Improved retrieval of land ice topography from CryoSat-2 data and its impact for volume-change estimation of the Greenland Ice Sheet

• Published in: The Cryosphere
• Main Authors: Nilsson, Johan, Gardner, Alex, Sørensen, Louise Sandberg, Forsberg, René
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Greenland; glacier; Ice Sheet; The Cryosphere
• Online Access: https://orbit.dtu.dk/en/publications/ba584952-c3de-4b93-b535-01a9f5644e0b; https://doi.org/10.5194/tc-10-2953-2016; https://backend.orbit.dtu.dk/ws/files/127858023/tc_10_2953_2016.pdf

A new methodology for retrieval of glacier and ice sheet elevations and elevation changes from CryoSat-2 data is presented. Surface elevations and elevation changes determined using this approach show significant improvements over ESA's publicly available CryoSat-2 elevation product (L2 Baseline-B). The results are compared to near-coincident airborne laser altimetry from NASA's Operation IceBridge and seasonal height amplitudes from the Ice, Cloud, and Elevation Satellite (ICESat). Applying this methodology to CryoSat-2 data collected in interferometric synthetic aperture mode (SIN) over the high-relief regions of the Greenland Ice Sheet we find an improvement in the root-mean-square error (RMSE) of 27 and 40% compared to ESA's L2 product in the derived elevation and elevation changes, respectively. In the interior part of the ice sheet, where CryoSat-2 operates in low-resolution mode (LRM), we find an improvement in the RMSE of 68 and 55% in the derived elevation and elevation changes, respectively. There is also an 86% improvement in the magnitude of the seasonal amplitudes when compared to amplitudes derived from ICESat data. These results indicate that the new methodology provides improved tracking of the snow/ice surface with lower sensitivity to changes in near-surface dielectric properties. To demonstrate the utility of the new processing methodology we produce elevations, elevation changes, and total volume changes from CryoSat-2 data for the Greenland Ice Sheet during the period January 2011 to January 2015. We find that the Greenland Ice Sheet decreased in volume at a rate of 289 ± 20km 3 a -1 , with high interannual variability and spatial heterogeneity in rates of loss. This rate is 65km 3 a -1 more negative than rates determined from ESA's L2 product, highlighting the importance of CryoSat-2 processing methodologies.