# Application of HY-2B Satellite Data to Retrieve Snow Depth on Antarctic Sea Ice
## 4 Results and Discussion
### Spatiotemporal Variations of Snow Depth on Antarctic Sea Ice in 2019  
Figure 6 displays the spatial distribution of monthly snow depth derived from HY-2B SNR in 2019. During the Antarctic summer season (December to February), thinner sea ice and its surface snow gradually melt as temperatures increase, leading to the minimum extent of sea ice coverage [19]. A small amount of thicker snow was distributed on the remnants of multi-year ice in the Weddell Sea and Bellingshausen Sea, as well as in nearshore regions of other Antarctic sea areas. In January, the average snow depth reaches its maximum at 36.2 cm. As temperatures decrease, the sea ice growth period begins in March, and, along with the growth of new ice [28], the spatial average snow depth on sea ice gradually decreases, reaching its lowest average value of 15.3 cm in May. During the Antarctic winter, snow continues to accumulate on the newly formed ice, with thicker snow accumulation observed in the northwest regions of the Weddell Sea and the Bellingshausen and Amundsen seas [25]. In early spring, the sea ice continues to grow until October, reaching its peak extent, and the snow accumulation rate slows down, leading to a decrease in snow depth on Antarctic sea ice. However, as temperatures rise again, both the snow and sea ice decay and melt, causing an increase in the remaining snow depth on the thicker Antarctic sea ice surviving in November and beyond. The time-series snow depth on sea ice in the Antarctic Ocean and its various sea areas were plotted in Figure 7. It can be observed that the variation trends in snow depth were generally consistent across different sea areas and the entire Antarctic Ocean. Throughout the summer season, except for the Weddell Sea, the daily snow depth exhibits significant variations. This phenomenon may be attributed to the frequent occurrence of melt-refreeze processes caused by the diurnal temperature difference in Antarctica. Consequently, the brightness temperature observed by passive microwave sensors undergoes substantial daily fluctuations, thereby affecting the retrieved snow depth based on the passive microwave data [40]. Unlike other sea areas, the snow depth on sea ice in the Ross Sea exhibits a significant increasing trend towards the end of summer. During the spring, changes in wind speed in the Ross Sea promote the early melting and reduction of sea ice thickness, thereby increasing the absorption rate of solar radiation. These changes significantly impact the autumn sea ice cover five months later, primarily manifesting as a reduction in sea ice area, which creates a precondition for the increase in snow depth at the end of the summer. This series of changes reveals the key driver behind the increase in late-summer snow depth in the Ross Sea region, highlighting the complex interplay between atmospheric conditions and sea ice dynamics [41]. Thick snow (over 30 cm) is primarily found in the Weddell Sea, Bellingshausen Sea, Amundsen Sea, and Ross Sea. During the autumn season, the snow depth decreases in all Antarctic sea areas; however, the rate of decline slows down gradually. In winter, the snow depth continues to rise in the southwestern Antarctic sea areas (Bellingshausen Sea, Amundsen Sea, and Ross Sea), which could be due to frequent cyclonic activity and higher precipitation, whereas the eastern Antarctic sea areas (Southern Indian and Southern Pacific oceans) experience relatively thinner snow depths due to the growth of new ice [25]. With the arrival of spring, snow depth decreases