National Aeronautics and Space Administration's (NASA's) Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) mission has provided routine, very high-resolution estimates of surface height/type (the ATL07 product) and freeboard (the ATL10 product) across the Arctic and Southern Oceans since data collection started in October 2018.
In recent work we have estimated sea ice thickness across the entire Arctic Ocean from ATL10 freeboards, using snow depth and density estimates from the NASA Eulerian Snow on Sea Ice Model (NESOSIM) (Petty et al., 2020). These thickness estimates are now hosted at the National Snow and Ice Data Center (NSIDC, https://nsidc.org/data/IS2SITMOGR4). Additionally, we have produced new estimates of higher-level sea ice state estimates related to concentration and floe size (Petty et al., 2021).
Here we provide an overview of new release updates made to the underlying ATL07/ATL10 products (now at Release 005) that impact basin-scale estimates of freeboard, lead fraction and chord length, together with updates to the NESOSIM model (now at v1.1), and the subsequent impacts on our estimates of sea ice thickness, including updated comparisons to data collected by the original ICESat mission, Operation IceBridge and ESA’s CryoSat-2. Misclassified leads were removed from the freeboard algorithm in the third release (Release 003) of ICESat-2 freeboard data which significantly increased freeboards in January and April 2019 (and increased the fraction of low freeboards in November 2018). These changes significantly improved comparisons of sea ice thickness (lower mean biases and standard deviations, higher correlations) with thickness estimates produced from ESA’s CryoSat-2 (using the same input snow and ice density assumptions). NESOSIM v1.1 generally produces thicker snow than v1.0, although these changes result in a less significant impact on thickness compared to the Release 003 freeboard changes.
With now three (going on four) winters of data collected by ICESat-2 over the entire Arctic, we highlight interannual differences in the seasonal evolution of freeboard, thickness and floe size. We also explore possible causes of differences based on an analysis of near-surface atmospheric conditions (ERA5), ice drift (NSIDC) ice type (OSI SAF) and freeze-up estimates (passive microwave).
Finally, we explore the production of a joint thickness-floe size distribution from these data and discuss optimal model assimilation strategies as we seek to integrate ICESat-2 sea ice data into state-of-the-art sea ice climate model components.
Petty, A. A., N. T. Kurtz, R. Kwok, T. Markus, T. A. Neumann (2020), Winter Arctic sea ice thickness from ICESat‐2 freeboards, Journal of Geophysical Research: Oceans, 125, e2019JC015764. doi:10.1029/2019JC015764
Petty, A. A., M. Bagnardi, N. T. Kurtz, R. Tilling, S. Fons, T. Armitage, C. Horvat, R. Kwok (2021), Assessment of ICESat-2 sea ice surface classification with Sentinel-2 imagery: implications for freeboard and new estimates of lead and floe geometry Earth and Space Science, 8, e2020EA001491. doi:10.1029/2020EA001491.