模数转换方式对地震数据信噪比的影响分析

Effects of A/D converting on the SNR of seismic data

模数(Analog/Digital,A/D)转换器是地震仪中的一个重要装置,用于将模拟电信号转换成数字信号,该转换器的参数设计基于人们对地震勘探中信号与噪声特性的认识。根据噪声与地震采集系统(检波器+地震仪)的关系对噪声类型进行了划分,标定了不同类型噪声的强度与模数转换位数之间的关系。在此基础上,根据模数转换原理计算了定点32位、24位A/D转换以及浮点15位A/D转换在无噪声和有噪声时的频谱。数值模拟结果证明,目前广泛采用的24位定点A/D转换器适用于当前地震勘探信号,32位定点A/D转换和15位浮点A/D转换对地震数据信噪比的提高并没有太大帮助;在噪声压制技术取得较大进步,将噪声再衰减-30^-40dB之前,扩大A/D转换器的动态范围不会显著提高有效弱反射信号的识别能力。

The A/D （Analog/Digital） converter,which converts the analog electric signal to a digital signal,is one of the most im-portant devices in a seismograph. The parameter design of an A/D converter is based on the recognition of the characteristics of signal and noise in seismic exploration Based on the relationship between noise and a seismic acquisition system, such as a seismo-graph and geophone, this paper presents a new classification of noise, while calibrating the relationship between the intensity of dif-ferent types of noise and the bits of an A/D converter.On that basis？the frequency spectra of simulation data from 32-fixed-bit,24- fixed-bit, and 15-floating-bit A/D converters were calculated in the absence and presence of noise. The results showed that the widely used 24-fixed-point A/D converter is suitable for current seismic acquisition, while the 32-fixed-point and 15-floating-point converters are not helpful for improving the SNR of seismic data. Expansion of the dynamic range for A/D converters will not sig-nificantly improve its ability to identify a weak reflection signal,unless noise suppression technology sufficiently progresses to at-tenuate noise by -30 to -40 dB more than the existing level.