Phase-Based Antarctica Ice Velocity Map

Complete map of ice motion in Antarctica combining phase data in the interior and speckle tracking in the fast-moving sectors.

We present a new map of Antarctic ice velocity that is ten times more precise than prior maps and reveals ice motion at a high precision over 80% of the continent versus 20% in the past. The ice motion vector map provides novel constrains on interior ice motion and its connection with the glaciers and ice stream that control the stability and mass balance of the Antarctic Ice Sheet.

Methods
This mosaic is a merge between phase-derived velocity and the earlier mosaic of ice velocity derived from speckle and feature tracking (Mouginot et al., 2017). Where available, the phase data takes priority. At the transition boundary, we apply a feathering technique to minimize the discontinuity in velocity and in spatial derivative in both horizontal directions, but preserving the phase data.

For the phase, we rely on the entire SAR archive since 1992 with six sensors from multiple space agencies. The data are the Canadian Space Agency (CSA) with RADARSAT-1 and RADARSAT-2, the European Space Agency (ESA) with the Earth Remote Sensing Satellites 1-2 (ERS-1/2) and the Envisat ASAR; the Japan Aerospace Exploration Agency (JAXA) with ALOS PALSAR-1 and a few scenes from ALOS2 PALSAR. We do not include data from the European Copernicus Sentinel-1a/b SARs because the TopSAR acquisition mode of the Sentinel-1a/b data produces residual phase jumps at burst boundaries that make it impractical for precision phase-mapping, even with data stacking and additional corrections (Scheuchl et al., 2016). Each sensor has its own advantage and inconvenience: Envisat ASAR and RADARSAT-2 are the only sensors providing descending passes over East Antarctica. ALOS PALSAR-1 provides ascending passes with a high temporal coherence along the periphery. RADARSAT-2 provides the most complete dataset with coverage of the southernmost regions including ascending and descending passes in left looking mode and right looking coverage with ascending and descending passes similar to Envisat ASAR. ERS-1/2 provides high coherence images (1-day repeat) over rapidly changing sectors of West Antarctica. Phase-derived velocity are mostly for years between 2007 and 2018 while regions covered by speckle- tracking-derived velocity (along the coasts) are mostly representative of years 2013-2017. SAR and interferogram processing, unwrapping and geocoding were done using GAMMA remote sensing processor.