An application study of 89.0 GHz brightness temperatures in the dual-polarized ratio algorithm for retrieving sea ice concentration

Sea ice concentration (SIC) is a core parameter for quantifying polar sea ice coverage and plays a crucial role in climate research, oceanographic studies, maritime safety, and remote sensing monitoring. The all-weather and large-scale observations of this parameter primarily rely on passive microwave remote sensing technology. In this study, atmospheric correction techniques are applied to the dual-polarized ratio (DPR) algorithm to retrieve SIC from vertically and horizontally polarized brightness temperatures observed at 89.0 GHz and a retrieval resolution of 6.25 km. Compared to existing SIC retrieval algorithms, the DPR algorithm is a theoretical method based on the passive microwave radiative transfer equation. The key parameter in the DPR algorithm is the ratio (α) of microwave emissivities of sea ice for horizontal (H) and vertical (V) polarizations, which can be determined from the brightness temperatures at HV 89.0 GHz with 100% sea ice coverage. The atmospheric effects are implicitly treated as a smooth function in the DPR algorithm. The results show that atmospheric compensation is unnecessary when SIC exceeds 0.82, whereas this compensation is required when SIC is below 0.82. The SIC error induced by atmospheric compensation is closely related to air temperature: the lower the temperature, the smaller the atmospheric impact on the DPR algorithm. When the temperature drops below -5 ℃, the error falls below 10%. The evaluation results indicate that when SIC exceeds 0.25, the DPR algorithm generally outperforms the ARTIST Sea Ice algorithm. Thus, the DPR algorithm can provide more reliable SIC data for Arctic sea ice monitoring, climate modeling, polar navigation safety, and global energy balance research.