基于自适应门限的改进BigBand算法

BigBand算法是一种利用信号普遍稀疏特性的欠采样算法。传统BigBand算法依靠经验设置固定门限,在低信噪比和噪声变化剧烈的情况下,频谱混叠会使噪声的值被叠加放大,信号与噪声难以明显区分,频谱感知能力差。针对该问题,提出了一种基于自适应门限的改进BigBand算法,利用预设信号虚警概率获得初始噪声门限和信号门限,并根据感知环境信噪比动态调整门限阈值,再依据经验选择噪声或信号门限作为门限阈值进行信号判决与感知。实验结果表明,相较于传统BigBand算法,该改进算法能适应低信噪比和噪声变化剧烈的环境,抗干扰性较好,具有更好的频谱感知能力。     

无人机复杂电磁环境频谱特征反演测量

针对复杂电磁环境对无人机用频设备的干扰和威胁，本文提出了一种复杂电磁环境信号频谱特征的反演方法。该方法基于小波变换原理对无人机典型用频频段电磁信号进行变换处理，对其频谱特征进行奇异性检测，结合信号降噪处理等技术去除频谱伪奇异点对接收信号频谱特征进行反演测量，并对该方法进行了仿真验证。仿真结果表明该方法反演复杂电磁环境频谱特征满足无人机数据链抗干扰设计要求。     

GNSS-IR双频数据融合的土壤湿度反演方法

目前全球导航卫星系统反射信号干涉测量（GNSS-IR）土壤湿度反演研究仅针对单一频点展开,提出用熵值法将2个频点数据进行融合以改进土壤湿度反演精度。首先,利用频谱分析法分别解析出各频点的信噪比（SNR）序列的振荡频率,计算出对应的等效天线高度,并利用最小二乘法求解各频点信噪比序列相位;然后,通过熵值法进行2个频点的相位观测量融合;最后,利用融合结果与实测土壤湿度建立经验模型,实现土壤湿度反演。利用地基观测实验获得的全球定位系统（GPS）L1和L2信噪比数据对该方法进行了验证,结果表明:L1和L2双频融合反演结果平均标准差为0.6%,比L1单频反演结果提高64.73%,比L2单频反演结果提高32.12%;均方根误差为0.37%,比L1频点降低72.8%,比L2频点降低73.4%。      

基于GPS掩星平均弯曲角的折射率反演研究

利用Abel积分变换通过掩星弯曲角计算折射率需要对高层弯曲角进行统计优化.目前由于所使用的背景场资料和具体反演方法不同,导致所发布的掩星大气数据气候统计值存在一定差异.本文使用2008年1,4,7,10月共4个月的COSMIC大气掩星附加相位数据,从纬圈平均弯曲角廓线反演相应月平均折射率,对反演结果进行比较分析.研究表明,利用掩星折射数据进行气候研究时无需逐一对掩星探测廓线进行统计优化,在40 km以下高度基于平均弯曲角的反演方法与传统统计相比能够获得几乎一致的月平均折射率,在50 km以上高度基于平均弯曲角的反演结果更加接近ECMWF资料统计.      

裂纹矩张量反演的传感器排布形式

裂纹矩张量反演方法利用声发射信号求解裂纹信息,是一种有效的裂纹扩展实时监测方法。在工程应用中,传感器接收到的声发射信号总包含一定比例的噪声。噪声信号会影响矩张量反演精度,甚至导致错误结果。研究通过优化传感器排布形式来降低噪声对矩张量反演精度的影响。基于矩张量初至波反演方法,分析了传感器位置选择的理论基础。进而利用人工合成声发射信号,定量研究了在不同传感器排布形式下,矩张量反演精度对噪声的敏感度。结果表明:正五边形传感器排布形式具有较好的精度表现,这种排布形式将5个传感器布置在一个圆环上,相邻传感器的传感器-圆心连线的夹角为72°,第6个传感器布置在圆心。此时矩张量求解方程的条件数较小,当声发射信号幅值因为噪声发生变化时,求解结果具有较高的精度和稳定性。研究针对矩张量反演中的传感器位置选择问题,为相关工程实践提供了建议和理论依据。      

微波干涉仪测量羽流电子密度反演方法

利用微波干涉仪进行推进器羽流密度测量的反演方法研究.重点针对羽流等离子体密度反演的Abel逆变换数值求解,采用离散化算法、三次样条插值算法、Hankel-Fourier算法以及Nestor-Olsen算法等四种方法进行仿真分析和比较.通过对这四种方法在无噪声和有噪声两种情况下反演误差的比较,找出适用于实际干涉仪数据处理的方法;通过对采样点数和反演之间的关系分析,给出解决欠采样问题的方法和数值参考;在分析比较的基础上,总结数值处理的必要步骤.利用模拟实验测试数据进行验证并对反演结果进行分析.      

基于MOF准则的原子钟噪声分离研究

按照MOF（the Method of Frame）准则,对原子钟信号进行噪声分离,并应用阿伦方差对基于不同小波字典的噪声分离结果进行评价。试验结果表明,应用余弦（DCT）字典、余弦包（CP）字典、Sym8小波包（WP）字典进行噪声分离后的阿伦方差分别从原始信号的4.5538e-15提高到2.2100e-15,3.3125e-15,8.2848e-16,说明MOF准则下,选取适当的小波字典对原子钟信号进行噪声分离,能够获得很好的稳定度。     

伪距噪声建模方法研究和分析

主要介绍从GPS原始数据中提取伪距噪声的方法,并利用MATLAB非线性拟合工具箱cftool中的参数逼近模型对提取出的伪距噪声建模,针对几种较好的建模结果进行数据回放和比较,确定最佳建模方案.建模结果可用于Galileo系统空间信号误差（signal-in-space error）的实时估计和用户完好性算法的研究.     

基于EMD的MEMS陀螺仪随机漂移分析方法

为了抑制微机械电子系统（MEMS）陀螺仪的随机漂移，基于经验模态分解（EMD）和模态集合选择标准，结合时间序列建模滤波法，提出了一种改进的MEMS陀螺仪随机漂移分析方法。首先，通过EMD将MEMS陀螺仪原始数据分解为多个本征模态函数（IMF），利用模态集合选择标准将IMF分为噪声IMF、噪声与信号混合IMF和信号IMF三类；然后，对混合IMF进行重构、时间序列建模及自适应卡尔曼滤波（AKF）；最后，将3类信号重构，实现MEMS陀螺仪信号去噪。实验表明:所提方法有更好的去噪效果和实时性，提高了MEMS陀螺仪的使用精度。      

基于改进HHT的非高斯噪声中瞬态通信信号检测

根据瞬态通信信号和非高斯噪声的特点,建立了相应的信号模型,并利用希尔伯特-黄变换（HHT）处理非线性非平稳信号的优势,提出了基于改进HHT的非高斯噪声中瞬态通信信号的检测算法。该检测算法分为集合经验模式分解（EEMD）和固有模态函数（IMF）分量筛选两部分,首先经过加入随机白噪声多次试验取均值得到待检测信号的IMF分量,再结合各个分量与原信号的能量差异和相关性剔除虚假IMF分量,从而实现对混叠在非高斯噪声中的瞬态通信信号的有效检测。仿真在不同的条件下对比了本文算法与其他算法对信号的检测效果,结果证明本文算法能够有效克服HHT中存在的缺陷,实现对瞬态信号更为准确的分析和检测。     

基于声光技术的扩频信号循环谱的检测

扩频信号是被伪随机码调制的周期信号,因此它应被建模为循环平稳随机信号.基于循环平稳随机信号的谱相关理论,提出了一种采用基于声光信号处理技术的扩频信号循环谱检测方法.通过研究扩频信号的循环频率、循环功率谱和基于时间积分的声光循环平稳处理模型,利用声光循环平稳时间积分相关器,在循环频率处对扩频信号的声光相关函数(循环谱)进行检测.相比于传统的能量检测方法,循环谱检测方法具有更好的检测性能;对于噪声和干扰,无论是平稳的、还是非平稳的,循环谱检测方法都具有较强的抗干扰能力,仿真结果证明了其有效性.     

Landsat thematic mapper studies of land cover spatial variability related to hydrology

The Landsat 4 and 5 Thematic Mapper (TM) provides increased spatial, spectral, and radiometric capability relative to the Multispectral Scanner (MSS). Visual inspection of TM imagery confirms this. Land cover detail is evident that would be of use in watershed management and planning activities. Specific studies have been conducted in Georgia, West Virginia, Michigan and Maryland to compare MSS and TM for urbanizing watersheds, wetlands, and floodplain mapping situations. These studies show that only modest improvements in classification accuracy (Anderson Level I/II) have been achieved using existing classification approaches. An attempt to identify the visibly apparent interstate highways and secondary and residential streets in TM data via conventional approaches failed due to an inability to derive separable spectral signatures. The basis for a non-parametric approach to classification is presented in which roads are identified by locating linear local minima in the greenness transformed dimension. Preliminary results indicate that such a method provides more reliable road locations than MSS or TM used singly.     

Estimating canopy cover in drylands with Landsat MSS data

The relationship between canopy cover and spectral characteristics of the corresponding areas was studied in a semi-arid savannah environment in Kordofan, The Sudan.The canopy cover was measured in 32 test plots through air photo interpretation. Achieved values were correlated with multitemporal Landsat MSS raw data and manipulated data.The highest correlation coefficients in general were obtained between crown cover and spectral data recorded during the dry season.The inverse relationship between amount of woody vegetation and nIR reflectance (MSS 6, MSS 7) was striking. This implied that other factors than a healthy foliage characterized the spectral responses.Destructive measurements of woody biomass were carried out to establish a relationship between woody wet weight and crown diameter for future biomass studies.     

Applicationof remote sensing techniques in geological studies of various mineralized belts in India. (National paper on IGCP — 143)

Geological interpretation, analysis and evaluation of LANDSAT and airborne MSS data, panchromatic and colour infrred photographs and spectral reflectance data for a number of test sites in different mineralized belts in India have led to certain significant results. Lithological discrimination on digitally processed enhanced MSS data products has helped in further subdivisions of major rock groups. Lineament pattern analyses reveals three prominent sets of fractures in Indian Precambrian Shield with predominant ENE-WSW megalineament probably representing earliest deep crustal fractures and subsequent NNW-SSE and NE-SW fractures, associated with polyphase tectonic movements. Correlation of structures and mineralization indicate structural control for most of the mineralized belts with intersecting locii type concentration of ore deposits in some cases. In a few cases control of mineralization is lithology and stratigraphy. Spectral groundtruth and laboratory studies indicate that major rock types have characteristic spectral patterns (signatures) which would be useful for lithological mapping by automatic classification techniques. The work also has led to the improvement of enhanced MSS data products for geological studies.     

Sensor data for forest policy information

NASA-Ames Research Center has investigated the role and performance capabilities of the Landsat Multi-Spectral Scanner (MSS) for forest policy analysis for the past four years in cooperation with the California Department of Forestry. A thorough series of studies, from a statewide land cover map to smaller, highly detailed studies including collateral data, have been conducted with a view to comprehensive forest policy needs. The strengths and limitations of MSS data have been evaluated. Some observations about the information needed from new satellite sensors such as the Thematic Mapper are discussed against this background.     

基于滑模观测器的机翼颤振主动抑制设计

颤振主动抑制(AFS)是国际上普遍推崇的颤振问题解决方案,对现代飞行器设计具有重要意义。基于国际上滑模观测器的二维机翼AFS应用,以双后缘控制面真实机翼模型为对象,发展一种低阶滑模观测器的三维机翼AFS设计方法。该观测器性能优越、特点鲜明,但传统的设计流程繁琐,限制了其在高阶模型对象上的使用。本文借助线性二次型高斯(LQG)方法中的最优滤波器增益矩阵,提出一种简化的滑模观测器设计流程。结合气动弹性物理背景,使本文方法理论上能够应用于实践。算例对比分析结果表明,本文方法比LQG方法具有更好的抵抗噪声能力。     

静电悬浮加速度计噪声测试数据的频谱分析方法

分析了不同系数的离散傅里叶变换公式的含意,并从中筛选出符合工程分析要求的正确公式。为使用快速傅里叶变换可采用多种方式使数据符合2的整数次幂,分析了各种方法的优缺点;分析了各种频谱的应用对象,得出静电悬浮加速度计噪声适宜采用功率谱密度,且在窗函数应用上宜选择与之符合的系数;给出了使用OriginLab公司Origin5.0/7.0软件计算功率谱密度时所必须采取的纠正措施,提出地面测试静电悬浮加速度计噪声需采用差分方法以仰制环境噪声,具体操作方法是,将两台加速度计已扣除平均值的时域噪声值相减后除以平方根2。      

Landsat image data quality studies

The July 1982 launch of Landsat-4 was immediately followed by a two-year comprehensive set of detailed investigations sponsored by the National Aeronautics and Space Administration (NASA) at Goddard Space Flight Center (GSFC). The Landsat Image Data Quality Analysis (LIDQA) research plans for these investigations were specified prior to launch, so that minimum time would be lost in assessing the performance of the long-awaited Thematic Mapper (TM) sensor that Landsat-4 carried in addition to a fourth Multispectral Scanner (MSS). The LIDQA investigations have been substantially completed, and have shown that the TM is a very good spaceborne multispectral radiometer, and has met or exceeded most of its design goals. TM's new short-wave infrared (SWIR) spectral capability yielded improved mineral and plant discrimination compared to the MSS, as anticipated by ground-based and airborne TM simulations. Moreover, the improved spatial resolution and geometric accuracy of Landsat-4 and the TM have resulted in satellite image maps exceeding 1:100,000 U.S. map accuracy standards. Finally, based on an information entropy measure, principal component analysis, and classification results, TM data has been shown to approach its theoretical limit in information content per pixel, exceeding the MSS by at least a factor of two.     

基于Riccati方程解的高增益未知输入观测器设计

针对具有未知输入和测量噪声的一类Lipschitz非线性系统,研究了状态估计、噪声估计及未知输入重构问题.通过将输出噪声看作扩展状态,把原系统转化为描述系统.针对描述系统,首先基于Riccati方程的解,提出了一种高增益观测器设计方法,实现对系统状态的估计和测量噪声的重构;之后,设计二阶高增益滑模观测器精确估计输出的微分,并利用状态和输出微分的估计,提出了一种未知输入的重构方法.在一Riccati方程有解的前提下,所提出的未知输入和测量噪声的重构,均适用于强时变信号.最后,对一个实际模型仿真,验证所提出方法的有效性.      

基于EEMD-Hilbert谱的涡街流量计尾迹振荡特性

为了研究涡街流量计尾迹振荡特征,采用集总经验模态分解(EEMD)-Hilbert谱方法,对测量介质为空气、流量范围为10.58~220 m~3/h的涡街流量计管壁差压信号进行处理,首先用EEMD方法对管壁差压信号进行分解,得到固有模态分量,然后对分解后的各个分量进行Hilbert变换,得到Hilbert谱和边际谱,进而提取管壁差压信号的旋涡脱落频率。比较了Fourier变换与EEMD-Hilbert谱方法在信号去噪和频率提取方面的性能。结果表明:EEMD-Hilbert谱方法可有效去除叠加在实际涡街成分之中的噪声,能够较完整保留尾迹振荡的固有成分;在流量较低时,EEMD-Hilbert谱方法对尾迹振荡频率的提取精度比Fourier变换高30%以上,有效拓展了涡街流量计的测量下限;通过计算能量比,揭示了EEMD-Hilbert谱方法提高频率提取精度的原因,即EEMD-Hilbert谱方法降低了信噪比;Hilbert谱直观表示信号的时间-频率-能量关系。