Evaluation of CryoSat-2 derived sea-ice freeboard over fast

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TitleEvaluation of CryoSat-2 derived sea-ice freeboard over fast ice in McMurdo Sound, AntarcticaAbstractUsing in situ data from 2011 and 2013, we evaluate the ability of CryoSat-2 (CS-2) to retrieve sea-ice freeboard over fast ice in McMurdo Sound. This provides the first systematic validation of CS-2 in the coastal Antarctic and offers insight into the assumptions currently used to process CS-2 data. European Space Agency Level 2 (ESAL2) data are compared with results of a Waveform Fitting (WfF) procedure and a Threshold-First-Maximum-Retracker-Algorithm employed at 40%(TFMRA40). A supervised freeboard retrieval procedure is used to reduce errors associated with sea surface height identification and radar velocity in snow. We find ESAL2 freeboards located between the ice and snow freeboard rather than the frequently assumed snow/ice interface. WfF is within 0.04m of the ice freeboard but is influenced by variable snow conditions causing increased radar backscatter from the air/snow interface. Given such snow conditions and additional uncertainties in sea surface height identification, a positive bias of 0.14 m away from the ice freeboard is observed. TFMRA40 freeboards are within 0.03 m of the snow freeboard. The separation of freeboard estimates is primarily driven by the different assumptions of each retracker, although waveform alteration by variations in snow properties and surface roughness is evident. Techniques are amended where necessary, and automatic freeboard retrieval procedures for ESAL2, WfF and TFMRA40 are presented. CS-2 detects annual fastice freeboard trends using all three automatic procedures that are in line with known sea-ice growth rates in the region. Copyright 2015, International Glaciology Society. All rights reserved.AcknowledgementsWe thank all participants in the 2011 and 2013 Antarctica New Zealand field event K063 as well as Scott Base staff for their support. CS-2 data were provided by the European Space Agency for project AOCRY2CAL-4512. The TerraSAR-X image was provided through DLR (German Aerospace Center) project OCE1592. The work of V. Helm and S. Hendricks was funded by the German Ministry of Economics and Technology (grant 50EE1008). We appreciate the efforts of Alec Casey who provided technical assistance in data processing. A research stay for the first author at the University of Alberta was supported by Air New Zealand. Further research support was provided by the National Institute of Water and Atmospheric Research, New Zealand, under contract CO1X1226. We thank Trimble NZ for the use of GNSS equipment, and Wolfgang Dierking for fruitful discussions. We are very grateful for the contributions of Nick Key and Justin Harrison in the design and preparation of field equipment. The comments of two anonymous reviewers and the sea-ice editor contributed to the manuscript. This work was collated at Gateway Antarctica, University of Canterbury, New Zealand.Funding DetailsDeutsches Zentrum fÃ¼r Luft- und Raumfahrt; AOCRY2CAL-4512, ESA, Deutsches Zentrum fÃ¼r Luft- und Raumfahrt; OCE1592, DLR, Deutsches Zentrum fÃ¼r Luft- und Raumfahrt

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1st AuthorPrice, D.AuthorPrice, D.Beckers, J.Ricker, R.Kurtz, N.Rack, W.Haas, C.Helm, V.Hendricks, S.Leonard, G.Langhorne, P.Year2015JournalJournal of GlaciologyVolume61Number226Pages285-300DOI10.3189/2015JoG14J157URLhttps://www.scopus.com/inward/recor.....f98d643dd324d4e711365fd56Keywordsalgorithmcontinental freeboardCryoSatremote sensingsea icesea surface heightsurface roughness, AntarcticaEast AntarcticaMcMurdo Sound, rank5Author KeywordsRemote sensingSea iceSea-ice growth and decayProgrammeK131 - Sea Ice and Southern Ocean Processes

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TypeArticleCitationPrice, D., Beckers, J., Ricker, R., Kurtz, N., Rack, W., Haas, C., Helm, V., Hendricks, S., Leonard, G. and Langhorne, P. (2015) Evaluation of CryoSat-2 derived sea-ice freeboard over fast ice in McMurdo Sound, Antarctica. Journal of Glaciology, 61(226): 285-300 doi:10.3189/2015JoG14J157