Modelling of Drop Size Distribution of Rain from Rain Rate and Attenuation Measurements at Millimeter and Optical Wavelengths

This paper describes a technique for modelling of rain drop size distributions at Calcutta in terms of negative exponential function, from the measurements of rain rate and attenuation over a dual wavelength LOS link at millimeter and optical frequencies. The DSD model obtained is then used to determine the attenuation at 94 GHz, for comparison with experimentally obtained attenuation at 94 GHz. This is also compared with the attenuation calculated by considering other experimentally obtained DSD models. The best fit negative exponential distribution function (modified M-P model) is presented along with some other experimentally obtained and reference models.     

星载SAR系统设计中的雨衰估算

主要讨论了微波信号大气传播中降雨衰减的估算方法。基于我国部分地区降雨强度长期累计分布 ,计算了部分地区X波段信号传输的降雨衰耗。针对星载SAR的特点 ,分析了雨衰对SAR的影响 ,提出了星载SAR设计时雨衰的指标     

1-Min Rain Rate Statistics Predictions From 1-Hour Rain Rate Statistics Measurements

A new method is presented, which allows the recovery of the cumulative distribution function (CDF) of point rain rate with 1-min integration time (P(R)₁) from rain rate CDFs with longer integration time (in this case, 1-hour time average rain rate statistics P(R)₆₀)- The method generates the scaling factors between P(R)₆₀) and P(R)₁) as a function of the probability level and of the site geographical coordinates. From the scaling factors, a scaling law of the form proposed by Chebil and Raman is devised. The method is applicable worldwide and produces predictions far more accurate than the ones provided by general P(R) estimation techniques.     

星源照射双/多基地SAR成像

星源照射双/多基地合成孔径雷达(SAR),采用卫星发射,卫星、临近空间、飞机、地面等平台接收,实现对地海面场景和目标的高分辨成像。该技术具有可成像范围广、隐蔽性好、抗干扰能力强等优点,且可以通过波束调控实现扫描、聚束、滑动聚束等多种组合成像模式,从而获取更加丰富的成像信息,具有十分广阔的民用和军事应用前景。目前,国内外针对星源照射双/多基地SAR成像技术开展了多年的研究,积累了诸多研究成果。该文分别从系统组成、构型方法、回波模型、成像方法、收发同步与试验验证等方面对该技术进行阐述与分析,同时对相关的研究工作进行较系统的回顾,并展望了星源照射双/多基地SAR成像技术未来的发展方向。     

Radiometric Measurements of Rain Attenuation at 22.2 and 31.4 GHz Over Calcutta

Measurements of rain attenuation over Calcutta have been made using radiometers operating at frequencies of 22.235 and 31.4 GHz. The results have been correlated with observations of rainfall rates made with a fast-response rain gauge. The distributions of peak rain rates over Calcutta for two different years and the cumulative occurrences of rainfall rates and attenuations at the two frequencies are presented.     

Radar Backscatter Measurement Accuracies Using Digital Doppler Processors in Spaceborne Scatterometers

The normalized standard deviation, Kp, of radar backscatter measurements using digital Doppler processors in spaceborne scatterometers is derived. The Kp expression for analog Doppler filter processors, such as that used in the Seasat scatterometer [7] is shown to be a special case of the derived Kp expression. A connection to Welch's power spectrum estimation results [6] is also made. Tradeoff studies in digital filter design such as hardware complexity, computational speed, and system performance can be performed based on this Kp expression. We briefly discuss a current application in the design of the NASA scatterometer (NSCAT) to be flown in 1990. This derivation should be useful for system design and analysis of other radar remotesensing instruments.     

由实测小时雨量预报地星通信雨致衰减的方法研究

利用１９９１年中国３３３个地面雨量站的小时雨量数据，进行降雨率累积概率对数正态和伽玛分蝗计算比较，得出伽玛分布在较大的降雨范围内能更好地反映实际降雨率累积概率分布。     

In Search of a Location-Centric Rain Attenuation Model

Wireless Personal Communications - In search of an accurate location-centric rain-induced attenuation model, in this paper, the authors have investigated the measured attenuation and rainfall...     

A Formula for the Conversion of 5-Minute Average, 10 Minute Average Rain Rate into 1-Minute Average Rain Rate for Prediction of Rain Induced Attenuation

The attenuation of microwave signal due to rain is a well established fact now. Localized models based on the rain rate and attenuation statistics is the basic necessity for a RF communication system designer. For development of any such model, we need long term statistics. These days most of the metrological data that is available is in the form of either 5-min or 10-min average rain rate and if we want to utilize this data, we need to convert this into 1-min equivalent average rain fall. In this paper, a formula has been purposed for the conversion of 5 min and 10 min average rain rate into 1 min equivalent average rain rate.     

Retrieval of Snow and Rain From Combined X- and W-Band Airborne Radar Measurements

Two independent airborne dual-wavelength techniques, based on nadir measurements of radar reflectivity factors and Doppler velocities, respectively, are investigated with respect to their capability of estimating microphysical properties of hydrometeors. The data used to investigate the methods are taken from the ER-2 Doppler radar (X-band) and cloud radar system (W-band) airborne Doppler radars during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment campaign in 2002. Validity is assessed by the degree to which the methods produce consistent retrievals of the microphysics. For deriving snow parameters, the reflectivity-based technique has a clear advantage over the Doppler-velocity-based approach because of the large dynamic range in the dual- frequency ratio (DFR) with respect to the median diameter D₀ and the fact that the difference in mean Doppler velocity at the two frequencies, i.e., the differential Doppler velocity (DDV), in snow is small relative to the measurement errors and is often not uniquely related to D₀. The DFR and DDV can also be used to independently derive D₀ in rain. At W-band, the DFR-based algorithms are highly sensitive to attenuation from rain, cloud water, and water vapor. Thus, the retrieval algorithms depend on various assumptions regarding these components, whereas the DDV-based approach is unaffected by attenuation. In view of the difficulties and ambiguities associated with the attenuation correction at W-band, the DDV approach in rain is more straightforward and potentially more accurate than the DFR method.     

主星带编队小卫星顺轨干涉GMTI及性能分析

该文针对主星带编队小卫星雷达系统,讨论了基于修正的顺轨干涉(ATI)原理进行地面动目标检测方法及其性能。利用小面单元模型仿真了一幅带动目标的地面起伏场景图像,验证了该方法的有效性。综合盲速、最小可检测速度、测速误差等指标,给出了适合执行ATI功能的编队构形部分参数,可为编队小卫星GMTI相对绕飞轨道设计提供一定指导。最后,对CartWheel和Pendulum两种典型系统构形进行了GMTI性能仿真分析。     

基于P-K滤波的X波段雷达雨衰补偿研究

X波段天气雷达的回波信号经过降雨区时会存在偏振参量的衰减现象,偏正参量的衰减对雨量估计和气象天气分类等会产生影响,针对这一问题,本文提出一种结合了粒子滤波和卡尔曼滤波的方法（P-K滤波）。该方法首先对天气雷达回波数据中的差分传播相移参量利用P-K滤波算法进行滤波处理,进而利用订正的结果采用自适应算法对水平反射率因子进行衰减订正。利用P-K滤波算法和其他算法对相同的雷达数据进行处理对比,其结果表明,P-K滤波算法能够更有效地对差分传播相移进行衰减订正,其处理结果的平滑性和准确性更高,进而对水平反射率因子的衰减订正效果更好。     

雨衰减的解析近似

本文对Ｌａｗｓ－Ｐａｒｓｏｎｓ和广州雨滴尺寸分布雨衰减和降雨经之间的指数关系中的ａ和ｂ值＾「１」「２」进行了分析和解析回归，给出其与频率的解析近似关系，利用其计算的雨衰减和数值计算结果有很好的一致性。     

紫外光在雨中的传输衰减研究

针对目前雨中衰减模型在紫外光波段的适用局限性,介绍了考虑雨滴对光传输的遮挡作用时光的传输衰减模型,通过与Modtran数据及相关文献比较验证了模型在紫外光波段的适用性,分析了降雨时影响紫外光衰减的主要因素,表明降雨时能见度对紫外光的衰减影响较大,并结合实际的降雨情况考虑能见度的影响提出了紫外光在雨中的传输衰减计算模型。     

卫星雷达高度计中准最大似然算法的高度误差估计

利用准最大准然估计算法，可以估计海洋卫星高度计中海平面到卫星平台之间的高度，本文首先讨论了最大似然算法的基本原理，然后根据高度计的测高原理，讨论了采用准最大似然估计带来的高度偏差，并提出了进行计算机仿真的有效方法，分析了均方根高度误差与信噪比，脉冲累积量和均方根波高之间的关系。     

Determining Attenuation of Waveguide from Electrical Measurements on Short Samples

improved method for accurately determining the attenuation of waveguide from measurements on very short samples is presented. First, two samples are measured separately and then in tandem. When the measurements are properly made, the sum of the attenuations when the samples are measured separately agrees with the attenuation when measured in tandem at each frequency of measurement. Second, the average effective resistivity is found over a band of frequencies. Using the average effective resistivity, the attenuation at any frequency in the band can be determined. Results for WR159 copper waveguide are shown.     

Mode Content Determination in a Multimode Waveguide from Radiation Pattern Measurements Using the Genetic Algorithm

This paper presents a novel technique for determining the mode content in a multimode waveguide from the radiation pattern measurements. The technique employs the Genetic Algorithm (GA) for determining the mode content in the waveguide from the measured pattern and a numerical method for simulating radiation patterns for the modes propagating in the waveguide. By numerical experiments, we validate the feasibility and effectiveness of the proposed technique, and illustrate its sensitivity to the number of observation points and random noise in the measurement.     

On the Space-Time Variations of Rain Attenuation

Rain attenuation shows a considerable temporal and spatial variability. To simulate fade mitigation techniques such as route diversity, a space-time channel model which accounts for the spatial and temporal variation of rain attenuation is needed. In this paper we investigate the space-time correlation of rain attenuation utilizing 42 GHz star-like network measurements. By combining the spatial and temporal correlation properties of rain attenuation, a simulation model for generating multiple correlated rain attenuation time series based on the Maseng–Bakken model is developed. The model is validated by comparing the statistical and angular diversity properties of the model with those of measurements and theoretical diversity gain models. Furthermore, parameters for the Maseng–Bakken dynamic rain attenuation model were extracted from the star-like network measurements. In addition, using a systematic multivariable technique a model for the parameter $beta _{s}$ which controls the dynamics of rain attenuation in the Maseng–Bakken model was developed. Moreover, using available rain attenuation measurements the advantage of route diversity with selection combining is investigated.      

星载Ku波段雷达方案设计与性能分析

空间微波雷达技术经过近四十年的发展，广泛应用在空间飞行器交会对接、地貌探测、卫星高度测量以及其他军事用途当中。文中根据国内微波雷达现有技术水平和用户要求设计了某星载Ku波段雷达总体方案，重点分析和论证了雷达体制和雷达工作模式，并对主要分系统进行了介绍，最后对雷达的精度、分辨率和探测能力进行了分析。结果表明，指标能够满足要求。     

A Stochastic Dynamic Model of Rain Attenuation

A dynamic mathematical model of rain attenuation has been developed and is presented in this paper. This model permits the expression of analytic relationships between parameters commonly used to describe the properties of interest for communication. The dynamic model is based on the lognormal distribution of rain attenuation and utilizes a memoryless nonlinear device to transform attenuation and rain intensity into a one-dimensional Gaussian stationary Markov process. Hence, only one parameter is required to introduce the dynamic properties of rain attenuation into the model. Experimental results and the known properties of rain have been used to derive and to verify the model; comparative results are presented and demonstrate good correspondence. The application of the model to the statistical analysis of the performance of communications systems is illustrated in the paper. The use of a dynamic rain attenuation model is necessary in order to analyze radio communication systems with transmit power control to offset the effects of rain attenuation, and where the finite response time of the control system affects the performance. An advantage of the model is the simplicity with which it allows simulation of communication link performance under the influence of rain attenuation. Such simulations are of great interest for complex models of adaptive networks where several deteriorating effects, including finite response times, are present.