Dependence of thermal infrared emissive behaviors of snow cover on the surface snow type

• Published in: Bulletin of Glaciological Research
• Main Authors: HORI, Masahiro, AOKI, Teruo, TANIKAWA, Tomonori, KUCHIKI, Katsuyuki, NIWANO, Masashi, YAMAGUCHI, Satoru, MATOBA, Sumito
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Japanese Society of Snow and Ice
• Subjects: spectral emissivity; snow and ice; thermal infrared; surface temperature; snow grain size; 分光射出率; 雪氷; 熱赤外; 表面温度; 積雪粒径; 450; Greenland; Ice Sheet
• Online Access: http://hdl.handle.net/2115/56972; https://doi.org/10.5331/bgr.32.33

The potential of the thermal infrared (TIR) remote sensing for discriminating surface snow types was examined by analyzing TIR radiances acquired from space over the Greenland ice sheet. The brightness temperature difference (BTD) between TIR wavelengths of 11 and 12μm was found to increase in accordance with in situ observed evolutions of surface snow type. Spatial and temporal distributions of BTD over the entire ice sheet indicated that BTD has a sensitivity of about 1.2 K for variations of the possible snow types. The observed behaviors of BTD were coincident with those predicted by a radiative transfer calculation using previous in situ measured snow emissivities, although some biases on the order of 0.1-0.3 K remain. The dependence of BTD on the surface snow type was also consistent with the behaviors of snow reflectance at the shortwave infrared (SWIR) wavelength 1.6μm, which is a measure of snow grain size, except for the case of melting wet snow. The inconsistency in the wet snow case was considered to be due to the different optical responses of the TIR and SWIR signals to wet snow, which suggested the possibility of using TIR signals to discriminate wet/dry conditions of snow cover in an old stage. As a result, it is determined that TIR remote sensing has potential not only as an approach supplementary to the SWIR method for assessing surface snow types in daytime but also as the only method for simultaneous retrieval of snow type and surface temperature in nighttime.