机载双基地SAR实测数据成像

建立双基地SAR的单基地等效模型,分析了系统时间同步误差的机理;提出了双基地SAR回波中的直达波数据进行时间同步误差校正的算法;在双基地SAR单站等效模型的基础上,利用时变阶梯变换算法进行成像处理。经过理论分析,实测数据处理验证,这一算法是有效的,能够校正双基地SAR时间同步误差,较好地进行实测数据的成像处理。     

近空间被动双站SAR的成像性能分析

近年来,近空间受到了越来越广泛的关注。近空间飞行器兼具卫星和航空飞机的优点,能提供类似卫星的宽覆盖、长续航能力和飞机的快速响应能力,这为研究新体制遥感技术创造了条件。基于此,文章提出了一种基于近空间平台的被动双站合成孔径雷达(SAR)成像方法。首先,通过分析近空间被动双站SAR的空间几何模型,建立了其相应的SAR回波信号模型;然后,根据发射机和接收机对成像目标产生的多普勒效应,对近空间被动双站SAR成像的距离分辨率和方位分辨率进行了分析和仿真,并分析了近空间被动双站SAR存在的方位向调频率空变特性。最后,以接收机静止模式为例,对其成像处理进行了仿真。理论分析和仿真实验结果表明,近空间被动双站SAR是一种具有良好应用前景的遥感新技术。     

双基地天气雷达系统的有效照射体积

根据"有效照射体"的基本概念,采用微分理论来回避椭球面近似为平面的假设,推导了双基地雷达系统有效照射体积表达式,证明双基地雷达系统有效照射体积与单基地雷达有效照射体积之比值V_b/V_m,在数值上等于双基地系统主站极轴长度R_t相对于半长轴长度a的导数.有效照射体积数值计算结果与以往相同,放宽了推导过程中的假设条件,显得更加严谨、易懂.还给出了双基地雷达系统各几何量(如V_b/V_m、R_t、主站共面方位Φ、辅站极轴长度Rr、辅站共面方位Φ_r、双基地角β)之间的一些关系式,分析了在双基地雷达系统探测过程中有效照射体积随有关量变化的特征,为双基地偏振雷达系统天线控制、资料处理、旁瓣影响分析、探测精度提高等提供理论依据.     

雷达遥感新技术及其在灾害性天气探测中的应用

为了推进我国雷达新技术的发展及其在灾害性天气监测和预测中的应用，分析了国内外雷达遥感新技术的发展现状，总结了我国特别是中国气象科学研究院在双多普勒雷达、双基地多普勒雷达、双线偏振雷达、相控阵雷达、激光雷达在灾害性天气的热力、动力和微物理中尺度结构探测中的应用研究所做的部分工作及其在外场试验中的应用情况。这些技术大部分是在新一代天气雷达技术上发展起来的。     

A Novel Method for Real-Time Monitoring of Channel Siltation Based on Bistatic Scattering Theory

Monitoring the thickness changes of channel siltation is paramount in safeguarding navigation and guiding dredging.This paper presents a novel method for realizing the field monitoring of channel siltation in real time.The method is based on the bistatic scattering theory and concerned more with the receiving and processing of multipath signal at high-frequency and small grazing angle.By use of the multipath propagation structure of underwater acoustic channel,the method obtains the silt thickness by calculating the relative time delay of acoustic signals between the direct and the shortest bottom reflected paths.Bistatic transducer pairs are employed to transmit and receive the acoustic signals,and the GPS time synchronization technology is introduced to synchronize the transmitter and receiver.The WRELAX (Weighted Fourier transform and RELAX) algorithm is used to obtain the high resolution estimation of multipath time delay.To examine the feasibility of the presented method and the accuracy and precision of the developed system,a series of sea trials are conducted in the southwest coast area of Dalian City,north of the Yellow Sea.The experimental results are compared with that using high-resolution dual echo sounder HydroBoxTM,and the uncertainty is smaller than ±0.06 m.Compared with the existing means for measuring the silt thickness,the present method is innovative,and the system is stable,efficient and provides a better real-time performance.It especially suits monitoring the narrow channel with rapid changes of siltation.     

Sea-surface acoustic backscattering measurement at 6–25 kHz in the Yellow Sea

Sea-surface acoustic backscattering measurements at moderate to high frequencies were performed in the shallow water of the south Yellow Sea, using omnidirectional spherical sources and omnidirectional hydrophones. Sea-surface backscattering data for frequencies in the 6–25 k Hz range and wind speeds of(3.0±0.5)and(4.5±1.0) m/s were obtained from two adjacent experimental sites, respectively. Computation of sea-surface backscattering strength using bistatic transducer is described. Finally, we calculated sea-surface backscattering strengths at grazing angles in the range of 16°–85°. We find that the measured backscattering strengths agree reasonably well with those predicted by using second order small-roughness perturbation approximation method with "PM" roughness spectrum for all frequencies at grazing angles ranged from 40° to 80°. The backscattering strengths varied slightly at grazing angles of 16°–40°, and were much stronger than roughness scattering. It is speculated that scattering from bubbles dominates the backscattering strengths at high wind speeds and small grazing angles. At the same frequencies and moderate to high grazing angles, the results show that the backscattering strengths at a wind speed of(4.5±1.0) m/s were approximately 5 d B higher than those at a wind speed of(3.0±0.5) m/s. However, the discrepancies of backscattering strength at low grazing angles were more than 10 d B. Furthermore the backscattering strengths exhibited no significant frequency dependence at 3 m/s wind speed. At a wind speed of 4.5 m/s, the scattering strengths increased at low grazing angles but decreased at high grazing angles with increasing grazing angle.     

双基地多普勒天气雷达天线架设高度设计及旁瓣污染分析

在双基地多普勒天气雷达的试验和应用研究中发现, 天线的高度设计和旁瓣污染是双基地天气雷达研究中需要直接面对的两个问题。探测目标的最低高度取决于天线的架设高度, 它的设计具有实用价值, 同时发现旁瓣污染影响探测资料的质量。基于双基地雷达探测原理, 对其进行分析, 给出在一定基线长度和最大探测距离乘积条件下, 以目标探测高度为参数的雷达天线架设的最低高度设计方案; 并分析双基地多普勒天气雷达旁瓣污染的主要原因, 进一步探讨在一定假设条件下减小或消除旁瓣污染的影响, 以控制观测资料质量。     

GNSS-R观测下的海面飓风风速反演

利用全球导航卫星系统在地球表面的反射信号（GNSS-R）进行海面风速反演已经被广泛研究并作为一种重要的遥感手段。目前,该L波段微波信号的相关功率已可以在多普勒频率和时延码片空间进行多普勒时延图像的成像。由于该图像的图像特征与海面粗糙度有较高的相关性,因此能够用来进行海面风场反演。然而,对于该遥感手段而言,其双基雷达前向散射截面（BRCS）理论上与海面粗糙度有更高的相关性,如同目前合成孔径雷达使用后向雷达散射截面而非相关功率。所以,本文通过改进已有的GNSS-R的双基雷达散射截面方程,代替相关功率在多普勒时延空间进行成像,得出了与海面粗糙度相关的双基雷达散射截面图像（BRCS map）。基于该图像,本文提出了三种与其形状特征相关的观测量,通过2005年Dennis飓风GNSS-R机载数据生成的16000多幅图像进行地球物理模式函数建模并与经典的一维时延波形匹配方法得出结果进行对比分析,得出更为精确的风速反演结果。