# Application of HY-2B Satellite Data to Retrieve Snow Depth on Antarctic Sea Ice
## 4 Results and Discussion
### Comparison of HY-2B SMR Snow Depth with GCOM-W1 AMSR-2 Snow Depth Product  
The retrieved snow depth on Antarctic sea ice using HY-2B SMR presents a similar trend to the GCOM-W1 AMSR-2 snow depth product (Figure 5), primarily due to the utilization of the same snow depth retrieval model (Comsio03 model) for both. Overall, the snow depth derived from HY-2B SMR was higher than that from GCOM-W1 AMSR-2. This disparity could be attributed to differences in brightness temperatures observed by the SMR and AMSR-2 sensors. Specifically, the average difference between the HY-2B SMR measured brightness temperature at 18.7 GHz (36.5 GHz) and the GCOM-W1 AMSR-2 measured brightness temperature is \(-\)5.1 K (\(-\)6.8 K). Table 3 shows the monthly snow depth differences between HY-2B SMR and the GCOM-W1 AMSR-2. Significant differences were mainly observed during the sea ice ablation period (November to March), with the MD ranging from 5.2 cm to 11.1 cm. During the sea ice melting season, snow on sea ice undergoes phase changes, melting during the day and retreezing at night. These phase changes result in variations in microwave emissivity measured by different passive microwave sensors [37; 38], such as SMR and AMSR-2, which have different measured brightness temperature sensitivities (Table 1). This leads to differences in the derived snow depth. The differences were relatively small during spring, autumn, and winter, with the difference being below 2.4 cm (Table 3). During the freeze-up period (April to October), the difference between the snow depth obtained from HY-2B SMR and the GCOM-W1 AMSR-2 product were relatively small, with a MD of 1.0 cm and a RMSD of 7.4 cm. However, during the melt period (November to March), the snow depth derived from HY-2B SMR was significantly higher than the GCOM-W1 AMSR-2 snow depth product exhibited larger differences compared to the sea ice growth period, with a MD of 5.0 cm and RMSD of 14.4 cm. The SMR-derived snow depth exhibits a high-frequency variability compared to the AMSR-2-derived snow depth. This could be attributed to the different brightness temperature sensitivity between SMR and AMSR-2 that was affected by synoptic-scale meteorological factors, such as water vapor and heat. To further analyze the spatiotemporal differences between the snow depth derived from HY-2B SMR and the GCOM-W1 AMSR-2 snow depth product, we conducted a statistical analysis of the differences in snow depth between the two across different Antarctic seas and seasons (Table 4). Except for the Weddell Sea during winter, the snow depth obtained from HY-2B SMR was consistently higher than that of the GCOM-W1 AMSR-2 product. The differences between the two were relatively small during spring (September to October), autumn (March to May), and winter (June to August), but exhibited significant disparities during summer (December to February), with the snow depth derived from HY-2B SMR being considerably higher than the GCOM-W1 AMSR-2 product. This snow depth discrepancy in summer could be attributed to the unstable snow phase on sea ice due to high summer air temperatures, resulting in different brightness temperatures observed  
Figure 5: Daily spatial average differences of HY-2B SMR snow depth and GCOM-W1 AMSR2 snow depth on Antarctic sea ice in 2019.  
by different passive microwave sensors. The spatial distribution of the HY-2B SMR snow depth and the GCM-W1 AMSR-2 snow depth is generally consistent, with thick snow mainly distributed in the Weddell Sea, and thin snow depth primarily distributed in East Antarctica sea areas. However, some localized differences were observed in different sea areas, particularly in the Bellingshausen and Amundsen seas, where the RMSD between the two was 13.2 cm. This finding is consistent with the validation results obtained by [PERSON] et al. (2011), who utilized ship-based snow depth observations at the Bellingshausen Sea in 2006 to validate the AMSR-E snow depth product, which underestimated the actual snow depth by up to 20 cm [20].