Accurate Ray-Tracing Modeling of Radiation From Leaky-Wave Antennas

A novel electronically scanned periodic microstrip leaky-wave (LW) antenna based on the concept of composite right/left-handed (CRLH) metamaterials is presented. This antenna includes varactors modulating the capacitive loading of the unit cell and therefore the propagation constant of the structure, which results in voltage scanning of the radiated beam. An accurate circuit model is proposed. The antenna is demonstrated experimentally to exhibit continuous scanning in the dominant mode from backward to forward angles. The scanning range is from -10/spl deg/ at 35 V to +7.5/spl deg/ at 0 V, and broadside occurs at 9 V, at the fixed frequency of 3.23 GHz.

Accurate two-dimensional mathematical model of the scattering of the natural electric-type guided modes of a slab dielectric waveguide from the finite number of rectangular grooves cut in the perfectly electric conducting (PEC) screen is built. A narrow beam with sidelobe level 2OdB is optimized with the aid of genetic algorithm. Application to leaky-wave antennas is discussed.

The image formation in coded aperture spectral imagers is key information for processing the acquired compress data, and the optical system design and calibration of these instruments require great care. We propose an analytical model for CASSI systems that builds upon ray-tracing equations of each optical component. The model takes into account optical distortions, sampling effects, and optical misalignments, and allows accurate modeling and fast calibration. Numerical comparisons with a simpler model usually exploited in the literature are provided, and an experimental validation is presented.

The development of factory noise prediction models over the past thirty years has parallelled the development of computer technology. There are currently two main approaches to this problem both of which have been extensively investigated, they are the image-source method and the ray-tracing technique. Presented are brief details of the background to the specific problems of factory noise prediction together with the various approaches used to solve the problem. An outline of how the two types of mathematical models work, together with details of their representational development is presented. A comparison of the current potential of each type of model, enabling an insight into when and where each type of model may be effectively used, is given. Three independent studies comparing various prediction models were considered. All three reviews drew the conclusion that the Ondet and Barbry, and the Lindqvist models were the most accurate ray-tracing and image-source models, respectively. Finally, a review of barrier prediction models is presented.

The accuracy of radiation models is a critical issue in climate studies. However, calculations from different radiation models used in climate calculations disagree with one another, and with more detailed models, at levels significant to many climate problems. With several new advances in the field of radiation modeling, it is possible to develop more accurate band models and validate them against radiation observations of known high accuracy. In this paper, a new accurate narrowband longwave radiative transfer model for clear-sky conditions is developed. In the first part of this study, only water vapor effects are included, and the model results are tested against line-by-line radiative transfer model (LBLRTM) calculations. In the model development, it is first shown that traditional techniques for estimating Malkmus statistical model parameters from the line compilation and line-by-line models cannot be trusted to give accurate transmittance function. A new technique is then described that ca...

A numerical simulation of a turbulent non-premixed flame as a two-dimensional problem is carried out to assess the performance of three thermal radiation models, namely, discrete transfer radiation model (DTRM), P-1 radiation model, and discrete ordinates method (DOM). A finite volume staggered grid approach is employed to solve the governing equations. The SIMPLEC algorithm is used to handle the velocity and pressure coupling. The eddy dissipation/finite rate model is employed to predict the heat release and the realizable κ − ε model is applied to simulate the flow behavior. Computational results with and without thermal radiation effects are compared with the available experimental data and the three radiation models are evaluated in terms of the computational efficiency and prediction accuracy. With the consideration of thermal radiation using all the presented models, the predicted radial temperatures of flame at different locations along the combustor are noticeably closer to the existing experimental data. The use of DTRM involves a relatively high computational cost from the time consumption viewpoint. The P-1 radiation model overpredicts the wall heat flux strongly. However, the DOM is a relatively useful and accurate model with acceptable time consumption.

The lower boundary condition in the atmosphere is provided by a land surface process model. One of the directions of research of the land surface model is to perfect land surface model in existence. Since the accurate estimation of the albedo is required in climate modeling and there are some shortages in either the accuracy or the application area for radiative transfer scheme within a canopy, it is necessary to develop an accurate and simple four-stream radiation transfer model within a canopy based on the second vegetation radiative transfer model. The four-stream model can simulate the process of short-wave solar radiative transfer within a canopy. The four-stream model utilizes the four-stream approximation method in the atmosphere to provide analytical solutions to the basic equation of radiative transfer within a canopy. The four-stream solar radiative transfer model within a canopy in the land surface process model is based on the two-stream short-wave radiative transfer model. The two-stream model developed by Dickinson is computational efficiency and can gain accurate analytical solution. Sellers ever calculate the canopy hemisphere albedo in visible band and near infrared band by use of the two-stream model and can gain analytical solution. Many land surface models still use the two-stream model. But the two-stream model is not very accurate, thus it is necessary to develop more accurate four-stream radiative model. The radiative transfer theory within a canopy is based on the radiative transfer theory in the atmosphere. Each parameter in the basic canopy equation canopy accounts for the special geometry and optical character of the leaf or canopy. The upward or downward radiative fluxes are related to the diffuse phase function, G -function, leaf reflectivity and leaf transmission, leaf area index, and the solar angle of incident beam direction. The four-stream model and the two-stream model can simulate the reflectance, transmittance and absorption of the canopy. The newly developed the four-stream model can reduce the calculate difference of land surface radiative in theory. To compare and determine differences between the results predicted by the two models, several experiments were carried out to examine the effects on the canopy albedo by varying the leaf area index, leave angle distribution and the optical properties of the leaf and ground surface under the canopy. To better assess the simulation performance of the new four-steam model in the application for a land surface model, we needed to determine the parameters for the four-steam scheme and the second-stream scheme to utilize in an off-line test. These parameters also included calculating the reflectance, absorbance and transmission at different sun angles and different leaf area indexes for the 16 kinds of vegetation canopy. The offline test results showed that the sun angle had a significant impact on the solar radiative transfer process within vegetation and on the simulations of two schemes for reflectance and transmittance and absorption varies with different vegetation types. The offline test results show that the sun angle has significantly impact on the solar radiative transfer process within vegetation, and the simulations of two schemes for reflectance and transmittance and absorption varies with different vegetation types. To evaluate the simulations of the four-stream model for solar radiative flux reflected by the land surface in the land surface model, the four-stream model and the two-stream models were coupled into a land surface process model. These tests indicated that the simulation of the land surface process model coupled to the four-stream scheme outperformed two-stream scheme radiative transfer models regarding the global surface albedo, leaf area index and net primary productivity.

An accurate model for propagation of infrared energy within the marine atmospheric surface layer remains an elusive goal. Within the first tens of meters of elevation above the sea surface there are substantial vertical gradients of mass and temperature. This has a strong effect on the prediction of extinction of the infrared signal. There exist models to enable the computation of the effects generated by these factors, but often these models contribute only extinction factors. The refractive propagation factor is proposed as a critical component of an accurate transmission model within the marine surface layer. The propagation factor is a multiplicative quantity that is derived entirely from the local refractive field and the geometry of the entire transmission system. A ray-trace model is used to compute the refractive magnification or minification. The ray-trace model also elucidates the importance of mirage images to account for all energy received at the sensor. I will present a comparison of the model with field data that contain episodes of anomalously large signal intensities. The core thesis of this paper is that the necessary final component in a complete model for near-sea-surface infrared transmission is the propagation factor induced by refractive effects.

Following the finding by the InterComparison of Radiation Codes used in Climate Models (ICRCCM) of large differences among fluxes predicted by sophisticated radiation models that could not be sorted out because of the lack of a set of accurate atmospheric spectral radiation data measured simultaneously with the important radiative properties of the atmosphere, our team of scientists proposed to remedy the situation by carrying out a comprehensive program of measurement and analysis called SPECTRE (Spectral Radiance Experiment). SPECTRE will establish an absolute standard against which to compare models, and will aim to remove the hidden variables'' (unknown humidities, aerosols, etc.) which radiation modelers have invoked to excuse disagreements with observation. The data to be collected during SPECTRE will form the test bed for the second phase of ICRCCM, namely verification and calibration of radiation codes used to climate models. This should lead to more accurate radiation models for use in parameterizing climate models, which in turn play a key role in the prediction of trace-gas greenhouse effects. Overall, the project is proceeding much as had been anticipated in the original proposal. The most significant accomplishments to date include the completion of the analysis of the original ICRCCM calculations, the completionmore » of the initial sensitivity analysis of the radiation calculations for the effects of uncertainties in the measurement of water vapor and temperature and the acquisition and testing of the inexpensive spectrometers for use in the field experiment. The sensitivity analysis and the spectrometer tests given us much more confidence that the field experiment will yield the quality of data necessary to make a significant tests of and improvements to radiative transfer models used in climate studies.« less

ABSTRACTIn this study, a radiation code based on the method of lines solution of the discrete ordinates method for the prediction of radiative heat transfer in nongray gaseous media is developed by incorporation of two different spectral gas radiative property models, banded spectral line-based weighted sum of gray gases (banded SLW) and gray wide band (GWB) approximation in the presence of nongray absorbing–emitting–scattering particles. The aim is to introduce an accurate and CPU efficient spectral gas radiation model, which is compatible with spectral fuel/ash particle property models. Input data required for the radiation code and its validation are provided from two combustion tests previously performed in a 300 kWt atmospheric bubbling fluidized bed combustor test rig burning low calorific value Turkish lignite with high volatile matter/fixed carbon (VM/FC) ratio in its own ash. The agreement between wall heat fluxes and source term predictions obtained by global and banded SLW models reveal that global SLW model can be converted to an accurate wide band gas model (banded SLW) which can directly be coupled with spectral particle radiation. Furthermore, assessment of GWB approximation by benchmarking its predictions against banded SLW model shows that GWB gives reasonable agreement with a higher CPU efficiency when the particle absorption coefficient is at least in the same order of magnitude with the gas absorption coefficient.

The light scattering is expected to provide a sensitive approach for non-invasive and label-free detection and classification of cells. Constructing accurate cell morphology models plays an important role in studying the relationship between light scattering and cell morphology. Currently, stacks of images obtained by laser scanning confocal microscope (LSCM) are used to construct three-dimensional (3D) morphology of cells. However, the actual scanning distance of the confocal microscope is not equal to the scanning step size because the refractive index of the lens immersion medium and the sample medium do not match, which caused the constructed cell model to be stretched. In order to solve this problem, the relationship between the equivalent focus position (EFP) and the nominal focus position (NFP) is calculated by using a ray-tracing model. A correction factor is calculated, which can be used to correct refractive index mismatch. The confocal images are reconstructed by using Duke standard polystyrene spheres, and the constructed model are more like spheres, with little deviation between the confocal scanning direction and the nominal diameter. Finally, a more accurate Jurkat T cell model is reconstructed, which can be used in the subsequent LSP inversion study.

A prototype of a three-dimensional (3-D) radiation model is developed using the lattice Boltzmann method (LBM) and implemented on a graphical processing unit (GPU) to accelerate the model’s computational speed. This radiative transfer-lattice Boltzmann model (RT-LBM) results from a discretization of the radiative transfer equation in time, space, and solid angle. The collision and streaming computation algorithm, widely used in LBM for fluid flow modeling, is applied to speed up the RT-LBM computation on the GPU platform. The isotropic scattering is assumed in this study. The accuracy is evaluated using Monte Carlo method (MCM) simulations, showing RT-LBM is quite accurate when typical atmospheric coefficients of scattering and absorption are used. RT-LBM runs about 10 times faster than the MCM in a same CPU. When implemented on a NVidia Tesla V100 GPU in simulation with a large number of computation grid points, for example, RT-LBM runs ~120 times faster than running on a single CPU. The test results indicate RT-LBM is an accurate and fast model and is viable for simulating radiative transfer in the atmosphere with ranges for the isotropic atmosphere radiative parameters of albedo scattering (0.1~0.9) and optical depth (0.1~12).

چکیده با توجه به ضرورت برآورد تبخیر- تعرق در مدیریت منابع آب، برنامه ریزی آبیاری و ارزیابی اثرات تغییر کاربری اراضی بر روی بازده وتأمین نیاز آبی گیاهان، تعیین دقیق تبخیر-تعرق گیاه مرجع بسیار مهم و حیاتی می‌باشد. با توجه به مشکلات متعددی که در به‌کارگیری لایسیمترها وجود دارد، استفاده از مدل‌هایی که بتواننداین فرآیند را با دقت نسبتا مطلوبی شبیه سازی و برآورد نمایند، امری ضروری بنظر می‌رسد. در این راستا، مدل‌های تبخیر-تعرقی که به مولفه‌های تابش نیاز دارند، به دلیل عدم دسترسی به داده‌های واقعی تابش، کمتر مورد استقبال کاربران قرار گرفته است. در این تحقیق، 4 مدل تبخیر-تعرق گیاه مرجع: جنسن هیز اصلاح شده (JH1)، جنسن-هیز (JH2)، پنمن-مانتیث فائو 56 (PMF56)، و پنمن-مانتیث فائو با تابش ایرماک (PMFI) برای تخمین تبخیر-تعرق مرجع روزانه چمن (ETo) در اقلیم سرد نیمه خشک مورد ارزیابی قرار گرفت. تابش کل(Rs) مورد نیاز با 4 مدل شامل: آنگستروم، پاتریج، دانشیار و صباغ محاسبه شد. در مجموع، 16 سناریوی مختلف تولید و تحت بررسی قرار گرفتند. واسنجی نتایج ETo بدست آمده با داده‌های چهار لایسیمتر زهکش دار در دوره رشد (اردیبهشت آبان) برای دو سال و با استفاده از معیارهای آماری R2، RMSE، MBE، و t انجام گرفت. نتایج بررسی نشان داد که از 16 سناریوی مطالعه شده، مدل جنسن-هیز که معادله تابش دانشیار در آن به‌کار گرفته شده است، در مقایسه با سایر مدل‌ها، مقدار ETo را در سطح معنی‌دار (5 % p ). نتایج برآورد مدل PMF56 با تابش کل (Rs) محاسبه شده به روش پاتریج و تابش خالص محاسبه شده به روش ایرماک، از نظر دقت برآورد در جایگاه بعدی قرار گرفت. اگر چه استفاده همه گیر از مدل تابش آنگستروم، در اغلب سناریوهایی که از مدل تابش آنگستروم استفاده شده بود، نتایج مطلوبی به‌دست نیامد. این تحقیق نشان داد، در صورتی که مدل مناسب تابش به‌کار برده شود، می‌توان مدل‌های ساده‌تر ETo را جهت تخمین مقدار تبخیر-تعرق مرجع روزانه جایگزین مدل‌های ترکیبی نظیر PMF56 نمود. تکرار این تحقیق برای محاسبه ETo ، با هدف استفاده بهینه از مدل‌های تابش در سایر اقلیم‌ها نیز توصیه می‌گردد. واژه‌های کلیدی: مدل‌های تبخیر- تعرق گیاه مرجع، لایسیمتر زهکشدار، مدل‌های تابش ، اقلیم سرد نیمه خشک.

A simplified radiative transfer model for the earth's atmosphere is presented. The simplification is achieved by a combination of band absorptance and emissivity formulation for treating radiative transfer due to H2O, CO2 and O3. The model incorporates the major and minor radiative transfer processes due to H2O, CO2 and O3. The radiative model is used to develop an efficient and accurate radiative-convective model. Results for the global surface temperature, stratospheric thermal structure, and the net outgoing longwave flux are presented. The computed thermal structure of the stratosphere and the stratospheric cooling rates are in excellent agreement with previous studies. The amplitude of the diurnal temperature difference in the upper stratosphere obtained from the present model is larger by about 50% than Leovy's (1964) results. This difference is due to the inclusion of Doppler broadening effects and CO2 hot and minor isotopic bands in the present model. The flux calculations indicate that the relatively minor bands like the CO2 hot and minor isotopic bands and the e-type absorption by the H2O continuum band have to be included in order to compute the outgoing flux F to within 1% accuracy. Results are also presented for the sensitivity of F to surface temperature. It is shown that the H2O e-type absorption has a substantial influence on the sensitivity parameter dF/dTs.

Pool fires are one of the most commonly encountered flame types in fire disasters, and the accurate and detailed modeling of pool fires is beneficial for the hazard analysis and assessment of liquid-related fire accidents. The radiation model is known to be the critical component in the accurate simulation of various fire scenarios. Therefore, to develop a proper radiation model, an LES study of a large-scale methanol pool fire was performed in this work by coupling four different radiation models into the open-source fire simulation code FDS and solving the radiation intensity transport equation using the discrete ordinates method. The impact characteristics of different radiation models are evaluated in detail with the NIST experiments, where the comparative analysis was carried out. Regarding the temperature calculations, the WSGG (weighted-sum-of-gray-gases)-based radiation model and Cassol’s model performed better. In addition, all models predict pulsation frequencies well. However, regarding the prediction of the radiative heat fluxes, Cassol’s two models and the FDS default model outperformed the other models, which indicates that the database for obtaining the spectral information of each species and the method to determine the WSGG coefficient of mixed gases are significant factors for the successful prediction of flame radiation.