基于小波变换和核独立分量分析的遥感图像变化检测

为了进一步提高基于独立分量分析(IndependentComponentAnalysis,ICA)的遥感图像变化检测精确度,并解决ICA分离的图像分量排序不确定问题,提出了基于小波变换和核独立分量分析(KernelIndependentComponentAnalysis,KICA)的遥感图像变化检测方法。首先通过小波变换对遥感图像进行分解,得到由图像的高频分量和低频分量组成的分块向量,然后利用核函数将分块向量映射到高维特征空间中,再在该空间中用ICA方法分离出互相独立的向量,最后根据分离出的向量中高频分量的差异自动分辨出变化分量。文章给出了遥感图像变化检测方法及近年提出的基于主分量分析(PrincipalComponentAnalysis,PCA)、基于ICA、基于KICA三种变化检测方法的试验结果,并进行了分析和定量比较。试验结果表明,文中方法能更好地分离出遥感图像的变化信息,具有更高的精确度,并实现了变化检测的智能化。     

基于视觉模型和图像特征的遥感图像压缩

遥感图像具有纹理复杂、边缘丰富的特点,通常难以实现高压缩比.统计了图像经过小波变换后在不同方向、不同级别子频带的能量分布.然后基于人类视觉系统(HVS)模型中的对比敏感度函数(CSF)和遥感图像的能量分布特征,提出一种不同频带小波系数的变步长量化方法,并把该方法应用于嵌入式小波图像编码器.实验结果表明,与不采用心理视觉量化的压缩方法相比,在相同压缩比下,峰值信噪比略为降低,但恢复图像的主观质量有一定程度的改善.     

Cost-driven design of small satellite remote sensing systems*

Earth remote sensing (alongside communications) is one of the key application of Earth-orbiting satellites. Civilian satellites in the LANDSAT and SPOT series provide Earth images which have been used for a vast spectrum of applications in agriculture, meteorology, hydrology, urban planning and geology, to name but a few. In the defence sector, satellite remote sensing systems are a critical tool in strategic and tactical planning – for the countries which can afford them. To date, remote sensing satellites have fallen into one of these two categories: military missions driven by the requirement for very high resolution and orbital agility; and multipurpose civil satellites using general purpose sensors to serve a diverse community of end users. For military-style missions, the drive to high resolution sets the requirements for optics, attitude control and downlink data bandwidth. For civil missions, the requirement to satisfy multiple, diverse user applications forces compromises on spectral band and orbit selection. Although there are exceptions, many small satellite remote sensing missions carry on in this tradition, concentrating on ultra high resolution products for multiple user communities. This results in satellites costing on the order of US $100 M, not optimised for any particular application. This paper explores an alternative path to satellite remote sensing, aiming simultaneously to reduce cost and to optimise imaging products for specific applications. By decreasing the cost of the remote sensing satellite system to a critical point, it becomes appropriate to optimise the sensor's spectral and temporal characteristics to fit the requirements of a small, specialised user base. The critical engineering trade-off faced in a cost driven mission is how to reduce mission cost while still delivering a useful product to the selected user. At the Surrey Space Centre, we have pursued an engineering path using two dimensional CCD array sensors, commercial off-the-shelf lenses and gravity-gradient stabilised microsatellites. In spite of the inherent limitations of such systems, recent successes with the Thai Microsatellite Company's Thai-Phutt satellite show that a system costing in the region of US $3 million, can approach the spectral and spatial characteristics of LANDSAT. Surrey's UoSAT-12 minisatellite (to be launched April, 1999) will further develop this cost-driven approach to provide 10 m panchromatic resolution and 30 m multi-spectral resolution. This paper describes the Thai-Phutt and UoSAT-12 imaging systems, explaining the engineering methods and trade-offs. Although Surrey is presently the only centre presently pursuing such implementations, our paper shows that they deserve wider consideration.     

数字图象表示的GD方法及其变形GD13方法

本文给出了一种属于线性四元树的图象表示方法—GD法(灰度值,阶数)并讨论了GD表示与CD表示以及与QC表示之间的关系;其次给出了GD表示、矩阵表示以及栅格表示等的转换算法;最后,针对常见的256个灰度级的图象,讨论了GD13方法。     

Observation of a 27-day solar signature in noctilucent cloud altitude

Previous studies have identified solar 27-day signatures in several parameters in the Mesosphere/Lower thermosphere region, including temperature and Noctilucent cloud (NLC) occurrence frequency. In this study we report on a solar 27-day signature in NLC altitude with peak-to-peak variations of about 400?m. We use SCIAMACHY limb-scatter observations from 2002 to 2012 to detect NLCs. The superposed epoch analysis method is applied to extract solar 27-day signatures. A 27-day signature in NLC altitude can be identified in both hemispheres in the SCIAMACHY dataset, but the signature is more pronounced in the northern hemisphere. The solar signature in NLC altitude is found to be in phase with solar activity and temperature for latitudes $?70°$N. We provide a qualitative explanation for the positive correlation between solar activity and NLC altitude based on published model simulations.     

一种高光谱图像的双压缩感知模型

高光谱图像因其海量数据性,给存储、传输及后续分析处理带来了挑战。压缩感知理论提供了一种全新的信号采集框架。针对高光谱数据的三维特性,提出一种双压缩感知的采样与重构模型。该模型在采样阶段兼顾高光谱数据的空间和谱间稀疏特性,构造了能同时实现空间和谱间压缩采样的感知矩阵;重构阶段不同于传统的压缩感知重构方法直接重构高光谱数据,而是将高光谱数据分离成端元和丰度分别进行重构,然后利用重构的端元和丰度信息合成高光谱数据。实验结果表明,所提双压缩感知在低采样率下重构精度较三维压缩采样提高了10 dB以上,更为显著的是运算速度提升了3个数量级,同时该方法还便于获得端元和丰度信息。     

日球层内外能量中性原子的探测

能量中性原子(Energetic Neutral Atoms, ENA, 简称能原子)是指在日球层内外空间, 拥有>0.1keV动能的原子.在此空间领域并没有温度>106K的中性气体, 但却充满动能>0.1keV的正离子.因此能原子A应该是A+离子与原地稀薄气体B原子或分子交换电荷所产生的, 即A++B→A+B+. 电荷交换涉及极小的动能变化, 新生的能原子A和离子B+基本上各自保持原有动能. 离子B+随即被当地磁场俘获, 能原子A则脱离磁场约束并携带其原属离子群的成分和能量信息而直线运动, 成为遥测空间等离子体的有效媒介. 美国人造卫星 IBEX (Interstellar Boundary Explorer) 直接探测得到来自日球层以外星际空间的能原子, 大幅延伸了利用能原子遥测空间等离子体的领域. 本文据此论述了空间能原子的发现, 综述了探测空间能原子的基本概念与实例、取得的主要成果、仪器设计和研制进展以及未来空间利用能原子遥测的发展趋势.      

双极性压缩观测光谱成像技术研究

压缩传感突破了 Nyquist-Shannon 采样定理的限制,从随机观测的少量测量值中即可高精度地获取图像,给成像设备的设计带来了巨大变革。压缩传感理论证明可以通过重构恢复获得比焦平面阵列分辨率更高的场景图像。尽管在理论上存在巨大优越性,压缩传感成像系统的物理实现需要考虑一些实际问题。文章围绕压缩传感成像设备进行了研究,提出了一种物理可实现的压缩成像方法,该方法利用双通道观测架构实现压缩成像中的双极性观测,解决了压缩成像理论与实际物理约束不一致的问题。采用多路技术和多膜技术实现大视场观测与多次视场观测,该方法可以单次曝光获取充足的观测值来高精度重构原图像。压缩光谱成像数值仿真实验验证了该方法的有效性和鲁棒性。     

柔性机械臂辅助空间站舱段对接阻抗控制

空间机械臂辅助舱段对接过程中存在测量与控制误差,易导致对接机构间存在较大接触力,传统FMA (Force MomentAccommodation)控制方法在测量接触力时无法消除大负载惯性力对测量的影响,且测量仪器的引入会进一步降低空间柔性机械臂的刚度。为此,文章提出了柔性机械臂辅助大负载空间舱段对接的阻抗控制方法,采用拉格朗日法推导了空间机械臂的关节输入力矩方程作为前馈输入,建立了含动力学前馈的空间机械臂阻抗控制程序,并以在商业软件ADAMS中建立的空间柔性机械臂与对接舱段组成的系统动力学模型作为控制对象,对系统进行ADAMS灢Matlab联合仿真。仿真结果表明,按照此控制方法,系统可克服外力干扰使目标解析点按照期望的方式运动;同时,通过测量机械臂关节运动参数即可实现对外力的准确感知,而不需额外添加力传感器,既消除了大负载惯性力对测量的影响,也不会导致柔性机械臂刚度的降低。     

利用高分辨率遥感数据的芦山地震道路损毁快速评估

道路损毁评估是地震损失评估工作的重要内容。文章根据芦山7.0级地震应急评估需求,提出利用多源遥感数据的道路损毁评估方法。首先,针对获取的高分辨率遥感数据特点,建立道路损毁遥感解译标准,进一步考虑地震平均烈度,建立以县为单元的灾区道路损毁等级快速评估模型,最后给出了地震灾区基于高分辨率遥感数据的快速制图产品和灾区道路损毁分县等级评估结果。结果表明,道路损毁极重灾区有芦山县、宝兴县,重灾区有天全县、雨城区、荥经县、名山区、邛崃市,一般灾区有汉源县等14个县(市、区)。相关研究和结果为震后救灾决策提供了重要支撑。