Characterization of L-band synthetic aperture radar (SAR) backscatter from floating and grounded thermokarst lake ice in Arctic Alaska

摘要

Radar remote sensing is a well-established method to discriminate lakesretaining liquid-phase water beneath winter ice cover from those that donot. L-band (23.6 cm wavelength) airborne radar showed great promise in the1970s, but spaceborne synthetic aperture radar (SAR) studies have focusedon C-band (5.6 cm) SAR to classify lake ice with no further attention toL-band SAR for this purpose. Here, we examined calibrated L-band single- andquadrature-polarized SAR returns from floating and grounded lake ice in tworegions of Alaska: the northern Seward Peninsula (NSP) where methane ebullitionis common in lakes and the Arctic Coastal Plain (ACP) where ebullition isrelatively rare. We found average backscatter intensities of ?13 dB and?16 dB for late winter floating ice on the NSP and ACP, respectively, and ?19 dBfor grounded ice in both regions. Polarimetric analysis revealed that themechanism of L-band SAR backscatter from floating ice is primarily roughnessat the ice–water interface. L-band SAR showed less contrast between floatingand grounded lake ice than C-band; however, since L-band is sensitive toebullition bubbles trapped by lake ice (bubbles increase backscatter), thisstudy helps elucidate potential confounding factors of grounded ice inmethane studies using SAR.