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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/tc-2020-283
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-283
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  05 Nov 2020

05 Nov 2020

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This preprint is currently under review for the journal TC.

Evaluating Airborne Ku-Band Radar Altimetry over Landfast First-Year Sea Ice

Paul Donchenko1, Joshua King2, and Richard Kelly1 Paul Donchenko et al.
  • 1Department of Geography, University of Waterloo, Waterloo, ON N2L 3G1, Canada
  • 2Climate Research Division, Environment and Climate Change Canada, Toronto, M3H5T4, Canada

Abstract. Recent studies have challenged the assumption that Ku-band radar used by the CryoSat-2 altimeter fully penetrates the dry snow cover of Arctic sea ice. There is also uncertainty around the proper technique for handling retracker threshold selection in the Threshold First-Maxima Retracker (TFMRA) method which estimates the ice surface elevation from the radar echo waveform. The purpose of this study was to evaluate the accuracy and penetration of the TFMRA retracking method applied to the Airborne Synthetic Aperture Radar and Interferometric Radar Altimeter System (ASIRAS), an airborne simulator of the CryoSat-2, to investigate the effect of surface characteristics and improve accuracy.

The ice surface elevation estimate from ASIRAS was evaluated by comparing to the snow surface measured by aggregating laser altimetry observations from the Airborne Laser Scanner (ALS), and the ice surface measured by subtracting ground observations of snow depth from the snow surface. The perceived penetration of the ice surface estimate was found to increase with the retracker threshold and was correlated with the value of surface properties. The slope of the relationship between penetration and threshold was greater for a deformed ice surface, a rough snow surface, a deeper snow cover, an absence of salinity and a larger snow grain size. As a result, the ideal retracked threshold, one that would achieve 100 % penetration, varies depending on properties of the surface being observed. Under conditions such deep snow or a large grain size, the retracked elevation sr was found in some cases to not penetrate fully the snowpack. This would cause an overestimation of the sea ice freeboard and as a consequence, the sea ice thickness.

Results suggest that using a single threshold with the TFMRA retracking method will not yield a reliable estimate of the snow-ice interface when observed over an area with diverse surface properties. However, there may be potential to improve the retracking method by incorporating knowledge of the sensed surface physical characteristics. This study shows that remotely sensed surface properties, such as the ice deformity or snow surface roughness, can be combined with the waveform shape to select an ideal retracker for individual returns with an additional offset to account for the incomplete penetration of Ku-band over appropriate surface characteristics.

Paul Donchenko et al.

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Paul Donchenko et al.

Data sets

CryoVEx ASIRAS Campaign 2014 S. M. Hvidegaard, J. E. Nielsen, L. Sandberg Sørensen, S. B. Simonsen, H. Skourup, R. Forsberg, V. Helm, and T. Bjerg https://doi.org/10.5270/esa-aa4xtkn

Model code and software

CryoVEx-Eureka Analysis Supplement Paul Donchenko https://doi.org/10.5281/zenodo.4243559

Paul Donchenko et al.

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Short summary
Estimating Arctic sea ice surface elevation from the CryoSat-2 instrument may not fully compensate for the incomplete penetration of radar through the snow cover and overestimate the ice thickness. This study investigates the accuracy of the ice surface measurement and how it is affected by the properties snow and ice properties. It was found that deep or salty snow, and rough ice can make the surface appear higher, but including these properties in the calculation may improve the estimate.
Estimating Arctic sea ice surface elevation from the CryoSat-2 instrument may not fully...
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