The role of electrical conductivity in radarwave reflection

Abstract

Abstract. We have examined a general expression giving the specular reflection coefficient for a radar wave approaching a reflecting interface with normal incidence. The reflecting interface separates two homogeneous media, the properties of which are fully described by three scalar quantities: dielectric permittivity, magnetic permeability, and electrical conductivity. The derived relationship indicates that electrical conductivity should not be neglected a priori in glaciological investigations of subglacial materials, and in GPR studies of saturated sediments and bedrock, even at the high end of typical linear radar frequencies used in such investigations (e.g., 100 MHz). Our own experience in resistivity surveying in Antarctica, combined with a literature review, suggests that a wide range of geologic materials can have electrical conductivity that is high enough to significantly impact the value of radar reflectivity. Furthermore, we have given two examples of prior studies in which inclusion of electrical conductivity in calculation of the radar bed reflectivity may provide an explanation for results that may be considered surprising if the impact of electrical conductivity on radar reflection is neglected. The commonly made assumption that only dielectric permittivity of the two media need to be considered in interpretation of radar reflectivity can lead to erroneous conclusions.

Radar Derived Subglacial Properties and Landforms Beneath Rutford Ice Stream, West Antarctica

“…In glaciology, the interpretation of high reflectivity originating from water has typically been made by assuming the glacier bed to be a low-loss medium. However, Tulaczyk and Foley (2020) stated that reflections at an interface between ice and a material with high conductivity can appear as bright (high reflectivity) or even brighter than a reflection of a water body (e.g., subglacial lake) for low frequency radars (e.g., the surface radar in our study). Highly conductive subglacial materials causing such high reflectivity could be, for instance, clay-bearing sediments, materials including seawater-or brine-saturated sediments and bedrock (Foley et al, 2016).…”

“…Most studies assume low‐loss conditions, where the contribution of electrical conductivity to reflectivity can be neglected, although Tulaczyk and Foley (2020) show that this may not be valid where clay‐rich material and/or saline pore water is present at the glacier bed. Our interpretation neglects electrical conductivity effects, but the validity of this assumption is revisited in later discussion.…”

Radar derived Subglacial Properties and Landforms beneath Rutford Ice Stream, West Antarctica

“…Most studies assume low-loss conditions, where the contribution of electrical conductivity to reflectivity can be neglected, although Tulaczyk and Foley (2020) show that this may not be valid where clay-rich material and/or saline pore water is present at the glacier bed. Our interpretation neglects electrical conductivity effects, but the validity of this assumption is revisited in later discussion.…”