Our knowledge of the state of sea ice (particularly areal extent and concentration) undertook a quantum leap in 1978 with the launch of the Scanning Multi-channel Microwave Radiometer (SMMR), a passive microwave radiometer on NASA’s Nimbus-7 polar orbiting satellite. Since that time, the field of sea ice remote sensing from space has progressed rapidly, with the availability of a wide range of sea ice parameters including ice thickness (particularly in the Arctic, from both laser and radar altimetry), progressively higher-resolution passive microwave-derived sea ice products, and very high resolution microwave backscatter measurements from synthetic aperture radar (SAR) imagery, giving a detailed description of ice properties and dynamics. Despite these advances, key scientific problems remain unsolved, including knowledge of the total volume of Antarctic sea ice. Finer-resolution passive microwave products are also highly desirable. We propose two new instrument/platform combinations to address these shortcomings: 1) a spaceborne fan-beam scatterometer operating at L-band; and 2) a passive microwave radiometer mounted on a remotely-operated High Altitude Pseudo-Satellite (HAPS; 20 km altitude; 90 day endurance; pilot program underway). Access to L-band scatterometer data would build on recent work showing a robust relation between backscatter and ice thickness (also between backscatter and roughness) in the Okhotsk and Weddell
seas, but give a circumpolar perspective impossible using narrow-swath SARs (i.e., a sea ice thickness proxy on very large spatial scales, which would be highly complementary to – and independent of – altimeter-based estimates). The HAPS-mounted passive microwave radiometer would provide very high resolution (sub-km) estimates of extant passive microwave-derived parameters such as sea ice concentration, coastal polynya sea ice production, enable better validation of spaceborne passive microwave radiometer parameter retrieval algorithms, and provide a quantum leap in Antarctic coastal physical oceanography (e.g., sea surface salinity retrieval in open water areas within the sea ice). This presentation will give the scientific case for each sensor, and present technical challenges of each.