数字化噪声对强震记录的影响及其消除方法
THE EFFECTS OF DIGITIZATION ERRORS ON ANALYSIS OF STRONG-MOTION RECORDS AND THEIR ELIMINATION
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摘要: 本文详细地分析了强震加速度记录的数字化噪声。分析表明:数字化噪声由数字化设备的系统误差和操作者的随机读数误差迭加而成,随机数字化误差是具有各态历经性质的,其振幅按高斯规律分布的平稳随机过程,在其频谱组成中,长周期分量占明显的优势,因此将对二次积分加速度记录的位移曲线产生严重的影响。 研究表明:随机数字化噪声位移主要分布在周期大于25秒的频段,对加速度记录来说,分布在周期小于25秒的频段内,其随机噪声是相当小的(假定记录纸速为1厘米/秒)。因此,利用数字滤波技术,可以除去数字化加速度记录中的大部份随机数字化噪声。 作为实例,对一个典型的强震加速度记录进行了滤波,给出了低噪声的加速度记录和由此算出的位移曲线,且和未经滤波的相应记录及其位移进行了比较。Abstract: Detailed analysis of digitization errors resulting from the processing of digitizing strong motion accelerograms is made in this paper. It shows that the digitization errors can be considered as a superposition of systematic errors introduced by the digitizing equipment and random noise errors produced mainly by operators. It also shows that the random noise is an ergodic stationary random process, the amplitudes of which are of Normal Gauss Distribution, and the long period components of their frequency content are apparently predominant. It will, thus, give a serious effect on the double integrated displacement from a digitized accelerogram containing these errors. But further studies indicate that random digitized noise displacemets are mainly distributed in the range of periods longer than 25 second and give relatively small values up to a period of 25 second for the accelerogram, the typical recording speed of which is 1 cm/ sec. Accordingly, a background of random noise is obtained and most parts of such noise could be filtered out from the digitized accelerograms by using of the digital filtering. A typical filtered accelerogram and its double integrated displacements are given as an example and a comparison with the unfiltered accelerogram and its respective displacements is also made.