The Cryosphere Discussions www.the-cryosphere-discuss.net 1994-0432 1994-0440 2 4 2008 10.5194/tcd-2-623-2008 http://www.the-cryosphere-discuss.net/2/623/2008/ http://www.the-cryosphere-discuss.net/2/623/2008/tcd-2-623-2008.html http://www.the-cryosphere-discuss.net/2/623/2008/tcd-2-623-2008.pdf 623 647 2008-07-22 Antarctic summer sea ice concentration and extent: comparison of ODEN 2006 ship observations, satellite passive microwave and NIC sea ice charts B. Ozsoy-Cicek burcu@drcicek.com H. Xie S. F. Ackley K. Ye Laboratory for Remote Sensing and Geoinformatics, Department of Geological Sciences, University of Texas at San Antonio, Texas 78249, USA Department of Management Science and Statistics, University of Texas at San Antonio, Texas, 78249, USA Antarctic sea ice cover has shown a slight increase in overall observed ice extent as derived from satellite mapping from 1979 to 2008, contrary to the decline observed in the Arctic regions. Spatial and temporal variations of the Antarctic sea ice however remain a significant problem to monitor and understand, primarily due to the vastness and remoteness of the region. While satellite remote sensing has provided and has great future potential to monitor the variations and changes of sea ice, uncertainties remain unresolved. In this study, the National Ice Center (NIC) ice edge and the AMSR-E (Advanced Microwave Scanning Radiometer – Earth Observing System) ice extent are examined, while the ASPeCt (Antarctic Sea Ice Process and Climate) ship observations from the Oden expedition in December 2006 are used as ground truth to verify the two products during Antarctic summer. While there is a general linear trend between ASPeCt and AMSR-E ice concentration estimates, there is poor correlation (<i>R</i>²=0.41) and AMSR-E tends to underestimate the low ice concentrations. We also found that the NIC sea ice edge agrees well with ship observations, while the AMSR-E shows the ice edge further south, consistent with its poorer detection of low ice concentrations. The northward extent of the ice edge at the time of observation (NIC) had mean values varying from 38 km to 102 km greater on different days for the area as compared with the AMSR-E sea ice extent. For the circumpolar area as a whole in the December period examined, AMSR-E therefore underestimates the area inside the ice edge at this time by up to 14% or, 1.5 million km² less area, compared to the NIC ice charts. These differences alone can account for more than half of the purported sea ice loss between the pre 1960s and the satellite era suggested earlier from comparative analysis of whale catch data with satellite derived data. Preliminary comparison of satellite scatterometer data suggests better resolution of low concentrations than passive microwave, and therefore better fidelity with ship observations and NIC charts of the area inside the ice edge during Antarctic summer. Ackley, S. F., Wadhams, P., Comiso, J. C., and Worby, A. P.: Decadal decrease of Antarctic sea ice extent inferred from whaling records revisited on the basis of historical and modern sea ice records, Polar Res., 22(1), 19–25, 2003. Cavalieri, D., Parkinson, C., Gloerson, P., and Zwally, H. J.: Sea ice concentrations from Nimbus-7 SMMR and DMSP SSM/I passive microwave data, June to September 2001, National Snow and Ice Data Center, Digital media and CD-ROM, Boulder, CO, USA, 1997, updated 2005. Cavalieri, D. and Comiso, J.: AMSR-E/Aqua Daily L3 12.5 km Tb, Sea Ice Conc., & Snow Depth Polar Grids V001, March to June 2004, National Snow and Ice Data Center, Digital media,updated daily, Boulder, CO, USA, 2004. Comiso, J. C. and Nishio, F.: Trends in the sea ice cover using enhanced and compatible AMSR-E, SSM/I and SMMR data, J. Geophys. Res., 113, C02S07, doi:1029/2007JC004257, 2008. Comiso, J. C., Cavalieri, D. J., and Markus T.: Sea ice concentration, ice temperature and snow depth using AMSR-E data, IEEE Trans. Geosci. Remote Sens., 41, 243–252, 2003. De la Mare, W. K.: Abrupt mid-twentieth-century decline in Antarctic sea ice extent from whaling records, Nature, 389, 57–60, 1997. Hunke, E. and Ackley, S.: A numerical investigation of the 1997–1998 Ronne Polynya, J. Geophys. Res., 106(C10), 22 373-22 382, 2001. Knuth, M. F. and Ackley, S. F.: Summer and early-fall sea-ice concentration in the Ross Sea: comparison of in situ ASPeCt observations and satellite passive microwave estimates, Ann. Glaciol., 44, 303–309, 2006. Markus, T. and Cavalieri, D. J.: An enhancement of the NASA Team sea ice algorithm, IEEE Trans. Geosci. Remote Sens., 38, 1387–1398, 2000. Nghiem, S. V., Van Woert, M. L., Neumann, G.: Rapid formation of a sea ice barrier east of Svalbard, J. Geophys. Res., 110, C11013, doi:10.1029/2004JC002654, 2005. Nihashi, S. and Cavalieri, D.: Observational evidence of a hemispheric-wide ice-ocean albedo feedback effect on Antarctic sea ice decay J. Geophys. Res., 111, C12001, doi:10.1029/2005JC003447, 2006. Nihashi, S. and Ohshima, K. I.: Relationship between the sea ice decay and solar heating through open water in the Antarctic sea ice zone, J. Geophys. Res., 106, 16 767–16 782, 2001. Parkinson, C. L.: Trends in the length of the Southern Ocean sea-ice season, 1979–1999, Ann. Glaciol., 34(6), 1.1, 435–440, 2002. Worby, A. P. and Comiso, J. C.: Studies of the Antarctic sea ice edge and sea ice extent from satellite and ship observations, Remote Sens. Environ., 92, 98–111, doi:10.1016/j.rse.2004.05.007, 2004. Worby, A. P. and Allison, I.: A ship-based technique for observing Antarctic sea ice: Part I Observational Techniques and Results, Antarctic CRC Research Report, 14, 63 pp., 1999. Worby, A. P., Geiger, C. A., Paget, M. J., Van Woert, M. L., Ackley, S. F., and DeLiberty,T. L.: Thickness distribution of Antarctic sea ice, J. Geophys. Res., 113, C05S92, doi:10.1029/2007JC004254, 2008.