A Novel Approach to Map the Intensity of Surface Melting on the Antarctica Ice Sheet Using SMAP L-Band Microwave Radiometry

The polar ice sheets have undergone unprecedented melt events in recent years, which have consequences for the ice sheet mass balance and stability, and global sea level. In this article, we employed L-band (1.4 GHz) brightness temperature observations collected by NASA's Soil Moisture Active Passive (SMAP) mission to investigate the extent, duration, and intensity of melt events on the Antarctic Ice Sheet from 2015 to 2020. The observed microwave response depends on the sensor measurement frequency. Our hypothesis for this article is that the relatively long wavelength (21 cm) SMAP observations can detect a wider range of surface wetness conditions relative to shorter wavelength microwave observations that attain signal saturation at relatively lower wetness levels and within shallower surface layers. SMAP provides nearly all-weather surface monitoring over all of Antarctica twice daily with morning and evening overpasses at about 40 km spatial resolution. We applied an empirical threshold algorithm using horizontally and vertically polarized microwave brightness temperature differences to detect surface melt events over Antarctica. The results show that the SMAP empirical algorithm can be used to detect melt extent and duration, and the geophysical model-based algorithm can be used to detect variations in snow wetness, which serve as an indicator of melt intensity. Analysis of the melt seasons between 2015 and 2020 shows that even though the melt extent in 2019–2020 was not as large as during the 2015–2016 melt season, it was significantly more intense, particularity on the West Antarctic Ice Sheet.