Abstract
One of the key sources of uncertainties in sea ice freeboard and thickness estimates derived from satellite radar altimetry results from changes in sea ice surface properties. In this study, we analyse this effect, comparing upward-looking sonar (ULS) measurements in the Beaufort Sea over the period 2003–2018 to sea ice draft derived from Envisat and Cryosat-2 data. We show that the sea ice draft growth underestimation observed for the most of winter seasons depends on the surface properties preconditioned by the melt intensity during the preceding summer. The comparison of sea ice draft time series in the Cryosat-2 era indicates that applying 50% retracker thresholds, used to produce the European Space Agency’s Climate Change Initiative (CCI) product, provide better agreement between satellite retrievals and ULS data than the 80% threshold that is closer to the expected physical waveform interpretation. Our results, therefore, indicate compensating error contributions in the full end-to-end sea-ice thickness processing chain, which prevents the quantification of individual factors with sea-ice thickness/draft validation data alone.
Highlights
Satellite radar altimeter measurements are widely used to retrieve sea ice thickness in the Arctic region at the basin-wide scale—e.g., [1,2,3,4,5]
2018 to validate sea ice draft time series derived from the Envisat and CS2 satellite radar altimeter data by the algorithm used to produce the ESA Climate Change Initiative (CCI)-2 sea ice thickness (SIT) climate data record
We used the Beaufort Gyre Exploration Project (BGEP) upward-looking sonar (ULS) measurements in the Beaufort Sea for the period 2003–2018 to validate sea ice draft time series derived from the Envisat and CS2 satellite radar altimeter data by the algorithm used to produce the ESA CCI Phase 2 (CCI-2) SIT climate data record
Summary
Satellite radar altimeter measurements are widely used to retrieve sea ice thickness in the Arctic region at the basin-wide scale—e.g., [1,2,3,4,5]. Sea ice draft measurements of the moored upward-looking sonars (ULS) [13,14,15] and Operation IceBridge (OIB) airborne measurements of sea ice freeboard and snow depth [16] are the main data sources used to validate satellite altimeter-based sea ice thickness. Since draft observations represent the main portion of the sea ice thickness, the ULS data allow an end-to-end validation of satellite SIT product, but do not provide information about sea ice freeboard. The CCI Phase 2 (CCI-2) SIT product was validated by Kern et al [17], where the comparison of the gridded sea ice draft estimated using radar altimeter observations from Envisat and Cryosat-2 (CS2) satellites with, in particular, the BGEP ULS measurements, is provided. The origin of these discrepancies is analysed in conjunction with the satellite and geophysical parameters
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