Studying supraglacial hydrology features on the Greenland Ice Sheet with NASA's Airborne Topographic Mapper (ATM) instrument suite

During the summer months, seasonal surface melting on the Greenland Ice Sheet (GIS) produces meltwater near the margins that pools in supraglacial lakes in topographic lows on the ice surface and forms meandering streams. These streams often connect several lakes and form a hydrological network on the surface of the GIS. Airborne measurements can map supraglacial hydrological features on the Greenland Ice Sheet at a level of detail that can currently not be accomplished by spaceborne instruments. Airborne measurements can also map supraglacial hydrological features at a spatial scale that cannot be achieved by in-situ measurements of short-range drones, which are often operated out of remote field camps and require line-of-sight communication. Here we use airborne laser altimetry and optical imagery collected as part of two Operation Ice Bridge campaigns in Spring and Fall of 2019 over the GIS. We have developed a robust method to automatically identify hydrological features using the normalized difference water index modified for ice (NDWIice) calculated from natural color, high-resolution (10 10 cm) ATM CAMBOT imagery. We then use the waveform data products from ATMs wide (15) and narrow (2.5) scanner available from NSIDC to estimate water depths over the hydrological features. We use a dual-peak Gaussian non-linear regression with 7 model parameters to estimate the slant range in water accounting for the refractive index of water in both travel time and geolocation, and assuming a flat and horizontal water surface within the extent of an ATM footprint (0.64 m). The dual-peak Gaussian waveform fitting is capable of separating returns from the air-water and water-ice interface for very shallow water depths that otherwise would appear as a single pulse for centroid-based tracking methods. ATMs small footprint, high shot density, swath coverage, and high-resolution imagery reveal fine scale hydrological features, such as very narrow meltwater channels and surface waves that cannot be detected from space. We will present an analysis of 9 flights from OIBs 2019 Arctic Spring campaign between May 5 and 16, 2019 and 4 flights from the Fall campaign between September 10 and 19, 2019. The Spring 2019 data shows a surprising absence of lakes in southern Greenland compared to central West Greenland.