Using englacial radar attenuation to better diagnose the subglacial environment: A review

The magnitude of the radar echo returned from beds underneath ice sheets has been used to identify subglacial lakes based on the prediction that wetter and flatter beds have larger reflectivities than dryer and/or rougher beds. Further quantitative diagnosis of the subglacial environment requires accurate correction for englacial dielectric attenuation, which is primarily a function of ice temperature and secondarily a function of ice chemistry. Models show that the attenuation contribution from chemistry (soluble ions) accounts for about one quarter of the attenuation averaged over the full ice thickness at Siple Dome and Vostok in Antarctica. These predictions suggest that a useful initial attenuation estimate across an ice sheet can be obtained simply with ice-temperature modeling. Methods for estimating attenuation from radar data are also reviewed, with an emphasis on the potential pitfalls of individual methods. Some discrepancies exist between attenuation estimated with ice-core data, temperature models, and radar data. We discuss strategies to improve these attenuation estimates.