Abstract
Abstract. Melt occurrence in Antarctica is derived from L-band observations from the Soil Moisture and Ocean Salinity (SMOS) satellite between the austral summer 2010–2011 and 2017–2018. The detection algorithm is adapted from a threshold method previously developed for 19 GHz passive microwave measurements from the special sensor microwave imager (SSM/I) and special sensor microwave imager sounder (SSMIS). The comparison of daily melt occurrence retrieved from 1.4 and 19 GHz observations shows an overall close agreement, but a lag of few days is usually observed by SMOS at the beginning of the melt season. To understand the difference, a theoretical analysis is performed using a microwave emission radiative transfer model. It shows that the sensitivity of 1.4 GHz signal to liquid water is significantly weaker than at 19 GHz if the water is only present in the uppermost tens of centimetres of the snowpack. Conversely, 1.4 GHz measurements are sensitive to water when spread over at least 1 m and when present in depths up to hundreds of metres. This is explained by the large penetration depth in dry snow and by the long wavelength (21 cm). We conclude that SMOS and higher-frequency radiometers provide interesting complementary information on melt occurrence and on the location of the water in the snowpack.
Highlights
Melt occurs in coastal Antarctica and on ice shelves during the austral summer
The Soil Moisture and Ocean Salinity (SMOS) mission was developed by the European Space Agency (ESA) in collaboration with the Centre National d’Études Spatiales (CNES) in France and the Centro para el Desarrollo Tecnológico Industrial (CDTI) in Spain
Melt occurrence can be retrieved using previously developed algorithms for higher frequencies (Zwally and Fiegles, 1994; Torinesi et al, 2003) after a slight adaptation to account for the lower sensitivity at 1.4 GHz
Summary
Melt occurs in coastal Antarctica and on ice shelves during the austral summer. Its duration and extent are useful climate indicators due to their connection to surface temperature and surface energy budget (e.g. Liu et al, 2006; Picard et al, 2007). M. Leduc-Leballeur et al.: Melt in Antarctica derived from SMOS observations at L band a frequency capable of penetrating much deeper into the ice sheets, on the order of several hundred metres at 1.4 GHz (Passalacqua et al, 2018) compared to only a few metres for the higher frequencies (Surdyk, 2002). Leduc-Leballeur et al.: Melt in Antarctica derived from SMOS observations at L band a frequency capable of penetrating much deeper into the ice sheets, on the order of several hundred metres at 1.4 GHz (Passalacqua et al, 2018) compared to only a few metres for the higher frequencies (Surdyk, 2002) This suggests that Lband observations could offer new information on melt.
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