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The severe changes in climate resulting in the polar oceans getting warmer – with drastic consequences to their physical, biogeochemical, and biological state – require forecasting systems that can accurately simulate and skilfully predict the state of the ice cover and its temporal evolution. Sea-ice processes significantly impact ocean circulation, water mass formation and modifications, and air–sea fluxes. They comprise vertical processes, mainly related to thermodynamics, and horizontal ones, due to internal sea-ice mechanics and motion. We provide an overview on how these processes can be modelled and how operational systems work, in combination with data assimilation techniques, to enhance accuracy and reliability. We also emphasise the need for advancing research on improving such numerical techniques by highlighting current limits and ways forward. 

This article reviews existing and planned contributions of spaceborne microwave radiometry from P to S band to new measurements of key geophysical variables with a particular focus on the polar regions. It summarizes the current state of spaceborne microwave radiometry to measure ice sheet thermal states, sea ice thickness (SIT), salinity, and sea surface salinity (SSS). Then, this article discusses the potential of wideband radiometry, with continuous sampling in the range of 0.4–2 GHz, as a breakthrough for enhancing the estimation of geophysical variables such as SSS and the geothermal heat flux beneath the polar ice sheets, which are currently monitored primarily using L-band radiometry satellites. Furthermore, this article describes opportunities for new unique observations that cannot be achieved with the current constellation of satellite sensors. In addition, this article demonstrates the advantages of using low-frequency radiometry in sensing soil moisture and biomass from space due to the great sensing depth. This article concludes with a discussion of mission concepts highlighting the CryoRad mission, which has been selected as one of the four candidates for European Space Agency Earth Explorer 12 competition and is now conducting Phase 0 feasibility studies, envisions a 0.4–2-GHz dedicated spaceborne radiometer operated with circular polarization.