Abstract
Satellite altimetry is the only method to monitor global changes in sea-ice thickness and volume over decades. Such missions (e.g., ERS, Envisat, ICESat, CryoSat-2) are based on the conversion of freeboard into thickness by assuming hydrostatic equilibrium. Freeboard, the height of the ice above the water level, is therefore a crucial parameter. Freeboard is a relative quantity, computed by subtracting the instantaneous sea surface height from the sea-ice surface elevations. Hence, the impact of geophysical range corrections depends on the performance of the interpolation between subsequent leads to retrieve the sea surface height, and the magnitude of the correction. In this study, we investigate this impact by considering CryoSat-2 sea-ice freeboard retrievals in autumn and spring. Our findings show that major parts of the Arctic are not noticeably affected by the corrections. However, we find areas with very low lead density like the multiyear ice north of Canada, and landfast ice zones, where the impact can be substantial. In March 2015, 7.17% and 2.69% of all valid CryoSat-2 freeboard grid cells are affected by the ocean tides and the inverse barometric correction by more than 1 cm. They represent by far the major contributions among the impacts of the individual corrections.
Highlights
There is notable evidence for the thinning of the Arctic sea ice and a loss of sea-ice volume during the last decades [1,2,3,4]
The first part is related to the impact of the geophysical corrections on the CS2 freeboard, while the second part shows the results of the comparison with airborne laser data in order to evaluate the corrections regarding potential improvements
We aimed to evaluate the impact of geophysical corrections on sea-ice freeboard due to atmospheric effects and tidal forces
Summary
There is notable evidence for the thinning of the Arctic sea ice and a loss of sea-ice volume during the last decades [1,2,3,4]. The instantaneous sea-surface height can be retrieved by interpolating between elevations of detected leads, which are openings in the ice that form due to diverging or shearing of ice floes. Residual gradients in radar range elevations can be assigned to the sea-ice freeboard only If such gradients occur between 2 lead elevation tie points, the interpolation between these lead elevations will cause a bias in the instantaneous sea-surface height and in sea-ice freeboard. Such biases can have a high correlation length and do not cancel out each other as usual statistical errors do. They stem from different sources, as models or static catalogues, and are provided by ESA in the raw orbit data
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