Inverse modeling is a quantitative approach for characterizing parameters of the subsurface. Tomographic surveys (collecting data using common sense) make an inverse problem better posed because each survey cross-validates the others so that the modeling result approaches reality. Tomographic surveys using different types of energy provide coverage and perspectives of a watershed or basin at difference scales. Artificial stimuli (i.e., pumping tests, tracer tests) are suitable for small scale tomographic surveys, where small energy sources are adequate.  Spatially and temporally varying natural stimuli (i.e., precipitation, barometric pressure, river stage, lightning, earthquakes, etc.) are ideal energy sources for watershed or basin scale tomographic surveys, where energy sources of great strengths are required. Fusion of tomographic surveys using artificial and natural stimuli will expand and enhance the capability of a particular type of survey, provide cross-validation, and drive new sampling strategies.

In this seminar, we demonstrate the robustness of hydraulic/partitioning tracer tomography and our successive linear estimator for characterizing DNAPL source zone at field scales.  In addition, we demonstrate the possibility of using a novel river stage tomography to image subsurface heterogeneity at groundwater basin scales. We believe that fusion of tomographic surveys of different scales and types for characterizing groundwater basin or calibrating a groundwater model is  the future of geohydrology.