Combining Earth cryosphere microwave radiometry and radar to understand the properties of planetary ices

Interpreting microwave data on icy moons in terms of physical parameters is a key challenge offered by observations of Ganymede and Europa by both the current Juno (NASA) MicroWave Radiometer (MWR) and the future JUICE (ESA) Submillimeter Wave Instrument (SWI). From sub-millimeter to decimeter scale wavelengths, radiometry is sensitive to different depths and scatterer sizes: each frequency offers complementary information. Despite the large volume of available passive and active microwave satellite observations over the Earth cryosphere, physical interpretation of the co-variability of the multi-frequency observations is still challenging, especially when trying to reconcile radiometry and radar observations. To help interpret icy moon observations and improve our understanding of Earth’s ices, we assemble a multi-frequency active and passive microwave observation dataset from the SMAP (1.4 GHz, passive), AMSR2 (6 to 89 GHz, passive) and ASCAT (5 GHz, active) missions. The data are gridded over Earth’s land and ocean ices and averaged over 10 days, over two full years and then classified using a k-means method. We identify regions with microwave behavior analogous to that observed on icy moons and simulate them using the Snow Microwave Radiative Transfer (SMRT) model. Identifying structures responsible for given microwave signatures will help interpret the Juno MWR observations on Jupiter’s moons as well as the joint active/passive 2.2-cm Cassini data acquired from 2004 to 2017 on Saturn’s icy satellites.