A framework for attenuation method selection evaluated with ice-penetrating radar data at South Pole Lake

Abstract

All radar power interpretations require a correction for attenuative losses. Moreover, radar attenuation is a proxy for ice-column properties, such as temperature and chemistry. Prior studies use either paired thermodynamic and conductivity models or the radar data themselves to calculate attenuation, but there is no standard method to do so; and, before now, there has been no robust methodological comparison. Here, we develop a framework meant to guide the implementation of empirical attenuation methods based on survey design and regional glaciological conditions. We divide the methods into the three main groups: (1) those that infer attenuation from a single reflector across many traces; (2) those that infer attenuation from multiple reflectors within one trace; and (3) those that infer attenuation by contrasting the measured power from primary and secondary reflections. To assess our framework, we introduce a new ground-based radar survey from South Pole Lake, comparing selected empirical methods to the expected attenuation from a temperature- and chemistry-dependent Arrhenius model. Based on the small surveyed area, lack of a sufficient calibration surface and low reflector relief, the attenuation methods that use multiple reflectors are most suitable at South Pole Lake.

Five decades of radioglaciology

“…These approaches can also be intercompared or combined (e.g. Hills and others, 2020; Jeofry and others, 2020). Additionally, investigating attenuation with variable offset can constrain englacial, attenuation, though there is a limit on the maximum offset achievable with commercial GPR systems (Holschuhand others, 2016).…”

Frontal collapse of San Quintín glacier (Northern Patagonia Icefield), the last piedmont glacier lobe in the Andes

“…This expression was obtained by linearising the equation 4 after normalising with the term L g . Thus, the attenuation of the ice N a (in dB•km -1 ) was calculated using the empirical method (Jacobel et al, 2009;Hills et al, 2020), through a linear regression based on the decay of the amplitude with the depth of the ice. For the linear regression, the linear range of the dispersion was considered from 200 to 600 m in ice thickness.…”

Geophysical constraints on the properties of a subglacial lake in northwest Greenland

“…While the presence and nature of subglacial lakes underlying the Antarctic ice sheet has been studied for more than 50 years, the existence of subglacial lakes below the Greenland ice sheet is a relatively recent discovery and comparatively little is known about their properties and origin. Detection of subglacial lakes has relied on a variety of methods, including radio-echo sounding (Robin et al, 1970;Siegert et al, 1996;Langley et al, 2011;Palmer et al, 2013;Young et al, 2016;Bowling et al, 2019), satellite altimetry measurements (Fricker et al, 2007;Palmer et al, 2015;Willis et al, 2015), and active-source seismic experiments (e.g., Horgan et al, 2012;Peters et al, 2008). Using these techniques, approximately 400 subglacial lakes have been detected in Antarctica (Wright and Siegert, 2012), of which 124 are considered "active" by Smith et al (2009).…”

“…This contrasts to results from seismic investigations of Lake Vostok, the largest of Antarctica's subglacial lakes, which show evidence for a much thicker water column (up to 1100 m) and a thicker layer of lake bottom sediments (up to 400 m) below approximately 4 km of ice (e.g., Filina et al, 2008). Seismic investigations have also been useful for illuminating the properties of subglacial lakes below much thinner ice columns in active ice streams, such as the subglacial Lake Whillans which is situated below approximately 800 m of ice and has a maximum water column thickness of less than 10 m (e.g., Horgan et al, 2012).…”