基于时频脊线旋转匹配的多普勒矫正方法研究

多普勒效应使信号产生畸变,增加了道旁高速列车声学故障诊断的难度。时域重采样是一种有效的多普勒畸变矫正方法,该方法需要对时间中心有一个准确估计。在深入分析多普勒畸变信号瞬时频率变化特征的基础上,提出一种新的多普勒畸变校正方法。用时频融合技术提高时频图的分辨率,对时频脊线旋转匹配以获得时间中心,从而求得重采样序列用以校正多普勒畸变。仿真信号和实验信号分析结果表明,该方法能有效实现多普勒矫正,在道旁声学故障诊断中有一定的可行性。     

基于时频脊线旋转匹配的多普勒矫正方法研究EI北大核心CSCD

多普勒效应使信号产生畸变,增加了道旁高速列车声学故障诊断的难度。时域重采样是一种有效的多普勒畸变矫正方法,该方法需要对时间中心有一个准确估计。在深入分析多普勒畸变信号瞬时频率变化特征的基础上,提出一种新的多普勒畸变校正方法。用时频融合技术提高时频图的分辨率,对时频脊线旋转匹配以获得时间中心,从而求得重采样序列用以校正多普勒畸变。仿真信号和实验信号分析结果表明,该方法能有效实现多普勒矫正,在道旁声学故障诊断中有一定的可行性。     

检测激光多普勒信号的新方法

为了准确地检测激光多普勒信号，提出了一种新的信号检测方法。在算法中应用梯度下降方法推导出算法的系统方程，并且应用庞加莱映射稳定原理给出系统稳定的存在条件。应用该算法能够检测激光多普勒信号，估计多普勒频移。测试结果表明，测出数据的相对误差小于0．7％。     

一种提高多普勒测速仪测频精度的方法

多普勒测速仪是水面或水下平台速度测量的主要设备。提出了利用随机样本一致(Random Sample Consensus,RANSAC)算法来估计多普勒频移,从而使速度测量具有更高的稳定性。多普勒测速仪信号处理的核心是测量多普勒频移,该方法利用回波复相关相位是多普勒频移的一次函数来估计多普勒频移,进而计算得到平台速度,在估计频移时采用RANSAC算法以提高测频精度。为了验证方法有效性,对信号形式为连续波(Continuous Wave,CW)脉冲对的情形进行了仿真。结果表明,提出方法的稳定性得到明显提高。     

基于多普勒频移的水下运动目标测距技术

研究了基于多普勒频移的水下运动目标测距的方法及关键技术,采用了基于Hilbert变换的信号平稳化方法,结合频率匹配和PMTM多锥度法功率谱估计改善处理增益并提高线谱的短时频率估计精度,并结合几何模型及频率导数求解目标斜距。对算法进行了仿真,仿真结果表明,算法正确可行,在谱级信噪比不低于10dB条件下能有效提高被动式水下运动目标测距的精度。最后给出一个应用实例。     

超声多普勒信号平均频率估计方法的比较研究

本文介绍了一些常用的超声多谱勒信号平均频率估计法,并引入一种新的估计法：基于Teager算法的平均频率估计,然后分别对计算机模拟的多普勒信号和流速校刻系统的多普勒信号进行平均频率的估计和比较,给出了不同估计方法的优缺点和适用范围。     

舰船辐射噪声线谱多普勒分析的ESPRIT方法

利用运动目标线谱的多普勒频移特性估计目标参数,需要精确提取出多普勒频移曲线。针对舰船辐射线谱噪声多普勒频移曲线提取的短时傅里叶变换（Short Time Fourier Transform,STFT）方法存在分辨率门限的问题,提出了一种利用子空间旋转不变技术（ESPRIT）高分辨频率估计法与STFT相结合的方法,提高了频率估计的精度和分辨率,可很精确地提取出频率间隔较近的多普勒频移曲线,而且计算量较小。计算机仿真和水池实验验证了该方法的有效性。     

合成孔径雷达高度计高度估计算法研究

本文对合成孔径雷达高度计高度估计算法进行研究.根据回波模型,推导出非聚焦合成孔径处理方式的回波相位补偿函数,消除了耦合相位对距离压缩的影响;通过多普勒条带中心校正方法,消除了俯仰角对高度估计算法的影响;利用多视处理方法减小了海浪对测高精度的影响,给出了合成孔径雷达高度计高度估计流程,根据算法流程对挂飞试验获得的湖面回波数据进行了分析与处理,并与差分GPS高度数据进行了对比.高度估计结果表明:经过相位补偿与多视处理方法后的回波谱线光滑且能量集中.估计精度满足高度计的要求,试验结果达到了预期目标.     

一种有效的水声通信多普勒处理方法

在水声通信中,由于发射和接收平台之间的相对运动,多普勒频移是无法避免的。多普勒频移使信号频率和相位发生变化,降低载波估计的精度,造成自适应均衡器的发散,使整个系统的性能下降。文中设计了一种应用于水声多载波相干调制系统的多普勒处理方法,采用块估计和线性插值以抵消多普勒频移的影响。仿真结果表明,该方法能有效地抵消多普勒频移对多载波相干调制系统的影响。在信噪比为-10dB、数据率为100bit/s的条件下,系统允许相对运动速度可达到±10m/s。     

全相位频谱校正技术在水声通信中的应用研究

多普勒效应是影响水下移动通信性能的主要因素,准确估计多普勒频移对提高通信系统可靠性具有重要意义。在进行离散频谱分析时,时域非整周期截断会造成频域能量的泄漏,导致频谱估计精度降低。全相位频谱分析具有良好的抑制频谱泄漏特性及相位不变性。仿真验证了全相位频谱校正技术相对于传统频谱校正技术在估计性能上的优势,并在此基础上探讨了全相位频谱校正技术在水声通信中的应用。采用全相位频谱校正技术进行多普勒频移估计,进而进行多普勒补偿以降低通信系统误码率。仿真结果表明,全相位频谱校正技术能够实现高精度多普勒频移估计,从而提高水下移动通信系统的可靠性。     

Quantitative assessment of flow velocity-estimation algorithms for optical Doppler tomography imaging

We present a quantitative comparison of three categories of velocity estimation algorithms, including centroid techniques (the adaptive centroid technique and the weighted centroid technique), the sliding-window filtering technique, and correlation techniques (autocorrelation and cross correlation). We introduce, among these five algorithms, two new algorithms: weighted centroid and sliding-window filtering. Simulations and in vivo blood flow data are used to assess the velocity estimation accuracies of these algorithms. These comparisons demonstrate that the sliding-window filtering technique is superior to the other techniques in terms of velocity estimation accuracy and robustness to noise.     

Time-domain calculation of spectral centroid from backscattered ultrasound signals

Spectral centroid estimation from backscattered ultrasound RF signals is the preliminary step for quantitative ultrasound analysis in many medical applications. The traditional approach of estimating the spectral centroid in the frequency domain takes a long time because discrete Fourier transform (DFT) processing for each RF segment is required. To avoid this, we propose time-domain methods to estimate the spectral centroid in this paper. First, we derive the continuous-time-domain equations for the spectral centroid estimation using Parseval's theorem and Hilbert transform theory. Then, we extend the method to the discrete-time domain to ease the implementation while maintaining the same accuracy as the calculation in the frequency domain. From the result, we observe that it is not practical to apply the discrete-time equations directly, because a high sampling rate is needed to approximate the time derivative in the discrete-time domain. Therefore, we also derive the feasible version of the discrete-time equations using a circular autocorrelation function, which has no constraints on the sampling rate for real RF signals acquired from pulse-echo ultrasound systems. Simulation results using numerical phantoms show that the time-domain calculation is approximately 4.4 times faster on average than the frequency-domain method when the software's built-in functions were used. The average estimation error compared with that of the frequency-domain method using DFT is less than 0.2% for the entire propagation depths. The proposed time-domain approach to estimate the spectral centroid can be easily implemented in real-time ultrasound systems.     

Wave-front slope estimation

The conventional way of measuring the average slope of the phase of a wave front is from the centroid of the image formed at the focal plane. We show the limitations of using the centroid and present an optimal estimator along with the derivation of its lower error bound for a diffraction-limited image. The method is extended to slope estimation in the case of a random aberration introduced by atmospheric turbulence. It was found that the variance of the error of the slope estimator can be improved significantly at low turbulence levels by using the minimum mean-square-error estimator instead of the centroid.     

Urban RF multipath mitigation

Sensing in urban environments is of growing interest to the surveillance community, as is observation of targets with micro-Doppler features ? elements of the target structure with independent range?Doppler behaviour about some target centroid. Multipath effects unique in character to urban sensing can conceal important features in the range?Doppler response of a target with micro-Doppler behaviour. The range- Doppler smearing because of multipath is analysed, and this analysis serves as the basis for a prominent point multipath mitigation algorithm. The effectiveness of this technique is evaluated with simulated micro-Doppler data with artificial multipath effects.     

Use of artificial neural networks for Hartmann-sensor lenslet centroid estimation

For adaptive optical systems to compensate for atmospheric-turbulence effects, the wave-front perturbation must be measured with a wave-front sensor (WFS). A Hartmann WFS typically divides the optical aperture into subapertures and then measures the slope of the wave front within each subaperture. Hartmann WFS slope measurements are based on estimating the location of the centroid of the image that is formed from a guide star within each subaperture. Conventional techniques for centroid estimation involve the use of a linear estimator and conversion tables. Neural networks provide nonlinear solutions to this problem. We address the use of neural networks for estimating the location of the centroid from the subaperture image. We find that neural networks provide more accurate estimates over a larger dynamic range and with less variance than do the conventional linear centroid estimator.     

Application of Bessel beam for Doppler velocity estimation

Limited-diffraction beams have a large depth of field and could be applied to medical imaging, tissue characterization, and nondestructive evaluation of materials. This paper reports the application of limited-diffraction beams, specifically, the Bessel beam, to Doppler velocity estimation. The Bessel beam has the advantage that velocity estimation is less subject to the depth of moving objects and the Doppler spectrum has distinct shoulders that increase the accuracy of velocity (both magnitude and Doppler angle) estimation in noisy environments. The shoulders of the Doppler spectrum might also help in solving the inverse problem, e.g., estimation of the velocity distribution in vessels     

分布式卫星 INSAR 系统中天线指向误差分析

基于分布式卫星INSAR(Interferometric Synthetic Aperture Radar)系统的特点,建立了分布式卫星INSAR系统中天线指向误差和由此引起的天线波束偏离的确定关系,分析了天线波束偏离引起的接收信号信噪比、多普勒中心以及方位模糊比的变化和由此产生的测高误差。根据分析结果和系统设计中的误差分配可以提出对天线指向误差的限制。     

星载合成孔径雷达多普勒调频斜率的时频估计方法

分析了星载合成孔径雷达（ＳＡＲ）回波的时频特性，提出了利用Ｖｉｌｌｅ－Ｍｏｙａｌ分布估计星载ＳＡＲ多普勒调频斜率的方法，处理ＥＲＳ－１实测数据的结果表明，其结果优于目前常的子孔径相关方法。     

CCD 超分辨率位置测量方法及性能分析

从理论上分析了光信号的分布形式及分布规律对 CCD 超分辨力位置测量的影响, 以高斯分布和均匀分布信号为例进行了具体分析与比较. 在此基础上提出了一种基于划分一维宏像素计算质心序列点, 通过拟合序列点剔除噪声影响的 CCD 超分辨力位置估计方法, 分析了这一算法的不确定度. 理论与实验表明, 这一算法的位置测量精度达到 0.02 个像素. 实验中通过与边缘拟合法、传统质心法的比较, 表明这一方法具有更强的抗噪声能力和较高的准确性.