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Abstract. We have examined a general expression giving the specularreflection coefficient for a radar wave approaching a reflecting interfacewith normal incidence. The reflecting interface separates two homogeneousisotropic media, the properties of which are fully described by three scalarquantities: dielectric permittivity, magnetic permeability, and electricalconductivity. The derived relationship indicates that electricalconductivity should not be neglected a priori in glaciological investigations ofsubglacial materials and in ground-penetrating radar (GPR) studies of saturated sediments and bedrock,even at the high end of typical linear radar frequencies used in suchinvestigations (e.g., 100–400 MHz). Our own experience in resistivitysurveying in Antarctica, combined with a literature review, suggests that awide range of geologic materials can have electrical conductivity that ishigh enough to significantly impact the value of radar reflectivity.Furthermore, we have given two examples of prior studies in which inclusionof electrical conductivity in calculation of the radar bed reflectivity mayprovide an explanation for results that may be considered surprising if theimpact of electrical conductivity on radar reflection is neglected. Thecommonly made assumption that only dielectric permittivity of the two medianeeds to be considered in interpretation of radar reflectivity can lead toerroneous conclusions. 

Abstract. Previous studies of the lakes of the McMurdo Dry Valleys haveattempted to constrain lake level history, and results suggest the lakeshave undergone hundreds of meters of lake level change within the last20 000 years. Past studies have utilized the interpretation of geologicdeposits, lake chemistry, and ice sheet history to deduce lake levelhistory; however a substantial amount of disagreement remains between thefindings, indicating a need for further investigation using new techniques.This study utilizes a regional airborne resistivity survey to provide novelinsight into the paleohydrology of the region. Mean resistivity mapsrevealed an extensive brine beneath the Lake Fryxell basin, which isinterpreted as a legacy groundwater signal from higher lake levels in thepast. Resistivity data suggest that active permafrost formation has beenongoing since the onset of lake drainage and that as recently as 1500–4000 years BP, lake levels were over 60 m higher than present. This coincideswith a warmer-than-modern paleoclimate throughout the Holocene inferred bythe nearby Taylor Dome ice core record. Our results indicate Mid to LateHolocene lake level high stands, which runs counter to previous researchfinding a colder and drier era with little hydrologic activity throughoutthe last 5000 years.