitivity of canopy reflectance to the distribution of damaged foliage with the variation of other key scene factors. For the three types of damaged tree crowns, the thresholds of detectable optical changes were quite different, in which 20% for top-only damage, 80% for bottom-only damage and 50% for random damage. The uncertainties caused by other scene factors were also considered. The extended SRT is promising for crown vertical profile specification, forest damage quantitative inversion, and other applications with coupling models.

Illuminating the dark side of the asteroid population: Visible near-infrared (0.7–2.45 μm) surface mineralogy modeling of D-type asteroids using Shkuratov theory

D-type asteroids are a prime example of the many dark, low-albedo asteroids which do not reflect sufficient light to reveal detectable mineral absorptions. While D-type asteroids are relatively rare in the inner solar system and the main asteroid belt, they are dominant among the Jovian Trojans. In this study, we have applied Shkuratov radiative transfer modeling to laboratory spectra of meteorites for which mineral abundances have been measured using X-ray diffraction (XRD) and Rietveld refinement. The general agreement of radiative transfer and XRD estimates of mineral abundances demonstrates the applicability of the radiative transfer approach to featureless, low-albedo spectra. Shkuratov modeling was then applied to new spectral observations of D-type asteroids, along with numerous previously published spectra. The surface mineral abundances of 81 D-type objects, including NASA's Lucy Mission target (21900) Orus, were modeled using assemblages that are plausible based on meteorite analogues. Modeling results reveal D-types are composed of: low-iron olivine; magnesium saponite-dominant phyllosilicates; opaques such as pyrrhotite and tholin; as well as traces of water-ice and other constituents. Subtle compositional differences in model mineralogies exist between Trojan and non-Trojan D-types as well as between L4 and L5 Trojans suggesting differing formational as well as evolutional conditions have affected these bodies.

Spectral and seasonal variations of aerosol radiative forcing with special reference to Kanpur, Indo-Gangetic Basin

Objective: To find the influence of aerosols on the sun rays arriving at the surface and to measure aerosol radiative forcing over Kanpur, Indo-gangetic basin. The study was performed during period 2001-2015. Methodology: The present work is credited to the availability of data through the network relying on the ground based optical observations obtained with the help of ground based instrument called Cimel sun photometer using AERONET (Aerosol Robotic Network) radiative transfer model with particular focus on Indo-Gangetic plain over Kanpur. The aerosol radiative forcing at the surface, atmosphere and top of atmosphere has been computed with the help of radiative transfer approach depending on AERONET aerosol retrievals. Findings: Our study investigated the seasonal and spectral variations of ARF along with aerosol radiative forcing with special reference to Kanpur region (IGP) by using AERONET data. The monthly average (±σ) ARF during the entire observational period (2001-2015), at three levels i.e., surface (ARFSFC), atmosphere (ARFATM) and the atmospheric top (ARFTOA) are recorded as – 89.6±18.6 Wm–2, +64.4±16.5 Wm–2 and –25.2±6.8 Wm–2 respectively. From the ARF measurements, it is found that there is a large reduction in surface arriving solar rays due to presence of absorbing and scattering types of aerosols. Novelty: Since this study provides an overview of the present state of prevailing aerosols and their climatic effects. So, findings may be used to create an aerosol climate map for the region under study. Keywords: Aerosol robotic network; aerosol radiative forcing; global atmospheric model; sun photometer