Sentinel-1 SAR Observations of Greenland Perennial Firn Aquifer Regions

The Greenland perennial firn aquifer represents a subsurface reservoir of liquid water estimated to be 140 ± 20 Gt holding a potential 0.4 mm of sea level rise (Koenig et al., 2014). As such, understanding the spatial extent and temporal variability of the Greenland perennial firn aquifer is crucial to gaining an accurate insight into ice sheet wide mass and energy balances (Forster et al., 2014). Previous studies have utilized NASA Operation IceBridge radar systems operating at 750 MHz to map firn aquifer extent at meter scale, but were limited to a single observation per year (Miege et al., 2016). Additional studies such as Miller et al. (2017) have utilized passive microwave datasets with a weekly temporal resolution but coarse kilometer-scale spatial resolution to gain insight into firn aquifer dynamics. In this work we illustrate the utility of combing Sentinel 1-A and 1-B synthetic aperture radar (SAR) data and associated variations in backscatter linked to subsurface water content at a spatial resolution of 5 m with a revisit time of 12 days. The relatively fine spatial resolution and medium temporal resolution of this Sentinel-1 SAR time series allows for direct comparisons between SAR backscatter and environmental parameters such as firn temperatures at surface and depth, subsurface water level, local topography, melt and accumulation. This work expands on previous mapping efforts of the Greenland perennial firn aquifer and aims to highlight the relationship between radar backscatter and subsurface conditions. Future work will involve a remote sensing based classification of regional to ice sheet wide firn aquifer extent and will provide insight into the volume and areal extent of the Greenland perennial firn aquifer.