The Cryosphere Discussions www.the-cryosphere-discuss.net 1994-0432 1994-0440 2 5 2008 10.5194/tcd-2-811-2008 http://www.the-cryosphere-discuss.net/2/811/2008/ http://www.the-cryosphere-discuss.net/2/811/2008/tcd-2-811-2008.html http://www.the-cryosphere-discuss.net/2/811/2008/tcd-2-811-2008.pdf 811 841 2008-11-25 A new 1 km digital elevation model of the Antarctic derived from combined satellite radar and laser data – Part 1: Data and methods J. L. Bamber j.bamber@bristol.ac J. L. Gomez-Dans J. A. Griggs Centre for Polar Observations and Modelling, School of Geographical Sciences, University of Bristol, UK Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, UK now at: Environmental Monitoring Group, Department of Geography, King's College London, UK and Remote Sensing Unit, Department of Geography, University College London, UK Digital elevation models (DEMs) of Antarctica have been derived, previously, from satellite radar altimetry (SRA) and limited terrestrial data. Near the ice sheet margins and in other areas of steep relief the SRA data tend to have relatively poor coverage and accuracy. To remedy this and to extend the coverage beyond the latitudinal limit of the SRA missions (81.5° S) we have combined laser altimeter measurements from the Geosciences Laser Altimeter System onboard ICESat with SRA data from the geodetic phase of the ERS-1 satellite mission. The former provide decimetre vertical accuracy but with poor spatial coverage. The latter have excellent spatial coverage but a poorer vertical accuracy. By combining the radar and laser data using an optimal approach we have maximised the vertical accuracy and spatial resolution of the DEM and minimised the number of grid cells with an interpolated elevation estimate. We assessed the optimum resolution for producing a DEM based on a trade-off between resolution and interpolated cells, which was found to be 1 km. This resulted in just under 35% of grid cells having an interpolated value. The accuracy of the final DEM was assessed using a suite of independent airborne altimeter data and used to produce an error map. The RMS error in the new DEM was found to be roughly half that of the best previous 5 km resolution, SRA-derived DEM, with marked improvements in the steeper marginal and mountainous areas and between 81.5 and 86° S. The DEM contains a wealth of information related to ice flow. This is particularly apparent for the two largest ice shelves – the Filchner-Ronne and Ross – where the surface expression of flow of ice streams and outlet glaciers can be traced from the grounding line to the calving front. The surface expression of subglacial lakes and other basal features are also illustrated. We also use the DEM to derive new estimates of balance velocities and ice divide locations. ADD Consortium: Antarctic Digital Database, Version 5, Database, Manual and Bibliography, Scientific Committee on Antarctic Research, Cambridge, 2006. Bamber, J. L.: Ice sheet altimeter processing scheme, Int. J. Remote Sens., 14, 925–938, doi:10.1080/01431169408954125, 1994. Bamber, J. L. and Huybrechts, P.: Geometric boundary conditions for modelling the velocity field of the Antarctic ice sheet, Ann. Glaciol., 23, 364–373, 1996. Bamber, J. L. and Bindschadler, R. A.: An improved elevation data set for climate and ice sheet modelling: Validation with satellite imagery, Ann. Glaciol., 25, 439–444, 1997. Bamber, J. L., Ekholm, S., and Krabill, W. B.: The accuracy of satellite radar altimeter data over the Greenland ice sheet determined from airborne laser data, Geophys. Res. Lett., 25, 3177–3180, 1998. Bamber, J. L., Vaughan, D. G., and Joughin, I.: Widespread complex flow in the interior of the Antarctic ice sheet, Science, 287, 1248–1250, 2000. Bamber, J. L. and Gomez-Dans, J. L.: The accuracy of digital elevation models of the Antarctic continent, Earth Planet. Sc. Lett., 217, 516–523, 2005. Blankenship, D. D., Morse, D. L., Finn, C. A., Bell, R. E., Peters, M. E., Kempf, S. D., Hodge, S. M., Studinger, M., Behrendt, J. C., and Brozena, J. M.: Geological controls on the initiation of rapid basal motion for the west Antarctic ice streams: A geophysical perspective including new airborne radar sounding and laser altimetry results, in: The west Antarctic ice sheet: Behavior and environment, edited by: Alley, R. B. and Bindschadler, R., American Geophysical Union, Washington DC, 105–122, 2001. Brenner, A. C., DiMarzio, J. R., and Zwally, H. J.: Precision and accuracy of satellite radar and laser altimeter data over the continental ice sheets, IEEE T. Geosci. Remote, 45, 321–331, doi:310.1109/TGRS.2006.887172, 2007. Budd, W. F. and Warner, R. C.: A computer scheme for rapid calculations of balance-flux distributions, Ann. Glaciol., 23, 21–27, 1996. Davis, C. H., Li, Y., McConnell, J. R., Frey, M. M., and Hanna, E.: Snowfall-driven growth in east Antarctic ice sheet mitigates recent sea-level rise, Science, 308, L15502, doi:10.1126/science.1110662, 2005. DiMarzio, J. P., Brenner, A. C., Schutz, B. E., Shuman, C. A., and Zwally, H. J.: GLAS/ICESat 500 m laser altimetry digital elevation model of Antarctica, Boulder, Colorado, USA, National Snow and Ice Data Center, Digital Media, 2007. Fricker, H. A. and Padman, L.: Ice shelf grounding zone structure from ICESat laser altimetry, Geophys. Res. Lett., 33, L15502, doi:10.1029/2006GL026907, 2006. Griggs, J. A. and Bamber, J. L.: A new digital elevation model of Antarctica derived from combined radar and laser data – Part 2: Validation and error estimates, The Cryosphere, XX, XX, 2008.\blackbox\bf Will be updated by Production Office! Helsen, M. M., van den Broeke, M. R., van de Wal, R. S. W., van de Berg, W. J., van Meijgaard, E., Davis, C. H., Li, Y., and Goodwin, I.: Elevation changes in Antarctica mainly determined by accumulation variability, Science, 1153894, doi:10.1126/science.1153894, 2008. Holt, J. W., Blankenship, D. D., Morse, D. L., Young, D. A., Peters, M. E., Kempf, S. D., Richter, T. G., Vaughan, D. G., and Corr, H. F. J.: New boundary conditions for the west Antarctic ice sheet: Subglacial topography of the Thwaites and Smith glacier catchments, Geophys. Res. Lett., 33, L09502, doi:10.1029/2005GL025561, 2006. Joughin, I. and Bamber, J. L.: Thickening of the ice stream catchments feeding the Filchner-Ronne ice shelf, Antarctica, Geophy. Res. Lett., 32, L17503, doi:10.1029/2005GL023844, 2005. King, M. A. and Padman, L.: Accuracy assessment of ocean tide models around Antarctica, Geophys. Res. Lett., 32, B08401, doi:10.1029/2004JB003390, 2005. Le Brocq, A. M., Hubbard, A., Bentley, M. J., and Bamber, J. L.: Subglacial topography inferred from ice surface terrain analysis reveals a large un-surveyed basin below sea level in east Antarctica, Geophys. Res. Lett., 35, L16503, doi:10.1029/2008GL034728, 2008. Liu, H. X., Jezek, K. C., and Li, B. Y.: Development of an Antarctic digital elevation model by integrating cartographic and remotely sensed data: A geographic information system based approach, J. Geophys. Res.-Sol. Ea., 104, 23 199–23 213, 1999. Lythe, M. B. and Vaughan, D. G.: Bedmap: A new ice thickness and subglacial topographic model of Antarctica, J. Geophys. Res.-Sol. Ea., 106, 11 335–11 351, 2001. Rignot, E. and Thomas, R. H.: Mass balance of polar ice sheets, Science, 297, 1502–1506, 2002. Rignot, E., Bamber, J. L., van den Broeke, M. R., Davis, C., Li, Y., van de Berg, W. J., and van Meijgaard, E.: Recent Antarctic ice mass loss from radar interferometry and regional climate modelling, Nature Geosciences, 1, 106–110, doi:10.1038/ngeo102, 2008. van de Berg, W. J., van den Broeke, M., and Reijmer, C. H.: Characteristics of the Antarctic surface mass balance (1958–2002) using a regional atmospheric climate model, Ann. Glaciol., 41, 97–104, 2005. van de Berg, W. J., van den Broeke, M. R., van Meijgaard, E., and Reijmer, C. H.: Reassessment of the Antarctic surface mass balance using calibrated output of a regional atmospheric climate model, J. Geophys. Res., 111, D11104, doi:10.1029/2005JD006495, 2006. Vaughan, D. G., Bamber, J. L., Giovinetto, M., Russell, J., and Cooper, A. P. R.: Reassessment of net surface mass balance in Antarctica, J. Climate, 12, 933–946, 1999. Warner, R. C. and Budd, W. F.: Derivation of ice thickness and bedrock topography in data-gap regions over Antarctica, Ann. Glaciol., 31, 191–197, 2000. Zwally, H. J., Giovinetto, M. B., Li, J., Cornejo, H. G., Beckley, M. A., Brenner, A. C., Saba, J. L., and Donghui, Y.: Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992–2002, J.Glaciol., 51, 509–527, 2005. Zwally, H. J., Schutz, B. E., Bentley, C. R., Bufton, J., Herring, T., Minster, J. F., Spinhirne, J., and Thomas, R.: GLAS/ICESat L2 Antarctic and Greenland Ice Sheet Altimetry Data V428, 25th September 2003 to 27th November 2006, Boulder, CO, National Snow and Ice Data Center, Digital Media, 2007.