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不同类型降水对毫米波传播特性的影响研究 总被引:2,自引:1,他引:1
为了提高复杂降水条件下毫米波传播衰减的评估精度,通过分析多个地区的降水谱特征,得出具有代表性的层状云降雨、积层混合云降雨、积雨云降雨以及干雪、湿雪的谱分布参数,然后结合降水粒子的形状、相态、介电模型,计算降水体目标在毫米波波段的散射特性.结果表明,降水强度不是唯一影响毫米波传播衰减的因素; 降水粒子相态、谱分布、入射波频率和温度等对毫米波传播特性均有不同程度的影响,其中谱分布和数密度是影响降雨对毫米波衰减的主要因素; 冰水构成比例是影响降雪对毫米波衰减的主要因素; 不同相态的降水,尤其是干雪、湿雪和雨对毫米波传播影响的差异较大; 而温度的影响较小.并建立了考虑谱分布和温度的降水衰减模型. 相似文献
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近年来,Ku和Ka卫星在广播、通信和军事等领域应用数量越来越多,传统的Ku和Ka波段星地链路降水衰减预报模型基于经验关系和理想假设,考虑降水微物理特性不足,针对此问题,在实测降水粒子微物理特征的基础上定量分析了降水垂直分布、粒子形状、粒子取向、粒子相态等对Ku和Ka频段信号衰减的影响特性.结果表明,与考虑降水非均匀垂直分布的计算结果相比,ITU和SAM模型是基于降水分布均匀的假设,无法代表降水垂直分布不均匀时的衰减情况;降水粒子形状和取向对衰减的影响较小,在13GHz和32GHz频段,球形和非球形粒子衰减值的平均绝对偏差均在0.01dB以下,不同粒子取向时衰减系数的平均绝对偏差最大值为0.00098dB/km和0.0207dB/km;不同相态的降水引起的衰减差异较大,衰减值从大到小依次是湿雪、水和冰.研究结果可以为Ku和Ka波段星地链路传播特性评估及降雨反演新方法提供基本的理论支撑和数据参考. 相似文献
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由于Ka及毫米波频段电磁波频率极高,大气传播特性不同于低频,受大气气体、降雨等大气环境的影响非常大。本文重点考虑大气中的氧气和水蒸气对电磁波的吸收衰减作用,分别从电磁波频率、大气含水量和温度三个方面具体分析大气对Ka及毫米波频段电磁波的衰减特性,并得出相关结论。 相似文献
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为了准确估计对流层大气环境对电磁波能量吸收衰减的影响,为电磁波发射测量装备进行作用距离估算、测控布设及辐射安全区设定提供理论基础,重点研究了对流层大气吸收气体对电磁波能量传播的衰减影响。依据国际电信联盟Rec.ITU-R P.676-9的建议及GJB/Z 87-97《雷达电波折射与衰减手册》给出的1~54 GHz电磁波大气衰减率近似估算模型、等效高度计算模型和等效路径折射模型,修订并完善了在对流层范围内跨等效高度的电磁波倾斜路径衰减量计算模型。仿真分析研究了不同大气压力、温度和水蒸气密度对衰减率的影响,以及不同传播仰角、温度和相对湿度对电磁波相同传播距离能量衰减的影响。 相似文献
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激光在大气中传输衰减特性研究 总被引:1,自引:0,他引:1
激光在大气中传输特性的研究是激光探测与制导、激光通信等光电系统设计中的一个主要问题.利用衰减的经验模型和Mie理论,分别计算了不同大气能见度下的霾粒子对激光大气传输产生的衰减,并对这两种方法计算的结果进行比较分析;再根据Mie理论和云雾的尺度分布模型计算了云雾的激光衰减.结果表明,在近红外波段对于对流层大气中霾粒子的衰减预测应用Mie理论计算更合理;云雾引起的衰减一般较大,并且随着能见度的减小,衰减增加较快.因此,当Vb<15km时,霾引起的衰减需要考虑;当Vb较小时,云雾的激光衰减是限制系统性能的主要因素. 相似文献
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沙尘暴多重散射对毫米波衰减影响研究 总被引:1,自引:0,他引:1
根据随机介质中电波传播理论,应用等效介电常数法和Mie理论,研究毫米波在沙尘暴中传播的衰减;并应用Monte Carlo方法,研究沙尘暴大气中毫米波多重散射对衰减的影响.分别得到了单次散射和多重散射时沙尘暴引起的毫米波段几个大气窗口频率的特征衰减,及随沙尘大气能见度和沙尘粒子水含量的变化关系.结果表明,当能见度小于1 km时,随着能见度的减小,特征衰减增大很快,多重散射的影响也愈来愈大.衰减随含水量的增加而增加,尤其当沙尘粒子水含量大于1%时增加较为显著.因此,对于预测自然沙尘暴大气对毫米波的衰减,当能见度小于1 km时,必须考虑粒子的多重散射效应.当沙尘粒子的水含量超过1%时,需要考虑水含量的影响.这些研究对民用和军用通信、遥感等系统的开发和应用均具有重要的实际意义. 相似文献
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为研究海洋大气气溶胶粒子数浓度时空分布和粒径谱分布特征,2014年8月至2016年3月期间,利用光学粒子计数器和自动气象站等设备在广州茂名海边、东海和南海海域、三亚近海海域以及太平洋和印度洋海域对海洋大气气溶胶粒子数密度谱及大气温度、湿度、气压、风速等进行了测量。对不同海域不同气象条件下的谱分布特征进行了统计分析,并对谱分布进行了拟合。结果表明海洋大气气溶胶粒子谱分布是由一个细粒模和一个中间模组成,但近海的粒子数浓度大于远海。远海气溶胶粒子谱型稳定,海面风力是引起粒子数浓度变化的主要原因。东海和南海的粒子谱分为二段,小于0.5 m时用Junge谱的指数分布来描述,0.5~4 m段用对数正态分布来描述。大风天气下海洋气溶胶的消光系数明显增加,且在1~3 m波段的消光特征基本不受波长的影响。 相似文献
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Liebe H.J. Manabe T. Hufford G.A. 《Antennas and Propagation, IEEE Transactions on》1989,37(12):1617-1612
Propagation properties of suspended water and ice particles which make up atmospheric haze, fog, and clouds were examined for microwave and millimeter-wave frequencies. Rates of attenuation α (dB/km) and delay τ (ps/km) are derived from a complex refractivity based on the Rayleigh absorption approximation of Mie's scattering theory. Key variables are particle mass content and permittivity, which depends on frequency and temperature both for liquid and ice states. Water droplet attenuation can be estimated within a restricted (10±10°C) temperature range using a simple two-coefficient approximation. Experimental data on signal loss and phase delay caused by fog at four frequencies (50, 82, 141, and 246 GHz) over a 0.81-km line-of-sight path were found to be consistent with the model 相似文献
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Bing Gong Guowei Lou Xingguo Li 《Journal of Infrared, Millimeter and Terahertz Waves》2009,30(11):1234-1242
In the sub-millimeter wave propagation process, attenuation is mainly due to the effects of atmospheric particles, such as
water vapor. It’s also caused by absorption and scattering by hydrometeors. This paper focuses on the effects of hydrometeors
on sub-millimeter wave propagation. The formula for calculating the attenuation cross-section of raindrops is given, as well
as the distance formula of sub-millimeter wave radiometers. Finally, this paper mentions the effects of some weather phenomena
on detection distance of sub-millimeter wave radiometers. Taking cloud attenuation as an example, the relation between distance
and temperature or moisture content is analyzed. 相似文献
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Cuccoli F. Facheris L. Tanelli S. Giuli D. 《Geoscience and Remote Sensing, IEEE Transactions on》2001,39(3):645-654
The authors address the problem of estimating vertical profiles of atmospheric water vapor by means of attenuation measurements simultaneously made at different frequencies along a vertical satellite-ground link. The operating frequencies selected are those around the spectral absorption lines of water vapor at 22.235 GHz. A simulation is presented of multifrequency attenuation measurements, based on an atmospheric propagation model and on radiosonde data providing true profiles of temperature, pressure, and water vapor. The results indicate that such multifrequency measurements are correlated to variations of the vertical profiles of water vapor. It is therefore expected that vertical detail of such profiles depends on number and position of the frequencies utilized 相似文献
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Quanhua Liu Fuzhong Weng 《Geoscience and Remote Sensing, IEEE Transactions on》2005,43(5):1087-1095
The measurements from satellite microwave imaging and sounding channels are simultaneously utilized through a one-dimensional (1-D) variation method (1D-var) to retrieve the profiles of atmospheric temperature, water vapor and cloud water. Since the radiative transfer model in this 1D-var procedure includes scattering and emission from the earth's atmosphere, the retrieval can perform well under all weather conditions. The iterative procedure is optimized to minimize computational demands and to achieve better accuracy. At first, the profiles of temperature, water vapor, and cloud liquid water are derived using only the AMSU-A measurements at frequencies less than 60 GHz. The second step is to retrieve rain and ice water using the AMSU-B measurements at 89 and 150 GHz. Finally, all AMSU-A/B sounding channels at 50-60 and 183 GHz are utilized to further refine the profiles of temperature and water vapor while the profiles of cloud, rain, and ice water contents are constrained to those previously derived. It is shown that the radiative transfer model including multiple scattering from clouds and precipitation can significantly improve the accuracy for retrieving temperature, moisture and cloud water. In hurricane conditions, an emission-based radiative transfer model tends to produce unrealistic temperature anomalies throughout the atmosphere. With a scattering-based radiative transfer model, the derived temperature profiles agree well with those observed from aircraft dropsondes. 相似文献
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Radiometric brightness temperatures below about 12 GHz provide accurate estimates of path attenuation through precipitation and cloud water. Multiple brightness temperature measurements at X-band frequencies can be used to estimate rainfall rate and parameters of the drop size distribution once correction for cloud water attenuation is made. Employing a stratiform storm model, calculations of the brightness temperatures at 9.5, 10, and 12 GHz are used to simulate estimates of path-averaged median mass diameter, number concentration, and rainfall rate. The results indicate that reasonably accurate estimates of rainfall rate and information on the drop size distribution can be derived over ocean under low to moderate wind speed conditions. 相似文献
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太赫兹(THz)波提供的通信带宽和容量远大于毫米波。与可见光和红外光相比,THz脉冲的波长较长,在随机介质中传播时,不但会发生时域和空域的形变,介质中的粒子还会对入射波发生散射,这些都会使得脉冲信号发生衰减。根据Mie理论与随机离散分布粒子的波传播与散射理论,计算了THz波信号入射下雾滴粒子的消光系数,分析了不同THz波波长下,雾滴粒子消光系数随粒子尺寸的变化。结合雾滴粒子谱分布,考虑粒子群的平均体系散射特性,得到了不同波长下的平均反照率与相函数。最后分析了THz波段信号在不同能见度雾中的传输特性。结果表明:大气环境中,雾对THz波产生的吸收和衰减不容忽视,不同THz信号的水的折射率虚部的变化严重影响了THz信号在雾中的传输。 相似文献
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T. Manabe Y. Furuhama T. Ihara S. Saito H. Tanaka A. Ono 《Journal of Infrared, Millimeter and Terahertz Waves》1985,6(4):313-322
Field line-of-sight propagation experiments were made at 80 and 240 GHz on a horizontal path of 810 m. The measured attenuations showed quadratic dependences on atmospheric water vapor density, and absorptions in excess of theoretical predictions were observed at both frequencies, while the measured refractive dispersion between these two frequencies showed a linear dependence on water vapor density and was in good agreement with theoretical prediction. Liebe's model for water vapor attenuation including empirical continuum absorption is confirmed to be effective for 80 and 240 GHz. 相似文献
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Skofronick-Jackson G.M. Gasiewski A.J. Wang J.R. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(1):187-196
The microphysical parameterization of clouds and rain cells plays a central role in atmospheric forward radiative transfer models used in calculating microwave brightness temperatures. The absorption and scattering properties of a hydrometeor-laden atmosphere are governed by particle phase, size distribution, aggregate density, shape, and dielectric constant. This study investigates the sensitivity of brightness temperatures with respect to the microphysical cloud parameterization. Calculated wideband (6-410 GHz) brightness temperatures were studied for four evolutionary stages of an oceanic convective storm using a rive-phase hydrometeor model in a planar-stratified scattering-based radiative transfer model. Five other microphysical cloud parameterizations were compared to the baseline calculations to evaluate brightness temperature sensitivity to gross changes in the hydrometeor size distributions and the ice-air-water ratios in the frozen or partly frozen phase. The comparison shows that enlarging the raindrop size or adding water to the partly frozen hydrometeor mix warms brightness temperatures by as much as 55 K at 6 GHz. The cooling signature caused by ice scattering intensifies with increasing ice concentrations and at higher frequencies. An additional comparison to measured Convection and Moisture Experiment (CAMEX-3) brightness temperatures shows that in general all but two parameterizations produce calculated TBs that fall within the CAMEX-3 observed minima and maxima 相似文献