INTERPRETATION OF SLINGRAM CONDUCTIVITY MAPPING IN NEAR-SURFACE GEOPHYSICS - USING A SINGLE-PARAMETER FITTING WITH 1D MODEL

Electrical conductivity mapping is a prerequisite tool for hydrogeolog ical or environmental studies. Its interpretation still remains qualit ative but advantages can be expected from a quantitative approach. How ever a full 3D interpretation is too laborious a task in comparison wi th the limited cost and time which are involved in the majority of suc h field studies. It is then of value to define the situations where la teral variations are sufficiently smooth for a 1D model to describe co rrectly the underlying features. For slingram conductivity measurement s, criteria allowing an approximate 1D inversion are defined: these ma inly consist of a limited rate of variation over three times the inter coil spacing. In geological contexts where the weathering has generate d a conductive intermediate layer between the underlying sound rock an d the soil, this processing can be applied to determine the thickness of the conductive layer from the apparent resistivity map when the oth er geoelectrical parameters are known. The examples presented illustra te this application.