Evaluating CryoRad Sea-Ice Performance Requirements with 0.4-2 GHz Brightness-Temperature Simulations: A Sensitivity Assessment Using ORAS6

CryoRad is a candidate satellite mission concept equipped with a broadband low-frequency microwave radiometer operating between 0.4 and 2 GHz with continuous frequency coverage. Its primary objective is to advance cryosphere science by delivering new geophysical variables critical for ocean and climate studies. CryoRad will provide temperature profiles of the Antarctic and Greenland ice sheets from surface to bedrock, previously accessible only through sparse borehole observations, and will address long-standing limitations of L-band radiometers in retrieving sea surface salinity (SSS) in cold waters. Furthermore, the mission aims to significantly improve estimates of sea ice thickness, volume, and salinity, thereby enabling a more comprehensive characterization of the polar ocean-sea ice system. To quantify the scientific return and support the definition of radiometer performance requirements, we combine forward modeling and sensitivity experiments with data from the ECMWF ORAS6 ocean reanalysis. ORAS6 includes a multicategory sea ice model with prognostic ice salinity, providing spatially and temporally consistent fields of sea ice concentration, thickness, volume, temperature, and salinity. These parameters serve as a physically consistent baseline for simulating CryoRad brightness temperatures using simplified one-layer emissivity models. Sensitivity analyses reveal the frequency-dependent impact of ice thickness, salinity, and ocean surface properties on measured brightness temperatures.