Analysis procedure and equipment for deep geoelectrical soundings in noisy areas

• Published in: Geothermics 1982, Vol.11 (4), p.269-280
• Main Authors: Alfano, L., Carrara, E., Pascale, G., Rapolla, A., Roberti, N.
• Format: Article
• Language: English
• Subjects: computer aided control; electric variables measurement; electricity; filtration; geothermal resources; noise; noise levels; numerical analysis; resistivity; signals; sound waves; spectral analysis; surveys
• ISSN: 0375-6505; 1879-3576
• DOI: 10.1016/0375-6505(82)90033-5

This paper discusses the problem involved in extracting the useful signal from background noise during geoelectrical soundings in noisy areas or where a considerable depth of penetration is required. This problem often arises in geothermal volcanic areas where the exploration target is a low resistivity formation and high resistivity surface rocks generally prevent the energization of the soil by strong currents. The spectral characteristics of the signal and noise are discussed, along with the possibility of data analysis of geoelectrical data by two numerical filtering techniques (stacking and cross-correlation). A brief description is given of a digital geoelectrical acquisition data system and of some examples of data filtering relative to a deep dipole-dipole sounding survey in the Neapolitan geothermal area. These show that an extremely low amplitude signal can clearly be singled out from a noisy background—several times larger—by the proposed numerical techniques, so that a small portable electrical power source can be utilized in the field.