Early Assessment of Sentinel-3A measurements over Arctic Sea Ice

Launched February 16, 2016, the European Sentinel-3A mission builds on the heritage of the ERS-2 and Envisat satellites, measuring surface topography and temperature. Over the Arctic Ocean, Sentinel-3A will provide critical measurements of sea ice freeboard and sea surface height, providing coverage to a latitudinal limit of 81.5 °N. Discrimination of waveform returns from floes and leads is required to determine freeboard, that portion of an ice floe floating above the local sea surface. Since 2002, the NOAA Laboratory for Satellite Altimetry has cooperated with ESA, EUMETSAT, and NASA to conduct airborne validation experiments over the Arctic Ocean to assess how well sea ice freeboard (and hence ice thickness) can be measured from space using satellite altimetry. NASA's Operation IceBridge (OIB) mission utilizes multi-instrumented aircraft to conduct annual surveys of the winter sea ice cover to monitor critical and rapidly-changing regions of the Arctic, so as to bridge gap in observations between the ICESat and ICESat-2 eras. Since 2009, OIB have conducted numerous validation experiments, under-flying Envisat, ICESat and CryoSat-2. On 21 April 2016, the OIB mission conducted an airborne survey over Arctic sea ice timed to coincide with an overpass of the Sentinel-3A satellite. This was the first coordinated survey while Sentinel-3A was operating in SAR mode. Spatially and temporally coincident data were collected in the eastern Beaufort Sea, in a study area that comprised large sea ice floes, interspersed with open and refrozen leads. The OIB instrument suite, including laser and radar altimeters, and high-resolution visible and infrared camera systems, provides measurements of sea ice freeboard, snow depth, and sea ice morphology. Here we present an early evaluation of Sentinel-3A waveforms and sigma-0 measurements over Arctic sea ice using coincident OIB data and MODIS imagery. We verify sea ice lead and floe delineations in Sentinel-3A waveforms, and the impact of snagging, via an assessment of Sentinel-3A waveform parameters. We also assess the accuracy of Sentinel-3A surface elevation measurements and, if available, we will present a first assessment of Senitnel-3A sea ice freeboard estimates via comparison with independent OIB freeboard and snow-depth measurements.