IFAC-CNR ISTITUTO DI FISICA APPLICATA ” NELLO CARRARA” (IT)
In recent years the possibility of using L-band space-borne radiometers for monitoring the Cryosphere has been investigated using data available from new space missions ((ESA SMOS and NASA Aquarius and SMAP). The interest in L-band relies on the very low absorption of ice at L-band and the low scattering by particles that are very small compared to the wavelength. As a consequence, in dry snow and ice the extinction is low and the penetration depth is very high, which open new opportunities to probe the soil or water under the ice, or the internal layers of the ice-sheet.
The CryoSMOS project, which was funded by ESA as Support To Science Elements (STSE), aims at investigating this topic by testing the capabilities of SMOS in the monitoring of Antarctica ice sheet and ice shelves. SMOS data were first in-depth analyzed and it has been observed that Tb can show temporal dynamic trends in the ice shelves and near to the coast where the snow could be wet, while it is more stable in time, but presents significant spatial features in the inner parts of the continent. Moreover, small but significant Tb temporal variations are observed also in the internal part at H polarization. Four case studies, which are in-depth analyzed within the project, have been considered: the estimate of the temperature profile of the ice sheet; the capability of investigating bedrock topography; the study of the ice shelves stability ; the monitoring of wet snow.
For each study case the SMOS data have been first interpreted by using different microwave emission models which use as inputs data collected on the ground, when available, or from glaciological models. Simulated and measured Tb is in general in good agreement confirming that most of the observed Tb spatial and temporal signatures can be theoretically explained. Model analysis also shows that a better knowledge of dielectric permittivity of ice (especially of its imaginary part which is indeed very small) is required to further improve the results.
Starting from this, inversion algorithms have been developed in order to derive geophysical parameters from SMOS data. Main obtained results are: the retrieval of temperature profile of ice sheet for large portion of Antarctica where the ice-sheet is stable (i.e. velocity < 5 m/year) ; the monitoring of significant changes of ice shelf properties and the identification of their origin ( i.e. bottom or surface changes) and the study of its stability; the improvement of bedrock map in the area affected by large incertitude (i.e. > 500 m); the detection of melt events which can be used in combination to information derived from higher passive microwave sensors.
SMOS derived products have been delivered and are free available at CATDS (https://www.catds.fr/Products/Available-products-from-CEC-SM/CryoSMOS-project) .
Results will be better assessed and validated by additional data (when they will be available). Moreover, future activity should be devoted to the investigation of other regions (i.e. Greenland) and to better evaluate the use of new glaciological models which are able to improve retrieval algorithms.
The Cryosphere (2020)
Remote Sensing of Environment (2019)