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Quantitative analysis of water-content estimation errors using ground-penetrating radar data and a low-loss approximation.

Giroux, Bernard; Chouteau, Michel (2010). Quantitative analysis of water-content estimation errors using ground-penetrating radar data and a low-loss approximation. Geophysics , vol. 75 , nº 4. WA241-WA249. DOI: 10.1190/1.3464329.

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Résumé

Expressions are derived to quantify the error when estimating permittivity that results from using the low-loss approximation under lossy conditions and to examine the repercussions on estimating water content θ. Values are computed under a range of porosity, clay-content, water-quality, and frequency conditions. Although in most cases the error is negligible, it can be significant for some hydrogeophysical applications involving cross-hole measurements or low-frequency surface ground-penetrating radar (GPR). For instance, when the loss tangent tanδ equals 0.5, corresponding to an effective conductivity of 30mS/m⁠, a dielectric constantof 11, and a frequency of 100MHz⁠, the relative error on dielectric permittivity is approximately 6%. If the conductivity doubles or the frequency is halved, the loss tangentdoubles but the error grows to 21%. In addition, considering a situation where the porosity is 20% and tanδ=0.5⁠, the use of the low-loss approximation leads to a 10% deviation from θ. In the context of water-content estimation, we therefore suggest to perform attenuation tomography, in addition to velocity tomography for crosshole data, or estimate the quality factor Q for surface GPR data to compute the loss tangent over the probed area. If proven necessary, the parameters sought can then be determined more accurately using a lossy formulation. We also propose to supplement GPR measurements with electrical-resistivity tomography to constrain the borehole GPR amplitude data-processing steps required by attenuation tomography or to complement the characterization of the survey area and improve the knowledge brought by Q estimates alone.

Type de document: Article
Mots-clés libres: boreholes; clastic sediments; clay; dielectric properties; electrical properties; electromagnetic methods; equations; geophysical methods; ground water; ground-penetrating radar; mathematical methods; mathematical models; moisture; natural attenuation; pore water; porosity; Q; quantitative analysis; radar methods; resistivity; sediments; soils; tomography; unsaturated zone
Centre: Centre Eau Terre Environnement
Date de dépôt: 08 janv. 2021 16:55
Dernière modification: 08 janv. 2021 16:55
URI: http://espace.inrs.ca/id/eprint/10711

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