Subsurface Characterization Using Geophysical and Geohydrological Data Fusion

Abstract

We are introducing a novel technology applicable to the robust interpretation of the spatial distribution of hydraulic conductivity in heterogenous formations. The evidence theory approach is based on a combination of directly measured hydrogeological and geophysical data together with expert opinion. The approach first utilizes fuzzy-set based approximate reasoning to quantify subjective expert opinion, especially when data are scarce, to create a fuzzy prior characterization of the hydraulic conductivity field. Subjective information includes, but is not limited to opinions of groundwater professionals regarding the relationship between soil type and grain size or on the grain size to hydraulic conductivity relationship. Utilization of qualitative insights into the effects of geological processes as interpreted by the groundwater professional on hydraulic conductivity properties at a site is also a good example. Secondly, we propose to provide a new framework for integrating available kriged borehole data as well as geophysical information with the prior estimated conductivity field. The resulting evidence theory based approach has its core strengths in 1) enabling the simultaneous use of probabilistic uncertainty and other (non-additive) representations of uncertainty (e.g., fuzzy or possibilistic), 2) integrating expert opinion with objective information, 3) solving the delicate problem of choosing an appropriate prior estimate of hydraulic conductivity for the conditioning process, and 4) enabling a complementary (rather than sequential) use of geophysical data during the characterization process. The framework described herein allows a sensitivity analysis of the resultant characterization with respect to available data which makes it possible to assess the value (in the sense of consistency or conflict) of information. A site application demonstrates the approach.