Assessment of ICESat-2 sea ice surface classification with Sentinel-2
imagery: implications for freeboard and new estimates of lead and floe
geometry
Abstract
NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) mission
launched in September 2018 and is now providing high-resolution surface
elevation profiling across the entire globe, including the sea ice cover
of the Arctic and Southern Oceans. For sea ice applications,
successfully discriminating returns between sea ice and open water is
key for accurately determining freeboard, the extension of sea ice above
local sea level, and new information regarding the geometry of sea ice
floes and leads. We take advantage of near-coincident optical imagery
obtained from the European Space Agency (ESA) Sentinel-2 (S-2) satellite
over the Western Weddell Sea of the Southern Ocean in March 2019 and the
Lincoln Sea of the Arctic Ocean in May 2019 to evaluate the surface
classification scheme in the ICESat-2 ATL07 and ATL10 sea ice products.
We find a high level of agreement between the ATL07 (specular) lead
classification and visible leads in the S-2 imagery in these two scenes
across all six ICESat-2 beams, increasing our confidence in the
freeboard products and deriving new estimates of the sea ice state. The
S-2 overlays provide additional evidence of the misclassification of
dark leads, which are no longer used to derive sea surface in the third
release (r003) ICESat-2 sea ice products. We show estimates of lead
fraction and more preliminary estimates of chord length (a proxy for
floe size) using two metrics for classifying sea surface (lead) segments
across both the Arctic and Southern Ocean for the first winter season of
data collection.