NOVEL RADAR SIGNAL SORTING METHOD BASED ON GEOMETRIC COVERING

With the increase of complexity of electromagnetic environment and continuous appearance of advanced system radars, signals received by radar reconnaissance receivers become even more intensive and complex. There- fore, traditional radar sorting methods based on neural network algorithms and support vector machine （SVM） cannot process them effectively. Aiming at solving this problem, a novel radar signal sorting method based on the cloud model theory and the geometric covering algorithm is proposed. By applying the geometric covering algo- rithm to divide input signals into different covering domains based on their distribution characteristics, the method can overcome a typical problem that it is easy for traditional sorting algorithms to fall into the local extrema due to the use of complex nonlinear equation to describe input signals. The method uses the cloud model to describe the membership degree between signals to be sorted and their covering domains, thus it avoids the disadvantage that traditional sorting methods based on hard clustering cannot deinterleave the signal samples with overlapped param- eters. Experimental results show that the presented method can effectively sort advanced system radar signals with overlapped parameters in complex electromagnetic environment.     

An overview of radar soundings of the martian ionosphere from the Mars Express spacecraft

The Mars Express spacecraft carries a low-frequency radar called MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) that is designed to study the subsurface and ionosphere of Mars. In this paper, we give an overview of the ionospheric sounding results after approximately one year of operation in orbit around Mars. Several types of ionospheric echoes are commonly observed. These include vertical echoes caused by specular reflection from the horizontally stratified ionosphere; echoes from a second layer in the topside ionosphere, possibly associated with O⁺ ions; oblique echoes from upward bulges in the ionosphere; and a variety of other echoes that are poorly understood. The vertical echoes provide electron density profiles that are in reasonable agreement with the Chapman photo-equilibrium model of planetary ionospheres. On the dayside of Mars the maximum electron density is approximately 2 × 10⁵ cm⁻³. On the nightside the echoes are often very diffuse and highly irregular, with maximum electron densities less than 10⁴ cm⁻³. Surface reflections are sometimes observed in the same frequency range as the diffuse echoes, suggesting that small isolated holes exist in the nightside ionosphere, possibly similar to those that occur on the nightside of Venus. The oblique echoes arise from upward bulges in the ionosphere in regions where the crustal magnetic field of Mars is strong and nearly vertical. The bulges tend to be elongated in the horizontal direction and located in regions between oppositely directed arch-like structures in the crustal magnetic field. The nearly vertical magnetic field lines in the region between the arches are thought to connect into the solar wind, thereby allowing solar wind electrons to heat the lower levels of the ionosphere, with an attendant increase in the scale height and electron density.     

半主动雷达寻的空空导弹作战技术运用研究

导弹的攻击区是衡量导弹的攻击能力的最重要的指标之一。通过仿真计算得出不同情况下半主动雷达寻的空空导弹的攻击区。具体分析了不同因素对攻击区的影响，以此为依据，讨论了在战术上如何运用该导弹，给出了充分发挥导弹作战能力的有效途径。可为飞行员使用该种导弹进行空空作战提供正确的理论指导和参考。     

ANALYSIS OF THE RETURNED SIGNAL MODEL IN BISTATIC RADAR SYSTEMS

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Bayesian edge detector for SAR imagery using discontinuity-adaptive Markov random feld modeling

Synthetic aperture radar（SAR）image is severely affected by multiplicative speckle noise,which greatly complicates the edge detection.In this paper,by incorporating the discontinuityadaptive Markov random feld（DAMRF）and maximum a posteriori（MAP）estimation criterion into edge detection,a Bayesian edge detector for SAR imagery is accordingly developed.In the proposed detector,the DAMRF is used as the a priori distribution of the local mean reflectivity,and a maximum a posteriori estimation of it is thus obtained by maximizing the posteriori energy using gradient-descent method.Four normalized ratios constructed in different directions are computed,based on which two edge strength maps（ESMs）are formed.The fnal edge detection result is achieved by fusing the results of two thresholded ESMs.The experimental results with synthetic and real SAR images show that the proposed detector could effciently detect edges in SAR images,and achieve better performance than two popular detectors in terms of Pratt＇s fgure of merit and visual evaluation in most cases.     

基于多载频MIMO雷达的Radon-Fourier变换盲速旁瓣抑制

 长时间相干积累方法Radon-Fourier变换(RFT)中盲速旁瓣(BSSL)现象会导致雷达虚警增加、目标检测性能降低。针对BSSL问题,给出了一种基于多输入多输出(MIMO)雷达多载频设计的BSSL抑制方法。首先根据载频与BSSL分布的关系,详细推导了BSSL不交叠的约束条件;然后基于该约束条件给出了具体的载频设计公式。利用设计的载频可得到具有不交叠BSSL的两个RFT输出,通过联合处理这两个RFT输出,可实现BSSL抑制。给出了BSSL抑制性能的评价方法。理论分析和数值实验结果表明,本文算法能够在不降低RFT相干积累性能的同时,有效实现BSSL抑制。     

复合高斯杂波中距离扩展目标的迭代近似GLRT检测器

 研究了结构化的复合高斯杂波(CGC)背景中距离扩展目标自适应检测问题。针对异质杂波背景中的近似广义似然比检验(AGLRT-HTG)检测器应用于CGC背景中时存在一定的信杂比损失问题,结构化的复合高斯杂波采用自回归过程建模,结合近似广义似然比检验(AGLRT)方法和迭代估计思想,提出了CGC背景中距离扩展目标的迭代近似广义似然比检测器(RAGLRT-CGC)。从理论上分析了极限情况下RAGLRT-CGC虚警概率与检测门限关系的解析表达式。仿真结果表明,在CGC背景中,RAGLRT-CGC对不同多主散射点目标具有较好的鲁棒性,并且检测性能明显优于AGLRT-HTG。     

利用信号特征的风电场对二次雷达影响评估

研究表明风力发电场可能会影响航管雷达系统,导致其工作性能下降,因此准确评估风电场对航管雷达的影响具有重要意义。利用二次雷达信号特征给出了一种风电场对二次雷达影响的评估方法。首先根据二次雷达信号特征从风电场反射信号干扰方面分析了风电场对航管二次雷达可能产生的影响．然后阐述了以反射信号的时延来划分风电场影响区域的评估方法。最后通过在DEM（digital elevation model数字高程模型）数据上的仿真实验来验证本文评估方法。     

基于超声波测距汽车倒车防撞雷达研究

通过声音或更直观的显示告知驾驶员周围障碍物的位置情况,帮助驾驶员扫除视野的死角和视线模糊的缺陷。介绍了一种低成本、高精度、微型化,并有数字显示和声光报警功能的倒车雷达,该倒车雷达根据超声波测距原理研制,采用温度补偿技术、开机自检技术和优化的软硬件技术,将测得的结果送至数码管显示,进行三级声光报警。使驾驶员做到心里有数,提高了泊车和倒车时的安全和效率。     

离散/堆积理论在大尺寸轻质模型设计中的应用

为了解决大尺寸金属雷达隐身测试模型在设计中遇到的重量问题,借鉴快速成型技术中的离散／堆积理论,提出采用离散化重点剖面框架加堆积式蒙皮的模型设计方法,基于此方法设计并加工隐身测试用的金属模型。试验证明该模型符合隐身试验要求,且实现了模型重量小于50k的轻质化目标。此设计方法可提高隐身模型设计加工的水平并可减少试验成本。