Improvedforward—lookingimagingmethodforairbornearrayFMCWSAR

机载阵列前视合成孔径雷达（SAR）信号模型中忽略载机速度会影响成像。针对该问题，在调频连续波（FMCW）SAR信号模型中考虑了载机速度，分析了栽机速度的影响和裁机连续运动引入的多普勒频率偏移的特点，结合FrequencyScaling算法，研究了机载阵列FMCWSAR前视成像。成像仿真和性能参数分析表明：改进方法可精确实现载机运动条件下的FMCWSAR前视成像。

Underwater Simultaneous Localization and Mapping Based on Forward-looking Sonar

A method of underwater simultaneous localization and mapping （SLAM） based on forward-looking sonar was proposed in this paper. Positions of objects were obtained by the forward-looking sonar, and an improved association method based on an ant colony algorithm was introduced to estimate the positions. In order to improve the precision of the positions, the extended Kalman filter （EKF） was adopted. The presented algorithm was tested in a tank, and the maximum estimation error of SLAM gained was 0.25 m. The tests verify that this method can maintain better association efficiency and reduce navigatioJ~ error.

RESEARCH ON THE BISTATIC FORWARD-LOOKING SAR IMAGING

The bistatic Synthetic Aperture Radar (SAR) systems with separate transmitter and receiver antennas provide a new potential to imaging in the forward-looking geometry. Analysis of the Doppler property in this paper indicates the feasibility of Bistatic Forward-Looking (BFL) SAR imaging. Considering the different Doppler property determined by the two platforms in BFL SAR, a new 2-D point target spectrum is derived in our study. Based on the spectrum, an imaging method is chosen for the configuration, and the point target simulation validates the analysis.

Nonlinear RCMC method for spaceborne/airborne forward-looking bistatic SAR

In the spaceborne/airborne forward-looking bistatic syn- thetic aperture radar （SA-FBSAR）, due to the system platforms＇ remarkable velocity difference and the forward-looking mode, the range cell migration （RCM） not only depends on the target＇s two- dimensional location, but also varies with the range location non- linearly. And the nonlinearity is not just the slight deviation from the linear part, but exhibits evident nonlinear departure in the RCM trajectory. If the RCM is not properly corrected, nonlinear image distortions would occur. Based on the RCM model, a modified two-step RCM compensation （RCMC） method for SA-FBSAR is proposed. In this method, firstly the azimuth-dependent RCM is compensated by the scaling Fourier transform and the phase multi- plication. And then the range-dependent RCM is removed through interpolation. The effectiveness of the proposed RCMC method is verified by the simulation results of both point scatterers and area targets.

High-resolution forward-looking imaging algorithm for missile-borne detectors

Aiming at a novel missile-borne detector in the optional burst height proximity fuze, a self-adaptive high-resolution forward-looking imaging algorithm (SAHRFL-IA) is presented. The echo data are captured by the missile-borne detector in the target regions;thereby the azimuth angulation accuracy at the same distance dimension is improved dynamically. Thus, azimuth information of the targets in the detection area may be obtained accurately. The proposed imaging algorithm breaks through the conventional misconception of merely using azimuth discrimination curves under ideal conditions during monopulse angulation. The real-time echo data from the target region are used to perform error correction for this discrimination curve, and finally the accuracy of the azimuth angulation may reach the optimum at the same distance dimension. A series of experiments demonstrate the validity, reliability and high performance of the proposed imaging algorithm. Azimuth angulation accuracy may reach ten times that of the detection beam width. Meanwhile, the running time of this algorithm satisfies the requirements of missile-borne platforms.

Property analysis of bistatic forward-looking SAR with arbitrary geometry

Bistatic forward-looking synthetic aperture radar（SAR） has many advantages and applications owing to its twodimensional imaging capability.There could be various imaging configurations because of the geometric flexibility of bistatic platforms,resulting in kinds of models built independently among which there could be some similar even the same motion features.Comprehensive research on such systems in a more comprehensive and general point of view is required to address their difference and consistency.Property analysis of bistatic forwardlooking SAR with arbitrary geometry is achieved including stripmap and spotlight modes on airborne platform,missile-borne platform,and hybrid platform of both.Emphasis is placed on azimuth space variance of some key parameters significantly affecting the subsequent imaging processing,based on which the frequency spectra are further described and compared considering respective features of different platforms for frequency imaging algorithm developing.Simulation results confirm the effectiveness and correctness of our analysis.

A NEW METHOD TO COMPENSATE CLUTTER RANGE DEPENDENCE FOR FORWARD LOOKING AIRBORNE RADARS

The clutter direction-Doppler curves are not aligned on the near range bins for forward looking airborne radar. As a result, the performance of clutter suppression by Space-Time Adaptive Processing (STAP) degrades greatly because of the clutter range dependence. To deal with this problem, a new compensated method is proposed in this paper. The method rebuilds the clutter covariance matrix based on spatial high resolution Minimum Variance Distortionless Response (MVDR) spectrum, and then finds a matrix to transform the covariance matrix of short-range gate to the referred far-range gate. The method can compensate the clutter range dependence well. The simulation results show validity of the method.

Railway Track Verification Using a Forward-Looking SAR GPR

It is a challenge to evaluate the conditions of railway track without interruption of regular traffic. In this paper, the authors introduce the detection of cavities under the railway substructure by using forward-looking ground penetrating radar （FLGPR）. Main advantages of FLGPR are that such a system can illuminate a large area and can stand off a long distance over its down-looking counterpart. Two methods, frequency wave-number （F-W） synthetic aperture imaging （SAI） and beam-forming by delay and sum （DAS）, are applied to process the collected data. Analysis and measuring show that the distinct radar image of the cavity beneath the substructure 1.2 m deep can be formed by these two methods.

LOOKING FORWARD TO APEC'S OSAKA SUMMIT

Established in 1989 as a forum for its member countries or areas to discuss eco-nomic and related issues, Asia-Pacific Economic Cooperation (APEC) is nowbecoming an increasingly important regional organization. With a membership of18 countries and areas, it accounts for 34. 5％ of total world population, 50％ oftotal world GNP and 40％ of total world trade. What is more significant of APECis that East Asia is now the most dynamic region in global economic growth. Theyear 1994 witnessed an historic event of APEC. the announcement of the BogorDeclaration by the APEC leaders’ informal meeting in Bogor. The Bogor Declara-

Monetary policy rules：Forward-looking and backward-looking in an overlapping generations model

In the framework of an overlapping generations model, forward-looking monetary policy roles and backward-looking monetary policy rules were investigated. It is shown that the monetary steady state is more likely to be indeterminate under an active forwardlooking rule than under the corresponding backward-looking rule. It is also shown that backward-looking roles can render the monetary steady state unstable.

Tibet is Looking Forward to the Olympic Torch

In June 2008 the Olympic torch,representing sport- ing ethos of the world,will embark on its primary journey to Mt.Qomolangma.The world will once again focus on"the roof of the world"-Tibet. On July 13^(th),2001,the Beijing Organizing Committee for the 29^(th) Olympic Games made its final statement with the promise that"if Beijing was accepted as the host of the 2008 Olympiad,Beijing will organize the route of

Strengthening Space Cooperation Looking Forward to 21st Century

Space Technology Development in China China began to develop space technology in the 1950s. After 40 years, China now has necessary facilities for the research, design, development, production and test of various satellites and series launch vehicles, many experts with rich experience and superb technology, three satellite launch bases in Jiuquan, Taiyuan and Xichang, and Xi’an TT&C Station, which have the ability to launch lowearth-orbit,

The World Looks Forward to China

Having devoted his life to building cultural,educational,and economic ties with China for over three decades,Tom Watkins shares his personal observations and perspectives on China’s latest development and its efforts to build a community with shared future for all mankind.

REVIEW THE PAST AND LOOK FORWARD TO THE FUTURE OF INTERNATIONAL SHIPPING MARKET

Ⅰ. Review the past of 1994 international shiPPing market: 1994 saw world economy begin a new cycle of boom. The economy of the West was on the way to a complete recovery, and that of East Asia was keeping up its steady growth. ACCOFding to the estimation 0f International Monetary Fund, the 1994 growth rate of world economy was 3％ and that of world—trade volume was about 5％. Thanks to these factors, the international shipping market had also Undergone considerable changes. 1. In 1994,world dry—bulk shipping market first sagged and thenstiffened. Affected by the negative growth of

声呐图像水下目标识别综述与展望

随着海洋资源开发和水下作业的增加,声呐图像水下目标识别已成为热门研究领域。该文全面回顾了该领域的现状和未来趋势。首先,强调了声呐图像水下目标识别的背景和重要性,指出水下环境复杂和样本稀缺增加了任务难度。其次,深入探讨了典型的成像声呐技术,包括前视声呐、侧扫声呐、合成孔径声呐、多波束测深仪、干涉合成孔径声呐和前视三维声呐等。接下来,系统地审视了二维和三维声呐图像水下目标识别方法,比较了不同算法的优劣,还讨论了声呐图像序列的关联识别方法。最后,总结了当前领域的主要挑战,展望了未来研究方向,旨在促进水下声呐目标识别领域的发展。

一种基于太赫兹成像的复杂地形自适应定高方法

针对现有近感探测器难以适应复杂地形情况下的精确定高问题,提出一种基于成像的图像域自适应对地高度估计方法。该方法将多普勒锐化成像原理应用到前下视场景,利用太赫兹频段分辨力高、孔径合成长度短的优势,采用太赫兹前下视成像实现地形感知,将传统近感探测器的一维距离测量扩展为二维成像测量,实现对运动轨迹前下方地形地貌的精确感知。在获得地面目标图像后,利用地面图像特征,采用图像域特征拟合方法实现对地高度估计。对前下视多普勒锐化成像的参数设计和成像算法进行了理论分析和仿真验证,开发了一套工作于220 GHz频段的太赫兹近感探测系统,并开展了无人机挂载试验。试验表明,该方法能有效感知地表目标环境,排除角反、树木等其他目标对地面高度测量的干扰,测高精确度达0.5 m,证明了该基于太赫兹成像的对地高度估计方法的可行性,为基于图像域特征提升近感探测器对复杂地形适应能力和感知能力奠定了工作基础。

基于变前视距离的四轮同步转向农机改进纯跟踪控制

路径跟踪控制是提高自主导航系统控制精度的关键。针对在复杂农田作业环境下转弯时纯跟踪算法跟踪精度不高的问题,本文提出了一种基于改进纯追踪模型的四轮同步转向农机路径跟踪控制算法。建立了基于四轮同步转向农机的运动学模型和纯跟踪模型,在此基础上考虑航向误差得到改进纯跟踪模型,进行RTK定位坐标修正,根据量化误差的评价函数搜索前视区域最优目标点,得到最优前视距离。本文算法能实时确定四轮同步转向农机改进纯跟踪模型中的前视距离,使航向误差和横向误差最小化,实现目标点的自适应优化。仿真结果表明,本文方法转弯时平均绝对横向误差减至0.035 m,平均绝对航向误差减至0.212°;水田实验结果表明,当四轮同步转向农机作业速度为3.6 km/h时,四轮转向农机轨迹跟踪平均绝对横向误差减至0.109 m,平均绝对航向误差减至2.799°,转弯跟踪精度显著提高。

面向“十五五”的黄河流域生态保护和高质量发展

黄河流域生态保护和高质量发展是一项系统性、历史性和长期性的国家重大战略。五年来,黄河流域在生态治理和经济格局上不断优化,时空特征加快演进,高质量发展态势明显,但一些深层次结构性矛盾仍然存在。面对国际国内发展新形势,黄河流域生态保护和高质量发展在推进路径上应重点以“两山论”引领绿色发展、以科技创新引领产业创新、以区域一体化推进城市群都市圈建设、以内外联动推进高水平开放、以文旅深度融合推进黄河文化繁荣发展。着眼中长期,谋划“十五五”,前瞻黄河流域生态保护和高质量发展的战略思路,应围绕流域高质量发展和高水平保护、高质量发展和高水平安全抓好“统筹”,围绕“十五五”规划、“两步走”战略做好“衔接”,围绕毫不动摇深化改革开放、推进全面创新育强“动能”,围绕与国家重大战略、区域战略的对接融入和叠加协同提升“势能”,围绕治理现代化在深化流域规划体系、政策体系联动中提高“效能”,以大保护、大治理推动流域生态效益、经济效益和社会效益相统一,打造大江大河治理的重要标杆,在推进中国式现代化进程中发挥关键作用。