背景噪声与地震信号的强度或周期差异决定了地震震相是否可以从视觉上有效识别。为寻找平稳背景噪声中地震信号的视觉可识别判据，本文研究了既能反映两者频率差异、又能反映强度差异的参量用于上述两种信号对比，得到了背景噪声中地震信号视觉可识别条件的量化判据，并用实际的观测资料及仿真数据对该判据进行验证。在此基础上，针对功率谱计算过程中的校正环节进行讨论，利用Albuquerque实验室给出的测试实例阐明了USGS标准中功率谱计算的规范步骤及细节。

 Small seismic event waves and weak teleseismic signals are always buried in background noise and can’t be identified visually; the difference both in strength and frequency between background noise and seismic signal decides whether the seismic signal can be distinguished from steady background noise. For searching a parameter which can indicate the difference both in strength and frequency between background noise and seismic signal, a criterion for distinguishing seismic signal from steady background noise visually are worked out and then demonstrated by practical data and its simulation. Furthermore, which kind of amending steps should be used in calculation of power spectral density are argued and then the normal way of USGS standard for power spectral density calculation is detailed and demonstrated by an example of Albuquerque Seismological Laboratory.