星载SAR影像辐射误差校正算法研究

从SAR影像辐射误差校正原理出发，发展了一种利用DEM和SAR地理编码模型计算地面散射面积和当地入射角，进而校正地形引起的辐射误差的算法，并对计算公式的推导过程进行了论述。通过研究实例对该校正算法的处理效果进行了分析，结果表明算法可以在一定程度上去除地形引起的辐射误差，而且该算法仅要求用户具备产生地理编码影像的能力，而不需要自己建立地理编码模型，因此具有一定的实际应用和推广价值。     

基于卫星参数预测的高分辨率光学影像精确定位方法

提出了一种基于预测的无地面控制点的高分辨率光学影像的精确定位方法.该方法利用了待校正遥感影像相邻景的成像参数,同时建立预测模型,内插或外推待校正遥感影像的成像参数,从而通过共线方程模型实现无地面控制点的高分辨率遥感影像地理定位.文中利用QuickBird影像进行实验,取得了4～5个像元校正精度.     

正射影像图在城市规划行业中的应用

数字正射影像图可以直观反映城市地貌的现状信息,是在城市建设、管理和城市规划中应用最为广泛的数据。其中高分辨率遥感影像还可以弥补地形图数据在局部地区更新不及时,或大比例尺地形图数据不全等现实问题。为城市现代化建设、防治灾害和公共城市建设规划各种调查和管理等提供可靠依据。本文根据正射影像图的特点,并在城市规划信息化的实际应用中探讨正射影像图的相关理论和该技术的实际应用。     

基于遥感卫星的系列正射影像图制作

本文重点介绍了北京地区遥感卫星系列影像图的制作过程，探讨了在通用遥感处理软件中进行推扫式卫星成像几何建模和相应正射纠正的方法。在给出纠正实例的基础上，对利用遥感卫星影像制作大比例尺系列正射影像图进行了评价。     

长基线的机载重轨InSAR影像配准方法

在长基线条件下,机载干涉合成孔径雷达(In SAR)系统重轨测量时由于载机飞行高度和姿态不稳定而偏离理想航迹,导致重轨影像对之间产生相对形变,同名像元对应的地面分辨单元大小不一致,从而造成的高精度配准困难,无法进行干涉处理。通过高精度相对定位,将辅影像按照主影像空间大小重采样,即从SAR成像精准几何关系出发,第一步利用少量地面控制点数据对初始斜距和航高进行标定,第二步通过高精度相对定位,计算主影像像元的同名像元的辅影像坐标,并将辅影像按照主影像空间大小重采样。实验采用机载C波段VV极化SAR重轨数据,分辨率为0.5m。结果表明,该方法适用于长基线机载重轨SAR影像的配准。     

无人机航摄影像测绘地形图的精度探讨

文中主要对无人飞机进行航空摄影的地形图测绘精度进行分析探讨,通过对相同地方的无人飞机影像进行区域网平差解算,并对平差结果进行精度的检查,这些都是利用不同像控点布设方案进行的。然后将所得结果和行业标准规范进行对比分析,从中选取满足精度要求的较好布点方案区域网平差结果进行地形图测制,并且对测制的地形图进行实地检核。     

摄影测量中相机倾斜引起的射影失真研究

根据成像原理,建立了理想光学系统成像的数学模型。通过分析该模型中物与像的对应关系,得出了射影失真产生的根源是光学系统放大率的不恒定,并与相机的外参数:倾角及视场的大小有着非线性的变化关系。提出了正射影失真与负射影失真的概念,对其进行了详尽的理论分析,并给出了数学模型及分布规律。依据上述结论,分析了二维射影对应与仿射对应在摄影测量应用中的实质区别,并利用物像平面间的射影对应关系,使试验中的测量精度达到了测试的要求。     

浅谈1976年航空影像的DOM制作

本文以实际建立历史影像数据库工程为例,详细阐述了制作1976年数字正射影像图时所遇到的问题和解决方法。对老的航空影像的正射影像图制作进行了探讨。     

数字影像边用边说-18 中国古代建筑立面模拟正射影像信息采集

正射影像是指当投射线互相平行且垂直于投影面时所成的像。中国古代建筑正射影像可以客观详尽地表现出古建筑立面的现有状况,准确地记录彩画、斗拱、墙面、台基、瓦面等各个立面的具体尺寸、损毁情况以及位置关系,为古建筑维修的设计与施工提供第一手参考资料。现在用古代建筑正射影像信息采集方法多为首先通过三维激光测绘仪器对古代建筑进行多站扫描。整合数据建立完整三维模型,然后根据古代建筑特点进行详尽影像采集,对影像进行相应的后期处理,再对三维模型进行贴图,最后根据具体需求输出二维平面图。现在我们讨论使用单纯摄影的方法不借助三维模型,是否可以制作古代建筑模拟正射影像。     

偏流角对TDICCD相机像质的影响分析

为分析TDICCD相机成像过程中偏流角对相机像质的影响,根据卫星轨道方程写出了偏流角随纬度变化的具体形式.基于此分别研究了其在卫星穿航方向和沿航方向引起的像移量和对相机成像质量的影响,并利用极地圆轨道参数详细计算了偏流角引起的像移对像质的影响程度和在MTFdrift＞0.95的情况下调整偏流角的时间间隔.结果表明,偏流角是纬度的函数,由它引起的像移在穿航方向对相机像质的影响较为严重,必须采取补偿措施加以校正.     

New SAR Imaging Algorithm via the Optimal Time-Frequency Transform Domain

To address the low-resolution imaging problem in relation to traditional Range Doppler (RD) algorithm, this paper intends to propose a new algorithm based on Fractional Fourier Transform (FrFT), which proves highly advantageous in the acquisition of high-resolution Synthetic Aperture Radar (SAR) images. The expression of the optimal order of SAR range signals using FrFT is deduced in detail, and the corresponding expression of the azimuth signal is also given. Theoretical analysis shows that, the optimal order in range (azimuth) direction, which turns out to be very unique, depends on the known imaging parameters of SAR, therefore the engineering practicability of FrFT-RD algorithm can be greatly improved without the need of order iteration. The FrFT-RD algorithm is established after an analysis of the optimal timefrequency transform. Experimental results demonstrate that, compared with traditional RD algorithm, the main-lobe width of the peak-point target of FrFT-RD algorithm is narrow in both range and azimuth directions. While the peak amplitude of the first sidelobe is reduced significantly, those of other side-lobes also drop in various degrees. In this way, the imaging resolution of range and azimuth can be increased considerably.     

High Resolution SAR Image Algorithm with Sample Length Constraints for the Range Direction

The traditional Range Doppler (RD) algorithm is unable to meet practical needs owing to the limit of resolution. The order of fractional Fourier Transform (FrFT) and the length of sampling signals affect SAR imaging performance when FrFT is applied to RD algorithm. To overcome the above shortcomings, the purpose of this paper is to propose a high-resolution SAR image algorithm by using the optimal order of FrFT and the sample length constraints for the range direction. The expression of the optimal order of SAR range signals via FrFT is deduced in detail. The initial sample length and its constraints are proposed to obtain the best sample length of SAR range signals. Experimental results demonstrate that, when the range sampling-length changes in a certain interval, the best sampling-length will be obtained, which the best values of the range resolution, PSLR and ISLR, will be derived respectively. Compared with traditional RD algorithm, the main-lobe width of the peak-point target of the proposed algorithm is narrow in the range direction. While the peak amplitude of the first side-lobe is reduced significantly, those of other side-lobes also drop in various degrees.     

3D multidomain BEM for solving the Laplace equation

An efficient 3D multidomain boundary element method (BEM) for solving problems governed by the Laplace equation is presented. Integral boundary equations are discretized using mixed boundary elements. The field function is interpolated using a continuous linear function while its derivative in a normal direction is interpolated using a discontinuous constant function over surface boundary elements. Using a multidomain approach, also known as the subdomain technique, sparse system matrices similar to the finite element method (FEM) are obtained. Interface boundary conditions between subdomains leads to an over-determined system matrix, which is solved using a fast iterative linear least square solver. The accuracy and robustness of the developed numerical algorithm is presented on a scalar diffusion problem using simple cube geometry and various types of meshes. Efficiency is demonstrated with potential flow around the complex geometry of a fighter airplane using tetrahedral mesh with over 100,000 subdomains on a personal computer.     

海面波合成孔径雷达成像仿真研究

目的：研究合成孔径雷达（SAR）对海面波成像的机理和海面波对雷波截面的调制机理。方法；选用速度聚束模型，采用不同参数仿真SAR对海面波成像的情况。结果：由于海面波的运动，使得SAR对海面波成像过程成为非线性，使SAR图像在方位向发生移位和模糊。结论：用这种仿真方法研究SAR对海面波成像是一种有效途径。     

一种星载合成孔径雷达数字成像算法

提出了一种星载合成孔径雷达数字成像抑制相干斑的算法--OMRD(Overlapped Multilook Range-Doppler)算法,该算法基于星载合成孔径雷达成像基本原理和传统的RD算法,通过距离向脉冲压缩,距离徙动校正,方位向合成孔径处理,去除相干斑噪声处理,实现了星载合成孔径雷达的数字成像,降低了相干斑噪声的影响,提高了图像信噪比.对ERS-1星载原始数据进行实验成像,得到了清晰的意大利罗马地区图像.实验结果表明,OMRD算法是一种有效的星载合成孔径雷达成像抑制相干斑的算法.     

A Method of Representing Nonstationary Temperature Fields in the Best Approximations

Depending on the body geometry and on the types of internal source and external boundary heat loadings, a space is found for the heat equation, in which a high accuracy of representing a multidimensional temperature field by a single component is attained. An application of the developed analytical-numerical algorithm to solutions of hyperbolic heat equations is given, for which the synthesis of the sought temperature leads to the sum of terms of responses of simple inertial-wave or wave links.     

Inelastic post buckling behavior of very short column

Abstract

This paper presents an unconditionally stable implicit algorithm for the direct integration of a linear structural dynamic equation of motion. The algorithm is based on two simultaneous difference equations and a weighting factor G for solving displacement at the next time step. Unconditional stability is proven for the weighting factor G in the range from –0.466 to 0.140 in all undamped and damped cases. The unconditionally stable range of G can be extended, from –1.0 to 0.333, for certain types of structure. The amplitude decay and period variation are used as the basic parameters to compare the accuracy of the present algorithm with various other integration methods. A spring‐mass‐dashpot model is applied to illustrate the algorithm for transient and quasi‐static analyses.     

基于小波多分辨率分析的时变结构参数识别研究

提出一种小波多分辨率分析的最优尺度选择方法,并将其应用于结构时变物理参数的识别。首先,从函数空间剖分的角度引入WMRA对时变参数进行多分辨率近似展开,将振动微分方程转化成多元线性回归方程,根据时变参数的频率范围及采样频率、线性方程组的个数等确定分解层数取值范围;其次,利用赤池信息准则（AIC）寻求最优分解尺度,为增强数据的稳定性,采用正交最小二乘算法（OLS）代替传统最小二乘算法（LS）对模型中小波系数进行估计并重构时变参数;最后,分别以突变和连续变化的两种时变参数的5层剪切框架模型进行数值模拟。分析结果表明:在预先确立的分解尺度范围内,采用无噪声干扰的响应信号进行识别时,识别精度随着分解尺度的增加而增加;采用噪声干扰的测量信号进行识别时,识别精度与分解尺度的增加无必然联系;通过选择适当的分解尺度,能够准确识别时变参数、提高方法的计算效率并保证很好的抗噪性能。