Assessing three waveform retrackers on sea ice freeboard retrieval from Cryosat-2 using Operation IceBridge Airborne altimetry datasets

Abstract

In this study, three previously proposed echo waveform retracking techniques are assessed for their performances in measuring lead and sea ice elevations from Cryosat-2 (CS-2) SAR L1b data. These derived CS-2 sea ice elevations and freeboards are compared with those from seven Operation IceBridge (OIB) flights, dedicated as the CS-2 underflights during the late winter/early spring of 2011, 2012 and 2013. Results show that sea ice elevation measured by CS-2 is mostly ranged between ~−1–0m, after the mean sea surface (MSS) is subtracted. The mean absolute biases between the CS-2 and ATM elevations in different underflights are mostly ranged between ~0.02–0.71m. For multi-year ice, empirical lead and threshold floe retracker (ELTF) is the best choice for ice elevation measurement and the waveform fitting retracker (WfF) is the best choice for ice freeboard retrieval. For first year ice, the WfF is the best choice for ice elevation measurement and the threshold first maximum retracker (TFMRA) is the best choice for ice freeboard retrieval. This study also suggests, when the TFMRA retracker is used to retrieve lead elevation, a 70% threshold of the first local maxima power is better than the 50% threshold previously used.