基于随机共振的GPS接收信号消噪方法

GPS接收信号中的噪声干扰一直以来都是研究人员想方设法消除的不利因素,但在某些非线性系统中,噪声的存在却能够提高信号的检测性能,利用Langevin方程构建的非线性随机共振系统对GPS接收信号进行消噪处理,经过对仿真信号的验证,消噪效果明显,将在GPS接收信号消噪领域得到很好的应用。     

多光谱激光雷达小波去噪效果评价体系

针对基于小波理论的多光谱激光雷达消噪信号,从能量、图形、统计多角度出发,提出了由信噪比、平滑度等6项指标组成的小波消噪效果评价体系。实验证明,该体系可以为多光谱激光雷达消噪信号提供更加全面客观的效果评价,为不同信号噪声去除方法的选择提供更加可靠的依据,同时也有利于对不同算法进行有针对性的改进。     

基于小波阈值算法的海杂波信号降噪

为有效提取噪声背景下的海杂波信号,针对海杂波信号非线性非平稳的特点,提出基于小波阈值算法对实测海杂波数据去噪。在噪声水平未知条件下,提出基于噪声主要在高频段且能量较小、信号主要集中在低频段思想的噪声判断准则。为验证小波去噪效果,将该算法对含有噪声的海杂波实测数据进行去噪,采用均方差和降噪信号信噪比两项指标衡量去噪效果,并与均值和中值等去噪方法对比,小波算法在这两项指标均优于其他算法;此外,实验结果还表明,db2小波在双曲线阈值函数和HeurSure阈值模式下优于其他小波去噪效果。     

风浪背景下舰船水压场信号的自适应AR模型预测滤波

为了有效地从风浪背景中检测舰船水压信号,首先根据舰船水压信号和波浪噪声的特点以时间序列的AR模型理论为依据,导出一种便于实现的自适应滤波器结构,并用NFTF自适应算法实现对舰船水压信号的预测滤波,取得了明显的效果.计算机仿真实验结果表明,给出的方法对抗波浪干扰具有良好的性能.     

基于小波消噪和希尔伯特黄变换的损伤检测技术研究

针对经验模式分解(EMD)易受噪声影响的缺点,提出采用小波消噪结合Hilbert-Huang变换的结构损伤检测方法。首先对含噪声振动信号进行小波消噪预处理实现信噪分离,再进行EMD分解得到若干固有模态函数(IMF),利用希尔伯特(Hilbert)变换得到其瞬时频率。提出了一个基于低阶瞬时频率变化率的损伤判定指标,利用此指标可以判断损伤是否发生。数值研究结果表明小波消噪结合HHT的方法是进行损伤检测比较有效的方法。     

海洋磁力测量中不同小波母函数的阈值消噪方法性能分析

首先介绍了小波阈值消噪的基本原理,认为小波阈值消噪的性能受三方面因素的影响:(1)小波母函数的选择;(2)阈值方法的选择;(3)阈值函数的选择.为了寻找小波母函数、阈值估计和阈值函数的最优组合,文中以实测海洋磁力测量数据为背景,采用小波阈值法进行消噪,把得到的磁异常值作为"真值".仿真了波浪噪声和随机噪声并加入到"真值"磁异常中,作为噪声磁异常.在此基础上采用两种小波族系(Symlets,Daubechies)、四种阈值选取方法和软、硬阈值函数对噪声磁异常进行了基于小波变换的消噪计算,客观分析了不同组合方法的消噪精度和可靠性.实际计算结果表明:对磁异常突变点较多且分布杂乱的测线进行消噪,Sym6、软阈值函数、混合阈值或基于Stein无偏似然估计消噪效果最好;对磁异常突变点少且大部分光滑的测线进行消噪,db7、基于Stein无偏似然估计和软阈值函数的消噪效果最好.     

改进的WOA-VMD算法在水声信号去噪中的应用

本文提出一种针对非平稳水声信号的改进WOA-VMD小波阈值去噪方法,首先,引入余弦收敛因子和自适应权值提升鲸鱼优化算法(WOA)的精度,然后利用WOA选取水声信号变分模态分解(VMD)的最佳参数组合。引入一种可调阈值函数克服传统阈值函数量化过程的缺陷,考虑到不同分解尺度下噪声小波系数的衰减特性,采用分层阈值法对有效信号分量进行去噪处理。通过仿真实验和实测数据的降噪分析,证明了该方法的有效性和应用价值,新方法的去噪性能优于其他方法。     

基于GPS-RTK技术的波浪能发电装置结构动态位移监测及滤波方法

利用全球定位系统实时差分技术（Global Positioning System Real-Time Kinematic,GPS-RTK）对波浪能发电装置进行结构变形监测得到的信号会存在噪声。针对这个问题,本文提出一种结合巴特沃斯（Butterworth）滤波器和自相关函数经验模态分解（Empirical Mode Decomposition,EMD）的滤波降噪算法,利用动态位移仿真信号进行了实验验证。结果表明：该滤波算法能够有效降低装置动态位移监测数据中噪声的影响,利用滤波算法对仿真信号进行降噪处理之后,可以提取出信号中包含的结构固有频率。     

LMS自适应时间延迟估计

本文研究了基于widrow的最小均方(LMS)算法的自适应时间延迟估计的基本原理、结构和算法,分析了这种估计方法的性能,并给出了计算机模拟的结果。在此基础上,讨论了自适应时间延迟估计器与广义相关时延估计算法中Roth处理器的关系,并利用维纳滤波器把二者联系和统一起来。     

基于火箭发动机的脉冲信号检测

水下火箭发动机工作时,尾部会产生高强度、宽频带背景噪声。在分析火箭发动机噪声产生机理和物理特性的基础上,主要研究了火箭发动机噪声背景下脉冲信号的检测流程和方法。采用自适应消噪和滤波,减弱背景噪声强度并提高了信噪比,建立了火箭发动机噪声背景下脉冲信号的检测方法,解决了强背景噪声脉冲信号难以检测的问题,为火箭发动机水下应用提供了新的思路。     

白噪声Kalman滤波模型在GPS单向授时中的应用

全球定位系统(GPS)的应用越来越广泛,尤其是高精度的星载原子钟使得授时的精度得到了很大的提高。针对GPS授时过程中接收机受到各种噪声的影响,利用Kalman滤波原理,建立状态方程和观测方程,对噪声进行分类并加以讨论。运用Kalman滤波原理对接收机钟差数据进行分析,计算结果表明Kalman滤波可提高GPS单向授时精度。     

Adaptive beamforming: spatial filter designed blocking matrix

Controlling the resolution in adaptive beamformers is often crucial. A simple method that works for both narrow-band and broad-band arrays is presented. This method is based on the normalized leaky LMS algorithm in conjunction with a generalized sidelobe canceller (GSC) structure, where the GSC is designed using a spatial filtering approach. In essence, the suppression of the spatial filters and the implicit noise of the leaky LMS algorithm together determine the adaptive beamformer. Analytical expressions are given for the Wiener filters and the output spectrum versus frequency and point source location. These expressions are employed in the design specification of the spatial filters and to obtain conditions for a controlled quiescent beamformer response. Simulation results are presented to illustrate the behavior of the array     

Testing and evaluation of an integrated GPS/INS system for smallAUV navigation

A Small Autonomous Underwater Vehicle Navigation System (SANS) is being developed at the Naval Postgraduate School. The SANS is an integrated Global Positioning System/Inertial Navigation System (GPS/INS) navigation system composed of low-cost and small-size components. It is designed to demonstrate the feasibility of using a low-cost strap-down inertial measurement unit (IMU) to navigate between intermittent GPS fixes. The present hardware consists of a GPS/DGPS receiver, IMU, compass, water speed sensor, water depth sensor, and a data processing computer. The software is based on a 12-state complementary filter that combines measurement data from all sensors to derive a vehicle position/orientation estimate. This paper describes hardware and software design and testing results of the SANS. It is shown that results from tilt table testing and bench testing provide an effective means for tuning filter gains. Ground vehicle testing verifies the overall functioning of the SANS and exhibits an encouraging degree of accuracy     

Optimal estimation of ship's attitudes and attitude rates

Estimation of ship rotational motions induced by ocean waves plays a central role in many navigation and fire control applications. Inertial-type instruments are available which give good measurements of the attitude, but some form of signal processing is necessary to obtain angular rates or predict attitudes. Using optimal moving-average (or transversal) filters, we can obtain very good estimates of attitude rates as well as predictions of these values. Filter parameters can be changed adaptively to maintain good performance as the ship changes heading or velocity. The problem of designing these optimal filters is examined in detail and numerical results are given for a particular set of conditions. Two implementations of the adaptive filter are discussed. One is based on a recursive estimation of the process autocorrelations with the filter coefficients being recomputed at periodic intervals or whenever nonstationary conditions are detected. The second implementation is based on Widrow's LMS algorithm. Both alternatives for the adaptive filter implementation are quite reasonable in terms of their computational requirements. The steady-state performance analysis can be considered to be a lower bound on the errors incurred by an adaptive filter.     

GPS浮标数据反演海浪谱的理论仿真与试验验证

GPS浮标作为一种新型的海洋测量设备,近年来在海面高度现场测量和星载高度计定标方面取得了重要应用。通过仿真试验对反演海浪谱的方法和流程进行研究,旨在探索从GPS浮标测量的海面高度序列中提取海浪谱的方法。首先,使用Longuest模型生成了海浪波面位移时间序列,并通过Pierson-Moscowitz风浪谱对波面位移的统计特性进行约束,其随机性由相位引入。结合典型潮汐和GPS浮标仪器噪声的仿真时间序列,合成了仿真时间长度1h的1Hz(每秒1次)随机海面高度序列。然后,利用自相关函数法,进行高通滤波和数据压缩,得到了仿真的海浪谱。该仿真结果和理论海浪谱非常接近,可满足海浪谱反演的需求。最后,通过山东石岛外海的GPS浮标现场试验,验证了本文提出的反演方法的适用性。本文的研究解决了GPS浮标反演海浪谱的关键问题,丰富了海浪谱反演的手段,拓展了GPS浮标的应用领域,有望为未来我国的星载波谱仪定标服务。     

水声扩谱通讯中的自适应多普勒补偿方法

本文介绍了一种水声扩谱通讯中，应用子波对多普勒效应进行补偿的方法。针对多普勒效应本身是否会随时间变化，分别应用直接估计、自适应估计的方法。其中自适应多普勒补偿方法同自适应信道均衡算法结合在一起，对多普勒漂移、信道参数进行联合估计。两种方法都应用了子波变换对多普勒展宽程度进行估计并用线性插值进行补偿。计算机仿真结果令人满意。     

GPS接收机与PC机间串口通信的实现

简要介绍了当前流行的几种串口通信程序开发模式以及GPS接收机广泛采用的NMEA0183通信协议，设计了串口通信类CSerialPortGPS，该类能够实现GPS接收机与Pc机问的串口通信，并且能够对遵循NMEA0183协议的GPS数据进行数据校验和数据提取，并成功地将该类应用到了车载定位导航系统的开发中。     

Adaptive beamforming of a towed array during a turn

During maneuvering, towed array beamforming degrades if a straight array is assumed. This is especially true for high-resolution adaptive beamforming. It is experimentally demonstrated that adaptive beamforming is feasible on a turning array, provided that array shape is estimated. The array shape can be inferred solely from the coordinates of the tow vessel's Global Positioning System (GPS) without any instrumentation in the array. Based on estimated array shape from the GPS, both the conventional beamformer and the white noise constrained (WNC) adaptive beamformer are shown to track the source well during a turn. When calculating the weight vector in the WNC approach, a matrix inversion of the cross-spectral density matrix is involved. This matrix inversion can be stabilized by averaging the cross-spectral density matrix over neighboring frequencies. The proposed algorithms have been tested on real data with the tow-vessel making 45/spl deg/ turns with a 500-m curvature radius. While turning, the improvement in performance over the assumption of a straight array geometry was up to 5 dB for the conventional beamformer and considerably larger for the WNC adaptive beamformer.     

Adaptive second-order Volterra filtering and its application tosecond-order drift phenomena

This paper presents an adaptive second-order Volterra filter and its application to model-test data of a prototype tension leg platform (TLP). The least-squares approach of a second-order Volterra model and its adaptive filtering algorithm based on recursive least-squares are introduced. The second-order Volterra filter is applied to identify the linear and quadratically nonlinear relationship between irregular sea wave excitation and the surge response of a tension leg platform. Next, a deconvolution technique, based on the impulse invariance standard Z-transform, is utilized to recover the linear and quadratic forces exerted on the TLP