Radar detection of subsurface features on Mars

The structure of the pulse radar signal reflected from continuously changing layered Martian crust is investigated theoretically. As a simple model of stratigraphy, we considered one layer with electrodynamics’ parameters increasing or decreasing exponentially upon a depth laying on monolith base and covered by homogeneous layer. This exponential changing of electromagnetic properties of the layer is assumed due to exponential changing of porosity (or saturation) in the bedrocks with pores filled by seawater. The conditions of subsurface features resolution are obtained. It is shown that the sign and value for gradient of the electromagnetic properties change can be resolved from the reflection peaks trend. These results are important for subsurface detection of liquid water on Mars by orbit-based radars.     

基于最小最大鉴别分析特征提取的雷达目标识别

针对基于雷达目标高分辨距离像的识别问题,本文提出了一种新的准则函数,并依据该准则函数采用神经网络来实现自适应的非线性特征提取、变换与识别。同时,由于准则函数只坜对特征提取后的类间散度和类内散度作出估计,因此在样本数相对较少的情况下也能得到较好的估计结果。该准则函数在形式上与Fisher准则函数相似,但它们之间存在着本质的差异。鉴于二者的形似之处,遂将基于该准则函数的特征提取方法冠以“最小最大鉴别分析特征提取”之名。将该方法用于五类缩比目标测量数据的特征提取与识别,取得了较好的识别效果。     

一种基于幂级数函数的混合域基函数的收敛性分析

为提高计算效率,以一种基于双线性四边形模拟物体形状的幂级数函数为混合域基函数,用伽列金矩量法(MOM)对电中、小尺寸金属散射体的雷达散射截面(RCS)进行计算。分析了幂数级函数阶数M与其收敛性的关系。对二面角、矩形平板、等边三角形平板和圆柱等不同目标的单站或双站RCS计算结果表明,在此特定条件下M=3时该算法计算值与文献结果较为吻合,计算速度和精度均可满足仿真要求。     

一种改进的正交投影自适应波束形成算法

为减少雷达正交投影自适应波束形成算法中采样协方差矩阵特征分解的运算量，提出了一种改进的正交投影自适应波束形成算法。改进算法利用总体最小二乘法得到噪声子空间。推导了算法的公式，并给出了计算步骤。该算法的计算量小于正交投影算法而性能相当。理论分析和计算机仿真结果表明此算法有效。     

基于AutoCAD几何建模的近场目标电磁散射计算技术

为了计算复杂目标的雷达散射截面（RCS），提出了一种基于AutoCAD几何建模的近场目标电磁散射计算技术，计算了单元体，组成体以及飞机的近场雷达散射截面，理论计算和实测结果较为吻合，为在微机上计算复杂目标近场RCS提供了一种理想的方法。     

某型导弹的电磁散射特性分析

通过综合运用物理光学法（PO），等效电磁流法（MEC）和几何光学法（GO）等，并考虑目标各部分散射场间的相对相位关系，分析了椭球体和橄榄体两种不同形状弹头导弹的电磁特性，计算出了它们的雷达散射截面积（RCS）。计算结果与相关文献结论吻合较好，表明该方法更正确有效的，能满足工程分析需要。     

一种鲁棒输出反馈线性化方法在导弹自动驾驶仪设计中的应用研究

针对具有多模型的HAVE DASHⅡ导弹对象，利用一种结构简单的鲁棒输出反馈线性化方法，为其设计了全弹道自动驾驶仪控制系统。设计中仅需要少量的模型集信息，并不依赖于某一具体子系统，对整个模型集具有通用性。由于不再需要设计多个控制器，因此避免了常规多模型切换摔制中抖动的产生。该方法利用模型估计器实时估计系统动态特性，只要参数选得合适，能无偏差地估计出模型集中每个系统动态特性，有很强的鲁棒性。此外。还利用了高增益观测器来获取控制律中所需的导数信息，使得整个闭环系统仪需要输出量反馈，降低该方法的工程实现难度。仿真结果表明，所设计的自动驾驶仪系统能够控制模型集中所有飞行条件下的状态准确快速地到达期望值上。     

Antarctic meteor observations using the Davis MST and meteor radars

This paper presents the meteor observations obtained using two radars installed at Davis (68.6°S, 78.0°E), Antarctica. The Davis MST radar was installed primarily for observation of polar mesosphere summer echoes, with additional transmit and receive antennas installed to allow all-sky interferometric meteor radar observations. The Davis meteor radar performs dedicated all-sky interferometric meteor radar observations. The annual count rate variation for both radars peaks in mid-summer and minimizes in early Spring. The height distribution shows significant annual variation, with minimum (maximum) peak heights and maximum (minimum) height widths in early Spring (mid-summer). Although the meteor radar count rate and height distribution variations are consistent with a similar frequency meteor radar operating at Andenes (69.3°N), the peak heights show a much larger variation than at Andenes, while the count rate maximum-to-minimum ratios show a much smaller variation. Investigation of the effects of the temporal sampling parameters suggests that these differences are consistent with the different temporal sampling strategies used by the Davis and Andenes meteor radars. The new radiant mapping procedure of [Jones, J., Jones, W., Meteor radiant activity mapping using single-station radar observations, Mon. Not. R. Astron. Soc., 367(3), 1050–1056, doi: 10.1111/j.1365-2966.2006.10025.x, 2006] is investigated. The technique is used to detect the Southern delta-Aquarid meteor shower, and a previously unknown weak shower. Meteoroid speeds obtained using the Fresnel transform are presented. The diurnal, annual, and height variation of meteoroid speeds are presented, with the results found to be consistent with those obtained using specular meteor radars. Meteoroid speed estimates for echoes identified as Southern delta-Aquarid and Sextantid meteor candidates show good agreement with the theoretical pre-atmospheric speeds of these showers (41 km s⁻¹ and 32 km s⁻¹, respectively). The meteoroid speeds estimated for these showers show decreasing speed with decreasing height, consistent with the effects of meteoroid deceleration. Finally, we illustrate how the new radiant mapping and meteoroid speed techniques can be combined for unambiguous meteor shower detection, and use these techniques to detect a previously unknown weak shower.     

Adaptive Square-Root Cubature–Quadrature Kalman Particle Filter for satellite attitude determination using vector observations

A novel algorithm is presented in this study for estimation of spacecraft?s attitudes and angular rates from vector observations. In this regard, a new cubature–quadrature particle filter (CQPF) is initially developed that uses the Square-Root Cubature–Quadrature Kalman Filter (SR-CQKF) to generate the importance proposal distribution. The developed CQPF scheme avoids the basic limitation of particle filter (PF) with regards to counting the new measurements. Subsequently, CQPF is enhanced to adjust the sample size at every time step utilizing the idea of confidence intervals, thus improving the efficiency and accuracy of the newly proposed adaptive CQPF (ACQPF). In addition, application of the q-method for filter initialization has intensified the computation burden as well. The current study also applies ACQPF to the problem of attitude estimation of a low Earth orbit (LEO) satellite. For this purpose, the undertaken satellite is equipped with a three-axis magnetometer (TAM) as well as a sun sensor pack that provide noisy geomagnetic field data and Sun direction measurements, respectively. The results and performance of the proposed filter are investigated and compared with those of the extended Kalman filter (EKF) and the standard particle filter (PF) utilizing a Monte Carlo simulation. The comparison demonstrates the viability and the accuracy of the proposed nonlinear estimator.     

Obstacle avoidance for multi-missile network via distributed coordination algorithm

A distributed coordination algorithm is proposed to enhance the engagement of the multi-missile network in consideration of obstacle avoidance. To achieve a cooperative interception,the guidance law is developed in a simple form that consists of three individual components for target capture, time coordination and obstacle avoidance. The distributed coordination algorithm enables a group of interceptor missiles to reach the target simultaneously, even if some member in the multi-missile network can only collect the information from nearest neighbors. The simulation results show that the guidance strategy provides a feasible tool to implement obstacle avoidance for the multi-missile network with satisfactory accuracy of target capture. The effects of the gain parameters are also discussed to evaluate the proposed approach.