Sedimentology · 2000 · 182 citations · 46 references
Natural SciencesEarth SciencesGeophysicsRemote SensingSedimentologyStratigraphyEngineering GeophysicsGeophysical Data ProcessingGround-penetrating RadarRadar ReflectivityRadar Wave PropagationSediment PropertiesGeophysical SurveyingGround-penetrating Radar SensingGround-penetrating Radar SurveysMagnetic PermeabilityPetrophysical Data AnalysisPetrophysical RelationshipsSediment CharacteristicsSedimentological Analysis
Ground‑penetrating radar is widely used to image shallow subsurface features, yet the precise physical causes of its reflections remain poorly understood because few studies have linked wave theory to petrophysical measurements. The authors surveyed aeolian deposits with 100‑ and 200‑MHz GPR, measured the product of relative permittivity and magnetic permeability using time‑domain reflectometry, correlated these values with sediment characteristics from lacquer peels, and generated synthetic radar traces that were compared to the field GPR data. Peaks in εr μr above the dry‑sand baseline of 4, associated with organic material or iron‑oxide bands, and sedimentary structures only produce reflections when volumetric water content exceeds 0.055; the synthetic traces reveal that GPR signals can be ambiguous due to multiples and interference.
Ground‐penetrating radar (GPR) is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves. However, little is known about the exact cause of GPR reflections because few studies have coupled wave theory to petrophysical data. In this study, a 100‐ and 200‐MHz GPR survey was conducted on aeolian deposits in a quarry. Time‐domain reflectometry (TDR) was used to obtain detailed information on the product of relative permittivity (ɛ r ) and relative magnetic permeability (μ r ), which mainly controls the GPR contrast parameter in the subsurface. Combining TDR data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and ɛ r μ r . Synthetic radar traces, constructed using the TDR logs and sedimentological data from the lacquer peels, were compared with the actual GPR sections. Numerous peaks in ɛ r μ r , which are superimposed on a baseline value of 4 for dry sand, are caused by potential GPR reflectors. These increases in ɛ r μ r coincide with the presence of either organic material, having a higher water content and relative permittivity than the surrounding sediment, or iron oxide bands, enhancing relative magnetic permeability and causing water to stagnate on top of them. Sedimentary structures, as reflected in textural change, only result in possible GPR reflections when the volumetric water content exceeds 0·055. The synthetic radar traces provide an improved insight into the behaviour of radar waves and show that GPR results may be ambiguous because of multiples and interference.
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