HR: 1340h
AN: H43F-0546 INVITED     [Abstracts]
TI: Pitfalls in Inversion and Interpretation of Continuous Resistivity Profiling Data: Effects of Resolution Limitations and Measurement Error
AU: * Lane, J W
EM: jwlane@usgs.gov
AF: U.S. Geological Survey, OGW Branch of Geophysics, 11 Sherman Place, Unit 5015, Storrs, CT 06269 United States
AU: Day-Lewis, F D
EM: daylewis@usgs.gov
AF: U.S. Geological Survey, OGW Branch of Geophysics, 11 Sherman Place, Unit 5015, Storrs, CT 06269 United States
AU: Loke, M H
EM: mhloke@tm.net.my
AF: School of Physics, Universiti Sains Malaysia , Penang, 11800 Malaysia
AU: White, E A
EM: eawhite@usgs.gov
AF: U.S. Geological Survey, OGW Branch of Geophysics, 11 Sherman Place, Unit 5015, Storrs, CT 06269 United States
AB: Water-borne continuous resistivity profiling (CRP), also called marine or streaming resistivity, increasingly is used to support hydrogeophysical studies in freshwater and saltwater environments. CRP can provide resistivity tomograms for delineation of focused ground-water discharge, identification of sediment types, and mapping the near-shore freshwater/saltwater interface. Data collection, performed with a boat-towed electrode streamer, is commonly fast and relatively straightforward. In contrast, data processing and interpretation are potentially time consuming and subject to pitfalls. Data analysis is difficult due to the underdetermined nature of the tomographic inverse problem and the poorly understood resolution of tomograms, which is a function of the measurement physics, survey geometry, measurement error, and inverse problem parameterization and regularization. CRP data analysis in particular is complicated by noise in the data, sources of which include water leaking into the electrode cable, inefficient data collection geometry, and electrode obstruction by vegetation in the water column. Preliminary modeling has shown that, as in other types of geotomography, inversions of CRP data tend to overpredict the extent of and underpredict the magnitude of resistivity anomalies. Previous work also has shown that the water layer has a strong effect on the measured apparent resistivity values as it commonly has a much lower resistivity than the subsurface. Here we use synthetic examples and inverted field data sets to (1) assess the ability of CRP to resolve hydrogeophysical targets of interest for a range of water depths and salinities; and (2) examine the effects of CRP streamer noise on inverted resistivity sections. Our results show that inversion and interpretation of CRP data should be guided by hydrologic insight, available data for bathymetry and water layer resistivity, and a reliable model of measurement errors.
DE: 0599 General or miscellaneous
DE: 1829 Groundwater hydrology
DE: 1835 Hydrogeophysics
DE: 3094 Instruments and techniques
SC: Hydrology [H]
MN: Fall Meeting 2005