Gaussian-process fusion of ICESat-2 and SMOS/SMAP data for daily estimates of Arctic sea ice thickness and volume

Abstract. We present IS2SMGPSIT-V1, a full-coverage, pan-Arctic, 25 km ×25 km sea ice thickness and volume dataset with daily output spanning seven winter growth seasons between 2018 and 2025. The product fuses ICESat-2 laser-altimetry data with SMOS/SMAP L-band radiometry using Gaussian-process (GP) regression implemented with the open-source GPSat package. ICESat-2 provides high-spatial-resolution thickness estimates along defined ground tracks, whereas SMOS and SMAP provide extensive daily coverage of thin ice (≤0.5 m) thickness. Using each observation’s acquisition time and location reduces sampling artifacts associated with existing monthly binning approaches and fills unobserved grid cells, particularly during early-fall freeze-up. Inner-Arctic-Ocean mean thickness seasonal cycles are broadly consistent with the established IS2SITMOGR4 (ICESat-2 Winter Arctic Monthly Gridded Sea Ice Thickness) Version 4 product, while the fused product extends coverage where the monthly product is sparse. Comparisons with upward-looking sonar measurements from the Beaufort Gyre Exploration Project moorings over 2018–2024 show improved monthly skill relative to IS2SITMOGR4-V4 (r² = 0.91 versus 0.83; RMSE = 0.19 versus 0.24 m), primarily through improved representation of thin ice. De-seasonalised comparisons show limited sub-monthly skill, indicating that further development and assessment are needed to improve representation of short-timescale variability. The full spatial coverage supports consistent pan-Arctic volume estimates and analysis of interannual anomalies. Version v0.1 of the monthly NetCDF archive is preserved on Zenodo (https://doi.org/10.5281/zenodo.22147361; Petty, 2026b). The data are also hosted on Amazon Web Services S3 as monthly NetCDF files, a single Zarr store, and a version-controlled Icechunk repository to enhance accessibility.