沈 滨,李 俊,陈信钦

摘 要:船舶轴频电场信号是船舶的固有特征之一。浅海船舶轴频电场测量信号受到了低频周期噪声和海洋环境电场噪声等噪声的多重干扰,使得信号的提纯存在困难。这里具有针对性地对浅海船舶轴频电场信号进行分析,先通过时频分析方法对所得信号进行预处理,最后利用基于LMS算法的自适应滤波方法对测量信号进行噪声抵消。结果证明,这种方法确实使得干扰噪声得到大幅度抵消。

关键词:自适应滤波;LMS算法;时频分析;轴频电场

中图分类号:TN911文献标识码:A

文章编号:1004-373X(2009)19-044-03

Extraction of Shaft-rate Modulated Electric Fields of Ship-based under Kinds of Noise

SHEN Bin1,2,LI Jun1,CHEN Xinqin1

(1.Naval University of Engineering,Wuhan,430033,China;2.Wuhan Non-commisioned Officers School for Ordance,Wuhan,430075,China)

Abstract:The electric field is the intrinsic characteristic of a ship.Measurement of the electric field of a ship is greatly disturbed by noise in shallow sea.As far as time frequency method is concerned,the original signals are first analyzed within the frequency band,and then they are compared with the measured ambient signals.After the range of shaft-modulated signals are found,the signals of required frequency band are extracted for further IFFT transform.After that,the measured signals can be processed using adaptive filtering.At last,the better result is brought out.

Keywords:adaptive filter;LMS algorithm;time-frequency analysis;shaft-rate electric field

0 引 言

当船舶的主轴转动时,由于接触不恒定,引起螺旋桨-轴承-船体回路中的电阻变化,导致流经主轴的腐蚀或防腐电流发生内调制而产生以轴转动速率为基频的极低频电场及其谐波成分;当辅助阳极靠近螺旋桨时,螺旋桨叶片不能看作一个整体,辅助阳极和桨叶之间的电阻会随螺旋桨的转动而发生变化,从而导致流经螺旋桨的腐蚀或防腐电流发生外调制而产生以轴转动速率和桨叶数目的乘积为基频的极低频电场,即船舶轴频电场。轴频电场是不可能被完全隐身的船舶特征信号[1,2]。

1 船舶轴频电场的探测

随着现代电子技术、测试手段、传感器和信号处理技术的快速发展,使得海水中的船舶电场探测成为可能。船舶轴频电场信号属于极低频电场,而海水属于良导体,其环境电场富含各种频率的噪声。因此对轴频电场的测量实际上是在强背景噪声下进行的。……