Propagation Characteristics of Elevation Angles and Three Dimensional Fading Channel Model with Angle Offset

Three dimensional(3D)Multiple Input and Multiple Output(MIMO)is one of the most promising techniques for the 5th generation(5G)mobile communication system.To support its research,the property of elevation angle in 3D channel model should be accurately modeled.Conventionally,3D channel is modeled with an assumption that the mean elevation angle of multipaths is coincided with the line-of-sight(LOS)direction.In order to investigate its authenticity and give the reliable 3D channel model,extensive 3D multiple antenna field channel measurements with 100 MHz bandwidth are conducted in three typical scenarios,including outdoor to indoor(O2I),urban microcell(UMi)and urban macrocell(UMa).The statistical characteristics and parameters are extracted and analyzed based on the measurement data.It is found that the assumption holds in the LOS condition.However,for non-line-of-sight(NLOS)condition,a difference exists between the mean elevation angle and the direction connecting transmitter and receiver,which is defined as the elevation angle offset.Then,the eigenvalue distribution and capacity are compared between the reconstructed 3D channels with and without elevation angle offset.Results show that the performance of 3D channel with angle offset fits the measurement data better whereas that without angle offset is underestimated.

Elevation estimation for low-angle target based on reffection paths suppression

In the signal processing for metrewave radar, the reflection paths of target echoes can cause severe error in the elevation estimation for the low-angle target tracking. The exact angles of the reflection paths are unknown beforehand, and therefore, the reflection paths can not be suppressed easily. Therefore, in this article, an improved reflection paths suppression approach is presented. A block matrix aggregate is constructed based on the possible angles of the reflection paths. Combined with the beamforming-like processing, a generalized maximum likelihood estimation is derived to optimize the estimation. Moreover, the noise reduction method based on the Toeplitz covariance matrix is used for better performance. This approach is applied to the real data collected by the low-angle tracking radar with 8-channel vertical array. The experiment results show that the reflection effects are reduced and the accuracy of the elevation estimate is improved.

A discussion on improving typhoon observation through radar by scanning the negative elevation angle

Certain feasibilities and features were discussed in typhoon detection by radar with a negative elevation angle according to the relationship between the remote detecting range and the elevation angle of the new generation weather radar, in order to rectify the disadvantages of detecting capability for remote low-level echo with a lowest elevation angle of 0.5° in the common detecting mode. The data obtained from detecting the typhoon of Haitang and Changmi with radar for their negative elevation angles and the observed data for the common lowest elevation angle of 0.5° were compared to each other. The results showed that the detection of remote low level cloud system with radar could be improved by using the negative elevation angle, and the structure and the evolution trend of a typhoon could be better judged. The increasing degree of detection for negative elevation angles in the current volume scanning mode should be helpful for predicting the intensity and developing trend of windstorms, to further improve the capability of warning and nowcasting. The detection of negative elevation angle could also help reveal the development and change of typhoon＇s low level cloud system. As far as the typhoons of Haitang and Changmi were concerned, the detecting area of Changmi was increased by 1.09 times with the negative elevation angle of 0.31°, compared with the elevation angle of 0.48° if the threshold value for the sea echo within 100 km was eliminated. Several volume scans of Haitang were increased by 2.1%-7.9% for the negative elevation angle of 0.36° compared with the elevation angle of 0.49° . Therefore, the radar detecting capability of typhoons could be improved by the detection of negative elevation angles to some extent. This could make up for the disadvantages of a low detecting capability for remote low-level echo in the common detecting mode. At the same time, a negative elevation angle could be easily influenced by the ground clutter and the close sea wave clutter which interfered with the assessment of the typhoon structure at times. Assessing these advantages and disadvantages, some advantages for using negative elevation angle were discovered from the observation of the typhoons Haitang and Changmi, if the negative elevation angle with radar was selected reasonably in some conditions. As a result, a certain value arose for improving and monitoring the early warning system for typhoons, paying close attention to the detection of negative elevation angles.

Discussion about the Application of CINRAD / SA Radar Using Negative Elevation Angle Mode in Observation of Tropical Cyclone

The study aimed to discuss the application of CINRAD/SA radar using negative elevation angle mode in observation of tropical cyclone. Firstly, the calculation formula of the lowest detecting height of CINRAD/SA radar was educed, and then the application of negative angle mode in Changle Radar Station was introduced. Through analyzing different observing abilities for tropical cyclone detected at different elevation angles, we discussed the limitation of CINRAD/SA radar using negative angle mode, and finally proposed some suggestions on CINRAD/SA radar using nega- tive elevation angle mode to observe tropical cyclone.

Dependence of epoch-wise two-way nested ANOVA estimates of variances of unmodeled effects present in relative GPS positioning on satellite elevation cutoff angle and PDOP mask

Impact of satellite elevation cutoff angle and position dilution of precision(PDOP)mask change on epoch-wise variance components of unmodeled effects that accompany relative Global Positioning System(GPS)positioning is presented herein.Data used for this study refer to the winter and summer periods of the years with minimal(2008)and maximal(2013)solar activity.These data were collected every 30 s in static mode,at two permanent GPS stations located in Montenegro,establishing a mediumdistance(116-km-long)baseline with a height difference of approximately 760 m between its endpoints.The study showed that changing satellite elevation cutoff angle,with a fixed PDOP mask,affects epochwise two-way nested ANOVA estimates of variances related to the‘far-field’multipath(considered as the nested factor herein)and the combined unmodeled effect of tropospheric and ionospheric refraction(considered as the nesting factor herein).However,changing of PDOP mask,with a fixed satellite elevation cutoff angle,doesn’t affect epoch-wise two-way nested ANOVA estimate of variance of the combined unmodeled effect of tropospheric and ionospheric refraction,but,generally,affects the estimate of variance of the‘far-field’multipath(possibly mixed with a part of a‘shorter-term’ionospheric refraction),which is especially pronounced for the summer period.It should also be noted that there is a significant influence of satellite elevation cutoff angle change on both epoch-wise horizontal and vertical position accuracy,only for the summer period,especially in the presence of maximal solar activity,while there is no significant impact of PDOP mask change on epoch-wise positional accuracy.

Spectral domain optical coherence tomography crosssectional image of optic nerve head during intraocular pressure elevation

AIM: To analyze changes of the optic nerve head(ONH) and peripapillary region during intraocular pressure(IOP) elevation in patients using spectral domain optical coherence tomography(SD-OCT).METHODS: Both an optic disc 200×200 cube scan and a high-definition 5-line raster scan were obtained from open angle glaucoma patients presented with monocular elevation of IOP(≥30 mm Hg) using SD-OCT. Additional baseline characteristics included age, gender, diagnosis,best-corrected visual acuity, refractive error, findings of slit lamp biomicroscopy, findings of dilated stereoscopic examination of the ONH and fundus, IOP, pachymetry findings, and the results of visual field.RESULTS: The 24 patients were selected and divided into two groups: group 1 patients had no history of IOP elevation or glaucoma(n =14), and group 2 patients did have history of IOP elevation or glaucoma(n =10). In each patient, the study eye with elevated IOP was classified into group H(high), and the fellow eye was classified into group L(low). The mean deviation(MD)differed significantly between groups H and L when all eyes were considered(P =0.047) and in group 2(P =0.042), not in group 1(P =0.893). Retinal nerve fiber layer(RNFL) average thickness(P =0.050), rim area(P =0.015),vertical cup/disc ratio(P =0.011), cup volume(P =0.028),inferior quadrant RNFL thickness(P =0.017), and clockhour(1, 5, and 6) RNFL thicknesses(P =0.050, 0.012, and0.018, respectively), cup depth(P =0.008), central prelaminar layer thickness(P =0.023), mid-inferior prelaminar layer thickness(P =0.023), and nasal retinal slope(P =0.034)were significantly different between the eyes with groups H and L.CONCLUSION:RNFLaveragethickness,rim area,vertical cup/disc ratio, cup volume, inferior quadrant RNFL thickness, and clock-hour(1, 5, and 6) RNFL thicknesses significantly changed during acute IOP elevation.

Effect of Helix Pitch Angle on the Modal Dispersion Characteristic of Step-Index Optical Fiber

The general characteristic equation is derived for the helically cladded step-index optical fiber. The dispersion curves are drawn for the different pitch angles Ψ and mode order ν = 1. The effect of helix pitch angle on the dispersion characteristics and also on the modal cut-off condition is examined. Except for the lowest order mode, all the modes appear in pairs. The lowest order mode displays the negative dispersion for the some value of normalized frequency V and depends on the helix pitch angle Ψ.

Angle Dependence Analysis Method to Determine SNRArc Applied to GNSSMRSea Level Retrieval

The Global Navigation Satellite Systems(GNSS)broadcast radio signals are continuously at two or more frequencies in the L-band,and the multipath signals from sea surface recorded by off-the-shelf geodetic receivers have been demonstrated they can be used to estimate sea level,using a technology called GNSS multipath reflectometry(GNSS-MR).Before proceeding to estimate reflection parameters,the azimuth range and elevation angle range are needed to be defined,as only with suitable azimuths and elevation angles the sensing zones can be guaranteed on water.So,this study presents an angle dependence analysis method to jointly select the azimuth range and elevation angle range based on wavelet analysis which can describe the nonstationary power of different sinusoidal oscillations changed with elevation angle.The key of this method is to use one grid model to screen the spectrum power of multipath oscillation on different elevation angles and azimuths in this work.Then the elevation angles and the azimuths can be determined by searching grids with greater power.The GPS and GLONASS data of two MultiGNSS Experiment(MGEX)stations named BRST and MAYG was analyzed and used to retrieve.Firstly,the angle dependence analysis was carried out to determine the elevation range and azimuth range.Secondly,the sea levels were retrieved from individual signals.Finally,the retrievals of individual signals are combined to form a 10-min sea level retrieval series.The RMSEs of the combined retrievals are both less than 15 cm.The results show the effectiveness of the selection of angle range based on the angle dependence analysis method.

Advances in research on factors of cranioauricular angle formation after auricular reconstruction

Objective To review the advances in research on factors of cranioauricular angle formation after auricular reconstruction.Methods The related literature concerning the main surgical methods and influencing factors for the ear elevation by Nataga method and dilated method was reviewed and summarized.Results The ear elevation by Nataga method and dilated method has achieved satisfactory clinical results.Although rapid prototyping technology and tissue engineering have developed rapidly,it is still some time before a beautiful and practical cranioauricular angle can be reconstructed.Conclusion The surgical programs for ear elevation by Nataga method and dilated method have been constantly improved in recent years,which provides a great deal of reference for obtaining a beautiful and practical cranioauricular angle.

摊铺机熨平装置的动力学建模与仿真分析

为了优化摊铺机熨平装置的设计参数,提供更好的施工操作策略,对摊铺机熨平装置进行了建模、仿真和实验。详述了摊铺厚度调整时仰角α变化的过程,对摊铺机熨平装置进行了受力分析,以仰角α为参数建立熨平装置的动力学模型。利用MATLAB搭建Simulink框图,对动力学模型进行仿真,分析了熨平装置底板宽度、牵引点O与底板的垂直距离、重力G绕牵引点O的力臂大小对摊铺性能的影响。仿真与实验结果表明:所建立的动力学模型能够正确反映熨平装置的工作原理,增大熨平装置底板宽度可以提高找平系统的灵敏度,利用手动调节机构调整初始工作仰角可以有效规避负仰角出现而又不失灵敏性,输料、分料和行走系统要协同工作、相互匹配,保持料位高度恒定才能提高摊铺路面的平整度。

基于机载多角度InSAR技术的复杂地形高精度DEM重建方法

干涉合成孔径雷达(Interferomtric Synthetic Aperture Radar,InSAR)是全天时、全天候获取三维地表信息重要的技术手段。机载InSAR系统具有机动灵活、多角度获取数据的优势,可以高效率、高精度获取数字高程模型(Digital Elevation Model,DEM)数据。但是,在地形复杂区域,InSAR侧视成像易在地形陡峭区域形成较大范围的阴影和严重的叠掩现象,阴影和叠掩区域在SAR图像上体现为信息的丢失,从而导致DEM数据大面积无效数据的存在,严重影响DEM数据的质量及应用。针对这一问题,本文提出了基于机载多角度InSAR技术的复杂地形高精度DEM重建方法,基于考虑地形起伏的机载多角度InSAR数据获取任务规划设计,最大程度的避免阴影和叠掩导致的无效数据;基于高精度InSAR数据处理,保证每个角度DEM数据精度的高度一致性;基于快速多角度DSM数据融合与滤波处理,实现多角度InSAR体制复杂地形DEM高精度重建。本文以四川省西部山区大坡度、非连续等复杂地形为例,基于本文提出的方法,利用3个角度InSAR数据融合处理,生成了高精度DEM数据,试验结果表明,本文提出的方法获取复杂地形DEM数据高程均方根误差为0.6 m,同时,数据有效率大于99%。

陆地生态系统碳监测卫星自主任务规划研究

低轨遥感卫星往往以全球或全国范围内的特定地物为探测目标。为提高卫星在轨运行的自主性,文章提出了一种面向地物目标属性的遥感卫星自主任务规划方法。首先外推出预报点90 min后的星下点经纬度,并根据星载地图和太阳高度角,得到预报点的阳照/阴影、陆地/海洋、境内/境外属性。对地物目标属性信息进行平滑处理后,根据各载荷的地物目标属性,识别出各载荷的工作任务时间段,可实时实现提前约1个轨道圈的载荷自主任务规划。

自行车控制人骑/推行姿态参数测量实验

该研究提出手工及软件辅助两种测量自行车骑/推行姿态的方法,并通过物理实验测得自行车控制人的背角、上臂抬高角、肘部弯曲角、左/右侧大腿抬高角及膝盖弯曲角共7种姿态参数。统计分析发现,背角、大腿抬高角是区分骑/推行姿态的主要特征参数,当控制人背角α>12°且大腿抬高角θ≤60°时为骑行;当控制人背角α≤12°且大腿抬高角θ>60°时为推行。以此为基础提出判断骑/推行姿态的方法。对464张真实照片的判别结果显示,仅凭一张图就能准确判别出90.3%的骑/推行姿态,说明了该方法的有效性。这种方法是一种测量自行车控制人骑/推行姿态的低成本解决方案。

高架火炬掺氢燃烧热辐射模拟研究

目的天然气掺氢后燃烧特性会发生改变,因此,有必要对掺氢天然气热放空过程进行研究,以确定掺氢输送条件下原有高架火炬适用的工况条件,从而确保天然气管输系统在掺氢输送时的安全。方法结合掺氢燃烧实验和CFD数值模拟,研究掺氢(摩尔分数0~20%)天然气进行扩散燃烧时燃烧特性及热辐射半径变化情况,揭示掺氢对燃烧热辐射半径的影响机理,明确API STD 521—2014《泄压和减压系统》中热辐射半径解析模型可用于掺氢天然气的计算。结果在等体积流量下,掺氢减小了热释放量从而减短了火焰长度,而在侧风作用下的火焰倾斜角几乎不变,因此缩小了热辐射半径;在等质量流量下,掺氢增加了热释放量从而增长了火焰长度,而火焰倾斜角变大,使得热辐射半径变化极小。同时,风速增大会导致热辐射半径扩大。结论在安全热辐射半径不变的前提下,按体积流量计算,掺氢条件下最多可提高19%~23%体积流量的放空量,火炬系统的排放效率有所提高;按质量流量计算,掺氢条件下高架火炬的质量流量放空量与掺氢前相比几乎保持不变。

基于联合时频差分析的高仰角卫星干扰信号定位

随着空间卫星的广泛使用,射电天文望远镜受到高仰角的干扰越来越多,进一步确定整个天空中卫星干扰源的频率、位置和分布,是有效规划天文观测的重要手段。本文介绍了一种基于时频差对高仰角卫星干扰源定位的方法,即基于时频差信息,将干扰源定位解构为时频差联合估计与定位的问题。首先建立用于时频差联合估计的地面接收信号模型,基于四阶最大似然进行到达时间差(time difference of arrival,TDOA)与到达频率差(frequency difference of arrival,FDOA)的联合估计;然后建立干扰源定位模型,根据两步加权最小二乘算法对干扰源进行定位。经过仿真验证,实现了对高仰角快速运动干扰源的定位与轨迹估计,对于300 km高度干扰源的定位误差最小可达到78 m。利用基于联合时频差分析的卫星干扰源定位算法进行射电天文台址无线电环境测量可提升射电望远镜的科学产出,并保障其平稳运行。

塔影效应下风轮仰角对风力机气动特性的影响

考虑风力机塔影效应的影响,针对风轮仰角导致风力机气动特性更为复杂的问题,文章对不同仰角水平轴风力机流场进行了数值模拟,分析了风力机叶片截面压力分布、涡量以及塔筒表面压力随相位角的变化规律,探究了风轮仰角对风力机输出功率的影响。结果表明:增大风轮仰角会降低叶片表面压力,减小叶尖部分压差,使得叶片表面高涡量区域减小;添加风轮仰角会使叶片对塔筒影响减小,塔筒表面高涡量区域随着风轮仰角的增大逐渐减小,降低塔筒表面压力波动。当叶片经过塔筒时,塔影效应对风力机影响较大,风力机输出功率降低;当叶片竖直向上时,风力机输出功率达到最大。为风力机添加仰角后,随着风轮仰角的增大,风力机的输出功率与输出功率波动均呈现先增大后减小的趋势;风力机输出功率在风轮仰角为3°时最大,输出功率波动在风轮仰角为6°时最小。

西藏墨脱复杂地形X波段相控阵偏振天气雷达降水观测和反演方法研究

墨脱的降水变化与印度洋、孟加拉湾的水汽向内陆的输送、夏季风及我国东部雨带的推进过程联系紧密。它的独特地形与西南气流的相互作用在当地形成了年均降水超过2000 mm的降水带。但墨脱的复杂地形与有限的电力交通条件造成了降水观测的困难。2019年,第二次青藏高原综合科学考察研究任务专题项目在墨脱设置了一部X波段双偏振相控阵雷达,实现了对墨脱云降水的连续观测,对当地生态环境和云水资源研究以及高原东南水汽通道特征研究等具有重要的意义。文中使用墨脱X波段双偏振相控阵雷达2020年6-8月的观测数据,使用统计手段筛选降水回波片段,整合后构造得到符合墨脱复杂地形的混合仰角;利用2019年墨脱雨滴谱数据计算雷达参量、拟合得到适合墨脱地区降水特点的X波段天气雷达定量降水估测(QPE)公式。在此基础上选取2020年7-8月三次累积降水量、平均雨强、持续时间各不相同的降水过程,使用线性规划方案计算ΦDP(差分传播相移)、最小二乘拟合计算KDP(差分传播相移率)、“ZPHI”降水廓线算法订正ZH(反射率因子);以ZH和KDP为阈值,使用R(ZH)与R(KDP)分段估测降水,与单独使用R(ZH)和R(KDP)的估测结果进行对比;并基于降水估测结果和雷达参量的水平分布探讨降水分布与地形的关系。本文经过质量控制的ZH、 KDP数据质量有明显改善;使用统计方法构造的混合仰角有效回波面积大于使用SRTM1 v3.0地形数据构造的混合仰角,三次降水的典型时刻参量与过程累积降水量和平均ZH、 ZDR能初步反映降水变化与地形的关系;本文的降水估测公式和分段估测降水方法整体结果表现良好,各评估参数均具有较好的表现;结果表明:(1)墨脱雷达周边地形变化剧烈,根据现有地形数据构造的混合仰角在降水估测中表现不如本文统计筛选雷达观测数据得到的混合仰角数据;(2)本文采用的数据质控方法、定量降水估测公式与分段估测方法(PEM)在降水反演中表现良好,与单一的R(ZH)、 R(KDP)方法相比,得到的结果在CC和RMSE无明显变化的情况下,估测误差明显减小;(3)墨脱降水的发生发展或与西南气流被河谷偏北方山坡抬升有关,较大雨强、较小粒子直径的云位于地势平缓的谷底。

基于SGP4模型的空间站轨道精度分析

针对在地面站天线对空间站观测任务中,通常基于卫星工具包(satellite tool kit,STK)软件规划出天线对空间站的方位角和俯仰角,实现天线对空间站的自动跟踪.为了保证天线跟踪的准确性和可靠性,需要定期计算出准确的空间站轨道和天线的方位俯仰角,并更新规划任务.因此科学分析与评估空间站两行轨道根数(two line elements,TLE)长期预报精度,对地面站实现空间站的精准跟踪具有重要意义.本文以中国空间站(China Space Station,CSS)梦天实验舱为例,基于TLE数据,利用STK软件提供的简化常规摄动规模型(simplified general perturbations4,SGP4)模型计算空间站轨道以及空间站相对于西安地面站的方位角和俯仰角,并分析不同策略下的精度效果.试验结果表明:在第二天更新空间站的TLE,可以获得较好的轨道结果,从而更好地保障天线的跟踪精度.

基于数字高程模型的民航甚高频地空通信信号覆盖仿真

为解决起伏地形下民航甚高频(very high frequency,VHF)地空通信信号覆盖范围计算精度低、冗余度大、数字高程模型(digital elevation model,DEM)数据获取缺乏自动性及信号覆盖图可视性差等问题,采用最大遮蔽角截止法等进行仿真研究。首先,考虑计算覆盖范围存在误差,提出利用反距离加权(inverse distance weight,IDW)插值法提高地形辨识度并在计算覆盖范围时考虑大气损耗;其次,为解决DEM数据获取缺乏自动性,利用MATLAB编码自动提取;再次,考虑遮蔽角计算存在冗余,采用“最大遮蔽角截止法”降低计算量;最后,为使覆盖范围直观可视,绘制二维及三维的覆盖显示图。结果表明,这些方法使遮蔽角计算量相较改进前降低了约64.60%,信号覆盖精度相较改进前提高了约3.315%。改进的覆盖仿真程序可以为VHF地面通信台站选址及飞行航线规划提供有效支撑。

水星可照时间与搜索半径影响因素研究

采用光线追踪算法模拟起伏地形下的可照时间时,随着对地形遮蔽状况进行搜索的半径不同将直接影响到可照时间计算的准确性与高效性.本研究基于DEM数据,针对水星独特的轨道运动特征,太阳高度角随水星运动变化缓慢的特点,研究了水星2种典型地貌下不同太阳高度角的搜索半径和基于搜索半径的平均可照时间变化状况.同时构建了以5种影响搜索半径与可照时间的因子作为输入变量,分别以搜索半径与平均可照时间作为输出变量的BP神经网络.模型通过了检验,5种影响因子与搜索半径影响的显著性由高到低:太阳高度角>高程标准差>地形开阔度平均值>地形起伏度>地表粗糙度平均值;与平均可照时间影响的显著性由高到低:太阳高度角>高程标准差>地表粗糙度平均值>地形开阔度平均值>地形起伏度.该模型可为计算水星最搜索半径以及可照时间提供参考.