Abstract
Abstract. Sea-ice thickness on a global scale is derived from different satellite sensors using independent retrieval methods. Due to the sensor and orbit characteristics, such satellite retrievals differ in spatial and temporal resolution as well as in the sensitivity to certain sea-ice types and thickness ranges. Satellite altimeters, such as CryoSat-2 (CS2), sense the height of the ice surface above the sea level, which can be converted into sea-ice thickness. Relative uncertainties associated with this method are large over thin ice regimes. Another retrieval method is based on the evaluation of surface brightness temperature (TB) in L-band microwave frequencies (1.4 GHz) with a thickness-dependent emission model, as measured by the Soil Moisture and Ocean Salinity (SMOS) satellite. While the radiometer-based method looses sensitivity for thick sea ice (> 1 m), relative uncertainties over thin ice are significantly smaller than for the altimetry-based retrievals. In addition, the SMOS product provides global sea-ice coverage on a daily basis unlike the altimeter data. This study presents the first merged product of complementary weekly Arctic sea-ice thickness data records from the CS2 altimeter and SMOS radiometer. We use two merging approaches: a weighted mean (WM) and an optimal interpolation (OI) scheme. While the weighted mean leaves gaps between CS2 orbits, OI is used to produce weekly Arctic-wide sea-ice thickness fields. The benefit of the data merging is shown by a comparison with airborne electromagnetic (AEM) induction sounding measurements. When compared to airborne thickness data in the Barents Sea, the merged product has a root mean square deviation (RMSD) of about 0.7 m less than the CS2 product and therefore demonstrates the capability to enhance the CS2 product in thin ice regimes. However, in mixed first-year (FYI) and multiyear (MYI) ice regimes as in the Beaufort Sea, the CS2 retrieval shows the lowest bias.
Highlights
Sea ice affects many climate-related processes, such as heat transfer between ocean and atmosphere or ocean circulation, and marine operations (Meier et al, 2014)
We presented methods to carry out the first joint data merging of CryoSat-2 sea-ice thickness fields and thin ice thickness estimates obtained from the L-band radiometer onboard the Soil Moisture and Ocean Salinity satellite
We have shown that the merged products have the capability to allow for weekly thickness estimates that are sensitive to the entire thickness range, using the complementary sensitivity of the individual products to different thickness regimes
Summary
Sea ice affects many climate-related processes, such as heat transfer between ocean and atmosphere or ocean circulation, and marine operations (Meier et al, 2014). The thickness of sea ice is a crucial parameter for the ice mass balance and is more difficult to observe. Recent satellite altimeter missions such as ICESat or CryoSat-2 (CS2) demonstrated the capability to provide Arctic sea-ice thickness and volume estimates (Kwok et al, 2009; Laxon et al, 2013). They are used to measure freeboard (Fb), the height of the ice or snow surface above the water level, which can be converted into sea-ice thickness assuming hydrostatic equilibrium.
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