A new digital elevation model of Antarctica derived from CryoSat-2 altimetry

Abstract

Abstract. We present a new digital elevation model (DEM) of the Antarctic ice sheet and ice shelves based on 2.5 × 10 8 observations recorded by the CryoSat-2 satellite radar altimeter between July 2010 and July 2016. The DEM is formed from spatio-temporal fits to elevation measurements accumulated within 1, 2, and 5 km grid cells, and is posted at the modal resolution of 1 km. Altogether, 94 % of the grounded ice sheet and 98 % of the floating ice shelves are observed, and the remaining grid cells north of 88 • S are interpolated using ordinary kriging. The median and root mean square difference between the DEM and 2.3 × 10 7 airborne laser altimeter measurements acquired during NASA Operation IceBridge campaigns are −0.30 and 13.50 m, respectively. The DEM uncertainty rises in regions of high slope, especially where elevation measurements were acquired in low-resolution mode; taking this into account, we estimate the average accuracy to be 9.5 m -a value that is comparable to or better than that of other models derived from satellite radar and laser altimetry.

Sentinel-3 Delay-Doppler altimetry over Antarctica

“…These geophysical corrections are provided at 1 Hz sampling, and so we used linear interpolation to resample these fields to the native 20 Hz rate of the altimeter measurements. The echoing point was then relocated to the point of closest approach (Roemer et al, 2007) within the SAR beam footprint using a DEM derived from 7 years of CryoSat-2 data (Slater et al, 2018), with echoing points that were relocated by more than ∼ 8 km, and therefore at the edge of antenna beamwidth, removed (∼ 3.7 % of data, based on statistics from a single cycle), together with relocated elevations that deviated by more than 100 m from the DEM (∼ 3.0 % of data, based on statistics from a single cycle). This dataset then formed the basis of the subsequent validation activities.…”

“…These sites allowed us to evaluate the performance of Delay-Doppler altimetry in regions representative of a large part of the Antarctic interior. Both sites have low and relatively uniform topographic slopes, with an average and standard deviation of 0.09 and 0.05 • (Lake Vostok) and 0.04 and 0.03 • (Dome C), respectively, based upon a 1 km digital elevation model (DEM) (Slater et al, 2018). Furthermore, the flat ice surface directly above Lake Vostok represents an established validation site for new altimetry missions (Richter et al, 2014;Schröder et al, 2017;Shuman et al, 2006), although it is important to note that our study site does extend beyond the region floating in hydrostatic equilibrium, so as to incorporate areas of grounded ice with topography that is more representative of the ice sheet interior.…”

“…We selected two 27-day cycles of Sentinel-3A data (cycles 12 and 24) and for each cycle computed the elevation difference at all locations where ascending and descending passes crossed. Specifically, we (1) removed outlier measurements that deviated by more than 50 m from our DEM (Slater et al, 2018), (2) identified crossing points in the remaining dataset as the intersection between two consecutive measurements of an ascending pass and two consecutive measurements of a descending pass, and (3) computed the elevation difference by interpolating the bracketing ascending and descending records to the crossover location. Finally, for each cycle we binned all the crossover differences within 0.2 • intervals of the surface slope to investigate the relationship between the magnitude of the surface slope and the cross-over elevation precision.…”

“…Alternative methods for selecting IceBridge measurements were also tested, such as bilinear interpolation of multiple surrounding measurements, but this approach produced a less comprehensive set of comparison points from which to generate our assessment statistics. As part of this process, we identified and removed anomalous IceBridge elevation records that deviated by more than 100 m from an independent DEM (Slater et al, 2018). This step removed 7.3 % of the total Antarctic IceBridge dataset.…”

“…Accurate knowledge of ice sheet topography and regional changes in ice volume is essential for developing a processbased understanding of ice sheet evolution and for monitoring the response of Greenland and Antarctica to climate change (Davis et al, 2005;Price et al, 2011;Shepherd et al, 2004). For the past quarter of a century, satellite radar altimeters have provided near-continuous coverage of Earth's polar regions, yielding detailed topographic information of ice sheets (Bamber et al, 2009;Bamber and Bindschadler, 1997;Helm et al, 2014;Remy et al, 1989;Slater et al, 2018), together with estimates of changes in ice sheet volume (Davis and Ferguson, 2004;Helm et al, 2014;Johannessen et al, 2005) and mass (McMillan et al, 2014(McMillan et al, , 2016Shepherd et al, 2012;Wingham et al, 2006b;Zwally et al, 2011). By resolving changes at the scale of individual glacier basins, these satellites have been able to identify emerging signals of imbalance (Flament and Rémy, 2012;Wingham et al, 2009), loci of rapid ice loss (Hurkmans et al, 2014;McMillan et al, 2016;Sørensen et al, 2015;Zwally et al, 2005), and the regional contribution of ice sheets to global sea level rise (Shepherd et al, 2012;The IMBIE team, 2018;Zwally et al, 2011).…”