Arctic Sea Ice Thickness Estimation From Passive Microwave Satellite Observations Between 1.4 and 36 GHz

Arctic sea ice thickness (SIT) has been mostly retrieved from lidar and radar altimeters since the 2000s. However, the repeatability of altimeters and their spatial coverage limit SIT estimates spatially and temporally. On the other hand, the passive microwave (PMW) radiometers have daily basin-scale coverage of the Arctic. In this study, we propose a SIT retrieval from PMW observations, derived from a statistical inversion technique. It is based on the evidence of high correlations between PMW observations and existing altimetric satellite-derived SIT, especially at 36 GHz. Lidar ICESat-2 SIT products are used to train a neural network with multiple combinations of brightness temperatures between 1.4 and 36 GHz as inputs over the 2018-2019 time period. The PMW retrieved SIT can mimic the lidar SIT product over the full winter over the Arctic, with a correlation of 0.85, and a root mean square difference (RMSD) of 0.54 cm. Results are also compared with the SIT product CS2SMOS (CryoSat-2 and Soil Moisture Ocean Salinity merged product), with SIT from a coupled ice/ocean reanalysis model and with the Operation IceBridge QuickLook airborne SIT measurements. The PMW SIT retrieval with all frequencies from 1.4 to 36 GHz shows a correlation of 0.72 and a RMSD of 57 cm when compared to OIB-QL measurements, for large SIT (mostly above 3 m), under multi-year ice environments. The PMW SIT retrieval using only 18 and 36 GHz has similar performances and could allow the calculation of long time series, these microwave frequencies being available from satellites since the 1980s.