Radar Target Detection and Map-Matching Algorithm Studies

Results of a study of adaptive threshold target detection and map-matching algorithms are presented. Log threshold processing is shown to be preferred over linear threshold processing when the clutter data surrounding the target cell is contaminated by other targets, decoy corner reflectors, or bright clutter cells. Whereas previous studies have resorted to extensive Monte-Carlo simulations of log threshold algorithms, the results were obtained using a novel analytical approach based upon Parseval's theorem.     

有限平面上圆口径辐射场的数值分析

计算由TE₁₁模激励的圆波导末端开口所形成的圆口径天线的辐射场.首先利用等效原理和矩量法计算嵌在无限大金属板上圆口径的等效磁流分布,允许圆波导中有任意多个高次模式存在,利用傅里叶变换法求得其辐射方向图,然后把该辐射场作为有限接地板边缘的入射场,利用几何绕射理论(GTD)计算有限接地板对圆口径方向图的贡献,其中在焦散区及接近焦散区区域采用等效磁流法计算有限接地板的影响,给出计算公式及计算例子,部分结果得到了文献的验证.     

基于半实物仿真的地磁导航等值线匹配算法评估

影响地磁导航匹配算法性能的因素很多,而现阶段算法的评估完全依靠计算机仿真,其可信性有待进一步验证.以等值线(ICCP)算法为研究对象,首先从理论上分析影响算法性能的因素;然后搭建了地磁匹配导航半实物仿真系统,通过引入磁场仿真环境和磁传感器,提高了仿真的可信度;最后从测量噪声、匹配长度、匹配区域和惯导误差4个方面对ICCP 匹配算法的性能进行半实物仿真试验分析.仿真结果表明,通过半实物仿真试验可以对算法的抗干扰性、算法匹配长度的确定、匹配区域的选择以及惯导误差的影响做出有效评估,从而推动地磁匹配导航及匹配算法的工程化进程.      

Fast Probabilistic Particle Identification algorithm using silicon strip detectors

Active detectors used as radiation monitors in space are not usually able to perform Particle Identification (PID). Common techniques need energy loss spectra with high statistics to estimate ion abundances. The ALTEA-space detector system is a set of silicon strip particle telescopes monitoring the radiation environment on board the International Space Station since July 2006 with real-time telemetry capabilities. Its large geometrical factor due to the concurrent use of six detectors permits the acquisition of good energy loss spectra even in a short period of observation. In this paper we present a novel Fast Probabilistic Particle Identification (FPPI) algorithm developed for the ALTEA data analysis in order to perform nuclear identification with low statistics and, with some limitations, also in real time.     

干涉测量宽带相关处理算法与验证

阐述了一种用于航天器精确角位置测量的干涉测量宽带相关信号处理算法,通过仿真验证了算法的有效性,并搭建卫星干涉测量实验系统,采集某地球同步卫星信号进行宽带相关信号处理,获得清晰干涉条纹,准确估计出反映测站与卫星位置关系的时延观测量。结果表明宽带相关信号处理的估计时延与卫星信号链路标定时延、测距时延组成系统时延闭合回路,初步验证了干涉测量实验系统的有效性,为后续飞行任务中航天器高精度干涉测量积累了技术和经验。     

A Comparison of Noncoherent and Coherent MTI Improvement Factors

An analysis based on statistical considerations and Monte Carlo simulations indicates that a noncoherent moving target indicator (MTI) using a linear envelope detector differs from one using a square law envelope detector. The square law envelope detector is usually described in the literature because of ease of analysis, and it is commonly stated or implied that the results are the same for the two cases because of the similar spectral characteristics of the detectors. A comparison is made between the two noncoherent MTIs and the coherent MTI in terms of clutter attenuation and MTI improvement factors.     

REM measurements aboard Mir during 1995

Measurements of the South Atlantic Anomaly (SAA) made with the Radiation Environment Monitor (REM) aboard Mir from November 1994 to February 1996 are presented. During this period an increase of the SAA radiation by ≈25% is observed, which coincides with a lowering of the radio solar flux. Radio solar flux is one of the parameters controlling the earth's atmospheric distribution and with it the absorption of inner radiation belt protons forming the SAA. Due to the altitude gradient of the atmospheric density, the proton fluxes in the SAA are anisotropic (loss cone, east-west effect). The measured distribution can be accounted for by basic models.     

Multistage integration model for human egomotion perception

Human computational vision models that attempt to account for the dynamic perception of egomotion and relative depth typically assume a common three-stage process: first, compute the optical flow field based on the dynamically changing image; second, estimate the egomotion states based on the flow; and third, estimate the relative depth/shape based on the egomotion states and possibly on a model of the viewed surface. We propose a model more in line with recent work in human vision, employing multistage integration. Here the dynamic image is first processed to generate spatial and temporal image gradients that drive a mutually interconnected state estimator and depth/shape estimator. The state estimator uses the image gradient information in combination with a depth/shape estimate of the viewed surface and an assumed model of the viewer's dynamics to generate current state estimates; in tandem, the depth/shape estimator uses the image gradient information in combination with the viewer's state estimate and assumed shape model to generate current depth/shape estimates. In this paper, we describe the model and compare model predictions with empirical data.     

A Parallel Adaptive 3D MHD Scheme for Modeling Coronal and Solar Wind Plasma Flows

A parallel adaptive mesh refinement (AMR) scheme is described for solving the governing equations of ideal magnetohydrodynamics (MHD) in three space dimensions. This solution algorithm makes use of modern finite-volume numerical methodology to provide a combination of high solution accuracy and computational robustness. Efficient and scalable implementations of the method have been developed for massively parallel computer architectures and high performance achieved. Numerical results are discussed for a simplified model of the initiation and evolution of coronal mass ejections (CMEs) in the inner heliosphere. The results demonstrate the potential of this numerical tool for enhancing our understanding of coronal and solar wind plasma processes. This revised version was published online in June 2006 with corrections to the Cover Date.