S变换在心肌声学造影图像降噪中的应用

提出一种基于二维S变换的时频滤波方法。S变换融合了短时傅里叶变换和小波变换的优点,适合医学图像处理。该方法在局部频谱利用硬阈值去噪,可用于心肌声学造影图像降噪。降噪实验表明了该方法的有效性和临床应用价值。     

基于Radon变换的浅海低SNR目标被动测距算法

针对在较低信噪比情况下,无法清晰观测浅海波导中宽带声源干涉条纹,利用Radon变换估计条纹斜率会出现误差,影响声源被动测距精度的问题,提出一种针对声强干涉条纹进行二维傅里叶变换,获得二维傅里叶变换脊,利用Radon变换估计脊的斜率,准确估计目标声源距离的方法.基于波导不变量的概念,对干涉条纹进行二维傅里叶变换,根据脊的斜率与干涉条纹的斜率之间对应关系,通过Radon变换估计脊的斜率换算出干涉条纹斜率,最终实现目标被动测距.数值仿真在不同信噪比情况下算法改进前后目标测距的效果对比,发现所提算法可以获得2dB增益,即在更低信噪比条件下实现被动测距,验证所提方法的有效性.     

FFT计算菲涅尔衍射相位的跳变与矫正研究

采用傅里叶变换算法计算菲涅尔衍射相位时,在相位未解包裹的情况下,接收面上提取的相位分布曲线会出现跳变,如果进行解包裹,必然会导致错误的结果。研究发现用傅里叶变换算法进行衍射计算导致接收面上相位跳变的原因,是因为快速傅里叶变换（FFT）对矩阵标注索引的方式与离散傅里叶变换（DFT）有所区别,从而导致计算结果的相位与真实相位有差异。本文提出在FFT运算前后分别进行一次倒谱的方法矫正这种相位跳变,并仿真利用单次FFT进行二维矩孔的菲涅尔衍射,用2次倒谱矫正接收面上的相位跳变,结果证明了该矫正方法的可行性。     

光学综合孔径目标信息的提取与仿真

提出了基于最小二乘法准则提取目标傅里叶信息的方法，结合传统的信息提取方法．对光学综合孔径目标信息的提取进行了仿真。仿真实验表明，相位调制法提取目标信息效果最好，但信息提取速度较慢；基于最小二乘法准则可同时高速提取观测目标的傅里叶幅度和相位。最后对多孔径综合干涉阵的信息提取进行了研究，指出基于条纹图像的频谱性质可成功分离各基线对应的条纹图像，从而实现信息的提取；基于最小二乘法准则也可实现多孔径综合干涉阵的信息提取。     

基于正余弦变换和BM3D滤波的DSPI图像去噪方法

数字散斑干涉(Digital Speckle Pattern Interferometry,简称DSPI)是一种高精度形变测量的方法,针对航天实验现场数字散斑干涉中的随机噪声影响相位求解精度的问题,提出了一种新的相位图去噪方法.这种方法将正余弦变换滤波技术和BM3D(块匹配三维滤波)技术相结合,首先将相位图分别进行正余...     

基于小波降噪与多项式拟合相位校正的干涉图处理方法

干涉图是傅里叶变换光谱仪测试的原始信号,理论上它是偶函数。在实际测量中,由于检测延时等因素会导致测量干涉图存在相位误差。此外,在光谱测量过程中必然还伴有噪声。干涉图中存在的相位误差和噪声会影响光谱的质量。本文提出了先采用小波对干涉图降噪,再用多项式拟合方法来校正干涉图的相位误差,然后由处理后的干涉图获得高质量光谱的方法。通过对酒精的近红外实验测试结果表明,该方法对于光谱的高质量估计有较好的效果,经过处理的干涉图计算得到的光谱在酒精的定量分析中获得了较好的分析结果。     

基于复Morlet小波的地层钻探识别

在低信噪比时,短时傅里叶变换和实小波变换无法准确提取钻头进入不同地层的时延信息。为此,提出一种复小波变换分析法。利用幅值和相位信息对信号突变点进行提取和定位,从而实时判断钻头钻进目的层的时刻。实验结果表明,该方法能准确表征振动信号的时频特征,与短时傅里叶变换和实小波变换相比,具有更好的时间定位和抑噪能力。     

基于残差点的干涉相位图自适应滤波

为了能有效地对InSAR干涉相位图进行滤波,利用残差点矩阵作为滤波控制因子,对两种干涉相位图滤波方法进行了改进。该措施在不破坏致密的干涉条纹的情况下,通过引用干涉相位图的残差矩阵,对不同区域的图像采用不同强度的滤波器来实现自适应的降噪,同时详细描述了滤波方法的实施步骤,并用ERS-1重复轨道数据进行了验证,结果表明,该改进方法可取得良好的滤波效果。     

一种基于并联卷积神经网络的InSAR相位滤波方法

为了提高InSAR干涉相位图的质量以及改善密集条纹区域的边缘信息保持效果,提出了一种基于并联卷积神经网络的InSAR相位滤波方法。该方法通过多个并联的卷积神经网络提取多尺度相位信息的特征层以及传统卷积神经网络结构的滤波层,将不连续跳变的干涉相位转换至连续的正、余弦分量,并送入到并联卷积网络中进行残差学习,最后输出相位残差并完成相位滤波。通过仿真实验与实测数据验证了该方法的有效性。分析结果表明,该方法的各项评价指标均优于Boxcar滤波、非局部均值滤波和Goldstein滤波,可用于实际的InSAR数据处理中,提高干涉相位质量。     

提高频域合成孔径超声阵列成像质量的方法

随着工业制造水平的不断提升,对于工业无损检测的要求也越来越高。为了实现更快更准确的检测,基于相位迁移算法的频域合成孔径超声成像方法在实际成像检测中应用越来越多。针对该成像理论,提出一种提高成像质量的方法。首先对时域阵列检测信号,依次进行卷积滤波、波形包络提取及信号锐化处理,提高信号信噪比。然后再将这些信号进行二维傅里叶变换,并通过相位迁移算法重建声场。最后使用二维傅里叶反变换对检测区域进行逐层成像,用多缺陷试块进行检测成像实验。结果表明,经过该方法处理,成像质量得到提高,与未预处理的成像结果比较,在相同实验条件下,信噪比平均提高3.9dB。     

A wavelet domain detail compensation filtering technique for InSAR interferograms

The quality of interferogram filtering affects the accuracy of interferometric synthetic aperture radar (InSAR) applications. This article presents a new wavelet domain filtering method for phase noise reduction in an InSAR interferogram. The method first transforms the real and imagery parts of the original interferogram into the wavelet domain using the stationary wavelet transform (SWT). Then the coefficients for each sub-band are filtered with detail compensation. Finally, the wavelet coefficients are reconstructed in the space domain by the inverse SWT. The results show that the proposed method can suppress the speckle effectively, maintain details of the interferogram well, and greatly reduce the number of residues.     

An iterative Goldstein SAR interferogram filter

This article presents a new modified Goldstein synthetic aperture radar (SAR) interferogram filter algorithm, named the iterative Goldstein filter. The main idea of this approach is to iteratively filter the SAR interferogram, by determining the filtering parameter alpha adaptively with respect to the pseudo-correlation value of the original and/or last filtered interferograms several times. The filter can be stopped automatically by pre-setting the threshold of mean value and the improvement of pseudo-correlation in given filter windows. Experimental results with both a simulated digital elevation model (DEM) interferogram and real SAR deformation interferogram show an improvement in the new algorithm results compared with those using the Goldstein filter, and its enhanced version, the Baran filter. In addition, from a pseudo-correlation map of the iteratively filtered interferogram, some valuable information can also be abstracted based on the signal residues.     

雷达干涉条纹图滤波方法研究

在合成孔径雷达干涉测量中,为滤除干涉图像中存在的各种噪声,提高相位解缠结果及生成的数字高程模型的精度.从分析干涉条纹图的特点入手,对干涉条纹图的圆周期中值滤波法进行了研究,提出一种基于高斯噪声估计的自适应圆周期中值滤波方法,给出了算法设计及详细的实验数据并与其它滤波方法进行比较.试验结果表明,该方法可以较好地消除干涉图像中存在的噪声,而且保留更多的图像边缘、细节信息.     

Probabilistic solutions of some multi-degree-of-freedom nonlinear stochastic dynamical systems excited by filtered Gaussian white noise

In this paper, the state-space-split method is extended for the dimension reduction of some high-dimensional Fokker–Planck–Kolmogorov equations or the nonlinear stochastic dynamical systems in high dimensions subject to external excitation which is the filtered Gaussian white noise governed by the second order stochastic differential equation. The selection of sub state variables and then the dimension-reduction procedure for a class of nonlinear stochastic dynamical systems is given when the external excitation is the filtered Gaussian white noise. The stretched Euler–Bernoulli beam with hinge support at two ends, point-spring supports, and excited by uniformly distributed load being filtered Gaussian white noise governed by the second-order stochastic differential equation is analyzed and numerical results are presented. The results obtained with the presented procedure are compared with those obtained with the Monte Carlo simulation and equivalent linearization method to show the effectiveness and advantage of the state-space-split method and exponential polynomial closure method in analyzing the stationary probabilistic solutions of the multi-degree-of-freedom nonlinear stochastic dynamical systems excited by filtered Gaussian white noise.     

基于小波变换和圆周期均值算法的InSAR干涉纹图噪声抑制

在分析InSAR干涉纹图特点的基础上,提出了一种基于小波变换和圆周期均值算法的干涉纹图噪声抑制方法,阐述了该方法的设计思想和具体算法实现步骤.利用德国欧洲空间局(ESA)提供的ERS-1/2串行SAR数据进行了实验,实验结果证明所提出方法不仅有效地抑制了干涉纹图中的噪声,而且很好地保留了干涉纹图中的边缘细节信息.     

基于加权联合导向矢量模型的InSAR干涉相位估计

基于干涉图的传统干涉相位估计方法,当由于图像配准误差而导致的干涉图质量较差时,就难以恢复出准确的真实干涉相位.本文提出了一种基于加权联合导向矢量模型的InSAR干涉相位估计方法.该方法构造最优联合观测矢量和加权联合导向矢量,同时利用相邻像素的相干信息,并采用波束形成技术,因此具有自适应图像配准和降低相位噪声的功能,因而可以在SAR图像配准精度很差(可以允许达到一个分辨单元)的条件下准确地估计相应像素间的干涉相位.仿真及实测数据的处理结果证明了此方法的有效性.     

Filtering method for SAR interferograms with strong noise

We develop a filtering method for SAR interferograms with strong noise based on the concept of the Vondrák filter and the commonly used Goldstein filter. The one‐dimensional Vondrák filter is first extended to two dimensions, and then utilized to smooth the Fourier spectra of overlapped interferogram patches. The smoothed spectra are then back‐transformed into the interferogram space. Experimental results with simulated and real datasets show that the proposed filter can eliminate up to 70% of noise in a SAR interferogram. The results also show a 15% to 35% improvement over some of the existing filters when the noise in an interferogram is strong, and the stronger the noise in an interferogram, the greater is the improvement.     

InSAR干涉纹图噪声抑制算法的比较及改进

干涉纹图中的噪声影响着InSAR的图像质量,使得相位解缠无法进行或者使生成的DEM精度降低。为了获得高质量的InSAR纹图,必须对噪声进行有效抑制,同时保持空间分辨率。文中探讨了InSAR干涉纹图的噪声抑制方法,提出了一种新的干涉纹图的滤波方法。并采用了真实数据验证了方法的有效性。     

一种提高INSAR干涉图质量的新方法

如何获取高质量的干涉图是INSAR技术的核心问题之一.首先概述了干涉图中存在的噪声,并对干涉图中频谱混叠现象的成因及其影响进行了重点分析.针对SAR影像距离向和方位向频谱的特性,通过增加影像频谱中空白带的带宽对影像进行过采样,从而成功消除了干涉图中的频谱混叠现象.针对过采样后干涉图数据量激增的问题,利用干涉图频谱的理论权函数推导了欠采样函数.最后,利用ERS数据验证了文中的过采样方法能有效消除干涉图中的频谱混叠现象,显著提高干涉图质量.同时,利用文中推导的欠采样函数可以使干涉图在恢复原始大小的同时,使噪声得到进一步抑制.     

SAR image processing using adaptive stack filter

Stack filters are a special case of non-linear filters. They have a good performance for filtering images with different types of noise while preserving edges and details. A stack filter decomposes an input image into several binary images according to a set of thresholds. Each binary image is filtered by a Boolean function. The Boolean function that characterizes an adaptive stack filter is optimal and is computed from a pair of images consisting of an ideal noiseless image and its noisy version. In this work the behavior of adaptive stack filters on synthetic aperture radar (SAR) data is evaluated. With this aim, the equivalent number of looks for stack filtered data are calculated to assess the speckle noise reduction capability of this filter. Then a classification of simulated and real SAR images is carried out on data filtered with a stack filter trained with selected samples. The results of a maximum likelihood classification of these data are evaluated and compared with the results of classifying images previously filtered using the Lee and the Frost filters.