An Information Theory Approach to the Data Compression and Imaging System for Synthetic Aperture Radar （SAR）

Synthetic aperture radar (SAR) is portrayed as a multiple access channel. An information theory approach is applied to the SAR imaging system, and the information content about a target that can be extracted from its radar image is evaluated by the average mutual information measure. A conditional (transition) probability density function (PDF) of the SAR imaging system is derived by analyzing the system and a closed form of the information content is found. It is shown that the information content obtained by the SAR imaging system from an independent sample of echoes will decrease and the total information content obtained by the SAR imaging system will increase with an increase in the number of looks. Because the total average mutual information is also used to define a measure of radiometric resolution for radar images, it is shown that the radiometric resolution of a radar image of terrain will be improved by spatial averaging. In addition, the imaging process and the data compression process for SAR are each treated as an independent generalized communication channel. The effects of data compression upon radiometric resolution for SAR are studied and some conclusions are obtained.

利用InSAR形变反演滑坡滑面运动特征——以汶川县布瓦村滑坡为例

当前滑坡滑面运动特征获取多采用接触式手段,费时费力、成本高昂,且仅能获取稀疏点位滑面运动状态。因此,本文提出一种非接触式滑坡滑面运动特征获取方法,其基本思路是:基于位错理论建立滑坡表面形变与滑面运动间的关系模型,同时引入滑面运动平滑约束条件,最终以InSAR等技术获取的地表形变为约束,反演获得滑面运动特征。本文选择四川省汶川县布瓦村滑坡作为研究对象,以时序InSAR技术获取的滑坡坡面升降轨形变数据为约束,基于发展的理论方法反演获得布瓦村滑坡滑面几何与运动学参数,并结合野外勘查、Lidar观测以及模型残差较好地验证了反演结果的可靠性,其中反演升降轨模型残差仅3.1 mm·a^(-1)和3.4 mm·a^(-1)。反演结果显示,布瓦村滑坡滑面位于坡表以下平均~15.0 m深度处,滑面整体以沿坡向运动为主,最大运动量级达~80 mm·a^(-1),同时在坡体西侧中下部发现微量的垂直坡向运动。本文提出方法可方便、快速的获取空间连续的滑坡滑面运动特征,为滑坡灾害预警和失稳风险评估提供更为直接可靠的科学参考。

A NEW UNSUPERVISED CLASSIFICATION ALGORITHM FOR POLARIMETRIC SAR IMAGES BASED ON FUZZY SET THEORY

In this letter, a new method is proposed for unsupervised classification of terrain types and man-made objects using POLarimetric Synthetic Aperture Radar (POLSAR) data. This technique is a combi-nation of the usage of polarimetric information of SAR images and the unsupervised classification method based on fuzzy set theory. Image quantization and image enhancement are used to preprocess the POLSAR data. Then the polarimetric information and Fuzzy C-Means (FCM) clustering algorithm are used to classify the preprocessed images. The advantages of this algorithm are the automated classification, its high classifica-tion accuracy, fast convergence and high stability. The effectiveness of this algorithm is demonstrated by ex-periments using SIR-C/X-SAR (Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar) data.

A new oil spill detection algorithm based on Dempster-Shafer evidence theory

Features of oil spills and look-alikes in polarimetric synthetic aperture radar(SAR)images always play an important role in oil spill detection.Many oil spill detection algorithms have been implemented based on these features.Although environmental factors such as wind speed are important to distinguish oil spills and look-alikes,some oil spill detection algorithms do not consider the environmental factors.To distinguish oil spills and look-alikes more accurately based on environmental factors and image features,a new oil spill detection algorithm based on Dempster-Shafer evidence theory was proposed.The process of oil spill detection taking account of environmental factors was modeled using the subjective Bayesian model.The Faster-region convolutional neural networks(RCNN)model was used for oil spill detection based on the convolution features.The detection results of the two models were fused at decision level using Dempster-Shafer evidence theory.The establishment and test of the proposed algorithm were completed based on our oil spill and look-alike sample database that contains 1798 image samples and environmental information records related to the image samples.The analysis and evaluation of the proposed algorithm shows a good ability to detect oil spills at a higher detection rate,with an identifi cation rate greater than 75%and a false alarm rate lower than 19%from experiments.A total of 12 oil spill SAR images were collected for the validation and evaluation of the proposed algorithm.The evaluation result shows that the proposed algorithm has a good performance on detecting oil spills with an overall detection rate greater than 70%.

Focusing of elliptically polarized Gaussian beams through an annular high numerical aperture

Based on the vectorial Debye theory, the focusing properties of the Gaussian beam through an annular high numerical aperture are studied numerically, including the intensity, the phase and the orbital angular momentum properties. Then the influence of certain parameters on the focusing properties is also investigated. It is shown that sub-wavelength elliptical light spots can be obtained. And there exists a vortex in the longitudinal component of the focused field even though the incident beam is Gaussian beam, indicating that the spin angular momentum of the elliptically polarized Gaussian beam is converted into the orbital angular momentum by the focusing.

SAR images classification method based on Dempster-Shafer theory and kernel estimate

To study the scene classification in the Synthetic Aperture Radar （SAR） image, a novel method based on kernel estimate, with the Maxkov context and Dempster-Shafer evidence theory is proposed. Initially, a nonpaxametric Probability Density Function （PDF） estimate method is introduced, to describe the scene of SAR images. And then under the Maxkov context, both the determinate PDF and the kernel estimate method axe adopted respectively, to form a primary classification. Next, the primary classification results are fused using the evidence theory in an unsupervised way to get the scene classification. Finally, a regularization step is used, in which an iterated maximum selecting approach is introduced to control the fragments and modify the errors of the classification. Use of the kernel estimate and evidence theory can describe the complicated scenes with little prior knowledge and eliminate the ambiguities of the primary classification results. Experimental results on real SAR images illustrate a rather impressive performance.

改进的L1/2阈值迭代高分辨率SAR成像算法

针对合成孔径雷达(SAR)在稀疏采样条件下方位向分辨率低、易受噪声干扰等问题,提出改进的高分辨率SAR成像算法。该文在现有的L1/2正则化理论及其阈值迭代算法的基础上,改进了其表达式中的梯度算子,提高重构图像的求解精度,降低计算量。然后,在全采样和欠采样条件下,将原有L1/2阈值迭代算法与所提改进L1/2阈值迭代算法,分别结合近似观测模型对SAR回波信号进行成像处理和性能对比。实验结果表明,改进的算法具有更加优越的收敛性能,并且对于SAR图像方位向分辨率有一定的改善。

高频有损斜开孔腔体屏蔽效能研究

针对带孔屏蔽腔体工作时受复杂电磁干扰问题,基于电磁拓扑理论和BLT方程,考虑开孔倾斜、偏心、任意平面波照射、任意观测点位置等情况,提出用于计算斜开孔腔体屏蔽效能的解析模型。同时将腔体材料考虑为有损导体,对BLT方程中散射矩阵和传播矩阵进行修改;并利用电压和电场分布关系,考虑腔体内多种传播模式,将模型的可计算频段拓展为0~3 GHz。最后,设计五组试验,对比CST仿真值、Robinson拓展算法计算值与文中所提模型计算值,验证所提模型的准确性与优化性。为实际工程中孔缝腔体屏蔽问题的预测与计算提供方法。

基于GTD模型的多视角多频带ISAR融合成像

多视角多频带逆合成孔径雷达(inverse synthetic aperture radar,ISAR)融合成像技术克服了单雷达成像分辨率受发射带宽和观测视角的限制,是提高ISAR成像的二维分辨率的新手段。在宽带小角度观测条件下,针对目标散射系数随频率变化的情况,提出一种基于几何绕射理论(geometrical theory of diffraction,GTD)模型的多视角多频带ISAR融合成像方法。首先,以GTD模型为基础建立ISAR成像回波模型;然后,将多视角多频带ISAR融合成像问题转化为信号稀疏重构问题,并采用正交匹配追踪算法求解,在保证融合成像质量的同时提高了的成像效率;最后,利用仿真实验验证了所提方法的有效性。

大口径反射镜组件的温度适应性

考虑温度适应性是大口径反射镜组件设计过程中的重要因素,本文研究了温度影响空间相机大口径反射镜组件的机理,讨论了进行温度适应性分析与试验的必要性。结合其设计流程,总结了大口径反射镜组件温度适应性分析的方法。采用有限元方法,建立了研究对象的物理模型,进行了结构-热耦合的优化设计,确定了最终设计状态。对优化设计结果进行了在轨状态及地面检测状态的温度适应性分析。结果显示:在轨工作状态下的温度适应范围为±4℃,温差适应范围为X向5℃、Y向4℃、Z向7℃;地面检测试验状态温度适应范围为±3℃,温差适应范围为X向4℃、Y向3℃、Z向4℃。在实验室进行了组件均匀温变的温度适应性试验,并与相应分析结果进行对比,结果表明:±5℃内PV值误差优于4%,RMS值误差优于7%。

矢量衍射理论的级数解及其标量近似的有效性

当光束具有较大的发散角或光束束腰可与波长相比拟时,傍轴近似,甚至标量衍射理论都不再成立。文章在平面孔矢量衍射理论角谱表示的基础上,给出了衍射场纵向分量的级数解,指出在非傍轴区对衍射场矢量修正的必要性,分析了标量衍射理论的有效性。并以圆孔衍射为例进行了详细的数值计算,并就一些相关的问题进行了讨论。

矢量衍射理论的比较研究及标量近似的有效性

光束束腰与波长相比拟时,标量近似已不再成立。以高斯光束的微小圆孔衍射为例,对矢量衍射场的级数解、非傍轴近似解以及精确解进行了详细的数值计算和比较研究。结果表明,对受硬边光阑限制的非傍轴光束,级数展开法适用于处理光束在近场区域的传播,而非傍轴近似解则适用于处理非近场区域光束的传播,具有一定的互补性。讨论了高斯光束圆孔衍射标量近似的有效性,当高斯光束的束腰半径、衍射孔孔径大于几个光波波长时,标量衍射理论是精确、有效的。

基于BLT方程的双层腔体屏蔽效能计算方法

基于波导理论,将BLT方程进一步拓展,提出一种可快速、准确地计算双层腔体内任意点屏蔽效能的方法。首先将腔体壁孔所在面等效为二端口网络,腔体等效为两端短路的波导,建立信号流图。引入孔阻抗计算二端口网络散射参数,依据信号流图构建广义BLT方程,得到内层腔体中心线上点的屏蔽效能;然后根据波导理论的场分布特性,推导出腔体内任意点电场与腔体中心线上电场的关系,最终得到内层腔体内任意点的屏蔽效能。将计算结果与等效电路法及CST数值仿真结果对比,三者吻合良好,计算结果在较大频率范围内比等效电路法精度更高。该方法可以准确预测双层腔体在0-2.5GHz范围内所有谐振点,有助于分析腔体谐振现象,且计算效率较高,占用资源大幅减少。

折反射式零位补偿检验

结合奥夫纳尔折射式零位补偿器和马克苏托夫反射式零位补偿器的优点,对大口径、大相对孔径凹非球面加工检验提出一种折反射式零位补偿检验法.该方法采用放置在非球面顶点曲率中心之前的两块透镜和一块反射镜来实现大口径凹非球面零位补偿检验.依据三级像差理论,推导了初始结构计算公式;通过对口径为1 000mm、顶点曲率半径为4 000mm、偏心率为1.05、中心孔为200mm的凹非球面进行补偿器设计,完成了原理验证,优化后系统剩余波像差峰谷值为0.004 2λ.研究结果表明该方法轴向光路长度短,补偿能力强,可用于允许部分中心遮拦的大口径、大相对孔径凹非球面检验.

大口径光学元件功率谱密度的统计法测量

针对ICF系统要求,提出了一种基于统计理论的大口径光学元件功率谱密度测量方法。该方法将大口径波前划分成足够多个子区域,分别求得每个子区域波前的功率谱密度,根据统计理论可将大口径波前功率谱密度表示为各个子区域波前功率谱密度的加权平均,其权重因子是各子区域对应的面积。模拟计算和实验结果验证了统计法测量的有效性,并表明当子区域个数大于等于8×8时,统计法测量和子孔径拼接测量得到的功率谱密度吻合较好。统计法测量对平台移动精度和环境稳定性要求不高,可应用于大口径光学元件功率谱密度的过程检测。

不同裂隙相对张开度下类岩石材料断裂试验与破坏机理

在伺服控制单轴加载系统下对含有1条水平裂隙的类岩石试件进行加载试验,在对实验过程及现象深入分析的基础上,结合数值分析结果,探索单压条件下含有1条水平裂隙的类岩石材料断裂破坏机制。为描述裂隙形态,引入相对张开度β,并规定其为裂隙张开度与裂隙长度的比值。结果表明:以β=0.005为分界点,根据β的变化,裂隙体呈现出裂隙尖端屈服破坏和裂隙中部受拉破坏2种不同的破坏模式;当β较小时,水平裂隙尖端邻域应力分布状态可以根据裂纹尖端附近渐进应力解析解折减后计算;当β较大时,水平裂隙中部材料受横向拉伸时微裂纹出现,此时裂纹尖端附近渐进应力分布理论不再适用。

非傍轴衍射光束横截面上的光强及其能量传输

运用角谱表示的矢量衍射理论,以平面波微小圆孔的非傍轴衍射为例,给出了垂直于光束传输方向的横截面上不同定义的三种光强(传统光强I、功率密度Jz、时间平均能流密度矢量的z分量〈Sz〉)的计算公式,并进行了详细的数值计算和比较研究.指出对微小孔衍射的能量传输,必须考虑光场的矢量特性.应用能流密度矢量S和功率流密度矢量J,分别计算了微小孔非傍轴衍射的透射系数,得到了一些新的结论.

基于多孔径映射的高光谱异常检测算法

针对高光谱遥感异常检测中复杂背景与异常目标之间光谱特征相关性导致背景模型难以准确估计的问题,提出了一种基于多孔径映射的高光谱遥感异常检测算法。首先,不同于背景建模提取背景特征的方法,多孔径映射从不同角度提取数据特征,通过构建基集合表征高光谱数据的光谱特性,获得用于衡量统计差异的异常显著性指标。其次,为了实现对具有适中及低异常显著性像素的精细分析,本文基于模糊逻辑理论构建隶属度函数获得关于像素异常显著性的连续性属性标记,并将隶属度值作为权重,通过加权迭代过程实现多孔径映射的自适应收敛。最后,借鉴模糊逻辑理论中的去模糊机制,对多孔径检测结果进行融合,获得最终的检测结果。本文仿真试验采用高光谱遥感数据,从稳健性及对低显著度目标敏感性方面对算法进行验证。

折反射式零位补偿检验(续)

为了研究双透镜和球面镜之间不同球差分配对折反射式补偿器补偿效果的影响,以三级像差理论为基础,针对两个不同相对口径的凹抛物面镜,采用不同内部球差分配,分别设计了一组折反射式补偿器,将结果绘制成曲线.从曲线可看出,当球面镜球差分配系数从0逐渐增大到0.5时,对应折反射式补偿器补偿能力先增强,达到极值后下降.球面镜球差分配系数为零时,球面镜不承担球差,球面镜变成半径无穷大的平面镜,折反射式补偿器即变为Offner补偿器.研究表明,折反射式补偿器补偿能力强,但不同内部球差分配对补偿效果影响较大,合理选择球面镜球差分配系数对折反射式补偿器设计是有利的.

偏心孔缝箱体屏蔽效能电磁拓扑分析算法

基于电磁拓扑理论,对Robinson等效电路模型进行改进,提出了箱体屏蔽效能分析的电磁拓扑算法.该算法将孔缝等效为二端口网络,通过散射矩阵准确地描述了箱体内部场的行驻波态,实现了内外场耦合的准确建模;结合偏心孔缝箱体分析理论,求解偏心孔缝散射矩阵,进而实现了偏心孔缝箱体的屏蔽效能分析.在0~2GHz频域内,分别对偏心单孔和孔阵箱体的屏蔽效能进行了仿真,通过与软件CST数值结果的对比,验证了算法的有效性.最后采用该算法详细分析了孔缝宽度、测试点距离、入射极化角和入射方位角对单孔箱体屏蔽效能的影响.