Computational Cost and Accuracy in Calculating Three-Dimensional Radiative Transfer: Results for New Implementations of Monte Carlo and SHDOM

2009 ◽  
Vol 66 (10) ◽  
pp. 3131-3146 ◽  
Author(s):  
Robert Pincus ◽  
K. Franklin Evans
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Variance Reduction ◽  
Parallel Implementation ◽  
Monte Carlo Model ◽  
Computational Cost ◽  
Three Dimensional ◽  
Computation Time ◽  
Flux Divergence ◽  
Pixel Intensity

Abstract This paper examines the tradeoffs between computational cost and accuracy for two new state-of-the-art codes for computing three-dimensional radiative transfer: a community Monte Carlo model and a parallel implementation of the Spherical Harmonics Discrete Ordinate Method (SHDOM). Both codes are described and algorithmic choices are elaborated. Two prototype problems are considered: a domain filled with stratocumulus clouds and another containing scattered shallow cumulus, absorbing aerosols, and molecular scatterers. Calculations are performed for a range of resolutions and the relationships between accuracy and computational cost, measured by memory use and time to solution, are compared. Monte Carlo accuracy depends primarily on the number of trajectories used in the integration. Monte Carlo estimates of intensity are computationally expensive and may be subject to large sampling noise from highly peaked phase functions. This noise can be decreased using a range of variance reduction techniques, but these techniques can compromise the excellent agreement between the true error and estimates obtained from unbiased calculations. SHDOM accuracy is controlled by both spatial and angular resolution; different output fields are sensitive to different aspects of this resolution, so the optimum accuracy parameters depend on which quantities are desired as well as on the characteristics of the problem being solved. The accuracy of SHDOM must be assessed through convergence tests and all results from unconverged solutions may be biased. SHDOM is more efficient (i.e., has lower error for a given computational cost) than Monte Carlo when computing pixel-by-pixel upwelling fluxes in the cumulus scene, whereas Monte Carlo is more efficient in computing flux divergence and downwelling flux in the stratocumulus scene, especially at higher accuracies. The two models are comparable for downwelling flux and flux divergence in cumulus and upwelling flux in stratocumulus. SHDOM is substantially more efficient when computing pixel-by-pixel intensity in multiple directions; the models are comparable when computing domain-average intensities. In some cases memory use, rather than computation time, may limit the resolution of SHDOM calculations.

A model setup for simulations of ground-based scattered sunlight measurements

2020 ◽  
Author(s):  
Constanze Wellmann ◽  
Christin Proß ◽  
Katja Bigge ◽  
André Butz
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Monte Carlo Model ◽  
Computational Cost ◽  
Computation Time ◽  
Fast Analysis ◽  
Radiative Transfer Models ◽  
First Results ◽  
Model Setup ◽  
Transfer Models

<pre>Remote sensing is an important measurement technique when probing the atmosphere as it is rather flexible and <br />allows for the measurement of numerous variables. For example, spectrometers are commonly used to quantify the <br />concentrations of trace gases by recording spectra of direct or scattered sunlight. Due to scattering, the light <br />paths between sun and detector can be rather complicated and radiative transfer models are necessary to retrieve <br />the information contained in the spectra. <br />Since these spectrometer measurements have to be made in spectral regions with strong absorption, it is necessary <br />to model many wavelengths to reach a sufficiently accurate representation of the absorption lines and their effects <br />on the light paths. <br />Thus, 1D models are often implemented for a fast analysis of the recorded spectra. However, this approach assumes <br />horizontal homogeneity and local sources cannot be resolved. In contrast, 3D Monte Carlo models are more realistic <br />and are able to represent this inhomogeneity, but they are computationally expensive and are not suitable for <br />operational use.</pre> <pre>We improve an existing Monte Carlo model by implementing efficient algorithms for the simultaneous calculation of <br />several wavelengths to decrease the required computation time. <br />Furthermore, we examine to which scatter order the 3D model provides more detailed results while maintaining a <br />reasonable run time.<br />This finally leads to a coupling of these two types of radiative transfer models via the scatter order into one <br />efficient model which performs realistic simulations at a computational cost comparable to 1D models.<br />So we are able to detect sources along the line of sight of ground-based measurements of scattered sunlight.<br />Here, we present our objective and first results.</pre>

scholarly journals Reduction of radiation biases by incorporating the missing cloud variability by means of downscaling techniques: a study using the 3-D MoCaRT model

2012 ◽  
Vol 5 (9) ◽  
pp. 2261-2276 ◽  
Author(s):  
S. Gimeno García ◽  
T. Trautmann ◽  
V. Venema
Keyword(s):  
Radiative Transfer ◽  
Spatial Resolution ◽  
Heterogeneous Media ◽  
Monte Carlo Model ◽  
Computational Cost ◽  
Three Dimensional ◽  
Accurate Solution ◽  
Stochastic Methods ◽  
Climate Modelling ◽  
One Dimensional

Abstract. Handling complexity to the smallest detail in atmospheric radiative transfer models is unfeasible in practice. On the one hand, the properties of the interacting medium, i.e., the atmosphere and the surface, are only available at a limited spatial resolution. On the other hand, the computational cost of accurate radiation models accounting for three-dimensional heterogeneous media are prohibitive for some applications, especially for climate modelling and operational remote-sensing algorithms. Hence, it is still common practice to use simplified models for atmospheric radiation applications. Three-dimensional radiation models can deal with complex scenarios providing an accurate solution to the radiative transfer. In contrast, one-dimensional models are computationally more efficient, but introduce biases to the radiation results. With the help of stochastic models that consider the multi-fractal nature of clouds, it is possible to scale cloud properties given at a coarse spatial resolution down to a higher resolution. Performing the radiative transfer within the cloud fields at higher spatial resolution noticeably helps to improve the radiation results. We present a new Monte Carlo model, MoCaRT, that computes the radiative transfer in three-dimensional inhomogeneous atmospheres. The MoCaRT model is validated by comparison with the consensus results of the Intercomparison of Three-Dimensional Radiation Codes (I3RC) project. In the framework of this paper, we aim at characterising cloud heterogeneity effects on radiances and broadband fluxes, namely: the errors due to unresolved variability (the so-called plane parallel homogeneous, PPH, bias) and the errors due to the neglect of transversal photon displacements (independent pixel approximation, IPA, bias). First, we study the effect of the missing cloud variability on reflectivities. We will show that the generation of subscale variability by means of stochastic methods greatly reduce or nearly eliminate the reflectivity biases. Secondly, three-dimensional broadband fluxes in the presence of realistic inhomogeneous cloud fields sampled at high spatial resolutions are calculated and compared to their one-dimensional counterparts at coarser resolutions. We found that one-dimensional calculations at coarsely resolved cloudy atmospheres systematically overestimate broadband reflected and absorbed fluxes and underestimate transmitted ones.

A Numerical Model to Study the Effect of Temperature on Electrical Conductivity of Polymer-CNT Nanocomposites

2013 ◽  
Author(s):  
Amirhossein B. Oskouyi ◽  
Uttandraman Sundararaj ◽  
Pierre Mertiny
Keyword(s):  
Electrical Conductivity ◽  
Finite Element ◽  
Monte Carlo ◽  
Electrical Properties ◽  
Monte Carlo Model ◽  
Computational Cost ◽  
Three Dimensional ◽  
Effect Of Temperature ◽  
Tunneling Resistance ◽  
Percolation Network

In this study the effect of the temperature on the electrical conductivity of nanocomposites with carbon nanotube (CNT) fillers was investigated. A three-dimensional continuum Monte Carlo model was developed and employed first to form a CNT percolation network. CNT fillers were randomly generated and dispersed in a cubic representative volume element. Periodic boundary conditions were applied in this model to minimize size effects while decreasing computational cost. CNT fibers that connected electrically to each other through electron hopping were recognized and grouped as clusters. In addition to tunneling resistance, the effect of intrinsic CNT resistivity was considered. A three-dimensional resistor network was subsequently developed to evaluate nanocomposite electrical properties. Modeling employing the finite element method was conducted to evaluate the electrical conductivity of the percolation network. Considering the determining role of tunneling resistance on electrical conductivity of CNT based nanocomposites, as well as results obtained from experimental studies, temperature was expected to play an important role in nanocomposite electrical properties. The effect of temperature on electrical conductivity of CNT nanocomposites was thus investigated through employing the developed Monte Carlo and finite element models. Other aspects, including the electrical behavior of the polymer, tunneling resistivity and the intrinsic resistivity of CNT were considered in this study as well. The comprehensiveness of the developed modeling approach enables an evaluation of results in conjunction with experimental data in future works.

Design and Verification of a New Monochromatic Thermal Emission Component for the I3RC Community Monte Carlo Model

2018 ◽  
Vol 75 (3) ◽  
pp. 885-906 ◽  
Author(s):  
Alexandra L. Jones ◽  
Larry Di Girolamo
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Analytical Solutions ◽  
Thermal Emission ◽  
Monte Carlo Model ◽  
Photon Emission ◽  
Flux Divergence ◽  
Computational Performance ◽  
Computational Implementation ◽  
External Sources

Abstract The Intercomparison of 3D Radiation Codes (I3RC) community Monte Carlo model has been extended to include a source of photon emission from the surface and atmosphere, thereby making it capable of simulating scalar radiative transfer in a 3D scattering, absorbing, and emitting domain with both internal and external sources. The theoretical basis, computational implementation, verification of the internal emission, and computational performance of the resulting model, the “IMC+emission,” is presented. Thorough verification includes fundamental tests of reciprocity and energy conservation, comparison to analytical solutions, and comparison with another 3D model, the Spherical Harmonics Discrete Ordinate Method (SHDOM). All comparisons to fundamental tests and analytical solutions are accurate to within the precision of the simulations—typically better than 0.05%. Comparison cases to SHDOM were typically within a few percent, except for flux divergence near cloud edges, where the effects of grid definition between the two models manifest themselves. Finally, the model is applied to the established I3RC case 4 cumulus cloud field to provide a benchmark result, and computational performance and strong and weak scaling metrics are presented. The outcome is a thoroughly vetted, publicly available, open-source benchmark tool to study 3D radiative transfer from either internal or external sources of radiation at wavelengths for which scattering, emission, and absorption are important.

Monte Carlo modeling of production of three alpha-particles in low energy n +12C interactions

2021 ◽  
Vol 36 (25) ◽  
pp. 2150182
Author(s):  
Khusniddin K. Olimov ◽  
Vladimir V. Lugovoi ◽  
Kosim Olimov ◽  
Maratbek Shodmonov ◽  
Kadyr G. Gulamov ◽  
...  
Keyword(s):  
Experimental Data ◽  
Monte Carlo ◽  
Monte Carlo Model ◽  
Three Dimensional ◽  
Alpha Particles ◽  
Incident Neutron ◽  
Excitation Energies ◽  
Collision Event ◽  
Direct Decay ◽  
Calculation Results

To describe [Formula: see text] interactions with production of three [Formula: see text]-particles at incident neutron kinetic energy of 14 MeV in a nuclear (photo) emulsion, a Monte Carlo model is proposed for four channels of decay of an excited carbon-12 nucleus into three [Formula: see text]-particles. The Monte Carlo calculation results describe well the experimental data on the distribution of the angle between the three-dimensional momenta of all pairs of [Formula: see text]-particles in a collision event, on the distribution of the angle between the projections of the momentum vectors of all pairs of [Formula: see text]-particles in collision event on each of the coordinate planes, on the distribution of the sum of the kinetic energies of all pairs of [Formula: see text]-particles in a collision event, and the distribution of projections of the momenta of [Formula: see text]-particles on the coordinate planes. The best agreement of the Monte Carlo model results with the experimental data is achieved if the direct decay [Formula: see text] and decay through the formation of an intermediate beryllium nucleus [Formula: see text] are generated with equal probabilities, while the excitation energies of 3.04 MeV, 1.04 MeV, and 0.1 MeV for the beryllium nucleus are generated with relative weights of 75%, 15%, and 10%, respectively.

Evaluation of shortwave radiation fluxes in the multi-layer SPARTACUS-Urban scheme using DART

2021 ◽  
Author(s):  
Megan Stretton ◽  
William Morrison ◽  
Robin Hogan ◽  
Sue Grimmond
Keyword(s):  
Radiative Transfer ◽  
Urban Form ◽  
Climate Models ◽  
Weather Prediction ◽  
Computational Cost ◽  
Three Dimensional ◽  
Shortwave Radiation ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Urban Structure

<p>The heterogenous structure of cities impacts radiative exchanges (e.g. albedo and heat storage). Numerical weather prediction (NWP) models often characterise the urban structure with an infinite street canyon – but this does not capture the three-dimensional urban form. SPARTACUS-Urban (SU) - a fast, multi-layer radiative transfer model designed for NWP - is evaluated using the explicit Discrete Anisotropic Radiative Transfer (DART) model for shortwave fluxes across several model domains – from a regular array of cubes to real cities .</p><p>SU agrees with DART (errors < 5.5% for all variables) when the SU assumptions of building distribution are fulfilled (e.g. randomly distribution). For real-world areas with pitched roofs, SU underestimates the albedo (< 10%) and shortwave transmission to the surface (< 15%), and overestimates wall-plus-roof absorption (9-27%), with errors increasing with solar zenith angle. SU should be beneficial to weather and climate models, as it allows more realistic urban form (cf. most schemes) without large increases in computational cost.</p>

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