使用金属球定标X波段固态天气雷达

天气雷达的定标直接影响着探测参量的准确度,因此对于雷达数据的应用是至关重要的。利用金属球对X波段固态天气雷达的反射率因子、差分反射率和径向速度同时进行标定。根据待测固态天气雷达的特点,制定了详细的定标实施方案,定标过程中选取远近两个测试点,采用3种不同类型的标准球。试验结果表明:反射率因子理论值和测试值平均相差3dB,标准球的材质对反射率因子的定标影响较小,标准球的直径对定标的有较大的影响;随着采样点数的减少不同类型的标准球对应的反射率因子存在下降的趋势,反射率因子的观测值在采样点数为256、128时分别比采样点数为512时平均降低0.12dB和0.4dB;金属球对应的差分反射率平均值为1.7dB,与理论值存在较大偏差,需要进一步分析原因;雷达观测的径向速度与通过GPS信息的计算值相差小于0.1m/s;金属球对应的反射率因子随方位角、仰角的变化可以反映雷达天线方向性图。试验为双偏振天气雷达定标提供参考。     

风云二号卫星资料在雷达降水估测中的应用

针对单一的气象卫星或者天气雷达估测降水存在的一些缺陷,介绍了风云二号(FY-2)气象卫星资料的一种应用方法。先根据红外亮温阈值划分降水云系,再选用适合的雷达反射率因子-降水强度(Z-I)模型进行降水估测;雷达未覆盖区域,基于不同红外亮温区各等级降水及其对应的亮温差的统计结果,查找最接近的降水强度并用不同云型的平均归一化误差进行修正。以2011年6—8月淮河流域地面站点1h雨量计资料为检验资料,验证卫星资料的应用效果。发现添加卫星资料后,会导致原本偏低的雷达估测1h降水量偏高,但准确估测样本量以及相似系数均有所增加;为雷达未覆盖区域降水量的反演提供资料的同时,对于雷达有效覆盖的区域而言,能够去除雷达定量估测降水中的奇异点。     

利用雨量雷达构建面雨量自动监测系统

雨量雷达是专门适用于气象目标中降雨量定量测量的雷达设备,高分辨区域面雨量自动监测系统则是应用雨量雷达进行区域内雨量监测,监测系统通过雨滴谱仪与模型算法解决衰减订正和雨量数据计算准确度问题,可以方便地获得区域内的降雨分布情况和有效的降雨量,与常规单点雨量定量测量相比,在较大区域内测量雨量,整体上精度高,成本低。经过大理监测区域的验证,面雨量自动监测系统具备较高的测量精确度,具有较好应用前景。     

37 GHz和94 GHz的大气微波衰减比较分析

毫米波更接近云粒子的尺度,因此毫米波及短厘米波段雷达已被应用于云层的探测,美国与加拿大的云卫星计划(CloudSat)将要上3 mm云雷达(CPR),如何与已在天上的TRMM/PR结合,获得从薄云到浓厚云的垂直结构信息,是一个值得关注的课题。但是,毫米波云雷达探测,必须考虑的问题之一是大气衰减订正。主要比较分析了在37 GHz和94 GHz大气的衰减特性,目的是对星载94 GHz云雷达进行大气的衰减订正。计算分析了在不同云、大气条件下37 GHz和94 GHz
的大气衰减,得出如下结论:①大气气体的微波吸收在测云波段产生明显的衰减,其中水汽衰减效应变化很大;即将上天的空间94 GHz测云雷达必须有水汽衰减订正方案。②37 GHz和94 GHz雷达测云,由于大气和云衰减不同和雷达反射率的很大差异,导致雷达回波信号强弱不同。③对云层较薄、含水量较少的云,在不计雷达参数的情况下,37 GHz雷达回波信号不如94 GHz测云雷达,也就是说94 GHz对薄云有更强的探测能力;对云层较厚、含水量大的云,由于强衰减的作用,94 GHz雷达回波信号小于37 GHz雷达。④从大气衰减的不利因素方面考虑,空间94 GHz雷达测高层薄云的效果最好;测低层薄云时需要考虑气体衰减订正;因浓厚云的强衰减作用,探测其中下部的能力大大减弱,不仅要进行衰减订正,而且要借助其它信息来反演整个云层的含水量垂直分布。⑤为了获得从极薄到极浓厚云的垂直分布探测能力,未来测云雷达系统最好采用双波长甚至三波长(如94、37和13 GHz)。     

天气雷达网资料拼图方法研究

天气雷达组网拼图,是克服单部雷达探测范围有限,发挥多部雷达相互辅助大范围监测灾害性天气的有效手段。本文在分析现有天气雷达组网拼图方法和存在问题的基础上,对天气雷达组网拼图的资料网格化、重叠区域处理、资料投影等方面作了进一步研究。对雷达反射率因子网格化问题,对比分析了Barnes和双线性插值算法的特性,说明Barnes插值算法网格化资料平滑且能较好地保存雷达资料特征;在重叠区域的资料订正方面,采用概率分布方法,实现了对雷达资料作用距离和天线指北等系统误差的订正,结果表明订正后的资料在重叠区域中各雷达资料的吻合度得到了加强;最后采用兰勃特投影法将天气雷达组网拼图投影到统一底图中。     

基于JAVA与MATLAB混编技术的毫米波测云雷达回波衰减订正仿真软件设计

毫米波雷达具有更接近小粒子尺度的短波长,更适合用来探测弱云,是云三维精细结构的重要探测工具。但是相比于厘米波段,毫米波信号在云雨天气的传输过程中更易受到云、雨、大气气体的衰减,导致回波面积的减小,毫米波雷达观测值要小于实际值,因此在毫米波测云雷达的探测与反演研究中需要考虑大气衰减的影响。根据逐库订正法,利用JAVA与MATLAB混合编程技术,设计了毫米波测云雷达回波衰减订正软件。该软件集合了JAVA和Matlab两者的优点,在高速计算的同时兼顾了可视化。     

星载雷达在评估地基天气雷达非降水回波识别算法效果中的应用

非降水回波识别算法的效果直接影响着雷达数据后续应用（如定量降水估测）的结果,因此对其进行客观定量检验是很重要的。文中所用算法在SWAN系统雷达反射率因子质量控制算法基础上增加了晴空回波识别算法,使用回波延展度因子并增加高度限制来对晴空回波进行识别和去除。使用星载雷达反射率强度数据与非降水回波去除前后的地基雷达数据进行时空匹配,对非降水回波识别算法效果进行客观的直观和定量验证。参照星载雷达观测结果,文中算法针对与降水回波无混叠的超折射回波有很好的识别效果,效果优于存在降水与超折射混叠的情况,当降水回波中存在与超折射回波水平纹理相近的对流降水时,经算法处理后该部分回波会丢失部分信息。针对存在降水与超折射回波混叠的情况,将算法处理前后的地基雷达降水区域反射率因子分别与星载雷达数据进行比较,结果表明经算法处理后的数据更接近星载雷达观测值。评价结果可为算法适用性分析及改进提供依据。     

星载雷达在评估地基天气雷达非降水回波识别算法效果中的应用

非降水回波识别算法的效果直接影响着雷达数据后续应用（如定量降水估测）的结果，因此对其进行客观定量检验是很重要的。文中所用算法在SWAN系统雷达反射率因子质量控制算法基础上增加了晴空回波识别算法，使用回波延展度因子并增加高度限制来对晴空回波进行识别和去除。使用星载雷达反射率强度数据与非降水回波去除前后的地基雷达数据进行时空匹配，对非降水回波识别算法效果进行客观的直观和定量验证。参照星载雷达观测结果，文中算法针对与降水回波无混叠的超折射回波有很好的识别效果，效果优于存在降水与超折射混叠的情况,当降水回波中存在与超折射回波水平纹理相近的对流降水时，经算法处理后该部分回波会丢失部分信息。针对存在降水与超折射回波混叠的情况，将算法处理前后的地基雷达降水区域反射率因子分别与星载雷达数据进行比较，结果表明经算法处理后的数据更接近星载雷达观测值。评价结果可为算法适用性分析及改进提供依据。     

相控阵天气雷达站环境参数计算及评估系统研发

作为S波段新一代天气雷达的重要补充,目前广东省正加快建设X波段双极化相控阵天气雷达;如何更好地做好优化布局提升全网覆盖率和探测能力,站点选择是否科学合理显得尤为重要;文章设计一套全新的基于数字高程DEM的探测环境参数智能分析系统,客观、定量、自动计算探测净空投影面积、净空占总投影面积比例、投影阻挡面积比例、探测净空体积、静锥盲区体积、低空盲区体积、扫描立体空域完备度等,在现场选址时能够1分钟内输出综合分析结果和建议;作为辅助选址系统,已经在广东省26部X波段双极化相控阵天气雷达选址中应用,输出结论对现场选址起到了很好的指导性作用,为雷达系统建设快速提供科学决策依据.     

Ka波段雨衰减时间序列的合成及性能仿真

在Ka波段(30/20GHz)卫星通信系统传输中,降雨衰减是导致信号衰落的重要原因之一.为了通过功率控制算法来补偿动态雨衰减,用ITU-R降雨衰减预测模式,通过最小二乘曲线拟合方法详细推导我国北京地区雨衰减统计分布的参数,获得北京地区的动态雨衰减时间序列;用下行链路雨衰减预测上行链路雨衰减的方法,为上行链路功率控制算法奠定了基础;采用QPSK调制,分别考虑AWGN信道和莱斯多径衰落信道,将有小雨、中雨、大雨这三种降雨与没有降雨情况进行性能对比,仿真结果表明雨量越大对系统的影响越严重.     

Calibration for X-band Solid-state Weather Radar with Metal Sphere

Calibration of weather radar has a direct impact on the accuracy of detection variables and therefore is critical for most applications of radar data.In this paper,we will focus on simultaneous calibration of reflectivity (Z),differential reflectivity (ZDR) and radial velocity (V) for X-band solid\|state weather radar.To conducting calibration experiments,detailed calibration implementation plan is formulated,two test points are selected and three kinds of spheres are used.Experiments results show that the theoretically calculated Zth and measured Zm have a mean bias of 3 dB and the bias is more affected by the radius than the material of the spheres.The reflectivity has a downward trend and decreases successively from 0.4 to 0.12 dB along with the decent of sampling number.The mean ZDR is about 1.7 dB,which is large deviation in comparison with the theoretical value.The radial velocity (Ve) calculated from GPS information and observed (Vob) have a difference less than 0.1m/s.It is also found that the radar reflectivity variation of metal sphere with azimuth and elevation angles can reflect radar antenna pattern.This calibration experiments provides reference for Dual\|polarization radar.     

Digital processing of weather radar signals for rainfall estimation

Abstract

Raw weather radar reflectivities are processed and registered to the ground before radar rainfall measurements are used conjunctively with rain-gauge data to produce areal surface rainfall estimates. However, there are several factors causing errors in the returned power of weather radar signals, as well as other sources of error affecting the accuracy of radar rainfall measurements. In this study, several deterministic corrective techniques are applied to the digital processing stage of raw radar data to consider a number of sources of error, namely non-rainfall echoes, signal attenuation and wind effect. The results indicate that the deterministic techniques are still a necessary step for the ultimate improvement of surface rainfall estimates by the use of weather radar.     

Estimating tropical rain attenuation on the Earth-satellite path using radar data

Radar-return echoes, known as ‘reflectivity’, are exploited in the course of estimating rain attenuation along a slant path. Relevant radar gates or ‘range bins’ are identified to correlate a specific satellite path. The reflectivity value of each range bin is converted to rainfall rate using established radar reflectivity values – rainfall rates, (Z–R relation). Specific attenuation is then derived for all associated range bins. The attenuation for each bin is the product of specific attenuation and its effective path length. The summation of attenuation endured by all range bins is inferred as the attenuation along the slant path. In this study, an X-band slant path rain attenuation was estimated using 2.85 GHz (S-band) Terminal Doppler Weather Radar (TDWR) data. A technique to estimate rain attenuation by exploitation of radar information is elaborated in this article. Comparisons between the radar-derived attenuation estimations and actual satellite signal measurements are also presented. The findings were verified by comparing the generated values to the directly measured rain attenuation from the Razak satellite (RazakSAT). Radar reflectivity data were obtained from Kuala Lumpur International Airport (KLIA) radar station operated by the Malaysian Meteorology Department (MMD). Preliminary findings using the most recent Z–R relation (i.e. the generated radar-derived rain attenuation estimations) appear to show lower values than the actual measurements.     

Pre-processing of images from shipborne X-band wave measuring radar

It is inevitable that the movement of vessels on the sea will be affected by the marine environmental extreme value parameters, such as wind, current, and wave. Driven by these factors, the vessels will produce the following movements: horizontal displacement, heave, and sway. With the shipborne X-band wave measuring radar installed on the vessel, the movements of the vessel will lead to the deviation between the actual position of the radar beam and the places we expect. It will result in an error that the intensity showed on the echo image is not the expected one. A pre-processing algorithm is developed to weaken the influence of the movements of vessel on information inversion of the ocean wave fields imaged by X-band radar. The algorithm utilizes the results of vessel motion model to correct the images from shipborne X-band wave measuring radar. Compared with simulated image sequences influenced by vessel motion, the non-direction wave height spectrum extracted from corrected image sequences matches well with that obtained from the original image sequences uninfluenced by vessel motion.     

天气雷达反射率数据方位分辨率提高

天气雷达反射率数据方位分辨率的提高,对中小尺度强对流天气过程的精细探测有重要的意义。以雷达气象积分方程为基础,通过对天气雷达反射率方位数据的过采样,建立雷达测量的低分辨反射率数据与真实气象目标高分辨率数据之间的矩阵方程,提出使用截断奇异值分解算法优化超分辨反演方程逆求解及改善解稳定性。实验结果验证,该方法对反射率数据方位分辨率的提高是行之有效的。     

Retrieving the median droplet diameter from Ka‐ and W‐band dual‐wavelength Doppler radar measurements

In this letter, a novel method is proposed for estimating the median droplet diameter by using the K_a‐ and W‐band dual‐wavelength differences of the mean Doppler velocity and the Doppler spectrum width. The estimated median diameter together with the dual‐wavelength ratio of the radar reflectivity can be effectively used to measure and compensate the attenuation in precipitation or clouds. The estimate of the median diameter is not affected by the attenuation and does not require an accurate radar calibration. Furthermore, the vertical air flows and the turbulent broadening of the Doppler spectra have no influence on the estimate.     

Uncertainty analysis of radar rainfall estimates over two different climates in Iran

Accuracy of rainfall quantification is one of the most important concerns in meteorological and hydrological modelling. Satellites and weather radars can provide meteorological information with higher temporal and spatial resolution than ground stations. Rain gauges measure rain rate directly; however, weather radars estimate rain rate by converting radar reflectivity aloft to rain rate at ground level. This conversion with a power law relation between radar reflectivity and rain rate could be altered from place to place or in various precipitation types. This variety may be the source of errors and uncertainty of radar rainfall estimates. One way to assess the uncertainty of radar rainfall is simulation of rainfall fields. In this article, after calibrating two radars located in the south-western and northern parts of Iran, uncertainty of rainfall estimates of these radars has been analysed using the Gaussian Copula model. Reliability of this model was examined for 10% of the rainfall events that were not included in the simulation process. Obtained results of the current research indicate that recalibration of radars can considerably reduce bias and root mean error. In addition, the Copula-based model can generate rainfall fields with similarly spatial structures to those of observed rainfall data.     

新一代多普勒天气雷达网探测数据对比分析系统

我国即将建成由216部多普勒天气雷达组成的观测网,组网雷达数据对比分析是及时发现雷达网故障、为雷达定标提供参考,提高短时临近天气预报准确率的基础。为解决上述问题,研发了雷达组网数据对比分析系统。首先,针对距离衰减和波束展宽对雷达探测数据的影响,提出利用相邻雷达等距离线垂直剖面内的网格数据进行对比分析;然后,为了满足实时计算需求,提出快速等距离线坐标变换算法,算法可节约85%的计算时间;针对雷达数据空间分布特点,提出三维混合插值算法,以便最大限度保留原始数据特征,提高数据对比分析精度。系统可自动处理相邻雷达时间同步数据,统计分析等距离线垂直剖面内的数据,实现组网数据可靠性和一致性的客观评估分析。实验结果表明,软件系统能够满足组网雷达数据客观评估需求。     

A microfabricated electrochemical actuator for large displacements

A large-displacement electrochemical actuator was designed, fabricated, and tested. The large displacement is obtained by using a corrugated membrane made by physical vapor deposition of Parylene sandwiched with an intermediate layer of sputtered platinum. The layered structure is approximately 8-μm thick, with 26 grooves approximately 120-μm deep, and with a radial period of 350 μm. The electrochemical cell consists of platinum electrodes with a 1 M H₂ SO₄ solution. Hydrogen and oxygen gas is generated to displace the membrane. Although the actuator can operate at a voltage as low as 1.23 V, the experimentally determined efficiency of converting electrical energy to mechanical work is only 0.37%. The governing equations for the conservation of mass, momentum (equilibrium), energy, and the entropy generation rate were formulated assuming that the gas bubbles either nucleate without growth or grow without nucleation. For the nucleation case, simulations were performed for constant pressure isothermal actuation, and the average experimental efficiency was bounded by simulations with gas bubble radii between 1×10^-6 m and 1×10^-6 m. The predicted ratio of the power dissipated to the electrical power supplied is 1.37 for isothermal actuation     

多云多雨地区遥感初探

多云多雨地区是指以年平均降水量不小于800mm、气候湿润、降水丰沛、年晴天日数少于50天、常年云雨覆盖的包括陆地与海洋的广大湿润地区。这也包括人口增长迅速、城市化进程显、经济最为活跃的地区。由于天气条件的影响使光学遥感在这些地区的应用受到了很大限制，而具有全天候工作能力的雷达遥感数据具有广阔的应用前景。本简要阐述了多云多雨地区遥感的特点和意义，分析了遥感技术尤其是微波遥感技术在这一地区各领域的应用前景，指出了相关基础设施建设的紧迫性以及服务机制转变的重要性，并提出了将多云多雨地区遥感与区域科学系统研究相联系的观点。