Sentinel-3 Delay-Doppler altimetry over Antarctica

Abstract

The launch of Sentinel-3A in February 2016 represented the beginning of a new long-term series of operational satellite radar altimeters, which will provide Delay-Doppler altimetry measurements over ice sheets for decades to come. Given the potential benefits that these satellites can offer to a range of glaciological applications, it is important to establish their capacity to monitor ice sheet elevation and elevation change. Here, we present the first analysis of Sentinel-3 Delay-Doppler altimetry over the Antarctic ice sheet, and assess the accuracy and precision of retrievals of ice sheet elevation across a range of topographic regimes. Over the low-slope regions of the ice sheet interior, we find that the instrument achieves both an accuracy and a precision of the order of 10 cm, with ∼ 98 % of the data validated being within 50 cm of co-located airborne measurements. Across the steeper and more complex topography of the ice sheet margin, the accuracy decreases, although analysis at two coastal sites with densely surveyed airborne campaigns shows that ∼ 60 %-85 % of validated data are still within 1 m of co-located airborne elevation measurements. We then explore the utility of the Sentinel-3A Delay-Doppler altimeter for mapping ice sheet elevation change. We show that with only 2 years of available data, it is possible to resolve known signals of ice dynamic imbalance and to detect evidence of subglacial lake drainage activity. Our analysis demonstrates a new, long-term source of measurements of ice sheet elevation and elevation change, and the early potential of this operational system for monitoring ice sheet imbalance for decades to come.

The Roles of the S3MPC: Monitoring, Validation and Evolution of Sentinel-3 Altimetry Observations

“…A second approach to monitoring mission precision is to study repeated profiles, over 6 or 12 month periods, for areas of very low slope. To do this, we compute (1) the mean elevation profile, (2) the residual elevations from the mean profile, and (3) the standard deviations of all elevation measurements within 400 m intervals along the satellite track, as per McMillan et al [57]. There is good agreement between the many S3A elevation profiles within a year, with the mean profile being 25-30 cm above the reference DEM from CryoSat-2.…”

“…Lake Vostok is chosen to study accuracy over smooth low slope topography, Dome-C for a rougher low slope surface, and Wilkes land and the SPIRIT zone in East Antarctica to represent regions of steeper and more complex topography. A detailed analysis of the S3MPC methods used and results obtained over these test areas when validating S3 with Operation IceBridge is available in McMillan et al [57].…”

Brief communication: Ice sheet elevation measurements from the Sentinel-3A and Sentinel-3B tandem phase

“…When radar altimeters overfly areas of complex surface topography, the returned echo diverges from its classical shape (Ray et al, 2015) and the range to the altimeter can also change rapidly. These effects can complicate the reliable retrieval of surface elevation information, because they can induce distortions in the theoretical waveform shape, impact upon the multi-looking process, and lead to multiple superimposed reflections from distinct surfaces within the Doppler beam footprint.…”

Ice Sheet Topography from a New CryoSat-2 SARIn Processing Chain, and Assessment by Comparison to ICESat-2 over Antarctica

“…The accuracy and precision of the estimated elevation, therefore, rely on the accuracy of the employed Digital Elevation Model (DEM). Geolocation errors are diminished in unfocused SAR mode compared to LRM, due to the reduced along-track footprint [14,15]. In fact, the POCA remains located within the Doppler band footprint and is therefore not, or weakly, sensitive to along-track topographic variations.…”