基于EEMD的SAR海洋内波参数反演

经验模态分解(EMD)方法对非平稳信号进行分解,容易出现模式混叠和边界效应,从而不能得到有物理意义的特征信息.集成经验模态分解(EEMD)能够有效地克服模式混叠和边界效应问题,可准确地提取信号的本质特征信息.在分析SAR图像反演海洋内波参数机理的基础上,本文提出了一种基于EEMD的海洋内波参数反演方法.实验结果表明:与小波分解和EMD方法相比,该方法能更有效地克服模式混叠现象,所提取的分量更接近内波波动的物理本质,所反演的内波参数与经验数据吻合.     

用二次相关的方法研究信道起伏

1.引言 本文对在南中国海进行的一次声场与水体相互作用实验的数据进行了匹配滤波预处理,利用二次相关来研究信道的起伏变化规律,其分析结果与同步观测的海洋环境参数相吻合.并利用二次相关特性反演内波周期,得到了初步结果.     

基于小波分析的近岸海面风场反演研究

提出了利用小波变换多尺度分析合成孔径雷达(SAR)影像获取海面风向信息并结合岛礁、船舶等物体背风面形成的风阴影进行风向模糊剔除的近岸海面风场反演算法.与二维傅里叶变换谱分析方法得到的风向反演结果相比,小波分析法可充分发掘不同尺度影像中包含的风向信息,降低了对影像周期性线性纹理特征的依赖,提高了风场反演的分辨率和精度.由...     

基于分割区域的SAR图像配准方法研究

合成孔径雷达(Synthetic Aperture Radar,简称SAR)图像受到斑点噪声影响以及成像条件的变化,使得同一场景的两幅SAR图像之间存在很大差异,利用基于边缘特征或灰度信息进行SAR图像配准,难以达到预期效果.基于此,本文提出一种基于分割区域的SAR图像配准方法,该方法首先利用主动轮廓方法对去噪后的SA...     

基于GA优选参数的SVR水质参数遥感反演方法

为进一步提高多光谱图像水质反演的精度,提出了一种基于GA优选参数的SVR水质参数遥感反演模型.该模型利用高分辨率多光谱遥感SPOT-5数据和水质实地监测数据,采用CV估计模型推广误差并使用GA优选SVR模型参数,实现了模型参数的自动全局优选,在训练好的SVR模型基础之上对水质进行反演.以渭河陕西段为例进行实证研究,实验结果表明,本文提出的水质反演模型较常规的线性回归模有更高的反演精度,为内陆河流环境遥感监测提供了一种新方法.     

基于小波分解的 K-分布 SAR 图像舰船检测

舰船目标检测是合成孔径雷达海洋应用的一个重要组成部分. 通过对合成孔径雷达图像中舰船目标和海杂波背景的结构差异特点进行分析,提出了一种利用小波分解技术和 K-分布海杂波模型的恒虚警率舰船目标检测方法,并对实际 SIR-C C 波段 SAR 图像进行了实验. 实验结果表明,该方法能够在复杂相干斑和海杂波背景中大幅增强舰船目标,并且有效保证了检测结果的准确性.     

基于SSM/I数据的神经网络方法反演海面风速

研究了单参数神经网络(SANN)模型、多参数神经网络(MANN)模型及复合多参数神经网络(CMANN)模型对使用SSM/I数据反演海面风速精度的影响,并对增加85.5GHz垂直和水平极化亮温作为输入项对反演精度的提高进行了验证.重点发展了一种新型的CMANN算法,并分析了它在不同风速范围下的反演效果.随着风速的增加,反演风速的精度也有提高,高风速(≥15m/s)较低风速有更小的风速误差.比较表明,此方法的反演效果优于以往的各种SSM/I反演风速算法.反演风速的范围为0～25m/s,在晴天和云天混合状况下反演风速与实测风速的均方根误差为1.61m/s,晴天则达到1.46m/s.     

基于遗传算法和后向散射模型的冲积扇地表参数反演

基于能够计算多参数全局最优组合的遗传算法,结合OH2002后向散射模型,利用航天飞机成像雷达3号(SIR-C)L波段全极化数据反演了中蒙边境地区的冲积扇地表参数,提出一种反演地表参数的新途径.同时,利用所反演结果,对冲积扇地区地表特征进行分析,并与已有的反演方法进行对比,结果证明该方法能够有效地对地表参数进行提取.     

基于PSO优选参数的SVR水质参数遥感反演模型

为进一步提高多光谱图像水质反演的精度,提出了一种基于PSO优选参数的SVR水质参数遥感反演模型。该模型利用高分辨率多光谱遥感SPOT-5数据和水质实地监测数据,采用CV估计模型推广误差,并使用PSO优选SVR模型参数,实现了模型参数的自动全局优选,在训练好的SVR模型基础之上对水质进行反演。以渭河陕西段为例进行实证研究,实验结果表明,所提出的水质反演模型较常规的线性回归模型有更高的反演精度,为内陆河流环境遥感监测提供了一种新方法。     

利用计算机图像处理技术消除SAR图像噪声的研究

本文介绍当前计算机数字图像处理技术消除图像噪声的基本情况,并总结分析了三类滤波方法:传统滤波算法、基于局域统计的自适应滤波算法、小波域斑点噪声滤波算法。随后应用增强Lee滤波方法对SAR(合成孔径雷达)图像进行实际处理,并对处理结果进行总结。     

高频地波雷达接收系统的补偿

针对高频地波雷达、逆合成孔径雷达等接收系统中因混频前为宽带系统、混频后为窄带系统的造成的幅相特性不理想,提出了两种补偿方法－时域补偿法和频域补偿法,仿真结果表明该方法是有效的。     

Feasibility study of synthetic aperture infrared laser radar techniques for imaging of static and moving objects

Techniques for two types of 10-mum band synthetic aperture infrared laser radar using a hypothetical reference point target (RPT) are presented. One is for imaging static objects with a single two-dimensional scanning aperture. Through the simple manipulation of a reference wave phase, a desired image can be obtained merely by the two-dimensional Fourier transformation of the correlator output between the intermediate frequency signals of the reference and object waves. The other, with a one-dimensional aperture array, is for moving objects that pass across the array direction without attitude change. We performed imaging by using a two-dimensional RPT correlation method. We demonstrate the capability of these methods for imaging and evaluate the necessary conditions for signal-to-noise ratio and random phase errors in signal reception through numerical simulations in terms of feasibility.     

Signal-to-noise ratio analysis to estimate ocean wave heights from X-band marine radar image time series

This work analyses the structure of the different contributions to the image spectrum derived by the three-dimensional Fourier decomposition of sea clutter time series measured by ordinary X-band marine radars. The goal of this investigation is to derive a method to estimate the significant wave height of the ocean wave fields imaged by the radar. The proposed method is an extension of a technique developed for the analysis of ocean wave fields by using synthetic aperture radar systems. The basic idea behind this method is that the significant wave height is linearly dependent on the square root of the signal-to-noise ratio, where the signal is assumed as the radar analysis estimation of the wave spectral energy and the noise is computed as the energy due to the sea surface roughness, which is closely related to the speckle of the radar image. The proposed method to estimate wave heights is validated using data sets of sea clutter images measured by a marine radar and significant wave heights derived from measurements taken by a buoy used as reference sensor.     

Optical synthetic aperture radar

A method is proposed for increasing the resolution of an object and overcoming the diffraction limit of an optical system installed on top of a moving imaging system, such as an airborne platform or satellite. The resolution improvement is obtained via a two-step process. First, three low resolution differently defocused images are captured and the optical phase is retrieved using an improved iterative Gershberg–Saxton based algorithm. The phase retrieval allows numerical back propagation of the field to the aperture plane. Second, the imaging system is shifted and the first step is repeated. The obtained optical fields at the aperture plane are combined and a synthetically increased lens aperture is generated along the direction of movement, yielding higher imaging resolution. The method resembles a well-known approach from the microwave regime called the synthetic aperture radar in which the antenna size is synthetically increased along the platform propagation direction. The proposed method is demonstrated via Matlab simulation as well as through laboratory experiment.     

Remote sensing based retrieval of snow cover properties

In order to overcome the restrictions of conventional observation methods, novel remote monitoring techniques such as terrestrial laser scanning (TLS) and ground based interferometric synthetic aperture radar (GB SAR) are concurrently operated. Snow depth and snow water equivalent (SWE) or the snow mass on ground are some of the key parameters in the assessment of avalanche hazard, for snow, snow drift and avalanche modelling as well as model verification. While the TLS provides maps of the spatial snow depth distribution, the GB SAR can in principle be used to retrieve snow depth and SWE. Remote sensing results are compared to traditional field work, additionally advantages and limitations of the techniques are identified. Finally, the applicability of the remote sensing based retrieval of these snow cover properties for snow and snow avalanche applications is summarized.     

Modelling and enhancement of interrupted synthetic aperture radar imagery

A synthetic aperture radar system can be made compatible with other interleaved modes if the impact of the interruptions in operation necessary to accommodate these can be ameliorated. The ways in which this might be done are discussed. Effects of regular and random interruptions are characterised by simulation and analysis. Two methods of image enhancement, based on interpolation and apodisation, are then discussed; the latter appears to hold more promise of practical usefulness.     

Two-dimensional synthetic aperture laser optical feedback imaging using galvanometric scanning

We have improved the resolution of our laser optical feedback imaging (LOFI) setup by using a synthetic aperture (SA) process. We report a two-dimensional (2D) SA LOFI experiment where the unprocessed image (i.e., the classical LOFI image) is obtained point by point, line after line using full 2D galvanometric scanning. The 2D superresolved image is then obtained by successively computing two angular SA operations while a one-dimensional angular synthesis is preceded by a frequency synthesis to obtain a 2D superresolved image conventionally in the synthetic aperture radar (SAR) method and their corresponding laser method called synthetic aperture ladar. The numerical and experimental results are compared.     

Uniform rotational motion compensation for inverse synthetic aperture radar with non-cooperative targets

In the current scenario of high-range resolution radars, the rotational motion of the target usually generates migration through resolution cells (MTRC) in the inverse synthetic aperture radar (ISAR) images. A technique to correct the MTRC in the case of uniform rotation rate is proposed. An estimation of the rotation vector of the non-cooperative targets is not required. The approach compensates the rotational motion in two steps: the slant-range rotation compensation (SRRC) and the cross-range rotation compensation (CRRC). CRRC is based on an extension of phase difference (PD) and on a robust method to delete outliers. The technique is verified both with simulated and live data from a millimetre-wave linear frequency-modulated continuous wave radar. A comparison with a minimum entropy-based technique is also made.     

混合采样机载MIMO雷达成像方法

针对传统合成孔径雷达(SAR)在进行机动目标成像时,极易造成SAR图像中出现散焦与模糊现象,本文通过融合MIMO雷达单次快拍与SAR合成孔径技术,提出了一种混合采样高分辨率机载MIMO雷达机动目标成像方法。该方法利用目标与载机的空间位置信息进行运动补偿,而无需估计目标多普勒信息,因此,能够有效避免传统SAR存在的机动目标多普勒参数估计难题。仿真实验证实了新方法实现机动目标聚焦成像的有效性。     

层状无砟轨道结构脱层缺陷超声成像

无砟轨道是典型的层状混凝土结构,脱层缺陷是其最常见的损伤形式,影响着高速列车的安全运行。传统的合成孔径聚焦成像方法是基于恒定声速的超声检测方法,忽略层间的声阻抗差异以及声波在层间界面处的折射,导致声束难以在缺陷处聚焦,声波在层状结构中传播的时间误差较大。鉴于此,提出了一种多层结构合成孔径聚焦成像方法,充分考虑多层结构中的层间声速差异,采用射线追踪方法准确获取声波在多层结构中的传播时间。在此基础上,分析了不同入射波模式以及不同激发频率对多层结构合成孔径聚焦成像结果的影响。结果表明：采用多层结构合成孔径聚焦成像方法,使用频率为50 kHz的横波入射成像分辨率更高,对无砟轨道脱层缺陷检测效果更好。该研究为该类缺陷检测提供了理论支撑。