Application of Snell's law in reflection raytracing using the multistage fast marching method

Accurate calculations of travel times and raypaths of reflection waves are important for reflection travel time tomography.The multistage shortest path method(MSPM)and multistage fast marching method(MFMM)have been widely used in reflection wave raytracing,and both of them are characterized by high efficiency and ac-curacy.However,the MSPM does not strictly follow Snell's law at the interface because it treats the interface point as a sub-source,resulting in a decrease in accuracy.The MFMM achieves high accuracy by solving the Eikonal equation in local triangular mesh.However,the implementation process is complex.Here we propose a new method which uses linear interpolation to compute the incident travel time of interface points and then using Snell's law to compute the reflection travel time of grid points just above the interface.Our new method is much simpler than the MFMM;furthermore,numerical simulations show that the accuracy of the MFMM and our new method are basically the same,thus the reflection tomography algorithms which use our new method are easier to implement without decreasing accuracy.Besides,our new method can be extended easily to other grid-based raytracing methods.

Towards 6G: Paradigm of Realistic Terahertz Channel Modeling

Terahertz(THz)communications are envisioned as a key technology for the sixth-generation wireless communication system(6G).However,it is not practical to perform large-scale channel measurements with high degrees of freedom at THz frequency band.This makes empirical or stochastic modeling approaches relying on measurements no longer stand.In order to break through the bottleneck of scarce fulldimensional channel sounding measurements,this paper presents a novel paradigm for THz channel modeling towards 6G.With the core of high-performance ray tracing(RT),the presented paradigm requires merely quite limited channel sounding to calibrate the geometry and material electromagnetic(EM)properties of the three-dimensional(3D)environment model in the target scenarios.Then,through extensive RT simulations,the parameters extracted from RT simulations can be fed into either ray-based novel stochastic channel models or cluster-based standard channel model families.Verified by RT simulations,these models can generate realistic channels that are valuable for the design and evaluation of THz systems.Representing two ends of 6G THz use cases from microscopy to macroscopy,case studies are made for close-proximity communications,wireless connections on a desktop,and smart rail mobility,respectively.Last but not least,new concerns on channel modeling resulting from distinguishing features of THz wave are discussed regarding propagation,antenna array,and device aspects,respectively.

Local events-based fast RTM surface-offset gathers via dip-guided interpolation

Reverse Time Migration(RTM)Surface Ofset Gathers(SOGs)are demonstrated to deliver more superior residual dip information than ray-based approaches.It appears more powerful in complex geological settings,such as salt areas.Still,the computational cost of constructing RTM SOGs is a big challenge in applying it to 3D feld data.To tackle this challenge,we propose a novel method using dips of local events as a guide for RTM gather interpolation.The residual-dip information of the SOGs is created by connecting local events from depth-domain to time-domain via ray tracing.The proposed method is validated by a synthetic experiment and a feld example.It mitigates the computational cost by an order of magnitude while producing comparable results as fully computed RTM SOGs.

Investigation of human motion effects on 60GHz indoor office propagation

A modified random walk model for human motion is proposed to investigate characteristics of 60GHz indoor office propagation.Compared with the classic random walk model,the movement tendency in the walking process is taken into account in the modified model.Based on the proposed model,path gains of the propagation environment are simulated under a variety of settings by using a ray tracing method.Simulation results and analysis show that human motion is a major source of disturbance to the indoor office propagation and results in performance degradation in some areas.

Methodical Approach to the Development of a Radar Sensor Model for the Detection of Urban Traffic Participants Using a Virtual Reality Engine

New approaches for testing of autonomous driving functions are using Virtual Reality (VR) to analyze the behavior of automated vehicles in various scenarios. The real time simulation of the environment sensors is still a challenge. In this paper, the conception, development and validation of an automotive radar raw data sensor model is shown. For the implementation, the Unreal VR engine developed by Epic Games is used. The model consists of a sending antenna, a propagation and a receiving antenna model. The microwave field propagation is simulated by a raytracing approach. It uses the method of shooting and bouncing rays to cover the field. A diffused scattering model is implemented to simulate the influence of rough structures on the reflection of rays. To parameterize the model, simple reflectors are used. The validation is done by a comparison of the measured radar patterns of pedestrians and cyclists with simulated values. The outcome is that the developed model shows valid results, even if it still has deficits in the context of performance. It shows that the bouncing of diffuse scattered field can only be done once. This produces inadequacies in some scenarios. In summary, the paper shows a high potential for real time simulation of radar sensors by using ray tracing in a virtual reality.

上海崇明东滩启动区两地块室内自然采光应用模拟分析

自然光是大自然赋予人类无可取代的、健康高效的、可再生的宝贵资源,自然光的利用率成为新型建筑设计的重要参考标准,充分的室内采光模拟分析是建筑设计的重要参照。采用 Dali2018 模拟软件对上海市崇明东滩启动区 CMS15-0501 单元 D07-01、D08-01 地块主要功能空间的室内光环境进行分析,从采光系数、达标状态方面分析,深度解析该地区的自然采光效果,得出最大的采光系数为 22%,满足 2.2% 的采光系数标准值。

利用Raytrace材质制作玻璃装饰球

在电视包装以及建筑模型的许多效果中,都会涉及到玻璃材质、金属材质等物体的制作,如何利用模型制作软件3dsMax,使我们要制作的模型更加真实而自然,是三维学习者以及工作者要面对的一个重要问题。在众多效果中,玻璃材质的制作方法有很多,其中光线跟踪Raytrace材质、mentalray材质等都可以模拟真实的玻璃效果。本文我们就用光线跟踪Raytrace材质来制作真实的玻璃装饰球。

真实感与新鲜感——用Shader的组合表现

下面，我们利用Maya的Shader对场景中的Translucent效果进行逼真的再现。

巧用RAYTRACE材质制作放大效果

在3DS MAX 中,物体材质的效果对于一个动画的好坏起着很大的作用,而在3DS MAX的材质编辑器中材质又扮演着重要的角色。现在制作一个新产品广告,为了突出产品的名称或者强调其它的功能,就可以用放大镜功能。要制作放大效果有许多技巧,由于材质的不同,影响材质的真实度。下面我给大家介绍一种方便快捷的方法,就是运用M A X 的独特的光影追踪(RAYTRACE)材质,制作放大镜的放大效果。本例是模拟一个放大镜镜片球体。

3DS MAX系列讲座——3DS MAX高级材质案例精解(一)

材质和贴图的设计制作是一个场景或者角色成败的关键。无数成功的作品证明,最有挑战性、最有创造性的工作就是调节材质贴图。这项工作需要相当的耐心,一点一点调节参数,一次一次渲染观看差别,直至满意为止。虽然很烦琐,但这样做一定是值得的。因为对于一个动画制作人来说,好的材质可以使一个非常简单的模型或场景变成世界级的作品。场景的真实性完全取决于材质的精细程度和贴图是否合适。更何况。

Analysis of the Light Concentration Loss of a Fresnel CPV/T System after Dust Accumulation

Dust accumulation is one of the reasons for the performance degradation of concentrating photovoltaic and thermal(CPV/T) systems due to the deposition of dust particles with different compositions, shapes, sizes, and masses. In this work, an optical model was developed to investigate the influence of the particle size, diameter, shape, and deposition density on the light concentration efficiency, using the Monte Carlo raytracing(MCRT) method in the Tracepro software. The triangular particles had a larger influence on the light ray deflection and energy flux degradation than the circular and square particles. An average increase in the dust density of 1 g/m^(2) decreased the light concentration efficiency of particles with sizes smaller than 50 μm and 60 μm by 3.31% and 3.26%, respectively. Furthermore, the effect of the incidence angle on the light concentration efficiency was considered at an angle less than 2°.

Ionospheric disturbance analysis of the January 15,2022 Tonga eruption based on GPS data

Hunga Tonga-Hunga Ha’apai climactic eruption on January 15,2022,released enormous energy that affected the ionosphere over the Pacific Rim.We analyzed ionospheric disturbance following volcanic eruptions using near-field(<1000 km),regional(1000–5000 km),and far-field(5000–12000 km) global positioning system(GPS) observations.The results indicate that the near-field ionospheric perturbation that occurred 8–15 min after the cataclysmic eruption was mainly derived from the shock wave(~1000 m/s) generated by the blast,while the low-frequency branch with long-distance propagation characteristics over the regional and the far-field was mainly associated with atmospheric Lamb waves(~330 m/s).Moreover,the amplitude of disturbance and background total electron content(TEC) are related proportionally.The intensity of the volcanic eruption and the background ionospheric conditions determine the magnitude of ionospheric responses.TEC perturbations were invisible on the reference days.Furthermore,the source location and onset time were calculated using the ray tracing technique,which confirms that the Tonga event triggered the ionospheric anomaly beyond the crater.Finally,the change in the frequency of the perturbations coincided with the arrival of the initial tsunami,implying the generation of a meteotsunami.