Deriving Antarctic Sea-Ice Thickness From Satellite Altimetry and Estimating Consistency for NASA's ICESat/ICESat-2 Missions

With the launch of the Ice, Cloud and Land Elevation Satellite-2 (ICESat-2), densely measuring the Antarctic ocean all year long, monthly sea ice thickness changes can be inspected. However, the consistency between ICESat-2 and its predecessor ICESat remains unknown if a long-term change of the Antarctic sea ice thickness is to be examined. Due to the complex physical structure of Antarctic sea ice, an improved One-Layer Method (OLMi) for sea-ice thickness retrieval, with an similar to 0.3 m uncertainty, is proposed in this study. Using this method, the monthly sea ice variation in each sea sector of Antarctica from ICESat-2 is inspected, revealing detailed characteristics of Antarctic sea ice over sector scale such as bi-modal distributions. The different retrieving methods for the total freeboard from ICESat are found to be similar to 0.036 m lower than that from ICESat-2. The circum-Antarctic sea ice thickness shows a decreasing tendency (2003-2020), especially in summer with -0.014 m/yr. Plain Language Summary Sea ice variations can reflect global climate change since sea ice has a very strong cyclical process of growing/expanding and melting/shrinking when the seasons change. Sea ice elevation has been monitored by satellite-borne laser altimetry, namely Ice, Cloud and Land Elevation Satellite-2 (ICESat) (2003-2009) and ICESat-2 (2018-2020), with accuracy in centimeters. However, whether the two datasets are consistent with each other and suitable for long-term analysis needs to be examined. Here, we first improve an existing method to get a better estimation of sea ice thickness. Monthly sea ice thickness computed from ICESat-2 elevations has nearly 10 times the data coverage than the older generation ICESat, and shows how the expansion of newly formed sea ice and sea ice thickness change in some sea sectors would influence the statistical distribution of sea ice thickness in detail. Based on the consistency analysis, the gaps between ICESat/ICESat-2 could reach 14%. The underestimation of sea ice thickness with ICESat supports a thinning tendency of Antarctic sea ice, especially in summer. Key Points A new sea ice thickness retrieval method based on Ice, Cloud and Land Elevation Satellite (ICESat)/ICESat-2 is proposed Monthly ICESat-2-based sea ice thickness shows detailed variation in each sea sector The consistency of total freeboard between ICESat and ICESat-2 is estimated