USGS Groundwater Information: Branch of Geophysics
F.D. Day-Lewis1,2 and J.W. Lane, Jr. 1
1U.S. Geological Survey
Office of Ground Water, Branch of Geophysics
11 Sherman Place, Unit 5015
Storrs, CT 06269
2Dept. of Geology, Bucknell University
Ph: 860 487-7402 x21; Fax: 860 487-8802
Geophysical tomograms are used increasingly as auxiliary data for geostatistical modeling of aquifer and reservoir properties. The correlation between tomographic estimates and hydrogeologic properties is commonly based on laboratory measurements, co-located measurements at boreholes, or petrophysical models. The inferred correlation is assumed uniform throughout the interwell region; however, tomographic resolution varies spatially due to acquisition geometry, regularization, data error, and the physics underlying the geophysical measurements. Blurring and inversion artifacts are expected in regions traversed by few or only low-angle raypaths. In the context of radar traveltime tomography, we derive analytical models for (1) the variance of tomographic estimates, (2) the spatially variable correlation with a hydrologic parameter of interest, and (3) the spatial covariance of tomographic estimates. Synthetic examples demonstrate that tomograms of qualitative value may have limited utility for geostatistics; moreover, the imprint of regularization may preclude inference of meaningful spatial statistics from tomograms.
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Citation: Day-Lewis, F. D., and J. W. Lane, Jr., 2004, Assessing the Resolution-Dependent Utility of Tomograms for Geostatistics: Geophysical Research Letters, vol. 31, L07503, doi:10.1029/2004GL019617, 4 p.