Multiple scattering and modeling of laser in fog

When a laser is transmitted in fog, and the water droplets will scatter and absorb the laser, which affects the intensity of the laser transmission and the accuracy of radar detection. Therefore, it is of great significance to study the laser transmission in the fog. At present, the main method of calculating the scattering and attenuation characteristics of fog is based on the radiation transmission theory, which is realized by a large number of numerical calculations or physical simulation methods, which takes time and cannot meet the requirements for obtaining the fast and accurate results. Therefore, in this paper established are a new laser forward attenuation model and backward attenuation model in low visibility fog. It is found that in low visibility environments, the results calculated by the Monte Carlo method are more accurate than those from most of the existing forward attenuation models. For the cases of 0.86-μm, 1.06-μm, 1.315-μm, 10.6-μm typical lasers incident on different fogs with different visibilities, a backscatter model is established, the error between the fitting result and the calculation result is analyzed, the backward attenuation fitting parameters of the new model are tested, and a more accurate fitting result is obtained.

Estimation of co-channel interference between cities caused by ducting and turbulence

With the rapid development of the fifth-generation(5 G)mobile communication technology,the application of each frequency band has reached the extreme,causing mutual interference between different modules.Hence,there is a requirement for detecting filtering and preventing interference.In the troposphere,over-the-horizon propagation occurs in atmospheric ducts and turbulent media.The effects of both ducting and turbulence can increase the probability of occurrence of long-distance co-channel interference(CCI),in turn,severely affecting the key performance indicators such as system access,handover and drop.In the 5 G era,to ensure communication channels and information security,CCI must be reduced.This paper introduces a scattering parabolic equation algorithm for calculating signal propagation in atmospheric ducts on irregular terrain boundaries.It combines Hitney’s radio physical optical model and Wagner’s nonuniform turbulent scattering model for calculating the tropospheric scattering in an evaporation duct or a surface-based duct.The new model proposes a tropospheric scattering parabolic equation algorithm for various tropospheric duct environments.Finally,as a specific case,the topographical boundaries between several cities in the East China Plain were considered,and the over-the-horizon propagation loss was simulated for various ducting and turbulent environments.The simulation results were used to evaluate whether CCI would occur between cities in a specific environment.

基于光致热弹光谱的硫化氢痕量气体高灵敏探测(特邀)

光致热弹光谱(LITES)技术是近年来发展迅速的一种新颖痕量气体检测技术,该技术以体积小巧、成本低廉且无波长选择性的音叉式石英晶振替代成本高、探测波段窄的光电探测器作为光电换能器,通过探测激光与目标气体相互作用后光强的变化量实现目标气体浓度的反演。LITES技术具有探测灵敏度高、响应时间短、无波长选择性等优点。本文以下水道中的硫化氢气体为测量目标,开展了基于LITES技术的痕量气体探测系统的研究。以输出波长为1.582μm的近红外连续波分布反馈单纵模二极管激光器作为激发光源,采用激光器波长调制和二次谐波探测技术,首先研究了激光波长调制深度对LITES系统产生的信号幅度的影响,而后详细研究了气体压强及环境压强对装置性能的影响。此外,为进一步提升装置探测灵敏度,有效光程长度为14.5 m的Herriott多通池被装配在激光器和作为光电探测器的音叉式石英晶振之间,从而使传感器在积分时间为300 ms时,获得4.87×10^(-7)的最低探测极限,当积分时间延长至52 s时其探测灵敏度可达7.78×10^(-8)。在完成装置各项参数优化之后开展了下水道中硫化氢气体的实测研究,结果显示,该系统完全可满足下水道臭气监测分析等领域的应用需求。