Satellite detection of sea fog and low clouds in the Arctic in the daytime during the summer through multiple sources of infrared remote sensing

A greater frequency of sea fog/low clouds may be observed in the Arctic under the effects of global warming, which strongly affects the safety of navigation in the Arctic. Using moderate-resolution imaging spectroradiometer (MODIS) infrared multiband remote sensing data, in this paper, we construct a detection algorithm for sea fog and low clouds in the daytime during the summer period in the Arctic through multiband infrared remote sensing. Physically, the algorithm relies on the spectral variation in the Arctic Sea route region with different solar zenith angles (SZAs). Specifically, for days with strong sunshine (SZA < 70°), the effect of the sea surface is removed by coupling the B7 (2.130 μm) near-infrared band reflectance (R_{2.130 μm}) and the radiation difference (BTD_{3.750 μm–11.030 μm}) between the B20 (3.750 μm) mid-infrared band (BT_{3.750 μm}) and B31 (11.030 μm) thermal infrared band (BT_{11.030 μm}). Then, the sea fog and low-cloud ratio index (SFLCRI) is constructed on the basis of two near-infrared bands, namely, the B5 (1.240 μm) water vapor absorption band and the B9 (0.936 μm) atmosphere window, to remove the middle and high clouds. Finally, the sea fog and low clouds are extracted according to the radiation threshold of BT_{11.030 μm}. At dawn and dusk (SZA > 70°), the SFLCRI is utilized to remove the sea surface and middle and high clouds, and then the undetected middle and high clouds are removed via BT_{11.030 μm}. The validation results reveal that the accuracy of the algorithm is high, and the probability of detection, false alarm ratio, and the critical success index of sea fog and low-cloud detection are 86 %, 13 %, and 76 %, respectively, as a whole. The algorithm accuracy was less affected by time. The research results are of great theoretical and practical importance for Arctic sea fog and low-cloud detection, and for ensuring the safety of Arctic shipping.