HR: 10:35h
AN: H42B-02 INVITED    [Abstracts]
TI: Estimating hydrological parameters using surface nuclear magnetic resonance (SNMR) tomography
AU: * Hertrich, M
EM: marian@aug.ig.erdw.ethz.ch
AF: ETH Zurich, Institute of Geophysics Schafmattstr. 30, Zurich, 8093, Switzerland
AB: Surface nuclear magnetic resonance (SNMR) takes advantage of precession phenomena that result from exciting groundwater hydrogen protons in the Earth's magnetic field by secondary magnetic fields generated by large surface loops. This method, which allows subsurface water content to be determined from inversions of surface measurements, is commonly employed in a 1-D mode. Conventionally, the same loop is used to generate the secondary magnetic fields and measure the tertiary magnetic fields that result from the excited hydrogen protons precessing back to their equilibrium state. Recent developments provide greater sensitivity in the shallow subsurface and extend the method to true 2-D investigations in which surface topography is correctly accounted for:
i) separated transmitter and receiver loops with variable offsets supply significantly improved subsurface coverage and sensitivity, with emphasis on shallow structures,
ii) state-of-the-art finite-element-based modelling and inversion techniques allow complex 2-D structures underlying complicated topography to be resolved.
In laboratory and borehole NMR applications, it is not only possible to estimate water content, but also hydraulic conductivity. Unfortunately, these well-established small-scale techniques cannot be employed in surface applications. We are in the process of developing and testing new measurement procedures that might eventually allow hydraulic conductivity to be estimated from surface NMR observations.
DE: 0545 Modeling (4255)
DE: 0600 ELECTROMAGNETICS
DE: 1835 Hydrogeophysics
SC: Hydrology [H]
MN: 2007 Fall Meeting