Subglacial Lake-Floor Characterization in Radar Data: From Archival to Modern

Abstract:

In the past fifty years, advances in radio-echo sounding (RES) collection and processing coupled with an increasing amount of available data have allowed the community to identify hundreds of Antarctic subglacial lakes. Although the bright, smooth, and flat appearance of a lake surface makes their detection by RES fairly easy, lake floors are not typically detectable with radar. As a result, the depth and water composition of subglacial lakes are poorly constrained. Here we investigate historic and modern Antarctic datasets for the presence of long-overlooked reflections from subglacial lake floors.

To investigate subglacial lakes and potential lake floor reflections, we use recently digitized radargrams recorded on 35 mm film. The data was collected in Antarctica in the late 60s and early 70s in a series of RES flyovers known as the SPRI-TUD-NSF collaboration (Scott Polar Research Institute, Technical University of Denmark, US National Science Foundation). The increased resolution in the digitized data allows us to radiometrically characterize the film’s ‘Z-scopes’ (radargram) and ‘A-scopes’ (power return over time) to analyze the potential penetration of the water bodies. Previous analysis of the dataset identified eight potential lake floor reflectors, however water conductivity was only calculated for one lake and no temporal conclusions with modern data were drawn. We use echo strength to constrain water conductivity and chemistry for the additional lakes and conduct proof-of-concept analyses to determine which radar system parameters and processing techniques are able to detect lake floors. We conducted a cross-platform analysis with modern CReSIS and HiCARS radar data of spatially-similar lakes to determine which lake conditions allow for floor reflector detection by different systems and investigate lake depth and compositional changes over the decades.