Detection Of Melt Ponds On Arctic Summer Sea Ice From Icesat-2

Hemisphere-wide observations of melt ponds on sea ice are needed to understand their influence on the surface radiation budget of the Arctic Ocean and to extend the satellite sea ice thickness data record. Here we present a first assessment of NASA's Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) over individual Arctic sea ice melt ponds with different reflective properties. We use coincident high-resolution satellite imagery from WorldView-2 and Sentinel-2 over different sea ice topographies to show that smooth ponds are highly reflective and can saturate the ICESat-2 photon detection system. Rougher ponds have a more varied backscatter signal, and in some cases both the water and underlying ice surfaces are visible in photon height distributions. Characterizing the complex photon backscatter signals of melt ponds on sea ice is a first step toward automating retrievals of pond parameters such as width, melt pond fraction and depth, and improving higher-level ICESat-2 sea ice height and freeboard products.Plain Language Summary In summer, surface melt water forms ponds that can cover up to half of the Arctic sea ice surface. Because melt ponds reduce the reflective and insulative properties of sea ice, they can alter the Arctic energy budget and ecosystem. The presence of melt ponds also complicates satellite altimeter (radar and laser) estimates of sea ice freeboard (the height of the ice above the ocean) and thickness. Here we combine data from NASA's Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) laser altimeter and high-resolution satellite imagery to locate individual melt ponds on Arctic sea ice. We explore how melt ponds affect the return laser signal and discuss how ICESat-2 data could be used to retrieve parameters of scientific interest such as melt pond width, fraction, and depth. We finish by summarizing the complications and potential solutions associated with sea ice height and freeboard retrievals from ICESat-2 in summer.Key PointsWe present a first assessment of NASA's ICESat-2 over a range of individual Arctic sea ice melt ponds ICESat-2 backscatter signatures over melt ponds vary significantly, depending on surface roughness Our ability to estimate melt pond width, fraction, and depth and improve ICESat-2 sea ice freeboard products depends on surface backscatter