Improving CryoSat-2 SARIn L1b Products to Account for Inaccurate Phase Difference: Impact on Sea Ice Freeboard Retrieval

CryoSat-2 (CS2) is the first mission carrying on board an altimeter instrument able to operate in Synthetic Aperture Radar Interferometric (SARIn) mode. CS2 SARIn acquisitions have been exploited for different scientific applications that take advantage of the capability to determine the across-track angle of the first return and, in particular, they have been proved to reduce the uncertainty of sea ice freeboard retrievals. Nonetheless, the analysis of pan-Arctic freeboard obtained by processing CS2 Baseline C L1b products has shown large negative freeboard estimates in correspondence of the beginning of SARIn acquisitions. Throughout this letter, the SARIn waveforms are analyzed to identify the cause of this behavior. An improvement of the CS2 L1b processor is then prototyped and used to obtain a pan-Arctic freeboard data set where the percentage of negative freeboard is successfully minimized.