m序列的功率谱密度分析,兼论伪随机信号电法仪的抗干扰性

Analyze the power spectral density of the m sequence and discuss the anti-interference ability of instruments for electrical and electromagnetic prospecting using pseudo random signal

近年来,基于伪随机信号系统辨识的“伪随机信号电法仪”受到广泛关注.普遍认为,伪随机信号电法仪具有两大优点:抗干扰能力强和一次观测便可获得大地阻抗频谱的高效性.本文基于对m序列的功率谱密度的计算和分析,探讨了伪随机信号电法仪的抗干扰性能.结果表明,至少对于频率域伪随机信号电法仪来说,与采用正反向连续方波的传统频率域电法仪相比,在相同供电电流强度条件下,其有效信号强度大约降低√N*2/π倍(N是m序列的位数);伪随机信号电法仪一次观测获得多频点频率响应的高效性,是以降低各个频点上的有效信号强度为代价的.这都不利于提高仪器的抗干扰性能.

In recent years, the instruments for electrical and electromagnetic prospecting using pseudo random signal are attracted a wide spread attention. It is pointed by the textbooks and many literatures, that the outstanding advantages of these instruments are of a strong anti-interference ability and of the high-efficiency for obtaining the frequency spectra of earth's impedance by once observation. Based on the calculations and analysis of the PSD(power spectrum density) of m-sequence, the anti-interference ability of these instruments was discussed in this paper. Result is at least for the instruments of electrical and electromagnetic prospecting using pseudo-random signal in frequency domain, at the same condition of supply current strength, the effective signal strength would √N*2/π times less than that for the conventional instruments of electrical and electromagnetic prospecting using square wave supply current. So the high-efficiency of the instruments in frequency domain using pseudo-random signal(to get the frequency response of the earth system at many frequency points just by once observation), would at the cost of lower effective signal strength at each frequency point. It should not benefit to improve the anti-interference ability of the instrument.