Polarimetric Synthetic Aperture Radar Altimeter (PoSARA): progress towards a new Earth Observation mission concept for snow depth and cryosphere remote sensing

Sea ice and its snow cover play key roles in Earth's climate. Snow depth and sea ice thickness are World Meteorological Organisation-designated Essential Climate Variables, but their complexity and heterogeneity can pose a challenge for remote sensing. Satellite radar altimetry can provide data over large length and timescales, but there are uncertainties associated with the penetration and scattering of the EM radiation used in these Earth Observation approaches and hence data products. Validation from satellite, airborne and surface-based campaigns do not present a coherent set of results, leading to a lack of clarity on the physics and the way forward for remote sensing approaches. 

The depth of snow on sea ice also remains a major source of uncertainty in sea ice thickness retrievals. Using the KuKa surface based, fully polarimetric dual-frequency radar instrument, deployed in multiple Arctic and Antarctic field campaigns, it has been demonstrated that using dual-polarisation techniques could provide accurate retrievals of snow depth, performing better than dual-frequency Ku- and Ka-band approaches at the surface-based scale, along with coincident sea ice freeboard estimates. We present data over Arctic and Antarctic sea ice, and Arctic tundra, demonstrating the performance of the techniques across these scenarios. Via funding from the European Space Agency's New Earth Observation Mission Ideas (NEOMI) grant, we have developed the concept through scientific readiness levels 1-3. We explore the possibility of scaling to satellite scale and future possibilities for polarimetric altimetry over the cryosphere, using modelling and considerations of upscaling of findings from surface-based campaigns, and contrast our techniques against dual-frequency approaches.