A NEW METHOD FOR GEOELECTRICAL INVESTIGATIONS UNDERWATER

A new electrical method is proposed for determining the apparent resis tivity of multi-earth layers located underwater. The method is based o n direct current geoelectric sounding principles. A layered earth mode l is used to simulate the stratigraphic target. The measurement array is of pole-pole type; it is located underwater and is orientated verti cally. This particular electrode configuration is very useful when con ventional electrical methods cannot be used, especially if the water d epth becomes very important. The calculated apparent resistivity shows a substantial quality increase in the measured signal caused by the u nderwater targets, from which little or no response is measured using conventional surface electrode methods. In practice, however, differen t factors such as water stratification, underwater streams or meteorol ogical conditions complicate the interpretation of the field results. A case study is presented, where field surveys carried out on Lake Gen eva were interpreted using the calculated apparent resistivity master- curves.