Albert Garcia-Mondéjar (isardSAT S.L., Spain); Ferran Gibert (isardSAT S.L., Spain); Mònica Roca i Aparici (isardSAT S.L., Spain)

Leads between ice floes are key elements to determine the sea surface height in sea ice scenarios since they provide a sea-level reference for the freeboard height measurements. Satellite-based techniques for lead-detection have traditionally required conventional delay-Doppler processing (DDP), where all echoes of a burst are coherently combined within the burst but then incoherently averaged with the other bursts received during the illumination time. DDP has a typical spatial resolution of 300m along-track, which in practice limits the type (orientation, width) of leads that can be detected. Fully-Focused SAR processing technique (Egido & Smith 2017) allows reductions of spatial resolution down to approximately 0.5m by coherently integrating all the echoes received within the illumination time, yielding significant improvements in terms of lead detection among other applications.
Future satellite altimeters such as Sentinel-6 and eventually the Copenicus polaR Ice and Snow Topography Altimeter (CRISTAL) mission will be operated at open bursts (or interleaved) and will provide fully-focused SAR echoes with high spatial resolution and unambiguous along-track backscattered echoes.
Currently flying altimeters such as CryoSat-2 and Sentinel-3 are not optimized for fully-focused SAR processing due to their close burst operation. They can still be used for lead detection using FFSAR applied together with additional steps to mitigate the ambiguities caused by not sampling the surface uniformly. They are expected to be particularly useful for the detection of small-sized leads down to ~10m in scenarios with leads properly separated some hundreds of meters.
In this contribution we present the current status of the fully-focused SAR analysis over Antarctica sea ice, combining data from current altimetry missions and validating it with satellite images. This work is part of our contribution to the "CryoSat+ Antarctica: Improved Sea Ice Thickness and Ocean Observations" project.