基于PCI9820的雷达回波信号实时采集系统

精确的雷达回波信号采集存储是完成目标识别和雷达成像的必要前提,随着A/D采样率和计算机总线技术的高速发展,已经可以在中频直接对雷达回波信号进行实时采集。本文介绍了一种ADLINK公司的基于PCI总线的高速高分辨率数据采集卡PCI9820的硬件结构及相关逻辑模块功能,基于它的双缓冲模式思想并利用板卡的相关驱动函数编写了实时采集程序,并说明了存储文件格式及数据格式。实验结果表明,此实时采集程序能够很好的控制数据采集卡PCI9820完成对雷达回波信号的高速高分辨率实时采集和存储,为信号处理提供了良好的数据基础。     

结合相位一致与全变差模型的高分辨率遥感图像边缘检测

目的边缘检测是有效利用遥感数据开展地物目标自动识别的重要步骤。高分辨率遥感图像地物类型复杂,细节信息过于丰富,使得基于相位一致的边缘检测结果中存在过多的噪声与伪边缘。为此提出了一种结合相位一致与全变差模型的高分辨率遥感图像边缘检测方法。方法根据相位一致原理,应用Log Gabor构造的2维相位一致模型,引入全变差去噪模型对基于相位一致的边缘强度图进行改进。结果借助有界变差空间对图像光滑性的约束,实现了高分辨率遥感图像噪声去除与伪边缘抑制,利用改进后的相位一致边缘强度图可有效检测高分辨率遥感图像的边缘。结论实验结果表明,与相位一致模型、Canny算法相比,该方法能消除了高分辨率遥感图像中同类地物内部细节特征形成的噪声,抑制相位一致边缘检测结果中的伪边缘,突出地物的真实边缘,并能正确地提取地物目标的整体轮廓信息,有助于后续地物目标的自动识别。     

The impact of raindrop drift in a three-dimensional wind field on a radar–gauge rainfall comparison

There are many causes for the discrepancies between weather radar and rain gauges, and among these, displacement of raindrops due to wind drift – which is especially a problem with high-spatial resolution weather radar – is largely ignored in the published literature. This is mainly due to the lack of high-resolution three-dimensional wind fields and feasible treatment of the raindrop size distribution (DSD). In this study, a new systematic approach is proposed to explore the radar–gauge relationship under the wind influence. The mass-weighted mean diameter of raindrops is derived for each radar grid from the DSD data. The reanalysis project ERA-40 data of the European Centre for Medium-range Weather Forecasts (ECMWF) are used to drive the numerical weather research and forecasting (WRF) model to generate high-resolution hourly three-dimensional wind fields. Trajectories and displacements of raindrops are then computed using a three-dimensional motion equation from the given radar beam height to the ground surface. Based on the radar rainfall surface interpolated by the bicubic spline method, the correlation of the radar–gauge pairs is used to validate the results. A case study with 20 storm events in the Brue catchment in South West England is chosen to evaluate the proposed scheme. It has been found that when wind drift is taken into account, the correlation coefficient in hourly gauge–radar comparisons can be enhanced by up to 30% and the average correlation coefficient for an event can be improved by 10%. However, there are still some situations in which the scheme fails to work, indicating the complexity and uncertainties in tackling this challenging problem. Further studies are needed to explore why those cases cause problems to the scheme and how it could be improved to cope with them.     

基于GA的SAR图像中主干道路提取

从高分辨率合成孔径雷达(SAR)图像中提取道路及其他线性特征已成为目前遥感图像信息提取研究的热点。由于高分辨率SAR图像中，目标背景复杂，同时由于受相干斑噪声的影响，因此很难直接从原始图像数据中提取道路特征。为了能够从背景复杂，受斑点噪声干扰的高分辨率SAR图像中准确提取道路，提出了一种利用遗传算法提取主干道路的方法。该方法利用模糊C均值聚类法对滤波后的SAR图像进行无监督聚类，首先将图像分为林地、建筑物、道路等基本类，并将道路类像素从图像中分离出来，使问题得到简化；然后根据道路类像素的隶属度和道路像素灰度值的均匀特性来建立具体的道路模型；最后利用遗传算法搜索全局最优道路。实验结果表明，该方法可以很好地从SAR图像中提取各种主干道路。     

基于非参数化最大间隔准则的雷达目标识别

针对线性判别分析（LDA）的“小样本”和要求数据须服从高斯分布的问题,提出一种基于非参数化最大间隔准则（NMMC）的雷达目标识别方法．首先,利用自相关小波变换提取目标高分辨距离像（HRRP）的非平稳特征,将其与HRRP原信号一起作为目标的分类特征,利用NMMC实现特征提取;然后,通过支持向量机进行分类．NMMC在解决小样本问题的同时,松弛了对数据分布的类高斯要求．最后,基于5种飞机高分辨距离像数据的仿真实验验证了所提出方法的有效性．     

一种合成孔径雷达图像阴影和目标检测的方法

提出了一种进行高分辨率SAR(synthetic aperture radar)图像阴影和目标检测的新思路.首先给出了基于等效视数模型的图像RCS(radar cross section)重构算法进行阴影检测,然后通过非线性积累,达到目标检测的目的.与CFAR(constant false alarm rate)检测相比,能够检测到阴影和更多感兴趣的目标.     

Waveform design and high-resolution imaging of cognitive radar based on compressive sensing

We introduce the compressive sensing(CS) theory for waveform design of cognitive radar,and then propose an algorithm for the high-resolution radar signal waveform and its corresponding imaging method based on the sparse orthogonal frequency division multiplexing-linear frequency modulation(OFDM-LFM) signal.We first present the principle of spectrum synthesis and high-resolution imaging based on OFDM-LFM signals.Then,we propose the spectrum-sparse waveform design criterion and the reconstruction algorithm for a highresolution range profile(HRRP) based on CS.Based on this,we analyze in detail the relationship between the scattering characteristics of the target and the parameters of the designed signal,and we construct the feedback of the target characteristics on the waveforms.Therefore,the "cognitive" function of radar can be achieved by adaptively adjusting the waveform with the target characteristics.Simulations are given to validate the effectiveness of the proposed algorithm.     

基于特征融合的高分辨率SAR 图像道路提取

随着机载和星载高分辨率SAR图像得到越来越多的应用, 人们开始研究新的有效的解译工具。虽然一个专业判读人员或许能够通过观察图像上亮的或暗的线性结构来检测道路网, 但是道路的自动检测仍然非常困难。提出一种简单的高分辨率SAR 图像主要道路自动提取方法。该方法分为三步: 第一步, 对原始图像进行预滤波, 分别进行了两个阈值化过程, 目的是去除不感兴趣区域;第二步, 输入第一步结果, 用Hough 变换分别进行道路识别; 最后一步基于特征融合技术, 利用一定的融合方法将检测的结果进行融合。根据对实际图像检测的结果, 证明该方法对于检测高分辨率SAR图像上的主要道路是有效的。     

利用高斯混合模型的SAR图像目标CFAR检测新方法

SAR（合成孔径雷达）图像杂波分布模型种类繁多且对实际地物的建模能力有限。在使用基于杂波统计模型的CFAR(恒虚警率)算法对SAR图像进行目标检测时,杂波统计模型的失配会导致检测结果产生较大的CFAR损失,算法精度不高。提出了一种基于高斯混合模型的CFAR检测新方法。该方法以理论上可以拟合任意形状概率密度分布的高斯混合模型对实际SAR图像的背景杂波进行拟合,利用拟合后得到的分布模型,根据CFAR检测的原理推导出目标检测阈值的计算公式完成目标的检测。新方法对服从不同分布模型的背景杂波,使用形式上统一的模型进行描述,克服了CFAR检测高度依赖背景杂波分布的缺点,提高了CFAR的通用性。实验结果表明,即使在背景杂波类型未知的情况下,新方法依然得到了良好的目标检测效果。     

ISAR imaging via sparse frequency-stepped chirp signal

Frequency-stepped chirp signal can simplify the designation of radar system.However,it has a shortcoming of Doppler ambiguity for high-speed moving targets.Therefore,it is of great significance to study how to increase its equivalent pulse repeat frequency.The back scattering field of the ISAR target has strong sparsity;that is to say,most energy is contributed merely by a few scattering centers.Hence,based on the theory of the sparse signal representation,a novel method for ISAR imaging via sparse frequency-stepped chirp signals is proposed by analyzing the signal model of the target.In the proposed method,part of sub-pulses of the frequency-stepped chirp signal is randomly selected to transmit,and then the 2D high-resolution image of the target can be constructed by sparse signal decomposition.At the cost of computational resources,the method can effectively resolve the problem of Doppler ambiguity,decrease the sidelobes and obtain a super-resolution image.Furthermore,the validity of the proposed approach is confirmed by the results of numerical simulations and real data.