The effect of melt geometry in ice on radar reflectivity, attenuation, and polarimetry

Estimating water content in ice is critical to our understanding of subsurface conditions and processes in both terrestrial and planetary ice masses. Knowledge of ice sheet hydrology, rheology, and thermal configuration can define more accurate models for informing sea level projections. Additionally, the presence and distribution of liquid water in ice serves as an important indicator for habitability on other planetary bodies. Past attempts to quantify water content using ice-penetrating radar tools of reflectivity, attenuation, and polarimetry have not accounted for melt inclusion geometry, leading to observational uncertainties. For instance, recent discussions regarding Mars and the Devon ice cap have highlighted the non-uniqueness of highly reflecting radar signals as being indicative of large water bodies. Other radar observables such as attenuation and polarimetry – commonly attributed to englacial water and ice fabric, respectively – may be similarly non-unique. Here, we use geometric mixing models to show how a variety of geophysical conditions can be replicated by small volume fractions of geometrically oriented melt, with strong implications for water content in both temperate and sub-temperate ice as well as ice fabric orientation. We further discuss how the combination of geometric mixing models with polarimetric radar can be a valuable tool in clarifying melt volume fraction and orientation.