便携式高频地波雷达东海洋山海域探测深度试验

为了验证采用紧凑型接收天线的便携式高频地波雷达系统(OSMAR-S)的探测性能,于2007年11月在洋山海域进行了OSMAR-S与其他海洋测量设备的现场探测对比验证试验。试验设计了定点固定水深测量与坐底剖面测量相结合的连续现场对比监测方式,把雷达获得的表面流探测数据与其他设备得到的不同深度的海流观测数据进行对比。通过试验数据分析,OSMAR-S系统的探测深度和精度都得到了验证,能够满足实时监测海洋表面流的需要。同时试验也填补了高频雷达探测深度没有试验验证的空白。     

高频地波雷达近海表面流探测初步研究

针对高频地波雷达的天线阵通常十分庞大,使得其推广应用比较困难这一特点,利用海洋回波进行了接收通道的自校准,研究了一种便携式的交叉环/单极子天线在高频地波雷达近海海洋表面流探测中的应用.采用不同工作频率观测所测得的海洋表面流的日变化规律与所探测海域的洋流特征相符合;并通过与采用相控阵接收的高频地波雷达OSMAR2000的现场对比验证试验,证明了近海海洋表面流探测可采用便携式的小天线.     

亚帆赛间便携式高频地波雷达的海态观测

2010年汕尾亚运会帆船赛期间,便携式高频地波雷达OSMAR-S作为一种重要的海态监测手段在汕尾海域进行观测,为保障亚帆赛顺利举行提供海洋气象服务。雷达获取了汕尾海域近1个月连续的流速、流向、浪高、浪周期、风向和风速等数据,并与海监船搭载的海流计与测风仪以及现场布放浮标实测的数据进行了对比。对比结果表明:雷达与现场海洋仪器的观测数据较为吻合,初步验证了OSMAR-S探测近海海态特别是风浪参数的能力。     

高频地波雷达的电离层杂波识别新试验

为了验证电离层杂波干扰的存在及研究其对高频地波雷达性能的影响,武汉大学电波传播实验室在浙江舟山东沙试验基地利用高频地波雷达完成了电离层杂波干扰识别新试验.试验采取改变地波雷达发射天线结构即改变发射天线的波束指向,使得电磁波垂直向上发射,进行电离层垂直探测试验;同时也有部分能量向海洋传播,从而获得海面Bragg散射回波.与此相对应地采用垂直极化的三元八木天线向海洋表面发射电磁波,同时获取海洋回波与电离层杂波.详细介绍了试验过程并对实测结果进行了初步分析,并介绍了新近研制的便携式高频地波雷达OSMAR-S的系统结构及其工作参数.     

遥感技术及其应用

Y2000-62207-134 0013956遥感(含4篇文章)=Session 8A:remote sensing[会,英]//1999 Oceans,Vol.1.—134～156(PC)本部分收录4篇论文,题名为:风易变性对低风速散射测量的影响,海空互作用与循环用的卫星海洋表面应力测量,采用超频谱传感器的无源鲸跟踪的可能性,以及海洋中的流可视化:实验室生物发光试验的意义。     

基于笔形波束扫描雷达散射计的海洋表面流测量

为了研究利用雷达散射计进行海洋表面流直接测量的可行性,本文对传统雷达散射计系统参数进行了改进,推导了相关系数模型及去相关因素的表示形式,给出了相位误差模型,并建立了利用雷达散射计进行海洋表面流直接测量的端到端仿真模型.仿真结果表明,在风速大于5m/s的海况条件下,顺轨向和交轨向速度分量标准差可达0.1m/s以下.风速大于7m/s时,可用于海洋表面流反演的刈幅范围大于散射计刈幅宽度的40%.新型散射计的风单元传递误差无论是在低风速还是在高风速条件下均优于扇形波束扫描散射计的风单元传递误差.     

高频地波雷达OSMAR2000通过验收

武汉大学高频地波雷达课题组经过 2年多的艰苦努力 ,自行研制了两台高频地波雷达ＯＳＭＡＲ2 0 0 0 .完成了国家 86 3计划海洋领域的重大项目“高频地波雷达海洋环境监测技术”的研究项目 ,于 2 0 0 0年底通过国家科技部的验收 .该项目研制的高频地波雷达ＯＳＭＡＲ 2 0 0 0采用一发八收相控天线 ,在中国大陆沿海首次实现双站岸基雷达监测海洋表面动力学参数 ,得到了海洋表面矢量流图 .与传统海洋测量仪器的对比验证试验表明 ,ＯＳＭＡＲ2 0 0 0探测海流和海面风向的距离超过2 0 0公里 ,探测浪高的距离达 15 0公里 .其整体性能已达到国外同…     

MUSIC算法提取海洋表面径向流方位的信号预处理

阐述从高频地波雷达海洋回波反演海洋表面流中,使用MUSIC算法提取径向流方位必须的信号预处理.海洋回波首先经线性调频中断连续波(FMICW)波形解调,分成不同距离元海洋回波.在各通道独立接收的海洋回波谱分析的基础上,针对每一距离元进行通道幅度的软件校准.接着从每一距离元合成的海洋回波多普勒功率谱中,分离包含海洋表面流信息的一阶谱区,再依据“局部噪声阈值扣除法”确定其中的可用信号.最终由MUSIC算法提取每一可用信号(其频偏对应径向流速)的多个存在方位,从而获得海洋表面径向流场的完整信息.本文阐述预处理使用的各种算法、效果及实测信号的部分处理结果.     

动态高温温场测量装置研究

在航天用试验件进行风洞加热热试验时,试验件表面特定区域的温度可达1700℃甚至更高,对这种动态变化的区域温度场测量难度较高,一般只能使用成本昂贵的测温型红外热像仪实现,且对恶劣环境适应性不高。采用比色温度测量模型,选用近红外波段900nm附近两个波长作为测量波长,采用高动态响应CCD成像器件作为信号采集设备,保证了两个测量通道采集图像在空间上的对应,实现了测量区域内温度分布的测量,测量帧频最高可达40Hz,测量准确度小于6%。     

超外差超光滑表面粗糙度的测量

本文用纵向塞曼双频稳频He-Ne激光器作光源,采用光学超外差技术与相位高精度测量相结合.测量超光滑光学表面粗糙度,测量灵敏度为0.1nm量级.实验结果与理论分析相符合,且与其他测量方法进行了比较.     

阻抗劈散射的MM-PO混合算法研究

本文系统地研究了各向异性阻抗劈绕射的矩量法-物理光学(MM-PO)混合算法.首先研究了任意各向异性阻抗面的物理光学模型,推导出表面物理光学等效电磁流计算式.其次,提出了一种有效的含Hankel函数的弱振荡被积函数无穷积分处理方法.最后,将作者已公开发表的修正绕射电流基函数用于各向异性阻抗劈散射场研究,数值结果和已知的一致性绕射理论结果高度吻合.     

复杂动态海面与目标电磁散射及回波仿真研究现状与展望

海洋表面是一种高度不规则和时空不重复的复杂动态体系。海杂波是雷达电磁信号照射到海面产生的大量散射体回波的叠加,受风力、洋流、海浪等的影响呈现非均匀性和非平稳性。海杂波信号对海上目标的探测具有一定的干扰作用,尤其是高海情条件下,海浪起伏更加剧烈,目标信号极易淹没在强海杂波信号中,严重限制着雷达对海上目标的检测能力。海杂波及目标电磁散射特性研究是提升复杂海洋环境下目标检测能力的基础,以电磁波与实际复杂动态海面及目标电磁散射机理为基础,形成实际海洋环境下目标回波数据,对海杂波及目标雷达回波特征分析,实测数据集的补充,均存在重大意义。为了让更多相关研究者获得基于物理机理的复杂海环境与目标回波仿真方法近些年的发展和未来趋势,该文总结了回波仿真的3类方法,并针对海面与目标仿真场景特点,分析了3类方法的优劣和适应性,给出了部分仿真结果;还介绍了一些基于实测的回波数据集,可方便学者对回波特性进行分析;最后对复杂海面与目标回波仿真方法和特性研究的发展趋势进行了展望。      

Rayonnement de réseaux périodiques avec conducteurs et diélectrique

This paper describes a numerical analysis of the electromagnetic behaviour of dielectric panels. These dielectric panels are very large comparatively to the wave length and can be seen as infinite and plane array of dielectric cylinders, illuminated by a plane wave. These dielectric cylinders can have any cross section and can include metallic wires. The conduction currents on the metallic wire and deplacement currents in the dielectric cylinders are determinated by a system of linear equations obtained by the application of vectors potential formalism. The use of Poisson summing gives the possibility to explicite over squared or rectangular boundaries the integrals relative to the deplacement currents. The knowledge of the currents permits to calculate the transmission coefficient of the array. The comparison between the numerical results and experimental measure shows a good agreement.     

Scattering of TE-polarized EM wave by discontinuity in groundeddielectric layer

The two-dimensional problem of EM wave interaction with a dielectric discontinuity in an infinite grounded dielectric layer is studied. An electric field integral equation (EFIE) for TE illumination has been derived based on the Green's function for the electric field produced by induced polarization currents in the discontinuity region. Impressed electric fields consist of either plane waves incident from space above the dielectric layer or surface waves supported by that layer. Method of Moments (MoM) numerical solutions for the induced electric field in the discontinuity region are implemented. The amplitudes of surface waves excited by excess discontinuity-region polarization currents are calculated, as well as the pattern of the scattered field and the associated scattering width. It is observed that the excitation of a surface-wave mode reduces the back scattered radiation for TE-polarized plane wave incidence. The accuracy of the theory is verified by comparison of numerical results with those of existing studies     

Dark currents in long wavelength infrared HgCdTe gated photodiodes

The fabrication of HgCdTe photodiodes using plasma-induced p-to-n type conversion for junction formation shows promise in improving array uniformity and device yields in comparison to more traditional fabrication technologies. Previously, characterization and analysis of the diode current-voltage (I–V) characteristics of fabricated devices have given indications that surface-leakage current mechanisms are limiting device performance. To further investigate the effectiveness of the surface passivation employed in the fabrication process, gated-diode structures have been fabricated. The gated-diode structure enables the semiconductor surface potential to be varied, thus allowing the characteristics of surface-leakage currents and their effect on device performance to be evaluated. The long wavelength infrared (LWIR) HgCdTe gated photodiodes used in this study have been characterized using I–V measurements for variable gate-bias voltage and variable temperature. Analysis of the experimental results indicates that plasma-induced type conversion produces an n (lightly doped)-on-p junction that is highly susceptible to a trapped positive charge in the passivation layer, which results in increased surface-tunneling currents. Modeling of the various dark-current mechanisms is used to show the effect on dark-current generation of the surface band bending induced by variations in surface potential. In addition, temperature-dependent I–V measurements and analysis have also been conducted.     

海上舰船目标检测预警系统

针对海上石油开采设备的保护,介绍了一种适合在海上长时间工作的水面舰船检测预警系统。着重论述了以DSP和FPGA为核心的数字处理模块的硬件设计。在该硬件系统基础上,提出了一种适用于DSP处理的被动目标检测算法。简单介绍了软件系统的编写流程和实验结果。实验表明,该系统能够有效地检测到舰船并且报警,具有一定的实用价值和参考意义。     

Measurement of river surface currents with coherent microwave systems

River surface currents have been measured using coherent microwave systems from a bridge, a cableway, several riverbanks, a helicopter, and an airplane. In most cases, the microwave measurements have been compared with conventional measurements of near-surface currents and found to be accurate to within about 10 cm/s. In all cases, the basis for the microwave measurement of surface current is the Doppler shift induced in the signal backscattered from the rough water surface. In this paper, we outline the principles of the measurements and the various implementations that have been used to make microwave measurements of surface currents. Continuous-wave (CW) microwave systems have been used from a bridge to make long-term measurements of surface currents; these are compared with current-meter measurements and with time series of stage. A compact CW system has been developed and used on a cableway to measure surface currents at various distances across a river; these measurements have been compared with acoustic ones. Pulsed Doppler radars have been used to measure river surface currents from a riverbank, a helicopter, and an airplane. In the first two cases, comparisons with both current-meter and acoustic measurements have been made. We suggest that the CW system would be preferable to the pulsed Doppler radar to make such measurements from helicopters in the future. Finally, we consider the implications of our experiments for the measurement of surface currents from aircraft or satellites using interferometric synthetic aperture radars (INSARs). We find that a combination along-track, cross-track INSAR is necessary but that significant limitations are inherent in the technique.     

Cadmium sulfide passivation of InGaAs/InP mesa p-i-n photodiodes

A cadmium sulfide (CdS) passivation process was demonstrated for the first time on InGaAs/InP p-i-n mesa photodetectors. The passivated devices produced lower reverse bias leakage currents in comparison to devices that received only a thermally deposited SiO₂ film. The subsequent deposition of SiO₂ on the passivated devices produced virtually no change to the aforementioned leakage currents even after undergoing a 3-h, 300°C thermal treatment. In contrast, similar SiO₂ capped devices, fabricated without the CdS passivating layer, show a large increase in leakage current when subjected to the same thermal cycle. Leakage current versus mesa diameter measurements suggest these results are due to reduce surface recombination at the exposed mesa sidewall. X-ray photoelectron spectroscopy (XPS) results indicate the S:Cd ratio of these films to be 0.77.