Visual Detection of Chart-Recorded Signals in the Presence of Noise

A series of experiments for the purpose of determining the limiting sensitivity of seismic detection systems developed the following criteria for the visual detectability of permanent chart-recorded sinusoidal signals in the presence of bandlimited random noise. 1) The visual detection process is capable of discriminating against unwanted signals or noise outside of some frequency band of interest. 2) This discriminatory ability of the visual detection process can be represented by a filter with a geometric-mean center frequency of 0.2 cycles/mm and an effective bandwidth of 3 octaves. 3) For a sinusoidal signal to be detectable within the bandpass of this visual filter a signal-to-noise ratio of 2 is required. 4) The above criteria are applicable to sinusoidal signals 3 cycles in duration or greater.