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The Cryosphere An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/tc-2016-293
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
17 Jan 2017
Review status
A revision of this discussion paper is under review for the journal The Cryosphere (TC).
Comparison of CryoSat-2 and ENVISAT freeboard height over Arctic sea ice: Toward an improved Envisat freeboard height retrieval
Kevin Guerreiro1, Sara Fleury1, Elena Zakharova1,2, Alexei Kouraev1,2,3, Frédérique Rémy1, and Philippe Maisongrande1 1Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Centre National de la Recherche Scientifique (LEGOS – CNRS, UMR5566), Université de Toulouse, 31400 Toulouse, France
2State Oceanography Institute, St. Petersburg Branch, St. Petersburg, Russia
3Tomsk State University, Tomsk, Russia
Abstract. During the past decade, sea ice freeboard height has been monitored with various satellite altimetric missions with the aim of producing long-term time series of ice thickness. To achieve this goal, it is essential to analyze potential inter-mission biases and to produce freeboard height datasets as free of instrumental error as possible. In the present study, we compare Envisat and CryoSat-2 freeboard height during the common flight period (2010–2012). Our results show that Envisat freeboard height is always thinner (−14 cm in average) when compared to CryoSat-2 (3 cm in average). In addition, Envisat freeboard height displays an unrealistive negative growth from November to April (−2.4 to −3.7 cm) while CryoSat-2 dispalys a positive and coherent winter growth (2.4 to 2.7 cm). The discrepancy between the two datasets is found to be related to a dissimilar impact of ice roughness and snow volume scattering on SAR (CryoSat-2) and pulse-limited (Envisat) altimetry. Following this result, we show that the freeboard height difference between the two datasets can be expressed as a function of the waveform pulse-peakiness. Based on the relation between the Envisat pulse-peakiness and the freeboard height difference, we produce a monthly CryoSat-2-like version of Envisat freeboard height that reduces the average RMSD with CryoSat-2 from ~ 16 cm to ~ 2 cm and improves the freeboard height growth cycle (2–3 cm). The comparison of the altimetric datasets with in situ ice draft measurements during the common flight period shows that the corrected Envisat dataset (RMSE = 16–29 cm) is as accurate as CryoSat-2 (RMSE = 13–25 cm) and highly more accurate than the uncorrected Envisat dataset (RMSE = 108–132 cm). The comparison of the improved Envisat freeboard height dataset is then extended to the rest of the Envisat mission to demonstrate the validity of the improved Envisat dataset out of the calibration period. As a result, we find a good agreement between the Envisat and the in situ ice draft datasets (RMSE = 14–30 cm), which demonstrates the potential of the pulse-peakiness-correction to produce accurate freeboard height estimates over the entire Envisat mission. Finally, we show the averaged-circumpolar ice thickness variations from 2002 to 2015 by combining CryoSat-2 and Envisat datasets.

Citation: Guerreiro, K., Fleury, S., Zakharova, E., Kouraev, A., Rémy, F., and Maisongrande, P.: Comparison of CryoSat-2 and ENVISAT freeboard height over Arctic sea ice: Toward an improved Envisat freeboard height retrieval, The Cryosphere Discuss., https://doi.org/10.5194/tc-2016-293, in review, 2017.
Kevin Guerreiro et al.
Kevin Guerreiro et al.
Kevin Guerreiro et al.

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Short summary
We analyse CryoSat-2 and Envisat freeboard height discrepancy over Arctic sea ice and we study the potential role of ice roughness and volume scattering. Based on our results, we build a CryoSat-2-like version of Envisat freeboard height. The improved Envisat freeboard is converted to sea ice draft and compared to in situ mooring observations to demonstrate the potential of the methodology developed in the present study to produce accurate ice thickness estimates over the 2002–2012 period.
We analyse CryoSat-2 and Envisat freeboard height discrepancy over Arctic sea ice and we study...
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