Reflection tomography of time-lapse GPR data for studying dynamic unsaturated flow phenomena

Abstract

Ground-penetrating radar (GPR) reflection tomography algorithms allow non-invasive monitoring of watercontent changes resulting from flow in the vadose zone. Theapproach requires multi-offset GPR data that are traditionallyslow to collect. We automate GPR data collection to reducethe survey time significantly, thereby making this approachto hydrologic monitoring feasible. The method was evaluated using numerical simulations and laboratory experimentsthat suggest reflection tomography can provide water contentestimates to within 5 % vol vol−1--10 % vol vol−1for the synthetic studies, whereas the empirical estimates were typicallywithin 5 %--15 % of measurements from in situ probes. Bothstudies show larger observed errors in water content near theperiphery of the wetting front, beyond which additional reflectors were not present to provide data coverage. Overall,coupling automated GPR data collection with reflection tomography provides a new method for informing models ofsubsurface hydrologic processes and a new method for determining transient 2-D soil moisture distributions