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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 4
The Cryosphere, 10, 1415-1425, 2016
https://doi.org/10.5194/tc-10-1415-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
The Cryosphere, 10, 1415-1425, 2016
https://doi.org/10.5194/tc-10-1415-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Jul 2016

Research article | 08 Jul 2016

About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice

Sandra Schwegmann1, Eero Rinne2, Robert Ricker1, Stefan Hendricks1, and Veit Helm1 Sandra Schwegmann et al.
  • 1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 2Finnish Meteorological Institute, Marine Research, Erik Palménin aukio 1, 00560 Helsinki, Finland

Abstract. Knowledge about Antarctic sea-ice volume and its changes over the past decades has been sparse due to the lack of systematic sea-ice thickness measurements in this remote area. Recently, first attempts have been made to develop a sea-ice thickness product over the Southern Ocean from space-borne radar altimetry and results look promising. Today, more than 20 years of radar altimeter data are potentially available for such products. However, the characteristics of individual radar types differ for the available altimeter missions. Hence, it is important and our goal to study the consistency between single sensors in order to develop long and consistent time series. Here, the consistency between freeboard measurements of the Radar Altimeter 2 on board Envisat and freeboard measurements from the Synthetic-Aperture Interferometric Radar Altimeter on board CryoSat-2 is tested for their overlap period in 2011. Results indicate that mean and modal values are in reasonable agreement over the sea-ice growth season (May–October) and partly also beyond. In general, Envisat data show higher freeboards in the first-year ice zone while CryoSat-2 freeboards are higher in the multiyear ice zone and near the coasts. This has consequences for the agreement in individual sectors of the Southern Ocean, where one or the other ice class may dominate. Nevertheless, over the growth season, mean freeboard for the entire (regionally separated) Southern Ocean differs generally by not more than 3cm (8cm, with few exceptions) between Envisat and CryoSat-2, and the differences between modal freeboards lie generally within ±10cm and often even below.

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Our study aimed to investigate whether CS-2 and Envisat radar freeboard can be merged without intermission biases in order to obtain a 20-year data set. The comparison revealed a reasonable regional agreement between radar freeboards derived from both sensors. Differences are mostly below 0.1 m for modal freeboard and even less for mean freeboard over winter months (May–October). The highest differences occur in regions with multi-year sea ice and along the coasts.
Our study aimed to investigate whether CS-2 and Envisat radar freeboard can be merged without...
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