CryoSat-2 Arctic Sea-Ice Thickness: Uncertainties and Outlook

Abstract:

The CryoSat-2 satellite is in the 4th year of its mission. It has collected a unique altimetry dataset with higher spatial resolution and a better coverage of Arctic sea ice than any previous radar altimeter mission. The along-track sharpened footprint allows resolving fine-scale features of the ice pack and the examination of retrievable information from the SAR waveforms is a field of ongoing research. Different methods can be applied to CryoSat-2 data: threshold retrackers that use the leading edge; or fitted forward models, which are applied to full waveforms. The uncertainty of these methods propagates into the uncertainty of the final sea-ice thickness estimate via the freeboard to thickness conversion. Theoretical considerations show that the magnitude of uncertainties in the radar retracking may be a major if not dominating contribution to the uncertainty budget of sea-ice thickness retrieval from CryoSat-2.

We present a break-down of the uncertainty budget of CryoSat-2 Arctic sea-ice thickness of the threshold retracker based sea-ice thickness data product of the Alfred Wegener Institute. We discuss the differences in the radar waveform properties and the identification of leads in first-year and multi-year ice covered areas with the aim to mitigate ice type dependent biases. Though threshold retrackers are prone to a simplistic interpretation of the SAR waveforms we investigate the potential of this fast and robust method to retrieve additional physical properties at the sea ice surface.