Abstract: In this study, MODIS SIT products derived from three retrieval models under different snow thickness parameterization schemes and two SMOS (Soil Moisture and Ocean Salinity mission) SIT maps released from the University of Hamburg (SSIT-UH) and the University of Bremen (SSIT-UB) are validated against ship-based SIT observations (SIT-OBS) acquired at 512 sites from October 4th to November 5th in 2015, in Beaufort Sea, Arctic. Results showed that the SIT retrievals derived from Model III with input from ship-based snow data observations offer the best performance with the lowest bias of 0.02 m and root-mean-square error (RMSE) of 0.12 m. Model I with the snow-free retrieval model matched quite well with SIT-OBS (R=0.72), and is more accurate under less snowy weather conditions. Model II takes the empirical snow-ice thickness relationship as snow thickness parameterization, and exhibits overall poor accuracy. Results also illustrate that the SSIT-UB retrievals agree better with the observations than SSIT-UH retrievals. Both of these methods are more accurate than Model III SIT retrievals, with a higher correlation and smaller RMSE. These results indicate that MODIS SIT products are not always ideal as the reference in evaluating other SIT results, and there are still some problems in the current MODIS SIT retrieval models that require further improvement.

Key words: thin ice thickness, ship observations, MODIS, SMOS