Day 4

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Paper title Advanced melt indicators from passive microwave satellite observations in Antarctica
  1. Marion Leduc-Leballeur IFAC-CNR Speaker
  2. Ghislain Picard Université Grenoble Alpes
  3. Giovanni Macelloni IFAC-CNR
Form of presentation Poster
  • A9. Polar Science and Cryosphere
    • A9.04 Mass Balance of the Cryosphere
Abstract text In the polar regions, the state of the surface is essential to understanding and predicting the surface energy and mass budgets, which are two key snow-meteorological variables for the study of the climate and the contribution to the sea level rise of ice-sheets. The inter-annual variations in melt duration and extent are valuable indicators of the summer climate in the coastal regions of the ice-sheets, especially on ice-shelves where melt water contributes to hydrofracturing and destabilisation.

Liquid water has a significant impact on the microwave emissivity of the surface and several studies exploited the brightness temperature timeseries at the 19, 37, 1.4 GHz to provide binary melt indicators (Torinesi et al., 2003, Picard et al., 2006, Leduc-Leballeur et al., 2020). However, these indicators showed differences, which point out difference of depth up to which it is possible to detect the water presence at the different freqeuncies. For example, comparisons performed between the melt seasons obtained from 1.4 GHz observations with the Soil Moisture and Ocean Salinity (SMOS) satellite and 19 GHz observations with the special sensor microwave imager (SSM/I) satellite showed that the large penetration depth at 1.4 GHz could detect wet snow in depth, contrary to 19 GHz which is limited to the upper centimeters from the surface. As a consequence also the duration of the melt season (onset, freeze up) as observed by the different frequency can varying. This highlights the potential of the multifrequency combination to provide complementary information.

In the framework of the ESA 4D-Antarctica project, we propose to combine the binary melt indicators from the single-frequency to provide enhanced insights of the melt process. We focus on the 36 GHz and 19 GHz observations from of the Advanced Microwave Scanning Radiometer 2 (AMSR2) satellite and the 1.4 GHz observations from SMOS. A deep theoretical analysis has been performed to explore the sensitivity of these frequencies to wet snow. In particular, we noted the potential of 36 GHz to distinguish different stage of close surface melting and the 1.4 GHz identifies the most intense period of melt during the summer. Moreover, AMSR2 provides observations in the afternoon (ascending pass) and in the night (descending pass). This allows to detect the possible presence of a refrozen surface layer based on 19 GHz and 36 GHz. The final combined indicator is composed of seven melt status, which match to a particular physical description of the snowpack. It allows determining if a melt event was limited to the surface of the snowpack or if it was intense enough to inject significant water amounts at depths, and if refreezing happens during the night. This new product provides a clear and synthetic description of the melt status along the season. This opens a good opportunity for a potential use for the Copernicus Imaging Microwave Radiometer (CIMR) perspective.