Using mm-wave observations to maximize the CRISTAL mission cryosphere science applications

Satellite observations are essential for monitoring changes in vast inaccessible polar regions. CRISTAL is the next polar altimetry mission being developed by the European Space Agency (ESA) and planned for launch in 2027. The payload includes an Interferometric Radar altimeter for Ice and Snow (IRIS, provided by ESA) operating at Ku- and Ka- bands and a potential NASA contribution of an Advanced Microwave Radiometer (AMR-CR) developed at NASA-JPL. The mission will include alongside AMR-CR, a High-Resolution Microwave Radiometer (HRMR). Together they provide radiometric measurement channels ranging from 18 to 166 GHz for open ocean topography and ice/snow applications. Changes in the polar regions have been widely documented by satellite microwave radiometer data. Frequencies up to 40 GHz are routinely used to derive sea ice extent, concentration, type, and thickness, as well as snow depth on sea ice. While higher frequency channels (mm-wave) provide improved spatial resolution, their use has been limited due to their sensitivity to atmospheric conditions and decreased penetration depths. For the first time, the CRISTAL mission will provide active and passive measurements of the polar regions over a wide range of frequencies. This new sensing capability will open up new avenues to explore novel cryosphere science that exploits the unique sensitivities of microwave and mm-wave observations to changes in atmospheric conditions and surface properties across a wide range of frequencies.