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The Cryosphere An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 Jul 2020

14 Jul 2020

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This preprint is currently under review for the journal TC.

Refining the sea surface identification approach for determining freeboards in the ICESat-2 sea ice products

Ron Kwok1, Alek A. Petty2,3, Marco Bagnardi2,4, Nathan T. Kurtz2, Glenn F. Cunningham5, and Alvaro Ivanoff2,4 Ron Kwok et al.
  • 1Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, Washington, USA
  • 2Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 3Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, USA
  • 4ADNET Systems, Inc., Rockville, Maryland, USA
  • 5Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

Abstract. In Release 1 and 2 of the ICESat-2 sea ice products, candidate height segments used to estimate the reference sea surface height for freeboard calculations included two surface types: specular and smooth dark leads. We found that the uncorrected photon rates, used as proxies of surface reflectance, are attenuated due to clouds resulting in the potential misclassification of sea ice as dark leads, biasing the reference sea surface height relative to those derived from the more reliable specular returns. This results in higher reference sea surface heights and lowering estimated ice freeboards. Resolution of available cloud flags from the ICESat-2 atmosphere data product are too coarse to provide useful filtering at the lead segment scale. In Release 3, we have modified the surface reference finding algorithm so that only specular leads are used. The consequence of this change can be seen in the freeboard composites of the Arctic and Southern Ocean. Broadly, coverages have decreased by ~10–20 % because there are fewer leads (by excluding the dark leads), and the composite means have increased by 0–4 cm because of the use of more consistent specular leads.

Ron Kwok et al.

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Ron Kwok et al.

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