Hidden Meltwater in the Ice: Extending Greenland Ice Sheet Subsurface Meltwater Records with Satellite Remote Sensing

The discovery of pervasive year-round englacial meltwater in southeastern Greenland by Forster et. al (2012) in the form of Perennial Firn Aquifers (PFAs) with an estimated 140+/-12 GT of water (pre-2011 melt season) has significantly changed the understanding of meltwater retention, energy balance models and hydrology of the Greenland ice sheet (GrIS). Prior to this, englacial meltwater was not considered a significant portion of the GrIS water budget. The cryosphere and hydrology communities are currently observing and studying PFAs through data obtained from the NASA ICEBridge Program. Due to environmental and time constraints, data are limited to a few months each year beginning in 2010. This leaves a significant need to explore new methods of monitoring PFAs both throughout the year and across time in order to improve the understanding of PFA formation and hydrologic consequences. Passive microwave radiation observations via satellite remote sensing have been recorded regularly over Greenland since 1979. While 19 and 37 GHz  microwaves are most commonly used to monitor surface melt, longer wavelengths have the potential to penetrate past the ice sheet surface and return a subsurface meltwater signal. Careful analysis of low-frequency microwave reflectance signals has the potential to identify subsurface meltwater distinct from surface melt throughout the year. This method of identifying englacial meltwater will be tested through comparisons with published PFA and meteorological datasets from automatic weather stations and reanalyses. If this method proves effective, it could significantly extend the records of PFA locations and physical and temporal extent so that hydrologic and climatic events and patterns can be better analyzed.