Noise in EM exploration systems

Abstract

The contamination of the geophysical signal by variations in the geomagnetic field, by natural EM signals, and by mechanical motion of the receiving inductor in the earth's field is studied in detail. It is shown that the noise in the data of the more sensitive EM systems is subject to substantial variations of a seasonal, diurnal, and regional nature that may combine to yield a ~ 104 variation in extreme cases. Operational procedures that minimize the effects of noise upon the geophysical data are enunciated. The amplitude distribution of sferics is measured, and used to evalute the effectiveness of sferic suppression techniques.